Platelet-derived growth factor-BB mediates pancreatic cancer malignancy via regulation of the Hippo/Yes-associated protein signaling pathway

Platelet-derived growth factor (PDGF) is a potent mitogen and chemoattractant that serves a role in the development of several types of solid cancer, and abnormal PDGF activity has been reported in numerous human tumors. Tumor-derived PDGF ligands are considered to act in either a paracrine or autocrine manner, serving roles in the phosphorylation of receptors on tumor and stromal cells in the tumor microenvironment. Despite the well-established association between PDGF and tumor progression, the precise mechanisms of autocrine PDGF signaling in pancreatic tumor cells remain elusive. Therefore, the present study aimed to analyze the influence of PDGF-BB in pancreatic cancer. Pancreatic adenocarcinoma BxPC-3 cells were cultured and treated with recombinant human PDGF-BB in vitro. Cell proliferation was tested using an MTT assay. Cell apoptosis was measured using flow cytometry. Tumor cell migration and invasion were examined via wound-healing and Transwell assays, respectively. The expression and subcellular localization of Yes-associated protein (YAP) was determined using western blotting and immunofluorescence. The transcriptional activity of target genes was tested using a luciferase assay and reverse transcription-quantitative PCR. The present study revealed that PDGF-BB significantly promoted cell proliferation in pancreatic adenocarcinoma BxPC-3 cells and enhanced the aggressiveness of this cell line, as demonstrated by Transwell and wound-healing assays. Anoikis resistance is an important mechanism by which metastatic cells avoid apoptosis when detaching from adjacent cells or the extracellular matrix. PDGF-BB treatment inhibited anoikis under anchorage-independent conditions. Mechanistic experiments revealed that PDGF-BB promoted the upregulation and activation of the transcriptional coactivator YAP, an effector of the Hippo signaling pathway. RhoA or protein phosphatase-1 (PP-1) inhibition partially abolished the accumulation and activation of YAP, suggesting PDGF-BB-mediated YAP dephosphorylation and transactivation via the RhoA/PP-1 cascade. Pharmacologic inhibition of the PDGF receptor directly downregulated YAP activity and the expression levels of downstream genes. Furthermore, verteporfin, a small molecular inhibitor of the Hippo/YAP signaling pathway, partially reversed the effects of PDGF-BB on cell proliferation, anoikis resistance and cell migration. In conclusion, the present study revealed that the Hippo/YAP signaling pathway may be involved in the tumor-promoting activity of PDGF-BB in pancreatic cancer.