A new transgenic mouse model for conditional overexpression of the Polycomb Group protein EZH2.

The Polycomb Group protein EZH2 is upregulated in most prostate cancers, and its overexpression is associated with poor prognosis. Most insights into the functional role of EZH2 in prostate cancer have been gained using cell lines and EZH2 inactivation studies. However, the question remains whether overexpression of EZH2 can initiate prostate tumourigenesis or drive tumour progression. Appropriate transgenic mouse models that are required to answer such questions are lacking. We developed one such transgenic mouse model for conditional overexpression of Ezh2. In this transgene, Ezh2 and Luciferase are transcribed from a single open reading frame. The latter gene enables intravital bioluminescent imaging of tissues expressing this transgene, allowing the detection of tumour outgrowth and potential metastatic progression over time. Prostate-specific Ezh2 overexpression by crossbreeding with Probasin-Cre mice led to neoplastic prostate lesions at low incidence and with a long latency. Compounding a previously described Bmi1-transgene and Pten-deficiency prostate cancer mouse model with the Ezh2 transgene did not enhance tumour progression or drive metastasis formation. In conclusion, we here report the generation of a wildtype Ezh2 overexpression mouse model that allows for intravital surveillance of tissues with activated transgene. This model will be an invaluable tool for further unravelling the role of EZH2 in cancer.

Physical and functional interaction between PML and TBX2 in the establishment of cellular senescence.

Cellular senescence acts as a potent barrier for tumour initiation and progression. Previous studies showed that the PML tumour suppressor promotes senescence, although the precise mechanisms remain to be elucidated. Combining gene expression profiling with chromatin-binding analyses and promoter reporter studies, we identify TBX2, a T-box transcription factor frequently overexpressed in cancer, as a novel and direct PML-repressible E2F-target gene in senescence but not quiescence. Recruitment of PML to the TBX2 promoter is dependent on a functional p130/E2F4 repressor complex ultimately implementing a transcriptionally inactive chromatin environment at the TBX2 promoter. TBX2 repression actively contributes to senescence induction as cells depleted for TBX2 trigger PML pro-senescence function(s) and enter senescence. Reciprocally, elevated TBX2 levels antagonize PML pro-senescence function through direct protein-protein interaction. Collectively, our findings indicate that PML and TBX2 act in an autoregulatory loop to control the effective execution of the senescence program.

Polycomb group gene Ezh2 regulates mammary gland morphogenesis and maintains the luminal progenitor pool.

Specification of the cellular hierarchy in the mammary gland involves complex signaling that remains poorly defined. Polycomb group proteins are known to contribute to the maintenance of stem cell identity through epigenetic modifications, leading to stable alterations in gene expression. The polycomb protein family member EZH2 is known to be important for stem cell maintenance in multiple tissues, but its role in mammary gland development and differentiation remains unknown. Our analyses show that EZH2 is predominantly expressed in luminal cells of the mouse mammary epithelium. As mammary gland development occurs mostly after birth, the analysis of EZH2 gene function in postnatal development is precluded by embryonic lethality of conventional EZH2 knockout mice. To investigate the role of EZH2 in normal mammary gland epithelium, we have generated novel transgenic mice that express doxycycline-regulatable short hairpin (sh) RNAs directed against Ezh2. Knockdown of EZH2 results in delayed outgrowth of the mammary epithelium during puberty, due to impaired terminal end bud formation and ductal elongation. Furthermore, our results demonstrate that EZH2 is required to maintain the luminal cell pool and may limit differentiation of luminal progenitors into CD61(+) differentiated luminal cells, suggesting a role for EZH2 in mammary luminal cell fate determination. Consistent with this, EZH2 knockdown reduced lobuloalveolar expansion during pregnancy, suggesting EZH2 is required for the differentiation of luminal progenitors to alveolar cells.

A Signal-Finding Study of Abemaciclib in Heavily Pretreated Patients with Metastatic Castration-Resistant Prostate Cancer: Results from CYCLONE 1.

