Antagonistic effects of retinoic acid and thyroid hormone on the expression of the tissue-specific splicing protein SmN in a clonal cell line derived from rat heart.

The SmN protein is a tissue-specific splicing factor which is expressed only in adult heart and brain but not in other tissues. Although a role for SmN in modulating tissue specific alternative splicing decisions in the heart and brain has been suggested, its precise function and the processes regulating its expression remain unclear. We show here that SmN is expressed in the H9c2 clonal cell line derived from rat heart and that its expression in these cells is affected by a variety of members of the steroid/thyroid hormone family. In particular thyroid hormone and retinoic acid exhibit antagonistic effects on SmN expression with thyroid hormone treatment producing large increases in expression whilst retinoic acid treatment virtually abolishes expression. These findings are discussed in terms of the regulation of SmN expression and the potential role of this factor in the response of cardiac cells to members of the steroid/thyroid hormone family.