Ubiquitination regulates expression of the serine arginine-rich splicing factor 1 (SRSF1) in normal and SLE T cells [Gene Regulation]

December 24th, 2013 by Moulton, V. R., Gillooly, A. R., Tsokos, G. C.

T cells from patients with SLE exhibit reduced expression of the critical T cell receptor (TCR) associated CD3 zeta signaling chain, and are poor producers of the vital cytokine IL-2. By oligonucleotide pulldown and mass spectrometry discovery approaches, we identified the splicing regulator serine arginine-rich splicing factor (SRSF) 1 or splicing factor 2 / alternative splicing factor (SF2/ASF) to be important in the expression of CD3 zeta chain. Importantly, increases in the expression of SRSF1 rescued IL-2 production in T cells from patients with SLE. In this study, we investigated the regulation of SRSF1 expression in resting and activated human T cells. We found that T cell stimulation induced a rapid and significant increase in mRNA expression of SRSF1, however protein expression levels did not correlate with this increase. Co-engagement of CD28 induced a similar mRNA induction and reduction in protein levels. Proteasomal but not lysosomal degradation was involved in this downregulation as evidenced by blocking with specific inhibitors MG132 and Bafilomycin respectively. Immunoprecipitation studies showed increased ubiquitination of SRSF1 in activated T cells. Interestingly, T cells from patients with SLE showed increased ubiquitination of SRSF1 when compared to those from healthy individuals. Our results demonstrate a novel mechanism of regulation of the splicing factor SRSF1 in human T cells and a potential molecular mechanism that controls its expression in SLE.