A dual role of RBM42 in modulating splicing and translation of CDKN1A/p21 during DNA damage response

p53-mediated cell cycle arrest during DNA damage is dependent on the induction of p21 protein, encoded by the CDKN1A gene. p21 inhibits cyclin-dependent kinases required for cell cycle progression to guarantee accurate repair of DNA lesions. Hence, fine-tuning of p21 levels is crucial to preserve genomic stability. Currently, the multilayered regulation of p21 levels during DNA damage is not fully understood. Herein, we identify the human RNA binding motif protein 42 (RBM42) as a regulator of p21 levels during DNA damage. Genome-wide transcriptome and interactome analysis reveals that RBM42 alters the expression of p53-regulated genes during DNA damage. Specifically, we demonstrate that RBM42 facilitates CDKN1A splicing by counteracting the splicing inhibitory effect of RBM4 protein. Unexpectedly, we also show that RBM42, underpins translation of various splicing targets, including CDKN1A. Concordantly, transcriptome-wide mapping of RBM42-RNA interactions using eCLIP further substantiates the dual function of RBM42 in regulating splicing and translation of its target genes, including CDKN1A. Collectively, our data show that RBM42 couples splicing and translation machineries to fine-tune gene expression during DNA damage response.

Evaluation of anterolateral thigh flap dimensions with virtual flap models

Free flaps are commonly used for head and neck reconstruction. However, flap dimensions are still evaluated by visual and tactile assessment. The aim of this study was to enable preoperative planning of flap dimensions for soft tissue reconstruction based on clinical parameters. Computed tomography records from 230 patients dated from 2009 to 2019 were analysed retrospectively. A virtual, three-dimensional anterolateral thigh flap model was standardized, aligned to segmented leg models in two positions, and flap thicknesses and volumes were determined. Associations of flap thickness and volume with clinical parameters were evaluated, and an approximative calculation method was derived. The laterally positioned anterolateral thigh flap showed an average (interquartile range) thickness of 15.6 mm (8.7 mm) and volume of 1.5 cm³ (0.9 cm³) per cm². The medially positioned anterolateral thigh flap showed an average (interquartile range) thickness of 16.3 mm (8.7 mm) and volume of 1.6 cm³ (0.9 cm³) per cm². For both flap positions, leg circumference was the strongest predictor of flap thickness (β = 0.545, P < 0.001 and β = 0.529, P < 0.001) and flap volume (β = 0.523, P < 0.001 and β = 0.480, P < 0.001). Flap dimensions can be calculated based on leg circumference, and this preoperative planning of flap dimensions can help the surgeon to select the appropriate flap.

Recruitment of RBM6 to DNA Double-Strand Breaks Fosters Homologous Recombination Repair

DNA double-strand breaks (DSBs) are highly toxic lesions that threaten genome integrity and cell survival. To avoid harmful repercussions of DSBs, a wide variety of DNA repair factors are recruited to execute DSB repair. Previously, we demonstrated that RBM6 splicing factor facilitates homologous recombination (HR) of DSB by regulating alternative splicing-coupled nonstop-decay of the HR protein APBB1/Fe65. Here, we describe a splicing-independent function of RBM6 in promoting HR repair of DSBs. We show that RBM6 is recruited to DSB sites and PARP1 activity indirectly regulates RBM6 recruitment to DNA breakage sites. Deletion mapping analysis revealed a region containing five glycine residues within the G-patch domain that regulates RBM6 accumulation at DNA damage sites. We further ascertain that RBM6 interacts with Rad51, and this interaction is attenuated in RBM6 mutant lacking the G-patch domain (RBM6del(G-patch)). Consequently, RBM6del(G-patch) cells exhibit reduced levels of Rad51 foci after ionizing radiation. In addition, while RBM6 deletion mutant lacking the G-patch domain has no detectable effect on the expression levels of its splicing targets Fe65 and Eya2, it fails to restore the integrity of HR. Altogether, our results suggest that RBM6 recruitment to DSB promotes HR repair, irrespective of its splicing activity.HIGHLIGHTSPARP1 activity indirectly regulates RBM6 recruitment to DNA damage sites.Five glycine residues within the G-patch domain of RBM6 are critical for its recruitment to DNA damage sites, but dispensable for its splicing activity.RBM6 G-patch domain fosters its interaction with Rad51 and promotes Rad51 foci formation following irradiation.RBM6 recruitment to DSB sites underpins HR repair.

