Overexpression of Focal Adhesion Kinase in Head and Neck Squamous Cell Carcinoma Is Independent of fak Gene Copy Number

Abstract

The development of human malignancies can involve the aberrant regulation of intracellular signal transduction pathways that regulate cell-extracellular matrix interactions. Purpose: In the current study, we aimed to evaluate focal adhesion kinase (FAK) at both genetic and protein expression levels in head and neck squamous cell carcinomas (HNSCC) and to explore the prognostic significance of FAK. Experimental Design: A total of 211tissue specimens, including 147 primary tumors, 56 lymph node metastases, 3 benign hyperplasias, and 5 dysplasias, were analyzed using immunohistochemistry. The fak gene dosage was determined in 33 tumors. Correlations among DNA, protein, and clinicopathologic variables were analyzed. Results: FAK protein was overexpressed in HNSCCs compared with corresponding normal mucosa. High expression levels were found in 62% of the samples. Positive immunostaining was also detected in benign hyperplasias and preinvasive dysplastic lesions. All lymph node metastases examined showed FAK overexpression, with significant correlation with the expression in matched primary tumor. DNA copy number ratios for fak were higher in 39% of the tumors compared with normal mucosa. However, elevated FAK expression did not correlate with gains on DNA level, and not all cases with an amplification of the fak gene displayed protein overexpression. Similar data were obtained in five HNSCC-derived cell lines, in which FAK mRNA levels were precisely correlated with FAK protein levels. FAK protein overexpression in tumors correlated with nodal metastases. Conclusions: These findings suggest an involvement of FAK in the onset and progression of HNSCC and provide aninsight into a mechanism of FAK activation alternative to gene amplification.Head and neck squamous cell carcinoma (HNSCC) is one of the most common types of tumors worldwide. Despite recent advancements in diagnosis and treatment, the overall survival has undergone little improvement over the past few decades (1, 2). The major cause of the lethal progression of this type of cancer is the spreading of the malignant cells to regional lymph nodes, which represents a major prognostic indicator and serves as a guide for therapeutic strategies. Although many efforts have been devoted to better understand the molecular mechanisms involved in the progression of this type of cancer, accurate and reliable biomarkers that predict patients at highest risk for lymphatic metastases have yet to be defined.Loss of adhesion of the epithelial cells to the extracellular matrix is one of the fundamental pathways that promote tumor cell migration, invasion, and metastasis. A key factor involved in the control of cell-extracellular matrix interactions is the focal adhesion kinase (FAK), an intracellular tyrosine kinase protein that is localized to cellular focal contact sites (3). FAK is activated and tyrosine phosphorylated upon integrins clustering (4). Evidences also suggest that FAK is a key component of growth factor receptor signaling pathways, such as those activa...

Involvement of focal adhesion kinase in cellular invasion of head and neck squamous cell carcinomas via regulation of MMP-2 expression

“…We have previously reported that FAK is overexpressed in tumour tissue samples and cell lines derived from HNSCC (Canel et al, 2006). Importantly, FAK overexpression in these carcinomas was found in all stages of cancer progression, and it was associated with the presence of lymph node metastasis, thus suggesting that the deregulation of FAK may have an active role in the invasion process of this type of tumors.…”

“…Protein extracts were obtained from SCC40 and SCC38 cells at 80 -90% confluence as previously described (Canel et al, 2006). Equal amounts of proteins were fractionated on SDS -PAGE and transferred to PVDF membranes.…”

“…We have previously reported that FAK is overexpressed in tumour tissue samples and cell lines derived from HNSCC (Canel et al, 2006). Here, to analyse the functional significance of FAK in HNSCC progression, we disrupted the FAK-mediated signal transduction pathway by expression of the FAK COOH-terminal domain (FAK-related nonkinase, FRNK) or small interfering RNA (siRNA) against FAK in the HNSCC-derived SCC40 and SCC38 cell lines.…”

“…Here, to analyse the functional significance of FAK in HNSCC progression, we disrupted the FAK-mediated signal transduction pathway by expression of the FAK COOH-terminal domain (FAK-related nonkinase, FRNK) or small interfering RNA (siRNA) against FAK in the HNSCC-derived SCC40 and SCC38 cell lines. Among the HNSCC-derived cell lines used in our previous report (Canel et al, 2006), we have selected SCC40 and SCC38 cells as systems to study the phenotypic effects of inhibiting FAK, because they express high levels of FAK and the predominant location of activated FAK (pTyr 397 -FAK) is at focal adhesion sites.…”

“…Furthermore, FAK overexpression has been correlated with the invasive potential of a tumour and poor patient prognosis Miyazaki et al, 2003;Recher et al, 2004;Sood et al, 2004). In a study of 106 matched pairs of larynx carcinomas and corresponding normal tissue, using immunohistochemistry, we have previously shown a significantly increased expression of FAK at the protein level in both the tumour tissues and the corresponding metastasis (Canel et al, 2006). Strikingly, we also found that the FAK expression levels of the primary metastatic tumors were maintained in their corresponding lymph node metastases, and FAK protein overexpression in primary tumors correlates with nodal metastasis.…”