Whole blood transcriptomics reveals granulocyte colony-stimulating factor as a mediator of cardiopulmonary bypass-induced systemic inflammatory response syndrome.

Objectives: Systemic inflammatory response syndrome (SIRS) is a frequent complication of cardiopulmonary bypass (CPB). SIRS is associated with significant morbidity and mortality, but its pathogenesis remains incompletely understood, and as a result, biomarkers are lacking and treatment remains expectant and supportive. This study aimed to understand the pathophysiological mechanisms driving SIRS induced by CPB and identify novel therapeutic targets that might reduce systemic inflammation and improve patient outcomes. Methods: Twenty-one patients undergoing cardiac surgery and CPB were recruited, and blood was sampled before, during and after surgery. SIRS was defined using the American College of Chest Physicians/Society of Critical Care Medicine criteria. We performed immune cell profiling and whole blood transcriptomics and measured individual mediators in plasma/serum to characterise SIRS induced by CPB. Results: Nineteen patients fulfilled criteria for SIRS, with a mean duration of 2.7 days. Neutrophil numbers rose rapidly with CPB and remained elevated for at least 48 h afterwards. Transcriptional signatures associated with neutrophil activation and degranulation were enriched during CPB. We identified a network of cytokines governing these transcriptional changes, including granulocyte colony-stimulating factor (G-CSF), a regulator of neutrophil production and function. Conclusions: We identified neutrophils and G-CSF as major regulators of CPB-induced systemic inflammation. Short-term targeting of G-CSF could provide a novel therapeutic strategy to limit neutrophil-mediated inflammation and tissue damage in SIRS induced by CPB.

CSL362 potently and specifically depletes pDCs invitro and ablates SLE-immune complex-induced IFN responses.

Systemic lupus erythematosus (SLE) is an autoimmune disease with significant morbidity and mortality. Type I interferon (IFN) drives SLE pathology and plasmacytoid dendritic cells (pDCs) are potent producers of IFN; however, the specific effects of pDC depletion have not been demonstrated. We show CD123 was highly expressed on pDCs and the anti-CD123 antibody CSL362 potently depleted pDCs in vitro. CSL362 pre-treatment abrogated the induction of IFNα and IFN-induced gene transcription following stimulation with SLE patient-derived serum or immune complexes. RNA transcripts induced in pDCs by ex vivo stimulation with TLR ligands were reflected in gene expression profiles of SLE blood, and correlated with disease severity. TLR ligand-induced protein production by SLE patient peripheral mononuclear cells was abrogated by CSL362 pre-treatment including proteins over expressed in SLE patient serum. These findings implicate pDCs as key drivers in the cellular activation and production of soluble factors seen in SLE.

CSL324, a granulocyte colony-stimulating factor receptor antagonist, blocks neutrophil migration markers that are upregulated in hidradenitis suppurativa.

BACKGROUND: Neutrophils have been shown to contribute to the pathophysiology of hidradenitis suppurativa (HS), a chronic, painful and debilitating inflammatory skin disease, yet their exact role remains to be fully defined. Granulocyte colony-stimulating factor (G-CSF), a major regulator of neutrophil development and survival, can be blocked by the novel, fully human anti-G-CSF receptor (G-CSFR) monoclonal antibody CSL324. OBJECTIVES: We investigated the activation and migration of neutrophils in HS and the impact of blocking G-CSFR with CSL324. METHODS: Biopsy and peripheral blood samples were taken from participants of two studies: 2018.206, a noninterventional research study of systemic and dermal neutrophils and inflammatory markers in patients with neutrophilic skin diseases, and CSL324_1001 (ACTRN12616000846426), a single-dose ascending and repeated dose, randomized, double-blind, placebo-controlled study to assess the safety, pharmacokinetics and pharmacodynamics of CSL324 in healthy adult subjects. Ex vivo experiments were performed, including neutrophil enumeration and immunophenotyping, migration, receptor occupancy and transcriptome analysis. RESULTS: The number of cells positive for the neutrophil markers myeloperoxidase (MPO) and neutrophil elastase (NE) was significantly higher in HS lesions compared with biopsies from healthy donors (HDs) (P < 0.0001 and P = 0.0223, respectively). In peripheral blood samples, mean neutrophil counts were significantly higher in patients with HS than in HDs (2.98 vs. 1.60 × 109 L-1, respectively; P = 8.8 × 10-4). Neutrophil migration pathways in peripheral blood were increased in patients with HS and their neutrophils demonstrated an increased migration phenotype, with higher mean CXCR1 on the surface of neutrophils in patients with HS (24453.20 vs. 20798.47 for HD; P = 0.03). G-CSF was a key driver of the transcriptomic changes in the peripheral blood of patients with HS and was elevated in serum from patients with HS compared with HDs (mean 6.61 vs. 3.84 pg mL-1, respectively; P = 0.013). Administration of CSL324 inhibited G-CSF-induced transcriptional changes in HDs, similar to those observed in the HS cohort, as highlighted by expression changes in genes related to neutrophil migratory capacity. CONCLUSIONS: Data suggest that neutrophils contribute to HS pathophysiology and that neutrophils are increased in lesions due to an increase in G-CSF-driven migration. CSL324 counteracted G-CSF-induced transcriptomic changes and blocked neutrophil migration by reducing cell-surface levels of chemokine receptors.

