A POSSIBLE ROLE OF A NUCLEAR FACTOR NF-LPH1 IN THE REGIONAL EXPRESSION OF LACTASE-PHLORHIZIN HYDROLASE ALONG THE SMALL-INTESTINE

Lactase-phlorizin hydrolase (LPH), an enterocyte-specific disaccharida se, displays not only a post weaning decline but also regional differe nces in the small intestine. To investigate the mechanisms of regional LPH expression along the small intestine, the correlation between LPH mRNA abundance, lactase activity and the amount of a nuclear factor ( NF-LPH1) binding to a cis-element was determined in various intestinal segments of suckling and adult rats. In suckling rats, both LPH mRNA and lactase activity were expressed at maximum in the jejunum, but the y were hardly detected in the colon. In adult rats, both LPH mRNA and lactase activity were the highest in the jejunum and virtually absent in the ileum. Lactase activity and LPH mRNA abundance in suckling rats were 2-3 times more than those of adult rats in all regions of the sm all intestine. An electromobility shift assays of nuclear proteins rev ealed that NF-LPH1 was present in rat small intestine as well as in Ca co-2 cells. The amount of NF-LPH1 binding to the cis-element was also approximately 2-fold more in the intestinal nuclear extracts of suckli ng rats than that of adult rats. NF-LPH1 was detected in all regions o f the small intestine in both suckling and adult rats. In both cases, the amounts of NF-LPH1 binding to the cis-element increased from the d uodenum to upper jejunum, and decreased toward the ileum. The coordina te postnatal declines of LPH mRNA and NF-LPH1 expression in various re gions of the small intestine suggest that NF-LPH1 might be involved no t only in the regulation of postnatal LPH gene expression but in regio n-specific LPH gene expression as well.