THYROID-HORMONE RECEPTOR MODULATES THE EXPRESSION OF THE RABBIT CARDIAC SARCO(ENDO)PLASMIC RETICULUM CA2-ATPASE GENE()

We have analyzed the effect of thyroid hormone (T3) on SERCA2 gene exp ression using fetal chicken primary cardiac myocytes and C2C12 skeleta l muscle cells in culture. Northern blot analysis of both cell types d emonstrated that T3 induced a 3-fold accumulation of SERCA2 mRNA compa red with cells grown in medium lacking T3. We have engineered deletion constructs containing various lengths of the 5'-flanking region from the rabbit SERCA2 gene which we have cloned previously (Zarain-Herzber g, A., MacLennan, D. H., and Periasamy, M. (1990) J. Biol. Chem. 265, 4670-4677). A stable transfectant in C2C12 containing a chimeric SERCA 2/CAT gene construct including -254 base pairs (bp) of SERCA2 5'-flank ing region showed increased transcription activity upon the addition o f 50 nm T3. We have analyzed the expression of several deletion constr ucts spanning 1,102 bp of the 5'-upstream sequence of the SERCA2 gene by functional expression assays. Transient coexpression of the T3 rece ptor alpha1 with various SERCA2/CAT deletion constructs showed trans-a ctivation of chimeric constructs containing more than -267 bp, indicat ing that a thyroid hormone-responsive element was localized, at least in part, to the region -267 to -72 bp. T3 receptor-DNA binding assays demonstrated binding of the rat T3 receptor al to a fragment containin g a proposed T3 response element located between position -254 and -72 in the 5'-flanking region of the SERCA2 gene.