Targeting MDM4 as a Novel Therapeutic Approach in Prostate Cancer Independent of p53 Status.

Metastatic prostate cancer is a lethal disease in patients incapable of responding to therapeutic interventions. Invasive prostate cancer spread is caused by failure of the normal anti-cancer defense systems that are controlled by the tumour suppressor protein, p53. Upon mutation, p53 malfunctions. Therapeutic strategies to directly re-empower the growth-restrictive capacities of p53 in cancers have largely been unsuccessful, frequently because of a failure to discriminate responses in diseased and healthy tissues. Our studies sought alternative prostate cancer drivers, intending to uncover new treatment targets. We discovered the oncogenic potency of MDM4 in prostate cancer cells, both in the presence and absence of p53 and also its mutation. We uncovered that sustained depletion of MDM4 is growth inhibitory in prostate cancer cells, involving either apoptosis or senescence, depending on the cell and genetic context. We identified that the potency of MDM4 targeting could be potentiated in prostate cancers with mutant p53 through the addition of a first-in-class small molecule drug that was selected as a p53 reactivator and has the capacity to elevate oxidative stress in cancer cells to drive their death.

E6AP Promotes a Metastatic Phenotype in Prostate Cancer.

Although primary prostate cancer is largely curable, progression to metastatic disease is associated with very poor prognosis. E6AP is an E3 ubiquitin ligase and a transcriptional co-factor involved in normal prostate development. E6AP drives prostate cancer when overexpressed. Our study exposed a role for E6AP in the promotion of metastatic phenotype in prostate cells. We revealed that elevated levels of E6AP in primary prostate cancer correlate with regional metastasis and demonstrated that E6AP promotes acquisition of mesenchymal features, migration potential, and ability for anchorage-independent growth. We identified the metastasis suppressor NDRG1 as a target of E6AP and showed it is key in E6AP induction of mesenchymal phenotype. We showed that treatment of prostate cancer cells with pharmacological agents upregulated NDRG1 expression suppressed E6AP-induced cell migration. We propose that the E6AP-NDRG1 axis is an attractive therapeutic target for the treatment of E6AP-driven metastatic prostate cancer.

E6AP goes viral: the role of E6AP in viral- and non-viral-related cancers.

Since its discovery, the E3 ubiquitin ligase E6-associated protein (E6AP) has been studied extensively in two pathological contexts: infection by the human papillomavirus (HPV), and the neurodevelopmental disorder, Angelman syndrome. Vital biological links between E6AP and other viruses, namely hepatitis C virus and encephalomyocarditis virus, have been recently uncovered. Critically, oncogenic E6AP activities have been demonstrated to contribute to cancers of both viral and non-viral origins. HPV-associated cancers serve as the primary example of E6AP involvement in cancers driven by viruses. Studies over the past few years have exposed a role for E6AP in non-viral-related cancers. This has been demonstrated in B-cell lymphoma and prostate cancers, where oncogenic E6AP functions drive these cancers by acting on key tumour suppressors. In this review we discuss the role of E6AP in viral infection, viral propagation and viral-related cancer. We discuss processes affected by oncogenic E6AP, which promote cancers of viral and non-viral aetiology. Overall, recent findings support the role of oncogenic E6AP in disrupting key cellular processes, including tumour suppression and the immune response. E6AP is consequently emerging as an attractive therapeutic target for a number of specific cancers.

