De novo expression of human polypeptide N-acetylgalactosaminyltransferase 6 (GalNAc-T6) in colon adenocarcinoma inhibits the differentiation of colonic epithelium

Abstract

Edited by Eric R. FearonAberrant expression of O-glycans is a hallmark of epithelial cancers. Mucin-type O-glycosylation is initiated by a large family of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts) that target different proteins and are differentially expressed in cells and organs. Here, we investigated the expression patterns of all of the GalNAc-Ts in colon cancer by analyzing transcriptomic data. We found that GalNAc-T6 was highly up-regulated in colon adenocarcinomas but absent in normal-appearing adjacent colon tissue. These results were verified by immunohistochemistry, suggesting that GalNAc-T6 plays a role in colon carcinogenesis. To investigate the function of GalNAc-T6 in colon cancer, we used precise gene targeting to produce isogenic colon cancer cell lines with a knockout/rescue system for GALNT6. GalNAc-T6 expression was associated with a cancer-like, dysplastic growth pattern, whereas GALNT6 knockout cells showed a more normal differentiation pattern, reduced proliferation, normalized cell-cell adhesion, and formation of crypts in tissue cultures. O-Glycoproteomic analysis of the engineered cell lines identified a small set of GalNAc-T6 -specific targets, suggesting that this isoform has unique cellular functions. In support of this notion, the genetically and functionally closely related GalNAc-T3 homolog did not show compensatory functionality for effects observed for GalNAc-T6. Taken together, these data strongly suggest that aberrant GalNAc-T6 expression and site-specific glycosylation is involved in oncogenic transformation.

Probing the contribution of individual polypeptide GalNAc-transferase isoforms to the O-glycoproteome by inducible expression in isogenic cell lines

“…cro ARTICLE glycopeptide substrates (12,20,21), but more recently, use of isogenic cell lines with knockout (KO) and/or knock-in (KI) of individual GALNT genes coupled with the development of quantitative differential O-glycoproteomics has provided more comprehensive insight into the contributions of individual Gal-NAc-Ts to the O-glycoproteome (22)(23)(24)(25). Perhaps surprisingly, this latter approach has indicated that the nonredundant contributions of GalNAc-T isoenzymes to the O-glycoproteome appear to be minor, and the majority of O-glycosites are redundantly glycosylated among the isoforms present in a cell (22).…”

Cosmc overexpression enhances malignancies in human colon cancer

“…We selected 5 types of ppGalNac-Ts (GALNT2, GALNT3, GALNT6, GALNT12, GALNT14), as these ppGalNac-Ts have been reported to be closely associated with CRC. [27][28][29][30][31] Our analysis did not detect obvious differences in the mRNA levels of these ppGalNAc-Ts between Cosmc-overexpressing cells and the control cells ( Figure 4C). Collectively, these results suggested that aberrant O-glycosylation is unlikely the cause for Cosmc overexpression-mediated oncogenic alterations.…”

OGT Controls the Expression and the Glycosylation of E‐cadherin, and Affects Glycosphingolipid Structures in Human Colon Cell Lines

“…Interestingly, GALNT6 transcripts are upregulated in colon adenocarcinoma, correlated with a cancer‐like dysplastic growth . GALNT6 knock‐down results in increased cell‐cell adhesion and a more differentiated phenotype . In addition, GALNT6 transcription is induced by over activation of HBP in A549 pulmonary cancer cells cultured in hyperglycemic conditions .…”

“…GALNTs are more active in CRC and responsible for initiating mucin‐type O ‐Glycan synthesis, the initial product being the Tn‐antigen (Ser/Thr‐αGalNAc) . Interestingly, GALNT6 transcripts are upregulated in colon adenocarcinoma, correlated with a cancer‐like dysplastic growth . GALNT6 knock‐down results in increased cell‐cell adhesion and a more differentiated phenotype .…”