Mir-133 microRNA precursor family

mir-133 is a type of non-coding RNA called a microRNA that was first experimentally characterised in mice and homologues have since been discovered in several other species including invertebrates such as the fruitfly Drosophila melanogaster. Each species often encodes multiple microRNAs with identical or similar mature sequence. For example, in the human genome there are three known miR-133 genes: miR-133a-1, miR-133a-2 and miR-133b found on chromosomes 18, 20 and 6 respectively. The mature sequence is excised from the 3' arm of the hairpin. miR-133 is expressed in muscle tissue and appears to repress the expression of non-muscle genes.

Targets of miR-133
microRNAs act by lowering the expression of genes by binding to target sites in the 3' UTR of the mRNAs. Luo et al.. demonstrated that the HCN2 K+ channel gene contains a target of miR-133. Yin et al.. showed that the Mps1 kinase gene in zebrafish is a target. Luo et al.. demonstrated that the voltage gated K+ channel KCNQ1 is a target. Boutz et al.. showed that nPTB (neuronal polypyrimidine tract-binding protein) is a target and likely contains two target sites for miR-133. Xiao et al.. show that ether-a-go-go related gene (ERG) a K+ channel is a target of miR-133.

miR-133 directly and negatively regulates NFATc4.

RhoA expression is negatively regulated by miR-133a in bronchial smooth muscles (BSM)and miR-133a downregulation causes an upregulation of RhoA, resulting in an augmentation of contraction and BSM hyperresponsiveness.