Identification of HuR target circular RNAs uncovers suppression of PABPN1 translation by CircPABPN1

Abstract

HuR influences gene expression programs and hence cellular phenotypes by binding to hundreds of coding and noncoding linear RNAs. However, whether HuR binds to circular RNAs (circRNAs) and impacts on their function is unknown. Here, we have identified en masse circRNAs binding HuR in human cervical carcinoma HeLa cells. One of the most prominent HuR target circRNAs was hsa_circ_0031288, renamed CircPABPN1 as it arises from the PABPN1 pre-mRNA. Further analysis revealed that HuR did not influence CircPABPN1 abundance; interestingly, however, high levels of CircPABPN1 suppressed HuR binding to PABPN1 mRNA. Evaluation of PABPN1 mRNA polysomes indicated that PABPN1 translation was modulated positively by HuR and hence negatively by CircPABPN1. We propose that the extensive binding of CircPABPN1 to HuR prevents HuR binding to PABPN1 mRNA and lowers PABPN1 translation, providing the first example of competition between a circRNA and its cognate mRNA for an RBP that affects translation.

The circRNA–microRNA code: emerging implications for cancer diagnosis and treatment

“…Consequently, circ‐PABPN1 reduces PABPN1 translation and lowers HeLa cell proliferation. This is an example of how circRNAs can affect the translation of their corresponding linear mRNAs competing with them for a RBP (Abdelmohsen et al ., ).…”

Past, present, and future of circ RNA s

“…Moreover, the interaction between HuR and the circRNA generally reduces translation (Abdelmohsen et al, 2017). In some of the cases, there might be a direct or indirect crosstalk between the circRNA and the protein product of the host gene.…”

Detection and Analysis of Circular RNAs by RT-PCR

“…However, the validation of true circRNAs identified by RNA sequencing requires other molecular biology techniques including reverse transcription (RT) followed by conventional or quantitative (q) polymerase chain reaction (PCR), and Northern blot analysis (Jeck and Sharpless, 2014). RT-qPCR analysis of circular RNAs using divergent primers has been widely used for the detection, validation, and sometimes quantification of circRNAs (Abdelmohsen et al ., 2015 and 2017; Panda et al ., 2017b). As detailed here, divergent primers designed to span the circRNA backsplice junction sequence can specifically amplify the circRNAs and not the counterpart linear RNA.…”

“…The protocol was tested and optimized by different researchers in the Gorospe laboratory, National Institute on Aging, NIH (Panda et al , 2017c and Abdelmohsen et al , 2017). The authors have no conflicts of interest or competing interests to declare.…”