Inhibition and stimulation of growth of Entamoeba histolytica in culture: association with PKC activity and protein phosphorylation

Chaudhuri, S., and Raha, S. 2000. Inhibition and stimulation of growth of Entamoeba histolytica in culture: Association with PKC activity and protein phosphorylation. Experimental Parasitology 95, 28–35. We studied the role of protein kinase C (PKC) and protein threonine phosphorylation in the inhibition and stimulation of growth of the protozoan parasite Entamoeba histolytica. PKC was activated after serum deprivation in E. histolytica and during this period proteins became threonine phosphorylated. Conversely, on serum stimulation of serum-deprived cells, PKC activation was rapidly reversed and the threonine phosphorylation of proteins quickly declined. Growth of E. histolytica was not affected by either PKC inhibitors H-7 and GF109203X or by down-regulation of PKC by Phorbol 12-Myristate 13-Acetate (PMA). Interestingly, very low doses of PMA which caused activation of PKC and were unable to down-regulate PKC after 48 h of culture, negatively influenced the growth of E. histolytica. Serine/threonine phosphatase inhibitors Okadaic acid and Calyculin A drasti cally inhibited growth of E. histolytica. In conclusion, the growth of E. histolytica is not adversely affected by PKC down-regulation. On the contrary, growth inhibition of E. histolytica is associated with activation of Ca 2+ , Diacylglyceol (DAG)-dependent PKC, and threo nine phosphorylation of proteins.