A novel cofactor for p300 that regulates the p53 response

WHAMM functions in kidney reabsorption and polymerizes actin to promote autophagosomal membrane closure and cargo sequestration

The actin cytoskeleton is essential for many functions of eukaryotic cells, but the factors that nucleate actin assembly are not well understood at the organismal level or in the context of disease. To explore the function of the actin nucleation factor WHAMM in mice, we examined how Whamm inactivation impacts kidney physiology and cellular proteostasis. We show that male WHAMM knockout mice excrete elevated levels of albumin, glucose, phosphate, and amino acids, and display structural abnormalities of the kidney proximal tubule, suggesting that WHAMM activity is important for nutrient reabsorption. In kidney tissue, the loss of WHAMM results in the accumulation of the lipidated autophagosomal membrane protein LC3, indicating an alteration in autophagy. In mouse fibroblasts and human proximal tubule cells, WHAMM and its binding partner the Arp2/3 complex control autophagic membrane closure and cargo receptor recruitment. These results reveal a role for WHAMM-mediated actin assembly in maintaining kidney function and promoting proper autophagosome membrane remodeling.

Autophagosome turnover requires Arp2/3 complex-mediated maintenance of lysosomal integrity

Autophagy is an intracellular degradation process that maintains homeostasis, responds to stress, and plays key roles in the prevention of aging and disease. Autophagosome biogenesis, vesicle rocketing, and autolysosome tubulation are controlled by multiple actin nucleation factors, but the impact of actin assembly on completion of the autophagic pathway is not well understood. Here we studied autophagosome and lysosome remodeling in fibroblasts harboring an inducible knockout (iKO) of the Arp2/3 complex, an essential actin nucleator. Arp2/3 complex ablation resulted in increased basal levels of autophagy receptors and lipidated membrane proteins from the LC3 and GABARAP families. Under both steady-state and starvation conditions, Arp2/3 iKO cells accumulated abnormally high numbers of autolysosomes, suggesting a defect in autophagic flux. The inability of Arp2/3 complex-deficient cells to complete autolysosome degradation and turnover is explained by the presence of damaged, leaky lysosomes. In cells treated with an acute lysosomal membrane-damaging agent, the Arp2/3-activating protein WHAMM is recruited to lysosomes, where Arp2/3 complex-dependent actin assembly is crucial for restoring intact lysosomal structure. These results establish the Arp2/3 complex as a central player late in the canonical autophagy pathway and reveal a new role for the actin nucleation machinery in maintaining lysosomal integrity.

NPFs-mediated actin cytoskeleton: a new viewpoint on autophagy regulation

Macroautophagy/autophagy is a lysosome-dependent catabolic process induced by various cellular stress conditions, maintaining the homeostasis of cells, tissues and organs. Autophagy is a series of membrane-related events involving multiple autophagy-related (ATG) proteins. Most studies to date have focused on various signaling pathways affecting ATG proteins to control autophagy. However, mounting evidence reveals that the actin cytoskeleton acts on autophagy-associated membranes to regulate different events of autophagy. The actin cytoskeleton assists in vesicle formation and provides the mechanical forces for cellular activities that involve membrane deformation. Although the interaction between the actin cytoskeleton and membrane makes the role of actin in autophagy recognized, how the actin cytoskeleton is recruited and assembles on membranes during autophagy needs to be detailed. Nucleation-promoting factors (NPFs) activate the Arp2/3 complex to produce actin cytoskeleton. In this review, we summarize the important roles of the actin cytoskeleton in autophagy regulation and focus on the effect of NPFs on actin cytoskeleton assembly during autophagy, providing new insights into the occurrence and regulatory mechanisms of autophagy. Video Abstract.

WHAMM functions in kidney reabsorption and polymerizes actin to promote autophagosomal membrane closure and cargo sequestration

The actin cytoskeleton is essential for many functions of eukaryotic cells, but the factors that nucleate actin assembly are not well understood at the organismal level or in the context of disease. To explore the function of the actin nucleation factor WHAMM in mice, we examined how Whamm inactivation impacts kidney physiology and cellular proteostasis. We show that male WHAMM knockout mice excrete elevated levels of albumin, glucose, phosphate, and amino acids, and display abnormalities of the kidney proximal tubule, suggesting that WHAMM activity is important for nutrient reabsorption. In kidney tissue, the loss of WHAMM results in the accumulation of the lipidated autophagosomal membrane protein LC3, indicating an alteration in autophagy. In mouse fibroblasts and human proximal tubule cells, WHAMM and its binding partner the Arp2/3 complex control autophagic membrane closure and cargo receptor recruitment. These results reveal a role for WHAMM-mediated actin assembly in maintaining kidney function and promoting proper autophagosome membrane remodeling.

p53-dependent DNA repair during the DNA damage response requires actin nucleation by JMY

The tumour suppressor p53 is a nuclear transcription factor with key roles during DNA damage to enable a variety of cellular responses including cell cycle arrest, apoptosis and DNA repair. JMY is an actin nucleator and DNA damage-responsive protein whose sub-cellular localisation is responsive to stress and during DNA damage JMY undergoes nuclear accumulation. To gain an understanding of the wider role for nuclear JMY in transcriptional regulation, we performed transcriptomics to identify JMY-mediated changes in gene expression during the DNA damage response. We show that JMY is required for effective regulation of key p53 target genes involved in DNA repair, including XPC, XRCC5 (Ku80) and TP53I3 (PIG3). Moreover, JMY depletion or knockout leads to increased DNA damage and nuclear JMY requires its Arp2/3-dependent actin nucleation function to promote the clearance of DNA lesions. In human patient samples a lack of JMY is associated with increased tumour mutation count and in cells results in reduced cell survival and increased sensitivity to DNA damage response kinase inhibition. Collectively, we demonstrate that JMY enables p53-dependent DNA repair under genotoxic stress and suggest a role for actin in JMY nuclear activity during the DNA damage response.

Branching out in different directions: Emerging cellular functions for the Arp2/3 complex and WASP-family actin nucleation factors

The actin cytoskeleton impacts practically every function of a eukaryotic cell. Historically, the best-characterized cytoskeletal activities are in cell morphogenesis, motility, and division. The structural and dynamic properties of the actin cytoskeleton are also crucial for establishing, maintaining, and changing the organization of membrane-bound organelles and other intracellular structures. Such activities are important in nearly all animal cells and tissues, although distinct anatomical regions and physiological systems rely on different regulatory factors. Recent work indicates that the Arp2/3 complex, a broadly expressed actin nucleator, drives actin assembly during several intracellular stress response pathways. These newly described Arp2/3-mediated cytoskeletal rearrangements are coordinated by members of the Wiskott-Aldrich Syndrome Protein (WASP) family of actin nucleation-promoting factors. Thus, the Arp2/3 complex and WASP-family proteins are emerging as crucial players in cytoplasmic and nuclear activities including autophagy, apoptosis, chromatin dynamics, and DNA repair. Characterizations of the functions of the actin assembly machinery in such stress response mechanisms are advancing our understanding of both normal and pathogenic processes, and hold great promise for providing insights into organismal development and interventions for disease.

