Discovery of Novel Non‐Coding Products of the Pax‐5 Gene and Their Clinical Significance in Lymphoid Cancers

Abstract

Circular RNAs (circRNAs) are a newly identified class of RNA which are highly expressed and conserved in mammalian cells. With the intrinsic property of being resistant to exonucleolytic activity due to their circular configuration, circRNAs are remarkably stable compared to their linear RNA species counterpart. CircRNAs regulate many biological processes and their aberrant expression is often associated with disease progression. Recently, we have characterized the expression of circRNAs of the potent Pax‐5 oncogene in B cell cancers. In this present study, we set out to identify and establish the expression profiles of Pax‐5 circRNAs in B cell cancers and also, to evaluate the potential of these non‐coding products to act as disease biomarkers. Using RT‐PCR in B cell lines, Pax‐5 circRNAs were amplified with divergent primers. PCR products were then sequenced and aligned for identification and validation. Pax‐5 circRNAs were also evaluated by qPCR from peripheral blood mononuclear cells (PBMCs) from healthy donors and clinical samples. Four circRNA isoforms of the Pax‐5 gene were isolated, sequenced and identified from various B cell models. These latter Pax‐5 circRNA variants consisted of a circular single RNA strand characterized with either exons 2, 3, 4; exons 2, 3, 4, 5; exons 2, 3, 4, 5, 6; or exons 2, 3, 4, 5, 6, 7, 8 of the human Pax‐5 gene. Profiling of Pax‐5 circRNA expression levels in clinical samples reveal an overexpression in chronic lymphocytic leukemia in comparison to other B cell cancer lesions and healthy donors. Altogether, we describe 4 novel gene products (i.e. circRNAs) of the Pax‐5 oncogene in B cell cancers. Preliminary results also support a potential role for Pax‐5 circRNAs as prognostic or diagnostic biomarkers for specific B cell cancers. Further studies are ongoing to validate the correlation between Pax‐5 circRNA levels and disease progression. In addition, the mechanistic elucidation of Pax‐5 circRNAs in cancer processes will also potentially identify new avenues for B cell cancer therapeutic interventions.Support or Funding InformationThis work was supported by grants from the New Brunswick (NB) Innovation Foundation, the Canadian Breast Cancer Foundation, the Canadian Breast Cancer Society/QEII Foundation, the NB Health Research Foundation and by the Beatrice Hunter Cancer Research Institute.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Pleiotropy of PAX5 Gene Products and Function

“…The previous sections describe multiple regulatory mechanisms, which lead to very diverse PAX5 transcripts, proteins, and functions. More recently, we and others have also characterized a new class of transcriptional PAX5 products, circular PAX5 RNAs ( circPAX5 ) [ 12 , 13 , 14 ]. Circular RNAs (circRNAs) represent a relatively new category of non-coding RNAs characterized by a covalent phosphodiester bond between the 5′ and 3′ extremities of the transcript [ 182 , 183 ].…”

“…They also demonstrate that circPAX5 directly binds to miR-124-5p in B-cell precursors to promote B-ALL progression through the interference of the B-cell maturation process [ 12 ]. More recently, we have mapped multiple circPAX5 isoforms in B-cells including: circPAX5_2-3 (containing exons 2 and 3); circPAX5_2-4 (exons 2, 3 and 4); circPAX5_2-5 (exons 2, 3, 4 and 5); circPAX5_2-6 (exons 2, 3, 4, 5 and 6); circPAX5_2-7 (exons 2, 3, 4, 5, 6, and 7); circPAX5_2-8 (exons 2, 3, 4, 5, 6, 7, and 8); circPAX5_8 (exon 8); circPAX5_7-8 (exons 7 and 8); circPAX5_5-8 (exons 5, 6, 7, 8); and finally, circPAX5_2-6+intron 5 (exons 2, 3, 4, 5, partial intron 5, and exon 6) [ 13 , 14 ]. Furthermore, using TaqMan probes designed to target each unique circPAX5 junction region created by both extremities, we demonstrate that circPAX5_2-5 and circPAX5_2-6 are overexpressed in chronic lymphocytic leukemia patients in comparison to peripheral B-cells from healthy individuals.…”

“…Multiple studies indicate that the human PAX5 gene undergoes various alterations that affect its spatiotemporal expression to function as an oncogene or tumor suppressor. Specifically (clockwise from the top), the PAX5 locus can undergo: genetic translocations resulting in chimeric fusion proteins and alternative promoter regulation [ 7 , 8 , 9 , 10 , 11 ]; transcriptional back-splicing resulting in circular PAX5 RNAs [ 12 , 13 , 14 ]; transcriptional alternative splicing of coding exons [ 15 , 16 , 17 ]; alternative use of poly-adenylation (pA) termination signals [ 18 ]; use of alternative promoter regions and transcription initiation sites [ 11 ]; and post-translational modifications, which impact its transactivation potential [ 19 , 20 , 21 ].…”