Epidermal growth factor is a positive in vivo regulator of CTP:cholinephosphate cytidylyltransferase

Regulation of choline deficiency apoptosis by epidermal growth factor in CWSV-1 rat hepatocytes

Previous studies show that acute choline deficiency (CD) triggers apoptosis in cultured rat hepatocytes (CWSV-1 cells). We demonstrate that prolonged EGF stimulation (10 ng/mL x 48 hrs) restores cell proliferation, as assessed by BrdU labeling, and protects cells from CD-induced apoptosis, as assessed by TUNEL labeling and cleavage of poly(ADP-ribose) polymerase. However, EGF rescue was not accompanied by restoration of depleted intracellular concentrations of choline, glycerphosphocholine, phosphocholine, or phosphatidylcholine. In contrast, we show that EGF stimulation blocks apoptosis by restoring mitochondrial membrane potential (Delta Psi(m)), as determined using the potential-sensitive dye chloromethyl-X-rosamine, and by preventing the release and nuclear localization of cytochrome c. We investigated whether EGF rescue involves EGF receptor phosphorylation and activation of the down-stream cell survival factor Akt. Compared to cells in control medium (CT, 70 micromol choline x 48 hrs), cells in CD medium (5 micromol choline) were less sensitive to EGF-induced (0-300 ng/mL x 5 min) receptor tyrosine phosphorylation. Compared to cells in CT medium, cells in CD medium treated with EGF (10 ng/mL x 5 min) exhibited higher levels of phosphatidylinositol 3-kinase (PI3K)-dependent phosphorylation of AktSer473. Inactivation of PI3K was sufficient to block EGF-stimulated activation of Akt, restoration of mitochondrial Delta Psi(m), and prevention of cytochrome c release. These studies indicate that stimulation with EGF activates a cell survival response against CD-apoptosis by restoring mitochondrial membrane potential and preventing cytochrome c release and nuclear translocation which are mediated by activation of Akt in hepatocytes.

Effects of epidermal growth factor (EGF) on the development of EGF-receptor (EGF-R) binding in fetal rabbit lung organ culture

Epidermal growth factor (EGF) causes gender- and development-specific changes in fetal lung surfactant synthesis. We hypothesized that the effects of EGF on development of surfactant synthesis are related to effects on EGF receptor (EGF-R) expression. We prepared sex-specific fetal rabbit lung organ cultures on gestational days 21 and 24 (term = 31 days) in Waymouth's medium + 10% charcoal-stripped fetal calf serum as control or with added EGF (10 ng/mL). After 3, 5, and 7 days of culture, we measured specific EGF-R binding in fetal lung plasma membrane preparations. Analysis of variance (ANOVA) revealed significant effects of fetal gender (P = 0.0003), time in culture (P = 0.01), and EGF treatment (P = 0. 0003) on EGF specific binding. In control cultures from days 21 and 24 (both male and female), EGF specific binding tended to decrease with time in culture. Specific binding in EGF-treated female 21-day cultures was significantly higher than in controls, both after 5 days (184% of control, P = 0.007) and after 7 days (151% of control, P = 0.01; Bonferroni multiple comparisons) of treatment, whereas males exhibited no response to EGF treatment. As opposed to these effects in 21-day cultures, EGF had little effect on 24-day cultures. We conclude that EGF affects the expression of the EGF-R on EGF specific binding in the fetal lung. The development of surfactant synthesis in the fetal lung may be controlled by upregulation of the EGF-R.