The p53 and Calcium Regulated Actin Rearrangement in Model Cells

Long-term cellular stress maintains high intracellular Ca²⁺ concentrations which ultimately initiates apoptosis. Our interest is focused on how the gelsolin (GSN) and junctional mediating and regulating Y protein (JMY) play important roles in stress response. Both of these proteins can bind p53 and actin. We investigated using in vitro fluorescence spectroscopy and found that the p53 competes with actin in GSN to inhibit p53–JMY complex formation. A high Ca²⁺ level initializes p53 dimerization; the dimer competes with actin on JMY, which can lead to p53–JMY cotransport into the nucleus. Here we investigated how the motility and division rate of HeLa cells changes due to low-voltage electroporation of GSN or JMY in scratching assays. We revealed that JMY inhibits their motion, but that it can accelerate the cell division. GSN treatment slows down cell division but does not affect cell motility. HeLa cells fully recovered the gap 20 h after the electroporation with JMY and then started to release from the glass slides. Taken together, our in vitro results indicate that GSN and JMY may play an important role in the cellular stress response.

WASP family proteins: Molecular mechanisms and implications in human disease

Proteins of the Wiskott-Aldrich syndrome protein (WASP) family play a central role in regulating actin cytoskeletal dynamics in a wide range of cellular processes. Genetic mutations or misregulation of these proteins are tightly associated with many diseases. The WASP-family proteins act by transmitting various upstream signals to their conserved WH2-Central-Acidic (WCA) peptide sequence at the C-terminus, which in turn binds to the Arp2/3 complex to stimulate the formation of branched actin networks at membranes. Despite this common feature, the regulatory mechanisms and cellular functions of distinct WASP-family proteins are very different. Here, we summarize and clarify our current understanding of WASP-family proteins and how disruption of their functions is related to human disease.

Evaluation of the Role of p53 Tumour Suppressor Posttranslational Modifications and TTC5 Cofactor in Lung Cancer

Mutations in the p53 tumor suppressor are found in over 50% of cancers. p53 function is controlled through posttranslational modifications and cofactor interactions. In this study, we investigated the posttranslationally modified p53, including p53 acetylated at lysine 382 (K382), p53 phosphorylated at serine 46 (S46), and the p53 cofactor TTC5/STRAP (Tetratricopeptide repeat domain 5/ Stress-responsive activator of p300-TTC5) proteins in lung cancer. Immunohistochemical (IHC) analysis of lung cancer tissues from 250 patients was carried out and the results were correlated with clinicopathological features. Significant associations between total or modified p53 with a higher grade of the tumour and shorter overall survival (OS) probability were detected, suggesting that mutant and/or modified p53 acts as an oncoprotein in these patients. Acetylated at K382 p53 was predominantly nuclear in some samples and cytoplasmic in others. The localization of the K382 acetylated p53 was significantly associated with the gender and grade of the disease. The TTC5 protein levels were significantly associated with the grade, tumor size, and node involvement in a complex manner. SIRT1 expression was evaluated in 50 lung cancer patients and significant positive correlation was found with p53 S46 intensity, whereas negative TTC5 staining was associated with SIRT1 expression. Furthermore, p53 protein levels showed positive association with poor OS, whereas TTC5 protein levels showed positive association with better OS outcome. Overall, our results indicate that an analysis of p53 modified versions together with TTC5 expression, upon testing on a larger sample size of patients, could serve as useful prognostic factors or drug targets for lung cancer treatment.

The role of microRNA-21 in the onset and progression of cancer

MicroRNAs (miRNAs), a class of small noncoding RNA, posttranscriptionally regulate the expression of genes. Aberrant expression of miRNA is reported in various types of cancer. Since the first report of oncomiR-21 involvement in the glioma, its upregulation was reported in multiple cancers and was allied with high oncogenic property. In addition to the downregulation of tumor suppressor genes, the miR-21 is also associated with cancer resistance to various chemotherapy. The recent research is appraising miR-21 as a promising cancer target and biomarker for early cancer detection. In this review, we briefly explain the biogenesis and regulation of miR-21 in cancer cells. Additionally, the review features the assorted genes/pathways regulated by the miR-21 in various cancer and cancer stem cells.

The actin nucleation factors JMY and WHAMM enable a rapid Arp2/3 complex-mediated intrinsic pathway of apoptosis

The actin cytoskeleton is a well-known player in most vital cellular processes, but comparably little is understood about how the actin assembly machinery impacts programmed cell death pathways. In the current study, we explored roles for the human Wiskott-Aldrich Syndrome Protein (WASP) family of actin nucleation factors in DNA damage-induced apoptosis. Inactivation of each WASP-family gene revealed that two of them, JMY and WHAMM, are necessary for rapid apoptotic responses. JMY and WHAMM participate in a p53-dependent cell death pathway by enhancing mitochondrial permeabilization, initiator caspase cleavage, and executioner caspase activation. JMY-mediated apoptosis requires actin nucleation via the Arp2/3 complex, and actin filaments are assembled in cytoplasmic territories containing clusters of cytochrome c and active caspase-3. The loss of JMY additionally results in significant changes in gene expression, including upregulation of the WHAMM-interacting G-protein RhoD. Depletion or deletion of RHOD increases cell death, suggesting that RhoD normally contributes to cell survival. These results give rise to a model in which JMY and WHAMM promote intrinsic cell death responses that can be opposed by RhoD.

Photobiomodulation therapy drives massive epigenetic histone modifications, stem cells mobilization and accelerated epithelial healing

Emerging evidence indicates the clinical benefits of photobiomodulation therapy (PBMT) in the management of skin and mucosal wounds. Here, we decided to explore the effects of different regiments of PBMT on epithelial cells and stem cells, and the potential implications over the epigenetic circuitry during healing. Scratch-wound migration, immunofluorescence (anti-acetyl-Histone H3, anti-acetyl-CBP/p300 and anti-BMI1), nuclear morphometry and western blotting (anti-Phospho-S6, anti-methyl-CpG binding domain protein 2 [MBD2]) were performed. Epithelial stem cells were identified by the aldehyde dehydrogenase enzymatic levels and sphere-forming assay. We observed that PBMT-induced accelerated epithelial migration and chromatin relaxation along with increased levels of histones acetylation, the transcription cofactors CBP/p300 and mammalian target of rapamycin. We further observed a reduction of the transcription repression-associated protein MBD2 and a reduced number of epithelial stem cells and spheres. In this study, we showed that PBMT could induce epigenetic modifications of epithelial cells and control stem cell fate, leading to an accelerated healing phenotype.

Using TUNEL Assay to Quantitate p53-Induced Apoptosis in Mouse Tissues

Critical to tumor surveillance in eukaryotic cells is the ability to perceive and respond to DNA damage. p53, fulfills its role as "guardian of the genome" by either arresting cells in the cell cycle in order to allow time for repair of DNA damage or regulating a process of programmed cell death known as apoptosis. This process will eliminate cells that have suffered severe damage from intrinsic or extrinsic factors such as X-ray irradiation or chemotherapeutic drug treatments that include doxorubicin, etoposide, cisplatin, and methotrexate. Assays designed to specifically detect cells undergoing programmed cell death are essential in defining the tissue specific responses to tumor therapy treatment, tissue damage, or degenerative processes. This chapter will delineate the TUNEL (terminal deoxynucleotidyl transferase nick-end labeling) assay that is used for the rapid detection of 3' OH ends of DNA that are generated during apoptosis.

