Essential role of PLD2 in hypoxia-induced stemness and therapy resistance in ovarian tumors

Ovarian cancer (OC) is the most lethal gynecological cancer due to its late diagnosis and, importantly, its high rate of chemoresistance. Hypoxia in solid tumors is an important source of chemoresistance that can determine poor patient prognosis. Such chemoresistance relies on the presence of cancer stem cells (CSCs), and hypoxia promotes their generation through transcriptional activation by HIF transcription factors. We use OC cell lines, xenograft models, OC patient samples, transcriptional databases, iPSCs and ATAC-seq. We show here that hypoxia induces the formation of ovarian CSCs through transcriptional activation of the PLD2 gene encoding phospholipase D2. HIF-1 activates PLD2 transcription through hypoxia response elements located within PLD2 promoter and an intronic enhancer. PLD2 overexpression leads to similar effects than hypoxia, increasing CSC-like features, stemness gene expression and enhancing cell reprogramming in OC cells, as well as chromatin accessibility around stemness genes detected by ATAC-seq. Conversely, PLD2 depletion in hypoxia partially suppresses these effects, indicating that PLD2 is a major determinant of hypoxia-induced CSC generation in OC. Indeed, PLD2 expression is high in OC patients leading to poor survival and a transcriptional switch in the genes related to the response to hypoxia and stemness. Finally, we demonstrate that PLD2 overexpression provokes resistance to platinum-based chemotherapy and that combination of cisplatin with pharmacological inhibition of PLD2 suppresses such resistance. Altogether, our work highlights the importance of the HIF-1-PLD2 axis for CSC generation and chemoresistance in OC and proposes an alternative treatment for patients with high PLD2 expression. ATAC-seq assays SKOV3 ovarian cancer cells, in normoxia and hypoxia, with PLD2 or shPLD2 expression