Abstract 1128: Role of STAT3 in pediatric sarcoma cell lines

Abstract

Abstract Signal transducer and activator of transcription-3 (STAT3) is a transcription factor that plays a major role in embryonic development, cell growth, differentiation and apoptosis. STAT3 becomes activated in the cytosol via phosphorylation at tyrosine-705 by JAK-1/2 kinases, in response to stimulation of either cytokine receptors or receptor tyrosine kinases. Phospho-STAT3 forms dimers, which then translocate into the nucleus to function as a transcription factor. Various pro-survival and anti-apoptotic genes including VEGF, Bcl-xL, Bcl-2 and survivin have been identified as STAT3 gene targets. Constitutive activation of STAT3 is observed in various cancers including breast, lung, pancreatic cancers and sarcomas. Since our studies indicate that STAT3 is upregulated in a number of pediatric sarcomas as well, we set out to understand the functional significance of STAT3 activation in these tumors in the context of tumor cell proliferation, survival, migration and resistance to apoptosis. High basal expression levels of phospho-STAT3 (Tyr705) were detected in a number of rhabdomyosarcoma, Ewing's sarcoma and osteosarcoma xenografts and cell lines. Interleukin-6 (IL-6) was capable of inducing STAT3 (Tyr705) phosphorylation in these cell lines in a time-dependent manner. On the other hand, stimulation with insulin-like growth factors-1 and 2 or IGF-1/2 resulted only in a weak induction in STAT3 phosphorylation during early timepoints. Treatment with a potent JAK-1/2 inhibitor, ruxolitinib suggested that STAT3 phosphorylation in these cell lines is dependent on JAK-1/2 activities. To understand the role of STAT3 in tumorigenesis, STAT3 was either knocked down using siRNAs or STAT3 phosphorylation was attenuated using ruxolitinib in sarcoma cell lines that express constitutively activated STAT3. Neither complete knockdown of STAT3, nor inhibition of STAT3 phosphorylation by ruxolitinib inhibited proliferation or decreased survival. These results indicate that activation of STAT3 may not have a significant role in tumor cell proliferation and survival under culture conditions. However, STAT3 inhibition resulted in decreased cell migration implicating STAT3 in regulation of tumor cell migration and invasion. Overall, our data demonstrates a role for STAT3 activation in sarcoma cell migration and invasion and we speculate that targeting STAT3 might serve as a useful therapeutic approach to control tumor invasion and metastasis. Supported by USPHS grant CA165995. Citation Format: Seethalakshmi Hariharan, Doris A. Phelps, Peter J. Houghton. Role of STAT3 in pediatric sarcoma cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1128.