AN ACTH-ACTIVATED PROTEIN TYROSINE PHOSPHATASE IS MODULATED BY PKA- DEPENDENT PHOSPHORYLATION

PAZ. C., CORNEJO MACIEL, M. F., PODEROSO, C., GOROSTIZAGA, A. AND PODESTÁ, E. J.

Toronto, Canada

Congreso; IX Adrenal Cortex Conference; 2000

We have already described that ACTH increases total protein tyrosine phosphatase (PTP) activity in the cytosolic fraction of zona fasciculata (ZF) from rat adrena! eortex, through a mechanism that involves PKA activation. Using an in-gel PTP assay with 32P-poly-glutamic-tyrosine incorporated into to the matrix gel, we detected several soluble PTPs in ZF, three of which are activated by in vivo and in vitro ACTH action. These enzyrnes migrate with molecular masses of 115, 82 and 50 kDa. ACTH activates the 115 kDa PTP in a dose-dependent fashion. The aim of the present work was to study the role of phospho-­dephosphorylation processes in the modulation of the l10 kDa enzyme. The involvement of serine/threonine phosphorylation in this activation was studied determining the effect of phosphate remotion on the 115 kDa band detected by the in-gel assay. Potato acíd phosphatase (PAP) treatment of ZF soluble proteins obtained from ACTH stímulated animals reduced the activity to the control level. This efteet was reversed by subsequent incubation with PKA catalytic subunit. The recovery of the activity was blocked when phosphorylation was performed in the presence of 50 mM H89, a PKA inhibitor. These results suggest that Serine/Threonine phosphorylation can regulate the activity of the PTP of 115 kDa. Thus, the increase of total PTP activity by ACTH might be attributed, at least partially, to the phosphorylation of this PTP by PKA.