Regulation of sucrase and lactase in developing rats: Role of nuclear factors that bind to two gene regulatory elements

Background & Aims: Sucrase-isomaltase and lactase-phlorizin hydrolase expressions change remarkably during postnatal development in rats. The aim of this study was to explore the role of trans-acting nuclear proteins, proteins that bind to the SIF1 cis-regulatory element of the sucrase-isomaltase gene and to the CE-LPH1 cis-regulatory element of the lactase-phlorizin hydrolase gene, in this regulation. Methods: Enzyme activity, Northern analysis, and electrophoretic mobility shift assays were used to study the relationship of these nuclear proteins to sucrase-isomaltase and lactase-phlorizin hydrolase gene expression in vats during development. Results: A rapidly migrating low-molecular-weight SIF1-binding protein was found in suckling animals without sucrase-isomaltase messenger RNA (mRNA), and a higher-molecular-weight-binding protein was found in older animals with expression of sucrase-isomaltase mRNA. Supershift experiments and Western analysis showed that neither protein is Cdx-2, the only previously described SIF1-binding protein. CE-LPH1-binding protein was found only in adult animals (with low lactase activity), and there was no relationship between enzymatic activity and levels of lactase-phlorizin hydrolase mRNA. Conclusions: SIF1-binding proteins may regulate sucrase-isomaltase expression during postnatal development, but CE-LPH1-binding proteins do not seem to regulate lactase-phlorizin hydrolase expression during this period.