PURPOSE: Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors radically changed the treatment paradigm for breast cancer. Similar to estrogen receptor in breast cancer, androgen receptor signaling activates cyclin D-CDK4/6, driving proliferation and resistance to hormonal manipulation in prostate cancer. This study was designed to detect signals of clinical activity for abemaciclib in treatment-refractory metastatic castration-resistant prostate cancer (mCRPC). PATIENTS AND METHODS: Eligible patients had progressive mCRPC, measurable disease, and previously received ≥1 novel hormonal agent(s) and 2 lines of taxane chemotherapy. Abemaciclib 200 mg twice daily was administered on a continuous dosing schedule. Primary endpoint was objective response rate (ORR) without concurrent bone progression. This study was designed to detect a minimum ORR of 12.5%. RESULTS: At trial entry, 40 (90.9%) of 44 patients had objective radiographic disease progression, 4 (9.1%) had prostate-specific antigen (PSA)-only progression, and 20 (46.5%) had visceral metastases (of these, 60% had liver metastases). Efficacy analyses are as follows: ORR without concurrent bone progression: 6.8%; disease control rate: 45.5%; median time to PSA progression: 6.5 months [95% confidence interval (CI), 3.2-NA]; median radiographic PFS; 2.7 months (95% CI, 1.9-3.7); and median OS, 8.4 months (95% CI, 5.6-12.7). Most frequent grade ≥3 treatment-emergent adverse events (AE) were neutropenia (25.0%), anemia, and fatigue (11.4% each). No grade 4 or 5 AEs were related to abemaciclib. CONCLUSIONS: Abemaciclib monotherapy was well tolerated and showed clinical activity in this heavily pretreated population, nearly half with visceral metastases. This study is considered preliminary proof-of-concept and designates CDK4/6 as a valid therapeutic target in prostate cancer.

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.

The SUMO pathway is essential for nuclear integrity and chromosome segregation in mice.

Covalent modification by SUMO regulates a wide range of cellular processes, including transcription, cell cycle, and chromatin dynamics. To address the biological function of the SUMO pathway in mammals, we generated mice deficient for the SUMO E2-conjugating enzyme Ubc9. Ubc9-deficient embryos die at the early postimplantation stage. In culture, Ubc9 mutant blastocysts are viable, but fail to expand after 2 days and show apoptosis of the inner cell mass. Loss of Ubc9 leads to major chromosome condensation and segregation defects. Ubc9-deficient cells also show severe defects in nuclear organization, including nuclear envelope dysmorphy and disruption of nucleoli and PML nuclear bodies. Moreover, RanGAP1 fails to accumulate at the nuclear pore complex in mutant cells that show a collapse in Ran distribution. Together, these findings reveal a major role for Ubc9, and, by implication, for the SUMO pathway, in nuclear architecture and function, chromosome segregation, and embryonic viability in mammals.

Human papillomavirus oncoprotein E7 targets the promyelocytic leukemia protein and circumvents cellular senescence via the Rb and p53 tumor suppressor pathways.

Cellular senescence can be triggered by a variety of signals, including loss of telomeric integrity or intense oncogenic signaling, and is considered a potent, natural tumor suppressor mechanism. Previously, it was shown that the promyelocytic leukemia protein (PML) induces cellular senescence when overexpressed in primary human fibroblasts. The mechanism by which the PML IV isoform elicits this irreversible growth arrest is believed to involve activation of the tumor suppressor pathways p21/p53 and p16/Rb; however, a requirement for either pathway has not been demonstrated unequivocally. To investigate the individual contributions of p53 and Rb to PML-induced senescence, we used oncoproteins E6 and E7 from human papillomaviruses (HPVs), which predominantly target p53 and Rb. We show that E7, but not E6, circumvents PML-induced senescence. Using different E7 mutant proteins, dominant negative cyclin-dependent kinase 4, and p16 RNA interference, we demonstrate that Rb-related and Rb-independent mechanisms of E7 are necessary for subversion of PML-induced senescence and we identify PML as a novel target for E7. Interaction between E7 and a functional prosenescence complex composed of PML, p53, and CBP perturbs transcriptional activation of p53, thus highlighting a significant effect also on the p53 tumor suppressor pathway. Given the importance of HPV in the pathogenesis of cervical cancer, our results warrant a more detailed analyses of PML in HPV infections.

