Phosphorylation of Ubc9 by Cdk1 Enhances SUMOylation Activity

Increasing evidence has pointed to an important role of SUMOylation in cell cycle regulation, especially for M phase. In the current studies, we have obtained evidence through in vitro studies that the master M phase regulator CDK1/cyclin B kinase phosphorylates the SUMOylation machinery component Ubc9, leading to its enhanced SUMOylation activity. First, we show that CDK1/cyclin B, but not many other cell cycle kinases such as CDK2/cyclin E, ERK1, ERK2, PKA and JNK2/SAPK1, specifically enhances SUMOylation activity. Second, CDK1/cyclin B phosphorylates the SUMOylation machinery component Ubc9, but not SAE1/SAE2 or SUMO1. Third, CDK1/cyclin B-phosphorylated Ubc9 exhibits increased SUMOylation activity and elevated accumulation of the Ubc9-SUMO1 thioester conjugate. Fourth, CDK1/cyclin B enhances SUMOylation activity through phosphorylation of Ubc9 at serine 71. These studies demonstrate for the first time that the cell cycle-specific kinase CDK1/cyclin B phosphorylates a SUMOylation machinery component to increase its overall SUMOylation activity, suggesting that SUMOylation is part of the cell cycle program orchestrated by CDK1 through Ubc9

SUMOylation of DRIL1 Directs Its Transcriptional Activity Towards Leukocyte Lineage-Specific Genes

DRIL1 is an ARID family transcription factor that can immortalize primary mouse fibroblasts, bypass RASV12-induced cellular senescence and collaborate with RASV12 or MYC in mediating oncogenic transformation. It also activates immunoglobulin heavy chain transcription and engages in heterodimer formation with E2F to stimulate E2F-dependent transcription. Little, however, is known about the regulation of DRIL1 activity. Recently, DRIL1 was found to interact with the SUMO-conjugating enzyme Ubc9, but the functional relevance of this association has not been assessed. Here, we show that DRIL1 is sumoylated both in vitro and in vivo at lysine 398. Moreover, we provide evidence that PIASy functions as a specific SUMO E3-ligase for DRIL1 and promotes its sumoylation both in vitro and in vivo. Furthermore, consistent with the subnuclear localization of PIASy in the Matrix-Associated Region (MAR), SUMO-modified DRIL1 species are found exclusively in the MAR fraction. This post-translational modification interferes neither with the subcellular localization nor the DNA-binding activity of the protein. In contrast, DRIL1 sumoylation impairs its interaction with E2F1 in vitro and modifies its transcriptional activity in vivo, driving transcription of subset of genes regulating leukocyte fate. Taken together, these results identify sumoylation as a novel post-translational modification of DRIL1 that represents an important mechanism for targeting and modulating DRIL1 transcriptional activity

Functional Connection between Rad51 and PML in Homology-Directed Repair

The promyelocytic leukemia protein (PML) is a tumor suppressor critical for formation of nuclear bodies (NBs) performing important functions in transcription, apoptosis, DNA repair and antiviral responses. Earlier studies demonstrated that simian virus 40 (SV40) initiates replication near PML NBs. Here we show that PML knockdown inhibits viral replication in vivo, thus indicating a positive role of PML early in infection. SV40 large T antigen (LT) induces DNA damage and, consequently, nuclear foci of the key homologous recombination repair protein Rad51 that colocalize with PML. PML depletion abrogates LT-induced Rad51 foci. LT may target PML NBs to gain access to DNA repair factors like Rad51 that are required for viral replication. We have used the SV40 model to gain insight to DNA repair events involving PML. Strikingly, even in normal cells devoid of viral oncoproteins, PML is found to be instrumental for foci of Rad51, Mre11 and BRCA1, as well as homology-directed repair after double-strand break (DSB) induction. Following LT expression or external DNA damage, PML associates with Rad51. PML depletion also causes a loss of RPA foci following γ-irradiation, suggesting that PML is required for processing of DSBs. Immunofluorescent detection of incorporated BrdU without prior denaturation indicates a failure to generate ssDNA foci in PML knockdown cells upon γ-irradiation. Consistent with the lack of RPA and BrdU foci, γ-irradiation fails to induce Chk1 activation, when PML is depleted. Taken together, we have discovered a novel functional connection between PML and the homologous recombination-mediated repair machinery, which might contribute to PML tumor suppressor activity

