Regulation of phosphorylation of neuronal microtubule-associated proteins MAP1b and MAP2 by protein phosphatase-2A and-2B in rat brain

The function of the neuronal high molecular weight microtubule-associated p roteins (MAPs) MAP1b and MAP2 is regulated by the degree of their phosphory lation, which in turn is controlled by the activities of protein kinases an d protein phosphatases (PP). To investigate the role of PP in the regulatio n of the phosphorylation of MAP1b and MAP2, we used okadaic acid and cyclos porin A to selectively inhibit PP2A and PP2B activities, respectively, in m etabolically competent rat brain slices. The alteration of the phosphorylat ion levels of MAP1b and MAP2 was examined by Western blots using several ph osphorylation-dependent antibodies to these proteins. The inhibition of PP2 A, and to a lesser extent of PP2B, was found to induce an increased phospho rylation of MAP1b and inhibit its microtubule binding activity. Immunocytoc hemically, a marked increase in neuronal staining in inhibitor-treated tiss ue was observed with antibodies to the phosphorylated MAP1b. The inhibition of PP2A but not of PP2B also induced phosphorylation of MAP2 at multiple s ites and impaired its microtubule binding activity. These results suggest t hat PP2A might be the major PP that participates in regulation of the phosp horylation of MAP1b and MAP2 and their biological activities. (C) 2000 Else vier Science B.V. All rights reserved.