Loss of Drp1 function alters OPA1 processing and changes mitochondrial membrane organization
ABSTRACT RNAi mediated loss of Drp1 function changes mitochondrial morphology in cultured HeLa and HUVEC cells by shifting the balance of mitochondrial fission and fusion towards unopposed fusion. Over time, inhibition of Drp1 expression results in the formation of a highly branched mitochondrial network along with "bulge"-like structures. These changes in mitochondrial morphology are accompanied by a reduction in levels of Mitofusin 1 (Mfn1) and 2 (Mfn2) and a modified proteolytic processing of OPA1 isoforms, resulting in the inhibition of cell proliferation. In addition, our data imply that bulge formation is driven by Mfn1 action along with particular proteolytic short-OPA1 (s-OPA1) variants: Loss of Mfn2 in the absence of Drp1 results in an increase of Mfn1 levels along with processed s-OPA1-isoforms, thereby enhancing continuous "fusion" and bulge formation. Moreover, bulge formation might reflect s-OPA1 mitochondrial membrane remodeling activity, resulting in the compartmentalization of cytochrome c deposits. The proteins Yme1L and PHB2 appeared not associated with the observed enhanced OPA1 proteolysis upon RNAi of Drp1, suggesting the existence of other OPA1 processing controlling proteins. Taken together, Drp1 appears to affect the activity of the mitochondrial fusion machinery by unbalancing the protein levels of mitofusins and OPA1.
- Advances in Experimental Medicine and Biology 01/2012; 749:83-95. DOI:10.1007/978-1-4614-3381-1_7 · 2.01 Impact Factor
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ABSTRACT: Mitochondria play a critical role in regulation of apoptosis, a form of programmed cell death, by releasing apoptogenic factors including cytochrome c. Growing evidence suggests that dynamic changes in mitochondrial morphology are involved in cellular apoptotic response. However, whether DRP1-mediated mitochondrial fission is required for induction of apoptosis remains speculative. Here, we show that siRNA-mediated DRP1 knockdown promoted accumulation of elongated mitochondria in HCT116 and SW480 human colon cancer cells. Surprisingly, DRP1 down-regulation led to decreased proliferation and increased apoptosis of these cells. A higher rate of cytochrome c release and reductions in mitochondrial membrane potential were also revealed in DRP1-depleted cells. Taken together, our present findings suggest that mitochondrial fission factor DRP1 inhibits colon cancer cell apoptosis through the regulation of cytochrome c release and mitochondrial membrane integrity.Biochemical and Biophysical Research Communications 04/2012; 421(1):81-5. DOI:10.1016/j.bbrc.2012.03.118 · 2.28 Impact Factor
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ABSTRACT: Huntington's disease (HD), a genetic neurodegenerative disease caused by a polyglutamine expansion in the Huntingtin (Htt) protein, is accompanied by multiple mitochondrial alterations. Here, we show that mitochondrial fragmentation and cristae alterations characterize cellular models of HD and participate in their increased susceptibility to apoptosis. In HD cells, the increased basal activity of the phosphatase calcineurin dephosphorylates the pro-fission dynamin related protein 1 (Drp1), increasing its mitochondrial translocation and activation, and ultimately leading to fragmentation of the organelle. The fragmented HD mitochondria are characterized by cristae alterations that are aggravated by apoptotic stimulation. A genetic analysis indicates that correction of mitochondrial elongation is not sufficient to rescue the increased cytochrome c release and cell death observed in HD cells. Conversely, the increased apoptosis can be corrected by manoeuvres that prevent fission and cristae remodelling. In conclusion, the cristae remodelling of the fragmented HD mitochondria contributes to their hypersensitivity to apoptosis.EMBO Molecular Medicine 12/2010; 2(12):490-503. DOI:10.1002/emmm.201000102 · 8.25 Impact Factor