Biodosimetric transcriptional and proteomic changes are conserved in irradiated human tissue.

Transcriptional dosimetry is an emergent field of radiobiology aimed at developing robust methods for detecting and quantifying absorbed doses using radiation-induced fluctuations in gene expression. A combination of RNA sequencing, array-based and quantitative PCR transcriptomics in cellular, murine and various ex vivo human models has led to a comprehensive description of a fundamental set of genes with demonstrable dosimetric qualities. However, these are yet to be validated in human tissue due to the scarcity of in situ-irradiated source material. This represents a major hurdle to the continued development of transcriptional dosimetry. In this study, we present a novel evaluation of a previously reported set of dosimetric genes in human tissue exposed to a large therapeutic dose of radiation. To do this, we evaluated the quantitative changes of a set of dosimetric transcripts consisting of FDXR, BAX, BCL2, CDKN1A, DDB2, BBC3, GADD45A, GDF15, MDM2, SERPINE1, TNFRSF10B, PLK3, SESN2 and VWCE in guided pre- and post-radiation (2 weeks) prostate cancer biopsies from seven patients. We confirmed the prolonged dose-responsivity of most of these transcripts in in situ-irradiated tissue. BCL2, GDF15, and to some extent TNFRSF10B, were markedly unreliable single markers of radiation exposure. Nevertheless, as a full set, these genes reliably segregated non-irradiated and irradiated tissues and predicted radiation absorption on a patient-specific basis. We also confirmed changes in the translated protein product for a small subset of these dosimeters. This study provides the first confirmatory evidence of an existing dosimetric gene set in less-accessible tissues-ensuring peripheral responses reflect tissue-specific effects. Further work will be required to determine if these changes are conserved in different tissue types, post-radiation times and doses.

Copper accumulation in senescent cells: Interplay between copper transporters and impaired autophagy.

Cellular senescence is characterized by irreversible growth arrest incurred through either replicative exhaustion or by pro-oncogenic cellular stressors (radioactivity, oxidative stress, oncogenic activation). The enrichment of senescent cells in tissues with age has been associated with tissue dyshomeostasis and age-related pathologies including cancers, neurodegenerative disorders (e.g. Alzheimer's, Parkinson's, etc.) and metabolic disorders (e.g. diabetes). We identified copper accumulation as being a universal feature of senescent cells [mouse embryonic fibroblasts (MEF), human prostate epithelial cells and human diploid fibroblasts] in vitro. Elevated copper in senescent MEFs was accompanied by elevated levels of high-affinity copper uptake protein 1 (Ctr1), diminished levels of copper-transporting ATPase 1 (Atp7a) (copper export) and enhanced antioxidant defence reflected by elevated levels of glutathione (GSH), superoxide dismutase 1 (SOD1) and glutaredoxin 1 (Grx1). The levels of intracellular copper were further increased in senescent MEFs cultured in copper supplemented medium and in senescent Mottled Brindled (Mobr) MEFs lacking functional Atp7a. Finally, we demonstrated that the restoration/preservation of autophagic-lysosomal degradation in senescent MEFs following rapamycin treatment correlated with attenuation of copper accumulation in these cells despite a further decrease in Atp7a levels. This study for the first time establishes a link between Atp7a and the autophagic-lysosomal pathway, and a requirement for both to effect efficient copper export. Such a connection between cellular autophagy and copper homeostasis is significant, as both have emerged as important facets of age-associated degenerative disease.

Exploring the oncoproteomic response of human prostate cancer to therapeutic radiation using data-independent acquisition (DIA) mass spectrometry.

