Ubiquitin-like polypeptide inhibits cAMP-induced p38 MAPK activation in Th2 cells.

Ubi-L, an isoform of the monoclonal nonspecific suppressor factor (MNSF), is an 8.5-kDa ubiquitin-like polypeptide. Ubi-L exhibits an antigen-nonspecific immunosuppressive function on various target cells including murine T helper type 2 (Th2) clone, D10 cells. Ubi-L specifically binds to cell surface receptors on D10 cells. In this study, we observed that Ubi-L inhibited cAMP-induced IL-5 mRNA expression in D10 cells but not in thymoma cell line EL4. In addition, Ubi-L effectively inhibited cAMP-induced p38 MAPK activation in D10 cells. Ubi-L also showed inhibitory activity on IL-5 and IL-13 production by D10 cells stimulated with phorbol ester plus dibutyryl cAMP. Furthermore, Ubi-L inhibited IL-4 production in Th2 cells derived from primary CD4+ T cells.