NFBD1/MDC1 Associates with p53 and Regulates Its Function at the Crossroad between Cell Survival and Death in Response to DNA Damage

In silico study reveals unconventional interactions between MDC1 of DDR and Beclin-1 of autophagy

DNA damage response (DDR) and autophagy are concerned with maintaining cellular homeostasis and dysregulation of these two pathways lead to pathologic conditions including tumorigenesis. Autophagy is activated as a protective mechanism during DDR which is indicative of their functional cooperativity but the molecular mechanism leading to the convergence of these two pathways during genotoxic stress remains elusive. In this study, through in silico analysis, we have shown an interaction between the Mediator of DNA damage checkpoint 1 (MDC1), an important DDR-associated protein, and Beclin-1, an autophagy inducer. MDC1 is an adaptor or scaffold protein known to regulate DDR, apoptosis, and cell cycle progression. While, Beclin-1 is involved in autophagosome nucleation and exhibits affinity for binding to Fork-head-associated domain (FHA) containing proteins. The FHA domain is commonly conserved in DDR-related proteins including MDC1. Through molecular docking, we have predicted the modeled complex between the MDC1 FHA domain and the Beclin-1 Coiled coil domain (CCD). The docking complex was modeled using ClusPro2.0, based on the crystal structure for the dimerized MDC1 FHA domain and Beclin-1 CCD. The complex stability and binding affinities were assessed using a Ramachandran plot, MD simulation, MM/GBSA, and PRODIGY webserver. Finally, the hot-spot residues at the interface were determined using computational alanine scanning by the DrugScorePPI webserver. Our analysis unveils significant interaction between MDC1 and Beclin-1, involving hydrogen bonds, non-bonded contacts, and salt bridges and indicates MDC1 possibly recruits Beclin-1 to the DSBs, as a consequence of which Beclin-1 is able to modulate DDR.

Highly Reproducible Quantitative Proteomics Analysis of Pancreatic Cancer Cells Reveals Proteome-Level Effects of a Novel Combination Drug Therapy That Induces Cancer Cell Death via Metabolic Remodeling and Activation of the Extrinsic Apoptosis Pathway

Pancreatic cancer patients have poor survival rates and are frequently treated using gemcitabine (Gem). However, initial tumor sensitivity often gives way to rapid development of resistance. Gem-based drug combinations are employed to increase efficacy and mitigate resistance, but our understanding of molecular-level drug interactions, which could assist in the development of more effective therapeutic regimens, is limited. Global quantitative proteomic analysis could provide novel mechanistic insights into drug combination interactions, but it is challenging to achieve high-quality quantitative proteomics analysis of the large sample sets that are typically required for drug combination studies. Here, we investigated molecular-level temporal interactions of Gem with BGJ398 (infigratinib), a recently approved pan-FGFR inhibitor, in multiple treatment groups (N = 42 samples) using IonStar, a robust large-scale proteomics method that employs well-controlled, ultrahigh-resolution MS1 quantification. A total of 5514 proteins in the sample set were quantified without missing data, requiring >2 unique peptides/protein, <1% protein false discovery rate (FDR), <0.1% peptide FDR, and CV < 10%. Functional analysis of the differentially altered proteins revealed drug-dysregulated processes such as metabolism, apoptosis, and antigen presentation pathways. These changes were validated experimentally using Seahorse metabolic assays and immunoassays. Overall, in-depth analysis of large-scale proteomics data provided novel insights into possible mechanisms by which FGFR inhibitors complement and enhance Gem activity in pancreatic cancers.

Functional analyses of rare germline BRCA1 variants by transcriptional activation and homologous recombination repair assays

BACKGROUND

Damaging alterations in the BRCA1 gene have been extensively described as one of the main causes of hereditary breast and ovarian cancer (HBOC). BRCA1 alterations can lead to impaired homologous recombination repair (HRR) of double-stranded DNA breaks, a process which involves the RING, BRCT and coiled-coil domains of the BRCA1 protein. In addition, the BRCA1 protein is involved in transcriptional activation (TA) of several genes through its C-terminal BRCT domain.

METHODS

In this study, we have investigated the effect on HRR and TA of 11 rare BRCA1 missense variants classified as variants of uncertain clinical significance (VUS), located within or in close proximity to the BRCT domain, with the aim of generating additional knowledge to guide the correct classification of these variants. The variants were selected from our previous study "BRCA1 Norway", which is a collection of all BRCA1 variants detected at the four medical genetic departments in Norway.

RESULTS

All variants, except one, showed a significantly reduced HRR activity compared to the wild type (WT) protein. Two of the variants (p.Ala1708Val and p.Trp1718Ser) also exhibited low TA activity similar to the pathogenic controls. The variant p.Trp1718Ser could be reclassified to likely pathogenic. However, for ten of the variants, the total strength of pathogenic evidence was not sufficient for reclassification according to the CanVIG-UK BRCA1/BRCA2 gene-specific guidelines for variant interpretation.

CONCLUSIONS

When including the newly achieved functional evidence with other available information, one VUS was reclassified to likely pathogenic. Eight of the investigated variants affected only one of the assessed activities of BRCA1, highlighting the importance of comparing results obtained from several functional assays to better understand the consequences of BRCA1 variants on protein function. This is especially important for multifunctional proteins such as BRCA1.