CDYL1-dependent decrease in lysine crotonylation at DNA double-strand break sites functionally uncouples transcriptional silencing and repair

Previously, we showed that CDYL1 is recruited to DNA double-strand breaks (DSBs) to promote homologous recombination (HR) repair and foster transcriptional silencing. However, how CDYL1 elicits DSB-induced silencing is not fully understood. Here, we identify a CDYL1-dependent local decrease in the transcriptionally active marks histone lysine crotonylation (Kcr) and crotonylated lysine 9 of H3 (H3K9cr) at AsiSI-induced DSBs, which correlates with transcriptional silencing. Mechanistically, we reveal that CDYL1 crotonyl-CoA hydratase activity counteracts Kcr and H3K9cr at DSB sites, which triggers the eviction of the transcription elongation factor ENL and fosters transcriptional silencing. Furthermore, genetic inhibition of CDYL1 hydratase activity blocks the reduction in H3K9cr and alleviates DSB-induced silencing, whereas HR efficiency unexpectedly remains intact. Therefore, our results functionally uncouple the repair and silencing activity of CDYL1 at DSBs. In a broader context, we address a long-standing question concerning the functional relationship between HR repair and DSB-induced silencing, suggesting that they may occur independently.

RBM6 splicing factor promotes homologous recombination repair of double-strand breaks and modulates sensitivity to chemotherapeutic drugs

RNA-binding proteins regulate mRNA processing and translation and are often aberrantly expressed in cancer. The RNA-binding motif protein 6, RBM6, is a known alternative splicing factor that harbors tumor suppressor activity and is frequently mutated in human cancer. Here, we identify RBM6 as a novel regulator of homologous recombination (HR) repair of DNA double-strand breaks (DSBs). Mechanistically, we show that RBM6 regulates alternative splicing-coupled nonstop-decay of a positive HR regulator, Fe65/APBB1. RBM6 knockdown leads to a severe reduction in Fe65 protein levels and consequently impairs HR of DSBs. Accordingly, RBM6-deficient cancer cells are vulnerable to ATM and PARP inhibition and show remarkable sensitivity to cisplatin. Concordantly, cisplatin administration inhibits the growth of breast tumor devoid of RBM6 in mouse xenograft model. Furthermore, we observe that RBM6 protein is significantly lost in metastatic breast tumors compared with primary tumors, thus suggesting RBM6 as a potential therapeutic target of advanced breast cancer. Collectively, our results elucidate the link between the multifaceted roles of RBM6 in regulating alternative splicing and HR of DSBs that may contribute to tumorigenesis, and pave the way for new avenues of therapy for RBM6-deficient tumors.

638 The Implication of Telephone Consultations During COVID-19 Pandemic on Informed Consent

Aim

Is to find whether telephone consultations have affected patient’s comprehension of the proposed surgical management and possible risks until the day of surgery and accordingly ability for informed consent.

Method

This study included a sample of patients admitted to QEQM hospital for elective day case surgery during November 2020 and had only telephone consultation when referred for surgery. A feedback survey assessing quality of information given to patients before and on day of surgery was filled by the patients after the procedure.

Results

The sample included 40 patients undergoing different procedures [cholecystectomy (25), inguinal hernia repair (25), rectal examination under anaesthesia (5), ventral hernia repair (2), incisional hernia (2), inguinal lymph node biopsy (1)]. It was found that 27.5% of patients didn’t have thorough explanation of possible risks and no explanation about postoperative care in 35%.20% were not provided a leaflet about procedure, 57.5% had concerns before surgery and 75% of patients wished for a leaflet with illustrative diagrams, explanation of risks with their management to be able to take the right decision and majority of these patients were from cholecystectomy subgroup.

Conclusions

The lack of face-face appointment affected greatly the informed consent process resulting in patient dissatisfaction which raised the need for new leaflets containing diagrammatic explanation of procedures and possible risks with their management to ensure fulfilment of autonomy principle.

465 No Role for Postoperative Antibiotics in Uncomplicated Appendicitis

Introduction

Several studies have shown benefit from use of preoperative antibiotics in reducing postoperative infection after appendectomy as well as efficacy of postoperative antibiotics in complicated appendicitis (defined as perforated appendix or presence of pus in peritoneum). While for uncomplicated appendicitis, several studies showed no benefit from antibiotics postoperatively but there are no clear NICE guidelines till now and so surgeons have different practice based on their preferences.

