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: The depolarization and subsequent repolarization of the actin cytoskeleton is a prominent and acute cellular response to hyperosmotic shock (Chowdhury et al., 1992). CN localization to sites of polarized growth and partial colocalization with Abp1 suggested that the phosphatase might regulate the actin cytoskeleton during hyperosmotic shock. To test this idea, cells were exposed to 1.25 M KCl, fixed at 30-min intervals, stained for actin with rhodamine–phalloidin, and polarization quantified using image-analysis software (see Materials and Methods). Control cells were maximally depolarized (50%) 2 h after exposure to 1.25 M KCl, and polarity was largely restored by 4 h (Figure 3, A and B). Inactivation of CN with FK506 exacerbated depolarization at 120 and 150 min; however, as in control cells, polarity was reestablished by 4 h (Figure 3, A and B). Analyzing the distributions of cellular fluorescence ratios at 120 and 150 min after hyperosmotic shock showed that FK506 significantly decreased polarization compared with the control (Figure 3C; p < 10−9). Thus CN promotes repolarization of the actin cytoskeleton after hyperosmotic challenge.
Affiliation: Department of Biology, Stanford University, Stanford, CA 94305.