CC BY
9Органический синтез и биотехнология
УДК 576.311.347+577.23/.24
D.D. Orlova1, T.A. Grigoreva2, O.A. Fedorova3, V.G. Tribulovich4
MITOCHONDRIAL MORPHOGENESIS ROLE IN APOPTOSIS REGULATION (REVIEW)
St. Petersburg State Technological Institute (Technical university), Moskovskiy Pr., 26, St. Petersburg, 190013, Russia e-mail: orlova.daria.d@gmail.com
Mitochondria are cellular organelles responsible for cell energy balance. Such organelles are in dynamic homeostasis maintained by two different processes: regulated fission (fragmentation), which leads to smaller organelle formation, and fusion, which mediates tubular and netlike mitochondrial structure formation. Regulation of such processes turned out to be more complex than it supposed to be and in spite of discovered proteins which regulate fission / fusion processes, new proteins which control these processes were recently identified. Recently, Bcl-2 family members have been shown to be implicated in mitochondrial netlike structure maintenance in addition to their key role in regulation of apoptosis. In this review we discuss mitochondrial fission / fusion mechanisms regulation and summarize available data on the role of Bcl-2 family members in the mitochondrial fission / fusion dynamics regulation.
Keywords: apoptosis, Bcl-2 family, cell death, mitochondrial fission / fusion.
Д.Д. Орлова, Т.А. Григорьева, О.А. Фёдорова, В.Г. Трибулович
РОЛЬ БЕЛКОВ СЕМЕЙСТВА BCL-2 В МИТОХОНДРИАЛЬНОЙ ДИНАМИКЕ КЛЕТОЧНОЙ ГИБЕЛИ (ОБЗОР)
Санкт-Петербургский государственный технологический институт (технический университет), Московский пр., 26, Санкт-Петербург, 190013, Россия e-mail: orlova.daria.d@gmail.com
Митохондрии - динамичные органеллы, подверженные регулируемому делению/фрагментации (производство органелл меньшего размера) или же слиянию (производство трубчатых или сетчатых митохондриальных структур). Показано, что эти процессы протекают по более сложному механизму, чем представлялось ранее. Исследования последних лет показали, что члены семейства Bcl-2 в дополнение к их ключевой роли в регулировании апоптоза вовлечены в поддержание сетчатой структуры митохондрий. В данном обзоре обсуждаются механизмы регулирования деления/слияния митохондрий и роль членов семейства Bcl-2 в регулировании динамики митохондриального деления/слияния.
Ключевые слова: апоптоз, семейство Bcl-2, гибель клеток, деление/слияние митохондрий.
DOI: 10.15217/issn1998984-9.2014.27.33
The role of mitochondria in cell energy cycle was established many years ago, however, the recent studies of mitochondrial dynamics have shown their role in a number of other physiological processes taking place at the cellular level in health and disease. Mitochondria are dynamic organelles exposed to regulated fission, fusion, branching, intracellular localization changes, compositional changes including mitochondrial genome, reshaping, and quantity adjustment. Mitochondrial morphology and their number depend on the balance between fusion and fission rates. Shift towards the fusion process enables the formation of extended interconnected mitochondrial networks, whereas shift towards fission provoke production of a large amount of morphologically and functionally different small spherical organelles. These processes are controlled by proteins of the mitochondrial dynamics machinery and play vital role in normal cell physiology.
Mitochondria act as key regulators of apoptosis in mammalian cells. Mitochondria-enriched fractions are necessary for caspase activation. Mitochondria involvement in apoptosis is regulated by Bcl-2 (B-cell lymphoma 2) protein. This protein retains cells from death and under certain conditions plays the role of oncogene. Besides, mitochondria contribute to cell death through caspase-independent mechanisms. So, mitochondria are key regulators of both processes [1]. Mitochondria outer membrane permeabilization (MOMP) leads to mitochondrial transmembrane potential reduction and proapoptotic proteins, including cytochrome C, release from mitochondria to cytosol [2, 3]. Bcl-2 family proteins accurately regulate MOMP. Some of Bcl-2 family members, such as Bcl-2 and Bcl-xL (B-cell lymphoma-extra-large), retain mitochondria integrity and avoid cytochrome C release, while others, such as Bax (Bcl-2-associated X protein) and Bak (Bcl-2 homologous antagonist killer), Bid (BH3 interacting-do-main death agonist) and Bim (Bcl-2-like protein 11), provoke
1 Orlova Daria D., engineer, Laboratory of Molecular Pharmacology, graduate student, department of Technology of Microbiological Synthesis, e-mail: orlova. daria.d@gmail.com
Орлова Дарья Дмитриевна, инженер НИЛ «Молекулярная фармакология», аспирант, каф. технологии микробиологического синтеза, e-mail: orlova. daria.d@gmail.com
2 Grigoreva Tatiana A., engineer, Laboratory of Molecular Pharmacology, graduate student, department of Technology of Microbiological Synthesis, e-mail:rozentatiana@gmail.com
Григорьева Татьяна Алексеевна, инженер, НИЛ «Молекулярная фармакология», аспирант, каф. технологии микробиологического синтеза, e-mail:rozentatiana@gmail.com
3 Fedorova Olga Andreevna, PhD (Biol.), junior research scientist, Laboratory of Molecular Pharmacology, e-mail: fedorovaolgand@mail.ru Фёдорова Ольга Андреевна, к.б.н., м.н.с. НИЛ «Молекулярная фармакология», СПбГТИ(ТУ), , e-mail: fedorovaolgand@mail.ru
4 Tribulovich Vyacheslav G., PhD (Chem.),, senior research scientist, of the Laboratory of Molecular Pharmacology, SPbSTI(TU) Трибулович Вячеслав Генрихович, к.х.н., с.н.с НИЛ «Молекулярная фармакология», СПбГТИ(ТУ), , e-mail: tribulovich@gmail.com
Received December, 2 2014
cytochrome C elution to cytosol [2, 3]. However, mechanism of the Bcl-2 proapoptotic family proteins action retains controversial and is not yet fully understood. Recently it has been suggested that extensive mitochondrial fragmentation that occurs during apoptosis contribute to cytochrome C release, but the latest data have questioned this hypothesis. In this review we discuss mechanisms of mitochondrial dynamics regulation by Bcl-2 family proteins and the role of such processes in apoptotic cell death.
