Phosphatidylcholine-specific phospholipase C and phospholipase D are respectively implicated in mitogen-activated protein kinase and nuclear factor kappa B activation in tumour-necrosis-factor-alpha-treated immature acute-myeloid-leukaemia cells

Tumour necrosis factor-alpha (TNF alpha) has been reported to induce potent growth inhibition of committed myeloid progenitor cells, whereas it is a p otential growth stimulator of human CD34(+) CD38(-) multipotent haematopoie tic cells. The present study was aimed at evaluating the respective role of two phospholipases, phosphatidylcholine-specific phospholipase C (PC-PLC) and phospholipase D (PLD) in the response of the CD34(+) CD38(-)KG1a cells to TNF alpha. In these cells TNF alpha triggered phosphoinositide 3-kinase (PI3K)-dependent FC hydrolysis within 4-8 min with concomitant production o f both diacylglycerol (DAG) and phosphocholine (P-chol), DAG and P-chol pro duction was accompanied by extracellular-signal-reiated protein kinase-l (' ERK-1') activation and DNA-synthesis stimulation. PC-PLC stimulation was fo llowed by PI3B-independent PLD activation with concomitant phosphatidic aci d (PA) production followed by PA-derived DAG accumulation and sustained nuc lear factor kappaB (NF-B) activation. PLD/NF-kappaB signalling activation p layed no r kappa ole in the TNF alpha proliferative effect and conferred no consistent protection of KG1a cells towards antileukaemic agents. Altogeth er these results suggest that, in KG1a cells, TNF alpha can stimulate in pa rallel PC-PLC and PLD, whose lipid products activate in turn mitogen-activa ted protein kinase (MAP kinase) and NF-kappaB signalling respectively. Fina lly, our study suggests that PC-PLC, but not PLD, plays a role in the TNF a lpha proliferative effect in immature myeloid cells.