Phospholipase C (PLC) plays an important role in cellular signal transduction and is thought to be critical in cellular growth, differentiation and transformation of certain malignancies. Two second messengers produced from the enzymatic action of PLC are diacylglycerol(DAG) and lnositol 1, 4, 5-trisphosphate(IP3). These two second messengers are important in down stream signal activation of protein kinase C and intracelluar calcium elevation. In addition, functional domains of the PLC isozymes, such as Src homology 2(SH2) domain, Src homology 3(SH3) domain, and pleckstrin homology(PH) domain play crucial roles in protein translocation, lipid membrane modification and intracellular memrane trafficking which occur during various mitogenic processes. We have previously reported the presence of PLC-γ1, γ2, β1, β3, and δ1 isozymes in normal human lung tissue and tyrosine-kinase-independent activation of phospholipase C-γisozymes by tau protein and AHNAK. We had also found that the expression of AHNAK protein was markedly increased in various histologic types of lung cancer tissues as compared to the normal lungs. However, the report concerning expression of various PLC isozymes in lung cancers and other lung diseases is lacking. Therefore, in this study we examined the expression of PLC isozymes in the paired surgical specimens taken from lung cancer patients.

Surgically resected lung cancer tissue samples taken from thirty seven patients and their paired normal control lungs from the same patients. The expression of various PLC isozymes were studied. Western bolt analysis of the tissue extracts for the PLC isozymes and immunohistochemistry was performed on typical samples for localization of the isozyme.

In 16 of 18 squamous cell carcinomas, the expression of PLC-γ1 was increased. PLC-γ1 was also found to be increased in all of 15 adenocarcinoma patients. In most of the non-small cell lung cancer tissues we had examined, expression of PLC-δ1 was decreased. However, the expression of PLC-δ1 was markedly increased in 3 adenocarcinomas and 3 squamous carcinomas. Although the numbers were small, in all 4 cases of small cell lung cancer tissues, the expression of PLC-δ1 was nearly absent.

We found increased expression of PLC-γ1 isozyme in lung cancer tissues. Results of this study, taken together with our earlier findings of AHNAK protein-a putative PLD-γ, activator-over-expression, and the changes observed in PLC-δ1 in primary human lung cancers may provide a possible insight into the derranged calcium-inositol signaling pathways leading to the lung malignancies.