SOX2-LGR5 signaling mediates ovarian cancer cell survival in response to loss of anchorage.

Ovarian cancer (OVCA) primarily metastasizes through the transcoelomic route, where tumor cells detach, passively disseminate through the peritoneal cavity and establish metastatic niches in the abdominal cavity. A feature of transcoelomic spread is the development of malignant ascites, which is characterized by tumor cells that adapt to survive anchorage-independence (a-i) by evading detachment-induced cell death, known as anoikis. Malignant ascites are frequently observed in advanced stage and recurrent patients and are associated with tumor aggressiveness and therapy resistance. We previously reported that OVCA cells manipulate their transcriptomic profile to promote the expression of anoikis resistance genes in a-i and identified SOX2 as a key detachment-responsive transcription factor necessary for OVCA cell survival in a-i and metastasis. However, the key factors downstream of SOX2 transcriptional regulation in a-i remain unknown. Here, we identified the leucine-rich G-protein coupled receptor, LGR5, as a novel SOX2 regulated gene that is specifically under the control of SOX2 in a-i conditions. LGR5 is a marker of cancer stemness known to promote cancer cell motility, epithelial-to-mesenchymal transition, and tumor formation by potentiating Wnt signaling upon binding with its ligand, R-spondin1 (RSPO1), which is abundant in OVCA ascites. We demonstrate that LGR5 expression is critical for OVCA cell a-i survival. Interestingly, the effects of LGR5 are not driven via canonical Wnt/beta-catenin signaling but are associated with widespread transcriptional repression. In addition, we find that LGR5 knock-down leads to upregulation Wilms' Tumor-1 (WT1) regulated transcription. These studies show for the first time that SOX2 has context specific functions as a transcription factor in a-i conditions, and that OVCA cells may compensate for inhibition of SOX2 or LGR5 by upregulating WT1 signaling. Current studies are focused on understanding the SOX2-LGR5-WT1 regulatory axis further and its impact on driving ovarian cancer cell survival and metastasis. In addition, using transcriptomics and CUT&RUN sequencing analysis we are exploring the context-specific SOX2 transcriptome and role of SOX2 on the epigenome in a-i. Although SOX2 remains a hard-to-drug target in cancer, identifying novel downstream pathways facilitating a-i survival and potential resistance mechanism to SOX2 inhibition are critical for therapeutic targeting of metastatic disease.