Distribution of protein phosphatases type 1 and 2A in RINm5F cells

In the insulin producing cell line RINm5F distribution of serine/threonine specific protein phosphatases type 1 (PPI) and 2A (PP2A) was studied. Using different agents which inhibit or stimulate PPI and PP2A we found that in membrane and nuclear fractions phosphatase activity was inhibited by okadaic acid (OA), protamine, heparin, and inhibitor-2 in a concentration-dependent manner. C-2-ceramide had no effect. In the cytosolic fraction the inhibitory effect of okadaic acid was tenfold higher. Protamine stimulated phosphatase activity at low concentrations and became inhibitory at higher concentrations. Inhibitor-2 and heparin caused a decrease in phosphatase activity whereas C-2-ceramide led to a slight activation. The data suggest that in membrane and nuclear fractions of RINm5F cells predominantly PPI is present, whereas in the cytosol PPI as well as PP2A can be detected. (C) 1998 Elsevier Science B.V. All rights reserved.