Mitochondrial morphology homeostasis machinery
The main components of machinery maintaining mitochondrial morphology homeostasis are evolutionarily conserved and identical in all organisms from yeast to human. So genetic studies in yeast are crucial for identification of molecular players responsible for mitochondrial morphogenetic processes because orthologs of most of such genes function similarly in mammalian cells [4].
Mitochondrial fusion is a coordinated fusion of both outer and inner mitochondrial membranes. Three proteins are implicated in the main fusion mechanism in yeast: Fzol and Ugol, which are localized on the outer membrane, and Mgml, a dynamin-related GTPase localized on the inner membrane. In yeast one of these proteins lacking in fragmented mitochondria is observed together with severe defects in mitochondrial DNA [5-9]. In mammalian cells the process of fusion is regulated by GTPases localized on the outer mitochondrial membrane and known as mitofusins. Two widespread expressed mitofusin genes, Mfn1 and Mfn2, were identified in mammalian cells [10]. Along with proteins Mfnl (Mitofusin-1) and Mfn2 (Mitofusin-2), there was found another enzyme - OPA1 (Optic atrophy 1), GTPase of dynamin family which is homologous to Mfnl protein and crucial for mitochondrial fusion in mammals (Figure) [11-12]. This protein is associated with the inner membrane and controls its structure. It should be noted that involvement of Mfn2 and OPA1 genes was revealed for neurodegenerative diseases.
Mittvlmiidftirt Етйж it bTitwhwulrial Сини!
Figure. Proteins involved in mitochondrial fission (a) and fusion (b) processes.
Drp1, involving transmembrane protein Fis-1, promotes mitochondrial membrane construction. Mfn1 and Mfn2 proteins activate outer mitochondrial membrane fusion; OPA1 is responsible for inner mitochondrial membrane fusion
An opposite process, mitochondrial fission, is controlled by four proteins in yeast: Fisl, localized on the outer mitochondrial membrane, and three cytosolic proteins - Dnml, Mdvl and Caf4. Yeast cells with defective mitochondrial fission mechanism contain extensively interconnected mitochondria, unopposed by the fission process [13-17]. In mammalian cells three proteins, that responsible for mitochondrial fission, are known: Drpl, Fisl and endophilin B1 (also called Bif-1). Drpl protein, dynamin family GTPase, mainly localized in cytosol and partly on the mitochondrial surface [18]. Fisl distributed
evenly on the outer mitochondrial membrane and may act as Drpl receptor, which shift from cytosol to outer mitochondrial membrane where it controls organelle fission (Figure) [19]. Based on similarity with dynamin, it may be assumed that Drp1 mediate GTP hydrolysis in conjunction with mitochondrial membrane constriction and following fission [18]. Another protein - endophilin B1 - is acetyltransferase responsible for normal morphology maintenance. Drp1 and endophilin B1 were shown to take part in different stages of mitochondrial dynamics regulation in mammalian cells [20-21].
Proteins involved in mitochondria transport process and their spatial localization also can control mitochondrial fission and fusion processes. For example, Rho-like gene subgroup called Miro (mitochondrial Rho) encode Rho GTPase-like proteins which contain GTPase domain at the N-terminus of the molecule and further they contain two calcium-bonding sites (EF-hand motif). It was shown that ectopically expressed Miro-1 and Miro-2 are present on the outer mitochondrial membrane and are implicated in homeostasis maintenance [22]. Furthermore, expression of constitutively active Miro-1 (Miro-1/Val-13) stimulates development of mitochondrial aggregation, which is probably connected with mitochondrial fusion increase [22]. Miro-1 protein is also highly implicated in mitochondrial motility in neurons as calcium level sensor [23-25]. Thus, mitochondrial motility can modulate dynamics of mitochondrial fission and fusion processes.
