Ca2+ channel modulation and kinase-C activation in a pituitary cell line: induction of immediate early genes and inhibition of proliferation.
We have studied the interaction between dihydropyridine (DHP) Ca2+ modulators and the phorbol ester phorbol 12-myristate 13-acetate (PMA) on whole cell Ca2+ currents, 45Ca2+ uptake, immediate early gene (IEG) expression, and proliferation in the rat pituitary GH4C1 cell line. When short (3- to 5-msec) depolarizing voltage clamp steps were used to activate L-type Ca2+ channels, the DHP Ca2+ agonist (-)Bay K 8644 markedly enhanced Ca2+ entry by slowing channel closing upon repolarization. In contrast, the Ca2+ agonist induced only small and inconsistent increases in c-fos mRNA and did not measurably increase NGFI-A. Ca2+ channel activation by depolarization with 50 mM KCl in the presence of (-)Bay K 8644 induced large increases in 45Ca2+ uptake, but failed to markedly induce either of the IEGs. The phorbol ester PMA did not alter T- or L-type Ca2+ current or 45Ca2+ uptake by GH4C1 cells, but triggered large increases in both c-fos and NGFI-A mRNA. In combination, PMA and (-)Bay K 8644 acted synergistically to increase mRNAs for both IEGs. The effect of the DHPs was stereospecific; (+)Bay K 8644, a Ca2+ antagonist, inhibited PMA-induced increases in c-fos and NGFI-A mRNAs. Both PMA and (-)Bay K 8644 inhibited the proliferation of GH4C1 cells, measured by cell count or [3H]thymidine incorporation. The inhibition by the Ca2+ agonist was stereoselective and approximately additive to that of PMA. These results indicate that the expression of c-fos IEG and that of NGFI-A IEG are differentially regulated by separate second messenger pathways in GH4C1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Duchemin
A M
AM
Department of Pharmacology, Ohio State University, Columbus 43210-1239.
Enyeart
J A
JA
Biagi
B A
BA
Foster
D N
DN
Mlinar
B
B
Enyeart
J J
JJ
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects; D004789:Enzyme Activation; D005809:Genes, Regulator / Q000187:drug effects*; D016762:Genes, fos / Q000187:drug effects; D007536:Isomerism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010911:Pituitary Neoplasms; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism
D015220:Calcium Channels; D012333:RNA, Messenger; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D013936:Thymidine