2264

FGFR4

fibroblast growth factor receptor 4;FGFR4;fibroblast growth factor receptor 4

hydroxyaryl-protein kinase|protein-tyrosine kinase|tyrosine kinase related to fibroblast growth factor receptor|tyrosylprotein kinase

5q35.2

protein-coding

tumor cells evolve by interacting with the local microenvironment; however, the tumor-stroma interactions that govern tumor metastasis are poorly understood. In this study, proteomic analyses reveal that coculture with tumor-associated fibroblasts (TAF) induces significant overexpression of FGFR4, but not other FGFRs, in colorectal cancer cell lines. Mechanistic study shows that FGFR4 plays crucial roles in TAF-induced epithelial-to-mesenchymal transition (EMT) in colorectal cancer cell lines. Accumulated FGFR4 in cell membrane phosphorylates beta-catenin, leading to translocation of beta-catenin into the nucleus. Further, TAF-derived CCL2 and its downstream transcription factor, Ets-1, are prerequisites for TAF-induced FGFR4 upregulation. Furthermore, FGFR4-associated pathways are shown to be preferentially activated in colorectal tumor samples, and direct tumor metastasis in a mouse metastasis model. Our study shows a pivotal role of FGFR4 in tumor-stroma interactions during colorectal cancer metastasis, and suggests novel therapeutic opportunities for the treatment of colorectal cancer.

We previously identified pituitary tumor-derived fibroblast growth factor receptor 4 (ptd-FGFR4), an alternatively transcribed N-terminally truncated cytoplasmic receptor isoform. Unlike wild-type FGFR4, ptd-FGFR4 facilitates cell transformation and results in pituitary tumor formation in transgenic mice. To investigate differences in the tumorigenic properties of FGFR4 and ptd-FGFR4, we examined their abilities to modulate cell adhesiveness. Introduction of ptd-FGFR4 into GH4 pituitary cells or NIH 3T3 fibroblasts resulted in significant reduction in cell adhesion to a collagen IV matrix compared with FGFR4- or empty vector-transfected cells. This adhesive difference was evident in the absence or presence of FGF stimulation. Furthermore, treatment with beta1-integrin neutralizing antibody markedly reduced adhesiveness in FGFR4-transfected cells but had little effect on the depressed adhesiveness of ptd-FGFR4-transfected cells. Unlike wild-type FGFR4, ptd-FGFR4 does not associate with neural cell-adhesion molecule (NCAM). Cells expressing FGFR4 demonstrate membranous N-cadherin with a noninvasive growth pattern identical to control GH4 cells when injected into immunodeficient mice. In contrast, ptd-FGFR4-expressing cells develop invasive tumors in vivo with marked loss of N-cadherin that localizes to the cytoplasm. Consistent with these changes, beta-catenin expression was diminished and its interaction with N-cadherin was disrupted in the presence of ptd-FGFR4, but both were intact in the presence of wild-type FGFR4. These data highlight the importance of membrane-anchored FGFR4 in assembling a multiprotein FGFR4 complex with NCAM and N-cadherin playing pivotal functions in maintaining normal cell adhesion. Disruption of distinct NCAM/N-cadherin proadhesive complexes by a tumor-derived FGFR4 isoform provides a novel mechanism beyond ligand independence that explains the pathobiology of proliferative and infiltrative but nonmetastatic neoplasms.

PURPOSE: Increased expression of FGFR-4 and its ligands have been linked to lethal prostate cancer (PCa). Furthermore, a germ line polymorphism in the FGFR-4 gene, resulting in arginine at codon 388 (Arg(3)(8)(8)) instead of glycine (Gly(3)(8)(8)), is associated with aggressive disease. The FGFR-4 Arg(3)(8)(8) variant results in increased receptor stability, sustained receptor activation, and increased motility and invasion compared with Gly(3)(8)(8). However, the impact of sustained signaling on cellular signal transduction pathways is unknown. EXPERIMENTAL DESIGN: expression microarray analysis of immortalized prostatic epithelial cells lines expressing FGFR-4 Arg(3)(8)(8) or Gly(3)(8)(8) was used to establish a gene signature associated with FGFR-4 Arg(3)(8)(8) expression. Transient transfection of reporters and inhibitors was used to establish the pathways activated by FGFR-4 Arg(3)(8)(8) expression. The impact of pathway knockdown in vitro and in an orthotopic model was assessed using inhibitors and/or short hairpin RNA (shRNA). RESULTS: expression of the FGFR-4 Arg(3)(8)(8) protein leads to increased activity of the extracellular signal-related kinase (ERK) pathway, increased activity of serum response factor (SRF) and AP1, and transcription of multiple genes that are correlated with aggressive clinical behavior in PCa. Increased expression of SRF is associated with biochemical recurrence in men undergoing radical prostatectomy. Consistent with these observations, knockdown of FGFR-4 Arg(3)(8)(8) in PCa cells decreases proliferation and invasion in vitro and primary tumor growth and metastasis in vivo. CONCLUSIONS: These studies define a signal transduction pathway downstream of FGFR-4 Arg(3)(8)(8) that acts via ERK and SRF to promote PCa progression.