Matrix mechanics, not hypoxia, modulate quiescin sulfhydryl oxidase 1 (QSOX1) in pancreatic tumor cells

Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer-related deaths in the U.S., despite only being the 11th most common cancer. The high mortality rates of PDAC can be partially attributed to the tumor microenvironment. Unlike most carcinomas, PDAC is characterized by a strong desmoplastic reaction, or a fibrotic stiffening of the extracellular matrix (ECM) in response to chronic inflammation. The desmoplastic reaction is mediated by cancer-associated fibroblasts that deposit ECM proteins (collagens, laminins, fibronectin, etc.) and secrete matrix-remodeling proteins in the tumor parenchyma. Within the past decade, the enzyme quiescin sulfhydryl oxidase 1 (QSOX1) has gained recognition as a significant contributor to solid tumor pathogenesis, but its biological role remains uncertain. QSOX1 is a disulfide bond-generating catalyst that participates in oxidative protein folding in the mammalian cell. Current studies show that inhibiting or knocking down QSOX1 reduces pancreatic cancer cell migration and invasion, alters ECM deposition and organization, and decreases overall tumor growth in mice. However, it is unclear which features of the tumor microenvironment modulate QSOX1 and cause its overexpression in cancer. In this study, we explored potential regulators of QSOX1 expression and secretion by testing two major features of PDAC: hypoxia and mechanical stiffness. To induce hypoxia, we exposed pancreatic cancer cells to atmospheric (low O2) and chemical (CoCl2) hypoxia for up to 48 hours. QSOX1 gene and protein expression did not change in response to hypoxia. Substratum stiffness was modulated using polyacrylamide gels to represent the dynamic pathological range of elastic moduli found in PDAC tissue. We discovered that QSOX1 levels were decreased on softer surfaces compared to conventional tissue culture plastic. This paper presents new results and challenges prior findings on QSOX1 regulation in pancreatic tumor cells.