Abstract 2370: Tumor suppression potential of tRNA modification enzyme TruBs via let-7

Abstract

Abstract MicroRNA (miRNAs) let-7 is firstly discovered and widely involved in various tumors. Let-7 suppresses mRNAs of many oncogenes, such as KRAS and MYC. This, let-7 is strongly and selectively regulated by Lin28A/B. The let-7-Lin28A/B relationship could explain the pathogenesis of many tumors. However, the control mechanism of let-7, which cannot be explained by Lin28A/B alone, is reported. Furthermore, the regulatory mechanism of microRNAs by RNA-binding proteins such as Lin28 remains unclear. We have reported that TruB1, one of the tRNA modifying enzymes, specifically regulates let-7 by whole RNA binding protein screen (Kurimoto et al., EMBO J (2020)39:e104708). In this study, we evaluated in detail the effect of this TruB1-let-7 axis on the tumor phenotype. In addition to TruB1, another tRNA modifying enzyme TruB2 and other candidate RNA binding proteins were evaluated for its let-7 regulatory mechanism and tumor suppressive potential. We evaluated the effects of these candidates on cell proliferation and stemness in MTT assay, sphere formation assay and Xenograft model with knock down (KD) or over expression (in A549, HeLa or THP-1 cells). To elucidate that the phenotype was associated with let-7, we also use RNAi for let-7 families. We also checked the let-7-candidate proteins binding by RIP and eCLIP (enhanced version of the crosslinking and immunoprecipitation) analysis. Clinical effectiveness was assessed by public database (GEO and TCGA). In results, overexpression of TruB1 and other several genes suppressed the tumor growth and sphere formation ability in vitro with let-7 elevation. Interestingly, these suppressions were also seen in TruB enzymatic null mutants in TruBs (as we have reported in recently (Kurimoto et al., EMBO J (2020)39:e104708)). However, only TruB1 KD and one other candidate (gene A) KD showed the tendency to increase the tumor growth in vitro or in Xenograft model. The eCLIP and RIP analysis showed direct binding of TruB1 and gene A to let-7, but not TruB2 and others. In public database, only TruB1 and gene A strongly inversely correlated with several tumors. There was no relationship in TruB2 and tumor. These data introduced the novel players TruB1 and gene A to regulate the specific miRNA biogenesis and its impact on tumor phenotypes. Our data highlighted the potential of RNA binding protein independing on its known activity. Citation Format: Ryota Kurimoto, Hiroki Tsutsumi, Saki Ikeuchi, Hiroshi Asahara. Tumor suppression potential of tRNA modification enzyme TruBs via let-7 [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 2370.