INTRODUCTION: The development of radioresistance in prostate cancer (PCa) is an important clinical issue and is still largely uninformed by personalized molecular characteristics. The aim of this study was to establish a platform that describes the early oncoproteomic response of human prostate tissue to radiation therapy (RT) using a prospective human tissue cohort. METHODS: Fresh and fixed transperineal biopsies from eight men with clinically localized tumors were taken prior to and 14 days following a single fraction of high-dose-rate brachytherapy. Quantitative protein analysis was achieved using an optimized protein extraction pipeline and subsequent data-independent acquisition mass spectroscopy (DIA-MS). Ontology analyses were used to identify enriched functional pathways, with the candidates further interrogated in formalin-fixed paraffin-embedded tissue biopsies from five additional patients. RESULTS: We obtained a mean coverage of 5660 proteins from fresh tissue biopsies; with the principal post-radiation change observed being an increase in levels amongst a total of 49 proteins exhibiting abundance changes. Many of these changes in abundance varied between patients and, typically to prostate cancer tissue, exhibited a high level of heterogeneity. Ontological analysis revealed the enrichment of the protein activation cascades of three immunological pathways: humoral immune response, leukocyte mediated immunity and complement activation. These were predominantly associated with the extracellular space. We validated significant expression differences in between 20% and 61% of these candidates using the separate fixed-tissue cohort and established their feasibility as an experimental tissue resource by acquiring quantitative data for a mean of 5152 proteins per patient. DISCUSSION: In this prospective study, we have established a sensitive and reliable oncoproteomic pipeline for the analysis of both fresh and formalin-fixed human PCa tissue. We identified multiple pathways known to be radiation-responsive and have established a powerful database of candidates and pathways with no current association with RT. This information may be beneficial in the advancement of personalized therapies and potentially, predictive biomarkers.

Proteotranscriptomic Measurements of E6-Associated Protein (E6AP) Targets in DU145 Prostate Cancer Cells.

Prostate cancer is a common cause of cancer-related death in men. E6AP (E6-Associated Protein), an E3 ubiquitin ligase and a transcription cofactor, is elevated in a subset of prostate cancer patients. Genetic manipulations of E6AP in prostate cancer cells expose a role of E6AP in promoting growth and survival of prostate cancer cells in vitro and in vivo However, the effect of E6AP on prostate cancer cells is broad and it cannot be explained fully by previously identified tumor suppressor targets of E6AP, promyelocytic leukemia protein and p27. To explore additional players that are regulated downstream of E6AP, we combined a transcriptomic and proteomic approach. We identified and quantified 16,130 transcripts and 7,209 proteins in castration resistant prostate cancer cell line, DU145. A total of 2,763 transcripts and 308 proteins were significantly altered on knockdown of E6AP. Pathway analyses supported the known phenotypic effects of E6AP knockdown in prostate cancer cells and in parallel exposed novel potential links of E6AP with cancer metabolism, DNA damage repair and immune response. Changes in expression of the top candidates were confirmed using real-time polymerase chain reaction. Of these, clusterin, a stress-induced chaperone protein, commonly deregulated in prostate cancer, was pursued further. Knockdown of E6AP resulted in increased clusterin transcript and protein levels in vitro and in vivo Concomitant knockdown of E6AP and clusterin supported the contribution of clusterin to the phenotype induced by E6AP. Overall, results from this study provide insight into the potential biological pathways controlled by E6AP in prostate cancer cells and identifies clusterin as a novel target of E6AP.

Iron accumulation in senescent cells is coupled with impaired ferritinophagy and inhibition of ferroptosis.

Cellular senescence is characterised by the irreversible arrest of proliferation, a pro-inflammatory secretory phenotype and evasion of programmed cell death mechanisms. We report that senescence alters cellular iron acquisition and storage and also impedes iron-mediated cell death pathways. Senescent cells, regardless of stimuli (irradiation, replicative or oncogenic), accumulate vast amounts of intracellular iron (up to 30-fold) with concomitant changes in the levels of iron homeostasis proteins. For instance, ferritin (iron storage) levels provided a robust biomarker of cellular senescence, for associated iron accumulation and for resistance to iron-induced toxicity. Cellular senescence preceded iron accumulation and was not perturbed by sustained iron chelation (deferiprone). Iron accumulation in senescent cells was driven by impaired ferritinophagy, a lysosomal process that promotes ferritin degradation and ferroptosis. Lysosomal dysfunction in senescent cells was confirmed through several markers, including the build-up of microtubule-associated protein light chain 3 (LC3-II) in autophagosomes. Impaired ferritin degradation explains the iron accumulation phenotype of senescent cells, whereby iron is effectively trapped in ferritin creating a perceived cellular deficiency. Accordingly, senescent cells were highly resistant to ferroptosis. Promoting ferritin degradation by using the autophagy activator rapamycin averted the iron accumulation phenotype of senescent cells, preventing the increase of TfR1, ferritin and intracellular iron, but failed to re-sensitize these cells to ferroptosis. Finally, the enrichment of senescent cells in mouse ageing hepatic tissue was found to accompany iron accumulation, an elevation in ferritin and mirrored our observations using cultured senescent cells.

