Fig. 6 Target regulation by microRNAs (as discussed by
Sengupta et al84). (a) After binding to the
mRNA, miRNA immediately activates the target mRNA degradation and causes
target repression. (b) Low target degradation after miRNA
binding and translation of miRNA bound complex can result in target
upregulation.
They predicted that the stabilization of the target mRNA due to miRNA
binding and translation of protein from miRNA bound mRNA are important
to achieve the target protein upregulation by the
miRNA.105 The above-mentioned studies suggest that
translation upregulation is possible when the miRNA:mRNA complex is
somehow stabilized and the degradation of mRNA along with the
translation inhibition is not high from the corresponding complex
(Fig. 6b ). It was further suggested by certain studies that the
presence of the regulatory sequences such as ARE binding motifs, poly C
motifs can facilitate the binding of RNA binding proteins, which
stabilizes mRNAs and upregulates translation.106,107