Isolation and functional analysis of a chk2 homologue from Entamoeba histolytica

Mammalian Chk2 is a Ser/Thr kinase required for cell-division arrest induced by DNA damage. We found six new kinase genes of Entamoeba histolytica by analysis in silico. One of the kinase genes was a homologue of human chk2 gene. The chk2 homologue gene (Eh chk2) was expected to encode 398 amino acids and showed nearly 50% homology to human Chk2 in amino acid sequence. Eh chk2 had a catalytic domain of Ser/Thr kinase and a fork head-associated (FHA) domain that is highly conserved among Chk2 homologues in vertebrates. To examine the biological functions of Eh chk2, we synthesized Eh chk2 mRNA in vitro and injected it into immature frog eggs (Xenopus laevis oocytes) as a model system of cell division. Eh chk2 markedly delayed the cell division of frog eggs by disrupting transition of G2 phase to M phase. Eh chk2 also inhibited the activation of p42 MAPK and Cdc2 kinase which are representative events induced by cell division. These results suggest that Eh chk2 gene should be a cell-division regulator in E. histolytica.