Role of the 1,25D3-MARRS receptor in the 1,25(OH)2D3-stimulated uptake of calcium and phosphate in intestinal cells

We have used mice with a targeted knockout (KO) of the 1,25D3-MARRS receptor (ERp57/PDIA3) in intestine to study rapid responses to 1,25-dihydroxyvitamin D3 [1,25D3] with regards to calcium or phosphate uptake. Western analyses indicated the presence of the 1,25D3-MARRS receptor in littermate (LM) mice, but not KO mice. Saturation analyses for [3H]1,25D3 binding revealed comparable affinities for the hormone in lysates from female and male LM, but a reduced Bmax in females. Binding in lysates from KO mice was absent or severely reduced. Enterocytes from KO mice failed to respond to hormone with regard to either ion uptake, while cells from LM mice exhibited an increase in uptake. For calcium uptake, the protein kinase (PK) A pathway mediated the response to 1,25D3. Enterocytes from LM mice responded to 1,25D3 with enhanced PKA activity, while cells from KO mice did not, although both cell types responded to forskolin. Calcium transport in LM mice in vivo was greater than in KO mice. Cells from LM and KO mice had cell surface VDR; however, anti-VDR antibodies had no effect on ion uptake. Unlike chicks, the PKC pathway was not involved in phosphate uptake. As in chicks and rats, intestinal cells from adult male mice lost the ability to respond to 1,25D3 with enhanced phosphate uptake, whereas in female mice, uptake in cells from adults was greater than that observed in young mice. Finally, when we tested phosphate uptake in vivo, we found that young female mice had a much greater rate of transport than young male mice.

► The sex-specific differences indicate that male animal models cannot always be representative.
► The signaling pathways for hormone stimulated calcium and phosphate uptake vary between species.
► An absolute requirement for rapid responses to 1,25D3 in enterocytes is the 1,25D3-MARRS receptor.