Abstract 1854: The regulation of angiogenin expression and the genes regulated by angiogenin
Authors: Sheng Jinghao , Hu Guo-fu , Xu Zhengping 
Published: July 2016

Angiogenin (ANG) is first isolated and identified by its ability to stimulate the growth of blood vessels. As a member of the vertebrate-specific secreted ribonuclease (RNase) family, ANG is encoded by a single exon and is usually located in the middle of its family gene cluster. Particularly, ANG gene locus has a unique gene arrangement, featured by shared promoters and 5’-untranslated regions (5’-UTR) which direct two distinct exons enconding ANG and ribounclease 4 (RNASE4, the 4th member of RNase family) respectively. However, the gene structure and regulation of these genetic regions are largely unknown. Here, we have characterized the promoters, defined the transcription start site, and identified a unique mechanism of transcription regulation. We demonstrated that two Pol III elements within the promoter regulate ANG and RNASE4 expression in a position- and orientation-dependent manner. Moreover, an intragenic chromatin loop formed between the two CCCTC-binding factor (CTCF)-binding sites located in two introns flanking ANG coding exon, which preferentially enhances ANG transcription. These results suggest a multilayer transcriptional regulation of ANG and RNASE4 gene locus. The data also add more direct evidence to the notion that Pol III elements are able to directly influence Pol II gene transcription. Furthermore, our data indicate that a CTCF-dependent chromatin loop is able to differentially regulate transcription of genes that share the same promoters.

On the other hand, the secreted ANG undergoes a receptor-mediated endocytosis from the cell surface to the nucleus and accumulates in the nucleoli. The nucleoli ANG can promote 47S pre-rRNA transcription by binding the ABE (Angiogenin Binding Element) and UCE (Upstream Core Element) region on the promoter of ribosomal DNA (rDNA), where ANG increases the number of actively transcribing rDNA and promotes the assembly of initiation complex by epigenetic activation through promoter methylation and histone modification. We have also shown that the surplus ANG in nucleus also related to mRNA transcription. ANG binds the first exon region of estrogen receptor-related receptor gamma (ERRγ) and inhibits the ERRγ expression. To screen and identify the mRNAs regulated by ANG at a genome-wide level, we carried out chromatin immunoprecipitation-chip assay (ChIP-on-chip) and found a total of 699 genes that may be regulated by ANG. These genes were significantly enriched to tumorigenesis, Wnt and TGF-beta pathways by the KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis. Based on the findings that ANG is able to remodel the histone modification through direct binding to the histone protein, we propose that ANG might act as a chromatin remodeling activator to regulate RNA transcription. However, there is still a long way to go before fully disclosing the roles and mechanisms of ANG in gene transcription.

Citation Format: Jinghao Sheng, Guo-fu Hu, Zhengping Xu. The regulation of angiogenin expression and the genes regulated by angiogenin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1854.