Expression of GRP and Its Receptor in Well-differentiated Colon Cancer Cells Correlates with the Presence of Focal Adhesion Kinase Phosphorylated at Tyrosines 397 and 407Kristina A. Matkowskyja, Kristin Kellera, Sarah Glovera, Lori Kornbergc, Roger Tran-Son-Tayb, and Richard V. Benyaa,da Department of Medicine, University of Illinois at Chicago and Chicago Veterans Administration Medical Center (West Side Division), Chicago, Illinois b Departments of Aerospace Engineering, University of Florida, Gainesville, Florida c Otolaryngology, University of Florida, Gainesville, Florida d Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois Correspondence to: Richard V. Benya, Dept. of Medicine, U. of Illinois at Chicago, 840 South Wood Street (M/C 716), Chicago, IL 60612. E-mail: rvbenya@uic.edu Gastrin-releasing peptide (GRP) and its receptor (GRP-R) are not normally expressed by epithelial cells lining the colon but are aberrantly expressed in cancer, where they act as morphogens and regulate tumor cell differentiation. Studies of colon cancer formation in mice genetically incapable of synthesizing GRP-R suggested that this receptor's morphogenic properties were mediated via focal adhesion kinase (FAK). We therefore set out to determine the presence of both total and phosphorylated forms of FAK in human colon cancer specimens as a function of tumor cell differentiation and GRP/GRP-R co-expression. Ten colon cancers containing 25 regions of distinct differentiation were randomly selected from our GI Cancer Tumor Bank. All specimens were immunohistochemically probed using antibodies recognizing GRP, GRP-R, total FAK, and FAK specifically phosphorylated at tyrosine (Y) 397, 407, 576, 577, 861, and 925. Antibody-specific chromogen was determined by quantitative immunohistochemistry (IHC) for each region of defined differentiation. Here we confirm that GRP/GRP-R co-expression is a function of differentiation, with highest levels observed in well-differentiated tumor cells. We also show that the amount of total FAK and of FAK phosphorylated at Y397 and Y407 tightly correlates with differentiation and with the amount of GRP/GRP-R co-expression. These findings are consistent with GRP/GRP-R acting as a morphogen by activating FAK, and suggest that this occurs via phosphorylation of this enzyme at two specific tyrosine residues. (J Histochem Cytochem 51:10411048, 2003) Key Words: bombesin, colorectal cancer, gastrin-releasing peptide, receptor
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