TYROSINE PHOSPHORYLATION AND DEPHOSPHORYLATlON OF ENDOGENOUS PROTEINS IN STEROIDOGENIC CELLS STIMULATED BY cAMP

PODEROSO C, MARTÍN PÉREZ J. PAZ C. PODESTÁ EJ, CORNEJO MACIEL F

Bariloche, Rio Negro

Congreso; XXXIX Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB).; 2003

SAIB

It is very well known that in steroidogenie cells Ser/Thr phosphor-dephosphorylation events are important regulators of hormone action. However, we have previously demonstrated that a protein basely phosphorylated in a tyrosine residue must be dephosphorylated after hormone action in order to obtain stimulation of steroid synthesis. Therefore, one can conclude that both tyrosine phospho and dephosphorylalion may be also important events in steroid synthesis. In order to study the participation of both processes, we studied the action of hormones in the tyrosine phosphorylation and dephosphorylation of endogenous substrates in intact cells. It was possible to dernonstrate a transient increase in the phosphotyrosine level of a 50 kDa protein in MA-10 celIs a well known Leydig cell line. The stimulation was maximal after 5 minutes of cAMP action and dephosphorylalion rapidly occurs afterwards. A parallel analysis of ERK 1/2 phosphorylation, also detected a hormone activation of this MAPK. In Y1 ceIls (adrenocortical cell line), the same stimulus provokes, after 15 minutes, the dephosphorylation of a protein of about 30 kDa, demonstrated by two dimensional gel electrophoresis. Taken together, these results show that after cAMP action, tyrosine dephosphorylation occurs together with tyrosine phosphorylation on different substrates, indicating that tyrosine kinases and phosphatases could be acting in parallel.