Role of mitochondrial morphological dynamics in regulation of apoptosis
Mitochondria play a key role in apoptosis process as these organelles are permeabilized by proapoptotic Bcl-2 family proteins, such as Bax and Bak [26-28]. Bax exists as inactive monomer in cytosol and its activation requires several steps including conformational changes, translocation and oligomerization. In opposition to Bax, Bak is usually localized in the outer mitochondrial membrane and requires different activation mechanism. Antiapoptotic Bcl-2 family proteins (Bcl-2, Bcl-XL and Mcl-1) regulate MOMP by inhibiting Bax and Bak activity [1]. MOMP maintains apoptosis promoting release of such proteins as cytochrome C which can act as Apaf-1/caspase-9 apoptosome assembly co-factor and/or maintain other events in the process of apoptosis [2, 27]. However, the mechanism underlying MOMP still remains unclear. Recently it has been suggested that processes of mitochondrial fission are involved in MOMP regulation. This hypothesis is based on the results that show that apoptosis associated mitochondrial fragmentation is very close in time with cytochrome C release [29]. However, despite the fact that the mitochondria fragmentation is associated with apoptosis, excessive mitochondrial fission which does not depend on apoptotic processes can occur under various conditions. Thus it was shown that mitochondrial fragmentation induced by carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) is reversible upon drug removal and does not lead to cytochrome C release and cell death [30].
It should be mentioned that proteins involved in mitochondrial fission, such as Drp1, Fis1 and endophilin B1, or in mitochondrial fusion, such as OPA1 or Mfn2, are able to modulate cell death progression by forcing mitochondrial dynamics effect on apoptosis regulation. However, the latest data suggest that morphological dynamics of mitochondria is involved in apoptosis in a lesser extent than previously assumed.
Mitochondrial fission and cell death
In response to apoptotic effect, Drp1 accumulates on the outer mitochondrial membrane where it colocolizes with Bax and Mfn2 [31]. Interestingly that dynamin-like GTPase dominant-negative mutant Drp1 (Drp1 K38A) expression or Drp1 deactivation by RNAi not only reduce mitochondrial
fragmentation, but inhibit cytochrome C release and cell death [32-35]. Based on these observations it is suggested that mitochondrial fragmentation is responsible for MOMP, cytochrome C release and apoptosis. However, some recent researches challenge this hypothesis. As it was shown, RNAi-mediated deletion of Drpl reduces mitochondrial fission, but cannot block apoptosis in response to a number of proapoptotic stimuli [36-37]. Moreover, the use of small molecular Drp1 inhibitor slows down mitochondrial cytochrome C release and cell death that indicates an independent role of Drpl function in mitochondrial fission process [38]. Also it was pointed that overexpression of Fisl, assumed Drpl receptor, initiates mitochondrial fragmentation followed by cytochrome C release and apoptosis activation [19]. Nevertheless, mitochondrial fission induced by Fisl may take place independent from apoptosis. There is evidence that the mutant Fisl K148R although stimulates mitochondrial fission, but is not able to trigger apoptosis [39]. Moreover, Fisl deletion, as it was shown, does not affect cell death [36]. It has been established that endophilin Bl, which participates in mitochondrial fusion, interacts with proapoptotic protein Bax [40]. Respectively, RNA interference or straight genetic knockout of endophilin Bl suppresses Bax translocation and cytochrome C release caused by apoptosis. There is evidence that such component of mechanism of mitochondrial morphology have influence on proapoptotic functions which are independent of its role in normal mitochondrial dynamics [4l].
It has been recently shown that Bax- and Bak-induced mitochondrial fragmentation may not be accompanied by cytochrome C release and apoptosis [42]. Indeed, even though Bcl-xL and Mcl-l decrease apoptotic markers release, such as cytochrome C, mitochondrial fragmentation retains in cells overexpressing Bax or Bak. This means that MOMP and mitochondrial fission are separate and independent events [42].
Indeed, mitochondrial fission is suggested to be necessary for intrinsic apoptosis pathways activated by proapoptotic Bcl-2 family proteins at least for a normal level of cytochrome C release and caspase activation. But these findings dispute the role of mitochondrial fragmentation as the main cause of apoptosis associated release of cytochrome C and rather describe it as a process that accompanies the activation of Bax/Bak.
Mitochondrial fusion and cell death
Several studies have shown that inhibition of mitochondrial fusion may contribute to apoptosis. Mfnl and Mfn2 deletion leads to mitochondrial fragmentation and increases sensitivity to apoptotic inductors [43]. Herein Mfnl and Mfn2 overexpression increases mitochondrial interaction and delays cytochrome C release and cell apopto-sis [44]. It should be noted that mutant Mfn2 - Mfn2 Ras-Gl2V - acts similar to the wild type and leads to fusion and lengthening of mitochondria activation and at the same time activated mutant Mfn2 RasGl2V significantly increases protection of neurons from cell death [34, 45]. These results support the role of Mfnl and Mfn2 in the regulation of cell death. However, there is evidence that overexpression of both mitofusins does not protect cells from death, induced by proapoptotic events. Stimulated mito-chondrial fusion does not effect on the rate of apoptosis [42]. Cytochrome C is mainly localized within mitochondrial cristae which are described as invaginations on the inner mitochondrial membrane in the location areas of respiratory complexes. It was suspected that cristae remodeling is necessary for rapid cytochrome C release. It has been shown that the reduction of OPAl level, which regulates inner membrane cristae reorganization, causes mitochondrial fission and spontaneous apoptosis [46-47]. Moreover, it was shown that stable to cristae disassembly mutant ÜPÄl Q297V blocks full release of cytochrome C and apoptosis activating at the same time Bax protein [48]. Thus, changes
in mitochondrial structure are more relevant for cytochrome C release and cell death in comparison with the balance between mitochondrial fission and fusion processes.
