Response Gene to Complement-32 promotes Th17 cell differentiation through TGF-β dependent and independent mechanisms

Abstract

Abstract Response Gene to Complement (RGC)-32 is an intracytoplasmatic protein expressed in a variety of cells in response to sublytic complement activation, TGF-β and several growth factors. Upon activation it translocates into the nucleus and plays an important role in cells proliferation, migration, angiogenesis and TGF-β induced epithelial mesenchymal transition and fibrosis. A number of signaling pathways including CDC2 kinase, NF-kB, Akt, SMAD2/3, ROCK2 and PKC have been reported to mediate RGC-32 effects in different cell types. We have recently shown that RGC-32 promotes Th17 but not Treg, Th1 or Th2 differentiation in murine CD4+ T cells in vitro. The molecular mechanisms underlying the enhanced Th17 generation by RGC-32 are unknown. Under Th17 conditions, CD4+ T cells from RGC-32 knockout (KO) mice displayed significantly lower IL-6Rα and TGF-βRI mRNA expression. Smad dependent TGFβ signaling was altered in RGC-32 KO T cells as demonstrated by decreased phosphorylation of Smad2, while IL-6 induced STAT3 phosphorylation did not differ between RGC-32 KO and wild-type CD4+T cells. mRNA and protein expression of RORyt, the Th17 lineage specific transcription factor, was significantly lower in RGC-32 KO CD4+ T cells. In addition, RGC-32 KO CD4+T cells expressed significantly lower mRNA levels of the initiator transcription factors, BATF and IRF4. These results suggest that RGC-32 positively regulates the differentiation of the Th17 lineage through TGFβ dependent and independent mechanisms by enhancing the activation of Smad2, IRF4, BATF and RORyt.