Abstract 1113: Novel recurrent glycosylation-associated gene mutations in colon cancer
Authors: Venkitachalam Srividya , Revoredo Leslie , Ravi Lakshmeswari , Lutterbaugh James , Markowitz Sanford , Gerken Thomas , Guda Kishore 
Published: August 2015

Abstract
Aberrant glycosylation is a hallmark of many human cancers including colon cancer and has been proposed to affect cell growth, differentiation, adhesion, transformation and metastasis. However, the molecular basis for aberrant glycosylation remains largely unknown. We previously reported the finding of somatic and germline inactivating mutations in the gene encoding for GALNT12 transferase, a key enzyme involved in the initiating step of mucin type O-glycosylation, in individuals with colon cancer (PNAS 106(31):12921-25). This study provided the first evidence for the presence of genetic defects in the glycosylation pathway that contribute to the pathogenesis of colon cancer, and is consistent with the hypothesis that multiple rare germline gene variants may account for many of the cases of colon neoplasia that arise in the population. Given that aberrant glycosylation is a recurrent alteration in colon cancers, it is highly likely that additional genes (other than GALNT12) within the glycosylation pathway may be targeted for somatic mutations and contribute to colon tumor development. Accordingly, we performed massively parallel targeted re-sequencing of 430 glycosylation pathway genes in 31 microsatellite stable colon cancer cell lines. We identified a total of 41 somatic mutations in 36 unique genes. Using the statistical method detailed in our prior study, we found 12 of the genes to be significantly mutated above the background rate (P≤0.01, FDR&lt;0.05). Intriguingly, three of these genes including B3GNT2, B4GALT2 and ST6GALNAC2, mapped to the polylactosamine and core 3 O-glycosylation pathway sub-network. Together, mutations in these three genes accounted for 20% of the CRC samples tested, with 3 mutations in B3GNT2 (R6*, P186T, D247H), 1 homozygous mutation in B4GALT2 (A146V) with loss of the wild-type allele, and 2 mutations in ST6GALNAC2 (D43H, R115W). Biochemical analyses using in vitro derived substrates demonstrated two of the three B3GNT2 mutants and the single B4GALT2 mutant as being functionally inactivate when compared to respective wild-type proteins. In comparison to the wild-type protein, mutations detected in ST6GALNAC2 however did not significantly alter its protein function, and additional biochemical analyses using alternate substrates is currently underway. Furthermore, curation of the COSMIC database revealed these genes as being mutational targets in colon cancers with the majority of the mutations mapping to the catalytic domains of respective proteins. Overall, these findings suggest that the polylactosamine and core 3 O-glycosylation pathway sub-network plays an important role in maintaining normal intestinal homeostasis, and mutational inactivation of the pathway members may lead to aberrant glycosylation and tumor progression in the colon.
Citation Format: Srividya Venkitachalam, Leslie Revoredo, Lakshmeswari Ravi, James Lutterbaugh, Sanford Markowitz, Thomas Gerken, Kishore Guda. Novel recurrent glycosylation-associated gene mutations in colon cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1113. doi:10.1158/1538-7445.AM2015-1113