The HIF1α/JMY pathway promotes glioblastoma stem-like cell invasiveness after irradiation

Human glioblastoma (GBM) is the most common primary malignant brain tumor. A minor subpopulation of cancer cells, known as glioma stem-like cells (GSCs), are thought to play a major role in tumor relapse due to their stem cell-like properties, their high resistance to conventional treatments and their high invasion capacity. We show that ionizing radiation specifically enhances the motility and invasiveness of human GSCs through the stabilization and nuclear accumulation of the hypoxia-inducible factor 1α (HIF1α), which in turn transcriptionally activates the Junction-mediating and regulatory protein (JMY). Finally, JMY accumulates in the cytoplasm where it stimulates GSC migration via its actin nucleation-promoting activity. Targeting JMY could thus open the way to the development of new therapeutic strategies to improve the efficacy of radiotherapy and prevent glioma recurrence.

Actin regulators in cancer progression and metastases: From structure and function to cytoskeletal dynamics

The cytoskeleton is a central factor contributing to various hallmarks of cancer. In recent years, there has been increasing evidence demonstrating the involvement of actin regulatory proteins in malignancy, and their dysregulation was shown to predict poor clinical prognosis. Although enhanced cytoskeletal activity is often associated with cancer progression, the expression of several inducers of actin polymerization is remarkably reduced in certain malignancies, and it is not completely clear how these changes promote tumorigenesis and metastases. The complexities involved in cytoskeletal induction of cancer progression therefore pose considerable difficulties for therapeutic intervention; it is not always clear which cytoskeletal regulator should be targeted in order to impede cancer progression, and whether this targeting may inadvertently enhance alternative invasive pathways which can aggravate tumor growth. The entire constellation of cytoskeletal machineries in eukaryotic cells are numerous and complex; the system is comprised of and regulated by hundreds of proteins, which could not be covered in a single review. Therefore, we will focus here on the actin cytoskeleton, which encompasses the biological machinery behind most of the key cellular functions altered in cancer, with specific emphasis on actin nucleating factors and nucleation-promoting factors. Finally, we discuss current therapeutic strategies for cancer which aim to target the cytoskeleton.

Bi-allelic TTC5 variants cause delayed developmental milestones and intellectual disability

BACKGROUND

Intellectual disability syndromes (IDSs) with or without developmental delays affect up to 3% of the world population. We sought to clinically and genetically characterise a novel IDS segregating in five unrelated consanguineous families.

METHODS

Clinical analyses were performed for eight patients with intellectual disability (ID). Whole-exome sequencing for selected participants followed by Sanger sequencing for all available family members was completed. Identity-by-descent (IBD) mapping was carried out for patients in two Egyptian families harbouring an identical variant. RNA was extracted from blood cells of Turkish participants, followed by cDNA synthesis and real-time PCR for TTC5.

RESULTS

Phenotype comparisons of patients revealed shared clinical features of moderate-to-severe ID, corpus callosum agenesis, mild ventriculomegaly, simplified gyral pattern, cerebral atrophy, delayed motor and verbal milestones and hypotonia, presenting with an IDS. Four novel homozygous variants in TTC5: c.629A>G;p.(Tyr210Cys), c.692C>T;p.(Ala231Val), c.787C>T;p.(Arg263Ter) and c.1883C>T;p.(Arg395Ter) were identified in the eight patients from participating families. IBD mapping revealed that c.787C>T;p.(Arg263Ter) is a founder variant in Egypt. Missense variants c.629A>G;p.(Tyr210Cys) and c.692C>T;p.(Ala231Val) disrupt highly conserved residues of TTC5 within the fifth and sixth tetratricopeptide repeat motifs which are required for p300 interaction, while the nonsense variants are predicted to decrease TTC5 expression. Functional analysis of variant c.1883C>T;p.(Arg395Ter) showed reduced TTC5 transcript levels in accordance with nonsense-mediated decay.

CONCLUSION

Combining our clinical and molecular data with a recent case report, we identify the core and variable clinical features associated with TTC5 loss-of-function variants and reveal the requirement for TTC5 in human brain development and health.

Role of Junction-Mediating and Regulatory Protein in the Pathogenesis of Glucocorticoid-Induced Endothelial Cell Lesions

Objective

Nontraumatic osteonecrosis of the femoral head (ONFH) is one of the most common diseases in orthopaedics. The damage to vascular endothelial (VE) cells caused by glucocorticoids (GC) has been reported as a possible mechanism of pathogenesis for ONFH. Junction‐mediating and regulatory protein (JMY), originally identified as a p53 coactivator, plays prominent roles in the DNA damage response and in cell motility. This study aimed to discover the role of JMY in the pathogenesis of GC‐induced endothelial cell lesions.

Methods

High‐throughput RNA sequencing was performed to identify the differentially expressed genes between GC‐treated human umbilical vein endothelial cells (HUVEC) and control cells. JMY knockdown and overexpressing HUVEC lines were treated with GC. Cell proliferation was examined with a survival cell count assay (Cell Counting Kit‐8, CCK‐8); cell apoptosis was measured by flow cytometry; a scarification assay was used to detect the capability of cell migration; a Transwell chamber assay was done to detect the cell motility . Differential expression of cell protein was detected by western blot.

Results

A total of 1561 differential genes were obtained through transcription sequencing, of which 789 mRNA were upregulated and 772 mRNA were downregulated in the GC‐treated HUVEC compared with the control cells. CCK‐8 assay results showed that: without GC treatment, overexpression or knockdown of JMY did not affect the proliferation activity of HUVEC. In the presence of GC treatment, the proliferation activity of HUVEC in the JMY knockdown group was significantly higher than that in the control group (P < 0.01). The proliferation activity of HUVEC in the overexpression JMY group was significantly lower than that in the control group (P < 0.01). The results of flow cytometry showed that without GC treatment, overexpression or knockdown of JMY did not affect the apoptosis proportion of HUVEC. With GC treatment, the apoptosis proportion of HUVEC in the JMY knockdown group was significantly lower than that in the control group (P < 0.01), and the apoptosis proportion of HUVEC in the overexpression JMY group was significantly higher than that in the control group (P < 0.01). Western blot results showed that with GC treatment, the JMY expression level of HUVEC increased with the reaction time. Moreover, the distribution of JMY was mainly concentrated in the nucleus. The expression level of Bax also increased with the reaction time. With GC treatment, overexpression of JMY could significantly increase the expression of Bax in HUVEC. JMY knockdown could reduce the expression of Bax in HUVEC. In the absence of GC treatment, HUVEC overexpression or knockdown of JMY did not affect the expression of Bax. The results of scarification and Transwell chamber assays showed that: without GC treatment, JMY knockdown could significantly decrease the cell motility and increase the expression level of VE‐cadherin in HUVEC; with GC treatment, JMY knockdown in HUVEC had lower cell motility compared with the control group (P < 0.01).

Conclusion

Glucocorticoids can induce the HUVEC apoptosis, and reduce its proliferation, cell motility. Our results mainly confirmed the role of JMY in the pathogenesis of GC‐inducing lesions in HUVEC. GC act on HUVEC, inducing cell damage. Following the event of cell damage, JMY levels upregulate in the nucleus to induce transcription of Bax, triggering apoptosis. JMY can also regulate HUVEC motility via its regulation of VE‐cadherin levels.

The prognostic capacities of CBP and p300 in locally advanced rectal cancer

Background

CREB-binding protein (CBP) and p300 represent histone acetyltransferases (HATs) and transcriptional coactivators that play essential roles in tumour initiation and progression. Both proteins are generally thought to function as tumour suppressors, although their distinct roles in colorectal cancer (CRC) remain inconsistent and ambiguous.

