Overlapping functions of different dynamin isoforms in clathrin-dependent and -independent endocytosis in pancreatic beta cells.

Previously, we identified a clathrin-dependent slow endocytosis and a clathrin-independent fast endocytosis in pancreatic beta cells, both triggered by elevated cytoplasmic Ca(2+) concentration. In the current study, we attempted to explore the roles of different dynamin isoforms in these endocytotic processes. We first confirmed the existence of both neuron-specific dynamin 1 and ubiquitous dynamin 2 in INS-1 cells using both quantitative RT-PCR and Western blot experiments. By specifically knocking down the endogenous level of either dynamin isoform from INS-1 cells, we showed that dynamin 1 and dynamin 2 simultaneously participate in the clathrin-independent and -dependent membrane retrieval in pancreatic beta cells. Transferrin internalization was also inhibited in cells with knock down of both dynamin 1 and dynamin 2. Based on these results, we argue that different dynamin isoforms play overlapping roles in different types of endocytosis.