Induction of secretogranin II mRNA by protein synthesis inhibitors in GH4C1 cells.
The effect of cycloheximide (CHX) on the expression of secretogranin II (SgII), a member of the granin family of secretory proteins, was investigated in rat pituitary GH4C1 (GH) cells. The administration of CHX resulted in a dose- and time-dependent increase in SgII mRNA expression, the greatest effect (3.8-fold above control) being achieved with 1 microgram/ml CHX, which resulted in > 90% inhibition of protein synthesis. Emetine (1 microgram/ml), pactamycin (0.6 microgram/ml), anisomycin (2.5 micrograms/ml), and puromycin (100 micrograms/ml), protein synthesis inhibitors structurally and mechanistically unrelated to CHX, also increased the level of SgII mRNA expression. Treatment with forskolin (10 microM) alone had no effect on SgII mRNA levels but potentiated the effect of CHX. Neither 100 nM phorbol 12-myristate 13-acetate nor 45 mM KCl affected SgII mRNA levels in the absence or presence of 1 microgram/ml CHX. The effect of CHX was blocked by the transcription inhibitors actinomycin D (5 micrograms/ml) and 5,6-dichlorobenzimidazole riboside (20 micrograms/ml) but not by the coadministration of the polysome destabilizer pactamycin (0.6 microgram/ml), suggesting that the effect of CHX was transcriptional. These studies show that the expression of SgII mRNA is induced by protein synthesis inhibitors in GH cells, suggesting the presence of a labile repressor, which not only controls the basal expression of the SgII gene but also completely inhibits the stimulatory effect of forskolin.
Department of Pharmacology, University of South Alabama, College of Medicine, Mobile 36688.
J G
JG
Scammell
D L
DL
Valentine
D000818:Animals; D002460:Cell Line; D002864:Chromogranins; D005576:Colforsin / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D014158:Transcription, Genetic
D002864:Chromogranins; D011506:Proteins; D012333:RNA, Messenger; D005576:Colforsin; D003513:Cycloheximide