MDC1 maintains active elongation complexes of RNA polymerase II

The role of MDC1 in the DNA damage response has been extensively studied; however, its impact on other cellular processes is not well understood. Here, we describe the role of MDC1 in transcription as a regulator of RNA polymerase II (RNAPII). Depletion of MDC1 causes a genome-wide reduction in the abundance of actively engaged RNAPII elongation complexes throughout the gene body of protein-encoding genes under unperturbed conditions. Decreased engaged RNAPII subsequently alters the assembly of the spliceosome complex on chromatin, leading to changes in pre-mRNA splicing. Mechanistically, the S/TQ domain of MDC1 modulates RNAPII-mediated transcription. Upon genotoxic stress, MDC1 promotes the abundance of engaged RNAPII complexes at DNA breaks, thereby stimulating nascent transcription at the damaged sites. Of clinical relevance, cancer cells lacking MDC1 display hypersensitivity to RNAPII inhibitors. Overall, we unveil a role of MDC1 in RNAPII-mediated transcription with potential implications for cancer treatment.

Targeting MDC1 promotes apoptosis and sensitizes Imatinib resistance in CML cells by mainly disrupting non-homologous end-joining repair

The first-line drug Imatinib (IM) has achieved a curative effect in most chronic myeloid leukemia (CML) patients, but drug resistance remains a problem. More alternative therapeutic strategies need to explore. In recent years, targeting dysregulated DNA repair mechanisms provided promising options for cancer treatment. Here, we discovered the versatile Mediator of DNA Damage Checkpoint 1 (MDC1) interacted with γ-H2AX and 53BP1 in the early stage of the DNA damage response of cells. MDC1 overexpressed in CML cell lines and patients' bone marrow mononuclear cells. By knocking down MDC1, non-homologous end-joining pathways were mainly inhibited, leading to an intense accumulation of unrepaired intracellular DNA damage and an apparent cell apoptosis promotion. Notably, targeting MDC1 further enhanced drug sensitivity in IM-resistant CML cells. Our work revealed that MDC1 is a prospective target for CML treatment through regulating DNA damage repair mechanism, and also an alternative option for IM resistance dilemma. This study extends the understanding of regulating dysfunctional DNA repair mechanisms for cancer treatment.

Identification of functional pathways and molecular signatures in neuroendocrine neoplasms by multi-omics analysis

BACKGROUND

Neuroendocrine neoplasms (NENs) represent a heterogeneous class of rare tumors with increasing incidence. They are characterized by the ability to secrete peptide hormones and biogenic amines but other reliable biomarkers are lacking, making diagnosis and identification of the primary site very challenging. While in some NENs, such as the pancreatic ones, next generation sequencing technologies allowed the identification of new molecular hallmarks, our knowledge of the molecular profile of NENs from other anatomical sites is still poor.

METHODS

Starting from the concept that NENs from different organs may be clinically and genetically correlated, we applied a multi-omics approach by combining multigene panel testing, CGH-array, transcriptome and miRNome profiling and computational analyses, with the aim to highlight common molecular and functional signatures of gastroenteropancreatic (GEP)-NENs and medullary thyroid carcinomas (MTCs) that could aid diagnosis, prognosis and therapy.

RESULTS

By comparing genomic and transcriptional profiles, ATM-dependent signaling emerged among the most significant pathways at multiple levels, involving gene variations and miRNA-mediated regulation, thus representing a novel putative druggable pathway in these cancer types. Moreover, a set of circulating miRNAs was also selected as possible diagnostic/prognostic biomarkers useful for clinical management of NENs.

CONCLUSIONS

These findings depict a complex molecular and functional landscape of NENs, shedding light on novel therapeutic targets and disease biomarkers to be exploited.

New Synthetic Lethality Re-Sensitizing Platinum-Refractory Cancer Cells to Cisplatin In Vitro: The Rationale to Co-Use PARP and ATM Inhibitors

The pro-apoptotic tumor suppressor BIN1 inhibits the activities of the neoplastic transcription factor MYC, poly (ADP-ribose) polymerase-1 (PARP1), and ATM Ser/Thr kinase (ATM) by separate mechanisms. Although BIN1 deficits increase cancer-cell resistance to DNA-damaging chemotherapeutics, such as cisplatin, it is not fully understood when BIN1 deficiency occurs and how it provokes cisplatin resistance. Here, we report that the coordinated actions of MYC, PARP1, and ATM assist cancer cells in acquiring cisplatin resistance by BIN1 deficits. Forced BIN1 depletion compromised cisplatin sensitivity irrespective of Ser15-phosphorylated, pro-apoptotic TP53 tumor suppressor. The BIN1 deficit facilitated ATM to phosphorylate the DNA-damage-response (DDR) effectors, including MDC1. Consequently, another DDR protein, RNF8, bound to ATM-phosphorylated MDC1 and protected MDC1 from caspase-3-dependent proteolytic cleavage to hinder cisplatin sensitivity. Of note, long-term and repeated exposure to cisplatin naturally recapitulated the BIN1 loss and accompanying RNF8-dependent cisplatin resistance. Simultaneously, endogenous MYC was remarkably activated by PARP1, thereby repressing the BIN1 promoter, whereas PARP inhibition abolished the hyperactivated MYC-dependent BIN1 suppression and restored cisplatin sensitivity. Since the BIN1 gene rarely mutates in human cancers, our results suggest that simultaneous inhibition of PARP1 and ATM provokes a new BRCAness-independent synthetic lethal effect and ultimately re-establishes cisplatin sensitivity even in platinum-refractory cancer cells.