The recent research demonstrated that full mitochondrial fusion and mitochondrial network organization in cells lead to stress and protein synthesis reduction [49]. Authors have also demonstrated that induced mitochondrial hyperfusion, which requires involvement of metabolically active mitochondria leads to increase in ATP production and promotes stress resistance of cells. To promote mitochondrial fusion Mfnl and OPA1 proteins are required. Thus, mitochondrial hyperfusion mediated by corresponding proteins apparently enhances the ability of mitochondria to protect cells against specific inducers of cell death.
Mitochondrial dynamics in healthy cells
Dynamics of mitochondrial morphogenesis is critical factor which determines physiology of healthy cells regardless of its potential role in cell death processes. For instance, recently it has been suggested that mitochondrial dynamics plays crucial role in lymphocyte migration [50]. Lymphocytes are sensitive to chemoattractant gradients and respond with changes in cell morphology and motility. Fusion and fission processes also suppress lymphocyte polarization and migration. It was indicated that mitochondrial accumulation in uropod (an appendage on the last abdominal segment) of migrating cell is necessary to provide high level of ATP [50]. It should be noted that mutations in proteins which regulate mitochondrial dynamics are responsible for severe neuropathy. Mutations in Mfn2 which are located mainly inside or near the GTPase domain initiate Charcot-Marie-Tooth disease (CMT) [51]. CMT is a group of diseases which is characterized by the pathology in the longest motor and sensory nerves that weakens limb activity. The most common CMT forms occur as peripheral nerve demyelization. Another neuropathy, Kjer's optic atrophy (autosomal dominant optic atrophy), leads to visual activity loss and is mediated by retinal ganglion cells degeneration. The major form of Kjer's optic atrophy is caused by mutation in OPAl [52].
Diseases discussed above shows that neurons are particularly vulnerable in cases of defects in mitochondrial dynamics. It is well known that axon synaptic areas contain an excess of the mitochondria. This highly specific mitochondrial allocation in neurons probably presents a high demand for ATP active neurons which take part in synaptic signal transmission. Mitochondrial fission may be critical in reallocation and proliferation of mitochondria in synaptic area while competing process, mitochondrial fusion, provides interaction between mitochondria facilitating mitochondrial motility.
Protein machinery involved in mitochondrial motility in neurons is connected with mitochondrial fission and fusion dynamics. Distant mitochondrial transportation depends on microtubules associated motor proteins. In order to accommodate the specific delivery of mitochondria to axons and synapses, neurons have to recruit mechanisms which attach the organelles to molecular motors. Some mitochondrial adaptor proteins including Miro and Milton have been shown to be involved in linking mitochondria with dynein motor that regulates mitochondrial motility [2325]. Both of these proteins may influence on mitochondrial fission and fusion dynamics that plays key role in neuron vitality maintenance. For instance it was found that Miro amplifies the process of mitochondrial net fusion at normal calcium concentrations but it promotes mitochondrial fragmentation at high concentrations [23]. Such Miro activity on mitochondrial morphology is apparently accomplished by suppression or activation of Drpl [23]. Nevertheless the potential involvement of mitochondrial transport in dynamic regulation of morphogenesis in neurons remains to be established.
Bcl-2 family proteins and their role in mitochondrial dynamics
It has been already mentioned that mitochondrial dynamics plays crucial role in neuronal vitality maintenance. Recently it has been demonstrated that Bcl-2 family proteins are implicated in mitochondrial morphology regulation in neurons. In particular, it was shown that antiapoptotic protein Bcl-w may regulate mitochondrial fission and fusion in Purkinje cells [53]. Indeed, bcl-w'1' mice have serve defects in dendrites, spines and synapses of Purkinje cells. This study suggests that Bcl-w does not control the number of cells in the brain but is likely to promote mitochondrial fission in Purkinje cells which is necessary for Purkinje cells synapses and motor learning. Bcl-w-' mice demonstrate increase in mitochondrial length which is mediated by Bcl-w effect on mitochondrial fission in vivo [53]. Some authors suppose that Bcl-xL, Bcl-2 family factor, increases fusion and fission of mitochondria [54]. It was shown that cortical neurons from Bcl-xL knockout mice possess shorter mitochondria compared with wild type mice neurons which mitochondria are characterized with larger size and tubular shape. It is also assumed that the Bcl-xL increases mitochondrial "biomass". It is interesting that Bcl-xL apparently regulates the balance between fusion and fission processes of mitochondria in Drp1-dependent manner while its involvement in mitochondrial biogenesis and degradation does not depend on Drp1 [54]. These results are confirmed by the fact that Bcl-xL stimulates Drp1-dependent synapsis formation in cultured hippocampal neurons [55]. Now therefore it can be expected that Bcl-xL overexpression increases synapses number as well as synaptic mitochondrial localization. It is likely that Bcl-xL function is mediated by Drp1 because wild type Drp1 overexpression increases synaptic markers level and dominate-negative Drp1-K38A overexpression decreases their level [55]. These data suggest that Bcl-xL positively regulates Drp1 resulting in stimulation of synapsis formation processes by mitochondria function changes.
Previously the ability of Bcl-2 family members to modulate mitochondrial fusion and fission rate is independent of its function in the process of cell death has been discussed. For instance, despite of proapoptotic properties of Bax and Bak, it was shown that they take part in regulation of mitochondrial fusion in healthy cells [56]. Cells with double Bax/Bak knockout demonstrate defects in mitochondrial morphology, in particular, contain shorter mitochondria in comparison with normal cells. Mitochondrial fusion process in such cells is reduced. It may be connected with the fact that Mfn2 complex assembly, its motility and allocation within mitochondrion in healthy cells changes in the presence of Bax and Bak. According to the ability of Bax and Bak to promote mitochondrial fusion by mitofusin activation in healthy cells, it was shown that both of these proteins can interact with Mfn1 and Mfn2 [31]. Another members of Bcl-2 family also interact with Mfn2. CED-9 protein homologous to Bcl-2 of C. elegans suppresses apoptosis via bonding with CED-4 which in turn appears to be homologous to proapoptotic protein Apaf-1. In the process of apoptosis EGL-1, another C. elegans protein which contains BH3 domain (so-called BH3-only proteins), binds to CED-9 releasing CED-4 to induce cell death. It was demonstrated [57] that CED-9 expression as well as Bcl-xL leads to mitochondrial fusion possibly through direct interaction with Mfn2. Moreover, it is supposed that CED-9 involvement in apoptosis and mitochondrial morphogenesis dynamics could be uncoupled, as overexpression of CED-9 stimulates mitochondrial fusion in mammalian cells without cell death blocking. In vivo research showed that CED-9 plays crucial role in mitochondrial fission and fusion regulation of nematode containing mutant CED-9, with cells displaying mitochondria with abnormal morphology [57]. It was also shown that CED-9 takes part in mitochondrial fission and fusion processes regulation of C. elegans muscles. Indeed, it was reported that, although Drp-1-mediated mitochondrial fusion in C. elegans muscles does not require the presence
of CED-9, and CED-9 may increase Drp1 activity and mitochondrial fragmentation process [58]. Therefore, it is thought that CED-9 provides mechanism of regulation to coordinate dynamic balance between mitochondrial fission and fusion depending on cell demands. However, recent works have shown that CED-9 is required neither for fusion nor for fission of mitochondria in muscle cells of C. elegans
[59]. These contradictory data are connected with the fact that experiments were conducted only in C. elegans embryos. Thus, there is possibility that CED-9 regulates coordination of mitochondrial fission and fusion processes only on the latest stages of C. elegans development.
Interestingly, the cytomegalovirus UL37 gene product, vMIA (viral inhibitor of apoptosis targeting mitochondria) also regulates mitochondrial dynamics rate
[60]. vMIA possesses antiapoptotic functions while interacting with two proapoptotic Bcl-2 family members - Bax [61-62] and Bak [56]. Besides, it was shown that vMIA possesses spatial structure similar to Bcl-xL [63]. vMIA expression leads to mitochondrial nets fission which appears in formation of fragmented mitochondria. It was established that vMIA ability to regulate mitochondrial dynamics is connected with the ability to deactivate Bax and Bak and promote the process of mitochondrial fusion [64]. In contrast with vMIA, cytomegalovirus viral m38.5 protein associating with Bax promotes its accumulation in mitochondria and blocks Bax-but not Bak-mediated MOMP [65-66]. It is important that m38.5 is not capable of mitochondrial fission and fusion modulation [64]. Following to the selective interaction of m38.5 with Bax, Bak can freely regulate mitochondrial fusion which leads to normal mitochondrial net development.
It should be noted that mitochondrial motility defects are appeared in cells with expression of Bcl-2 family proteins [42]. As mentioned above, Bcl-2 family proteins play crucial role in mitochondrial morphology in neurons. Mitochondrial motility is also important to maintain neuronal vitality. It is likely that Bcl-2 family members can influence on the mitochondrial and cytoskeleton association while interacting with the specific proteins, which are responsible for the mitochondrial motility, such as Miro and Milton, thereby modifying mitochondrial dynamics.
Data stated in this review generalize the role of Bcl-2 family antiapoptotic proteins in mitochondrial dynamics regulation. But it still remains unclear how Bcl-2 family proteins do influence on the dynamics of mitochondrial net formation at the molecular level.
Conclusions
Bax- and Bak-induced mitochondrial net remodeling appears to take place just before cytochrome C release from mitochondria and these processes are independent of one another. Therefore, mitochondrial fragmentation is not a reason but a consequence of apoptosis. The role of excessive mitochondrial fission during apoptosis is not yet established and understanding of this process under cell death conditions requires further investigations. There is also growing evidence that Bcl-2 family proteins have got an effect on morphological characteristics and mitochondrial localization in healthy cells. Intracellular localization dynamics of mitochondria is necessary for accumulating such organelles in intracellular areas which require high metabolic activity and thus is tightly related with pathogenesis of such diseases as neuropathy. It is necessary to figure out how Bcl-2 family proteins promote changes in morphological characteristics of mitochondria and decrease its motility. Unexpected role of Bcl-2 family proteins in ex facto unrelated processes such as the regulation of MOMP and apoptosis may partly explain why the Bcl-2 family proteins does not regulate apoptosis in drosophila. In spite of the fact that in drosophila were found two of Bcl-2 family proteins, they both does not play critical role in apoptosis initiation in cells of this organism. Thus, there is a possibility that such proteins in some cases serve as regulators of mitochondrial fusion and fission processes but not as regulators of cell death.
