THE S100B PROTEIN INHIBITS PHOSPHORYLATION OF GFAP AND VIMENTIN IN A CYTOSKELETAL FRACTION FROM IMMATURE RAT HIPPOCAMPUS

The S100B protein belongs to a family of small Ca2+-binding proteins i nvolved in several functions including cytoskeletal reorganization. Th e effect of S100B on protein phosphorylation was investigated in a cyt oskeletal fraction prepared from immature rat hippocampus. An inhibito ry effect of 5 mu M S100B on total protein phosphorylation, ranging fr om 25% to 40%, was observed in the presence of Ca2+ alone, Ca2+ plus c almodulin or Ca2+ plus cAMP. Analysis by two dimensional electrophores is revealed a Ca2+/calmodulinaependent and a Ca2+/cAMP-dependent inhib itory effect of S100B, ranging from 62% to 67% of control, on the phos phorylation of the intermediate filament proteins glial fibrillary aci dic protein (GFAP) and vimentin. The fact that S100B binds to the N-te rminal domain of GFAP and that the two proteins are co-localized in as trocytes suggests a potential in vivo role for S100B in modulating the phosphorylation of intermediate filament proteins in glia.