Regulation of human glycoprotein hormone alpha-subunit gene transcription in LbetaT2 gonadotropes by protein kinase C and extracellular signal-regulated kinase 1/2.
Transcriptional activation of the human glycoprotein hormone alpha-subunit (alphaGSU) promoter in response to GnRH and phorbol-12-myristate-13-acetate (PMA) has been well characterized in alphaT3-1 gonadotropes but not investigated in the more differentiated LbetaT2 clonal gonadotrope. We have evaluated alphaGSU transcription in the more mature LbetaT2 cell line, using deletion and heterologous constructs of the alphaGSU promoter linked to a luciferase reporter gene. Basal alphaGSU-promoter activity was significantly less in LbetaT2 cells than in alphaT3-1 cells, but stimulation of transfected cells with GnRH and PMA resulted in similar increases in alphaGSU-promoter activity. Deletional analysis of the human alphaGSU promoter in LbetaT2 cells indicated that sequences between -398 and -244 and between -244 and -195 base pairs (bp) were involved in regulating basal alphaGSU-promoter transcription, whereas the region between -244 and -195 bp regulated PMA-stimulated promoter activity. Deletion of this promoter region containing a steroidogenic factor-1 (SF-1) binding site abolished basal and PMA-stimulated transcription. Site-directed mutagenesis of the SF-1 binding site resulted in a significant attenuation of basal and PMA-stimulated alphaGSU transcription. Pretreatment of LbetaT2 cells with a mitogen-activated protein kinase kinase-specific inhibitor, U0126, abolished the PMA-stimulated increase in MAPK activity and significantly reduced basal and PMA-stimulated promoter activity. Electrophoretic mobility shift assays for SF-1 and GATA revealed that PMA failed to affect SF-1 binding but enhanced GATA binding to a consensus GATA oligonucleotide, an effect that was blocked with U0126 pretreatment, suggesting that GATA may mediate ERK activation of alphaGSU transcription. Our data suggests that, in the mature LbetaT2 gonadotrope cell line, two regions of the human alphaGSU promoter regulate basal transcription and that SF-1 is involved in mediating basal and PMA-stimulated promoter activity. Furthermore, PKC-stimulated transcription partially relies on ERK acting on elements downstream of -244 bp of the human alphaGSU promoter.
Fowkes
Robert C
RC
Department of Endocrinology, St. Bartholomew's and the Royal London School of Medicine and Dentistry, West Smithfield, London EC1A 7BE, United Kingdom. r.c.fowkes@qmul.ac.uk
King
Peter
P
Burrin
Jacky M
JM
D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D051717:Fushi Tarazu Transcription Factors; D005786:Gene Expression Regulation / Q000187:drug effects; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D018398:Homeodomain Proteins; D006801:Humans; D008156:Luciferases / Q000235:genetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010902:Pituitary Gland / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D054339:Steroidogenic Factor 1; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D004268:DNA-Binding Proteins; D051717:Fushi Tarazu Transcription Factors; D015292:Glycoprotein Hormones, alpha Subunit; D018398:Homeodomain Proteins; C515057:NR5A1 protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D054339:Steroidogenic Factor 1; D014157:Transcription Factors; C515058:steroidogenic factor 1, mouse; D007987:Gonadotropin-Releasing Hormone; D008156:Luciferases; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate