The Widespread Distribution of Phospholipase C-γ1 and PLC-γ1 Gene Positive Element 1 (GPE1)-binding Proteins

Phospholipase C-γ1 (PLC-γ1) is a mediator of growth factor-induced signal cascade, which generates two second messengers, inositol 1,4,5-trisphosphate and diacylglycerol, upon occupation of cell’surface receptors by growth factors. We have previously cloned and analyzed the promoter region of the PLC-γ1 gene and demonstrated the cooperation between the DNA binding proteins of the GPE1 region, one of the transcriptional regulatory regions. In this study, the distributions of the transcriptional activation function of the PLC-γ1 gene positive element 1 (GPE1) region and its binding proteins (GES1, GES2, and GES3 binding proteins) were examined in various cell lines, along with that of the PLC-γ1 protein. PLC-γ1 was expressed in every organ and cell line examined when assessed by immunoblot analysis. All the cell lines used in transient transfection assays also revealed the transcriptional activation function of the GPE1 region. Consistently, the GPE1 binding proteins, GES1, GES2, and GES3 binding proteins, were observed to exist ubiquitously by eletrophoretic mobility shift assay. However, the GPE1 binding proteins from different cell lines may not be identical proteins since the electrophoretic mobility of the DNA-protein complexes seemed to differ among cell lines, implying the presence of multiple types of GPE1-binding proteins. Taken together, we suggest that the widespread distribution of GPE1-binding proteins might explain the ubiquitous expression of PLC-γ1.