of work: Cell cycle progression is subject to numerous checkpoints or points of restriction, which serve to arrest growth if certain processes are incomplete, or damage is incurred. While treatment of cells with genotoxic agents often leads to activation of one or more of these checkpoints and results in growth arrest, in some instances such treatment leads to apoptosis. The factors responsible for determining whether a cell will undergo apoptosis or growth arrest have yet to be clarified and this is the focus of this project. Representative model systems being employed and relevant findings obtained with these over the past year are as follows: 1. Role of the cyclin dependent kinase (CDK) inhibitor p21 in growth arrest and protection against cytotoxic agents. Using an adenoviral vector to achieve high level expression of p21, or antisense technology to inhibit p21 expression, we have shown that p21 over expression generally confers protection against cytotoxic effects of toxic treatments (i.e. prostaglandin A2, UVC irradiation, phenylacetate treatment, and p53 mediated apoptosis in melanoma cells). Some exceptions were noted. These include H2O2 treatment, for which p21 expression did not influence survival, and Rat 1 cells which underwent cell death in response to p21 expression. 2. Role of the CDK inhibitor p27Kip1 in inducing apoptosis. We have observed that unlike, p21 over expression, which causes G1 arrest and confers protection against stress, over expression of p27Kip1 itself leads to apoptosis of mammalian cells. This suggests a novel mechanism whereby p27Kip1 might function to regulate tissue growth. 3. Serum-deprivation induced apoptosis in human lung carcinoma cells. We have examined the mechanisms contributing to apoptosis of A549 cells following serum withdrawal and found that apoptosis is associated with high sustained activation of JNK MAPK. TGF? treatment reversed this cell death and associated with an inhibition of JNK activity.
