Background: Gastrointestinal neuroendocrine (NE) tumors frequently metastasize and have limited treatments. We have recently found that over-expression of focal adhesion kinase (FAK), a non-receptor tyrosine kinase that plays an important role in cancer biology, led to a significant reduction in NE tumor markers in gastrointestinal NE tumor cells. However, the role of FAK on gastrointestinal NE tumor growth is not known. We hypothesize that over-expression of FAK might inhibit gastrointestinal NE tumor cell growth.
Methods: Human pancreatic carcinoid BON cells were transiently transfected with recombinant pKH3-FAK constructs encoding the full-length of wild-type FAK protein or vector alone and analyzed by Western blot for evidence of FAK over-expression in transfected cells. MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) rapid colorimetric assay was used to measure cell viability in FAK transfected BON cells. Finally mechanism of growth inhibition was analyzed by Western blotting.
Results: At baseline, no FAK protein was present in BON cells. Transfection with recombinant pKH3-FAK constructs resulted in FAK over-expression and a concomitant decrease in cell viability (percentage) compared to vector alone in BON cells. Moreover, Western blotting identified an increase in phosphorylation of FAK Tyr407 only, and no change in FAK Tyr397 or FAK Tyr576/577 in BON cells transfected with pKH3-FAK plasmid. FAK over-expression in BON cells led to an increase in p21 and a decrease in CyclinD1 protein, indicating that the growth inhibition was mediated by cell cycle arrest.
Conclusions: FAK expression leads to a reduction in cellular proliferation in gastrointestinal NE tumor cells. The mechanism of growth suppression is mediated by cell cycle arrest. FAK Tyr407 phosphorylation may contribute to negative regulation of kinase activity. Therefore, FAK is a potential target for the development of new treatments for advanced gastrointestinal NE tumors.