NA+-K+-ATPASE GENE-EXPRESSION IN RAT INTESTINE AND CACO-2 CELLS - RESPONSE TO THYROID-HORMONE

Expression of the Na+-K+-adenosinetriphosphatase (ATPase) gene family in rat intestinal epithelial cells was examined using RNA blot hybridization analyses. Rat intestinal epithelial cells express only the alpha1- and beta1-subunit mRNAs. A gradient in expression of alpha1- and beta1-subunit mRNA was seen along the villus-crypt unit in both jejunum and ileum, i.e., villus tip >> crypt cells. Regional differences in expression were observed along the intestine alpha1-and beta1-subunit mRNA abundance was similar in jejunum, ileum, and colon white enzymatic activity was highest in the jejunum and lowest in the ileum. Administration of thyroid hormone to thyroidectomized rats increased the expression of alpha1- and beta1-subunit mRNAs in jejunum but not in colon. Hypothyroidism had no effect on subunit mRNA expression. The human intestinal cell line Caco-2 was also studied. These cells also expressed only the alpha1 and beta1-isoform mRNAs and demonstrated a developmental profile in both mRNA and enzymatic activity. Furthermore, in Caco-2 cells both alpha1- and beta1-mRNAs and Na+-K+-ATPase enzymatic activity were stimulated by thyroid hormone. Caco-2 cells transfected with 5' flanking regions of the human Na+-K+-ATPase beta1-gene linked to the chloramphenicol acetyltransferase (CAT) reporter gene responded to 3,5,3'-triiodothyronine (T3) treatment with increased expression of CAT activity. This suggests that the 5' flanking region of the beta1-gene contains a thyroid hormone response element and that T3 upregulation occurs at the transcriptional level. The Caco-2 cell system may be an excellent model to study Na+-K+-ATPase gene expression in the intestine.