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 proteins (MAPs) MAP1b and MAP2 is regulated by the degree of their phosphorylation, which in turn is controlled by the activities of protein kinases and protein phosphatases (PP). To investigate the role of PP in the regulation of the phosphorylation of MAP1b and MAP2, we used okadaic acid and cyclosporin A to selectively inhibit PP2A and PP2B activities, respectively, in metabolically competent rat brain slices. The alteration of the phosphorylation levels of MAP1b and MAP2 was examined by Western blots using several phosphorylation-dependent antibodies to these proteins. The inhibition of PP2A, and to a lesser extent of PP2B, was found to induce an increased phosphorylation of MAP1b and inhibit its microtubule binding activity. Immunocytochemically, a marked increase in neuronal staining in inhibitor-treated tissue was observed with antibodies to the phosphorylated MAP1b. The inhibition of PP2A but not of PP2B also induced phosphorylation of MAP2 at multiple sites and impaired its microtubule binding activity. These results suggest that PP2A might be the major PP that participates in regulation of the phosphorylation of MAP1b and MAP2 and their biological activities.