HORMONAL-REGULATION OF FOCAL ADHESIONS IN BOVINE ADRENOCORTICAL-CELLS- INDUCTION OF PAXILLIN DEPHOSPHORYLATION BY ADRENOCORTICOTROPIC HORMONE

A study of bovine adrenocortical cell shape on adrenocorticotropic hor mone (ACTH) challenge showed that the cells round up and develop arbor ized processes. This effect was found to be (1) specific for ACTH beca use angiotensin II and basic fibroblast growth factor have no effect; (2) mediated by a cAMP-dependent pathway because forskolin reproduces the effect of the hormone; (3) inhibited by sodium orthovanadate, a ph osphotyrosine phosphatase inhibitor, but unchanged by okadaic acid, a serine/threonine phosphatase inhibitor; and (4) correlated with a comp lete loss of focal adhesions. Biochemical studies of the focal-adhesio n-associated proteins showed that pp125(fak), vinculin (110 kDa) and p axillin (70 kDa) were detected in the Triton X-100-insoluble fraction from adrenocortical cells. During cell adhesion on fibronectin as subs tratum, two major phosphotyrosine-containing proteins of molecular mas ses 125 and 68 kDa were immunodetected in the same fraction. A dramati c decrease in the extent of tyrosine phosphorylation of these proteins was observed within 60 min after treatment with ACTH. No change in pp 125(fak) tyrosine phosphorylation nor in Src activity was detected. In contrast, paxillin was found to be tyrosine-dephosphorylated in a tim e-dependent manner in ACTH-treated cells. Sodium orthovanadate complet ely prevented the effect of ACTH. These observations suggest a possibl e role for phosphotyrosine phosphatases in hormone-dependent cellular regulatory processes.