1. Ligand- and signal-activated transcription factors (represented by the round and the rectangular symbols, respectively) can bind to the promoter regions (green in the DNA strand) of the protein-coding genes and the miRNA-coding genes and upregulate or downregulate their transcription, thereby directly influencing the expression of mRNA and/or miRNA and ultimately affecting the synthesis of specific proteins. Transcription factors and miRNAs thus regulate diverse cellular pathways. It is important to note that miRNAs, as a rule, repress the translation of proteins. Therefore, upregulation of miRNA transcription results in downregulation of protein translation from the target mRNAs, whereas downregulation of miRNA causes derepression of protein translation from the target mRNAs, thereby increasing the synthesis of specific proteins.
Source: Mechanisms of Toxicity, Casarett and Doull's Toxicology: The Basic Science of Poisons, 8e
Citation: Klaassen CD. Casarett and Doull's Toxicology: The Basic Science of Poisons, 8e; 2012 Available at: Accessed: October 25, 2017
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