Steroid and pulsatile gonadotropin-releasing hormone (GnRH) regulation of luteinizing hormone and GnRH receptor in a novel gonadotrope cell line.
Properties of a pituitary gonadotrope include the capacity to regulate gonadotropin synthesis and secretion in response to a GnRH signal. Progress in identifying the steps involved in these processes has been impeded by the lack of a homogeneous in vitro model of gonadotropes. This paper presents functional characterization of a L beta T2 gonadotrope cell line generated by tumorigenesis in transgenic mice carrying the rat LH beta-subunit regulatory region linked to the SV40 T-antigen oncogene. This cell line expresses LH beta, alpha-subunit, and GnRH-receptor (GnRH-R) mRNAs (though not FSH beta), responds to glucocorticoid treatment with a reversible dampening of proliferation, and responds to pulsatile, concentration-dependent GnRH administration with LH secretion. L beta T2 cells presented with four GnRH pulses (10 nM, 90-min interpulse interval) on each of 4 days respond with incremental increases in LH secretion on successive days. This increase was greatest (15-fold) in the presence of estradiol and dexamethasone. Part of the enhanced responsiveness is apparently due to an increase in GnRH-R; pulsatile GnRH treatment alone as well as steroid treatment alone led to an increase in GnRH-R mRNA levels. When secretion was stimulated on day 4 with 54 mM [K+] pulses, bypassing the GnRH-R, the LH-secretory response indicated that the GnRH pulse history as well as estradiol and dexamethasone have actions on L beta T2-secretory capacity distinct from changes in the GnRH-R. This increase can be explained in part by the marked up-regulation of LH beta, but not alpha-subunit, mRNA observed in GnRH-pulsed cells. In summary, L beta T2 clonal gonadotropes exhibit functional characteristics consistent with those of normal pituitary gonadotropes such as LH secretion via a regulated pathway and changes in GnRH-R and LH beta gene expression in response to signaling by GnRH and steroid hormones and therefore should be a useful tool for dissecting the cellular and molecular events involved in these fundamental gonadotrope properties.
Turgeon
J L
JL
Department of Human Physiology, University of California, Davis 95616, USA.
Kimura
Y
Y
Waring
D W
DW
Mellon
P L
PL
D000704:Analysis of Variance; D000818:Animals; D000957:Antigens, Viral, Tumor / Q000096:biosynthesis / Q000235:genetics; D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects; D017931:DNA Primers; D003907:Dexamethasone / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone; D037201:Follicle Stimulating Hormone, beta Subunit; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D015292:Glycoprotein Hormones, alpha Subunit / Q000096:biosynthesis; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009857:Oncogenes; D010911:Pituitary Neoplasms / Q000503:physiopathology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011966:Receptors, LHRH / Q000096:biosynthesis*; D013539:Simian virus 40 / Q000235:genetics; D013997:Time Factors; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D000957:Antigens, Viral, Tumor; D017931:DNA Primers; D037201:Follicle Stimulating Hormone, beta Subunit; D015292:Glycoprotein Hormones, alpha Subunit; D012333:RNA, Messenger; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D003907:Dexamethasone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone