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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 transacting 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 rats 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.