Calcineurin regulates the yeast synaptojanin Inp53/Sjl3 during membrane stress.
Bottom Line: By activating Inp53, calcineurin repolarizes the actin cytoskeleton and maintains normal plasma membrane morphology in synaptojanin-limited cells.This response has physiological and molecular similarities to calcineurin-regulated activity-dependent bulk endocytosis in neurons, which retrieves a bolus of plasma membrane deposited by synaptic vesicle fusion.We propose that activation of Ca(2+)/calcineurin and PI(4,5)P2 signaling to regulate endocytosis is a fundamental and conserved response to excess membrane in eukaryotic cells.
Affiliation: Department of Biology, Stanford University, Stanford, CA 94305.Show MeSH
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Mentions: Therefore we tested whether any of the established or predicted protein–protein interactions for Inp53 were altered by hyperosmotic shock or its regulation by CN. In unstressed cells, Inp53 functions primarily to regulate phosphoinositide-dependent sorting of proteins at the TGN and interacts directly with clathrin via an LLDID motif in the Inp53-PRD (Ha et al., 2001, 2003; Daboussi et al., 2012). Equivalent amounts of clathrin heavy chain (Chc1) copurified with Inp53 and Inp53ARAQAA, but copurification of Chc1 with both proteins decreased after hyperosmotic shock (Figure 9A). Hyperphosphorylation of the Inp53-PRD may be responsible for reduced clathrin binding; we identified numerous phosphorylation sites in the Inp53-PRD that increased during osmotic stress, including S914, which immediately precedes LLDID915-919 (unpublished data). Loss of interaction with clathrin may indicate a repurposing of Inp53 from its normal role at the TGN to a function at actin patches and is consistent with reports of Inp53 translocation to actin patches during hyperosmotic shock (Ooms et al., 2000).
Affiliation: Department of Biology, Stanford University, Stanford, CA 94305.