Actin induction during PMA and cAMP-dependent signal pathway activation inEntamoeba histolytica trophozoites

Activation of PKC or cAMP-dependent signalling pathways in Entamoeba histol ytica triggers the phosphorylation of proteins involved in actin rearrangem ents necessary for adhesion and locomotion. Analogous motifs to SRE and CRE sequences - known to respond to PMA and cAMP - were identified within the 5' regulatory region (5'RR) of one of the parasite actin genes. These seque nces could be involved in the actin transcriptional upregulation reported d uring signalling. To test this hypothesis, a plasmid containing the 5'RR of the actin gene fused to the bacterial neomycin gene (neo) was used for sta ble transfection. Expression of neo and endogenous actin was measured after stimulation of transfected amoebae by PMA and dcAMP. It was found that bot h compounds induced neo and actin expression and showed a co-operative effe ct in the induction of neo. Induction by PMA or dcAMP failed if the directi ng amoebic 5'RR lacked SRE and CRE motifs. Transfection of amoebae with pla smid constructs, containing either progressive deletions of the actin 5'RR or site-directed mutations of the SRE and CRE-like motifs, corroborated tha t these sequences and a co-ordinated participation of PKC- and PKA-activate d transcription factors are responsible for the increments in neo and actin mRNAs. In vivo, these PMA and cAMP-response elements could play an importa nt role in regulating actin expression and organization in signalling proce sses activated during tissue invasion.