Characterization of phosphatidylinositol phospholipase C activity in human melanoma.

Phosphoinositide phospholipase C activity was investigated in human melanoma grown as solid tumor xenografts in nude mice. The enzyme was dependent on calcium for activity and was stimulated by the detergent deoxycholate. The pH optimum was 5.5 in the absence of detergent, and in the presence of deoxycholate two pH maxima were present, 5.5 and 7.2. Phospholipase C activity was inhibited by the sulfhydryl reagent dithionitrobenzoate with an IC50 in the micromolar range. Phospholipase C activity was distributed widely in mouse tissues. The enzyme showed a progressive increase in activity from heart, liver, lung, colon, spleen, to brain tissue. Mouse and human melanomas grown as solid tumors had higher phospholipase C activity than mouse brain. The relatively high activity of this enzyme in melanoma may suggest a biological role for phospholipase C in solid tumor growth.