Yaqi Zhang

Complement activation at the interface between adipocytes and cancer cells drives tumor progression

The omentum is the primary site of metastasis for ovarian cancer (OC). Interactions between cancer cells and adipocytes drive an invasive and prometastatic phenotype. Here we studied cancer cell-adipocyte crosstalk by using a direct coculture model with immortalized human visceral nondiabetic pre-adipocytes (VNPADs) and OC cells. We demonstrated increased proliferation, invasiveness, and resistance to cisplatin of cocultured compared with monocultured OC cells. RNA sequencing of OC cells from coculture versus monoculture revealed significant transcriptomic changes, identifying over 200 differentially expressed genes common to OVCAR5 and OVCAR8 cell lines. Enriched pathways included PI3K/AKT and complement activation. Lipid transfer into OC cells from adipocytes induced upregulation of complement C3 and C5 proteins. Inhibiting C3 or C5 reversed the invasive phenotype and C3 knockdown reduced tumor progression in vivo. Increased C3 expression was observed in omental implants compared with primary ovarian tumors and C3 secretion was higher in OC ascites from high-BMI versus low-BMI patients. C3 upregulation in OC cells involved activation of the ATF4-mediated integrated stress response (ISR). Overall, adipocyte-cancer cell interactions promoted invasiveness and tumorigenesis via lipid transfer, activating the ISR, and upregulating complement proteins C3 and C5.

SOX9 drives a stem-like transcriptional state and platinum resistance in high-grade serous ovarian cancer

Chemotherapy resistance remains a formidable challenge to the treatment of high-grade serous ovarian cancer (HGSOC). The drug-tolerant cells may originate from a small population of inherently resistant cancer stem cells (CSCs) in primary tumors. In contrast, sufficient evidence suggests that drug tolerance can also be transiently acquired by nonstem cancer cells. Regardless of the route, key regulators of this plastic process are poorly understood. Here, we utilized multiomics, tumor microarrays, and epigenetic modulation to demonstrate that SOX9 is a key chemo-induced driver of chemoresistance in HGSOC. Epigenetic upregulation of SOX9 was sufficient to induce chemoresistance in multiple HGSOC lines. Moreover, this upregulation induced the formation of a stem-like subpopulation and significant chemoresistance in vivo. Mechanistically, SOX9 increased transcriptional divergence, reprogramming the transcriptional state of naive cells into a stem-like state. Supporting this, we identified a rare cluster of SOX9-expressing cells in primary tumors that were highly enriched for CSCs and chemoresistance-associated stress gene modules. Notably, single-cell analysis showed that chemo treatment results in rapid population-level induction of SOX9 that enriches for a stem-like transcriptional state. Altogether, these findings implicate SOX9 as a critical regulator of early steps of transcriptional reprogramming that lead to chemoresistance through a CSC-like state in HGSOC.

FOXK2 promotes ovarian cancer stemness by regulating the unfolded protein response pathway

Understanding the regulatory programs enabling cancer stem cells (CSCs) to self-renew and drive tumorigenicity could identify new treatments. Through comparative chromatin-state and gene expression analyses in ovarian CSCs versus non-CSCs, we identified FOXK2 as a highly expressed stemness-specific transcription factor in ovarian cancer. Its genetic depletion diminished stemness features and reduced tumor initiation capacity. Our mechanistic studies highlight that FOXK2 directly regulated IRE1α (encoded by ERN1) expression, a key sensor for the unfolded protein response (UPR). Chromatin immunoprecipitation and sequencing revealed that FOXK2 bound to an intronic regulatory element of ERN1. Blocking FOXK2 from binding to this enhancer by using a catalytically inactive CRISPR/Cas9 (dCas9) diminished IRE1α transcription. At the molecular level, FOXK2-driven upregulation of IRE1α led to alternative XBP1 splicing and activation of stemness pathways, while genetic or pharmacological blockade of this sensor of the UPR inhibited ovarian CSCs. Collectively, these data establish what we believe is a new function for FOXK2 as a key transcriptional regulator of CSCs and a mediator of the UPR, providing insight into potentially targetable new pathways in CSCs.