P125 focal adhesion kinase promotes malignant astrocytoma cell proliferation in vivo

p125 focal adhesion kinase (p125FAK) is a cytoplasmic tyrosine kinase that is activated upon engagement of integrin cell adhesion receptors, and initiates several signaling events that modulate cell function in vitro. To determine the biologic role of p125FAK in malignant astrocytic tumor cells, U-251MG human malignant astrocytoma cells were stably transfected with p125FAK cDNA using the TET-ON system, and stable clones isolated that exhibited an estimated 5- or 20-fold increase in p125FAK expression on administration of 0.1 or 2.0 μg/ml doxycycline, respectively. In vitro studies demonstrated that induction of p125FAK resulted in a 2- to 3-fold increase in cell migration, increased p130CAS phosphorylation, localization of exogenous p125FAK to focal adhesions, and a 2-fold increase in soft agar growth. To determine the role of p125FAK in vivo, clones were injected stereotactically into the brains of scid mice. A 4.5-fold estimated increase in p125FAK expression was induced by administration of doxycycline in the drinking water. Analysis of xenograft brains demonstrated that, upon induction of p125FAK, there was a 1.6- to 2.8-fold increase in tumor cell number, and an increase in mAb PCNA-labeling of tumor cells in the absence of a change in the apoptotic index. Compared to normal brain, the expression of p125FAK was elevated in malignant astrocytic tumor biopsies from patient samples. These data demonstrate for the first time that p125FAK promotes tumor cell proliferation in vivo, and that the underlying mechanism is not associated with a reduction in apoptosis.