miRNAs (micro RNAs): Little Engines that Can Regulate a Broad Range of Cellular Functions

So the first question one might ask themselves when reading this post, if not already familiar, is "what exactly is a microRNA (miRNA) and why should I care". First let me point out that the identification and ongoing understanding of miRNAs is not entirely new. The first miRNA activity was discovered in 1993. However, more and more details about the number of miRNA genes and their wide ranging activities are being discovered all the time. MicroRNAs are small non-coding RNAs (also designated sncRNAs) generated from endogenous genes. Non-coding does NOT mean non-functional, it just refers to the fact that these RNAs are not used as templates for the synthesis of proteins. The mechanisms of action of miRNAs are exerted on coding RNAs (the messenger RNAs, mRNAs) in, primarily, a post-transcriptional manner (after an mRNA is produced from a gene). However, miRNAs exert transcriptional control as well. The power of miRNAs is that one is capable of regulating the expression levels of hundreds of transcripts (mRNAs) and each of these mRNA targets may have more than one (i.e. multiple different) miRNA recognition sequences.

For more details of the synthesis of miRNAs go to the RNA: Transcription & Processing page of my website.

The primary functions of miRNAs are to target mRNA stability and inhibition of protein synthesis as a means to change the level of gene expression. However, miRNAs have been shown to interfere with gene expression through alterations in the processes of histone modification and DNA methylation at promoter sites in target genes. These effects represent a form of epigenetic regulation of gene expression. The mechanisms by which miRNAs exert epigenetic regulation is by altering the level of DNA methyltransferases and histone deacetylases. Of profound clinical significance is that dysregulation of miRNA expression and regulation is associated with a contributory effect in the development of numerous human cancers. In addition, the activity of miRNAs appears to be associated with the oncogenic character of several genes as well at to be involved in the down-regulation of tumor suppressor genes in certain cancers. Many of the miRNAs whose activities have been shown to be deregulated in cancers have been shown to have a normal function that would exert tumor suppressive activity and/or to inhibit tumor metastasis. In addition to involvement in cancer, dysregulation or mutation in miRNA genes has been associated with numerous diseases in humans.

Within the past several years there has been an increasing amount of research published on the correlation between dietary constituents and the regulation of miRNA functions. In particular the role of plant derived polyphenolic compounds and regulation of miRNA gene expression and function.

This post is just a brief introduction to miRNA functions, and a hint of the importance of diet on these processes, but I will be adding more posts about the research in this area over the coming days and weeks, so stay tuned!!!