Expression of a 118 Kd protein in colon carcinoma cells that is immunologically related to PLC-gamma 1 and is augmented by serum-free conditions.

Immunoprecipitation of cell lysates from serum-starved HCT-8 colon carcinoma cells with monoclonal antibodies raised to PLC-gamma 1 precipitates proteins which can be detected by immunoblotting; the 148 Kd PLC-gamma 1 and a smaller protein of approximately 118 Kd (p118). Expression of p118 is suppressed in cells grown in serum but is present 8 to 12 h after cells are placed in serum-free medium. Conversely, serum-starved cells that express this protein suppress it 6 to 8 h after exposure to 10% fetal calf serum. Pulse chase experiments indicate that the protein is not a degradation product of PLC. This protein has thus far been detected only in human carcinoma cells and not in normal or transformed fibroblasts. Although the protein has not been identified, its expression pattern may suggest a role contributing to the serum-independent nature of human carcinoma cell lines.