Phosphatidylethanolamine deficiency in membrane lipids inhibits keratinocyte intercellular networks formation

Ethanolamine (Etn) is required for the growth of epithelial cells in culture. Without Etn, the amount of phosphatidylethanolamine (PE) in membrane lipids is reduced, and cell proliferation stops. When the membrane lipids are deficient of PE, some extracellular signaling processes become impaired. In this study, we examined the effect of Etn deprivation on the formation of intercellular networks in immortalized human oral keratinocytes. Keratinocytes proliferate with undifferentiated morphologies in a low-calcium medium, whereas they undergo differentiation to form intercellular networks in a high-calcium medium. The cells were first cultured with or without Etn supplement in a low-calcium (0.07 mM) medium, and then the calcium concentration was raised to 1.8 mM. The localization and organization of the following proteins were examined: (1) desmogleins and plakoglobin in desmosomes, (2) E-cadherin and beta-catenin in adherens junctions and (3) actin and keratin filaments in cytoskeletons. As expected, in the Etn-supplemented cells, the elevated level of calcium induced the junctional localization of the proteins associated with desmosomes and adherens junctions and also induced the formation of keratin and actin networks. On the contrary, in the Etn-deprived cells, the elevated level of calcium induced none of the above processes. The results suggest that having a sufficient amount of PE or proper phospholipid composition in the membranes is crucial for differentiation in epithelial cells.