SRC TYROSINE KINASE-ACTIVITY IN RAT THECAL-INTERSTITIAL CELLS AND MOUSE TM3 LEYDIG-CELLS IS POSITIVELY ASSOCIATED WITH CAMP-SPECIFIC PHOSPHODIESTERASE ACTIVITY

Phosphodiesterases (PDEs) play a critical role in the regulation of in tracellular cyclic nucleotide concentration and, consequently, regulat e the state of cellular differentiation. We have reported that the Src -selective tyrosine kinase inhibitor, herbimycin A, potentiates lutein izing hormone (LH)-stimulated cAMP accumulation in culture media by ov arian thecal-interstitial cells (TIC; see Taylor, C. and Terranova, P. F. (1995) Lipopolysaccharide inhibits rat ovarian thecal-interstitial cell steroid secretion in vitro. Endocrinology 136, 5527-5532). The pr esent study was conducted to investigate the effects of herbimycin, an d changes in Src tyrosine kinase activity, on PDE activity in rat TIC and in the mouse TM3 Leydig cell line. Treatment of TIC with herbimyci n (1 mu M) for 24 h inhibited basal and LH-stimulated PDE activity (ap proximate to 50 and 70%, respectively) and was associated with an incr ease in cAMP and progesterone accumulation in culture media. Treatment of TM3 cells with herbimycin inhibited PDE activity and increased cAM P accumulation in a dose- and time-dependent manner. TM3 cell cultures challenged with herbimycin had lower Src tyrosine kinase activity tha n controls (approximate to 50%); however, protein kinase A activity wa s unaffected. TM3 cells stably transfected with a dominant negative Sr c tyrosine kinase (TM3(Srck-)) had lower PDE activity than cells trans fected with a G418 resistance gene alone (TM3(pSV2neo)) which served a s control cells. Conversely, TM3 cells expressing a temperature-sensit ive Src kinase had significantly greater PDE activity at the Src activ e temperature (35 degrees C; the temperature at which the enzyme is ac tive) than TM3(pSV2neo) control cells grown at the same temperature. T M3 cell lysates hydrolyzed minimal amounts of cGMP, indicating a cAMP- specific PDE. Phosphodiesterase activity in both TM3 and rat TIC was s ensitive to the PDE4-selective inhibitor RO20-1724, indicating the pre dominant active enzyme is probably a member of the cAMP-specific PDE4 family. From the present data, we conclude that a tyrosine kinase of t he Src family may play an important role in regulating phosphodiestera se activity in thecal and Leydig cells, and thus regulate intracellula r cAMP and the state of cellular differentiation. Copyright (C) 1997 E lsevier Science Ireland Ltd.