Amoebiasis caused by the protozoan parasite Entamoeba histolytica is one of the leading parasitic causes of morbidity and mortality in the developing countries. Among the variety of
virulence factors, an adherence
lectin (
Gal/GalNAc, 260 kDa) has been known to mediate colonization and subsequent host responses. It is a major
cell surface antigen which is universally recognized by the
immune sera of patients with
amoebic liver abscess (ALA). The role of this
lectin in cytolysis and phagocytosis of human colonic
mucin glycoproteins has also been established. The objective of the present study was to elucidate the signal transduction events induced in response to Entamoeba histolytica derived
Gal/GalNAc lectin in the target epithelial cells. We have attempted to define a pathway in target cells that could link this immunodominant
antigen to a known
biological pathway for target cell activation and triggering of subsequent disease pathology/parasite survival.
Lectin stimulated cells showed immediate rise in (Ca2+)i concentration corresponding to 1517.31+/-16.3 nM (approximately) at 0-2 min. The intracellular
calcium also extruded from the cells as was measured by increase in
calcium green-1 fluorescence. Expression of several
protein kinases was checked by western blotting to delineate the signaling pathway. Results showed that the expression of PLA2, PI3K, Ras
p21, Ras GAP, ERK-MAPK, p38MAPK and PKC was significantly increased. Expression of Raf-1 and MEK-1 was also found to be significant, as determined by intensity analysis. Overall, it indicated activation of MAPKinase pathway which is implicated in a variety of cellular functions. On the basis of our observations it can be stated that there is a
calcium mediated activation of PKC in target cells, by
lectin, which inturn activates
cyclic nucleotides and other
protein kinases. These
protein kinases further phosphorylated downstream signals in a sequential manner, thus leading to the activation of MAPKinase cascade. Activation of MAPK cascade, in our studies, is implicated in a variety of physiological cellular functions including apoptosis, proliferation, cytoskeleton rearrangements and permeability changes. However, future screening of the genes responsible for the transcription and translation of new
proteins and their
biological functions in response to
lectin stimulation will prove useful in understanding this host-parasite relationship.