Ras is mutated in up to 30% of cancers, including 90% of pancreatic ductal adenocarcinomas, causing it to be constitutively GTP-bound, and leading to activation of downstream effectors that promote a ...tumorigenic phenotype. As targeting Ras directly is difficult, there is a significant effort to understand the downstream biological processes that underlie its protumorigenic activity. Here, we show that expression of oncogenic Ras or direct activation of the MAPK pathway leads to increased mitochondrial fragmentation and that blocking this phenotype, through knockdown of the mitochondrial fission-mediating GTPase Drp1, inhibits tumor growth. This fission is driven by Erk2-mediated phosphorylation of Drp1 on Serine 616, and both this phosphorylation and mitochondrial fragmentation are increased in human pancreatic cancer. Finally, this phosphorylation is required for Ras-associated mitochondrial fission, and its inhibition is sufficient to block xenograft growth. Collectively, these data suggest mitochondrial fission may be a target for treating MAPK-driven malignancies.
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•Drp1 is required for xenograft growth•MAPK promotes mitochondrial fragmentation through Drp1•Erk2 phosphorylates Drp1 to promote mitochondrial fission•Drp1 S616 phosphorylation is required for mitochondrial fission and tumor growth
Mitochondrial function is important for the growth of tumors driven by oncogenic Ras or the MAPK pathway. Kashatus et al. demonstrate that activation of these pathways leads to Mek-dependent phosphorylation of the GTPase Drp1 and subsequent mitochondrial fragmentation. They further demonstrate that inhibition of Drp1 or its phosphorylation blocks tumor growth.
Mitochondrial dynamics are increasingly recognized to play an important role in regulating mitochondrial function in response to diverse stimuli. Given the overlap in the physiological processes ...influenced by mitochondria and the physiological processes disrupted in tumor cells, we speculate that tumor cells alter mitochondrial shape to promote the tumorigenic phenotype. Here, we briefly review the evidence linking changes in mitochondrial fusion and fission to a number of key tumorigenic processes, including metabolic rewiring, inhibition of cell death, cell migration, cell proliferation and self-renewal capacity. The role of mitochondrial dynamics in tumor growth is an important emerging area of research, a better understanding of which may lead to promising new therapeutic options for the treatment of cancer.
•Mitochondrial fusion and fission can influence mitochondrial function.•Mitochondrial function underlies a number of physiological changes associated with cancer.•Mitochondrial dynamics represent a potential mechanism cancer cells use to promote tumorigenic growth.
Oncogenic Ras proteins rely on a series of key effector pathways to drive the physiological changes that lead to tumorigenic growth. Of these effector pathways, the RalGEF pathway, which activates ...the two Ras-related GTPases RalA and RalB, remains the most poorly understood. This review will focus on key developments in our understanding of Ral biology, and will speculate on how aberrant activation of the multiple diverse Ral effector proteins might collectively contribute to oncogenic transformation and other aspects of tumor progression.
•The RalGEF-Ral pathway is a key effector pathway downstream of oncogenic Ras.•RalA and RalB exhibit distinct and redundant roles in tumorigenesis.•RalA and RalB activate a diverse set of effector pathways.•Ral GTPases potentially regulate several hallmarks of human cancer.
Mitochondria undergo fission and fusion to maintain homeostasis, and tumors exhibit the dysregulation of mitochondrial dynamics. We recently demonstrated that ectopic HRasG12V promotes mitochondrial ...fragmentation and tumor growth through Erk phosphorylation of the mitochondrial fission GTPase Dynamin-related protein 1 (Drp1). However, the role of Drp1 in the setting of endogenous oncogenic KRas remains unknown. Here, we show that Drp1 is required for KRas-driven anchorage-independent growth in fibroblasts and patient-derived pancreatic cancer cell lines, and it promotes glycolytic flux, in part through the regulation of hexokinase 2 (HK2). Furthermore, Drp1 deletion imparts a significant survival advantage in a model of KRas-driven pancreatic cancer, and tumors exhibit a strong selective pressure against complete Drp1 deletion. Rare tumors that arise in the absence of Drp1 have restored glycolysis but exhibit defective mitochondrial metabolism. This work demonstrates that Drp1 plays dual roles in KRas-driven tumor growth: supporting both glycolysis and mitochondrial function through independent mechanisms.
