BOX 123, 44 Lincoln's Inn Fields, London WC2A 3PX, United Kingdom, and the qpharrnaceutical Division, CIBA-GEIGY,. Basel, Switzerland. GH4Cl cells, which ...
Vol. 266, No.35, Issue of December 15, pp. 23761-23768,1991 Printed in U.S. A.
THEJOURNAL OF BIOLOGICAL CHEMISTRY @ 1991by The American Society for Biochemistry and Molecular Biology, Inc.
Differential Regulationof Protein KinaseC Isozymes by Thyrotropinreleasing Hormone in GH4C1 Cells* (Received for publication, August 7, 1991)
Susan C. KileyS, Peter J. Parkerg, Doriano Fabbrogll, and SusanJakenSII From the $W. AltonJones Cell Science Center, Inc., Lake Placid, New York 12946-1099,the $Imperial Cancer Research Fund, P . 0.BOX123, 44 Lincoln’s Inn Fields, London WC2A 3PX, United Kingdom, and the qpharrnaceutical Division, CIBA-GEIGY, Basel, Switzerland
GH4Cl cells, which express Ca2+-dependenta- and @- that protein kinase C (PKC)l is directly involved in the as well as Ca2+-independenty-, e- and {-protein kinase regulation of prolactin synthesis and secretion in these cells. C (PKC) isozymes, provide a cell culture model for Tumor-promoting phorbol esters which bind to and activate studying isozyme-specific propertiesand functions. PKC (2) stimulate these responses (3). Thyrotropin-releasing Hormonal activation of PKCs regulates the differen- hormone (TRH), a physiological regulator of pituitary cell tiated functions of these cells, namely secretion and function, also stimulates prolactin secretion and synthesis in synthesis of prolactin (PRL). We previously reported GH cells (4, 5). TRH activates phospholipase C mediated that thyrotropin-releasing hormone (TRH) selectively phosphatidylinositol 4,5-bisphosphate (PIPz) hydrolysis redown-modulates e-PKC with no effect on a- or @-PKCs sulting in increased cellular levels of two PKC cofactors, (Kiley, S . C., Schaap, D., Parker, P., Hsieh, L.-L., and diacylglycerol (DAG) and Caz+ (6-9). The time course of Jaken, S . (1990)J. Biol. Chern. 266, 16704-16712). TRH-mediated PKC redistribution from the soluble to the We now extend those studies to explore the relationship between TRH-stimulated diacylglycerol (DAG) levels particulate subcellular fraction corresponds to thetime course and e-PKC down-modulation. TRH stimulates three of PIPz hydrolysis (10-13). Redistribution from the soluble to distinct DAG phases in GH cells. Phase 1 DAG peaks the particulate fraction is considered the first step in PKC at 16 s, is accompanied by a 6-fold increase in intra- activation (10-13). Hence, TRH receptor occupancy is coucellular Ca2+,and causes the redistribution of a-,@-, 6, pled to PKC activation in GH cells. Protein kinase C is a growing family of enzymes which can and e-PKC isozymes from a soluble to a detergentinsoluble particulate compartment. Phase 2DAG peaks be grouped into two categories based on Caz+ requirements a t 10 min, is not associated with a Ca2+signal, anddoes for activation: Ca2+-dependent and Caz+-independent. PKC not activatePKC by any criteriatested. Phase 3 DAG isozymes a , p, BII, and y are Caz+andphospholipid-dependent peaks at 6 h and is sustained through 12 h. This novel kinases (14-16), whereas, the 6-, e ,
