Evidence on microRNA-mediated regulation of CDK5R1 gene expression

CDK5R1 encodes for p35, an activator of CDK5, which is involved in neuronal migration and differentiation during central nervous system development and has been candidated for mental retardation. We recently reported that the large 3’ untranslated region (3’UTR) of CDK5R1 contains regulatory elements affecting transcript stability. Besides several AREs, many microRNAs (miRNAs) target sites have been predicted by PicTar software. We evaluated the expression of nine pre-miRNAs, among the 20 miRNAs predicted to bind CDK5R1, in six cell lines, including two neuroblastoma derived lines. Among the expressed miRNAs, we observed that miR-15a, miR-103 and miR- 107 presented a high number of target sites with a free energy <-20 kcal/mol. A preliminary quantitative analysis of the three above miRNAs and p35 showed an inverse correlation between miR-107 and p35 expression, suggesting a negative effect of miR-107 on CDK5R1 expression. Overexpression of miR-107 by transfection of the specific precursor in neuroblastoma SK-N-BE cells showed, after 72 hours, a 45 and 75% decrease in p35 expression respectively using 50 and 100 nM of the precursor. Transfection of anti-miR-107 will be tested. Luciferase constructs will be used to validate the predicted miRNA target sites in CDK5R1 3’UTR. These preliminary data allow us to hypothesize a role of miRNAs in post-transcriptional CDK5R1 regulation.