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MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate genes at the translation level. MiRNAs regulate genes by binding to complementary mRNA strands and degrading them or inhibiting their translation. MiRNAs are predicted to regulate a third of the human genome or over 5000 genes.

MiR-103 and miR-103 are two identical mature miRNAs and share almost identical amino acid sequence with miR-107. The genes that encode for these 3 miRNAs are present on different chromosomes and the miR-103 and miR-106 gees differs only at a single nucleotide. These three miRNAs can be grouped together as miR-103/107 because of their similarity in structure and possibly function. MiR-103/7 have been shown to be expressed in many human organs with highest concentration in brain tissue. MiR-103/107 are also known to be differentially expressed during development[6, 7], oncogenesis[8], hypoxia[9], and both cold and heat stress[ 10, 11]. It has been predicted through bioinformatics that miR-103 and miR-107 play a role in regulation of lipid metabolism.

Function
There seems to be a clear association between miR-103/107 and pantothenate kinase (PANK). The genes coding for miR-103/107 are present in the introns of the genes coding for PANK. The three homologous PANK genes, PANK 3, PANK 2 and PANK 1 genes carry in their introns, miR-103 (1), miR-103 (2) and miR-107, respectively [25]. The location of miR-103/7 genes within introns of the PANK genes is physiologically relevant because they are co-transcribed [4, 12] and work together in regulating lipid metabolism.

PANK enzymes carry an important catalytic function of phosphorylating pantothenate (Vitamin B5) [13]. Since this catalytic reaction is the rate-limiting step in producing Co-enzyme A (CoA), PANKs are responsible for regulating the levels of CoA at the cellular level [13, 17]. CoA is an important cofactor for several enzymes that are involved in several metabolism reactions and one of the important reactions is the metabolism and synthesis of fatty acids [15, 18]. Through regulating the CoA levels and acetyl CoA levels, PANK regulate the metabolism of fatty acids via, TCA cycle. As mentioned above, bioinformatics predict that miR-103/7 also regulate lipid metabolism [25]. Hence, miR-103/7 act on genes involved in lipid metabolism in a way that is coordinated with the function of PANK.

As mentioned above, PANK regulates cellular levels of CoA which affects the levels of Acetyl CoA. It was found that miR-103/107 also increase the levels of Acetyl CoA in cells and channel Acetyl CoA into the TCA cycle[25]. The promoter of PANK1 genes appears to be one that is targeted by a PRAR-alpha transcription factor [19]. PPAR-alpha transcription factors have receptors that are stimulated by high levels of fatty acids and lipids. Hence, high fatty acid levels stimulate PRAR-alpha which turn on the PANK genes and decrease fatty acid levels via TCA cycle [20-24]. Acting accordingly with PANK, miR-103/107 decrease fatty acid synthesis and uptake by down-regulation of FASN, ACOX1 and other genes as well as increase the acetyl CoA levels and entry into the TCA cycle by down-regulation of PDK4, PISD, and PDPR [25]. Overall miR-103/107 is co-expressed with PANK genes to work together to metabolize fatty acid to produce energy and decrease fatty acid synthesis.