Bd. Ragland et al., ENTAMOEBA-HISTOLYTICA - TARGET-CELLS KILLED BY TROPHOZOITES UNDERGO DNA FRAGMENTATION WHICH IS NOT BLOCKED BY BCL-2, Experimental parasitology, 79(3), 1994, pp. 460-467
Amebic destruction of neutrophils and macrophages is contact-dependent
. Adherence is mediated by a galactose-specific surface lectin on the
amebic membrane. The pathway by which contact-dependent cytolysis of t
he target cell occurs is unknown. We hypothesized that target cell dea
th is due to the triggering of apoptosis (programmed cell death) by th
e amebae. The purpose of this study was to determine whether target ce
ll DNA is fragmented into a ladder pattern characteristic of apoptosis
and to test whether overexpression of Bcl-2, a protein that confers r
esistance to apoptotic death from some stimuli, blocks target cell kil
ling. The murine myeloid cell line FDC-P1 transfected with a retroviru
s construct expressing the Bcl-2 protein was shown to be resistant to
the apoptotic death that the parental line undergoes upon growth facto
r deprivation. Cr-51-labeled FDC-P1 control or bcl-2-transfected cells
were incubated with Entamoeba histolytica (4:1 cell/ameba ratio) and
killing of the cells was assessed by Cr-51 release. Both cell lines we
re susceptible to contact-dependent killing. Death induced by the ameb
ae in the bcl-2-transfected cells resulted in a DNA ladder fragmentati
on pattern (using [I-125]iododeoxyuridine-labeled target cell DNA) ide
ntical to that seen in the control cells undergoing apoptosis upon gro
wth factor withdrawal. Target cell DNA fragmentation was inhibited by
blocking adherence with galactose. Our data suggest that target cell k
illing by E. histolytica can occur via Bcl-2-independent apoptotic mec
hanism. (C) 1994 Academic Press, Inc.