Method

This study included patients who had appendectomy for uncomplicated appendicitis in Worthing hospital from 1st July 2019 till 30th June 2020. The end point was 30-day follow up postoperatively for wound infection or collection.

Results

90 patients were admitted with uncomplicated appendicitis with age 6-80 years (mean of 31.3). 46 patients (51%) did not receive postoperative antibiotics (group A) and 44 (49%) received postoperative antibiotics (group B) with a variable practice from one dose to 8-day course. postoperatively, only 1 patient (2.1%) in group A developed wound infection requiring drainage while none in group B developed complications (p-value=1).

Conclusions

Administration of postoperative antibiotics in uncomplicated appendicitis showed no superiority over non-administration. in addition, they add extra cost on NHS. So, their routine use postoperatively is not recommended, however, larger studies are required to confirm this.

459 Implication of Changes in Management of Acute Pancreatitis During COVID-19 Pandemic

Introduction

when COVID-19 pandemic stroked the country, the Royal College of Surgeons recommended cholecystectomy for gall stone pancreatitis could be delayed up to 12 weeks during Covid-19 pandemic. This may have exposed patients to recurrent gall stone morbidity and serious complications.

Method

Patients admitted with gall stone pancreatitis during Covid-19 period 12^th March 2020 till 15^th June 2020 to Western Sussex hospitals were analysed retrospectively for a period of 3 months post index submission. The endpoints were readmission rates and complication relating to gall stones.

Results

Conclusions

Delaying cholecystectomy for gallstone pancreatitis to 3 months is associated with significant readmission rates and serious complications. Cholecystectomy for gallstone pancreatitis should be categorised as 1B or 2 during Covid-19 period.

Correlation between extent of sinus surgery, radiographic disease, and postoperative outcomes

BACKGROUND

The extent of endoscopic sinus surgery (ESS) required for optimal outcomes in chronic rhinosinusitis (CRS) is undefined. We evaluated whether concordance between the extent of surgery and degree of radiographic disease influences postoperative outcomes.

METHODS

247 CRS patients who underwent ESS were retrospectively assigned a concordance score reflecting the similarity between the extent of surgery and degree of radiographic disease. 0 points were assigned when sinusotomy was performed on a diseased sinus, or no sinusotomy was performed on a nondiseased sinus; plus 1 for sinusotomy on a nondiseased sinus; and -1 for a diseased sinus left unopened. The total possible score ranged from minus 10 to plus 10. Patients were divided into 5 subgroups according to variance from complete concordance. SNOT-22 scores and revision rates were compared at 6 and 24 months.

RESULTS

All five subgroups had similar preoperative SNOT-22 scores and improved at 6 months postoperatively. At 6 months postoperatively, the most conservatively operated and most extensively operated subgroups each achieved equivalent improvements in SNOT-22 as the completely concordant subgroup. At 24 months, the most extensively operated subgroup had a 12.5-point smaller improvement in SNOT-22 scores compared to the completely concordant subgroup. Multivariate analysis showed no association between concordance score and revision rate.

CONCLUSIONS

Symptom improvement and revision rates after ESS do not appear to correlate with the degree of concordance between extent of surgery and radiographic disease. More extensive surgery than indicated by CT confers neither greater symptomatic improvement nor long-term detriment.

Transcriptional Regulation at DSBs: Mechanisms and Consequences

Defective double-strand break (DSB) repair leads to genomic instabilities that may augment carcinogenesis. DSBs trigger transient transcriptional silencing in the vicinity of transcriptionally active genes through multilayered processes instigated by Ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), and poly-(ADP-ribose) polymerase 1 (PARP1). Novel factors have been identified that ensure DSB-induced silencing via two distinct pathways: direct inhibition of RNA Polymerase II (Pol II) mediated by negative elongation factor (NELF), and histone code editing by CDYL1 and histone deacetylases (HDACs) that catalyze H3K27me3 and erase lysine crotonylation, respectively. Here, we highlight major advances in understanding the mechanisms underlying transcriptional silencing at DSBs, and discuss its functional implications on repair. Furthermore, we discuss consequential links between DSB-silencing factors and carcinogenesis and discuss the potential of exploiting them for targeted cancer therapy.

