Poster abstracts

Poster number 29 submitted by Zihan Dong

Towards Understanding of the Role of Circular RNAs circ5615 and circCcnb1 in Cancerogenesis

Zihan Dong (Department of Chemistry, Mellon College of Science, Carnegie Mellon University), James M. Shockley (Department of Chemistry, Mellon College of Science, Carnegie Mellon University), Anna M. Kietrys (Department of Chemistry, Mellon College of Science, Carnegie Mellon University)

Abstract:
Circular RNAs (circRNAs) are a novel class of RNA molecules that are characterized by the covalent bond between the 3’ and 5’ ends generated through back-splicing 1. Various circular RNAs have the ability to sponge microRNAs (miRNAs) and proteins, affecting their cellular activities and leading to disease development and progression 1. Our project focuses on two circRNAs that have contrasting effects on carcinogenesis. First, a hsa_circ_0005615 (circ5615) has been linked to colorectal cancer progression when overexpressed. Circ5615 sponges miR-149-5p, and subsequently causes overexpression of the TNKS gene and upregulation of the cyclin D1 gene (CCND1) 2. In contrast, it has been found that expression of hsa_circ_0072758 (circCcnb1) helps to slow down the progression of breast cancer. This circRNA binds both Cyclin B1 and Cyclin Dependent Kinase 1(Cdk1) proteins, inhibiting formation of Cdk1-Cyclin B1 complex 3. CircCcnb1 sponge-like activity decreases cell proliferation and ultimately the progression of breast cancer in mice 3. However, how circ5615 and circCcnb1 interact with various proteins and miRNAs, and why the linear forms of mRNA cannot have the same inhibitory effect has not been studied.
In our work, we focus on the structural aspects of circRNAs to understand how the RNA structure may determine their sponge-like activity towards proteins and miRNAs. To map secondary structure of circRNAs, and mRNAs of their origin, we apply bioinformatic methods and in vivo selective 2’-hydroxyl acylation analyzed by primer extension (SHAPE). The difference between each circRNA’s structure and its linear counterpart provides insight into the various interactions possible for each circRNA and helps to explain its mode of action. Further, we localize sequential and structural binding motifs involved in interactions with proteins and miRNAs. These motifs may be further used to analyze the regulatory roles of other circRNAs, hopefully providing new targets for therapeutic treatment and early diagnosis.

References:
(1) Lee, E. C. S.; Elhassan, S. A. M.; Lim, G. P. L.; Kok, W. H.; Tan, S. W.; Leong, E. N.; Tan, S. H.; Chan, E. W. L.; Bhattamisra, S. K.; Rajendran, R.; Candasamy, M. The Roles of Circular RNAs in Human Development and Diseases. Biomedicine and Pharmacotherapy. Elsevier Masson SAS March 1, 2019, pp 198–208. https://doi.org/10.1016/j.biopha.2018.12.052.

(2) Ma, Z., Han, C., Zia, W. et al. circ5615 functions as a ceRNA to promote colorectal cancer progression by upregulating TNKS. Cell Death Dis 11, 356 (2020) http://doi.org/10.1038/s41419-020-2514-0

(3) Fang, L.; Du, W. W.; Awan, F. M.; Dong, J.; Yang, B. B. The Circular RNA Circ-Ccnb1 Dissociates Ccnb1/Cdk1 Complex Suppressing Cell Invasion and Tumorigenesis. Cancer Lett. 2019, 459 (May), 216–226. https://doi.org/10.1016/j.canlet.2019.05.036.

Keywords: circular RNA, cancerogenesis, RNA structure and function