Transactivation of a growth hormone (GH) promoter-luciferase construct in canine mammary cells.
The gene encoding growth hormone (GH) is expressed not only in the pituitary but also in a variety of non-pituitary tissues. In the female dog, progestins are known to stimulate GH expression in the mammary gland. In order to investigate the regulation of the GH gene expression in the mammary gland, we transfected the canine mammary tumor cell line CMT-U229 with 3 different canine GH promoter-luciferase constructs. The constructs, varying in length between 252 bp and 673 bp, were transfected followed by an incubation for 4 h, 24 h and 48 h with cAMP, all-trans-retinoic acid (RA), 3,3',5-triiodothyronine (T3), 1,25-dihydroxy-vitamin D (VitD), progesterone and EGF. Promoter activity was stimulated by cAMP, T3 and RA whereas VitD clearly inhibited gene expression. However, despite the presence of nuclear and membrane receptors for progesterone, no direct effects of progesterone on promoter activity could be demonstrated. It is concluded that progesterone alone has no direct stimulatory effect on GH transcription. This finding is discussed in relation to the slow onset of progesterone-stimulated GH release in vivo and the absence of Pit-1 in canine mammary tissue.
Timmermans-Sprang
Elpetra P M
EP
Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 104, 3584 CM Utrecht, The Netherlands.
Rao
Nagesha A S
NA
Mol
Jan A
JA
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology; D004285:Dogs / Q000235:genetics*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D017930:Genes, Reporter; D013006:Growth Hormone / Q000235:genetics* / Q000378:metabolism; D008156:Luciferases / Q000235:genetics* / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000502:physiology*; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology; D014807:Vitamin D / Q000494:pharmacology
D014284:Triiodothyronine; D014807:Vitamin D; D011374:Progesterone; D014212:Tretinoin; D004815:Epidermal Growth Factor; D013006:Growth Hormone; D000242:Cyclic AMP; D008156:Luciferases