References
1 Pradelli L. A., Beneteau, M., Ricci J. E. Mitochondrial control of caspase-dependent and -independent cell death // CMLS. 2010. Vol. 67. P. 1589-97.
2. Goldstein J. C., Waterhouse N. J., Juin P. [et. al.] The coordinate release of cytochrome c during apoptosis is rapid, complete and kinetically invariant // Nat. Cell Biol. 2000. Vol. 2. P. 156-162.
3. Green D. R. At the gates of death // Cancer Cell. 2006. Vol. 9. P. 328-330.
4. Shaw J. M., Nunnari J. Mitochondrial dynamics and division in budding yeast // Trends in cell biology. 2002. Vol. 12. P. 178-84.
5. Hermann G. J., Thatcher J. W., Mills J. P. [et. al.] Mitochondrial fusion in yeast requires the transmembrane GTPase Fzo1p // J. Cell Biol. 1998. Vol. 143. P. 359-73.
6. Rapaport D., Brunner M., Neupert W., Westermann B. Fzo1p is a mitochondrial outer membrane protein essential for the biogenesis of functional mitochondria in Saccharomyces cerevisiae // J. Biol. Chem. 1998. Vol. 273. P. 20150-5.
7. Sesaki H., Jensen R. E. UGO1 encodes an outer membrane protein required for mitochondrial fusion // J. Cell Biol. 2001. Vol. 152. P. 1123-34.
8. Wong E. D., Wagner J. A., Scott S. V. [et. al.] The intramitochondrial dynamin-related GTPase, Mgm1p, is a component of a protein complex that mediates mitochondrial fusion // J. Cell Biol. 2003. Vol. 160. P. 303-311.
9. Meeusen S., DeVay R., Block J. [et. al.] Mitochondrial inner-membrane fusion and crista maintenance requires the dynamin-related GTPase Mgm1 // Cell. 2006. Vol. 127. P. 383-95.
10. Chen H. C., Detmer S. A., Ewald A. J. [et. al.] Mitofusins Mfn1 and Mfn2 coordinately regulate mitochondrial fusion and are essential for embryonic development // J. Cell Biol. 2003. Vol. 160. P. 189-200.
11. Cipolat S., de Brito O. M., Dal Zilio B., Scorrano L. OPA1 requires mitofusin 1 to promote mitochondrial fusion // P. Nat. Acad. Sci. USA. 2004. Vol. 101. P. 15927-15932.
12. Chen H. C., ChomynA., Chan D. C. Disruption of fusion results in mitochondrial heterogeneity and dysfunction // J. Biol. Chem. 2005. Vol. 280. P. 26185-26192.
13. Bleazard W., McCaffery J. M., King E. J. [et. al.] The dynamin-related GTPase Dnm1 regulates mitochondrial fission in yeast // Nat. Cell Biol. 1999. Vol. 1. P. 298-304.
14. Sesaki H., Jensen R. E. Division versus fusion Dnm1p and Fzo1p antagonistically regulate mitochondrial shape // J. Cell Biol. 1999. Vol. 147. P. 699-706.
15. Mozdy A. D., McCaffery J. M., Shaw J. M. Dnm1p GTPase-mediated mitochondrial fission is a multi-step process requiring the novel integral membrane component Fis1p // J. Cell Biol. 2000. Vol. 151. P. 367-379.
16. Tieu Q., Nunnari J. Mdv1p is a WD repeat protein that interacts with the dynamin-related GTPase, Dnm1p, to trigger mitochondrial division // J. Cell Biol. 2000. Vol. 151. P. 353-365.
17. Griffin E. E., Graumann J., Chan D. C. The WD40 protein Caf4p is a component of the mitochondrial fission machinery and recruits Dnm1p to mitochondria // J. Cell Biol. 2005. Vol. 170. P. 237-248.
18. Smirnova E., Griparic L., Shurland D. L., van der Bliek A. M. Dynamin-related protein Drp1 is required for mitochondrial division in mammalian cells // Mol. Biol. Cell. 2001. Vol. 12. P. 2245-2256.
19. James D. I., Parone P. A., Mattenberger Y., Martinou J. C. hFis1, a novel component of the mammalian mitochondrial fission machinery // J. Biol. Chem. 2004. Vol. 279. P. 36166.
20. Cuddeback S. M., Yamaguchi H., Komatsu K. [et. al.] Molecular cloning and characterization of Bif-1 - A novel Src homology 3 domain-containing protein that associates with Bax // J. Biol. Chem. 2001. Vol. 276. P. 20559-20565.
21. Pierrat B., Simonen M., Cueto M. [et. al.]
SH3GLB, a new endophilin-related protein family featuring an SH3 domain // Genomics. 2001. Vol. 71. P. 222-34.
22. Fransson A., Ruusala A., Aspenstom P. The atypical Rho GTPases Miro-1 and Miro-2 have essential roles in mitochondrial trafficking // Biochem. Bioph. Res. Co. 2006. Vol. 344. P. 500-510.
23. Saotome M., Safiulina D., Szabadkai G. [et. al.] Bidirectional Ca2+-dependent control of mitochondrial dynamics by the Miro GTPase // P. Nat. Acad. Sci. USA. 2008. Vol. 105. P. 20728-20733.
