Calcineurin Is Universally Involved in Vesicle Endocytosis at Neuronal and Nonneuronal Secretory Cells

• Calcineurin is involved in rapid and slow endocytosis in synapses and endocrine cells
• Calcineurin is involved in endocytosis in both mature and immature synapses
• Calcineurin and calmodulin blockers’ effects on endocytosis depend on calcium influx
• The debate about calcineurin’s universal involvement in endocytosis may be resolved

SummaryCalcium influx triggers and accelerates endocytosis in nerve terminals and nonneuronal secretory cells. Whether calcium/calmodulin-activated calcineurin, which dephosphorylates endocytic proteins, mediates this process is highly controversial for different cell types, developmental stages, and endocytic forms. Using three preparations that previously produced discrepant results (i.e., large calyx-type synapses, conventional cerebellar synapses, and neuroendocrine chromaffin cells containing large dense-core vesicles), we found that calcineurin gene knockout consistently slowed down endocytosis, regardless of cell type, developmental stage, or endocytic form (rapid or slow). In contrast, calcineurin and calmodulin blockers slowed down endocytosis at a relatively small calcium influx, but did not inhibit endocytosis at a large calcium influx, resulting in false-negative results. These results suggest that calcineurin is universally involved in endocytosis. They may also help explain the discrepancies among previous pharmacological studies. We therefore suggest that calcineurin should be included as a key player in mediating calcium-triggered and -accelerated vesicle endocytosis.

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