Evaluation of the bactericidal effect of cold atmospheric pressure plasma on contaminated human bone: an in vitro study

The use of cold atmospheric pressure plasma (CAPP) as a bacterial decontaminant for chronic wounds has shown good results. The purpose of this in vitro study was to evaluate the bactericidal effects of CAPP on the cancellous area of the bone. Sterile glass slides and processed sterile human bone allografts 1, 2, 3, and 4mm thick were used for initial contamination and further CAPP treatment. Each block was contaminated with Staphylococcus aureus suspension on one side. Each slide was turned 180° and treated on the reverse side. The bacterial count in colony-forming units (CFU) was then measured and compared with that of a control group, and the bactericidal effects of CAPP in relation to bone density evaluated. A significant reduction in count was measured between treated and untreated groups (groups A-D: p<0.01 and group E: p=0.04). A strong positive linear relation was found between bone density and the S aureus count (r=0.844, p=0.156). Treatment with CAPP had a bactericidal effect on bone structures with a penetration depth of up to 4mm. It might be used for all diseases involving infected bone, and so extends the existing range of treatments.

An Interaction with PARP-1 and Inhibition of Parylation Contribute to Attenuation of DNA Damage Signaling by the Adenovirus E4orf4 Protein

The adenovirus (Ad) E4orf4 protein was reported to contribute to inhibition of ATM- and ATR-regulated DNA damage signaling during Ad infection and following treatment with DNA-damaging drugs. Inhibition of these pathways improved Ad replication, and when expressed alone, E4orf4 sensitized transformed cells to drug-induced toxicity. However, the mechanisms utilized were not identified. Here, we show that E4orf4 associates with the DNA damage sensor poly(ADP-ribose) polymerase 1 (PARP-1) and that the association requires PARP activity. During Ad infection, PARP is activated, but its activity is not required for recruitment of either E4orf4 or PARP-1 to virus replication centers, suggesting that their association occurs following recruitment. Inhibition of PARP-1 assists E4orf4 in reducing DNA damage signaling during infection, and E4orf4 attenuates virus- and DNA damage-induced parylation. Furthermore, E4orf4 reduces PARP-1 phosphorylation on serine residues, which likely contributes to PARP-1 inhibition as phosphorylation of this enzyme was reported to enhance its activity. PARP-1 inhibition is important to Ad infection since treatment with a PARP inhibitor enhances replication efficiency. When E4orf4 is expressed alone, it associates with poly(ADP-ribose) (PAR) chains and is recruited to DNA damage sites in a PARP-1-dependent manner. This recruitment is required for inhibition of drug-induced ATR signaling by E4orf4 and for E4orf4-induced cancer cell death. Thus, the results presented here demonstrate a novel mechanism by which E4orf4 targets and inhibits DNA damage signaling through an association with PARP-1 for the benefit of the virus and impacting E4orf4-induced cancer cell death.IMPORTANCE Replication intermediates and ends of viral DNA genomes can be recognized by the cellular DNA damage response (DDR) network as DNA damage whose repair may lead to inhibition of virus replication. Therefore, many viruses evolved mechanisms to inhibit the DDR network. We have previously shown that the adenovirus (Ad) E4orf4 protein inhibits DDR signaling, but the mechanisms were not identified. Here, we describe an association of E4orf4 with the DNA damage sensor poly(ADP-ribose) polymerase 1 (PARP-1). E4orf4 reduces phosphorylation of this enzyme and inhibits its activity. PARP-1 inhibition assists E4orf4 in reducing Ad-induced DDR signaling and improves the efficiency of virus replication. Furthermore, the ability of E4orf4, when expressed alone, to accumulate at DNA damage sites and to kill cancer cells is attenuated by chemical inhibition of PARP-1. Our results indicate that the E4orf4-PARP-1 interaction has an important role in Ad replication and in promotion of E4orf4-induced cancer-selective cell death.

CDYL1 fosters double-strand break-induced transcription silencing and promotes homology-directed repair

