TSH-induced differentiated functions correlate with enhancement of phosphotyrosine phosphatase activity in thyroid cells. Effect of phorbol 12-myristate 13-acetate

TSH-treated pig thyroid cells reorganize into follicle-like structures and exhibit differentiated functions. TSH also induces a phosphotyrosine phosph atase (PTPase) activity evaluated by phosphorylated substrate hydrolysis. I ncubation of thyrocytes with various concentrations of 8-bromo-cyclic AMP o r forskolin induces an increase of PTPase activity ill a dose-dependent man ner. During the culture period, adenylyl cyclase sensitivity. protein bindi ng iodine and PTPase activity progressively increase from the first to the fourth day of the culture. Chronic treatment with phorbol 12-myristate 13-a cetate (PMA) significantly inhibits PTPase activity during the first 24 h f ollowing PMA addition. GF 109203X a specific inhibitor of protein kinase C, abolishes the inhibitory effect of PMA. Electrophoresis of membrane extrac ts allowed us to demonstrate a phosphatase activity at 111 kDa (p111). Vana date inhibits this activity, indicating that pill is a PTPase. This p111 is significantly reduced in PMA-treated cells. These data suggest chat PTPase activity evidenced at 111 kDa is correlated with a differentiated state of primary cultured pig thyroid cells induced by TSH.