Date of Graduation
Doctor of Philosophy (PhD)
Gary E. Gallick, Ph.D.
Menashe Bar-Eli, Ph.D.
David J. McConkey, Ph.D.
Jian Kuang, Ph.D.
Scott E. Kopetz, M.D., Ph.D.
Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that mediates interactions between the extracellular matrix and intracellular signaling pathways critical in promoting numerous cellular functions including adhesion, proliferation, survival and migration. Most FAK functions result from phosphorylation by Src family kinases, which trigger numerous signaling cascades. Overexpression of FAK is associated with metastasis in many solid tumors, including prostate cancer. Hence, understanding the mechanisms by which FAK is regulated in prostate cancer will better elucidate its role in prostate cancer metastasis. Work in this dissertation tested the hypothesis that altered phosphorylation of FAK is critical for cell migration and promotion of prostate cancer metastasis.
To address the hypothesis, I developed highly migratory variants of prostate cancer cells. These cells were increased in invasion, decreased in adhesion and had increased metastatic potential. A hallmark of the migratory variants was increased phosphorylation of FAK Y861. To examine the mechanism for this increased phosphorylation, expression and activity of Src family members were assessed. The migratory variants were increased in expression and total activity of the SFK, Yes, but no other members of the Src family kinases. I demonstrated that Yes was specifically responsible for the phosphorylation of FAK Y861 using both prostate tumor cells and src-/-, yes-/-, fyn-/- mouse embryo fibroblasts and that increased Yes expression was directly responsible for increased migration of the selected migratory variants. Using shRNA plasmids directing knockdown of Yes, I further demonstrated that silencing Yes inhibits prostate cancer lymph node metastasis in vivo in an orthotopic model of prostate cancer tumor growth and metastasis. Furthermore, in human specimens, I demonstrated that Yes expression and phosphorylation of FAK Y861 was increased in lymph node metastases relative to primary tumors, with the latter correlating with decreased patient survival.
In summary, I have identified novel roles for Yes in selectively phosphorylating FAK relative to other SFKs, resulting in increased migration and metastasis of prostate cancer cells. Therefore, increased expression of phosphorylated FAK at tyrosine 861 and Yes kinase may be predictive markers for prostate cancer progression.
FAK, Yes kinase, Prostate Cancer, Metastasis