Cells have evolved DNA damage response (DDR) to repair DNA lesions and thus preserving genomic stability and impeding carcinogenesis. DNA damage induction is accompanied by transient transcription repression. Here, we describe a previously unrecognized role of chromodomain Y-like (CDYL1) protein in fortifying double-strand break (DSB)-induced transcription repression and repair. We showed that CDYL1 is rapidly recruited to damaged euchromatic regions in a poly (ADP-ribose) polymerase 1 (PARP1)-dependent, but ataxia telangiectasia mutated (ATM)-independent, manner. While the C-terminal region, containing the enoyl-CoA hydratase like (ECH) domain, of CDYL1 binds to poly (ADP-ribose) (PAR) moieties and mediates CDYL1 accumulation at DNA damage sites, the chromodomain and histone H3 trimethylated on lysine 9 (H3K9me3) mark are dispensable for its recruitment. Furthermore, CDYL1 promotes the recruitment of enhancer of zeste homolog 2 (EZH2), stimulates local increase of the repressive methyl mark H3K27me3, and promotes transcription silencing at DSB sites. In addition, following DNA damage induction, CDYL1 depletion causes persistent G2/M arrest and alters H2AX and replication protein A (RPA2) phosphorylation. Remarkably, the 'traffic-light reporter' system revealed that CDYL1 mainly promotes homology-directed repair (HDR) of DSBs in vivo. Consequently, CDYL1-knockout cells display synthetic lethality with the chemotherapeutic agent, cisplatin. Altogether, our findings identify CDYL1 as a new component of the DDR and suggest that the HDR-defective 'BRCAness' phenotype of CDYL1-deficient cells could be exploited for eradicating cancer cells harboring CDYL1 mutations.

A role of human RNase P subunits, Rpp29 and Rpp21, in homology directed-repair of double-strand breaks

DNA damage response (DDR) is needed to repair damaged DNA for genomic integrity preservation. Defective DDR causes accumulation of deleterious mutations and DNA lesions that can lead to genomic instabilities and carcinogenesis. Identifying new players in the DDR, therefore, is essential to advance the understanding of the molecular mechanisms by which cells keep their genetic material intact. Here, we show that the core protein subunits Rpp29 and Rpp21 of human RNase P complex are implicated in DDR. We demonstrate that Rpp29 and Rpp21 depletion impairs double-strand break (DSB) repair by homology-directed repair (HDR), but has no deleterious effect on the integrity of non-homologous end joining. We also demonstrate that Rpp29 and Rpp21, but not Rpp14, Rpp25 and Rpp38, are rapidly and transiently recruited to laser-microirradiated sites. Rpp29 and Rpp21 bind poly ADP-ribose moieties and are recruited to DNA damage sites in a PARP1-dependent manner. Remarkably, depletion of the catalytic H1 RNA subunit diminishes their recruitment to laser-microirradiated regions. Moreover, RNase P activity is augmented after DNA damage in a PARP1-dependent manner. Altogether, our results describe a previously unrecognized function of the RNase P subunits, Rpp29 and Rpp21, in fine-tuning HDR of DSBs.

NELF-E is recruited to DNA double-strand break sites to promote transcriptional repression and repair

Double-strand breaks (DSBs) trigger rapid and transient transcription pause to prevent collisions between repair and transcription machineries at damage sites. Little is known about the mechanisms that ensure transcriptional block after DNA damage. Here, we reveal a novel role of the negative elongation factor NELF in blocking transcription activity nearby DSBs. We show that NELF-E and NELF-A are rapidly recruited to DSB sites. Furthermore, NELF-E recruitment and its repressive activity are both required for switching off transcription at DSBs. Remarkably, using I-SceI endonuclease and CRISPR-Cas9 systems, we observe that NELF-E is preferentially recruited, in a PARP1-dependent manner, to DSBs induced upstream of transcriptionally active rather than inactive genes. Moreover, the presence of RNA polymerase II is a prerequisite for the preferential recruitment of NELF-E to DNA break sites. Additionally, we demonstrate that NELF-E is required for intact repair of DSBs. Altogether, our data identify the NELF complex as a new component in the DNA damage response.

The emerging role of lysine demethylases in DNA damage response: dissecting the recruitment mode of KDM4D/JMJD2D to DNA damage sites

KDM4D is a lysine demethylase that removes tri- and di- methylated residues from H3K9 and is involved in transcriptional regulation and carcinogenesis. We recently showed that KDM4D is recruited to DNA damage sites in a PARP1-dependent manner and facilitates double-strand break repair in human cells. Moreover, we demonstrated that KDM4D is an RNA binding protein and mapped its RNA-binding motifs. Interestingly, KDM4D-RNA interaction is essential for its localization on chromatin and subsequently for efficient demethylation of its histone substrate H3K9me3. Here, we provide new data that shed mechanistic insights into KDM4D accumulation at DNA damage sites. We show for the first time that KDM4D binds poly(ADP-ribose) (PAR) in vitro via its C-terminal region. In addition, we demonstrate that KDM4D-RNA interaction is required for KDM4D accumulation at DNA breakage sites. Finally, we discuss the recruitment mode and the biological functions of additional lysine demethylases including KDM4B, KDM5B, JMJD1C, and LSD1 in DNA damage response.

