Structure, Function and Role in Cancer
microRNA (miRNA) is becoming one of the most interesting research areas in modern microbiology. miRNA is one aspect of the human transcriptome that regulates gene expression. Although introduced in 2001, it was not until 2004 in which the role of miRNA in gene regulation became clear. miRNA controls how genes are turned on or off and also regulate or limit the production of proteins through a process called RNA interference (RNAi). Research in gene expression regulation, particularly microRNA, gained an increase in significance as geneticists concluded that the human genome contained far fewer genes than previously theorized. There is some speculation that the somewhat newly discovered role of microRNA could be as important as the process of transcription.
Current theories suggest that microRNAs control nearly 30% of all the genes in humans. Despite this significance, microRNAs are tiny units in the human genome. Endogenous microRNA are comprised of a single strand of RNA and are 20-23 nucleotides in length. Although difficult to isolate and detect in early attempts due to its small size, modern advances and technologies allow microRNA to be detected, amplified, and sequenced.
RNAi is a function of the action of miRNA which regulate gene expression by inhibiting translation or transcription of its complementary mRNA sequence. Much like siRNA (a double-stranded 18-24 bp RNA ending with two overhanging nucleotides and phosphorylated 5′ ends and hydroxylated 3′ ends), miRNA may be inherent to the cell or introduced by artificial means and are similarly short-lived. miRNA perform their function of gene silencing by entering the RISC complex, loaded into Argonaut-2 and then binding to its complementary mRNA target sequence. Since mRNA is the template for protein synthesis, a microRNA that is bound to the 3’-UTR of mRNA signals ribosomes to skip protein production for this molecule.
Role in Cancer
For the past decade, publications relating to miRNA and related gene expression have grown exponentially in numbers. Numerous experiments have helped determine gene dysregulation and involvement in disease. miRNA research is leading to major breakthroughs in the understanding of several diseases, such as leukemia, heart disease, obesity, and resistance to HIV in AIDS patients.
The role of miRNA in the initiation and spread of cancer is of utmost importance. The details of how a cancerous melanoma region travels to the lungs, liver, or brain from tumors located on the skin’s surface has been a point of discussion among scientists and is considered a key point of interest in cancer research. Current views regarding miRNA’s involvement with tumor suppressors and oncogenes leads scientists to believe that miRNA could be the key player in making melanoma more resistant to therapy. Details were published in the Proceedings of the National Academy of Sciences (PNAS) and provide reasoning as to why microRNA is a highly targeted area in cancer research.