Abstract 463: The small nucleolar RNA SNORD46 and SNORD72 have tumor suppressor activity in diffuse large B cell lymphoma

Abstract Background. Following the identification of an 11q24.3 gain upregulating the ETS factors ETS1 and FLI1 in diffuse large B cell lymphoma (DLBCL) (Bonetti et al. Blood 2013), we observed the anti-lymphoma activity of blocking the protein-protein interaction of ETS factors with RNA helicases, using YK-4-279 and its clinical derivative TK-216 (Spriano, Chung et al. CCR 2019). DLBCL cells exposed to the two small molecule inhibitors presented a significant upregulation of small nucleolar RNAs (snoRNAs). Besides their primary functions in rRNA processing, snoRNAs are often deregulated in cancers, with microRNA-like actions and direct interaction with proteins. Here, we characterized SNORD46 and SNORD72, the two snoRNAs most upregulated cells after YK-4-279 and TK-216 and mapped to the 1p34.1 locus recurrently lost in DLBCL. Methods. Real-time PCR, immunoblotting, and shRNA silencing were conducted based on established protocols. RNA-Protein Interaction Prediction (RPISeq) was used to calculate the interaction probabilities of snoRNAs with proteins of interest. The prediction was made using both the Random Forest (RF) and the Support Vector Machine (SVM) classifiers, using a stringent threshold of >0.6. Results. The time-dependent changes of SNORD46 and 74 were validated with real-time PCR in the U2932 activated B cell-like (ABC) DLBCL cell line exposed to YK- 4-279 for 4 or 8 h. Upregulation of SNORD46 and 74 were significantly upregulated compared to their host genes upon YK-4-279 treatment, suggesting these snoRNAs have different functions from the genes in which they are encoded. Across 48 lymphoma cell lines, SNORD74 was more expressed in ABC DLBCL than in the remaining cell lines (P 0.03) or GCB DLBCL (P 0.05), while SNORD46 did not differ. Stable lentiviral-based overexpression of SNORD46 and 74, U2932 ABC DLBCL demonstrated that both SNORD46 and SNORD74 overexpression impaired growth while SNORD92, the control did not SNORD74 overexpression inhibited pAKT-Ser473, suggesting it could exert its anti-tumor effect by negatively impacting BCR signaling. Since constitutive BCR is the main driver for the pathogenesis in ABC DLBCL, we studied the impact of BCR signaling on SNORD46 and 74 expressions. IgM stimulation downregulated the snoRNAs in U2932 and TMD8 ABC DLBCL cell lines at 1 and 2.5 h poststimulation, with a more substantial effect for SNORD74. Furthermore, the snoRNAs were upregulated in four ABCs and four GCB DLBCLs cell lines exposed to the PI3K/mTOR inhibitor bimiralisib. Bioinformatic analysis indicated the possible binding of SNORD46 and especially of SNORD74 to BCR signaling molecules (SYK, LYN, BTK, PI3Kδ, IRAK4, IRAK1, CARD11), RNA helicases (RHA, DDX21, DDX5) and essential DLBCL proteins (BCL6, IRF4). Conclusions. SNORD46 and SNORD74 exert tumor suppressor activity in DLBCL cells, possibly as negative regulators of the BCR signaling. Citation Format: Elaine YL Chung, Filippo Spriano, Sara Napoli, Giulio Sartori, Luciano Cascione, Francesco Bertoni. The small nucleolar RNA SNORD46 and SNORD72 have tumor suppressor activity in diffuse large B cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 463.