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Kinase signaling and mitochondria May, 2012
Edited by James Murray, PhD
Thousands of researchers around the world are studying the connection between mitochondria, metabolism and disease. MitoNews summarizes a selection of the latest published findings and highlight how Abcam's MitoSciences range of research tools has contributed to this effort. The full list of 33 original research papers published this month using MitoSciences range of products can be found here.
Past issues are available for review in the archives.
Table of Contents
I. Cell signaling kinases and mitochondria
II. Mitochondrial biogenesis, protein turnover and mitophagy
III. Bax, apoptosis and necrosis
I. Cell signaling kinases and mitochondria
Research on mitochondria has undergone significant changes in recent years. The field has evolved from the study of bioenergetics to the organelle's role in development, aging and numerous diseases. Since mitochondria are key integrators in the signaling pathways of hormones, growth factors and also reactive oxygen species, they are key players in cell growth, division and survival/death pathways. Several papers were published this month using products from the MitoSciences range to explore kinases signaling directly within mitochondria.
In 2009, Wang et al had demonstrated that cardiac mitochondria from a diabetic mouse model exhibited a deficiency in OXPHOS Complex V (ATP synthase). The authors showed that acute insulin treatment induced phosphorylation of Akt and translocation to mitochondria with a subsequent activation of Complex V activity. This month, Wang et al created a constitutively active Akt specifically targeted to mitochondria in primary cardiomyocytes, shown by Western blotting. This resulted in reduced caspase activation and the number of apoptotic cells, an effect not seen with expressed dominant negative Akt, or a cytosolic Akt inhibitor. The authors propose that a mitochondrial Akt suppresses apoptosis by stabilizing mitochondrial membranes and that this mitochondrial signaling pathway may be impaired in diabetes.
Mitochondrial Akt-regulated mitochondrial apoptosis signaling in cardiac muscle cells. Am J Physiol Heart Circ Physiol. 2012 Su CC, Yang JY, Leu HB, Chen Y, Wang PH.
The non-receptor protein tyrosine kinase Src plays a crucial role in the signal transduction pathways involved in cell division, motility, adhesion and survival in both normal and cancer cells. Recent papers have shown that Src is also targeted to mitochondria and may be responsible for Complex IV subunit II phosphorylation in osteoclasts. In a recent paper by Hebert-Chatelain et al, Src inhibition resulted in decreased respiration and Complex I activity. An intra-mitochondrial localization for Src was demonstrated by gradient centrifugation and Western blotting. Phosphotyrosine analysis of isolated Complex I shows Src inhibitor sensitive phosphorylation of subunit NDUFB10, which is proposed to regulate Complex I and respiratory chain activity.
Preservation of NADH ubiquinone-oxidoreductase activity by Src kinase-mediated phosphorylation of NDUFB10. Biochim Biophys Acta. 2012 Hebert-Chatelain E, Jose C, Gutierrez Cortes N, Dupuy JW, Rocher C, Dachary-Prigent J, Letellier T.
Ki et al. examined the effect of the insecticide Fipronil on neuroblastoma SH-SY5Y cells. They showed directly that reactive oxygen species were generated and that Complex I activity is acutely sensitive to this stress. Multiple activated apoptotic markers were subsequently measured. To examine the role of stress response pathways in this system, mitogen activated kinases (MAPKs) p38, JNK and ERK1/2, were examined and shown by Western blotting to be active and this activation occurred rapidly after treatment. Inhibitors of these kinases reduced ROS and increased cell viability. The mechanism by which this occurs is unclear however mitochondrial ROS generation clearly has a role upstream of stress response signaling and apoptotic pathways.
Reactive oxygen species and mitogen-activated protein kinase induce apoptotic death of SH-SY5Y cells in response to fipron Toxicol Lett. 2012 Ki YW, Lee JE, Park JH, Shin IC, Koh HC.
Also this month:
Proteolytic regulation of the mitochondrial cAMP-dependent protein kinase. Biochemistry. 2012 Shell JR, Lawrence DS
Restoration of glucose metabolism in leptin-resistant mouse hearts after acute myocardial infarction through the activation of survival kinase pathways. J Mol Cell Cardiol. 2012 Witham W, Yester K, O'Donnell CP, McGaffin KR.
II. Mitochondrial biogenesis, protein turnover and mitophagy
Transcription involving PGC1 coactivators and transcription factors Nrf1, Nrf2, and ERRA are known to control mitochondrial biogenesis. However little more is known about the events that regulate cellular mitochondrial content. This month Kitami et al published a cellular imaging study analyzing the effect of a large number of small molecules on mitochondrial biogenesis in HUVEC cells. The effect of 28,786 small molecules on mitochondrial content and cell size was determined by high content analysis. Hundreds of molecules affected both cell size and mitochondrial content and 160 were selected for immunoflorescence analysis and testing mtDNA content. Twenty of these compounds were tested for respiration studies. Three compounds showed statistically significantly increases in uncoupled respiration. BRD68907 showed the greatest dose dependence effect. Interestingly while OXPHOS protein levels increased after treatment with BRD68907, mtDNA levels decreased. Therefore novel regulating pathways are likely involved. Mitochondria appeared denser, and cytochrome c turnover was reduced. While the pathway affected by BRD68907 is unknown, the authors proposed an inhibitory effect upon mitochondrial degradation pathways.
A Chemical Screen Probing the Relationship between Mitochondrial Content and Cell Size.PLoS One. 2012 Kitami T, Logan DJ, Negri J, Hasaka T, Tolliday NJ, Carpenter AE, Spiegelman BM, Mootha VK.
Also this month:
A role for ubiquitinylation and the cytosolic proteasome in turnover of mitochondrial uncoupling protein 1 (UCP1). Biochim Biophys Acta. 2012 Clarke KJ, Adams AE, Manzke LH, Pearson TW, Borchers CH, Porter RK
Nicotinamide-induced mitophagy: An event mediated by high NAD+/NADH ratio and SIRT1 activation. J Biol Chem. 2012 Jang SY, Kang HT, Hwang ES.
III. Bax, apoptosis and necrosis
Mitochondrial outer membrane permeabilization (MOMP) during apoptosis is well known to be reliant upon Bax and Bak protein oligomerization. However, in a paper this month by Whelan et al., the authors show that necrosis is also Bax dependant. Absence of Bax confers protection to necrosis as judged by specific cell morphology changes in vivo. Subsequent reconstitution of Bax restores necrotic sensitivity. In a cell culture model Bax deficient cells were also less sensitive to MPTP opening, consistent with the in vivo observations. Furthermore oligomerization of Bax does not appear to be important for necrosis. Interestingly Bax deficient cells exhibit a fragmented state. When the authors returned the mitochondria to a fused state by reconstituting Bax or inhibiting mitochondrial fission, sensitivity to MPTP opening was restored. This indicates that Bax may have a role in regulating mitochondrial dynamics and that the fused mitochondrial state is critical for MPTP opening and necrotic cell death.
Bax regulates primary necrosis through mitochondrial dynamics. PNAS. 2012 Whelan RS, Konstantinidis K, Wei AC, Chen Y, Reyna DE, Jha S, Yang Y, Calvert JW, Lindsten T, Thompson CB, Crow MT, Gavathiotis E, Dorn GW 2nd, O'Rourke B, Kitsis RN.
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