The Transcriptional Landscape of Radiation-Treated Human Prostate Cancer: Analysis of a Prospective Tissue Cohort.

PURPOSE: The resistance of prostate cancer to radiation therapy (RT) is a significant clinical issue and still largely unable to be guided by patient-specific molecular characteristics. The present study describes the gene expression changes induced in response to RT in human prostate tissue obtained from a prospective tissue acquisition study designed for radiobiology research. METHODS AND MATERIALS: A prospective cohort of 5 men with intermediate-risk and clinically localized tumors were treated with high-dose-rate brachytherapy with 2 × 10-Gy fractions. Image-guided transperineal biopsy specimens were taken immediately before and 14 days after the first high-dose-rate brachytherapy fraction. Using genome-wide 3' RNA sequencing on total RNA extracted from 10 biopsy specimens, we obtained quantitative expression data for a median of 13,244 genes. We computed the fold-change information for each gene and extracted high-confidence lists of transcripts with either increased or decreased expression (≥1.5-fold) after radiation in ≥4 of the 5 patients. Several gene ontology analyses were then used to identify functionally enriched pathways. RESULTS: The predominant change in response to RT was elevation of the transcript levels, including that of DNA damage binding protein 2 and p21, and collagens, laminins, and integrins. We observed strong upregulation of the p53 pathway, without observable dysregulation of p53 itself. Interstitial remodeling, extracellular matrix proteins, and focal adhesion pathways were also strongly upregulated, as was inflammation. Functional network analysis showed clustering of the changes inherent in apoptosis and programmed cell death, extracellular matrix organization, and immune regulation. CONCLUSIONS: In the present prospective study of matched clinical tissues, we successfully recognized known radiation-sensitive transcriptional pathways and identified numerous other novel and significantly altered genes with no current association with RT. These data could be informative in the development of future personalized therapeutic agents.

E6AP promotes prostate cancer by reducing p27 expression.

Prostate cancer (PC) is the most common cancer in men. Elevated levels of E3 ligase, E6-Associated Protein (E6AP) were previously linked to PC, consistent with increased protein expression in a subset of PC patients. In cancers, irregular E3 ligase activity drives proteasomal degradation of tumor suppressor proteins. Accordingly, E3 ligase inhibitors define a rational therapy to restore tumor suppression. The relevant tumor suppressors targeted by E6AP in PC are yet to be fully identified. In this study we show that p27, a key cell cycle regulator, is a target of E6AP in PC. Down regulation of E6AP increases p27 expression and enhances its nuclear accumulation in PC. We demonstrate that E6AP regulates p27 expression by inhibiting its transcription in an E2F1-dependent manner. Concomitant knockdown of E6AP and p27 partially restores PC cell growth, supporting the contribution of p27 to the overall effect of E6AP on prostate tumorigenesis. Overall, we unravelled the E6AP-p27 axis as a new promoter of PC, exposing an attractive target for therapy through the restoration of tumor suppression.

MDM4 is a rational target for treating breast cancers with mutant p53.