Thus, we analysed the expression of these two HATs in human tissue samples from patients with locally advanced rectal cancer via immunohistochemistry and evaluated their potential impacts on future CRC diagnosis and treatment.

Methods

In our analysis, we included ninety-three (n = 93) patients diagnosed with adenocarcinoma in the upper third of the rectum. None of the patients received preoperative chemoradiotherapy, but the patients did undergo primary resection of the tumour within the phase II GAST-05 trial. By using H-scores, the expression of both proteins was visualised via immunohistochemistry in resected specimens from the patients. CBP and p300 expression were correlated with clinical and follow-up data.

Results

Our analysis showed that high expression of CBP was significantly associated with prolonged cancer-specific survival (CSS; p = 0.002). In univariate analysis, CBP was an independent prognostic parameter for CSS (p = 0.042). High nuclear CBP expression was observed in two-thirds of patients. In contrast, we could not find any significant correlation between the expression of p300 and cancer-specific survival in this cohort of patients (p = 0.09). We did not observe any cooperation between CBP and p300 in our analysis.

Conclusions

High expression of CBP was significantly associated with improved oncological outcomes. This finding could help to stratify patients in the future for CRC treatment. Histone deacetylase (HDAC) inhibitors are increasingly playing a role in oncological treatment and could additionally become therapeutic options in CRC. Our findings need to be further evaluated and verified in future clinical analyses.

A Maternal Transcription Factor, Junction Mediating and Regulatory Protein is Required for Preimplantation Development in the Mouse

Junction-mediating and regulatory protein (JMY) is a regulator of both transcription and actin filament assembly. The actin-regulatory activity of JMY is based on a cluster of three actin-binding Wiskott-Aldrich syndrome protein homology 2 (WH2) domains that nucleate actin filaments directly and promote nucleation of the Arp2/3 complex. In addition to these activities, we examined the activity of JMY generation in early embryo of mice carrying mutations in the JMY gene by CRISPR/Cas9 mediated genome engineering. We demonstrated that JMY protein shuttled expression between the cytoplasm and the nucleus. Knockout of exon 2, CA (central domain and Arp2/3-binding acidic domain) and NLS-2 (nuclear localization signal domain) on the JMY gene by CRISPR/Cas9 system was effective and markedly impeded embryonicdevelopment. Additionally, it impaired transcription and zygotic genome activation (ZGA)-related genes. These results suggest that JMY acts as a transcription factor, which is essential for the early embryonic development in mice.

Prognostic role of upregulated P300 expression in human cancers: A clinical study of synovial sarcoma and a meta-analysis

E1A binding protein p300 (P300) is a member of the histone acetyltransferase family of transcriptional co-activators, which are associated with various types of cancer. Numerous studies have evaluated the diagnostic value of P300, but their results are not consistent. Therefore, a clinical study and a meta-analysis were performed in the present study to investigate the prognostic value of P300 expression in human malignant neoplasms. Immunohistochemical (IHC) analysis was used to assess P300 expression in 43 paraffin-embedded primary synovial sarcoma (SS) samples. For the meta-analysis, eligible studies published until January 21, 2018 were identified by searching the PubMed, EMBASE and Web of Science databases. The IHC analysis indicated a high P300 expression rate in 33.3% (10/30) of biphasic SS (BSSs) and in 60% (6/10) of monophasic fibrous SS tissues. In BSS, the expression rate was significantly higher in the epithelial component (80.0%, 24/30) than that in the spindle-cell component (30.0%, 9/30; P<0.05). The meta-analysis indicated that high expression of P300 was associated with poor overall survival (OS) in digestive system malignant neoplasms (HR=1.54, 95% CI: 1.20-2.23), as well as with poor progression-free survival, recurrence-free survival and disease-free survival combined (HR=1.84, 95% CI: 1.36-2.47). Analysis of subgroups by ethnicity demonstrated that high expression of P300 was associated with poor OS in Asians (HR=1.72, 95% CI: 1.20-2.47) but favourable OS in Caucasians (HR=0.59, 95% CI: 0.47-0.73). Furthermore, high expression of P300 was associated with clinical stage [Relative Risk (RR)=1.30, 95% CI: 1.07-1.58], lymph node metastasis (RR=1.30, 95% CI: 1.03-1.64) and depth of invasion (RR=1.31, 95% CI: 1.07-1.60). P300 expression may therefore be a useful biomarker for predicting patient prognosis in various types of human cancer.

Cyclin C Regulated Oxidative Stress Responsive Transcriptome in Mus musculus Embryonic Fibroblasts

The transcriptional changes that occur in response to oxidative stress help direct the decision to maintain cell viability or enter a cell death pathway. Cyclin C-Cdk8 is a conserved kinase that associates with the RNA polymerase II Mediator complex that stimulates or represses transcription depending on the locus. In response to oxidative stress, cyclin C, but not Cdk8, displays partial translocation into the cytoplasm. These findings open the possibility that cyclin C relocalization is a regulatory mechanism governing oxidative stress-induced transcriptional changes. In the present study, the cyclin C-dependent transcriptome was determined and compared to transcriptional changes occurring in oxidatively stressed Mus musculus embryonic fibroblasts. We observed a similar number (∼2000) of genes up or downregulated in oxidatively stressed cells. Induced genes include cellular repair/survival factors while repressed loci were generally involved in proliferation or differentiation. Depleting cyclin C in unstressed cells produced an approximately equal number of genes (∼2400) that were repressed by, or whose transcription required, cyclin C. Consistent with the possibility that cyclin C nuclear release contributes to transcriptional remodeling in response to oxidative stress, we found that 37% cyclin C-dependent genes were downregulated following stress. Moreover, 20% of cyclin C- repressed genes were induced in response to stress. These findings are consistent with a model that cyclin C relocalization to the cytoplasm, and corresponding inactivation of Cdk8, represents a regulatory mechanism to repress and stimulate transcription of stress-responsive genes.

LC3 and STRAP regulate actin filament assembly by JMY during autophagosome formation

During autophagy, actin filament networks move and remodel cellular membranes to form autophagosomes that enclose and metabolize cytoplasmic contents. Two actin regulators, WHAMM and JMY, participate in autophagosome formation, but the signals linking autophagy to actin assembly are poorly understood. We show that, in nonstarved cells, cytoplasmic JMY colocalizes with STRAP, a regulator of JMY's nuclear functions, on nonmotile vesicles with no associated actin networks. Upon starvation, JMY shifts to motile, LC3-containing membranes that move on actin comet tails. LC3 enhances JMY's de novo actin nucleation activity via a cryptic actin-binding sequence near JMY's N terminus, and STRAP inhibits JMY's ability to nucleate actin and activate the Arp2/3 complex. Cytoplasmic STRAP negatively regulates autophagy. Finally, we use purified proteins to reconstitute LC3- and JMY-dependent actin network formation on membranes and inhibition of network formation by STRAP. We conclude that LC3 and STRAP regulate JMY's actin assembly activities in trans during autophagy.

Regulation of JMY's actin nucleation activity by TTC5/STRAP and LC3 during autophagy

Actin plays indispensable roles in autophagosome biogenesis. Branched actin networks assembled within phagophore membranes are required for generating the autophagosome membrane shape and movement. The ARP2/3 complex and its regulators, such as JMY (junction mediating and regulatory protein, p53 cofactor), translocate to phagophore membranes to promote local actin filament formation during autophagy. Hu et al., recently showed that during autophagy LC3 recruits JMY to the phagophore and promotes its actin nucleation activity. They also characterized TTC5/STRAP (tetratricopeptide repeat domain 5) as a negative autophagy regulator via binding to JMY and antagonizing its activation. Moreover, an in vitro reconstitution system was developed to demonstrate that membrane-bound LC3 is sufficient to recruit JMY and stimulate JMY-mediated actin filament assembly.

