1,25(OH)₂D₃ increases membrane associated protein kinase C in MDBK cells

To determine whether 1,25-dihydroxycholecalciferol [1,25(OH)₂D₃] affects protein kinase C (PKC) activity in kidney, as has benn demonstrated in HL-60 cells we measured 1,25(OH)₂D₃ binding, PKC activity and PKC immunoreactivity in Madin Darby bovine kidney (MDBK) cells, a normal renal epithelial cell line derived from kidney. Our data demonstrate that MDBK cells exhibit specific high affinity binding for 1,25(OH)₂D₃, indicating the presence ofthe vitamin D receptor (VDR). Treatment of MDBK cells with 1,25(OH)₂D₃ for 24 h increased membrane PKC activity and immunoreactivity. The effect of 1,25(OH)₂D₃ was dose-dependent, with a peak effect observed at 10^-10 M 1,25(OH)₂D₃. The 1,25(OH)₂D₃ induced increase in membrane PKC was paralleled by a comparable decrease in cytosolic PKC activity and amount. Although time course studies were consistent with a VDR mediated effect of 1,25(OH)₂D₃ on PKC protein synthesis, total PKC activity was not increased by 1,25(OH)₂D₃, suggesting an effect on PKC translocation of localization. These results suggest that 1,25(OH)₂D₃ modulates PKC mediated events in kidney, a classic target for this steroid hormone.