Tumor-specific glycoforms of CD73 unmask defective components of the protein secretory pathway in hepatocellular carcinoma (2016)

Undergraduates: Deekshita Ramanarayanan, Ricardo Rivera-Soto Natasha T. Snider

Faculty Advisor: Natasha Snider
Department: Biology

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Protein N-linked glycosylation involves the covalent attachment carbohydrates to asparagine residues. Glycosylation changes are universal in hepatocellular carcinoma (HCC) cells, the most prevalent form of liver cancer. However, their biological basis is largely unknown. The goal of this proposal is to characterize the molecular mechanisms behind differences in N-linked glycosylation between HCC tumors and non-tumor adjacent liver tissues. Ecto-5-nucleotidase (CD73) is a glycosyl-phosphatidylinositol (GPI)-linked plasma membrane N-linked glycoprotein that is expressed on hepatocytes and activated hepatic stellate cells. Subjecting human normal or paired HCC tumor and adjacent non-tumor liver tissues to biochemical and glycoproteomic analyses uncovered HCC tumor-specific alterations in the overall and site-specific glycan composition on CD73. These results, coupled with RNA-seq analysis of the tissues uncovered significant differences in the expression levels and alternative splicing of genes that encode enzymes involved in transporting nucleotide sugars in the Golgi apparatus. We are currently investigating the specific role of the Golgi nucleotide sugar transporter SLC35A3 and an alternative splice variant on CD73 glycosylation in normal hepatocytes and in HCC cell lines. This forms the basis for our hypothesis that perturbations in the abundance, localization, and utilization of sugar nucleotides in the Golgi leads to aberrant glycosylation of CD73 in HCC tumors.