Regulation of MRTF-A by JMY via a nucleation-independent mechanism

Background

MRTF-A (myocardin-related transcription factor A) is a coactivator for SRF-mediated gene expression. The activity of MRTF-A is critically dependent on the dissociation of G-actin from N-terminal RPEL motifs. MRTF-SRF induction often correlates with enhanced polymerization of F-actin. Here we investigate MRTF regulation by the multifunctional JMY protein, which contains three WASP/verprolin homology 2 (WH2/V) domains and facilitates Arp2/3-dependent and -independent actin nucleation.

Methods

Co-immunoprecipitation experiments, immunofluorescence and luciferase reporter assays were combined with selective inhibitors to investigate the effect of JMY and its domains on MRTF-A in NIH 3 T3 mouse fibroblasts.

Results

JMY induced MRTF-A transcriptional activity and enhanced its nuclear translocation. Unexpectedly, MRTF-A was hyperactivated when the Arp2/3-recruiting CA region of JMY was deleted or mutated, suggesting an autoinhibitory mechanism for full-length JMY. Moreover, isolated WH2/V domains which are unable to nucleate actin were sufficient for nuclear accumulation and SRF activation. Recombinant WH2/V regions of JMY biochemically competed with MRTF-A for actin binding. Activation of MRTF-A by JMY was unaffected by Arp3 knockdown, by an Arp2/3 inhibitor, and by latrunculin which disassembles cellular F-actin. Restriction of JMY to the nucleus abrogated its MRTF-A activation. Finally, JMY RNAi reduced basal and stimulated transcriptional activation via MRTF-A.

Conclusions

Our results suggest that JMY activates MRTF-SRF independently of F-actin via WH2/V-mediated competition with the RPEL region for G-actin binding in the cytoplasm. Furthermore, the C-terminal region facilitates an autoinhibitory effect on full-length JMY, possibly by intramolecular folding.

The Role of JMY in p53 Regulation

Following the event of DNA damage, the level of tumour suppressor protein p53 increases inducing either cell cycle arrest or apoptosis. Junctional Mediating and Regulating Y protein (JMY) is a transcription co-factor involved in p53 regulation. In event of DNA damage, JMY levels also upregulate in the nucleus where JMY forms a co-activator complex with p300/CREB-binding protein (p300/CBP), Apoptosis-stimulating protein of p53 (ASPP) and Stress responsive activator of p53 (Strap). This co-activator complex then binds to and increases the ability of p53 to induce transcription of proteins triggering apoptosis but not cell cycle arrest. This then suggests that the increase of JMY levels due to DNA damage putatively "directs" p53 activity toward triggering apoptosis. JMY expression is also linked to increased cell motility as it: (1) downregulates the expression of adhesion molecules of the Cadherin family and (2) induces actin nucleation, making cells less adhesive and more mobile, favouring metastasis. All these characteristics taken together imply that JMY possesses both tumour suppressive and tumour metastasis promoting capabilities.

2'-Hydroxyflavanone effectively targets RLIP76-mediated drug transport and regulates critical signaling networks in breast cancer

Breast cancer (BC) is the most common cancer in women. Estrogen, epidermal growth factor receptor 2 (ERBB2, HER2), and oxidative stress represent critical mechanistic nodes associated with BC. RLIP76 is a major mercapturic acid pathway transporter whose expression is increased in BC. In the quest of a novel molecule with chemopreventive and chemotherapeutic potential, we evaluated the effects of 2'-Hydroxyflavanone (2HF) in BC. 2HF enhanced the inhibitory effects of RLIP76 depletion and also inhibited RLIP76-mediated doxorubicin transport in BC cells. RNA-sequencing revealed that 2HF induces strong reversal of the gene expression pattern in ER⁺MCF7, HER2⁺ SKBR3 and triple-negative MDA-MB-231 BC cells with minimal effects on MCF10A normal breast epithelial cells. 2HF down regulated ERα and enhanced inhibitory effects of imatinib mesylate/Gleevec in MCF7 cells. 2HF also down regulated ERα and HER2 gene networks in MCF7 and SKBR3 cells, respectively. 2HF activated TP53 and inhibited TGFβ1 canonical pathway in MCF7 and MDA-MB-231 BC cells. 2HF also regulated the expression of a number of critical prognostic genes of MammaPrint panel and their upstream targets including TP53, CDKN2A and MYC. The collective findings from this study provide a comprehensive, direct and integrated evidence for the benefits of 2HF in targeting major and clinically relevant mechanistic regulators of BC.

p53 is required for brain growth but is dispensable for resistance to nutrient restriction during Drosophila larval development

BACKGROUND

Animal growth is influenced by the genetic background and the environmental circumstances. How genes promote growth and coordinate adaptation to nutrient availability is still an open question. p53 is a transcription factor that commands the cellular response to different types of stresses. In adult Drosophila melanogaster, p53 regulates the metabolic adaptation to nutrient restriction that supports fly viability. Furthermore, the larval brain is protected from nutrient restriction in a phenomenon called 'brain sparing'. Therefore, we hypothesised that p53 may regulate brain growth and show a protective role over brain development under nutrient restriction.

RESULTS

Here, we studied the function of p53 during brain growth in normal conditions and in animals subjected to developmental nutrient restriction. We showed that p53 loss of function reduced animal growth and larval brain size. Endogenous p53 was expressed in larval neural stem cells, but its levels and activity were not affected by nutritional stress. Interestingly, p53 knockdown only in neural stem cells was sufficient to decrease larval brain growth. Finally, we showed that in p53 mutant larvae under nutrient restriction, the energy storage levels were not altered, and these larvae generated adults with brains of similar size than wild-type animals.

CONCLUSIONS

Using genetic approaches, we demonstrate that p53 is required for proper growth of the larval brain. This developmental role of p53 does not have an impact on animal resistance to nutritional stress since brain growth in p53 mutants under nutrient restriction is similar to control animals.

The Arp2/3 Regulatory System and Its Deregulation in Cancer

The Arp2/3 complex is an evolutionary conserved molecular machine that generates branched actin networks. When activated, the Arp2/3 complex contributes the actin branched junction and thus cross-links the polymerizing actin filaments in a network that exerts a pushing force. The different activators initiate branched actin networks at the cytosolic surface of different cellular membranes to promote their protrusion, movement, or scission in cell migration and membrane traffic. Here we review the structure, function, and regulation of all the direct regulators of the Arp2/3 complex that induce or inhibit the initiation of a branched actin network and that controls the stability of its branched junctions. Our goal is to present recent findings concerning novel inhibitory proteins or the regulation of the actin branched junction and place these in the context of what was previously known to provide a global overview of how the Arp2/3 complex is regulated in human cells. We focus on the human set of Arp2/3 regulators to compare normal Arp2/3 regulation in untransformed cells to the deregulation of the Arp2/3 system observed in patients affected by various cancers. In many cases, these deregulations promote cancer progression and have a direct impact on patient survival.

