For children, adolescents and young adults with T-lineage acute lymphoblastic leukemia, event free survival following relapse is <10%. A variety of hematologic malignancies activate JAK-STAT signaling through activating mutations in JAK1-3, IL7R and downregulation of negative regulators. SOCS5 belongs to the suppressor of the cytokine signaling (SOCS) family, which are known cytokine-inducible negative regulators of JAK-STAT and other signaling pathways. SOCS5 is involved in negative regulation of Th2 development. However, the roles of SOCS5 in blood cancer, in particular T-ALL have not been elucidated so far. Using Affymetrix U133 Plus 2.0 microarray we assessed SOCS5 expression levels in a cohort of 100 T-ALL samples derived from AALL0434 COG study. SOCS5 was deregulated in T-ALL cells, and its expression was lowered in cases harboring MLL gene rearrangements (MLL-R) compared to the remaining cases (P < 0.0001). Because we did not identify any mutations in SOCS5 gene in the cohort of 100 cases, we hypothesized that SOCS5 expression is regulated by aberrant DNA methylation in T-ALL. Using methyl-specific PCR (MS-PCR) and bisulfite sequencing we found that SOCS5 expression is regulated by promoter/1st exon CpG island methylation in T-ALL. CCRF-CEM and ALL-SIL cells, and selected primary T-ALL samples showed hypermethylation in promoter/1st exon region corresponding to lower levels of SOCS5 expression. In contrary, Koptk1 and PF382 cells, and T-ALL samples with higher levels of SOCS5 had hypomethylated SOCS5 promoter/1st region. SOCS5 transcript and protein expression were induced by DNA demethylating agent, 5-azacitidine in ALL-SIL and CCRF-CEM cells (P < 0.0001). The increase in SOCS5 expression was correlated with its promoter demethylation as shown by MS-PCR. SOCS5 mRNA and protein levels were also increased in ALL-SIL cells transduced with DNMT1 shRNA compared to negative control (P < 0.0001) indicating that inhibition of DNA methyltransferase activity restores SOCS5 expression in T-ALL. To assess whether histone deacetylation is involved in epigenetic regulation of SOCS5 expression, we treated CCRF-CEM and ALL-SIL cells with deacetylase inhibitor Trichostatin A (TSA). Treatment with TSA restored histone acetylation and caused upregulation of SOCS5 (P < 0.0001). We next examined the effects of SOCS5 on leukemogenesis by shRNA-mediated knock down of SOCS5 in KoptK1 and PF382 cells. Silencing of SOCS5 increased cellular proliferation as shown by an increase in T-ALL cell number (P < 0.0001). Reduced expression of SOCS5 led to an increase in MYC, IL4, IL4Rα, IL7R expression and STAT6 activation. These results indicate that SOCS5 is epigenetically deregulated in T-ALL. Future studies are required to evaluate the tumor suppressor roles of SOCS5 in a subset of T-ALL, in particular, in MLL-R cases via the regulatory effect on cytokine and growth factor receptor signaling.

Citation Format: Nitesh Sharma, Huining Kang, Christian C. Nickl, Scott A. Ness, Stuart S. Winter, Ksenia Matlawska-Wasowska. Epigenetic deregulation of SOCS5 expression in T cell lineage acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3874. doi:10.1158/1538-7445.AM2017-3874