INFLUENCE OF CIRCULAR TARGET RNA TOPOLOGY ON miRNA STABILITY AND FUNCTION

FUCHS WIGHTMAN F.; REFOJO D; LUKIN J; DE LA MATA M; GIUSTI S

Congreso; LVI Reunión Anual de SAIB - SAIB-SAMIGE 2020; 2020

Sociedad Argentina de Investigación Bioquímica (SAIB)

MicroRNAs are small regulatory RNAs which confer cellsthe possibility of fine-tuning gene expression at a post-transcriptional level.Consequently, regulation of miRNAs levels themselves is of crucial importance.Accordingly, the mechanisms of microRNA biogenesis and function have beenstudied extensively, while their degradation mechanisms remain less explored.On the one hand, a mechanism called TDMD (for TargetDirected MicroRNA Degradation) has emerged as one of the processes affectingmiRNA turnover. During TDMD, targets with extensive base-pair complementaritytowards the 3? end lead to miRNA degradation, contrary to the canonical targetsilencing. A number of examples of this mechanism have arisen in the past fewyears, including both endogenous targets capable of destabilizing specificmiRNAs and viral transcripts which in doing so facilitate infection.Onthe other hand, there have been reports proposing circular RNAs as microRNAsponges. CircRNAs originate from pre-mRNA back-splicing and, despite most ofthem lack a functional annotation, recent findings have showed that many may beimportant for gene regulation through miRNAs. However, although a plethora ofpublications claim to have expressed circRNAs as sponges that prevent miRNAsfrom exerting their typical function, their capability of cleanly and exclusivelyover-expressing exogenous circRNAs without suffering from a linear isoform?leak? remains questionable. Thus, assigning the observed effects to thecircRNAs while ignoring the potential participation of the counterpart lineartranscripts might seem far-fetched.In this study, we aimed at shedding light on whetherlinear versus circular topologies of targets can produce different effects onboth miRNA stability and function. We started by examining the well describedCDR1as/miR-7/Cyrano network of noncoding RNAs, where the lncRNA Cyranodestabilizes miR-7-5p through TDMD, while the circRNA CDR1as yields an apparentprotection by sponging it, leaving it unavailable for degradation. Byexpressing a linear version of CDR1as in combination with knocking theendogenous circRNA, we show that the circular topology of CDR1as is crucial forits function. Furthermore, using a strategy in which we expressed an artificialcircRNA aimed at binding miR-132, designed in way that it minimizes the linearcounterpart leak, we showed that the differences between topologies are notcircumscribed to CDR1as. Finally, we analyzed publicly available sequencingdata to show that this kind of regulation is potentially widespread through anumber of miRNAs and circRNAs during neuron differentiation.