Pb1841: nucleolin interacts with nucleophosmin as a predictor of prognosis in acute myeloblastic leukemia

Topic: 4. Acute myeloid leukemia - Clinical Background: Nucleolin (NCL) is a nucleolar phosphoprotein involved in DNA repair, ribosomal biogenesis, and mRNA metabolism, and is localized to the nucleolus through its interaction with Nucleophosmin (NPM). NCL and NPM shuttle between the nucleoli and the cytoplasmic membrane, as protein chaperones. Cellular stress leads to translocation of NCL and NPM to the cytoplasm and membrane, with heterotopic NCL overexpression in acute myeloid leukemia (AML) blasts. C-terminal NPM1 mutations – conferring a favorable prognosis (Px) in AML – cause decreased nucleolar localization of NPM, its translocation to the cytoplasm, loss of interaction with NCL, and loss of the nucleolar localization of NCL. Aims: To analyze the Px impact of NCL expression in AML patients (pts) and its relationship to NPM1 mutation status. Methods: We analyzed Gene Expression Profiling (GEP), clinical and NPM1mut data for AML pts included in The Cancer Genome Atlas (TCGA) program and in the phs001657.v1.p1 dataset of The Database of Genotypes and Phenotypes (DbGaP). The optimal NCL expression cut-off for overall survival (OS) prediction was determined on the R2 Genomics Analysis and Visualization Platform. Pts were stratified into High Expressors (NCL-Hi; expression equal to or over that cut-off) and Low Expressors (NCL-Low; expression under the cut-off). Findings were confirmed on the Gene Expression Profiling Interactive Analysis tool (GEPIA). Results: The TCGA database included 150 AML pts with a mean age at diagnosis of 54.3±16.0 years (range: 21-88). Mean NCL expression was 219.2±69.5 (range: 51.5 to 397.3), unaffected by gender or age (p=NS). While NCL and NPM1 expressions were strongly positively correlated (r=0.79, p<0.001), mean NCL expression was lower in pts with NPM1mut than in patients with NPM1wt (p=0.044, DbGaP dataset). At a median follow-up of 40.1 m, median OS was 19.0 m. The optimal NCL expression cut-off for survival prediction for the TCGA dataset was at >p88, with overexpressors having worse OS (median OS: 10.0 m for NCL-Hi vs 20.0 m for NCL-Low, p=0.023). GEPIA confirmed that NCL overexpression predicts OS, with pts with an expression >p85 having shorter OS (p=0.04). Likewise, in the DbGaP dataset, NCL-Low pts had a median OS of 20.8 m, compared to 14.0 m for NCL-Hi (p=0.04), with a cut-off at >p10. The mean NCL expression was identical across cytogenetic risk groups (favorable, intermediate and poor, 215.0±71.3, 214.9±65.7 and 231.6±77.6, p=NS). However, NCL-Hi patients were more likely to have Poor Risk cytogenetics than NCL-Low (45.4% vs 20.63%, p=0.04), whereas NCL-Low were more likely to have Favorable cytogenetics (21.4% vs 13.6%, p=0.04). Although the mean NCL expression was not statistically different between acute promyelocytic leukemia (APL) pts and non-APL pts (186.1±58.5 vs 222.4±69.8, p=0.07), 100% of APL pts were low-expressors of NCL. Summary/Conclusion: We found that NCL expression strongly correlated with NPM1 expression, as predicted from their interaction in the nucleolus. NPM1mut associated with significantly lower NCL expression. In turn, lower NCL expression associated with a two-fold improvement in OS. Considering the molecular roles of NCL in cell survival and proliferation, these findings could contribute to the understanding of the improved Px conferred by NPM1mut in AML. Additionally, we found that NCL overexpressors were twice as likely to present with Poor Risk cytogenetics, whereas underexpressors were twice as likely to have Favorable cytogenetics; of note, all APL pts in the TCGA dataset were underexpressors of NCL, again suggesting a role for NCL expression in the determination of Px in AML pts. Keywords: Genetic modifiers, Acute myeloid leukemia, Prognostic factor