Specific processing of poly(ADP-ribose) polymerase, accompanied by activation of caspase-3 and elevation/reduction of ceramide/hydrogen peroxide levels, during induction of apoptosis in host HL-60 cells infected by the humangranulocytic ehrlichiosis (HGE) agent

We studied the mechanism by which the human granulocytic ehrlichiosis (HGE) agent induces programmed cell death (apoptosis) in human promyelocytic HL- 60 leukemia cells. Using several New York HGE isolates, we show that the HG E agent-elicited apoptosis is accompanied by increased processing of nuclea r enzyme poly (ADP-ribose) polymerase (PARP), concurrent with a noticeable increase in caspase 3 activities, A marked increase in the amounts of the s ignaling molecule ceramide but not of diacylglycerol was also observed in H GE agent-infected HL-60 cells, compared with the amounts in uninfected cont rols, Simultaneous or prior treatment of infected HL-60 cells with the cera mide synthase inhibitor funonisin B-1 did not affect the magnitude of infec tion by the intracellular pathogen, as determined by both the presence of m orulae and the expression of its outer surface membrane protein, p44, These results suggest that the observed changes in ceramide are generated throug h the sphingomyelinase pathway and not by way of de novo synthesis of ceram ide, We also assayed for changes in intracellular hydrogen peroxide and sho w that the HGE agent causes a decrease in its concentrations in infected ce lls.