Focal adhesion kinase is expressed in the angiogenic blood vessels of malignant astrocytic tumors in vivo and promotes capillary tube formation of brain microvascular endothelial cells.
OBJECTIVE
Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that has been shown to promote proliferation, migration, and invasion of several cell types in vitro, and we have shown recently that FAK promotes proliferation of malignant astrocytoma cells in vivo. To determine the role of FAK in angiogenesis in malignant astrocytic tumors, we investigated the expression and function of FAK in brain endothelial cells.


METHODS
We characterized the expression of FAK and activated FAK in endothelial cells by immunohistochemistry. We also determined the function of FAK in brain microvascular endothelial cells by transfecting these cells with a dominant interfering form of FAK [FAK-related nonkinase (FRNK)] or a mutant FRNK (Leu-1034 to Ser) and assessed the effect on capillary tube formation and cell migration.


RESULTS
We found that FAK was expressed in the endothelial cells of grade III (4 of 9 samples) and IV (9 of 10 samples) astrocytoma biopsies but not in the endothelial cells of normal brain (0 of 9 samples) and not in grade I (0 of 5 samples) or II (0 of 4 samples) astrocytoma biopsies. Furthermore, we found that both FAK and activated FAK were expressed in the endothelial cells in malignant astrocytoma tumors propagated intracerebrally in the severe combined immunodeficient mouse brain. As expected, immunofluorescence analysis showed FRNK protein to localize to focal adhesions, whereas mutant FRNK protein did not. FRNK-transfected endothelial cells showed a 55% reduction in branched tube formation and a 40% reduction in tube length when propagated in three-dimensional collagen gels, compared with cells transfected with the mutant FRNK construct. Furthermore, FRNK-transfected cells showed a 35-50% reduction in haptotactic migration toward fibronectin and collagen, compared with mutant FRNK-transfected cells.


CONCLUSIONS
These data suggest that FAK promotes angiogenesis and that this occurs, at least in part, through the promotion of endothelial cell migration.
Haskell
Henry
H
Department of Pathology, Division of Neuropathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Natarajan
Meera
M
Hecker
Timothy P
TP
Ding
Qiang
Q
Stewart
Jerry
J
Grammer
J Robert
JR
Gladson
Candece L
CL
D000818:Animals; D001254:Astrocytoma / Q000098:blood supply*; D001921:Brain / Q000098:blood supply*; D002196:Capillaries / Q000502:physiology; D002465:Cell Movement; D042783:Endothelial Cells / Q000502:physiology*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000209:etiology*; D011505:Protein-Tyrosine Kinases / Q000032:analysis / Q000502:physiology*; D014183:Transplantation, Heterologous
C113183:FAK-related nonkinase; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse