UP-REGULATION OF ACTIN MESSENGER-RNA AND REORGANIZATION OF THE CYTOSKELETON IN ENTAMOEBA-HISTOLYTICA TROPHOZOITES

Actin mRNA levels were measured in Entamoeba histolytica trophozoites after experimentally inducing changes in the organization of the cytos keleton. The treatment of trophozoites with forskolin, N-6,2'-O-dibuty ryl-adenosine 3':5'-cyclic monophosphate, and phorbol myristate acetat e induced the organization of actin into multiple dots and defined str uctures with a concomitant increase in F-actin content. Cytochalasin D elicited polarization of the structured actin and formation of aggreg ates, as well as an increment in F-actin. Simultaneously, up-regulatio n of actin mRNA levels was produced by all the drugs. De novo synthesi s of actin mRNA, as measured by nuclear run-ons, showed increased tran scription of actin mRNA. On the other hand, treatment of cells with ac tinomycin D blocked the elevation of actin mRNA synthesis induced by f orskolin, dibutyryl cyclic AMP, or cytochalasin D whereas, the increme nt induced by PMA was not affected. These data indicate a regulatory c ontrol of actin mRNA synthesis at the transcriptional level by forskol in, dibutyryl cyclic AMP and cytochalasin D, and transcriptional as we ll as post-transcriptional controls by phorbol myristate acetate. The experiments presented here suggest the possibility that, regulation of actin mRNA transcription in E. histolytica trophozoites is linked to growth conditions, that are accompanied by reorganization of the actin cytoskeleton and thus, related to the motility and invasiveness of th e parasite.