Cells of epithelial origin generally require ethanolamine to grow in culture; when these cells are grown without ethanolamine, the phosphatidylethanolamine content of their membrane phospholipid becomes 1/2 to 1/3 of the normal amount, and growth stops. We have hypothesized that growth ceases because the phospholipid environment becomes unsuitable for membrane-associated func- tion. Using ethanolamine-requiring rat mammary cells, we have investigated the possible effect of phosphatidylethanolamine deficiency on the binding characteristics of epidermal growth factor. Apparent dissociation constant for the high-affinity sites in cells having normal membrane phospholipid was 1.7 x 1 O-'OM, whereas that of phosphatidylethanolamine-deficient cells was 2.7 X 10-'OM: the difference was small, but significant. Pretreatment with phorbol ester caused the loss of high-affinity sites in cells having normal membrane, whereas binding characteristics of epidermal growth factor became refractory to the pretreatment in phosphatidylethanolamine-deficient cells. In addition, the rate of internalization of bound epidermal growth factor in phosphatidylethanolamine-deficient cells was about 1/4 of normal cells. Further, whether cells had normal or phosphatidylethanolamine-deficient membranes seemed to affect the phosphorylation patterns of membrane proteins in response to epidermal growth factor or phorbol ester. These results suggest that membrane phospholipid environment affects the activity of the epidermal growth factor receptor.
Cells of epithelial origin generally require ethanolamine (Etn) (or phosphatidylethanolamine [PEN to grow in culture, whereas fibroblasts or neurocells proliferate well in the absence of Etn (Kano-Sueoka and King, 1987a,b). The composition of membrane (plasma and total) phospholipid of Etn-requiring cells is similar to that of in vivo tissue when they are grown in the presence of Etn (Kano-Sueoka et al., 1983). However, in the absence of supplemental Etn, the content of PE in their membrane becomes 1/2 to 1/3 of the normal amount and that of phosphatidylcholine (PC) increases by 30% (Kano-Sueoka et al., 1983;Kano-Sueoka and King, 198713). In the absence of Etn, the rate of growth slows down as PE content is reduced (and PC content