Overexpression of KDM4 lysine demethylases disrupts the integrity of the DNA mismatch repair pathway

The KDM4 family of lysine demethylases consists of five members, KDM4A, -B and -C that demethylate H3K9me2/3 and H3K36me2/3 marks, while KDM4D and -E demethylate only H3K9me2/3. Recent studies implicated KDM4 proteins in regulating genomic instability and carcinogenesis. Here, we describe a previously unrecognized pathway by which hyperactivity of KDM4 demethylases promotes genomic instability. We show that overexpression of KDM4A-C, but not KDM4D, disrupts MSH6 foci formation during S phase by demethylating its binding site, H3K36me3. Consequently, we demonstrate that cells overexpressing KDM4 members are defective in DNA mismatch repair (MMR), as evident by the instability of four microsatellite markers and the remarkable increase in the spontaneous mutations frequency at the HPRT locus. Furthermore, we show that the defective MMR in cells overexpressing KDM4C is mainly due to the increase in its demethylase activity and can be mended by KDM4C downregulation. Altogether, our data suggest that cells overexpressing KDM4A-C are defective in DNA MMR and this may contribute to genomic instability and tumorigenesis.

RNA-dependent chromatin localization of KDM4D lysine demethylase promotes H3K9me3 demethylation

The JmjC-containing lysine demethylase, KDM4D, demethylates di-and tri-methylation of histone H3 on lysine 9 (H3K9me3). How KDM4D is recruited to chromatin and recognizes its histone substrates remains unknown. Here, we show that KDM4D binds RNA independently of its demethylase activity. We mapped two non-canonical RNA binding domains: the first is within the N-terminal spanning amino acids 115 to 236, and the second is within the C-terminal spanning amino acids 348 to 523 of KDM4D. We also demonstrate that RNA interactions with KDM4D N-terminal region are critical for its association with chromatin and subsequently for demethylating H3K9me3 in cells. This study implicates, for the first time, RNA molecules in regulating the levels of H3K9 methylation by affecting KDM4D association with chromatin.

KDM4C (GASC1) lysine demethylase is associated with mitotic chromatin and regulates chromosome segregation during mitosis

Various types of human cancers exhibit amplification or deletion of KDM4A-D members, which selectively demethylate H3K9 and H3K36, thus implicating their activity in promoting carcinogenesis. On this basis, it was hypothesized that dysregulated expression of KDM4A-D family promotes chromosomal instabilities by largely unknown mechanisms. Here, we show that unlike KDM4A-B, KDM4C is associated with chromatin during mitosis. This association is accompanied by a decrease in the mitotic levels of H3K9me3. We also show that the C-terminal region, containing the Tudor domains of KDM4C, is essential for its association with mitotic chromatin. More specifically, we show that R919 residue on the proximal Tudor domain of KDM4C is critical for its association with chromatin during mitosis. Interestingly, we demonstrate that depletion or overexpression of KDM4C, but not KDM4B, leads to over 3-fold increase in the frequency of abnormal mitotic cells showing either misaligned chromosomes at metaphase, anaphase-telophase lagging chromosomes or anaphase-telophase bridges. Furthermore, overexpression of KDM4C demethylase-dead mutant has no detectable effect on mitotic chromosome segregation. Altogether, our findings implicate KDM4C demethylase activity in regulating the fidelity of mitotic chromosome segregation by a yet unknown mechanism.

PARP1-dependent recruitment of KDM4D histone demethylase to DNA damage sites promotes double-strand break repair

Members of the lysine (K)-specific demethylase 4 (KDM4) A-D family of histone demethylases are dysregulated in several types of cancer. Here, we reveal a previously unrecognized role of KDM4D in the DNA damage response (DDR). We show that the C-terminal region of KDM4D mediates its rapid recruitment to DNA damage sites. Interestingly, this recruitment is independent of the DDR sensor ataxia telangiectasia mutated (ATM), but dependent on poly (ADP-ribose) polymerase 1 (PARP1), which ADP ribosylates KDM4D after damage. We demonstrate that KDM4D is required for efficient phosphorylation of a subset of ATM substrates. We note that KDM4D depletion impairs the DNA damage-induced association of ATM with chromatin, explaining its effect on ATM substrate phosphorylation. Consistent with an upstream role in DDR, KDM4D knockdown disrupts the damage-induced recombinase Rad51 and tumor protein P53 binding protein foci formation. Consequently, the integrity of homology-directed repair and nonhomologous end joining of DNA breaks is impaired in KDM4D-deficient cells. Altogether, our findings implicate KDM4D in DDR, furthering the links between the cancer-relevant networks of epigenetic regulation and genome stability.

