Identification of vitamin D-stimulated alkaline phosphatase in IEC-6 cells, a rat small intestine crypt cell line

The IEC-6 cell line was derived from newborn rat small intestinal crypts and maintains characteristics of nontransformed crypt epithelial cells. We have reported that alkaline phosphatase (ALP) activity, a differentiation marker for intestinal epithelial cells, is regulated in IEC-6 cells by 1,25- dihydroxycholecalciferol (1,25(OH)₂D₃). Using reverse transcription polymerase chain reaction, we determined that the ALP in IEC-6 cells is the liver/bone/kidney ALP (LALP) isoenzyme and not the mature enterocyte form. Levamisole, a specific blocker for LALP, blocked the ALP activity of IEC-6 cells. Kinetic studies showed that 1,25(OH)₂D₃ increases V(m) values of ALP in IEC-6 cells while K(m) values remain the same. Northern analysis of LALP mRNA levels in IEC-6 cells indicated that 10^-7 M 1,25(OH)₂D₃ acts by increasing alkaline phosphatase activity at the gene expression level.