The ratio of phosphatidylcholine to phosphatidylethanolamine does not predict integrity of growing MT58 Chinese hamster ovary cells.

Phosphatidylcholine (PC) homeostasis is important for maintaining cellular growth and survival. Cellular growth and apoptosis may also be influenced by the PC to phosphatidylethanolamine (PE) ratio as a reduction in this ratio can result in a loss of membrane integrity. To investigate whether a reduced PC:PE ratio influences cellular growth and apoptosis, we utilized the MT58 cell line, which contains a thermo-sensitive mutation in CTP:phosphocholine cytidylyltransferase-α, the rate-limiting enzyme for PC biosynthesis. Incubation of MT58 cells at the restrictive temperature of 41°C results in a reduction of cellular PC and induces apoptosis. Furthermore, MT58 cells have a 50% reduction in the PC:PE ratio when incubated at 41°C. In an attempt to normalize the PC:PE ratio, which may stabilize cellular membranes and rescue MT58 cells from apoptosis, the cells were treated with either silencing RNA to impair PE biosynthesis or lysophosphatidylcholine to increase PC mass. Impairing PE biosynthesis in MT58 cells reduced cellular PE and PC concentrations by 30% and 20%, but did not normalize the PC:PE ratio. Loss of both phospholipids enhanced the onset of apoptosis in MT58 cells. Lysophosphatidylcholine normalized cellular PC, increased PE mass by 10%, restored cellular growth and prevented apoptosis of MT58 cells without normalizing the PC:PE ratio. Furthermore, total amount of cellular PC and PE, but not the PC:PE ratio, correlated with cellular growth (R(2)=0.76), and inversely with cellular apoptosis (R(2)=0.97). These data suggest the total cellular amount of PC and PE, not the PC:PE ratio, influences growth and membrane integrity of MT58 cells.