UP-REGULATION OF DYNAMIN-II EXPRESSION DURING THE ACQUISITION OF A MATURE PANCREATIC ACINAR CELL PHENOTYPE

Members of the dynamin superfamily are GTPases which have been shown t o support receptor-mediated endocytosis in vivo and bind to growth fac tor receptor-associated proteins in vitro. In acinar cells of the panc reas, receptor-mediated endocytosis is very important for the recyclin g of membranes after secretory granule release. Therefore, characteriz ation of the molecular machinery responsible for this process is criti cal for a better understanding of this phenomenon. In this study we so ught to determine the expression pattern of the endocytic GTPase dynam in II during pancreatic acinar cell differentiation in developing rat embryos and in dexamethasone-treated AR42J cells using Western blot, N orthern blot, and immunocytochemical analyses. During pancreatic devel opment, dynamin imnunoreactivity is almost undetectable until day E17 but undergoes significant upregulation in acinar cells starting at E18 . In addition, the levels of dynamin mRNA and protein in AR42J cells i ncrease approximately threefold during dexamethasone-induced acinar di fferentiation. The increase in dynamin levels that occurs in both embr yonic pancreatic cells and dexamethasone-treated AR42J cells correlate s with the establishment of a more differentiated acinar phenotype. Th erefore, these results suggest a potential role for dynamin in support ing receptor-mediated endocytosis in mature pancreatic acinar cells.