Impaired mitotic progression and preimplantation lethality in mice lacking OMCG1, a new evolutionarily conserved nuclear protein.

While highly conserved through evolution, the cell cycle has been extensively modified to adapt to new developmental programs. Recently, analyses of mouse mutants revealed that several important cell cycle regulators are either dispensable for development or have a tissue- or cell-type-specific function, indicating that many aspects of cell cycle regulation during mammalian embryo development remain to be elucidated. Here, we report on the characterization of a new gene, Omcg1, which codes for a nuclear zinc finger protein. Embryos lacking Omcg1 die by the end of preimplantation development. In vitro cultured Omcg1-null blastocysts exhibit a dramatic reduction in the total cell number, a high mitotic index, and the presence of abnormal mitotic figures. Importantly, we found that Omcg1 disruption results in the lengthening of M phase rather than in a mitotic block. We show that the mitotic delay in Omcg1-/- embryos is associated with neither a dysfunction of the spindle checkpoint nor abnormal global histone modifications. Taken together, these results suggest that Omcg1 is an important regulator of the cell cycle in the preimplantation embryo.

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 (8.2-11.3) 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.

Non-small cell lung cancer patients with brain metastases treated with first-line platinum-doublet chemotherapy: Analysis from the European FRAME study.

OBJECTIVES: We report on a post-hoc analysis of patients with brain metastases from a large prospective observational study of first-line treatment of non-small cell lung cancer (NSCLC). The aim was to describe baseline characteristics of NSCLC patients with brain metastases, understand their first-line treatment and report outcomes attained in real-world settings. MATERIALS AND METHODS: This post-hoc analysis included all patients in the European observational FRAME study who had brain metastases at initiation of first-line treatment. Descriptive statistics were used for continuous and categorical variables and survival outcomes were assessed using the Kaplan-Meier approach. RESULTS: Our data showed that 17% of patients (263/1564) had spread of the disease to the brain at initiation of first-line treatment. Patients with brain metastases were slightly younger, and more likely to have NSCLC of non-squamous histology than the overall study sample. 34% had received prior palliative radiotherapy to the brain. Our analysis showed a median overall survival (OS) of 7.2 months [95% confidence interval (CI) 6.1-8.2] for all patients with brain metastases treated with first-line platinum-based chemotherapy, ranging from 5.6 months for those treated with gemcitabine plus platinum up to 9.3 months for those treated with pemetrexed plus platinum. Further analysis showed that patients with brain metastases were more frequently treated with pemetrexed platinum-doublet therapy than with any other regimen. CONCLUSIONS: Our analysis provides a unique set of real-world data which adds to current understanding about treatment decisions and outcomes for NSCLC patients with brain metastases for whom there is little clinical trial data available.

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.

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.

BMI1 is recruited to DNA breaks and contributes to DNA damage-induced H2A ubiquitination and repair.

DNA damage activates signaling pathways that lead to modification of local chromatin and recruitment of DNA repair proteins. Multiple DNA repair proteins having ubiquitin ligase activity are recruited to sites of DNA damage, where they ubiquitinate histones and other substrates. This DNA damage-induced histone ubiquitination is thought to play a critical role in mediating the DNA damage response. We now report that the polycomb protein BMI1 is rapidly recruited to sites of DNA damage, where it persists for more than 8 h. The sustained localization of BMI1 to damage sites is dependent on intact ATM and ATR and requires H2AX phosphorylation and recruitment of RNF8. BMI1 is required for DNA damage-induced ubiquitination of histone H2A at lysine 119. Loss of BMI1 leads to impaired repair of DNA double-strand breaks by homologous recombination and the accumulation of cells in G(2)/M. These data support a crucial role for BMI1 in the cellular response to DNA damage.

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 RAS(V12)-induced cellular senescence and collaborate with RAS(V12) 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.