Interleukin 2 induces a transient downregulation of protein phosphatase 1 and 2A activity in human T cells

Stimulation of human CD4(+) T cell lines with interleukin 2 (IL-2) induces tyrosine, serine and threonine phosphorylation of a series of proteins involved in the IL-2 receptor (IL-2R) signaling pathway. Here, we examined whether IL-2 induces changes in the activity of protein serine/threonine phosphatases in antigen specific, CD4(+) human T cell lines. Using inhibitors of protein phosphatases 1 (PPI), PP2A, and PP2B, we provide evidence, that IL-2 induces a downregulation of PP activity in the cytoplasmic/membrane fraction. Thus, IL-2R ligation for 30 min triggers a 16 percent decrease in total PP2A activity (p<0.00005, n=17) and a seven percent decrease in PP1 activity (p<0.00005, n=17). Cytokine-induced downregulation of PP2A activity reaches a maximum 60 min after IL-2R ligation, and returns to baseline levels within two hours. Downregulation of PP1 activity reaches a maximum after 30 min and is largely reversed one hour after IL-2 stimulation. As determined from immunoblotting experiments using a specific anti-PP1 or anti-PP2A antibody, the amount of PP1 and PP2A recovered from cytosolic/membrane fraction remains unchanged after IL-2 treatment suggesting that the drop in PP1/PP2A activity might be due to a regulatory change rather than to a change in the amount of PP1 and PP2A. In conclusion, we provide evidence, for the first time, that IL-2 induces a transient downregulation of PP2A activity in T cells. In addition, our findings indicate that cytoplasmic PP1 activity is transiently downregulated following IL-2R ligation in antigen-specific, human CD4(+) T cells.