Molecular characterization of the role of PTK2/FAK amplification in oral squamous cell carcinoma (OSCC)

3398 Background: The PTK2/FAK ( PTK2 ) gene on 8q24 codes for focal adhesion kinase (FAK), which is a critical nonreceptor tyrosine kinase involved in cell motility and growth. PTK2 has been implicated in many types of cancer including breast and ovarian, mainly through PTK2 expression studies on lymph node and distant metastasis. Previous genomic studies have identified PTK2 as an amplification target, setting the stage for this study of the genomic and expression alterations in PTK2 using a large set of primary oral squamous cell carcinomas (OSCCs). Study Design: Using high-resolution, array-based Comparative Genomic Hybridization (aCGH), we documented copy number alterations (CNAs) in 8q24.3, including PTK2 , in over 35 primary oral cavity squamous cell carcinomas (OSCCs). Results were confirmed using quantitative Real-Time PCR (Q-PCR). Total RNA isolated from the same tumors was hybridized to Affymetrix HG-U113A and HG-U113B microarrays to characterize the expression of genes identified by aCGH. This allowed identification of genes in regions of CNA that were also under or overexpressed. Immunohistochemistry (IHC) for PTK2 was performed on the same samples with varying CNAs of PTK2 , in order to characterize the result of the CNAs in OSCC tissues. We have also examined tumors with PTK2 amplification for the presence of additional cancer gene CNAs in order to identify interactions with molecular pathways associated with PTK2 overactivity. Results: The 8q24.3 amplicon harbors the genes T1 , EIF2C2, PTK2, GPR20 , and PTP4A3 , and was amplified in over 60% of our samples. Of the five genes studied, the only gene found to also be overexpressed in our OSCCs was PTK2 (p=0.0165). IHC using a monoclonal PTK2 antibody revealed elevated protein expression levels of PTK2 throughout the cytoplasm, in agreement with both the aCGH data and the RNA expression data. Finally, we have begun to examine the correlation of PTK2 amplification to the alteration of other genes involved in OSCC, and have found a positive correlation with genomic gains in BRCA1 in one subset, and with genomic losses in PTK2B in another subset of OSCCs. Conclusion: Using aCGH, Q-PCR expression profiling, and IHC we have identified PTK2 as the candidate gene most likely driving the 8q24.3 amplification, and shown that the amplification results in overexpression of PTK2 mRNA and protein in OSCC cells. We have also correlated amplification in PTK2 in additional subsets of OSCCs with CNAs in other cancer related genes, which we anticipate will shed light on the molecular pathways most involved in the evolution of OSCC.