SUMO regulates p21Cip1 intracellular distribution and with p21Cip1 facilitates multiprotein complex formation in the nucleolus upon DNA damage

We previously showed that p21Cip1 transits through the nucleolus on its way from the nucleus to the cytoplasm and that DNA damage inhibits this transit and induces the formation of p21Cip1-containing intranucleolar bodies (INoBs). Here, we demonstrate that these INoBs also contain SUMO-1 and UBC9, the E2 SUMO-conjugating enzyme. Furthermore, whereas wild type SUMO-1 localized in INoBs, a SUMO-1 mutant, which is unable to conjugate with proteins, does not, suggesting the presence of SUMOylated proteins at INoBs. Moreover, depletion of the SUMO-conjugating enzyme UBC9 or the sumo hydrolase SENP2 changed p21Cip1 intracellular distribution. In addition to SUMO-1 and p21Cip1, cell cycle regulators and DNA damage checkpoint proteins, including Cdk2, Cyclin E, PCNA, p53 and Mdm2, and PML were also detected in INoBs. Importantly, depletion of UBC9 or p21Cip1 impacted INoB biogenesis and the nucleolar accumulation of the cell cycle regulators and DNA damage checkpoint proteins following DNA damage. The impact of p21Cip1 and SUMO-1 on the accumulation of proteins in INoBs extends also to CRM1, a nuclear exportin that is also important for protein translocation from the cytoplasm to the nucleolus. Thus, SUMO and p21Cip1 regulate the transit of proteins through the nucleolus, and that disruption of nucleolar export by DNA damage induces SUMO and p21Cip1 to act as hub proteins to form a multiprotein complex in the nucleolus

SUMO, the Three Rs and Cancer

International audienceSUMO modification (sumoylation) plays important roles in nucleo-cytoplasmic transport, maintenance of sub-nuclear architecture, the regulation of gene expression and in DNA replication, repair and recombination. Here we review recent evidence for SUMO's role in protecting genomic integrity at both the chromosomal and the DNA level. Furthermore, the involvement of sumoylation and of specific SUMO targets in cancer is discussed

Cisplatin and carboplatin-based chemotherapy in the first-line treatment of non-small cell lung cancer: Analysis from the European FRAME study

Objectives: To explore patient and disease factors, and reasons behind the physician's choice of platinum backbone for the first-line treatment of non-small cell lung cancer (NSCLC), as observed in a European prospective observational study of patients receiving platinum-based chemotherapy as first-line treatment for advanced or metastatic NSCLC (the FRAME study). Additionally, overall survival (OS) for patients who received cisplatin or carboplatin was evaluated. Materials and methods: A post-hoc analysis of the prospective study population was conducted. Baseline characteristics of patients receiving cisplatin versus carboplatin were compared and summarized by propensity score. Survival for matched patients was summarized using the Kaplan-Meier approach. Results: Of the 1564 patients who were included in the prospective study, 1520 received either cisplatin (54%) or carboplatin (46%) in combination with pemetrexed, gemcitabine, taxanes or vinorelbine. Patients treated with carboplatin were older than patients receiving cisplatin (mean age 67 versus 61 years; p < 0.001), had poorer performance status (p < 0.001), and more comorbidities (p < 0.001). Cisplatin was most frequently combined with pemetrexed (47%), and carboplatin most frequently with taxanes (31%). Unadjusted median OS estimates for patients from the total prospective study sample were 11.5 months (95% confidence interval [CI] 10.1-12.9) for cisplatin recipients and 9.0 months (95% CI 8.1-10.6) for carboplatin recipients. Median (95% CI) overall survival for the matched cohorts was 10.8 months (8.8-14.3) for cisplatin versus 9.5 months (8.2-113) for carboplatin; p = 0.086. Conclusion: This post-hoc analysis illustrated real-life differences in patients with NSCLC prescribed platinum-based first-line treatment, and suggested that baseline patient and disease characteristics were associated with physician's choice of platinum agent, with cisplatin being more frequently prescribed to younger and fitter patients. (C) 2015 Elsevier Ireland Ltd. All rights reserved

Outcomes and resource use of non-small cell lung cancer (NSCLC) patients treated with first-line platinum-based chemotherapy across Europe: FRAME prospective observational study