Exploring Somatic Alteration Associating With Aggressive Behaviors of Papillary Thyroid Carcinomas by Targeted Sequencing

Wisely differentiating high-risk papillary thyroid carcinoma (PTC) patients from low-risk PTC patients preoperatively is necessary when comes to making a personalized treatment plan. It is not easy to stratify the risk of patients according to sonography or lab results before surgery. This study aims to seek out potential mutation gene markers that may be helpful in stratifying the risk of PTC. A custom panel of 439 PTC relevant and classic tumor metabolic pathway relevant genes was designed. Targeted capture sequencing was performed on 35 pairs of samples from 35 PTC tumors and 35 para-tumor thyroid tissues obtained during surgery. Variant calling and detection of cancer gene mutations were identified by bio-information analysis. Ingenuity Pathway Analysis (IPA) was performed to do functional enrichment analysis of high-frequency mutant genes. Immunohistochemistry (IHC) was performed on 6 PTC patients to explore the expression of protein associated with interested genes. Event-free survival (EFS) was calculated to determine which genes might affect the prognosis of patients. We have identified 32 high-frequency mutant genes in PTC including BRAF. RBL2 was found to be significantly correlated to event-free survival, FOXO1, MUC6, PCDHB9, NOTCH1, FIZ1, and RTN1 were significantly associated with EFS, while BRAF mutant was not correlated to any of the prognosis indicators. Our findings in this study might open more choices when designing thyroid gene panels used in FNA samples to diagnose PTC and predict the potentially aggressive behavior of PTC.

rigrag: high-resolution mapping of genic targeting preferences during HIV-1 integration in vitro and in vivo

HIV-1 integration favors recurrent integration gene (RIG) targets and genic proviruses can confer cell survival in vivo. However, the relationship between initial RIG integrants and how these evolve in patients over time are unknown. To address these shortcomings, we built phenomenological models of random integration in silico, which were used to identify 3718 RIGs as well as 2150 recurrent avoided genes from 1.7 million integration sites across 10 in vitro datasets. Despite RIGs comprising only 13% of human genes, they harbored 70% of genic HIV-1 integrations across in vitro and patient-derived datasets. Although previously reported to associate with super-enhancers, RIGs tracked more strongly with speckle-associated domains. While depletion of the integrase cofactor LEDGF/p75 significantly reduced recurrent HIV-1 integration in vitro, LEDGF/p75 primarily occupied non-speckle-associated regions of chromatin, suggesting a previously unappreciated dynamic aspect of LEDGF/p75 functionality in HIV-1 integration targeting. Finally, we identified only six genes from patient samples-BACH2, STAT5B, MKL1, MKL2, IL2RB and MDC1-that displayed enriched integration targeting frequencies and harbored proviruses that likely contributed to cell survival. Thus, despite the known preference of HIV-1 to target cancer-related genes for integration, we conclude that genic proviruses play a limited role to directly affect cell proliferation in vivo.

VCP maintains nuclear size by regulating the DNA damage-associated MDC1-p53-autophagy axis in Drosophila

The maintenance of constant karyoplasmic ratios suggests that nuclear size has physiological significance. Nuclear size anomalies have been linked to malignant transformation, although the mechanism remains unclear. By expressing dominant-negative TER94 mutants in Drosophila photoreceptors, here we show disruption of VCP (valosin-containing protein, human TER94 ortholog), a ubiquitin-dependent segregase, causes progressive nuclear size increase. Loss of VCP function leads to accumulations of MDC1 (mediator of DNA damage checkpoint protein 1), connecting DNA damage or associated responses to enlarged nuclei. TER94 can interact with MDC1 and decreases MDC1 levels, suggesting that MDC1 is a VCP substrate. Our evidence indicates that MDC1 accumulation stabilizes p53A, leading to TER94^K2A-associated nuclear size increase. Together with a previous report that p53A disrupts autophagic flux, we propose that the stabilization of p53A in TER94^K2A-expressing cells likely hinders the removal of nuclear content, resulting in aberrant nuclear size increase.

Cells maintain a constant cytoplasm to nucleus volume ratio, although the role of DNA damage is not well explored. Here, the authors use Drosophila to connect TER94, the fly homolog of VCP, to disruption of DNA damage repair, leading to ubiquitinated Mu2 protein accumulation and enlarged nuclei.

Roles for MDC1 in cancer development and treatment

The DNA damage response (DDR) is necessary to maintain genome integrity and prevent the accumulation of oncogenic mutations. Consequently, proteins involved in the DDR often serve as tumor suppressors, carrying out the crucial task of keeping DNA fidelity intact. Mediator of DNA damage checkpoint 1 (MDC1) is a scaffold protein involved in the early steps of the DDR. MDC1 interacts directly with γ-H2AX, the phosphorylated form of H2AX, a commonly used marker for DNA damage. It then propagates the phosphorylation of H2AX by recruiting ATM kinase. While the function of MDC1 in the DDR has been reviewed previously, its role in cancer has not been reviewed, and numerous studies have recently identified a link between MDC1 and carcinogenesis. This includes MDC1 functioning as a tumor suppressor, with its loss serving as a biomarker for cancer and contributor to drug sensitivity. Studies also indicate that MDC1 operates outside of its traditional role in DDR, and functions as a co-regulator of nuclear receptor transcriptional activity, and that mutations in MDC1 are present in tumors and can also cause germline predisposition to cancer. This review will discuss reports that link MDC1 to cancer and identify MDC1 as an important player in tumor formation, progression, and treatment. We also discuss mechanisms by which MDC1 levels are regulated and how this contributes to tumor formation.

