CELL ADHESION AND APOPTOSIS

大多数人类癌症起源于上皮细胞。许多癌细胞

Most human cancers arise from epithelial cells. Many carcinoma cells have nearly normal morphologies and growth rates in culture, suggesting that their primary defect is in their failure to respond to an unidentified apoptotic challenge in vivo. Recently, I reported that the disruption of epithelial integrin-mediated cell-matrix interactions causes apoptosis (termed "anoikis"). I further demonstrated that the sensitivity of cells to anoikis was in fact reduced by oncogenes and increased by tumor suppressor genes, demonstrating that genes may contribute to cancer by controlling anoikis. This project will test the role of integrins and integrin-related signal transducers in the control of anoikis. Specifically, the role of the integrin beta subunit cytoplasmic domains, which are known to initiate some aspects of integrin signaling, will be tested. These domains, arising from multiple genes, also vary as a result of alternative splicing and phosphorylation. Anomalous integrin expression is often seen in tumor cells. By expressing anomalous integrin types, tumor cells may be able to escape anoikis. This hypothesis will be tested by comparing the various beta subunit cytoplasmic domains for their ability, after clustering, to rescue cells from anoikis. Other investigators have established a central role for Focal Adhesion Kinase (FAK) in integrin signaling. An activated form of FAK was recently found to rescue epithelial cells from anoikis (Preliminary Studies). The role of FAK in anoikis will be investigated further by the use of specific mutations affecting various aspects of its signaling and cytoskeletal associations. Several reports have indicated the importance of ras or the ras-like G- protein, rho, in integrin signaling. The function of these molecules and their downstream effectors in anoikis will be examined in two stages. First, their activation by adhesion will be assayed. Secondly, we will test the effects of expressing mutationally activated forms on anoikis. Certain activating signaling molecules may contribute to epithelial transformation primarily by alleviating anoikis. This project has already identified FAK as one such molecule. The identification of others will elucidate a pathway that controls anoikis, strengthening our understanding of epithelial carcinogenesis.