title: Ubiquitination regulates expression of the serine/arginine-rich splicing factor 1 (SRSF1) in normal and systemic lupus erythematosus (SLE) T cells.
abstract: T cells from patients with systemic lupus erythematosus (SLE) exhibit reduced expression of the critical T cell receptor (TCR)-associated CD3ζ 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 CD3ζ 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 down-regulation 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 with 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.
authors.affiliation: From the Division of Rheumatology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215.
authors.forename: Vaishali R
authors.initials: VR
authors.lastname: Moulton
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Gillooly
authors.forename: George C
authors.initials: GC
authors.lastname: Tsokos
mesh_terms: D018106:CD28 Antigens / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D017252:CD3 Complex / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D008213:Lymphocyte Activation; D008297:Male; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D059748:Proteolysis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology; D016601:RNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D000068103:Serine-Arginine Splicing Factors; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D054875:Ubiquitination
chemical_list: D018106:CD28 Antigens; D017252:CD3 Complex; C115335:CD3E protein, human; D009687:Nuclear Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D000068103:Serine-Arginine Splicing Factors; D046988:Proteasome Endopeptidase Complex
keywords: Autoimmunity; Immunology; Proteasome; Protein Turnover; T Cell; T Cell Receptor; Ubiquitin