THE WIDESPREAD DISTRIBUTION OF PHOSPHOLIPASE C-GAMMA-1 AND PLC-GAMMA-1 GENE POSITIVE ELEMENT-1 (GPE1)-BINDING PROTEINS

Phospholipase C-gamma 1 (PLC-gamma 1) is a mediator of growth factor-i nduced signal cascade, which generates two second messengers, inositol 1,4,5-trisphosphate and diacylglycerol, upon occupation of cell surfa ce receptors by growth factors. We have previously cloned and analyzed the promoter region of the PLC-gamma 1 gene and demonstrated the coop eration between the DNA binding proteins of the GPE1 region, one of th e transcriptional regulatory regions. In this study, the distributions of the transcriptional activation function of the PLC-gamma 1 gene po sitive element 1 (GPE1) region and its binding proteins (GES1, GES2, a nd GES3 binding proteins) were examined in various cell lines, along w ith that of the PLC-gamma 1 protein. PLC-gamma 1 was expressed in ever y organ and cell line examined when assessed by immunoblot analysis. A ll the cell lines used in transient transfection assays also revealed the transcriptional activation function of the GPE1 region. Consistent ly, the GPE1 binding proteins, GES1, GES2, and GES3 binding proteins, were observed to exist ubiquitously by eletrophoretic mobility shift a ssay. However, the GPE1 binding proteins from different cell lines may not be identical proteins since the electrophoretic mobility of the D NA-protein complexes seemed to differ among cell lines, implying the p resence of multiple types of GPE1-binding proteins. Taken together, we suggest that the widespread distribution of GPE1-binding proteins mig ht explain the ubiquitous expression of PLC-gamma 1.