Cell Survival Failure in Effector T Cells From Patients With Systemic Lupus Erythematosus Following Insufficient Up‐Regulation of Cold‐Shock Y‐Box Binding Protein 1

OBJECTIVE The importance of the cold-shock Y-box protein-1 (YB-1) for cell homeostasis is well documented by its association with certain cancer entities. Here, we explored the role of YB-1 in T-cell homeostasis and survival, and the potential contribution of YB-1 in the pathogenesis of systemic lupus erythematosus (SLE). METHODS We analyzed the expression of YB-1 and apoptosis by qPCR and FACS of CD4+ T-cells from peripheral blood of healthy donors (n=25) and SLE patients (n=25) ex vivo as well as in vitro after a 6-day-stimulation with αCD3- or αCD3/αCD28-coupled microspheres. YB-1 was overexpressed using lentiviral transduction with GFP-YB-1wt and knock-down using specific shRNA (-3 fold reduction, p < 0.0001), respectively. RESULTS YB-1 expression was significantly lower in apoptosis-prone and in activated T-cells of patients suffering from SLE compared to those of non-apoptotic and of activated T-cells of healthy volunteers (p=0.001). Knock-down of YB-1 demonstrates that reduced expression of YB-1 in T-cells inevitably led to expression of pro-apoptotic molecules and caspase 3 activation (1.6 fold), and subsequently to apoptosis. Furthermore, we revealed that YB-1 promotes survival pathways involving enhanced protein expression of the kinase Akt (2 fold) and Bcl-2 (3 fold), even when Fas was triggered. YB-1-mediated survival was reversed by Akt and PI3K inactivation. In SLE patients rescue of YB-1 expression strongly promotes survival of T-cells and even prevents cell death in those that were extremely apoptosis-prone. CONCLUSION Our data show that failure of YB-1 upregulation in T-cells of SLE patients leads to enhanced apoptosis. These findings have implications for diagnostics and possibly new treatment strategies for hematopoietic alterations in SLE.