Aberrant O-glycosylation contributes to tumorigenesis in human colorectal cancer

Aberrant O-glycosylation is frequently observed in colorectal cancer (CRC) patients, but it is unclear if it contributes intrinsically to tumorigenesis. Here, we investigated the biological consequences of aberrant O-glycosylation in CRC. We first detected the expression profile of Tn antigen in a serial of human CRC tissues and then explored the genetic and biosynthetic mechanisms. Moreover, we used a human CRC cell line (LS174T), which express Tn antigen, to assess whether aberrant O-glycosylation can directly promote oncogenic properties. It showed that Tn antigen was detected in around 86% human primary and metastatic CRC tissues. Bio-functional investigations showed that T-synthase and Cosmc were both impaired in cancer tissues. A further analysis detected an occurrence of hypermethylation of Cosmc gene, which possibly caused its loss-of-function and a consequent inactive T-synthase. Transfection of LS174T cells with WT Cosmc restored mature O-glycosylation, which subsequently down-regulated cancer cell proliferation, migration and apoptotic-resistant ability. Significantly, the expression of MUC2, a heavily O-glycosylated glycoprotein that plays an essential role in intestinal function, was uniformly reduced in human CRC tissues as well as in LS174T cells. These data suggest that aberrant O-glycosylation contributes to the development of CRC through direct induction of oncogenic properties in cancer cells.