The expression and functional roles of the actin filament -associated protein AFAP-110 in human prostate carcinoma
The actin filament-associated protein, AFAP-110, is an actin cross-linking protein that regulates actin cytoskeleton integrity. AFAP-110 also functions as an adaptor protein that affects crosstalk between Src and protein kinase C (PKC). This dissertation sought to investigate the potential roles of AFAP-110 in the tumorigenic process of human prostate carcinoma. Using tissue arrays, I found that AFAP-110 was absent or expressed at very low levels in normal prostatic epithelium, but was significantly increased in prostate carcinomas. Additionally, the expression of AFAP-110 positively correlated with Gleason grading of prostate cancer. Down-regulation of AFAP-110 in PC3 prostate cancer cells by siRNA resulted in decreased cell proliferation and anchorage-independent growth in vitro, as well as reduced tumorigenicity and growth in orthotopic nude mouse models. Furthermore, down-modulation of AFAP-110 significantly decreased cell-matrix adhesion and migration, correlated with defects in focal adhesions and reduced integrin β1 expression. These properties were restored by re-introduction of either a wild type avian AFAP-110 or a mutant variant disabled in the ability to interact with Src. Expression of a mutant AFAP-110 lacking the PKC-interacting domain failed to rescue parental phenotype. Therefore, AFAP-110 may regulate prostate cancer cell tumorigenic properties through a PKC-dependent mechanism. Among downstream signaling pathways of PKC are the MAP kinase cascades, including extracellular signal-regulated kinase (ERK)-1/2, c-Jun-N-terminal kinase (JNK) and p38. Down-regulation of AFAP-110 in PC3 cells selectively led to a significantly increased induction of p38 phosphorylation and activity, but not ERK or JNK, upon PKC stimulation by phorbol ester. A selective inhibitor of PKCα in PC3 cells, Gö6976, completely abrogated phorbol ester-induced p38 activation, suggesting AFAP-110 regulates a novel pathway by which PKCα activates p38. In summary, studies in this dissertation provide the first demonstration that aberrant expression of AFAP-110 plays a role in a human cancer. Increased expression of AFAP-110 is associated with progressive stages of prostate carcinoma, and is critical for tumor growth, in part by regulating focal contacts and by selectively regulating a PKCα/p38 signaling axis. AFAP-110 thus may be a novel diagnostic and prognostic marker, and a potential therapeutic target for prostate cancer.
Zhang, Jing, "The expression and functional roles of the actin filament -associated protein AFAP-110 in human prostate carcinoma" (2007). Texas Medical Center Dissertations (via ProQuest). AAI3256571.