Dysregulation of the IFN-?-STAT1 signaling pathway in a cell line model of large granular lymphocyte leukemia.

ABSTRACT: T cell large granular lymphocyte leukemia (T-LGLL) is a rare incurable disease that is characterized by defective apoptosis of cytotoxic CD8+ T cells. Chronic activation of the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) pathway is a hallmark of T-LGLL. One manifestation is the constitutive phosphorylation of tyrosine 701 of STAT1 (p-STAT1). T-LGLL patients also exhibit elevated serum levels of the STAT1 activator, interferon-? (IFN-?), thus contributing to an inflammatory environment. In normal cells, IFN-? production is tightly controlled through induction of IFN-? negative regulators. However, in T-LGLL, IFN-? signaling lacks this negative feedback mechanism as evidenced by excessive IFN-? production and decreased levels of suppressors of cytokine signaling 1 (SOCS1), a negative regulator of IFN-?. Here we characterize the IFN-?-STAT1 pathway in TL-1 cells, a cell line model of T-LGLL. TL-1 cells exhibited lower IFN-? receptor protein and mRNA expression compared to an IFN-? responsive cell line. Furthermore, IFN-? treatment did not induce JAK2 or STAT1 activation or transcription of IFN-?-inducible gene targets. However, IFN-? induced p-STAT1 and subsequent STAT1 gene transcription, demonstrating a specific IFN-? signaling defect in TL-1 cells. We utilized siRNA targeting of STAT1, STAT3, and STAT5b to probe their role in IL-2-mediated IFN-? regulation. These studies identified STAT5b as a positive regulator of IFN-? production. We also characterized the relationship between STAT1, STAT3, and STAT5b proteins. Surprisingly, p-STAT1 was positively correlated with STAT3 levels while STAT5b suppressed the activation of both STAT1 and STAT3. Taken together, these results suggest that the dysregulation of the IFN-?-STAT1 signaling pathway in TL-1 cells likely results from low levels of the IFN-? receptor. The resulting inability to induce negative feedback regulators explains the observed elevated IL-2 driven IFN-? production. Future work will elucidate the best way to target this pathway, with the ultimate goal to find a better therapeutic for T-LGLL.

SUBMITTER: Kulling PM 

PROVIDER: S-EPMC5825082 | biostudies-other | 2018

REPOSITORIES: biostudies-other