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 407

Abstract

S U M M A R YGastrin-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.

Transforming Growth Factor-β Stimulates Intestinal Epithelial Focal Adhesion Kinase Synthesis via Smad- and p38-Dependent Mechanisms

“…16 Induction of differentiation in dedifferentiated, rounded, detached Colo201/205 human cancer cells increases both …”

“…14,15 Total and activated FAK levels are also directly related to the state of differentiation in human colon cancer. 16 Induction of differentiation in dedifferentiated, rounded, detached Colo201/205 human cancer cells increases both FAK protein and FAK activation and enhances cell adhesion. 17 Furthermore, inhibition of FAK activation via transfection of FRNK, a nonphosphorylatable, truncated FAK, decreases adhesion and wound healing in 293 nonmalignant colon cancer cells exposed to gastrin-releasing peptide.…”

CFTR Cl– channel functional regulation by phosphorylation of focal adhesion kinase at tyrosine 407 in osmosensitive ion transporting mitochondria rich cells of euryhaline killifish

“…FAK phosphoryation at Y407 has been linked to both stimulatory and inhibitory actions. Gastrin releasing peptide stimulates gastric tumour cells and phosphorylates FAK at Y397 and Y407, connected to tumour cell differentiation (Matkowskyj et al, 2003), yet in NIH3T3 cells, FAK Y397 and Y407 operate inversely and FAK Y407 phosphorylation may negatively regulate these cells (Lim et al, 2007). It is clear that FAK Y407 can be phosphorylated by multiple pathways of which osmosensing is only one.…”

Inhibition of focal adhesion kinase as a potential therapeutic strategy for imatinib-resistant gastrointestinal stromal tumor

“…FAK is a non-receptor type tyrosine kinase that is activated from integrin and growth factor receptors by autophosphorylation at Tyr 397 (4) followed by subsequent activations of other functional phosphorylation sites to advance the signals to downstream pathways, such as phosphatidylinositol 3-kinase/AKT and Ras/mitogen-activated protein kinase (5 -9), whose activations are critical for cell proliferation, differentiation, and apoptosis (10 -14). Based on these facts, FAK is thought to be an important molecule for tumor aggressiveness such as tumor progression, invasion, and metastasis (15 -19).…”