E3 ubiquitin ligases SIAH1/2 regulate hypoxia-inducible factor-1 (HIF-1)-mediated Th17 cell differentiation.

IL-17 is known to be a cytokine mainly secreted from Th17 cells, which well associate with autoimmune inflammatory responses. In the generation of Th17 cells, RORc and RORa have pivotal roles in controlling the transcription of Il17. We speculated additional regulation in Il17a transcription and randomly screened a 6344 clone cDNA library to identify specific modulators for Il17a promoter activity. After the screen, the E3 ubiquitin ligases SIAH1 and SIAH2 were investigated further and confirmed to increase Il17a promoter activity in a T-cell line and to promote Th17 development ex vivo. This enhancement was a consequence of enhanced expression of hypoxia-inducible factor-1α (HIF-1α) protein, which is reported to directly regulate expression of Il17a and Rorgt at the transcriptional level. In the absence of HIF-1α, both ubiquitin ligases had little effect on Th17 cell differentiation. These results suggest that the SIAH1 and SIAH2 play a pivotal role to promote Th17 cell differentiation through maintaining the stability of HIF-1α protein.

Elevation of Sema4A implicates Th cell skewing and the efficacy of IFN-ß therapy in multiple sclerosis.

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the CNS and a leading cause of lasting neurologic disabilities in young adults. Although the precise mechanism remains incompletely understood, Ag presentation and subsequent myelin-reactive CD4(+) T cell activation/differentiation are essential for the pathogenesis of MS. Although semaphorins were initially identified as axon guidance cues during neural development, several semaphorins are crucially involved in various phases of immune responses. Sema4A is one of the membrane-type class IV semaphorins, which we originally identified from the cDNA library of dendritic cell (DC). Sema4A plays critical roles in T cell activation and Th1 differentiation during the course of experimental autoimmune encephalomyelitis, an animal model of MS; however, its pathological involvement in human MS has not been determined. In this study, we report that Sema4A is increased in the sera of patients with MS. The expression of Sema4A is increased on DCs in MS patients and shed from these cells in a metalloproteinase-dependent manner. DC-derived Sema4A is not only critical for Th1 but also for Th17 cell differentiation, and MS patients with high Sema4A levels exhibit Th17 skewing. Furthermore, patients with high Sema4A levels have more severe disabilities and are unresponsive to IFN-ß treatment. Taken together, our results suggest that Sema4A is involved in the pathogenesis of MS by promoting Th17 skewing.