[Prokaryotic expression of human vitamin D receptor (hVDR) and its binding activities to Cd and Pb]

Human vitamin D receptor (hVDR) is a potential receptor channel for heavy metals to affect bone metabolism, while to date there is no report about the binding activity between heavy metals and hVDR. This study established a prokaryotic expression of hVDR system, by cloned hVDR-LBD into pGEX-4T-1 vector. Then according to the principle that the nuclear receptor binding with its ligand can be combined with nuclear receptor coactivator 2-bacterial alkaline phosphatase fusion protein (TIF2-BAP), we established a method of p-nitrophenylphosphate-alkaline phosphatase to analyse the effects of chemical on the binding activity between hVDR and TIF2-BAP. Using this method, we studied the binding activities between hVDR and TIF2-BAP after exposure of cadmium and lead. The results showed that the binding activities significantly increased to 3.95 and 4.39 times that of the control after exposure of 100 micromol/L and 1 000 micromol/L cadmium chloride (CdCl2), and the binding activities significantly increased to 2.29 and 3.52 times that of the control after exposure of 100 micromol/L and 1 000 micromol/L lead acetate (PbAc2), respectively. These results indicate that cadmium and lead can mimic the activity of 1,25-(OH)2D3, disrupt the normal function of hVDR receptor channel, which may be the underlying mechanism of abnormal bone metabolism and osteoporosis caused by cadmium and lead.