Pittet, MikaelSweeney, Jenna Geddes2019-12-112018-032018-01-022018Sweeney, Jenna Geddes. 2018. Glycan-Mediated Regulation of Melanoma Growth and Survival. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.http://nrs.harvard.edu/urn-3:HUL.InstRepos:42015619Malignant transformation and tumor progression are often associated with aberrant glycosylation of cell surface proteins and lipids. Commonly observed changes in glycan composition during malignancy include truncation of serine/threonine O-linked glycans, altered expression of mucins, an increase in overall sialylation and enhanced synthesis of tri- and tetra-antennary complex N-glycans. Increasing evidence supports the idea that the presence of certain glycans correlates with cancer progression, affects tumor cell invasiveness, alters binding to pro-tumorigenic galectins, and promotes metastasis to distant organs. Yet the molecular details underlying how glycans functionally contribute to malignant transformation and progression are poorly understood. From expression-based analyses across multiple cancer lineages, we found that melanomas exhibit significant transcriptional changes in glycosylation-related genes. This glycosylation gene-signature revealed that compared to normal melanocytes, melanomas downregulate the β1,6 N-acetylglucosaminyltransferase, GCNT2, leading to a loss of asparagine(N)-linked I-branched glycans. Moreover, immunohistochemical analyses of clinical melanoma specimens revealed that GCNT2 expression is inversely correlated with progression. Functionally, we found that knockdown of GCNT2/loss of I-branched glycans significantly enhanced melanoma xenograft growth and promoted three-dimensional in vitro melanoma colony formation and survival. Whereas enforced expression of GCNT2/I-branched glycans decreased melanoma xenograft growth and inhibited in vitro colony formation and survival. Mechanistic studies further revealed that GCNT2/I-branched glycans negatively regulated growth factor receptor and adhesion-mediated cell growth and survival, specifically through insulin-like growth factor-1 receptor (IGF1R) and integrin-extracellular matrix mediated signaling pathways. In addition, we found that GCNT2/I-branched glycans reduced ligand binding to IGF1R and fibronectin-binding integrins. In all, our studies expand our current understanding of the role of aberrant glycans in melanoma and how subtle changes in glycan structure can regulate several malignancy-associated pathways to alter melanoma cell signaling, growth and survival.application/pdfenglycosylationcancermelanomasignalingsurvivalgrowthGCNT2Thesis or Dissertation2019-12-11