Abstract 2316: Analysis of APC-1B promoter region responsible for familial adenomatous polyposis

Abstract

Abstract APC (APC regulator of WNT signaling pathway) is not only a gene responsible for familial adenomatous polyposis (FAP), a hereditary disease characterized by hundreds or thousands adenomatous polyps in the colon, but also plays a crucial role in sporadic human cancers. Although most of FAP cases are caused by germline mutations in the coding region of APC, deletions or point mutations in the promoter regions are involved in a limited number of cases. Previously, we reported an FAP case with a large deletion of approximately 10 kb encompassing APC promoter 1B and exon1B of the APC gene. Since precise regulatory mechanism(s) of the transcription of APC remains to be clarified, we searched in this study the regulatory domain(s) in the deleted region. First, we performed cap analysis of gene expression (CAGE) analysis, and compared the amount of APC-1A and APC-1B transcripts in the peripheral blood cells of the patient with that of healthy volunteers. As a result, we found that the deletion decreased the amount of APC-1B to 39% - 45% in the patient compared to the healthy controls, and that it did not change the amount of APC-1A in the patient. In addition, an allele-specific expression analysis by deep cDNA sequencing revealed that the amount of APC transcripts from the mutated APC allele is reduced to 11.2% by the deletion in the patient, suggesting that the deletion resulted in the marked decrease of the transcription of the affected allele and that the remaining expression of deleted allele may be driven by other regulatory region(s) such as promoter 1A. Consistently, CAGE analysis demonstrated that APC-1B transcripts are more abundantly expressed than APC-1A transcripts in all tissues tested except for the brain, suggesting that promoter 1B plays a crucial role in the expression of APC transcription. Analysis of promoter 1B by reporter assay identified a critical region for the transcriptional activation between -117 bp and -49 bp of promoter 1B. These data will contribute to the better understanding of regulatory mechanisms of APC transcription and the evaluation of genetic variants located in promoter 1B. Citation Format: Saya Nakagawa, Kiyoshi Yamaguchi, Kimiko Saito, Kiyoko Takane, Tsuneo Ikenoue, Yoichi Furukawa. Analysis of APC-1B promoter region responsible for familial adenomatous polyposis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2316.