MDC1 depletion promotes cisplatin induced cell death in cervical cancer cells

OBJECTIVE

Cisplatin, the most common chemotherapeutic drug for the treatment of advanced stage cervical cancers has limitations in terms of drugs resistance observed in patients partly due to functional DNA damage repair (DDR) processes in the cell. Mediator of DNA damage checkpoint 1 (MDC1) is an important protein in the Ataxia telangiectasia mutated (ATM) mediated double stranded DNA break (DSB) repair pathway. In this regard, we investigated the effect of MDC1 change in expression on the cisplatin sensitivity in cervical cancer cells.

RESULTS

Through modulation of MDC1 expression in the cervical cancer cell lines; Hela, SiHa and Caski, we found that all the three cell lines silenced for MDC1 exhibited higher sensitivity to cisplatin treatment with inefficiency in accumulation of p γH2AX, Ser 139 foci and increased accumulation of pChk2 Thr 68 at the damaged chromatin followed by enhanced apoptosis. Further, we observed the increased p53 Ser 15 phosphorylation in the MDC1 depleted cells. Our studies suggest that MDC1 expression could be a key determinant in cervical cancer prognosis and its depletion in combination with cisplatin has the potential to be explored for the sensitisation of chemo-resistant cervical cancer cells.

Loss of NFBD1/MDC1 disrupts homologous recombination repair and sensitizes nasopharyngeal carcinoma cells to PARP inhibitors

BACKGROUND

Nasopharyngeal carcinoma (NPC), a highly invasive tumor, exhibits a distinctive racial and geographic distribution. As options of agents for effective combination chemoradiotherapy for advanced NPC are limited, novel therapeutic approaches are desperately needed. Here the potential of silencing NFBD1 in combination with PARP inhibition as a novel therapeutic strategy for NPC was investigated.

METHODS

To investigate the function of NFBD1, we created NFBD1-depleted NPC cell lines via lentivirus mediated shRNA, and the colony formation, MTS assay, comet assay and apoptosis analysis were used to evaluate the sensitivity of NFBD1 knockdown on PARP inhibition. The signaling change was assessed by western blot, Immunofluorescence and flow cytometry. Furthermore, Xenografts model was used to evaluate the role of silencing NFBD1 in combination with PARP inhibition.

RESULTS

We find that silencing NFBD1 in combination with PARP inhibition significantly inhibits the cell proliferation and cell cycle checkpoint activity, and increases the apoptosis and DNA damage. Mechanistic studies reveal that NFBD1 loss blocks olaparib-induced homologous recombination repair by decreasing the formation of BRCA1, BRCA2 and RAD51 foci. Furthermore, the xenograft tumor model demonstrated significantly increases sensitivity towards PARP inhibition under NFBD1 deficiency.

CONCLUSIONS

We show that NFBD1 depletion may possess sensitizing effects of PARP inhibitor, and consequently offers novel therapeutic options for a significant subset of patients.

Long non-coding RNA MDC1-AS inhibits human gastric cancer cell proliferation and metastasis through an MDC1-dependent mechanism

Gastric cancer is the third leading cause of cancer-associated mortality worldwide and is one of the most common malignancies in China. However, the molecular mechanisms underlying the tumorigenesis of gastric cancer remain largely unclear. Long non-coding (Lnc)RNAs have been demonstrated to serve significant roles in the tumorigenesis of various types of cancer. The present study aimed to explore the role of the LncRNA mediator of DNA damage checkpoint protein 1-antisense RNA (MDC1-AS), the antisense transcript of MDC1, in human gastric cancer. The results revealed that the expression of MDC1-AS in human gastric cancer was significantly suppressed in vivo and in vitro. In addition, overexpression of MDC1-AS in the poorly differentiated gastric cancer cell line MKN28 significantly inhibited cell proliferation and metastasis, while the knockdown of MDC1-AS in well-differentiated MKN45 gastric cancer cells significantly increased proliferation and metastasis. The knockdown of MDC1 relieved the inhibitory effect of MDC1-AS on MKN28 cell proliferation and metastasis, while the overexpression of MDC1 attenuated the stimulatory effect of MDC1-AS knockdown in MKN45 cells. Thus, the present study demonstrated that MDC1-AS had an inhibitory on gastric tumorigenesis through an MDC1-dependent mechanism. This indicates that MDC1-AS is a potential novel therapeutic target for the diagnosis and treatment of human gastric cancer in the clinic.

NFBD1/MDC1 participates in the regulation of proliferation and apoptosis in human laryngeal squamous cell carcinoma

PURPOSE

The objective of the study was to investigate the role of NFBD1 in the proliferation and apoptosis of laryngeal squamous cell carcinoma (LSCC) cells.

METHODS

Immunohistochemistry (IHC) and qRT-PCR was employed to determine the expressions of NFBD1 protein and mRNA in LSCC tissues and adjacent noncancerous tissues. After the downregulation of NFBD1 expression, the colony formation assay, MTS assay and apoptosis assay were used to investigate the changes in the proliferation and apoptosis of Hep2 cells. The mechanisms by which silencing NFBD1 promote apoptosis of Hep2 cells were examined by western blotting. Furthermore, xenograft models were used to evaluate the proliferation of Hep2 cells in vivo.

