Clinical significance of FAK expression in human neoplasia.

Focal Adhesion Kinase is a 119-121 kDa nonreceptor protein kinase widely expressed in various tissues and cell types. Several studies showed that FAK plays an important role in integrin signaling. Once activated by integrin and non-integrin stimuli, it binds and activates several other molecules, such as Src, p130Cas, Grb2, PI3K and paxillin, thus promoting signaling transduction. In normal cells FAK activity is under constant regulation by mechanisms such as gene amplification, alternative splicing and action of phosphatases. On the contrary, in vitro studies showed that in transformed cells unopposed FAK signaling promoted cancer cells' malignant characteristics. FAK was held responsible for cancer cells' uninhibited proliferation, protection from apoptosis, invasion, migration, adhesion and spreading, as well as tumor angiogenesis. Several in vivo studies supported the above observations and further correlated FAK expression with various clinicopathological parameters of several types of human malignancies. The purpose of this article is a comprehensive review of the existing data on FAK expression and signaling and their clinical significance in human malignancy.