Regulation of serum-responsive transmembrane kinase EhTMKB1-9 by an unsaturated lipid, oleic acid in protistan parasite Entamoeba histolytica

• The stimulating activity of fatty acids resides in the fatty acyl chain.
• The unsaturated fatty acid activates EhTMKB1-9 expression by Class I PI3 kinases.
• Serum responsive element (SRE) of EhTMKB1-9 has been identified.
• SRE of EhTMKB1-9 binds with specific factors that regulate its expression.
• Actin dynamics is not required for the activation of EhTMKB1-9.

Transmembrane kinases of Entamoeba histolytica are known to play a wide range of roles from virulence, phagocytosis, and proliferation to stress response. Transmembrane kinase EhTMKB1-9 is thought to be involved in early proliferative response and it was originally identified as a serum inducible gene. Ability to stimulate EhTMKB1 expression of serum starved cells resides in unsaturated fatty acids associated with albumin fraction of serum and the mechanism of stimulation follows activation of EhTMKB1-9 promoter. Gel shift assay showed the presence of proteins that bind to the specific site of EhTMKB1-9 upstream region and the concentration of these protein(s) go down on serum starvation, but level of binding protein(s) go up on serum or fatty acid replenishment. This increase in concentration of binding molecule(s) is due to new synthesis rather than activation of existing molecule(s) as a protein synthesis inhibitor blocked enhanced level of gel shifted material on replenishment. The stimulating activity resides in the fatty acyl chain, but not in the head group. Moreover, the fatty acid initiates signaling through class I PI3 kinases that result in activation of EhTMKB1-9 expression. These results suggest a novel mechanism of gene regulation in E. histolytica, and unsaturated fatty acids as potential new signaling molecules.

Regulation of EhTMKB1-9 gene expression by lipids via PI3K pathway.Figure optionsDownload high-quality image (101 K)Download as PowerPoint slide