A cancer-associated BRCA2 mutation reveals masked nuclear export signals controlling localization

Germline missense mutations affecting a single BRCA2 allele predispose humans to cancer. Here we identify a protein-targeting mechanism that is disrupted by the cancer-associated mutation, BRCA2(D2723H), and that controls the nuclear localization of BRCA2 and its cargo, the recombination enzyme RAD51. A nuclear export signal (NES) in BRCA2 is masked by its interaction with a partner protein, DSS1, such that point mutations impairing BRCA2-DSS1 binding render BRCA2 cytoplasmic. In turn, cytoplasmic mislocalization of mutant BRCA2 inhibits the nuclear retention of RAD51 by exposing a similar NES in RAD51 that is usually obscured by the BRCA2-RAD51 interaction. Thus, a series of NES-masking interactions localizes BRCA2 and RAD51 in the nucleus. Notably, BRCA2(D2723H) decreases RAD51 nuclear retention even when wild-type BRCA2 is also present. Our findings suggest a mechanism for the regulation of the nucleocytoplasmic distribution of BRCA2 and RAD51 and its impairment by a heterozygous disease-associated mutation.

Heat shock protein 90 (Hsp90) selectively regulates the stability of KDM4B/JMJD2B histone demethylase

The family of KDM4A-D histone demethylases selectively demethylates H3K9 and H3K36 and is implicated in key cellular processes including DNA damage response, transcription, cell cycle regulation, cellular differentiation, senescence, and carcinogenesis. Various human cancers exhibit elevated protein levels of KDM4A-D members, and their depletion impairs tumor formation, suggesting that their enhanced activity promotes carcinogenesis. However, the mechanisms regulating the KDM4 protein stability remain largely unknown. Here, we show that the molecular chaperon Hsp90 interacts with and stabilizes KDM4B protein. Pharmacological inhibition of Hsp90 with geldanamycin resulted in ubiquitin-dependent proteasomal degradation of KDM4B, but not of KDM4C, suggesting that the turnover of these demethylases is regulated by distinct mechanisms. This degradation was accompanied by increased methylation of H3K9. We further show that KDM4B is ubiquitinated on lysines 337 and 562; simultaneous substitution of these residues to arginine suppressed the geldanamycin-induced degradation of KDM4B, suggesting that the ubiquitination of Lys-337 and Lys-562 targets KDM4B for proteasomal degradation upon Hsp90 inhibition. These findings constitute a novel pathway by which Hsp90 activity alters the histone code via regulation of KDM4B stability. This pathway may prove a druggable target for the treatment of tumors driven by enhanced KDM4B activity.

Investigation of phenolic leaf extract of Heimia myrtifolia (Lythraceae): Pharmacological properties (stimulation of mineralization of SaOS-2 osteosarcoma cells) and identification of polyphenols

Evaluation of the activity of an aqueous alcoholic extract obtained from the leaves of Heimia myrtifolia (Lythraceae) by determining its stimulating effect on two human osteoblastic cell lines HOS58 and SaOS-2 indicated its potential for use in the prevention and treatment of osteoporosis. In addition, the extract was found to significantly increase the mineralization of cultivated human bone cell SaOS-2, in which a strong dose-dependent increase was observed. A phytochemical investigation of the extract also confirmed that H. myrtifolia is capable of synthesizing and accumulating appreciable amounts of several phenolics, thus leading to the isolation and characterization of sixteen of these constituents. Identified among these isolates were a new natural product, 1,6-di-O-dehydrotrigalloyl-β-D-(4)C(1)-glucopyranose, and a rare natural product (this marks its second report), 5,7,4'-trihydroxy-3-methoxyflavanone (dihydrokaempferol-3-O-methyl ether). Structures of these isolates were fully elucidated on the basis of conventional methods of analysis and confirmed by ESI/MS and (1)H and (13)C-NMR analysis.

