Retinoid X receptor agonists increase Bc12a1 expression and decrease apoptosis of naive T lymphocytes

Vitamin A affects many aspects of T lymphocyte development and function. The vitamin A metabolites all-trans- and 9-cis-retinoic acid regulate gene expression by binding to the retinoic acid receptor (RAR), while 9-cis-retinoic acid also binds to the retinoid X receptor (RXR). Naive DO11.10 T lymphocytes expressed mRNA and protein for RAR-alpha, RXR-alpha, and RXR-beta. DNA microarray analysis was used to identify RXR-responsive genes in naive DO11.10 T lymphocytes treated with the RXR agonist AGN194204. A total of 128 genes was differentially expressed, including 16 (15%) involved in cell growth or apoptosis. Among these was Bcl2a1, an antiapoptotic Bc12 family member. Quantitative real-time PCR analysis confirmed this finding and demonstrated that Bc12a1 mRNA expression was significantly greater in nonapoptotic than in apoptotic T lymphocytes. The RXR agonist 9-cis-retinoic acid also increased Bc12a1 expression, although all-trans-retinoic acid and ligands for other RXR partner receptors did not. Treatment with AGN194204 and 9-cis-retinoic acid significantly decreased apoptosis measured by annexin V staining but did not affect expression of Bc12 and Bcl-x(L). Bc12a1 promoter activity was examined using a luciferase promoter construct. Both AGN194204 and 9-cis-retinoic acid significantly increased luciferase activity. In summary, these data demonstrate that RXR agonists increase Bc12a1 promoter activity and increase expression of Bc12a1 in naive T lymphocytes but do not affect Bc12 and Bcl-x(L) expression in naive T lymphocytes. Thus, this effect on Bcl2a1 expression may account for the decreased apoptosis seen in naive T lymphocytes treated with RXR agonists.