SIGNAL TRANSDUCTION EVENTS AND THE REGULATION OF CELL GROWTH

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This project is designed to increase our understanding of cancer cell biology, with an emphasis on hormone-refractory prostate cancer, estrogen receptor-negative breast cancer, primitive neuronal progenitor tumors, and to develop a new approach to cancer treatment through the study of growth-regulatory signal transduction events. This work is currently focused on (1) novel aspects of the regulation of cancer cell growth by the retinoblastoma gene product, and (2) the regulation of transcription factors and signal transducting proteins by a unique form of O-glycosylation. The retinoblastoma protein is currently thought to function only in the cell nucleus and only in the GI phase of the cell cycle. In contrast, we found that the retinoblastoma protein is prominently localized in the cell cytoplasm during logarithmic growth. Our data show that this peripheral localization is masked in most studies of the Rb protein because the antibody used only detects the nuclear form of Rb. Unexpectedly, using confocal microscopy and coimmuno-precipitation techniques we found that peripheral Rb is associated with the cell cytoskeleton, and that peripheral Rb protein is localized in the growing tip of logarithmic phase cells. These data suggest a new model of tumor suppressor gene function, in which the tumor suppressor gene product registers cell-cell interaction and sends a growth arrest signal to the nucleus. While studying the anticancer action of the HMG-CoA reductase inhibitor lovastatin we identified a new posttranslational modification of the Rb protein- the addition of O-linked N-acetylglucosamine (O-GlcNAc addition). We found that lovastatin greatly increased the amount of O-GlcNAc modification of the Rb protein, dramatically blocked Rb phosphorylation and markedly changed Rb subcellular distribution. These studies identify O-GlNAc addition as a new target in anticancer drug development and lovastatin as the first example of a drug that regulates O-GlcNAc metabolism. We have established a cooperative agreement with the British biotechnology company Oxford GlycoSystems, aimed at developing new carbohydrate-directed anticancer drugs.