Gonadotropin-releasing hormone stimulation of gonadotropin subunit transcription: evidence for the involvement of calcium/calmodulin-dependent kinase II (Ca/CAMK II) activation in rat pituitaries.
The intracellular pathways mediating GnRH regulation of gonadotropin subunit transcription remain to be fully characterized, and the present study examined whether calcium/calmodulin-dependent kinase II (Ca/CAMK II) plays a role in the rat pituitary. Preliminary studies demonstrated that a single pulse of GnRH given to adult rats stimulated a transient 2.5-fold rise in Ca/CAMK II activity (as determined by an increase in Ca/CAMK II phosphorylation), with peak values at 5 min, returning to basal 45 min after the pulse. Further studies examined the alpha, LHbeta, and FSHbeta transcriptional responses to GnRH or Bay K 8644+KCl (BK+KCl) pulses in vitro in the absence or presence of the Ca/CAMK II-specific inhibitor, KN-93. Gonadotropin subunit transcription was assessed by measuring primary transcripts (PTs) by quantitative RT-PCR. In time-course studies, both GnRH and BK+KCl pulses given alone increased all three subunit PTs after 6 h (2- to 4-fold). PT responses to GnRH increased over time (3- to 8-fold over basal at 24 h), although BK+KCl was ineffective after 24 h. KN-93 reduced the LHbeta and FSHbeta transcriptional responses to GnRH by 50-60% and completely suppressed the alphaPT response. In contrast, KN-93 showed no inhibitory effects on basal transcriptional activity or LH or FSH secretion. In fact, KN-93 tended to increase basal alpha, LHbeta, and FSHbeta PT levels and enhance LH secretory responses to GnRH. These results reveal that Ca/CAMK II plays a central role in the transmission of pulsatile GnRH signals from the plasma membrane to the rat alpha, LHbeta, and FSHbeta subunit genes.
Haisenleder
D J
DJ
Division of Endocrinology and Metabolism, Department of Medicine, University of Virginia Health Sciences Center, Aurbach Medical Research Building, PO Box 801412, Charlottesville, VA 22908, USA. djh2q@virginia.edu
Burger
L L
LL
Aylor
K W
KW
Dalkin
A C
AC
Marshall
J C
JC
D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005260:Female; D037201:Follicle Stimulating Hormone, beta Subunit / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006062:Gonadotropins / Q000235:genetics*; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000201:enzymology*; D011673:Pulsatile Flow / Q000502:physiology; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
D037201:Follicle Stimulating Hormone, beta Subunit; D015292:Glycoprotein Hormones, alpha Subunit; D006062:Gonadotropins; D037101:Luteinizing Hormone, beta Subunit; D007987:Gonadotropin-Releasing Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases