YAP1 Overexpression Enhances the Aerobic Glycolysis Process via Suppression of EGLN2 in Pancreatic Ductal Adenocarcinoma.

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive diseases and has remarkably high mortality rates. In recent years, altered metabolism has been shown to contribute to the maintenance of pancreatic cancer malignancies. However, the molecular mechanism underlying glucose metabolism reprogramming remains elusive. The aim of this study was to elucidate the role of Yes-associated protein (YAP1), an important effector of the Hippo pathway, in the regulation of aerobic glycolysis in pancreatic cancer. Moreover, the contributions of YAP1 and its associated glycolytic enzymes to prognosis were assessed via The Cancer Genome Atlas (TCGA) dataset.

Methods: YAP1 expression was silenced by short hairpin RNA (shRNA), and its effects on glycolytic activity and mitochondrial respiration were analysed via Agilent Seahorse XF Analysers. The effects of YAP1 on hypoxia-inducible factor-1α (HIF-1α) and its transcriptional activity on glycolytic genes were examined via shRNA-mediated silencing of YAP1. The underlying mechanism by which YAP1 controls the HIF-1α protein level was analysed by exploring the interaction between YAP1 and egg-laying-defective nine family (EGLN) members, which are well-established regulators of the HIF-1α protein level. Finally, the effects of YAP1, EGLN and glycolytic genes on prognosis were analysed via TCGA dataset.

Results: We found that silencing YAP1 expression inhibited anabolic glycolysis in pancreatic cancer cells. YAP1 was demonstrated to regulate the HIF-1α protein level, transcriptional activity and the expression of HIF-1α-targeted glycolytic genes. In-depth analysis demonstrated that EGLN2, a modulator of the HIF-1α protein level, was a direct target of YAP1. Low EGLN2 expression was associated with a poor prognosis. By analysing TCGA dataset and performing immunohistochemical staining, we demonstrated that YAP1 expression was negatively correlated with EGLN2 expression at the mRNA level and protein levels.

Conclusions: The present study demonstrated that YAP1 positively regulates aerobic glycolysis by inhibiting EGLN2 expression, which results in an increased HIF-1α protein level and transcriptional activity. YAP1 was positively regulated and significantly correlated with HIF-1α-targeted glycolytic genes, including glucose transporter type 1(GLUT1), hexokinase2 (HK2) and lactate dehydrogenase A (LDHA). Elevated YAP1 expression and concomitant downregulation of EGLN2 contributed to poor survival in patients with pancreatic cancer. Our results suggest that YAP1 may be a promising predictive marker and treatment target for human pancreatic cancer.