This project is based on our observation that glucocorticoids can initiate division of density-inhibited fibroblasts. Division of spontaneously-transformed and virally-transformed malignant fibroblasts is not stimulated, even if their growth rate is greatly slowed by placing them in medium containing low levels of serum. The goal of these studies is to analyze the involvement of previously identified surface membrane changes and glucocorticoid-specific cell components in the initiation of division of density-inhibited fibroblasts by cortisol. Levels of cortisol which initiate division bring about increased Concanavalin A-specific agglutinability of the cells, a cell surface change which has been linked to malignancy and loss of density- dependent growth control. We have shown that the protease-mediated surface change measured by increased Concanavalin A-specific agglutinability is not a change that is sufficient to initiate cell division. We now plan to probe whether it is a necessary change in the initiation of division by glucocorticoids. We also plan to investigate some transport changes that have been implicated in initiation of cell division by serum, and determine if they are causally involved in initiation of proliferation. Studies on other systems have shown that glucocorticoid-specific cell components and interactions among them appear to be involved in the action of the hormone. We plan to study their involvement in the initiation of cell division by glucocorticoids. A basic feature of our approach is to employ a series of our unresponsive cell lines. We anticipate that these "mutants" will have a series of altered glucocorticoid-specific components that account for their inability to respond to cortisol. We will assay for functional components in cell- free extracts of sensitive and unresponsive cells using previously described binding assays. Functional alteration of certain components in unresponsive lines would implicate these components in the initiation by glucocorticoids.