Up-stream mechanisms for up-regulation of miR-125b from triclosan exposure to zebrafish (Danio rerio)

Abstract

Triclosan (TCS) exposure has widely adverse biological effects such as influencing biological reproduction and endocrine disorders. While some studies have addressed TCS-induced expression changes of miRNAs and their related down-stream target genes, no data are available concerning how TCS impairs miRNA expression leading us to study up-stream regulating mechanisms. Four miRNAs (miR-125b, miR-205, miR-142a and miR-203a) showed differential expression between TCS-exposure treatments and the control group; their functions mainly involved fatty acid synthesis and metabolism. TCS exposure led to the up-regulation of mature miR-125b that was concomitant with consistent changes in pri-mir-125b-1 and pri-mir-125b-3 among its 3 pri-mir-125bs. Up-regulation of miR-125b originated from direct shear processes involving the two up-regulated precursors, but not pri-mir-125b2. Increased expression of pri-mir-125b-1 and pri-mir-125b-3 resulted from nfe2l2- and c/ebpα-integration with positive control elements of promoters for the two precursors. The overexpression of transcriptional factors, nfe2l2 and c/ebpα, initiated the promoter activity for the miR-125b precursor. CpG islands and Nfe2l2 were involved in constitutive expression of mir-125b-1 and mir-125b-3. The activities of two promoter regions, −487 to −1bp for pri-mir-125b1 and −1327 to +14bp for pri-mir-125b-3 having binding sites for NFE2 and Nfe2l2/MAF:NFE2, were higher than other regions, further demonstrating that the transcriptional factor Nfe2l2 was involved in the regulation of pri-mir-125b1 and pri-mir-125b-3. TCS’s estrogen activity resulted from its effects on GPER, a novel membrane receptor, rather than the classical ERα and ERβ. These results explain, to some extent, the up-stream mechanism for miR-125b up-regulation, and also provide a guidance to future mechanistic study on TCS-exposure.