Cellular functions of WASP family proteins at a glance

Proteins of the Wiskott-Aldrich syndrome protein (WASP) family function as nucleation-promoting factors for the ubiquitously expressed Arp2/3 complex, which drives the generation of branched actin filaments. Arp2/3-generated actin regulates diverse cellular processes, including the formation of lamellipodia and filopodia, endocytosis and/or phagocytosis at the plasma membrane, and the generation of cargo-laden vesicles from organelles including the Golgi, endoplasmic reticulum (ER) and the endo-lysosomal network. Recent studies have also identified roles for WASP family members in promoting actin dynamics at the centrosome, influencing nuclear shape and membrane remodeling events leading to the generation of autophagosomes. Interestingly, several WASP family members have also been observed in the nucleus where they directly influence gene expression by serving as molecular platforms for the assembly of epigenetic and transcriptional machinery. In this Cell Science at a Glance article and accompanying poster, we provide an update on the subcellular roles of WHAMM, JMY and WASH (also known as WASHC1), as well as their mechanisms of regulation and emerging functions within the cell.

Functional Genomics Identifies Tis21-Dependent Mechanisms and Putative Cancer Drug Targets Underlying Medulloblastoma Shh-Type Development

We have recently generated a novel medulloblastoma (MB) mouse model with activation of the Shh pathway and lacking the MB suppressor Tis21 (Patched1^+/-/Tis21^KO ). Its main phenotype is a defect of migration of the cerebellar granule precursor cells (GCPs). By genomic analysis of GCPs in vivo, we identified as drug target and major responsible of this defect the down-regulation of the promigratory chemokine Cxcl3. Consequently, the GCPs remain longer in the cerebellum proliferative area, and the MB frequency is enhanced. Here, we further analyzed the genes deregulated in a Tis21-dependent manner (Patched1^+/-/Tis21 wild-type vs. Ptch1^+/-/Tis21 knockout), among which are a number of down-regulated tumor inhibitors and up-regulated tumor facilitators, focusing on pathways potentially involved in the tumorigenesis and on putative new drug targets. The data analysis using bioinformatic tools revealed: (i) a link between the Shh signaling and the Tis21-dependent impairment of the GCPs migration, through a Shh-dependent deregulation of the clathrin-mediated chemotaxis operating in the primary cilium through the Cxcl3-Cxcr2 axis; (ii) a possible lineage shift of Shh-type GCPs toward retinal precursor phenotype, i.e., the neural cell type involved in group 3 MB; (iii) the identification of a subset of putative drug targets for MB, involved, among the others, in the regulation of Hippo signaling and centrosome assembly. Finally, our findings define also the role of Tis21 in the regulation of gene expression, through epigenetic and RNA processing mechanisms, influencing the fate of the GCPs.

Regulation of actin nucleation and autophagosome formation

Autophagy is a process of self-eating, whereby cytosolic constituents are enclosed by a double-membrane vesicle before delivery to the lysosome for degradation. This is an important process which allows for recycling of nutrients and cellular components and thus plays a critical role in normal cellular homeostasis as well as cell survival during stresses such as starvation or hypoxia. A large number of proteins regulate various stages of autophagy in a complex and still incompletely understood series of events. In this review, we will discuss recent studies which provide a growing body of evidence that actin dynamics and proteins that influence actin nucleation play an important role in the regulation of autophagosome formation and maturation.

Introducing STRaNDs: shuttling transcriptional regulators that are non-DNA binding

Many proteins originally identified as cytoplasmic - including many associated with the cytoskeleton or cell junctions - are increasingly being found in the nucleus, where they have specific functions. Here, we focus on proteins that translocate from the cytoplasm to the nucleus in response to external signals and regulate transcription without binding to DNA directly (for example, through interaction with transcription factors). We propose that proteins with such characteristics are classified as a distinct group of extracellular signalling effectors, and we suggest the term STRaND (shuttling transcriptional regulators and non-DNA binding) to refer to this group. Crucial roles of STRaNDs include linking cell morphology and adhesion with changes in transcriptional programmes in response to signals such as mechanical stresses.

Wiskott-Aldrich syndrome proteins in the nucleus: aWASH with possibilities

Actin and proteins that regulate its dynamics or interactions have well-established roles in the cytoplasm where they function as key components of the cytoskeleton to control diverse processes, including cellular infrastructure, cellular motility, cell signaling, and vesicle transport. Recent work has also uncovered roles for actin and its regulatory proteins in the nucleus, primarily in mechanisms governing gene expression. The Wiskott Aldrich Syndrome (WAS) family of proteins, comprising the WASP/N-WASP, SCAR/WAVE, WHAMM/JMY/WHAMY, and WASH subfamilies, function in the cytoplasm where they activate the Arp2/3 complex to form branched actin filaments. WAS proteins are present in the nucleus and have been implicated as transcriptional regulators. We found that Drosophila Wash, in addition to transcriptional effects, is involved in global nuclear architecture. Here we summarize the regulation and function of nuclear WAS proteins, and highlight how our work with Wash expands the possibilities for the functions of these proteins in the nucleus.

Signalling Pathways Controlling Cellular Actin Organization

The actin cytoskeleton is essential for morphogenesis and virtually all types of cell shape changes. Reorganization is per definition driven by continuous disassembly and re-assembly of actin filaments, controlled by major, ubiquitously operating machines. These are specifically employed by the cell to tune its activities in accordance with respective environmental conditions or to satisfy specific needs.Here we sketch some fundamental signalling pathways established to contribute to the reorganization of specific actin structures at the plasma membrane. Rho-family GTPases are at the core of these pathways, and dissection of their precise contributions to actin reorganization in different cell types and tissues will thus continue to improve our understanding of these important signalling nodes. Furthermore, we will draw your attention to the emerging theme of actin reorganization on intracellular membranes, its functional relation to Rho-GTPase signalling, and its relevance for the exciting phenomenon autophagy.

SUMOylation-disrupting WAS mutation converts WASp from a transcriptional activator to a repressor of NF-κB response genes in T cells

In Wiskott-Aldrich syndrome (WAS), immunodeficiency and autoimmunity often comanifest, yet how WAS mutations misregulate chromatin-signaling in Thelper (TH) cells favoring development of auto-inflammation over protective immunity is unclear. Previously, we identified an essential promoter-specific, coactivator role of nuclear-WASp in TH1 gene transcription. Here we identify small ubiquitin-related modifier (SUMO)ylation as a novel posttranslational modification of WASp, impairment of which converts nuclear-WASp from a transcriptional coactivator to a corepressor of nuclear factor (NF)-κB response genes in human (TH)1-differentiating cells. V75M, one of many disease-causing mutations occurring in SUMO*motif (72-ψψψψKDxxxxSY-83) of WASp, compromises WASp-SUMOylation, associates with COMMD1 to attenuate NF-κB signaling, and recruits histone deacetylases-6 (HDAC6) to p300-marked promoters of NF-κB response genes that pattern immunity but not inflammation. Consequently, proteins mediating adaptive immunity (IFNG, STAT1, TLR1) are deficient, whereas those mediating auto-inflammation (GM-CSF, TNFAIP2, IL-1β) are paradoxically increased in TH1 cells expressing SUMOylation-deficient WASp. Moreover, SUMOylation-deficient WASp favors ectopic development of the TH17-like phenotype (↑IL17A, IL21, IL22, IL23R, RORC, and CSF2) under TH1-skewing conditions, suggesting a role for WASp in modulating TH1/TH17 plasticity. Notably, pan-histone deacetylase inhibitors lift promoter-specific repression imposed by SUMOylation-deficient WASp and restore misregulated gene expression. Our findings uncovering a SUMOylation-based mechanism controlling WASp's dichotomous roles in transcription may have implications for personalized therapy for patients carrying mutations that perturb WASp-SUMOylation.