RESULTS

NFBD1 protein was upregulated in 55.6% of LSCC cancer tissues compared with adjacent normal tissues (26.7%). NFBD1 knockdown in Hep2 cells significantly impacted proliferation and apoptosis, and silencing NFBD1 might promote apoptosis of Hep2 cells by activating the mitochondrial apoptotic pathway. Xenograft models showed that silencing NFBD1 also significantly inhibited tumor growth.

CONCLUSIONS

Our data highlight that NFBD1 participates in the regulation of proliferation and apoptosis in LSCC, and suggest that NFBD1 could be a promising therapy target.

Senescence-Associated MicroRNAs

Senescent cells arise as a consequence of cellular damage and can have either a detrimental or advantageous impact on tissues and organs depending on the specific cell type and metabolic state. As senescent cells accumulate in tissues with advancing age, they have been implicated in many age-related declines and diseases. The major facets of senescence include two pathways responsible for establishing and maintaining a senescence program, p53/CDKN1A(p21) and CDKN2A(p16)/RB, as well as the senescence-associated secretory phenotype. Numerous MicroRNAs influence senescence by modulating the abundance of key senescence regulatory proteins, generally by lowering the stability and/or translation of mRNAs that encode such factors. Accordingly, understanding the molecular mechanisms by which MicroRNAs influence senescence will enable diagnostic and therapeutic opportunities directed at senescent cells. Here, we review senescence-associated (SA)-MicroRNAs and discuss their implications in senescence-relevant pathologies.

Depletion of NFBD1/MDC1 Induces Apoptosis in Nasopharyngeal Carcinoma Cells Through the p53-ROS-Mitochondrial Pathway

NFBD1, a signal amplifier of the p53 pathway, is vital for protecting cells from p53-mediated apoptosis and the early phase of DNA damage response under normal culture conditions. Here we investigated its expression in patients with nasopharyngeal carcinoma (NPC), and we describe the biological functions of the NFBD1 gene. We found that NFBD1 mRNA and protein were more highly expressed in NPC tissues than in nontumorous tissues. To investigate the function of NFBD1, we created NFBD1-depleted NPC cell lines that exhibited decreased cellular proliferation and colony formation, an increase in their rate of apoptosis, and an enhanced sensitivity to chemotherapeutic agents compared with in vitro controls. However, N-acetyl cysteine (NAC) and downregulation of p53 expression could partially reverse the apoptosis caused by the loss of NFBD1. Further analysis showed that loss of NFBD1 resulted in increased production of intracellular reactive oxygen species (ROS) depending on p53, which subsequently triggered the mitochondrial apoptotic pathway. Using a xenograft model in nude mice, we showed that silencing NFBD1 also significantly inhibited tumor growth and led to apoptosis. Taken together, our data suggest that inhibition of NFBD1 in NPC could be therapeutically useful.

Autocrine Wnt regulates the survival and genomic stability of embryonic stem cells

Wnt signaling plays an important role in the self-renewal and differentiation of stem cells. The secretion of Wnt ligands requires Evi (also known as Wls). Genetically ablating Evi provides an experimental approach to studying the consequence of depleting all redundant Wnt proteins, and overexpressing Evi enables a nonspecific means of increasing Wnt signaling. We generated Evi-deficient and Evi-overexpressing mouse embryonic stem cells (ESCs) to analyze the role of autocrine Wnt production in self-renewal and differentiation. Self-renewal was reduced in Evi-deficient ESCs and increased in Evi-overexpressing ESCs in the absence of leukemia inhibitory factor, which supports the self-renewal of ESCs. The differentiation of ESCs into cardiomyocytes was enhanced when Evi was overexpressed and teratoma formation and growth of Evi-deficient ESCs in vivo were impaired, indicating that autocrine Wnt ligands were necessary for ESC differentiation and survival. ESCs lacking autocrine Wnt signaling had mitotic defects and showed genomic instability. Together, our study demonstrates that autocrine Wnt secretion is important for the survival, chromosomal stability, differentiation, and tumorigenic potential of ESCs.

MDC1-AS, an antisense long noncoding RNA, regulates cell proliferation of glioma

BACKGROUND

Growing number of long noncoding RNAs (lncRNAs) are emerging as new modulators in cancer origination and progression. A lncRNA, mediator of DNA damage checkpoint protein 1antisense RNA (MDC1-AS), with unknown function, is the antisense transcript of tumor suppressor MDC1.

METHOD

In this study, we investigated the expression pattern and functional role of lncRNA MDC1-AS in glioma by using real time PCR and gain-/loss-of-function studies.

RESULT

The results showed that the expression levels of lncRNA MDC1-AS and MDC1 were significantly downregulated in glioma tissues compared with normal brain tissues, and in glioma cell lines U87MG, U251 and HEB. Overexpression of MDC1-AS resulted in significant inhibition of cell proliferation and cell cycle in U87MG and U251. We also found that MDC1-AS expression was positively correlated with MDC1 expression. In addition, the inhibitory role of MDC1-AS was remarkably diminished when MDC1 was knockdown.

CONCLUSION

Together, the results suggest that MDC1-AS is a novel tumor suppressor through up-regulation of its antisense tumor-suppressing gene MDC1 in glioma and leads us to propose that MDC1-AS may serve as a potential biomarker and therapeutic target for glioma.