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•Drp1 is required for oncogenic KRas-driven transformation•Drp1 promotes KRas-driven glycolysis•Loss of Drp1 inhibits pancreatic tumorigenesis•Loss of Drp1 impairs mitochondrial metabolism in tumor cells
Nagdas et al. find that the mitochondrial fission GTPase Drp1 is required for KRas-driven transformation and pancreatic tumor growth. The inhibition of Drp1 in cells expressing oncogenic KRas leads to impaired glycolytic flux and the eventual loss of mitochondrial metabolic function.
The proximal tubule epithelium relies on mitochondrial function for energy, rendering the kidney highly susceptible to ischemic AKI. Dynamin-related protein 1 (DRP1), a mediator of mitochondrial ...fission, regulates mitochondrial function; however, the cell-specific and temporal role of DRP1 in AKI
is unknown. Using genetic murine models, we found that proximal tubule-specific deletion of
prevented the renal ischemia-reperfusion-induced kidney injury, inflammation, and programmed cell death observed in wild-type mice and promoted epithelial recovery, which associated with activation of the renoprotective
-hydroxybutyrate signaling pathway. Loss of DRP1 preserved mitochondrial structure and reduced oxidative stress in injured kidneys. Lastly, proximal tubule deletion of DRP1 after ischemia-reperfusion injury attenuated progressive kidney injury and fibrosis. These results implicate DRP1 and mitochondrial dynamics as an important mediator of AKI and progression to fibrosis and suggest that DRP1 may serve as a therapeutic target for AKI.
Mitochondrial dynamics play an important role within several pathological conditions, including cancer and neurological diseases. For the purpose of identifying therapies that target aberrant ...regulation of the mitochondrial dynamics machinery and characterizing the regulating signaling pathways, there is a need for label-free means to detect the dynamic alterations in mitochondrial morphology. We present the use of dielectrophoresis for label-free quantification of intracellular mitochondrial modifications that alter cytoplasmic conductivity, and these changes are benchmarked against label-based image analysis of the mitochondrial network. This is validated by quantifying the mitochondrial alterations that are carried out by entirely independent means on two different cell lines: human embryonic kidney cells and mouse embryonic fibroblasts. In both cell lines, the inhibition of mitochondrial fission that leads to a mitochondrial structure of higher connectivity is shown to substantially enhance conductivity of the cell interior, as apparent from the significantly higher positive dielectrophoresis levels in the 0.5-15 MHz range. Using single-cell velocity tracking, we show ∼10-fold higher positive dielectrophoresis levels at 0.5 MHz for cells with a highly connected versus those with a highly fragmented mitochondrial structure, suggesting the feasibility for frequency-selective dielectrophoretic isolation of cells to aid the discovery process for development of therapeutics targeting the mitochondrial machinery.
Brain tumor initiating cells (BTICs) co-opt the neuronal high affinity glucose transporter, GLUT3, to withstand metabolic stress. We investigated another mechanism critical to brain metabolism, ...mitochondrial morphology, in BTICs. BTIC mitochondria were fragmented relative to non-BTIC tumor cell mitochondria, suggesting that BTICs increase mitochondrial fission. The essential mediator of mitochondrial fission, dynamin-related protein 1 (DRP1), showed activating phosphorylation in BTICs and inhibitory phosphorylation in non-BTIC tumor cells. Targeting DRP1 using RNA interference or pharmacologic inhibition induced BTIC apoptosis and inhibited tumor growth. Downstream, DRP1 activity regulated the essential metabolic stress sensor, AMP-activated protein kinase (AMPK), and targeting AMPK rescued the effects of DRP1 disruption. Cyclin-dependent kinase 5 (CDK5) phosphorylated DRP1 to increase its activity in BTICs, whereas Ca(2+)-calmodulin-dependent protein kinase 2 (CAMK2) inhibited DRP1 in non-BTIC tumor cells, suggesting that tumor cell differentiation induces a regulatory switch in mitochondrial morphology. DRP1 activation correlated with poor prognosis in glioblastoma, suggesting that mitochondrial dynamics may represent a therapeutic target for BTICs.
