Abstract
Ovarian cancer remains a deadly disease due in part to ovarian cancer metastasis. Recent work has demonstrated that ovarian cancer forms clusters of cells (spheroids) that attach to the peritoneum by clearing the mesothelial cell layer and then invade the underlying matrix to metastasize. Understanding the key pathways and downstream transcription factors that are driving ovarian cancer metastasis may allow us to develop new therapies to treat metastatic ovarian cancer. Importantly, we have found that the STAT3 transcription factor is necessary for mesothelial clearance by ovarian spheroids. To identify key downstream STAT3 target genes involved in ovarian cancer metastasis, we analyzed publicly available STAT3 chromatin immunoprecipitation (ChIP)-seq datasets for genes associated with epithelial-to-mesenchymal transition. One of the genes that we identified was the transcriptional modulator Snai2 (Slug). To verify that Snai2 was downstream of STAT3, we transfected ovarian cancer cells with siRNA to STAT3 and analyzed Snai2 gene expression. We found reduced expression of Snai2 with siRNA to STAT3 suggesting that STAT3 upregulates Snai2 expression. To determine the effects of Snai2 on mesothelial clearance by ovarian spheroids, we transfected ovarian cancer cells with siRNA to Snai2 or control, generated spheroids, and performed a mesothelial clearance assay. We found that reduced expression of Snai2 decreased the ability of the ovarian cancer cells to clear the mesothelial cell layer suggesting that Snai2 plays an important role in the early stages of ovarian cancer metastasis. Recognizing that Snai2 is a transcriptional modulator, we were interested in determining if Snai2 affected STAT3 activity. Analysis of available Snai2 ChIP-seq data identified three putative Snai2 binding sites associated with the STAT3 gene, suggesting that Snai2 may also regulate STAT3 gene expression. To determine if Snai2 affects STAT3 gene expression, ovarian cancer cells were transfected with siRNA to Snai2 and STAT3 mRNA expression was analyzed. From this, we found that reducing Snai2 expression also reduced STAT3 expression. Taken together, our data suggests that STAT3 and Snai2 form a feedforward loop promoting upregulation of each other and together they promote the early stages of ovarian cancer metastasis. Therefore, developing an inhibitor to one of these transcription factors would affect both proteins and may be beneficial to prevent or treat metastatic ovarian cancer.
Citation Format: David F. Walker, Sarah J. Lacroix, Yuri Makar, Sarah R. Walker. The role of STAT3 and Snai2 in ovarian cancer metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6077.