Silencing NFBD1/MDC1 enhances the radiosensitivity of human nasopharyngeal cancer CNE1 cells and results in tumor growth inhibition

NFBD1 functions in cell cycle checkpoint activation and DNA repair following ionizing radiation (IR). In this study, we defined the NFBD1 as a tractable molecular target to radiosensitize nasopharyngeal carcinoma (NPC) cells. Silencing NFBD1 using lentivirus-mediated shRNA-sensitized NPC cells to radiation in a dose-dependent manner, increasing apoptotic cell death, decreasing clonogenic survival and delaying DNA damage repair. Furthermore, downregulation of NFBD1 inhibited the amplification of the IR-induced DNA damage signal, and failed to accumulate and retain DNA damage-response proteins at the DNA damage sites, which leaded to defective checkpoint activation following DNA damage. We also implicated the involvement of NFBD1 in IR-induced Rad51 and DNA-dependent protein kinase catalytic subunit foci formation. Xenografts models in nude mice showed that silencing NFBD1 significantly enhanced the antitumor activity of IR, leading to tumor growth inhibition of the combination therapy. Our studies suggested that a combination of gene therapy and radiation therapy may be an effective strategy for human NPC treatment.

In vitro antiproliferative and antioxidant effects of urolithin A, the colonic metabolite of ellagic acid, on hepatocellular carcinomas HepG2 cells

The intestinal metabolites of ellagic acid (EA), urolithins are known to effectively inhibit cancer cell proliferation. This study investigates antiproliferative and antioxidant effects of urolithin A (UA) on cell survival of the HepG2 hepatic carcinomas cell line. The antiproliferative effects of UA (0-500 μM) on HepG2 cells were determined using a CCK assay following 12-36 h exposure. Effects on β-catenin and other factors of expression were assessed by using real-time PCR and Western blot. We found that UA showed potent antiproliferative activity on HepG2 cells. When cell death was induced by UA, it was found that the expression of β-catenin, c-Myc and Cyclin D1 were decreased and TCF/LEF transcriptional activation was notably down-regulated. UA also increased protein expression of p53, p38-MAPK and caspase-3, but suppressed expression of NF-κB p65 and other inflammatory mediators. Furthermore, the antioxidant assay afforded by UA and EA treatments was associated with decreases in intracellular ROS levels, and increases in intracellular SOD and GSH-Px activity. These results suggested that UA could inhibit cell proliferation and reduce oxidative stress status in liver cancer, thus acting as a viably effective constituent for HCC prevention and treatment.

MDC1 Enhances Estrogen Receptor-mediated Transactivation and Contributes to Breast Cancer Suppression

Estrogen receptor α (ERα) is a key transcriptional factor in the proliferation and differentiation in mammary epithelia and has been determined to be an important predictor of breast cancer prognosis and therapeutic target. Meanwhile, diverse transcriptional co-regulators of ERα play crucial and complicated roles in breast cancer progression. Mediator of DNA damage checkpoint 1 (MDC1) has been identified as a critical upstream mediator in the cellular response to DNA damage, however, some non-DNA damage responsive functions of MDC1 haven't been fully defined. In this study, we have identified MDC1 as a co-activator of ERα in breast cancer cells and demonstrated that MDC1 associates with ERα. MDC1 was also recruited to estrogen response element (ERE) of ERα target gene. Knockdown of MDC1 reduced the transcription of the endogenous ERα target genes, including p21. MDC1 depletion led to the promotion of breast cancer progression, and the expression of MDC1 is lower in breast cancer. Taken together, these results suggested that MDC1 was involved in the enhancement of ERα-mediated transactivation in breast cancer cells. This positive regulation by MDC1 might contribute to the suppression of breast cancer progression by acting as a barrier of positive to negative ERα function transformation.

MDC1 functionally identified as an androgen receptor co-activator participates in suppression of prostate cancer

Mediator of DNA damage checkpoint protein 1 (MDC1) is essential for DNA damage response. However, the role of MDC1 in modulating gene transcription independently of DNA damage and the underlying mechanisms have not been fully defined. Androgen receptor (AR) is the central signaling pathway in prostate cancer (PCa) and its target genes are involved in both promotion and suppression of PCa. Here, we functionally identified MDC1 as a co-activator of AR. We demonstrate that MDC1 facilitates the association between AR and histone acetyltransferase GCN5, thereby increasing histone H3 acetylation level on cis-regulatory elements of AR target genes. MDC1 knockdown promotes PCa cells growth and migration. Moreover, depletion of MDC1 results in decreased expression of a subset of the endogenous androgen-induced target genes, including cell cycle negative regulator p21 and PCa metastasis inhibitor Vinculin, in AR positive PCa cell lines. Finally, the expression of MDC1 and p21 correlates negatively with aggressive phenotype of clinical PCa. These studies suggest that MDC1 as an epigenetic modifier regulates AR transcriptional activity and MDC1 may function as a tumor suppressor of PCa, and provide new insight into co-factor-AR-signaling pathway mechanism and a better understanding of the function of MDC1 on PCa.

