Regulation of prolactin, thyrotropin subunit, and gonadotropin subunit gene expression by pulsatile or continuous calcium signals.
We investigated the importance of calcium (Ca2+) influx in increasing the steady state concentrations of mRNAs coding for the pituitary peptides PRL, alpha, and TSH, LH, and FSH beta-subunits. Adult female rat pituitaries were dissociated, plated for 48 h, then inserted into perifusion chambers. Secretory responses were measured after 2 and 22 h of perifusion, and after 24 h, the cells were recovered, total RNA was extracted, and mRNAs were assayed by dot blot hybridization. The first experiment examined the effect of the Ca2+ channel blocker verapamil (100 microM) on the stimulatory action of pulsatile TRH (4 nM; 60-min interval) or GnRH (100 pM; 60-min interval) on pituitary mRNAs. TRH pulses induced a significant increase (49-56%) in PRL, alpha, and TSH beta mRNAs. Similarly, GnRH pulses stimulated a rise in alpha (64%) and FSH beta (50%) mRNAs, but not LH beta. The effects of pulsatile TRH or GnRH were eliminated when verapamil was added to the medium, suggesting that Ca2+ influx is critical to the stimulatory action of TRH or GnRH. The second experiment examined the effect of pulsatile vs. continuous increases in intracellular Ca2+ on pituitary mRNA expression. Pulsatile Ca2+ signals were produced by giving 60-min pulses of 50 mM KCl, Bay K 8644 (10 microM), or Bay K 8644 (10 microM; in the presence of 10 mM KCl in the injectate) and vehicle pulses to controls. Continuous increases in intracellular Ca2+ were induced by perifusion with medium containing the Ca2+ ionophore A23187 (20 microM), and these groups were compared to that receiving continuous verapamil. Pulsatile increases in Ca2+ influx (KCl or Bay K 8644) stimulated significant elevations in all mRNAs studied (36-74% increase vs. controls), with the exception of TSH beta. The magnitude of the mRNA responses to pulsatile Ca2+ (vs. controls) was similar to that observed after TRH and GnRH pulses. In contrast, only LH beta was increased by A23187 (42% increase vs. controls; P < 0.05). PRL and alpha mRNAs were selectively diminished by A23187 (57% and 83% decreases vs. controls, respectively; P < 0.05) and verapamil (67% and 60%; P < 0.05). The data show that expression of these pituitary genes is regulated by Ca2+ and that a pulsatile Ca2+ signal is required to stimulate PRL, alpha, and FSH beta (but not LH beta).(ABSTRACT TRUNCATED AT 400 WORDS)
Haisenleder
D J
DJ
Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.
Yasin
M
M
Yasin
A
A
Marshall
J C
JC
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000235:genetics; D037201:Follicle Stimulating Hormone, beta Subunit; D005786:Gene Expression Regulation; D006065:Gonadotropins, Pituitary / Q000235:genetics*; D007986:Luteinizing Hormone / Q000235:genetics; D010507:Periodicity; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D013972:Thyrotropin / Q000235:genetics*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D015220:Calcium Channels; D037201:Follicle Stimulating Hormone, beta Subunit; D006065:Gonadotropins, Pituitary; D012333:RNA, Messenger; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013972:Thyrotropin; D014700:Verapamil; D002118:Calcium