Multiple signal transduction pathways including protein kinase C, tyrosine phosphorylation, and an independent third signaling mechanism are involved in the activation of monocyte chemotactic protein-1 gene. Northern blot analysis showed that the incubation of endothelial cell with dioctanoylglycerol induced maximum level of monocyte chemotactic protein-1 transcripts. The TPA-induced monocyte chemotactic protein-1 expression was abolished by treating the cells with both staurosporine and genistein; however, only a portion of the LPS-induced expression was inhibited by staurosporine/genistein. This is in accordance with the observation that LPS induced the expression of monocyte chemotactic protein-1 in desensitized cells. Thus, a third signal transduction pathway other than protein kinase C or tyrosine kinase is involved in the LPS-induced monocyte chemotactic protein-1 expression in human endothelial cell.