title: Thyrotropin-releasing hormone and phorbol esters induce phosphatidylcholine synthesis in GH3 pituitary cells. Evidence for stimulation via protein kinase C.
abstract: Phorbol esters have been shown to stimulate phosphatidylcholine synthesis via the CDP-choline pathway. The present study compares the effects of phorbol esters and thyrotropin-releasing hormone (TRH) on phosphatidylcholine metabolism in GH3 pituitary cells. In a previous study (Kolesnick, R.N., and Paley, A.E. (1987) J. Biol. Chem. 262, 9204-9210), the potent phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA) induced time- and concentration-dependent incorporation of 32Pi and [3H]choline into phosphatidylcholine in short-term labeling experiments. In this study, TPA is shown to activate choline-phosphate cytidylyltransferase (EC 2.7.7.15), the regulatory enzyme of the CDP-choline pathway, by stimulating redistribution of the inactive cytosolic form of the enzyme to the membrane. Redistribution was quantitative. TPA reduced cytosolic activity from 3.5 +/- 0.4 to 1.5 +/- 0.3 nmol . min-1 x 10(7) cells-1 and enhanced particulate activity from 2.5 +/- 0.4 to 4.9 +/- 0.6 nmol . min-1 x 10(7) cells-1. TRH also stimulated time- and concentration-dependent 32Pi and [3H]choline incorporation into phosphatidylcholine. An increase was detectable after 5 min; and after 30 min, the levels were 164 +/- 9 and 150 +/- 11% of control, respectively; EC50 congruent to 2 X 10(-10) M TRH. These events correlated directly with TRH-induced 32Pi incorporation into phosphatidylcholine. TRH also stimulated redistribution of cytidylyl-transferase specific activity. TRH reduced cytosolic activity 45% and enhanced particulate activity 51%. Neither TRH nor TPA stimulated phosphatidylcholine degradation. In cells down-modulated for protein kinase C (Ca2+/phospholipid-dependent protein kinase), the effects of TPA and TRH on 32Pi incorporation into phosphatidylcholine were abolished. However, TRH-induced incorporation into phosphatidylinositol still occurred. These studies provide evidence that hormones may regulate phosphatidylcholine metabolism via the protein kinase C pathway.
mesh_terms: D002460:Cell Line; D002794:Choline / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D010710:Phosphates / Q000378:metabolism; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D010902:Pituitary Gland / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D010710:Phosphates; D010713:Phosphatidylcholines; D013973:Thyrotropin-Releasing Hormone; D011493:Protein Kinase C; D002794:Choline; D013755:Tetradecanoylphorbol Acetate