24. MacAskillA. F., Rinholm J. E., Twelvetrees A. E. [et. al.] Miro1 Is a Calcium Sensor for Glutamate Receptor-Dependent Localization of Mitochondria at Synapses // Neuron. 2009. Vol. 61. P. 541-555.
25. Wang X. N., Schwarz T. L. The Mechanism of Ca2+-Dependent Regulation of Kinesin-Mediated Mitochondrial Motility // Cell. 2009. Vol. 136. P. 163-174.
26. Desagher S., Osen-Sand A., Nichols A. [et. al.] Bid-induced conformational change of Bax is responsible for mitochondrial cytochrome c release during apoptosis // J. Cell Biol. 1999. Vol. 144. P. 891-901.
27. Wei M. C., Zong W. X., Cheng E. H. [et. al.] Proapoptotic BAX and BAK: a requisite gateway to mitochondrial dysfunction and death // Science. 2001. Vol. 292. P. 727-30.
28. Kuwana T., Mackey M. R., Perkins G. [et. al.] Bid, Bax, and lipids cooperate to form supramolecular openings in the outer mitochondrial membrane // Cell. 2002. Vol. 111. P. 331-42.
29. Suen D. F., Norris K. L., Youle R. J. Mitochondrial dynamics and apoptosis // Gen. Dev. 2008. Vol. 22. P. 157790.
30. Pletjushkina O. Y., Lyamzaev K. G., Popova E. N. [et. al.] Effect of oxidative stress on dynamics of mitochondrial reticulum // Bioch. Biophys. Acta. 2006. Vol. 1757. P. 518-24.
31. Karbowski M., Lee Y. J., Gaume B. [et. al.] Spatial and temporal association of Bax with mitochondrial fission sites, Drp1, and Mfn2 during apoptosis // J. Cell Biol. 2002. Vol. 159. P. 931-8.
32. Frank S., Gaume B., Bergmann-Leitner E. S. [et. al.] The role of dynamin-related protein 1, a mediator of mitochondrial fission, in apoptosis // Dev. Cell. 2001. Vol. 1. P. 515-525.
33. Arnoult D., Rismanchi N., Grodet A. [et. al.] Bax/Bak-dependent release of DDP/TIMM8a promotes Drp1-mediated mitochondrial fission and mitoptosis during programmed cell death // Cur. Biol. 2005. Vol. 15. P. 2112-8.
34. Neuspiel M., Zunino R., Gangaraju S. [et. al.] Activated mitofusin 2 signals mitochondrial fusion, interferes with Bax activation, and reduces susceptibility to radical induced depolarization // J. Biol. Chem. 2005. Vol. 280. P. 25060-25070.
35. Brooks C., Wei Q., Feng L. [et. al.] Bak regulates mitochondrial morphology and pathology during apoptosis by interacting with mitofusins // Proc. Nat. Acad. Sci. USA. 2007. Vol. 104. P. 11649-54.
36. Parone P. A., James D. I., Da Cruz S. [et. al.] Inhibiting the mitochondrial fission machinery does not prevent Bax/Bak-dependent apoptosis // Mol. Cell Biol. 2006. Vol. 26. P. 7397-7408.
37. Estaquier J., Arnoult D. Inhibiting Drp1-mediated mitochondrial fission selectively prevents the release of cytochrome c during apoptosis // Cell death and diff. 2007. Vol. 14. P. 1086-94.
38. Cassidy-Stone A., Chipuk J. E., Ingerman E. [et. al.] Chemical inhibition of the mitochondrial division dynamin reveals its role in Bax/Bak-dependent mitochondrial outer membrane permeabilization // Dev. Cell. 2008. Vol. 14. P. 193-204.
39. Alirol E., James D., Huber D. [et. al.] The mitochondrial fission protein hFis1 requires the endoplasmic reticulum gateway to induce apoptosis // Mol. Biol. Cell. 2006. Vol. 17. P. 4593-605.
40. Takahashi Y., Coppola D., Matsushita N. [et. al.] Bif-1 interacts with Beclin 1 through UVRAG and regulates autophagy and tumorigenesis // Nat. Cell Biol. 2007. Vol. 9. P. 1142-1151.
41. Etxebarria A., Terrones O., Yamaguchi H. [et. al.] Endophilin B1/Bif-1 Stimulates BAX Activation Independently from Its Capacity to Produce Large Scale Membrane Morphological Rearrangements // J. Biol. Chem. 2009. Vol. 284. P. 4200-4212.
42. Sheridan C., Delivani P., Cullen S. P., Martin S. J. Bax- or Bak-induced mitochondrial fission can be uncoupled from cytochrome c release // Mol. Cell. 2008. Vol. 31. P. 570585.
43. Sugioka R., Shimizu S., Tsujimoto Y. Fzo1, a protein involved in mitochondrial fusion, inhibits apoptosis // J. Biol. Chem. 2004. Vol. 279. P. 52726-34.
44. Lee Y. J., JeongS. Y., KarbowskiM. [et. al.] Roles of the mammalian mitochondrial fission and fusion mediators Fis1, Drp1, and Opa1 in apoptosis // Mol. Biol. Cell. 2004. Vol. 15. P. 5001-5011.
