John Muschler, PhD.
Email: muschler@cpmcri.org
Introduction
My laboratory is dissecting the molecular changes that arise in breast cancer cells that contribute to aberrant cell behavior and to progression of the disease. This work has dual aims; it requires identification of the critical molecules regulating of normal cell function and the identification of those critical molecules that are damaged or altered in cancer cells. Through our efforts, we expect to gain a better understanding of the root causes of cancer cell behavior and, most importantly, identify new strategies aimed at taming cancer cells.
Our current work is focused on changes that arise on the external surface of cancer cells. Molecules embedded in the surface of cells are very important for sensing the cells environment and directing normal cell behavior. Among these molecules (called “receptors”) are those that sense the extracellular matrix (ECM), a complex meshwork of proteins found between cell layers, similar to the mortar between bricks. Increasingly, evidence is showing that an altered cell response to the ECM is a very important step in the progression of cancers.
In recent years, we have revealed important roles for an ECM receptor called "dystroglycan" in maintaining normal breast epithelial cell functions. Dystroglycan has been extensively studied in muscle cells, because it is defective in some muscular dystrophies, but has been largely ignored in studies of epithelial cell function and cancer progression. We have discovered that dystroglycan induces proper cell growth control and normal tissue architecture in response to binding molecules in the ECM. Excitingly, we and others have found that dystroglycan is functionally compromised in the majority human breast tumor cells tested, and a loss of dystroglycan expression or function is evident in a wide variety of carcinomas, ranging from those of the breast, prostate and colon. In addition, we have demonstrated that restoration of dystroglycan function a tumor cell line can restore normal responses to the ECM and reduced their tumorigenic potential.
Through molecular dissection of the dystroglycan molecule in functionally normal cells, we have determined that a key role of dystroglycan is to anchor the extracellular matrix protein laminin to the cell surface, which facilitates the assembly of laminin into the ECM and facilitates laminin’s interaction with other receptors. By this model, loss of dystroglycan function in cancer cells will reduce or abolish normal ECM assembly. This defect will alter the ECM itself and cell interactions with the ECM, and these events may play a significant role in the loss of normal tissue architecture and ultimately in tumor cell metastasis. We have also shown that the loss of dystroglycan function in cancer cells can be attributed mainly to the improper addition of sugars (i.e. abnormal glycosylation) to the dystroglycan protein, which abolishes the ligand-binding function of the receptor. This is a dramatic demonstration of the importance of post-translational protein modifications to normal cell functions, and points to critical modifications that arise in cancer cells. In a very recent study, we have performed biochemical and structural analysis of a cleaved domain of dystroglycan and found that dystroglycan resides within the family of proteins called SEA domain mucins. This discovery reveals a previously unrecognized evolutionary connection between dystroglycan and molecules such as Muc1, another cell-surface glycoprotein modified in cancer cells and implicated in progression of the disease.
Our research is presenting new players and new models to explain normal and tumor cell behavior. We continue to explore new molecular changes that determine cancer cell behavior, and are exploring ways to use these new insights in our fight against cancer.
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My Lab
From left to right
Marisa Oppizzi, Ph.D., John Muschler Ph.D., Jimmie Fata, Ph.D., Roozbeh Mohajer, M.D., Manisha Singh M.S.
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Figures
“We have determined the sequence of post-translational modifications that determine the functional state of the dystroglycan molecule in normal epithelial cells and carcinoma cell. Importantly, this work demonstrated that hypoglycosylation of dystroglycan occurs in carcinoma cells, which leads to a loss of receptor activity that likely contributes to cancer progression. (See Singh et al., Cancer Research, 2004.)”
“We have used conditional receptor knockout models to demonstrate that dystroglycan is key mediator of laminin assembly in epithelial cells, and mediates early steps for signaling for cell polarity and tissue-specific gene expression. The figure shows assays of epithelial cell polarity using normal and knockout cells grown in a 3-dimensional matrix. (See Weir et al., 2006, Journal of Cell Science).”
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Publications
Click to see List of publications by John Muschler, PhD. in PubMed.
Representative publications include:
Akhavan, A., Crivelli, S., Singh, M., Lingappa, V.R., Muschler, J.L. (2007) SEA domain proteolysis determines the functional composition of dystroglycan. FASEB J. 2008 Feb;22(2):612-21. Epub 2007 Sep 28.
Weir, L., Oppizzi, M.L., Henry, M.D., Onishi, A., Campbell, KP., Bissell, M.J., Muschler, J. (2006) Dystroglycan loss disrupts polarity and beta-casein induction in mammary epithelial cells by perturbing laminin anchoring. J. Cell Science. 119:4047-58.
Singh, J, Itahana, Y, Knight-Krajewski, S., Kanagawa, M., Campbell, KP., Bissell, M.J., Muschler J. (2004) Proteolytic enzymes and altered
glycosylation modulate dystroglycan function in carcinoma cells. Cancer Research. 64: 6152-9.
Kanagawa, M., Saito, F., Kunz, S., Yoshida-Moriguchi, T., Barresi, R.,
Kobayashi, Y. M., Muschler J., Dumanski, J. P. , Michele, D. E.,
Oldstone, M. B., and Campbell, K.P. (2004) Molecular recognition by
LARGE is essential for expression of functional dystroglycan. Cell.
117: 953-64
Weir, M.L. and Muschler J. (2003) Dystroglycan: emerging roles in mammary gland function. J. Mammary Gland Biol. Neoplasia 8 (4): 409- 420.
Muschler J., Levy, D., Boudreau, R., Henry, M. and Campbell, K.C. and Bissell, M.J. (2002). A role for dystroglycan in epithelial polarization: loss of function in breast tumor cells. Cancer Research. 60: 7102-09.
Radisky, D., Muschler J. and Bissell, M.J. (2002). Order and disorder: the role of extracellular matrix in epithelial cancer. Cancer Investigations. 20 (1): 1-16.
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