The endogenous caspase-8 inhibitor c-FLIPL regulates ER morphology and crosstalk with mitochondria.
Ontology highlight
ABSTRACT:
SUBMITTER: Marini ES
PROVIDER: S-EPMC4572861 | biostudies-other | 2015 Jul
REPOSITORIES: biostudies-other
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Project description:The endoplasmic reticulum (ER) and mitochondria form tight functional contacts that regulate several key cellular processes. The formation of these contacts involves "tethering proteins" that function to recruit regions of ER to mitochondria. The integral ER protein VAPB (VAMP associated protein B and C) binds to the outer mitochondrial membrane protein, RMDN3/PTPIP51 (regulator of microtubule dynamics 3) to form one such set of tethers. Recently, we showed that the VAPB-RMDN3 tethers regulate macroautophagy/autophagy. Small interfering RNA (siRNA) knockdown of VAPB or RMDN3 to loosen ER-mitochondria contacts stimulates autophagosome formation, whereas overexpression of VAPB or RMDN3 to tighten contacts inhibit their formation. Artificial tethering of ER and mitochondria via expression of a synthetic linker protein also reduces autophagy and this artificial tether rescues the effects of VAPB- or RMDN3-targeted siRNA loss on autophagosome formation. Finally, our studies revealed that the modulatory effects of ER-mitochondria contacts on autophagy involve their role in mediating ITPR (inositol 1,4,5-trisphosphate receptor) delivery of Ca2+ from ER stores to mitochondria.
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Project description:We have identified Rab10 as an ER-specific Rab GTPase that regulates ER structure and dynamics. We show that Rab10 localizes to the ER and to dynamic ER-associated structures that track along microtubules and mark the position of new ER tubule growth. Rab10 depletion or expression of a Rab10 GDP-locked mutant alters ER morphology, resulting in fewer ER tubules. We demonstrate that this defect is due to a reduced ability of dynamic ER tubules to grow out and successfully fuse with adjacent ER. Consistent with this function, Rab10 partitions to dynamic ER-associated domains found at the leading edge of almost half of all dynamic ER tubules. Interestingly, this Rab10 domain is highly enriched with at least two ER enzymes that regulate phospholipid synthesis, phosphatidylinositol synthase (PIS) and CEPT1. Both the formation and function of this Rab10/PIS/CEPT1 dynamic domain are inhibited by expression of a GDP-locked Rab10 mutant. Together, these data demonstrate that Rab10 regulates ER dynamics and further suggest that these dynamics could be coupled to phospholipid synthesis.
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