Spicatic acid: A 4-carboxygentisic acid from Gentiana spicata extract with potential hepatoprotective activity

Due to our interest in bioactive plant derived materials, the hepatoprotective activity of the aqueous alcoholic extract of Gentiana spicata AEGS (Gentianaceae) on carbon tetrachloride treated rats was investigated. CCl4 used at a concentration of 1 mL/kg.b.wt. significantly increased the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). However, pre-treatment with AEGS and its individual components significantly prevented the increase in these enzymes, which are the major indicators of liver injury. Biochemical assays of liver homogenate showed that AEGS and its components restored reduced glutathione (GSH) depletion reduced the level of thiobarbituric acid reactive substances (TBARS). Furthermore, liver histological observation also showed an obvious amelioration in liver cell necrosis, liver lesions, and fatty changes in pre-treated groups. Phytochemical investigation of the extract showed high phenolic content and led to the isolation and identification of the new carboxygentisic acid, 1,4-dicarboxy 2,5-dihydroxybenzene, for which we suggest the name spicatic acid, together with the known flavonoids, quercetin 3-O-[(2,3,4-triacetyl-α-rhamnopyranosyl)1'''→6''] 3-acetyl-β-galactopyranoside and quercetin 3-O-[(2,3,4-triacetyl-α-rhamnopyranosyl)1'''→6'']-4-acetyl-β-galactopyranoside, epicatechin, catechin and their gallolyated derivatives. All structures were elucidated on the basis of conventional analytical methods and confirmed by high resolution ESIMS, 1D- and 2D-NMR data. The new phenolic 4-carboxygentisic acid, spicatic acid is of special interest as it represents the first phenolic acid in nature which bears two carboxyl functions in one aromatic ring.

Mobilization and recruitment of HP1: a bimodal response to DNA breakage

The pathways that signal double-strand DNA breaks (DSBs) in mammalian cells are central to the maintenance of genome integrity. We have reported (Ayoub et al., Nature 2008; 453: 682-6) that the rapid mobilization of the heterochromatin protein, HP1beta, within seconds from DSB sites promotes chromatin changes like H2AX phosphorylation that trigger this response. Notably, this paper and a subsequent report (Ayoub et al., Cell Cycle 2009; 8: 1494-500), demonstrate that transient HP1beta mobilization is followed by its accumulation over time at DSB sites. Indeed, two recent papers (Luijsterburg et al., J Cell Biol 2009; 185:577-86 and Zarebski et al., Cytometry A May 2009) suggest that HP1 recruitment to damage sites, rather than its rapid mobilization, is the predominant behaviour exhibited by this protein. Here, we present new experimental analyses which corroborate that fluorophore-tagged HP1beta exhibits two distinct behaviours at DSB sites in living cells - rapid, transient mobilization, most evident in heterochromatic regions, followed by slower recruitment. Experimental methods allowing visualization of these behaviours are described. Interestingly, chemical inhibition of the DNA-damage responsive enzyme, casein kinase 2 (CK2), suppresses HP1beta mobilization while permitting recruitment. Our findings reconcile recent findings in a new model, wherein rapid HP1beta mobilization from DSBs mediated by its phosphorylation on Thr51 by CK2, is followed by, and may overlap with, its accumulation at these sites via the chromoshadow domain, independent of Thr51. Our analyses provide fresh insight into the earliest events that trigger the DNA damage response in mammalian cells.

Paving the way for H2AX phosphorylation: chromatin changes in the DNA damage response

The dynamics of chromatin-associated proteins control the accessibility of DNA to essential biological transactions like transcription, replication, recombination and repair. Here, we briefly outline what is known about the chromatin changes that occur during the cellular response to DNA breakage, focusing on our recent findings revealing that the chromatin factor HP1beta is mobilized within seconds after DNA damage by an unrecognized signaling cascade mediated by casein kinase 2 (CK2) phosphorylation, paving the way for histone H2AX phosphorylation. We also show here that HP1beta mobilization is neither associated with histone H3 modification on Ser10, an alteration proposed to assist in HP1 ejection from chromatin, nor with evidence of a physical interaction between HP1beta and the CK2 regulatory subunit. Interestingly, following its rapid mobilization, we find that HP1beta gradually re-accumulates on damaged chromatin over a longer time period, suggesting that temporal changes in HP1beta dynamics and interaction with chromatin may assist in different stages of the cellular response to DNA breakage.