MicroRNA transfection and AGO-bound CLIP-seq data sets reveal distinct determinants of miRNA action.

Microarray expression analyses following miRNA transfection/inhibition and, more recently, Argonaute cross-linked immunoprecipitation (CLIP)-seq assays have been used to detect miRNA target sites. CLIP and expression approaches measure differing stages of miRNA functioning-initial binding of the miRNP complex and subsequent message repression. We use nonparametric predictive models to characterize a large number of known target and flanking features, utilizing miRNA transfection, HITS-CLIP, and PAR-CLIP data. In particular, we utilize the precise spatial information provided by CLIP-seq to analyze the predictive effect of target flanking features. We observe distinct target determinants between expression-based and CLIP-based data. Target flanking features such as flanking region conservation are an important AGO-binding determinant-we hypothesize that CLIP experiments have a preference for strongly bound miRNP-target interactions involving adjacent RNA-binding proteins that increase the strength of cross-linking. In contrast, seed-related features are major determinants in expression-based studies, but less so for CLIP-seq studies, and increased miRNA concentrations typical of transfection studies contribute to this difference. While there is a good overlap between miRNA targets detected by miRNA transfection and CLIP-seq, the detection of CLIP-seq targets is largely independent of the level of subsequent mRNA degradation. Also, models built using CLIP-seq data show strong predictive power between independent CLIP-seq data sets, but are not strongly predictive for expression change. Similarly, models built from expression data are not strongly predictive for CLIP-seq data sets, supporting the finding that the determinants of miRNA binding and mRNA degradation differ. Predictive models and results are available at http://servers.binf.ku.dk/antar/.