Objective   To examine expression patterns of focal adhesion kinase (FAK) and its activated form, phosphorylated FAK (pFAK), in human osteosarcoma and to investigate the correlation of FAK expression with clinicopathological parameters and prognosis. Functional consequence of manipulating FAK protein levels was also investigated in human osteosarcoma cell lines.

  Methods   Immunohistochemical staining was used to detect FAK and pFAK levels in pathologically archived materials from 113 patients with primary osteosarcoma. KaplanMeier survival and Cox regression analyses were used to evaluate prognoses. The role of FAK in cytological behavior of MG63 and 143B human osteosarcoma cell lines was studied via the FAK protein knockdown with siRNA. Cell proliferation, migration, invasiveness, and apoptosis were assessed using cell counting kit-8, Transwell, and Annexin V/PI staining methods.

  Results  Both FAK and pFAK were overexpressed in osteosarcoma patients. Tumor cells exhibited cytoplasmicity and occasional membranous immunoreactivity for FAK. A total of 42 cases (37.17%) mainly showed expressed pFAK in cytoplasm of osteosarcoma cells. No overexpression staining of anti-FAK and anti-pFAK antibodies was observed in normal cancellous bone tissues or negative controls. Significant differences were observed in overall survival between FAK-/pFAK-and FAK+/pFAK-groups (P=0.016), FAK+/pFAK-and FAK+/pFAK+ groups (P=0.012), and FAK-/pFAK-and FAK+/ pFAK+ groups (P < 0.001). All groups showed similar metastasis-free survival. Cox proportional hazard analysis showed that FAK expression profile is an independent indicator of both overall and metastasis-free survival. siRNA-based knockdown of FAK significantly reduced migration and invasion of MG63 and 143B cells and affected proliferation and apoptosis in osteosarcoma cells.

  Conclusion   Osteosarcoma malignancies in vitro and in vivo were correlated with overexpression and phosphorylation of FAK. These findings suggest that FAK plays an important biological role in osteosarcoma carcinogenesis. This study provides a better understanding of diagnostic and prognostic relevance of FAK overexpression and phosphorylation in osteosarcoma patients. Therefore, FAK and pFAK can be used as independent predictors of overall and metastasis-free survival in osteosarcoma patients.