Phospholipase C-gamma1 is required for calcium-induced keratinocyte differentiation

Phospholipase C-gamma1 is the most abundant member of the phospholipase C family in keratinocytes and is induced by calcium. Phospholipase C-gamma1, therefore, may be involved in the signal transduction system leading to calcium regulation of keratinocyte differentiation. To test this hypothesis, expression of phospholipase C-gamma1 in human keratinocytes was blocked by transfecting cells with the antisense human phospholipase C-gamma1 cDNA construct. These cells demonstrated a dramatic reduction in phospholipase C-gamma1 protein level compared with the empty vector-transfected cells and a marked reduction in the mRNA and protein levels of the differentiation markers involucrin and transglutaminase following administration of calcium. Similarly, cotransfection of antisense phospholipase C-gamma1 constructs with a luciferase reporter vector containing involucrin or transglutaminase promoters led to a substantial reduction in calcium-stimulated involucrin and transglutaminase promoter activities. Similar results were seen following treatment with a specific phospholipase C inhibitor U73122. To determine whether phospholipase C-gamma1 regulated differentiation by controlling intracellular calcium, we examined the ability of antisense phospholipase C-gamma1 to block the calcium-induced rise in intracellular calcium and found that it could. These findings indicate that phospholipase C-gamma1 is a critical component of the signaling pathway mediating calcium regulation of keratinocyte differentiation via its mobilization of intracellular calcium.