Actin nucleation by WH2 domains at the autophagosome

Autophagy is a catabolic process whereby cytosolic components and organelles are degraded to recycle key cellular materials. It is a constitutive process required for proper tissue homoeostasis but can be rapidly regulated by a variety of stimuli (for example, nutrient starvation and chemotherapeutic agents). JMY is a DNA damage-responsive p53 cofactor and actin nucleator important for cell survival and motility. Here we show that JMY regulates autophagy through its actin nucleation activity. JMY contains an LC3-interacting region, which is necessary to target JMY to the autophagosome where it enhances the autophagy maturation process. In autophagosomes, the integrity of the WH2 domains allows JMY to promote actin nucleation, which is required for efficient autophagosome formation. Thus our results establish a direct role for actin nucleation mediated by WH2 domain proteins that reside at the autophagosome.

Autophagy is a catabolic process whereby cellular components are degraded by the autophagosome, but the role of the actin cytoskeleton is not clear. Here Coutts and La Thangue show that the actin nucleator JMY is recruited to the autophagosome via binding LC3, and promotes actin nucleation that is required for autophagosome maturation.

Identification of novel target genes specifically activated by deregulated E2F in human normal fibroblasts

The transcription factor E2F is the principal target of the tumor suppressor pRB. E2F plays crucial roles not only in cell proliferation by activating growth-related genes but also in tumor suppression by activating pro-apoptotic and growth-suppressive genes. We previously reported that, in human normal fibroblasts, the tumor suppressor genes ARF, p27(Kip1) and TAp73 are activated by deregulated E2F activity induced by forced inactivation of pRB, but not by physiological E2F activity induced by growth stimulation. In contrast, growth-related E2F targets are activated by both E2F activities, underscoring the roles of deregulated E2F in tumor suppression in the context of dysfunctional pRB. In this study, to further understand the roles of deregulated E2F, we explored new targets that are specifically activated by deregulated E2F using DNA microarray. The analysis identified nine novel targets (BIM, RASSF1, PPP1R13B, JMY, MOAP1, RBM38, ABTB1, RBBP4 and RBBP7), many of which are involved in the p53 and RB tumor suppressor pathways. Among these genes, the BIM gene was shown to be activated via atypical E2F-responsive promoter elements and to contribute to E2F1-mediated apoptosis. Our results underscore crucial roles of deregulated E2F in growth suppression to counteract loss of pRB function.

WHAMM Directs the Arp2/3 Complex to the ER for Autophagosome Biogenesis through an Actin Comet Tail Mechanism

Nucleation-promoting factors (NPFs) control the spatio-temporal activity of Arp2/3 complex in cells]. Thus, WASP and the WAVE complex direct the formation of branched actin networks at the leading edge during cell motility and endo/exocytosis, whereas the WASH complex is involved in endosomal transport. Less understood are WHAMM and JMY, two NPFs with similar domain architecture. JMY is found in the nucleus and the cytosol and is involved in transcriptional regulation, cell motility, and trans-Golgi transport. WHAMM was reported to bind microtubules and to be involved in ER to cis-Golgi transport. Here, we show that WHAMM directs the activity of Arp2/3 complex for autophagosome biogenesis through an actin-comet tail motility mechanism. Macroautophagy--the process by which cytosolic material is engulfed into autophagosomes for degradation and/or recycling--was recently shown to involve actin, but the mechanism is unknown. We found that WHAMM forms puncta that colocalize and comigrate with the autophagy markers LC3, DFCP1, and p62 through a WHAMM-dependent actin-comet tail mechanism. Under starvation, WHAMM and actin are observed at the interface between neighboring autophagosomes, whose number and size increase with WHAMM expression. Interfering with actin polymerization, inhibiting Arp2/3 complex, knocking down WHAMM, or blocking its interaction with Arp2/3 complex through mutagenesis all inhibit comet tail formation and reduce the size and number of autophagosomes. Finally, JMY shows similar localization to WHAMM and could be involved in similar processes. These results reveal a link between Arp2/3-complex-dependent actin assembly and autophagy.

Junction-mediating and regulatory protein (JMY) is essential for early porcine embryonic development

Junction-mediating and regulatory protein (JMY) is a regulator of both transcription and actin filament assembly. JMY is a critical nucleation-promoting factor (NPF); however, its role in the development of mammalian embryos is poorly understood. In the current study, we investigated the functional roles of the NPF JMY in porcine embryos. Porcine embryos expressed JMY mRNA and protein, and JMY protein moved from the cytoplasm to the nucleus at later embryonic developmental stages. Knockdown of JMY by RNA interference markedly decreased the rate of blastocyst development, validating its role in the development of porcine embryos. Furthermore, injection of JMY dsRNA also impaired actin and Arp2 expression, and co-injection of actin and Arp2 mRNA partially rescued blastocyst development. Taken together, our results show that the NPF JMY is involved in the development of porcine embryos by regulating the NPF-Arp2-actin pathway.

Nuclear roles for actin

Actin's presence in the nucleus is a subject that has ignited a lot of controversy in the past. With our review, we attempt to reach out not only to the specialists but also to a broader audience that might be skeptical in light of the controversies. We take a rather conservative approach to build an argument that recent studies provide multiple independent lines of evidence substantiating actin's diverse nuclear functions, especially in its monomeric state. We then particularly focus on how the concentration of monomeric actin, and potentially of specific polymerized forms of actin, can be used by the cell as indicators of cellular state and how this information can be transduced into the nucleus by transcriptional regulators, eliciting a response. We also provide examples that in specific cell types and specific physiological conditions, actin is functional in the nucleus in its polymeric form. However, we also discuss that in many instances, the presence of actin regulators in the nucleus, which is often seen as proof of their function within this compartment, may simply reflect an additional means of their regulation by compartmentalization.

Negative regulation of the p300-p53 interplay by DDX24

Numerous studies indicate that p300 acts as a key transcriptional cofactor in vivo, at least, in part, through modulating activities of p53 by acetylation. Nevertheless, the regulation of the p53-p300 interplay is not completely understood. Here, we have identified the DEAD box RNA helicase DDX24 as a novel regulator of the p300-p53 axis. We found that DDX24 interacts with p300, and this interaction leads to suppression of p300 mediated acetylation of p53. Notably, RNAi-mediated knockdown of endogenous DDX24 significantly increases the acetylation levels of endogenous p53 in human cancer cells and subsequently promotes p53-mediated activation of its transcriptional targets such as p21 and PUMA. In contrast, DDX24 expression inhibits the p300-p53 interaction and suppresses p300-mediated acetylation of p53. Moreover, DDX24 is overexpressed in human cancer cells and reduction of DDX24 protein levels by RNAi induces cell cycle arrest and senescence in a p53 dependent manner. These results reveal DDX24 as an important regulator of p300 and suggest that the modulation of the p53-p300 interplay by DDX24 is critical in controlling p53 activities in human cancer cells.

