Abstract
UDP-glucose dehydrogenase (UGDH) catalyzes oxidation of UDP-glucose to yield UDP-glucuronic acid, a substrate for synthesis of glycosaminoglycans in extracellular matrix and for glucuronidation of certain xenobiotics to aid in their solubilization. Accumulating evidence has demonstrated that glycosaminoglycans play an important role in regulating normal cell physiology and signaling during tumor progression. Although association of extracellular matrix with cell proliferation and migration has been well documented, the importance of UGDH in these behaviors is not clear. Using specific small interference RNA to down regulate UGDH expression, the levels of cellular UDP-glucuronic acid, glycosaminoglycans and hyaluronic acid were decreased in the HCT-8 colorectal carcinoma cells. Treatment of HCT-8 cells with either UGDH-specific siRNA or HA synthesis inhibitor 4-methylumbelliferone effectively delayed cell aggregation into multicellular spheroids and impaired cell motility in both three-dimensional collagen gel and transwell migration assays. The reduction in cell aggregation and migration rates could be restored by addition of exogenous HA. Continuously, the aim of this study is to determine whether modulating UGDH activity can affect tumor formation and drug susceptibility of HCT-8 colorectal carcinoma cells. Further analysis of several cancer stem cell properties in the UGDH down regulated HCT-8 cells revealed that the anchorage independent growth ability of the cells was reduced and the cellular distribution of the cancer stem cell marker CD44 was altered. Moreover, UGDH knockdown decreased the side population cell fraction and increased the susceptibility of HCT-8 cells to anticancer drug Irinotecan. The enhancement of the drug susceptibility in the UGDH knockdown cells was accompanied with a decrease of Irinotecan metabolism. Finally, the tumorigenicity of the sphere-derived HCT-8 cells was significantly reduced upon UGDH knockdown in a xenograft mouse model. All these results indicate that UGDH plays an important role in colorectal cancer development and can serve as a potential therapeutic target.