Introduction: FRAME was a prospective observational study that captured real-world data on patients with advanced or metastatic non-small cell lung cancer (NSCLC) receiving platinum-based chemotherapies as first-line treatment (FLT) across Europe. As previously reported, most patients observed in the study had initiated FLT with either pemetrexed, gemcitabine, vinorelbine or taxanes in combination with a platinum. Baseline patient and disease characteristics including age, performance status, and histology varied (all p < 0.01) across cohorts. Methods: Consenting adult patients initiating FLT for advanced or metastatic NSCLC with platinum-based chemotherapy, with or without a targeted agent, entered the study between April 2009 and February 2011. The choice of FLT was left to physicians' discretion per routine clinical practice. The primary objective was to evaluate overall survival (OS) across platinum-based doublet chemotherapy cohorts and key secondary objectives included the evaluation of OS in patients with different histological subtypes of NSCLC. Survival outcomes were assessed using Kaplan-Meier analysis, and unadjusted estimates are presented. Results: Median OS in months was 10.3 across cohorts (n = 1524), 10.7 for pemetrexed (n = 569), 10.0 for gemcitabine (n = 360), 9.1 for taxanes (n = 295), and 10.7 for vinorelbine (n = 300). For patients with non-squamous NSCLC who received cisplatin (n = 616, 40% of total), median OS in months was 10.6 across the cohorts, 11.6 for pemetrexed, 8.4 for gemcitabine, 9.6 for taxanes, and 9.9 for vinorelbine. Conclusions: FRAME describes real-world treatment patterns and survival for patients initiating FLT for advanced or metastatic NSCLC between 2009 and 2011 across Europe. (C) 2015 Elsevier Ireland Ltd. All rights reserved

Sumoylation by Ubc9 Regulates the Stem Cell Compartment and Structure and Function of the Intestinal Epithelium in Mice

BACKGROUND & AIMS:: Small ubiquitin-like modifiers (SUMOs) are attached to other proteins to regulate their function (sumoylation). We investigated the role of Ubc9, which covalently attaches SUMOs to proteins, in the gastrointestinal tract of adult mice. METHODS:: We investigated the effects of decreased sumoylation in adult mammals by generating mice with an inducible knockout (by injection of 4-hydroxytamoxifen) of the E2 enzyme Ubc9 (Ubc9fl/-/ROSA26-CreERT2 mice). We analyzed the phenotypes using a range of histologic techniques. RESULTS:: Loss of Ubc9 from adult mice primarily affected the small intestine. Ubc9fl/-/ROSA26-CreERT2 mice died within 6 days of 4-hydroxytamoxifen injection, losing 20% or less of their body weight and developing severe diarrhea on the second day after injection. Surprisingly, other epithelial tissues appeared to be unaffected at that stage. Decreased sumoylation led to the depletion of the intestinal proliferative compartment and to the rapid disappearance of stem cells. Sumoylation was required to separate the proliferative and differentiated compartments from the crypt and control differentiation and function of the secretory lineage. Sumoylation was required for nucleus positioning and polarized organization of actin in the enterocytes. Loss of sumoylation caused detachment of the enterocytes from the basal lamina, as observed in tissue fragility diseases. We identified the intermediate filament keratin 8 as a SUMO substrate in epithelial cells. CONCLUSIONS:: Sumoylation maintains intestinal stem cells and the architecture, mechanical stability, and function of the intestinal epithelium of mice.

Akt-mediated phosphorylation of Bmi1 modulates its oncogenic potential, E3 ligase activity, and DNA damage repair activity in mouse prostate cancer

Prostate cancer (PCa) is a major lethal malignancy in men, but the molecular events and their interplay underlying prostate carcinogenesis remain poorly understood. Epigenetic events and the upregulation of polycomb group silencing proteins including Bmi1 have been described to occur during PCa progression. Here, we found that conditional overexpression of Bmi1 in mice induced prostatic intraepithelial neoplasia, and elicited invasive adenocarcinoma when combined with PTEN haploinsufficiency. In addition, Bmi1 and the PI3K/Akt pathway were coactivated in a substantial fraction of human high-grade tumors. We found that Akt mediated Bmi1 phosphorylation, enhancing its oncogenic potential in an Ink4a/Arf-independent manner. This process also modulated the DNA damage response and affected genomic stability. Together, our findings demonstrate the etiological role of Bmi1 in PCa, unravel an oncogenic collaboration between Bmi1 and the PI3K/Akt pathway, and provide mechanistic insights into the modulation of Bmi1 function by phosphorylation during prostate carcinogenesis