A Newfound association between MDC1 functional polymorphism and lung cancer risk in Chinese

Mediator of DNA damage checkpoint protein 1 (MDC1) plays an early and core role in Double-Strand Break Repair (DDR) and ataxia telangiectasia-mutated (ATM) mediated response to DNA double-strand breaks (DSBs), and thus involves the pathogenesis of several DNA damage-related diseases such as cancer. We hypothesized that the single nucleotide polymorphisms (SNPs) of MDC1 which have potencies on affecting MDC1 expression or function were associated with risk of lung cancer. In a two-stage case-control study, we tested the association between 5 putatively functional SNPs of MDC1 and lung cancer risk in a southern Chinese population, and validated the promising association in an eastern Chinese population. We found the SNP rs4713354A>C that is located in the 5′-untranslated region of MDC1 was significantly associated with lung cancer risk in both populations (P = 0.001), with an odds ratio as 1.33(95% confidence interval = 1.14–1.55) for the rs4713354C (CA+CC) genotypes compared to the rs4713354AA genotype. The correct sixth sentence is: The gene-based analysis rested with these SNPs suggested the MDC1 as a susceptible gene for lung cancer (P = 0.057) [corrected]. Moreover, by querying the gene expression database, we further found that the rs4713354C genotypes confer a significantly lower mRNA expression of MDC1 than the rs4713354AA genotype in 260 cases of lymphoblastoid cells (P = 0.002). Our data suggested that the SNP rs4713354A>C of MDC1 may be a functional genetic biomarker for susceptibility to lung cancer in Chinese.

NFBD1/MDC1 is phosphorylated by PLK1 and controls G2/M transition through the regulation of a TOPOIIα-mediated decatenation checkpoint

Although it has been established that nuclear factor with BRCT domain 1/ mediator of the DNA damage checkpoint protein 1 (NFBD1/MDC1) is closely involved in DNA damage response, its possible contribution to the regulation of cell- cycle progression is unclear. In the present study, we have found for the first time that NFBD1 is phosphorylated by polo-like kinase 1 (PLK1) and has an important role in G2/M transition. Both NFBD1 and PLK1 are co-expressed in cellular nuclei throughout G2/M transition, and binding assays demonstrated direct interaction between NFBD1 and PLK1. Indeed, in vitro kinase reactions revealed that the PST domain of NFBD1 contains a potential amino acid sequence (845-DVTGEE-850) targeted by PLK1. Furthermore, enforced expression of GFP-PST but not GFP-PST(T847A) where threonine at 847 was substituted by alanine inhibited the phosphorylation levels of histone H3, suggesting a defect of M phase entry. Because PLK1 has been implicated in promoting the G2/M transition, we reasoned that overexpressed PST might serve as a pseudosubstrate for PLK1 and thus interfere with phosphorylation of endogenous PLK1 substrates. Interestingly, siRNA-mediated knockdown of NFBD1 resulted in early M phase entry and accelerated M phase progression, raising the possibility that NFBD1 is a PLK1 substrate for regulating the G2/M transition. Moreover, the constitutive active form of PLK1(T210D) overcame the ICRF-193-induced decatenation checkpoint and inhibited the interaction between NFBD1 and topoisomerase IIα, but kinase-deficient PLK1 did not. Based on these observations, we propose that PLK1-mediated phosphorylation of NFBD1 is involved in the regulation of G2/M transition by recovering a decatenation checkpoint.

Acetylation of lysine 382 and phosphorylation of serine 392 in p53 modulate the interaction between p53 and MDC1 in vitro

Occurrence of DNA damage in a cell activates the DNA damage response, a survival mechanism that ensures genomics stability. Two key members of the DNA damage response are the tumor suppressor p53, which is the most frequently mutated gene in cancers, and MDC1, which is a central adaptor that recruits many proteins to sites of DNA damage. Here we characterize the in vitro interaction between p53 and MDC1 and demonstrate that p53 and MDC1 directly interact. The p53-MDC1 interaction is mediated by the tandem BRCT domain of MDC1 and the C-terminal domain of p53. We further show that both acetylation of lysine 382 and phosphorylation of serine 392 in p53 enhance the interaction between p53 and MDC1. Additionally, we demonstrate that the p53-MDC1 interaction is augmented upon the induction of DNA damage in human cells. Our data suggests a new role for acetylation of lysine 382 and phosphorylation of serine 392 in p53 in the cellular stress response and offers the first evidence for an interaction involving MDC1 that is modulated by acetylation.

RUNX Family Participates in the Regulation of p53-Dependent DNA Damage Response

A proper DNA damage response (DDR), which monitors and maintains the genomic integrity, has been considered to be a critical barrier against genetic alterations to prevent tumor initiation and progression. The representative tumor suppressor p53 plays an important role in the regulation of DNA damage response. When cells receive DNA damage, p53 is quickly activated and induces cell cycle arrest and/or apoptotic cell death through transactivating its target genes implicated in the promotion of cell cycle arrest and/or apoptotic cell death such as p21^WAF1, BAX, and PUMA. Accumulating evidence strongly suggests that DNA damage-mediated activation as well as induction of p53 is regulated by posttranslational modifications and also by protein-protein interaction. Loss of p53 activity confers growth advantage and ensures survival in cancer cells by inhibiting apoptotic response required for tumor suppression. RUNX family, which is composed of RUNX1, RUNX2, and RUNX3, is a sequence-specific transcription factor and is closely involved in a variety of cellular processes including development, differentiation, and/or tumorigenesis. In this review, we describe a background of p53 and a functional collaboration between p53 and RUNX family in response to DNA damage.

