NOP53 Suppresses Autophagy through ZKSCAN3-Dependent and -Independent Pathways

Autophagy is an evolutionally conserved process that recycles aged or damaged intracellular components through a lysosome-dependent pathway. Although this multistep process is propagated in the cytoplasm by the orchestrated activity of the mTOR complex, phosphatidylinositol 3-kinase, and a set of autophagy-related proteins (ATGs), recent investigations have suggested that autophagy is tightly regulated by nuclear events. Thus, it is conceivable that the nucleolus, as a stress-sensing and -responding intranuclear organelle, plays a role in autophagy regulation, but much is unknown concerning the nucleolar controls in autophagy. In this report, we show a novel nucleolar–cytoplasmic axis that regulates the cytoplasmic autophagy process: nucleolar protein NOP53 regulates the autophagic flux through two divergent pathways, the ZKSCAN3-dependent and -independent pathways. In the ZKSCAN3-dependent pathway, NOP53 transcriptionally activates a master autophagy suppressor ZKSCAN3, thereby inhibiting MAP1LC3B/LC3B induction and autophagy propagation. In the ZKSCAN3-independent pathway, NOP53 physically interacts with histone H3 to dephosphorylate S10 of H3, which, in turn, transcriptionally downregulates the ATG7 and ATG12 expressions. Our results identify nucleolar protein NOP53 as an upstream regulator of the autophagy process.

HIV-1 Vpr Induces Degradation of Nucleolar Protein CCDC137 as a Consequence of Cell Cycle Arrest

Expression of HIV-1 accessory proteins Vif and Vpr results in G2/M cell cycle arrest by hijacking the host ubiquitin-proteasome system. Vif directs cell cycle arrest by targeting protein phosphatase 2, regulatory subunit B alpha (PP2AB56) for degradation. However, the ubiquitination target(s) of Vpr that is directly responsible for G2/M arrest has remained elusive. Recently, Vpr directed degradation of nucleolar protein coiled-coil domain containing 137 (CCDC137), also known as retinoic acid resistance factor (RaRF), has been implicated as the proximal event leading to G2/M cell cycle arrest. In this study we aimed to further investigate this finding. We confirm that CCDC137 is targeted for degradation in the presence of Vpr with a requirement for the CUL4ADDB1.DCAF1 E3 ligase complex. However, degradation of CCDC137 is a general consequence, rather than a trigger, of G2/M arrest. Thus, whether induced by Vpr expression or pharmacologically via CDK1 inhibition, G2/M blockade results in degradation of CCDC137. Furthermore, siRNA-mediated depletion of CCDC137 failed to induce G2/M arrest.

Nucleolar protein 10 (NOP10) predicts poor prognosis in invasive breast cancer

Purpose Nucleolar protein 10 (NOP10) is required for ribosome biogenesis and telomere maintenance and plays a key role in carcinogenesis. This study aims to evaluate the clinical and prognostic significance of NOP10 in breast cancer (BC). Methods NOP10 expression was assessed at mRNA level employing the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) (n = 1980) and Cancer Genome Atlas (TCGA) BC cohorts (n = 854). Protein expression was evaluated on tissue microarray of a large BC cohort (n = 1081) using immunohistochemistry. The correlation between NOP10 expression, clinicopathological parameters and patient outcome was assessed. Results NOP10 expression was detected in the nucleus and nucleolus of the tumour cells. At the transcriptomic and proteomic levels, NOP10 was significantly associated with aggressive BC features including high tumour grade, high nucleolar score and poor Nottingham Prognostic Index. High NOP10 protein expression was an independent predictor of poor outcome in the whole cohort and in triple-negative BC (TNBC) class (p = 0.002 & p = 0.014, respectively). In chemotherapy- treated patients, high NOP10 protein expression was significantly associated with shorter survival (p = 0.03) and was predictive of higher risk of death (p = 0.028) and development of distant metastasis (p = 0.02) independent of tumour size, nodal stage and tumour grade. Conclusion High NOP10 expression is a poor prognostic biomarker in BC and its expression can help in predicting chemotherapy resistance. Functional assessments are necessary to decipher the underlying mechanisms and to reveal its potential therapeutic values in various BC subtypes especially in the aggressive TNBC class.