ABSTRACT
Objective To detect the effects of 17 β-estradiol(E2)on the expression of Calbindin-D9k (CaBP-9k) in pituitary GH3 cells,and to investigate the antagonistic effect of a selective estrogen receptor antagonist,ⅡCI 182780 on CaBP-9k expression.Methods A rat pituitary prolactinoma cell line,GH3 cell was used as the in vitro model.The localization of CaBP-9k in GH3 cells was observed by immunofluorescence.GH3 cells were cultured with exogenous E2-added medium for 24 hours,and the concentrations of E2 were 10-8,10-9,10-10M,respectively.mRNA and protein expression levels of CaBP-9k in different groups were analyzed by RT-PCR and Western blot analysis.The estrogen receptor antagonist,and ⅡCI 182780 was added to GH3 cells before E2 administration (10-8M)with the concentration of 10-6M,in order to investigate the regulation of ER-mediated pathway on the expression of CaBP-9k.Immunoprecipitation was used to detect the interaction between CaBP-9k and ERα.Results E2 had significant stimulatory effect on the CaBP-9k expression of GH3 cells in a dose dependent manner,and the expression level of CaBP-9k was higher when treated with a higher concentration of E2.ⅡCI 182780 could suppress the stimulatory effect of E2 on the CaBP-9k expression of GH3 cells.The expression level of CaBP-9k was significantly reduced by coadministration of E2 with ⅡCI 182780 in GH3 cells,which meant the CaBP-9k expression was mediated through ERα pathway.The immunoprecipitation results further illustrated the fact that CaBP-9k could directly interact with ERα,and E2 could increase the interaction between CaBP-9k and ERα.Conclusion Estrogen might induce CaBP-9k expression via ERα mediated pathway and CaBP-9k could directly combine with ERα,suggesting that CaBP-9k might be involved in the biological effects mediated by ER pathway in GH3 cells.
ABSTRACT
Calbindin-D9k (CaBP-9k) is a cytosolic calcium-binding protein expressed in tissues in the intestine, uterus, placenta, kidney, pituitary gland and bone. Its exact function is unknown, but it is considered to regulate intracytoplasmic concentration and transport of free ions (Ca2+). CaBP-9k protein is involved in intestinal calcium absorption in the intestine and in the regulation of myometrial activity by intracellular calcium in the uterus. Renal CaBP-9k protein is expressed at the site of calcium re-absorption in the kidney and expressed in distal convoluted tubules, where it is thought to facilitate calcium re-absorption. Expression of the CaBP-9k gene has been explored in most mammalians except in a canine model. Presently, we elucidated the expression of CaBP-9k mRNA and protein in the duodenum, kidney and uterus in a canine model involving two adult (2.5-year-old) female beagles. To collect tissues, the dogs were euthanized and then the abdominal cavity was exposed by midline incision. The proximal duodenum, cortex of kidney and uterine horn were collected. Expression of CaBP-9k mRNA was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. CaBP-9k protein expression and localization were ascertained by Western blot analysis and immunohistochemistry, respectively. CaBP-9k mRNA was detected in the duodenum, but not in the kidney and uterus. Its protein was expressed only in the enterocytes of the duodenum. Taken together, the results indicate that CaBP-9k mRNA and protein are highly expressed in the enterocytes of the duodenum of a canine model, consistent with findings in other mammalian species.