An ACTH-activated protein tyrosine phosphatase (PTP) is modulated by PKA-mediated phosphorylation

In adrenal cortex, ACTH regulation of steroidogenesis depends on PKA-depend ent serine/threonine phosphorylation and also on the activity of protein ty rosine phosphatases (PTPs). In addition, ACTH increases total PTPs involvin g at least three soluble PTPs (50, 82 and 115 kDa). Serine/threonine phosph orylation of these enzymes themselves could be a regulatory mechanism of th eir activity since the increase of total PTP activity is dependent on PKA-a ctivation. In this report we analyzed the effect of in vitro phospho-dephos phorylation processes on the activity displayed by the ACTH-activated PTP o f 115 kDa. Using an in-gel PTP assay we demonstrate that dephosphorylation catalyzed by potato acid phosphatase (PAP) reduces the activity of the 115 kDa PTP present in ZF from ACTH-treated animals and PKA-mediated phosphoryl ation reverses this effect.