45. Jahani-Asl A., Cheung E. C. C., Neuspiel M. [et. al.] Mitofusin 2 protects cerebellar granule neurons against injury-induced cell death // J. Biol. Chem. 2007. Vol. 282. P. 23788-23798.
46. Arnoult D., GrodetA., Lee Y. J. [et. al.] Release of OPA1 during apoptosis participates in the rapid and complete release of cytochrome c and subsequent mitochondrial fragmentation // J. Biol. Chem. 2005. Vol. 280. P. 35742-50.
47. Frezza C., Cipolat S., de Brito O. M. [et. al.] OPA1 controls apoptotic cristae remodeling independently from mitochondrial fusion // Cell. 2006. Vol. 126. P. 177-189.
48. Yamaguchi R., Lartigue L., Perkins G. [et. al.] Opa1-mediated cristae opening is Bax/Bak and BH3 dependent, required for apoptosis, and independent of Bak oligomerization // Mol. Cell. 2008. Vol. 31. P. 557-569.
49. Tondera D., Grandemange S., Jourdain A. [et. al.] SLP-2 is required for stress-induced mitochondrial hyperfusion // Embo. J. 2009. Vol. 28. P. 1589-1600.
50. Campello S., Lacalle R. A., Bettella M. [et. al.] Orchestration of lymphocyte chemotaxis by mitochondrial dynamics // J. Exp. Med. 2006. Vol. 203. P. 2879-2886.
51. Züchner S., Mersiyanova I. V., Muglia M. [et. al.] Mutations in the mitochondrial GTPase mitofusin 2 cause Charcot-Marie-Tooth neuropathy type 2A // Nat. Genet. 2004. Vol. 36. P. 660-660.
52. Delettre C., Lenaers G., Pelloquin L. [et. al.] OPA1 (Kjer type) dominant optic atrophy: A novel mitochondrial disease // Mol. Genet. Metab. 2002. Vol. 75. P. 97-107.
53. Liu Q. A., Shio H. Mitochondrial Morphogenesis, Dendrite Development, and Synapse Formation in Cerebellum
Require both Bcl-w and the Glutamate Receptor delta 2 // Plos. Genet. 2008. Vol. 4.
54. Berman S. B., Chen Y. B., Qi B. [et. al.] Bcl-x(L) increases mitochondrial fission, fusion, and biomass in neurons // J. Cell Biol. 2009. Vol. 184. P. 707-719.
55. Li H., Chen Y., Jones A. F. [et. al.] Bcl-X-L induces Drp1-dependent synapse formation in cultured hippocampal neurons // P. Natl. Acad. Sci. USA. 2008. Vol. 105. P. 21692174.
56. Karbowski M., Norris K. L., Cleland M. M. [et. al.] Role of Bax and Bak in mitochondrial morphogenesis // Nature. 2006. Vol. 443. P. 658-662.
57. Delivani P., Adrain C., Taylor R. C. [et. al.] Role for CED-9 and Egl-1 as regulators of mitochondrial fission and fusion dynamics // Mol. Cell. 2006. Vol. 21. P. 761-773.
58. Tan F. J., Husain M., Manlandro C. M. [et. al.] CED-9 and mitochondrial homeostasis in C-elegans muscle // J. Cell Sci. 2008. Vol. 121. P. 3373-3382.
59. Breckenridge D. G., Kang B. H., Xue D. Bcl-2 Proteins EGL-1 and CED-9 Do Not Regulate Mitochondrial Fission or Fusion in Caenorhabditis elegans // Cur. Biol. 2009. Vol. 19. P. 768-773.
60. McCormickA. L., Smith V. L., Chow D., Mocarski E. S. Disruption of mitochondrial networks by the human cytomegalovirus UL37 gene product viral mitochondrion-localized inhibitor of apoptosis // J. Virol. 2003. Vol. 77. P. 631-641.
61. Arnoult D., Bartle L. M., Skaletskaya A. [et. al.] Cytomegalovirus cell death suppressor vMIA blocks Bax- but not Bak-mediated apoptosis by binding and sequestering Bax at mitochondria // P. Nat. Acad. Sci. USA. 2004. Vol. 101. P. 7988-7993.
62. Poncet D., Larochette N., Pauleau A. L. [et. al.] An anti-apoptotic viral protein that recruits bax to mitochondria // J. Biol. Chem. 2004. Vol. 279. P. 22605-22614.
63. Pauleau A. L., Larochette N., Giordanetto F. [et. al.] Structure-function analysis of the interaction between Bax and the cytomegalovirus-encoded protein vMIA // Oncogene. 2007. Vol. 26. P. 7067-7080.
64. Norris K. L., Youle R. J. Cytomegalovirus proteins vMIA and m38.5 link mitochondrial morphogenesis to Bcl-2 family proteins // J. Virol. 2008. Vol. 82. P. 6232-6243.
65. Arnoult D., Skaletskaya A., Estaquier J. [et. al.] The murine cytomegalovirus cell death suppressor m38.5 binds Bax and blocks Bax-mediated mitochondrial outer membrane permeabilization // Apoptosis. 2008. Vol. 13. P. 1100-1110.
66. Jurak I., Schumacher U., Simic H. [et. al.] Murine cytomegalovirus m38.5 protein inhibits Bax-mediated cell death // J. Virol. 2008. Vol. 82. P. 4812-22.