In this issue of Molecular Cell, Adachi et al. (2016) describe a novel interaction between the mitochondrial fission GTPase Drp1 and phosphatidic acid that restrains Drp1 activity and shifts the ...balance toward mitochondrial fusion, adding another layer of complexity to the regulation of mitochondrial dynamics.
In this issue of Molecular Cell, Adachi et al. (2016) describe a novel interaction between the mitochondrial fission GTPase Drp1 and phosphatidic acid that restrains Drp1 activity and shifts the balance toward mitochondrial fusion, adding another layer of complexity to the regulation of mitochondrial dynamics.
Oncogenic KRas activates mitochondrial fission through Erk-mediated phosphorylation of the mitochondrial fission GTPase Drp1. Drp1 deletion inhibits tumorigenesis of KRas-driven pancreatic cancer, ...but the role of mitochondrial dynamics in other Ras-driven malignancies is poorly defined. Here we show that in vitro and in vivo growth of KRas-driven lung adenocarcinoma is unaffected by deletion of Drp1 but is inhibited by deletion of Opa1, the GTPase that regulates inner membrane fusion and proper cristae morphology. Mechanistically, Opa1 knockout disrupts cristae morphology and inhibits electron transport chain (ETC) assembly and activity, which inhibits tumor cell proliferation through loss of NAD+ regeneration. Simultaneous inactivation of Drp1 and Opa1 restores cristae morphology, ETC activity, and cell proliferation indicating that mitochondrial fission activity drives ETC dysfunction induced by Opa1 knockout. Our results support a model in which mitochondrial fission events disrupt cristae structure, and tumor cells with hyperactive fission activity require Opa1 activity to maintain ETC function.
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•KRas-mutant lung adenocarcinoma requires Opa1, but not Drp1, in vitro and in vivo•Acute Opa1 deletion inhibits LUAD by disrupting ETC function, not fusion or apoptosis•Mitochondrial fission unopposed by Opa1 inhibits ETC assembly and NAD+ regeneration
Sessions et al. find that KRas-mutant lung adenocarcinoma requires the mitochondrial fusion GTPase Opa1 to maintain cristae structure and ETC function. Opa1 deletion leads to mitochondrial fission-mediated ETC disassembly and inhibition of NAD+ regeneration required for oxidative metabolism. Drp1 deletion does not inhibit LUAD development, but it rescues effects of Opa1 deletion.
Mitochondria exist as dynamic interconnected networks that are maintained through a balance of fusion and fission. Equal distribution of mitochondria to daughter cells during mitosis requires ...fission. Mitotic mitochondrial fission depends on both the relocalization of the large GTPase DRP1 to the outer mitochondrial membrane and phosphorylation of Ser 616 on DRP1 by the mitotic kinase cyclin B-CDK1 (ref. ). We now report that these processes are mediated by the small Ras-like GTPase RALA and its effector RALBP1 (also known as RLIP76, RLIP1 or RIP1; refs , ). Specifically, the mitotic kinase Aurora A phosphorylates Ser 194 of RALA, relocalizing it to the mitochondria, where it concentrates RALBP1 and DRP1. Furthermore, RALBP1 is associated with cyclin B-CDK1 kinase activity that leads to phosphorylation of DRP1 on Ser 616. Disrupting either RALA or RALBP1 leads to a loss of mitochondrial fission at mitosis, improper segregation of mitochondria during cytokinesis and a decrease in ATP levels and cell number. Thus, the two mitotic kinases Aurora A and cyclin B-CDK1 converge on RALA and RALBP1 to promote mitochondrial fission, the appropriate distribution of mitochondria to daughter cells and ultimately proper mitochondrial function.
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