Serum deprivation leads to growth inhibition and protein tyrosine phosphorylation in Entamoeba histolytica

Growth of Entamoeba histolytica in culture was found to be entirely depende nt upon the presence of serum in the culture media. Very little protein pho sphorylation was detected in growing E. histolytica cells by quantitative i mmunofluorescence and immunoblotting. Intense augumentation of antiphosphot yrosine immunofluorescence was observed after 1 h of serum deprivation. Ant iphosphotyrosine immunofluorescence levels increased moderately between 1 h and 1.5 h of serum deprivation, after which no further increase was observ ed till 4 h serum deprivation. At 1 h of serum deprivation, a very high tyr osine kinase activity was detected. Sodium orthovanadate, a potent tyrosine phosphatase inhibitor, increased tyrosine phosphorylation of a 38 kDa prot ein after 1 h of incubation and also inhibited the growth of E. histolytica in culture. Our data demonstrated that protein tyrosine phosphorylation wa s associated with growth inhibition of E. histolytica.