CALPAIN-MEDIATED PROTEOLYSIS OF MICROTUBULE-ASSOCIATED PROTEIN-2 (MAP-2) IS INHIBITED BY PHOSPHORYLATION BY CAMP-DEPENDENT PROTEIN-KINASE, BUT NOT BY CA2+/CALMODULIN-DEPENDENT PROTEIN KINASE-II

The effects of cAMP-dependent protein kinase (cAMP-PK) and Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylation on the calpain-mediated degradation of microtubule-associated protein 2 (MAP-2) were studied. Both cAMP-PK and CaMKII readily phosphorylated MAP-2. However, cAMP-PK phosphorylated MAP-2 to a significantly greater extent than did CaMKII (4.5 mol P-32/mol MAP-2 and 1.4 mol P-32/mol MAP-2, respectively). Phosphorylation of MAP-2 by cAMP-PK, but not by CaMKII, significantly inhibited the calpain-induced hydrolysis of MAP-2. These results demonstrate that the phosphorylation of sites on the MAP-2 molecule accessible to cAMP-PK, but not to CaMKII, result in increased resistance to calpain proteolysis.