Mutation of the key tumour suppressor p53 defines a transition in the progression towards aggressive and metastatic breast cancer (BC) with the poorest outcome. Specifically, the p53 mutation frequency exceeds 50% in triple-negative BC. Key regulators of mutant p53 that facilitate its oncogenic functions are potential therapeutic targets. We report here that the MDM4 protein is frequently abundant in the context of mutant p53 in basal-like BC samples. Importantly, we show that MDM4 plays a critical role in the proliferation of these BC cells. We demonstrate that conditional knockdown (KD) of MDM4 provokes growth inhibition across a range of BC subtypes with mutant p53, including luminal, Her2+ and triple-negative BCs. In vivo, MDM4 was shown to be crucial for the establishment and progression of tumours. This growth inhibition was mediated, at least in part, by the cell cycle inhibitor p27. Depletion of p27 together with MDM4 KD led to recovery of the proliferative capacity of cells that were growth-inhibited by MDM4 KD alone. Consistently, we identified low levels of p27 expression in basal-like tumours corresponding to high levels of MDM4 and p53. This predicts a signature for a subset of tumours that may be amenable to therapies targeted towards MDM4 and mutant p53. The therapeutic potential of MDM4 as a target in BC with mutant p53 was shown in vitro by use of a small-molecule inhibitor. Overall, our study supports MDM4 as a novel therapeutic target for BC expressing mutant p53. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Reduced abundance of the E3 ubiquitin ligase E6AP contributes to decreased expression of the INK4/ARF locus in non-small cell lung cancer.

The tumor suppressor p16INK4a, one protein encoded by the INK4/ARF locus, is frequently absent in multiple cancers, including non-small cell lung cancer (NSCLC). Whereas increased methylation of the encoding gene (CDKN2A) accounts for its loss in a third of patients, no molecular explanation exists for the remainder. We unraveled an alternative mechanism for the silencing of the INK4/ARF locus involving the E3 ubiquitin ligase and transcriptional cofactor E6AP (also known as UBE3A). We found that the expression of three tumor suppressor genes encoded in the INK4/ARF locus (p15INK4b, p16INK4a, and p19ARF) was decreased in E6AP-/- mouse embryo fibroblasts. E6AP induced the expression of the INK4/ARF locus at the transcriptional level by inhibiting CDC6 transcription, a gene encoding a key repressor of the locus. Luciferase assays revealed that E6AP inhibited CDC6 expression by reducing its E2F1-dependent transcription. Chromatin immunoprecipitation analysis indicated that E6AP reduced the amount of E2F1 at the CDC6 promoter. In a subset of NSCLC samples, an E6AP-low/CDC6-high/p16INK4a-low protein abundance profile correlated with low methylation of the gene encoding p16INK4a (CDKN2A) and poor patient prognosis. These findings define a previously unrecognized tumor-suppressive role for E6AP in NSCLC, reveal an alternative silencing mechanism of the INK4/ARF locus, and reveal E6AP as a potential prognostic marker in NSCLC.

Ubiquitin ligase E6AP mediates nonproteolytic polyubiquitylation of ß-catenin independent of the E6 oncoprotein.

Recently, we showed that the ubiquitin ligase E6AP stabilizes ß-catenin and activates its transcriptional activity. These activities were enhanced by the human papillomavirus (HPV) E6 protein. In the present study, we explored the function of E6AP, which increases ß-catenin stabilization and transcriptional activation. Here, we report that E6AP interacts with ß-catenin and mediates its nonproteolytic ubiquitylation, as evidenced in transiently transfected cell-based and in vitro reconstitution ubiquitylation assays. Overexpression of E6AP increased ß-catenin polyubiquitylation and, consistent with that, knockdown or knock-out of E6AP expression reduced ß-catenin polyubiquitylation. The ubiquitylation of ß-catenin by E6AP was dependent on its E3 ubiquitin ligase activity, but it was proteasome-independent and did not require HPV-E6, phosphorylation of ß-catenin by glycogen synthase kinase 3ß (GSK3ß) or activity of the ß-catenin 'destruction complex'. We also show that transcriptional activation of ß-catenin by E6AP is coupled with ß-catenin protein stabilization, but not its ubiquitylation. In contrast to ß-catenin ubiquitylation, ß-catenin protein stability and its transcriptional activity were absolutely dependent on the activity of the destruction complex and phosphorylation by GSK3ß. Collectively, our data uncover a dual role for E6AP in the regulation of ß-catenin ubiquitylation, stability and transcriptional activity, with HPV-E6 enhancing only part of E6AP activities.

