Upregulation by retinoic acid of interleukin-2-receptor mRNA in human T lymphocytes.

It was previously demonstrated that retinoic acid (RA) can enhance the functional responses of human T lymphocytes by increasing surface IL-2R alpha chain protein expression on proliferating T blasts, resulting in augmented IL-2-dependent growth. In the present study, we used IL-2-maintained lymphoblasts generated from human thymocytes to show that RA enhancement of IL-2R alpha is accompanied by an increase in steady-state levels of IL-2R alpha mRNA. This increase occurred within 1 hr after the addition of RA to the culture and was inhibited by the presence of the protein synthesis inhibitor cycloheximide. RA did not alter the stability of either IL-2R alpha on the cell surface or IL-2R alpha mRNA, suggesting regulation by RA at the level of transcription. This contention was supported by the demonstrated ability of RA to activate the IL-2R alpha promoter in a chloramphenicol acetyltransferase plasmid construct that was transfected into the blast cells. In addition to inducing IL-2R alpha expression, RA also increased the surface expression and mRNA levels of IL-2R beta, the 75-kDa component of the IL-2 receptor that mediates IL-2 signal transduction. These new findings showing regulation by RA of both IL-2R alpha and IL-2R beta suggest multiple pathways by which this retinoid can modulate functional IL-2 receptors.