P839: gain of chromosome 1q leads to high expression of snord78 and aberrant ribosome methylation

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Emerging evidence has shown that small RNAs and related RNA modifications are involved in the development of cancer. Small nucleolar RNAs (snoRNAs) are non-coding small RNAs which guide the 2’-O-modification of ribosomal RNA and facilitate the ribosome maturation. Current studies indicate that dynamic snoRNA expression patterns and associated ribosomal methylation impact the initiation and progression of leukemia. Although multiple myeloma (MM) is a disease characterized by extensive protein synthesis and dependence on ribosomal function, the role of snoRNAs in MM progression remains ambiguous. Aims: We used small RNA sequencing and ribosome methylation sequencing (RiboMeth Seq) to explore the impact of snoRNAs expression and ribosome 2’-O-methylation on MM progression. We focused on gain of chromosome 1q (+1q), as this is the most common cytogenetic abnormality associated with disease progression and poor prognosis in MM. Methods: Purified CD138+ cells from 71 newly diagnosed MMs (NDMM) and 4 refractory/relapsed MMs were included. Total RNA was isolated with the AllPrep DNA/RNA kit (Qiagen, Germany). All samples underwent snoRNA sequencing, and among them, 26 NDMM samples were fragmented and subjected to RiboMeth Seq. The sequencing libraries were prepared using the NEBNext multiplex small RNA library kit. SnoRNA seq and RiboMeth Seq were performed on an Illumina NextSeq 500 platform. RiboMeth Seq reads were mapped to rDNA sequences and methylation was calculated by ScoreC. Differentially expressed snoRNAs were identified using DESeq2 (padj < 0.05). The Kaplan-Meier method was used for survival analyses. Progression-free survival (PFS) time was measured from enrolment to relapse or death from any cause, whichever occurred first. Results: Using snoRNA Seq, we observed 43 snoRNAs with higher expression level in +1q patients compared to patients without +1q. 13 of them (30%) were located on chr1q, including SNORD78, SNORD75 and SNORD47 on 1q25. SNORD78, which was recently identified as a prognostic marker in prostate cancer and lung cancer, was also associated with inferior PFS (HR = 2.38, p =0.02) and overall survival (HR = 4.95, p = 0.01) in MM. SNORD78 expression level showed a gradient from amp1q (>3 copies, high expression) to no-gain1q (low expression), indicating a copy-number effect (p < 0.0001). Consistently, the methylation level of the rRNA site, which is guided by SNORD78 (28S-4593), decreased in a stepwise manner from patients with amp1q to patients without gain1q. Summary/Conclusion: Numerical aberrations of 1q are associated with upregulation of SNORD78 and increased ribosome 2’-O-methylation, indicating a role of aberrant ribosomal methylation in disease progression of MM. Keywords: Cytogenetic abnormalities, Multiple myeloma