JMY protein, a regulator of P53 and cytoplasmic actin filaments, is expressed in normal and neoplastic tissues

JMY is a p300-binding protein with dual action: by enhancing P53 transcription in the nucleus, it plays an important role in the cellular response to DNA damage, while by promoting actin filament assembly in the cytoplasm; it induces cell motility in vitro. Therefore, it has been argued that, depending of the cellular setting, it might act either as tumor suppressor or as oncogene. In order to further determine its relevance to human cancer, we produced the monoclonal antibody HMY 117 against a synthetic peptide from the N-terminus region and characterized it on two JMY positive cell lines, MCF7 and HeLa, wild type and after transfection with siRNA to switch off JMY expression. JMY was expressed in normal tissues and heterogeneously in different tumor types, with close correlation between cytoplasmic and nuclear expression. Most noticeable was the loss of expression in some infiltrating carcinomas compared to normal tissue and in in situ carcinomas of the breast, which is consistent with a putative suppressor role. However, as in lymph node metastases, expression of JMY was higher than in primary colorectal and head and neck carcinomas, it might also have oncogenic properties depending on the cellular context by increasing motility and metastatic potential.

JMY functions as actin nucleation-promoting factor and mediator for p53-mediated DNA damage in porcine oocytes

Junction-mediating and regulatory protein(JMY) is a multifunctional protein with roles in the transcriptional co-activation of p53 and the regulation of actin nucleation promoting factors and, hence, cell migration; however, its role in the maturation of porcine oocytes is unclear. In the current study, we investigated functional roles of JMY in porcine oocytes. Porcine oocytes expressed JMY mRNA and protein, and the mRNA expression level decreased during oocyte maturation. Knockdown of JMY by RNA interference decreased the rate of polar body extrusion, validating its role in the asymmetric division of porcine oocytes. JMY knockdown also down-regulated the mRNA and protein levels of actin and Arp2/3. Furthermore, JMY accumulated in the nucleus in response to DNA damage, and JMY knockdown suppressed DNA damage-mediated p53 activation. In conclusion, our results show that JMY has important roles in oocyte maturation as a regulator of actin nucleation-promoting factors and an activator of p53 during DNA damage during DNA damages in porcine oocytes.

WISP 1 is an important survival factor in human mesenchymal stromal cells

WNT-induced secreted protein 1 (WISP1/CCN4), a member of the CCN protein family, acts as a downstream factor of the canonical WNT signaling pathway. Its expression is known to affect proliferation and differentiation of human mesenchymal stromal cells (hMSCs), which are fundamental for the development and maintenance of the musculoskeletal system. Whereas a dysregulated, excessive expression of WISP1 often reflects its oncogenic potential via the inhibition of apoptosis, our study emphasizes the importance of WISP1 signaling for the survival of primary human cells. We have established the efficient and specific down-regulation of endogenous WISP1 transcripts by gene silencing in hMSCs and observed cell death as a consequence of WISP1 deficiency. This was confirmed by Annexin V staining for apoptotic cells. DNA microarray analyses of WISP1 down-regulated versus control samples revealed several clusters of differentially expressed genes important for apoptosis induction such as TNF-related apoptosis-inducing ligand 1 (TRAIL) and the corresponding apoptosis-inducing receptors TRAIL-R1 and -R2. An increased expression of TRAIL and its receptors TRAIL-R1 and -R2 in WISP1-deficient hMSCs was confirmed by immunocytofluorescence. Accordingly, WISP1 deficiency is likely to cause TRAIL-induced apoptosis. This is an important novel finding, which suggests that WISP1 is indispensable for the protection of healthy hMSCs against TRAIL-induced apoptosis.

Loss of TBL1XR1 disrupts glucocorticoid receptor recruitment to chromatin and results in glucocorticoid resistance in a B-lymphoblastic leukemia model

Although great advances have been made in the treatment of pediatric acute lymphoblastic leukemia, up to one of five patients will relapse, and their prognosis thereafter is dismal. We have previously identified recurrent deletions in TBL1XR1, which encodes for an F-box like protein responsible for regulating the nuclear hormone repressor complex stability. Here we model TBL1XR1 deletions in B-precursor ALL cell lines and show that TBL1XR1 knockdown results in reduced glucocorticoid receptor recruitment to glucocorticoid responsive genes and ultimately decreased glucocorticoid signaling caused by increased levels of nuclear hormone repressor 1 and HDAC3. Reduction in glucocorticoid signaling in TBL1XR1-depleted lines resulted in resistance to glucocorticoid agonists, but not to other chemotherapeutic agents. Importantly, we show that treatment with the HDAC inhibitor SAHA restores sensitivity to prednisolone in TBL1XR1-depleted cells. Altogether, our data indicate that loss of TBL1XR1 is a novel driver of glucocorticoid resistance in ALL and that epigenetic therapy may have future application in restoring drug sensitivity at relapse.

JMY is involved in anterograde vesicle trafficking from the trans-Golgi network

Junction-mediating and regulatory protein (JMY) was originally identified as a transcriptional co-factor in the p53-response to DNA damage. Aside from this nuclear function, recent years have uncovered an additional function of JMY, namely in cytoskeleton remodelling and actin assembly. The C-terminus of JMY comprises a canonical VCA-module, the sequence signature of Arp2/3 complex activators. Furthermore, tandem repeats of 3 WH2 (V, or more recently also W) domains render JMY capable of Arp2/3 independent actin assembly. The motility promoting cytoplasmic function of JMY is abrogated upon DNA-damage and nuclear translocation of JMY. To address the precise cellular function of JMY in cellular actin rearrangements, we have searched for potential new interaction partners by mass spectrometry. We identified several candidates and correlated their localization with the subcellular dynamics of JMY. JMY is localized to dynamic vesiculo-tubular structures throughout the cytoplasm, which are decorated with actin and Arp2/3 complex. Moreover, JMY partially colocalizes and interacts with VAP-A, which is involved in vesicle-based transport processes. Finally, overexpression of JMY results in Golgi dispersal by loss from the trans-site and affects VSV-G transport. These analyses, together with biochemical experiments, indicate that JMY drives vesicular trafficking in the trans-Golgi region and at ER-membrane contact sites (MCS), distinct from other Arp2/3 activators involved in vesicle transport processes such as the related WHAMM or WASH.

The chemosensitivity of testicular germ cell tumors

Although rare cancers overall, testicular germ cell tumors (TGCTs) are the most common type of cancer in young males below 40 years of age. Both subtypes of TGCTs, i.e., seminomas and non-seminomas, are highly curable and the majority of even metastatic patients may expect to be cured. These high cure rates are not due to the indolent nature of these cancers, but rather to their sensitivity to chemotherapy (and for seminomas to radiotherapy). The delineation of the cause of chemosensitivity at the molecular level is of paramount importance, because it may provide insights into the minority of TGCTs that are chemo-resistant and, thereby, provide opportunities for specific therapeutic interventions aimed at reverting them to chemosensitivity. In addition, delineation of the molecular basis of TGCT chemo-sensitivity may be informative for the cause of chemo-resistance of other more common types of cancer and, thus, may create new therapeutic leads. p53, a frequently mutated tumor suppressor in cancers in general, is not mutated in TGCTs, a fact that has implications for their chemo-sensitivity. Oct4, an embryonic transcription factor, is uniformly expressed in the seminoma and embryonic carcinoma components of non-seminomas, and its interplay with p53 may be important in the chemotherapy response of these tumors. This interplay, together with other features of TGCTs such as the gain of genetic material from the short arm of chromosome 12 and the association with disorders of testicular development, will be discussed in this paper and integrated in a unifying hypothesis that may explain their chemo-sensitivity.