Protein phosphatase 2A promotes IL-2R signaling in human regulatory T cells

Abstract

Abstract Low-dose IL-2 therapy is a direct approach to boost Tregs and promote immune tolerance in autoimmune patients. The selective response of Tregs to low-dose IL-2 has been suggested to be due to high level of CD25 and activity of the Ser/Thr phosphatase, PP2A. Here we directly assessed the contribution of these two parameters in promoting IL-2 signaling in human Tregs. IL-2-induced tyrosine phosphorylation of STAT5 (pSTAT5) was proportional to CD25 levels on human CD4+ T cells, directly demonstrating that high IL-2R levels promote the Treg response to low-dose IL-2. To evaluate the role of PP2A, expanded human Tregs were transduced with lentivirus to overexpress or knock down the PP2A catalytic subunit (PP2Ac). Overexpression of PP2Ac increased the level of all IL-2R subunits and promoted phosphorylation of Jak3 at Tyr980/981. Compared to control-transduced cells, PP2Ac-overexpressed Tregs were 3-fold more sensitive to IL-2 based on pSTAT5 activation. Increased expression of CD25 only partially accounted for this enhanced activation of pSTAT5. Consistent with these findings, knockdown of PP2Ac in Tregs significantly reduced the pSTAT5 responses to IL-2. Overexpression of PP2Ac in Tregs also increased the expressions of proteins related to growth, survival, activation, and immunosuppressive function, and included several IL-2-regulated genes. Collectively, these findings indicate that PP2A promotes IL-2R signaling through multiple mechanisms, one related to control of IL-2R expression and another that may directly regulate IL-2R signaling.