A common variant rs2272804 in the 5’UTR of RIBC2 inhibits downstream gene expression by creating an upstream open reading frame

M. Xiong, Y.-Y. Wang, W.-W. Guo, S.-W. Cai, X.-Y. Ning, H.-Y. Yang, X.-W. Chen, B. Li, M. Xu

Department of Gastroenterology, Guangdong Second Provincial General Hospital, Guangzhou, China. xm177@163.com

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• Oncology

OBJECTIVE: The RIB43A domain with coiled-coils 2 (RIBC2) encodes an uncharacterized vertebrate protein exhibiting similarity with Chlamydomonas protofilament ribbon proteins, required for ciliary motility. To date, no functional variants capable of triggering a change in the expression of RIBC2 have been reported.

PATIENTS AND METHODS: The genotypes of rs2272804 in 30 individuals were identified with Sanger sequencing to estimate allele frequencies. Dual-Luciferase and mutagenesis assays were carried out to investigate the impact of rs2272804 on transcriptional and translational levels. The microarray data of 7 types of cancer were obtained from the Gene Expression Omnibus (GEO) to explore the role of rs2272804 in those diseases.

RESULTS: In this study, we identified a common variant in the 5’UTR of RIBC2, rs2272804, which can create an upstream open reading frame (uORF) in the 5’UTR significantly inhibiting the expression of its host gene. Using Dual-Luciferase constructs, we found that this variant leads to an 85% reduction in translational efficiency, but only a 20% decrease was observed at the transcriptional level. In terms of population studies, mRNA levels of RIBC2 varied according to their rs2272804 genotypes. The “A” allele homozygotes, which created a uORF, showed the lowest transcriptional levels while the transcriptional activity of the “C” allele homozygotes without an uORF was the highest, consistent with the in-vitro studies. Furthermore, we explored its role in 7 types of cancer and identified RIBC2 as a significantly differentially expressed gene (DEG) in breast cancer (BRCA), ovarian serous cystadenocarcinoma (OV), and kidney renal clear cell carcinoma (KIRC). Finally, we showed that the overexpression of RIBC2 enhanced the expression of TRIM37 and down-regulated TRAF2. TRIM37 is a member of the tripartite motif (TRIM) family involved in developmental patterning and oncogenesis while TRAF2 is associated with the signal transduction from members of the TNF receptor superfamily.

CONCLUSIONS: Our reports identified a common variant that exerts a dramatic impact on expression efficiency and provides further functional insight into RIBC2.

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