HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 79/5/947    most recent biolreprod.108.070987v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal My Folders Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Burger, L. L. Articles by Marshall, J. C. Search for Related Content PubMed PubMed Citation Articles by Burger, L. L. Articles by Marshall, J. C. Agricola Articles by Burger, L. L. Articles by Marshall, J. C.

Regulation of Intracellular Signaling Cascades by GNRH Pulse Frequency in the Rat Pituitary: Roles for CaMK II, ERK, and JNK Activation¹

Division of Endocrinology and Metabolism, Department of Medicine, and the Center for Research in Reproduction, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908

ABSTRACT

Pulsatile GnRH (GNRH) differentially regulates LH and FSH subunit genes, with faster frequencies favoring Lhb transcription and slower favoring Fshb. Various intracellular pathways mediate the effects of GNRH, including CaMK II (CAMK2), ERK, and JNK. We examined whether activation of these pathways is regulated by GNRH pulse frequency in vivo. GNRH-deficient rats received GNRH pulses (25 ng i.v. every 30 or 240 min for 8 h, vehicle to controls). Pituitaries were collected 5 min after the last pulse, bisected, and one half processed for RNA (to measure beta subunit primary transcripts [PTs]) and the other for protein. Phosphorylated CAMK2 (phospho-CAMK2), ERK (mitogen-activated protein kinase 1/3 [MAPK1/3], also known as p42 ERK2 and p44 ERK1, respectively), and JNK (MAPK8/9, also known as p46 JNK1 and p54 JNK2, respectively) were determined by Western blotting. The 30-min pulses maximally stimulated Lhb PT (8-fold), whereas 240 min was optimal for Fshb PT (3-fold increase). Both GNRH pulse frequencies increased phospho-CAMK2 4-fold. Activation of MAPK1/3 was stimulated by both 30- and 240-min pulses, but phosphorylation of MAPK3 was significantly greater following slower GNRH pulses (240 min: 4-fold, 30 min: 2-fold). MAPK8/9 activation was unchanged by pulsatile GNRH in this paradigm, but as previous results showed that GNRH-induced activation of MAPK8/9 is delayed, 5 min after GNRH may not be optimal to observe MAPK8/9 activation. These data show that CAMK2 is activated by GNRH, but not in a frequency-dependant manner, whereas MAPK3 is maximally stimulated by slow-frequency GNRH pulses. Thus, the ERK response to slow pulse frequency is part of the mechanisms mediating Fhb transcriptional responses to GNRH..

CaMKII, ERK, follicle-stimulating hormone, follistatin, GNRH, gonadotropin-releasing hormone, gonadotropins, JNK, luteinizing hormone, signal transduction

¹Supported by U.S. Public Health Service grants HD-33039 and HD-11489 to J.C.M., and the National Institute of Child Health and Human Development/National Institutes of Health through a cooperative agreement (U54-HD28934, Ligand Assay and Analysis Core, Molecular Core) as part of the Specialized Cooperative Centers Program in Reproductive Research to J.C.M. and D.J.H.

Correspondence: ²Laura L. Burger, Aurbach Medical Research Building, P.O. Box 801412, University of Virginia Health Sciences Center, Charlottesville, VA 22908. FAX: 434 243 9143; e-mail: llb3k{at}virginia.edu