CLL cells share unique expression profile of circular RNAs.

Introduction

MicroRNAs (miRs) are involved in the initiation and progression of CLL. The role of other non-coding RNAs in the pathobiology of CLL is less clear.

Circular RNAs (circRNAs) are endogenous noncoding RNAs that represent approximately 10% of the human transcriptome. They result from noncanonical alternative splicing generating a circular form through a covalent bond between their 3` and 5` ends. circRNAs may function in multiple biological processes, such as miRNA binding (sponge effect), protein binding and regulation of transcriptional and post-transcriptionalal modifications. Via these functions, circRNAs may act as tumor suppressors or as oncogenes, depending on the context. Whether circRNA contribute to the pathogenesis and/or progression of CLL is currently unknown.

Methods

Using a microarraybased platform, provided by Arraystar Inc, we identified and quantified circRNA expression in CLL cells of 6 patients and compared it to B-lymphocytes of healthy volunteers. Real-time PCR was used to validate the microarray results and bioinformatics analysis was performed in order to construct circRNA-miRNA-mRNA--protein networks and to identify pathways that may be influenced by these differently expressed circRNAs.

Result

Of the 13,438 circRNAs transcripts that are represented in the array, 397 circRNAs were upregulated and 688 were downregulated. The number of cirRNAs that were downregulated was 2 folds more than is expected by chance (P<0.01), suggesting that there is global downregulation of circRNA transcription activity in CLL cells. Then, to model a putative sponge function of microRNAs we constructed two circRNA-miR-mRNA networks each consisting of one circRNA (hsa_circRNA_102680, hsa_circRNA_104424), five miRNAs for each circRNA and over 1000 target genes. Annotation analysis revealed fundamental biological processes that may be associated with the deregulated circRNAs. These processes include; apoptosis, cell cycle regulation, B cell activation and RNA transcription and processing.

Conclusions

We found that the circRNA profiling of CLL cells is different from that of normal B-cells. Via their roles as miR-sponges or through other alternative putative mechanisms this layer of regulation may have profound impact on the cells. Whether a specific expression pattern is associated with prognosis and whether targeting circRNAs may have therapeutic benefit in CLL remain to be answered.