462 Gametocyte Specific Factor 1 contributes to the Th phenotype in Cutaneous T-Cell Lymphomas

Abstract

Ectopic expression of Gametocyte Specific Factor 1 (GTSF1) in Cutaneous T-Cell Lymphoma (CTCL) patients has been reported by several groups. Moreover, it has been associated with a worse prognosis and late-stage CTCL. GTSF1 is a gamete gene that participates in the piRNA pathway to silence retrotransposons on the genome. Despite the established association with a worse prognosis the molecular function of GTSF1 expression remains unknown. Therefore, we established shRNA-mediated GTSF1 knockdown CTCL cell lines. Using qRT-PCR, Western blot and a retrotransposition assay, we demonstrated that GTSF1 knockdown does not lead to mobilization of the retrotransposon LINE-1. These data suggest GTSF1 has a novel role in CTCL. Interestingly, after GTSF1 knockdown in the Mac2A cell line, we observed striking growth inhibition, suggesting this gene is a key player in CTCL carcinogenesis. To further explore this role, we performed RNA-Seq, comparing GTSF1 knockdown to control cells. Differential gene expression analysis using DESeq2, revealed 12496 differentially expressed genes (p adjusted <0.05). Pathway enrichment analysis was performed via GO, KEGG, Reactome and WikiPathways. We observed an enrichment of several pathways including response to stimulus, immune response, response to cytokine and inflammatory response. More specifically, transcriptome analysis showed an increased expression of cytokine induced genes, such as XAF1, IFI27 and IFI44L, and genes associated with a Th1 phenotype, IFNG and TNF. Research shows that CTCL progression leads to defects in Th1 cytokine production (IFN-γ and TNF-α) by antitumor immune cells and an enhanced Th2 cytokine production (IL-4 and IL-5) by malignant T cells. The chronic production of Th2 cytokines by malignant cells leads to immune deficiency in patients, allowing malignant cells to proliferate and the disease to progress. Taken together, these data suggest GTSF1 as a novel regulator of the Th phenotype on CTCL, thereby placing it as a potential treatment target for regulating disease progression.