Abstract C100: Towards better understanding a role of STAT3 in glioma pathology: Identification of novel transcriptional targets of STAT3.

Abstract

Abstract Aberrant activation of signal transducer and activator of transcription 3 (STAT3) occurs frequently in diverse human tumors. Constitutively activated STAT3 induces specific target genes that stimulate cell proliferation, prevent apoptosis, promote angiogenesis and facilitate tumor immune evasion. In glioma pathogenesis STAT3 has been found to play opposing tumor suppressive and oncogenic roles depending on the genetic background of the tumor. Although hundreds of genes have been identified as potential STAT3 targets, only a small fraction of those genes have been proven to be direct STAT3 targets. To further elucidate the role of STAT3 in glioma pathogenesis we searched for novel, direct STAT3 targets in glioma cells. Here, by using microarray techniques, computational methods for genome-wide identification of transcription factor binding sites and chromatin immunoprecipitation we identified the novel, direct STAT3 target genes. Global gene expression profiling in C6 glioma cells treated with 25 uM the inhibitor of JAK/STAT3 signaling pathway (a derivative of previously described WP1066 by Iwamaru et al., Oncogene, 2007, 26) or DMSO as control revealed considerable changes in gene expression. Inhibition of JAK/STAT3 signaling significantly modulated expression of numerous genes involved in many different biological processes such as inflammatory response, apoptosis, signal transduction, proliferation, but also RNA processing or lipid metabolism. We analyzed promoter regions of differentially expressed genes searching for putative STAT3 targets. First, we selected conserved, noncoding regions between human and rat genome in those promoters using the global alignment program. Phylogenetic conservation between rat and human sequences was used to select the binding sites most likely to be functional. Next, within conserved, non-coding regions we found putative STAT3 binding sites using MathInspector employing the canonical STAT3 Positional Weight Matrix. For further validation we selected 12 genes with at least two putative STAT3 binding sites within the promoter regions. Our computational approaches applied to microarray selected genes are valid tools to identify functional TF binding sites in gene regulatory regions as confirmed by chromatin immunoprecipitation. All of the tested sites were bound by STAT3 in C6 glioma cells. Interestingly, we found that STAT3 can mediate expression of genes involved both in tumor suppression and oncogenesis. Altogether, our results demonstrate identification of a group of novel STAT3 targets that shed light on complexity of a genetic network regulated by JAK/STAT3 signaling in glioma cells. The study was supported by grant N N405 621938 from the Polish Ministry of Science and Higher Education (BK). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C100.