Serial subculture of primary normal human oral keratinocytes (NHOKs) to the post-mitotic stage induces terminal differentiation, which is in part linked to elevated levels of phospholipase C (PLC)-γ1. Therefore, PLC-γ1 may be involved in the signal transduction system that leads to the calcium regulation of subculture-induced keratinocyte differentiation. To test this hypothesis, the expression of PLC-γ1 in primary NHOKs was blocked by transfecting cells with the antisense PLC-γ1 cDNA construct. These cells demonstrated dramatic reductions in PLC-γ1 protein and in the differentiation markers involucrin and transglutaminase following calcium exposure and an increase (15≈20%) in in vitro life span versus empty vector-transfected cells. In addition, we established the ability of antisense PLC-γ1 to block the serial subculture-induced rise in intracellular calcium. Similar observations were made following treatment with the specific PLC inhibitor U73122. These results indicate that the terminal differentiation of NHOKs by serial subculture is associated with PLC-γ1, which mediates calcium regulation by mobilizing intracellular calcium.

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