PML tumour suppression and beyond: therapeutic implications.

Recognition of the tumour suppressive capacity of the Promyelocytic Leukemia protein (PML) has emerged beyond its identification through APL, to a broad spectrum of tumors. This ability has chiefly been linked to its role as a core component of dynamic structures termed PML Nuclear Bodies (PML-NBs). In response to a variety of stresses, key factors and their molecular modifiers are recruited to PML-NBs, where activating modifications are facilitated, leading to a cellular stress response. PML was also found to perform anti-tumourigenic functions through cytoplasmic activities. Surprisingly, important recent research defined growth promoting capabilities of PML, which significantly challenges the notion of a 'classic' tumour suppressor. Through metabolic reprogramming, PML can afford a selective advantage for tumor cells in certain settings. The multiple forms in which PML exists are the likely explanation of this functional diversity. This behavioral ambiguity however raises a significant challenge to the design of strategies to therapeutically target PML. In this review we discuss this change of paradigm in the PML field and its ramifications, particularly for tailoring cancer therapies.

LIMK2 mediates resistance to chemotherapeutic drugs in neuroblastoma cells through regulation of drug-induced cell cycle arrest.

Drug resistance is a major obstacle for the successful treatment of many malignancies, including neuroblastoma, the most common extracranial solid tumor in childhood. Therefore, current attempts to improve the survival of neuroblastoma patients, as well as those with other cancers, largely depend on strategies to counter cancer cell drug resistance; hence, it is critical to understand the molecular mechanisms that mediate resistance to chemotherapeutics. The levels of LIM-kinase 2 (LIMK2) are increased in neuroblastoma cells selected for their resistance to microtubule-targeted drugs, suggesting that LIMK2 might be a possible target to overcome drug resistance. Here, we report that depletion of LIMK2 sensitizes SHEP neuroblastoma cells to several microtubule-targeted drugs, and that this increased sensitivity correlates with enhanced cell cycle arrest and apoptosis. Furthermore, we show that LIMK2 modulates microtubule acetylation and the levels of tubulin Polymerization Promoting Protein 1 (TPPP1), suggesting that LIMK2 may participate in the mitotic block induced by microtubule-targeted drugs through regulation of the microtubule network. Moreover, LIMK2-depleted cells also show an increased sensitivity to certain DNA-damage agents, suggesting that LIMK2 might act as a general pro-survival factor. Our results highlight the exciting possibility of combining specific LIMK2 inhibitors with anticancer drugs in the treatment of multi-drug resistant cancers.

Tubulin polymerization promoting protein 1 (TPPP1) increases ß-catenin expression through inhibition of HDAC6 activity in U2OS osteosarcoma cells.

The Rho-associated coiled-coil kinase (ROCK) family of proteins, including ROCK1 and ROCK2, are key regulators of actin and intermediate filament morphology. The newly discovered ROCK substrate Tubulin polymerization promoting protein 1 (TPPP1) promotes microtubule polymerization and inhibits the activity of Histone deacetylase 6 (HDAC6). The effect of TPPP1 on HDAC6 activity is inhibited by ROCK signaling. Moreover, it was recently demonstrated that ROCK activity increases the cellular expression of the oncogene ß-catenin, which is a HDAC6 substrate. In this study, we investigated the interplay between ROCK-TPPP1-HDAC6 signaling and ß-catenin expression. We demonstrate that ß-catenin expression is increased with ROCK signaling activation and is reduced with increased TPPP1 expression in U2OS cells. Further investigation revealed that ROCK-mediated TPPP1 phosphorylation, which prevents its binding to HDAC6, negates TPPP1-mediated reduction in ß-catenin expression. We also show that increased HDAC6 activity resulting from ROCK signaling activation reduced ß-catenin acetylation at Lys-49, which was also accompanied by its decreased phosphorylation by Caesin kinase 1 (CK1) and Glycogen synthase kinase 3ß (GSK3ß), thus preventing its proteasomal degradation. Overall, our results suggest that ROCK regulates ß-catenin stability in cells via preventing TPPP1-mediated inhibition of HDAC6 activity, to reduce its acetylation and degradation via phosphorylation by CK1 and GSK3ß.