The long term objective of our research is to understand the regulatory mechanisms of cell proliferation and differentiation of mammary epithelial cells. Mammalian cells in culture can be classified as ethanolamine (Etn)-responsive and -nonresponsive type with regard to the growth response. The Etn-responsive type includes normal rat mammary epithelial cells and some human and rat mammary carcinoma cells. Etn-responsiveness and prolactin-responsiveness of a mammary cell line seem to be coupled: some mammary cell lines are responsive to both agents and some others do not respond to either one of them. When Etn-responsive cells grow in Etn-deficient medium, phosphatidylethanolamine (PE) content in membrane phospholipid significantly reduces, suggesting that Etn-responsive cells can not synthesize or maintain adequate amounts of PE without the exogenous Etn, and that the PE-deficient membrane is not suitable for proper biological functions. Our immediate objective is 1) to elucidate the biochemical mechanism of Etn-responsiveness and 2) to examine the effect of PE-deficiency on prolactin action and other aspects of cellular metabolism. Etn-responsive and -nonresponsive rat mammary carcinoma cell lines will be used for the study. To achieve the first objective, various synthetic and turnover processes of PE will be examined. These include the examination of the activities of phosphatidylserine decarboxylase and enzymes that incorporate Etn into PE, the role of sphingomyelin and choline on PE synthesis, and the synthetic/turnover rate of individual phospholipids. To achieve the second objective, we will examine prolactin, insulin and phorbol ester bindings; active transport; macromolecular synthesis; and membrane associated enzyme activities of Etn-responsive cells grown in the presence or absence of Etn. These studies will contribute in understanding the role of the membrane phospholipids, particularly of PE, in regulation of various cellular metabolic processes, cell proliferation and differentiation.
