Cell-surface glycans play essential roles in diverse cell surface interactions, yet glycobiology studies are complicated by the varied and dynamic nature of glycan presentation. New techniques to precisely modify and engineer glycans on the cell surface are of paramount importance for crucial insights into processes such as immune cell activation, embryonic development, and cancer progression. An illustrative example of the glycobiology challenge is the membrane associated mucin glycoprotein MUC1. MUC1 is highly over-expressed and aberrantly glycosylated on ca. 90% of breast, ovarian, lung, colon, and pancreatic carcinomas, is a biomarker for detection of epithelial tissue derived cancers, and is a target for cancer vaccines. MUC1 studies have been complicated by its sheer size (150-300 kDa), polymorphism, variable glycosylation patterns, and because both the cytosolic and extracellular domains can participate in signaling that affects cell survival and migration. There is a widespread assumption that cancer-associated mucins sterically block access of cell surface adhesion molecules to the extracellular matrix and shield cancer cells from the immune system;yet molecular evidence is lacking and recent evidence has suggested more sophisticated roles. The proposed research seeks to understand the functional significance of cancer-associated mucin overexpression by using a new method of cell surface engineering that will enable correlation of subtle changes in glycosylation with biochemical actions. A library of synthetic glycopolymer mimics of MUC1's extracellular glycodomain will be prepared, attached to membrane anchoring lipids or engineered MUC1 protein chimeras, and displayed on live cells. Using microscopic and biochemical methods, I will investigate how changes in the mucin glycocalyx influence mechanical regulation of integrin clustering, focal adhesion formation, and signaling that has downstream effects on cellular adhesion, survival, and migration. This research could lead to a new understanding of how the glycocalyx affects extracellular matrix interactions pertinent to cancer progression. Additionally, development of our cell surface engineering method has strong potential for broad applications in studying diverse cell surface interactions. Overall, this interdisciplinary approach will combine techniques in polymer chemistry and cell biology to answer important questions about cancer progression that cannot be undertaken by biological methods alone.

Public Health Relevance

The surface of every cell is covered with a diverse array of glycans that are involved in virtually every aspect of biology, yet glycobiology studies are complicated because glycan presentation is a product of complex metabolic pathways that over 1000 genes contribute to. Cancer cells have strikingly different glycan patterns compared to healthy cells, but the causes are poorly understood because biological methods to modify cell-surface glycans are currently extremely limited. The aim of the proposed research is to use an interdisciplinary approach to precisely engineer the cell surface using synthetic glycopolymer mimics of natural glycans, which will allow correlation of changes in glycan pattern with biochemical actions that affect cancer.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZRG1)
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Barski, Oleg
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University of California Berkeley
Schools of Arts and Sciences
United States
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Kramer, Jessica R; Onoa, Bibiana; Bustamante, Carlos et al. (2015) Chemically tunable mucin chimeras assembled on living cells. Proc Natl Acad Sci U S A 112:12574-9