Prediction of molecular mimicry candidates in human pathogenic bacteria

Molecular mimicry of host proteins is a common strategy adopted by bacterial pathogens to interfere with and exploit host processes. Despite the availability of pathogen genomes, few studies have attempted to predict virulence-associated mimicry relationships directly from genomic sequences. Here, we analyzed the proteomes of 62 pathogenic and 66 non-pathogenic bacterial species, and screened for the top pathogen-specific or pathogen-enriched sequence similarities to human proteins. The screen identified approximately 100 potential mimicry relationships including well-characterized examples among the top-scoring hits (e.g., RalF, internalin, yopH, and others), with about 1/3 of predicted relationships supported by existing literature. Examination of homology to virulence factors, statistically enriched functions, and comparison with literature indicated that the detected mimics target key host structures (e.g., extracellular matrix, ECM) and pathways (e.g., cell adhesion, lipid metabolism, and immune signaling). The top-scoring and most widespread mimicry pattern detected among pathogens consisted of elevated sequence similarities to ECM proteins including collagens and leucine-rich repeat proteins. Unexpectedly, analysis of the pathogen counterparts of these proteins revealed that they have evolved independently in different species of bacterial pathogens from separate repeat amplifications. Thus, our analysis provides evidence for two classes of mimics: complex proteins such as enzymes that have been acquired by eukaryote-to-pathogen horizontal transfer, and simpler repeat proteins that have independently evolved to mimic the host ECM. Ultimately, computational detection of pathogen-specific and pathogen-enriched similarities to host proteins provides insights into potentially novel mimicry-mediated virulence mechanisms of pathogenic bacteria.

Variant 1 of KIAA0101, overexpressed in hepatocellular carcinoma, prevents doxorubicin-induced apoptosis by inhibiting p53 activation

KIAA0101 overexpression was detected in numerous malignant solid tumors and involved in tumor progression; however, the correlation between KIAA0101 expression level and human hepatocellular carcinoma (HCC) was controversial. Our data revealed abnormal expression of the KIAA0101 transcript variant 1 (KIAA0101 tv1) at both messenger RNA and protein levels in HCC tissues and cell lines assessed by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR), virtual northern blot, western blot, and immunohistochemical analysis, especially in stage 3-4 HCCs. NIH3T3 cells transfected with KIAA0101 tv1 induced colony formation in vitro and tumor xenorafts in vivo, implying the oncogenic potential of KIAA0101 tv1. Semiquantitative RT-PCR, real-time quantitative RT-PCR, and western blot analysis demonstrated that doxorubicin (Adriamycin, ADR) treatment down-regulated expression of the KIAA0101 tv1, whereas it increased the acetylation of the p53 protein. Additionally, KIAA0101 tv1 prevented cells from apoptosis caused by ADR through suppressing the acetylation of p53 at Lys382. Immunoprecipitation analysis and mammalian two-hybrid assay indicated that KIAA0101 tv1 bound to the transactivation region (1-42 amino acids) of p53 and strongly inhibits its transcriptional activity. Taken together, our data suggest that KIAA0101 tv1 played an important role in the late stage of metastatic HCC and prevented apoptosis after chemotherapeutic drug treatment through inhibiting the transcriptional activity of the p53 gene.

CONCLUSION

KIAA0101 tv1 may function as a regulator, promoting cell survival in HCC through regulating the function of p53. Suppression of the KIAA0101 tv1 function is likely to be a promising strategy to develop novel cancer therapeutic drugs.

Oligomerization of MDC1 protein is important for proper DNA damage response

Mediator of DNA damage checkpoint 1 (MDC1) plays an important role in the DNA damage response (DDR). MDC1 functions as a mediator protein and binds multiple proteins involved in different aspects of the DDR. However, little is know about the organization of MDC1 complexes. Here we show that ataxia telangiectasia, mutated (ATM) phosphorylates MDC1 at Thr-98 following DNA damage, which promotes its oligomerization. Oligomerization of MDC1 is important for the accumulation of MDC1 complex at the sites of DNA damage. Mutation of Thr-98 (T98A) would abolish its oligomerization and result in a defect in DNA damage checkpoint activation and increased sensitivity to irradiation. Taken together, these results suggest that the oligomerization of MDC1 plays an important role in DDR and help understand the formation of proteins complexes at the sites of DNA damage.

NFBD1/MDC1 regulates Cav1 and Cav2 independently of DNA damage and p53

NFBD1/MDC1 is involved in DNA damage checkpoint signaling and DNA repair. NFBD1 binds to the chromatin component γH2AX at sites of DNA damage, causing amplification of ataxia telangiectasia-mutated gene (ATM) pathway signaling and recruitment of DNA repair factors. Residues 508-995 of NFBD1 possess transactivation activity, suggesting a possible role of NFBD1 in transcription. Furthermore, NFBD1 influences p53-mediated transcription in response to adriamycin. We sought to determine the role of NFBD1 in ionizing radiation (IR)-responsive transcription and if NFBD1 influences transcription independently of p53. Using microarray analysis, we identified genes altered upon NFBD1 knockdown. Surprisingly, most NFBD1 regulated genes are regulated in both the absence and presence of IR, thus pointing toward a novel function for NFBD1 outside of the DNA damage response. Furthermore, NFBD1 knockdown regulated genes mostly independent of p53 knockdown. These genes are involved in pathways including focal adhesion signaling, carbohydrate metabolism, and insulin signaling. We found that CAV1 and CAV2 mRNA and protein levels are reduced by both NFBD1 knockdown and knockout independently of IR and p53. NFBD1-depleted cells exhibit some similar phenotypes to Cav1-depleted cells. Furthermore, like Cav1-depletion, NFBD1 shRNA increases Erk phosphorylation. Thus, Cav1 could act as a mediator of the DNA-damage independent effects of NFBD1 in mitogenic signaling.

Role of p53 in Cell Death and Human Cancers

p53 is a nuclear transcription factor with a pro-apoptotic function. Since over 50% of human cancers carry loss of function mutations in p53 gene, p53 has been considered to be one of the classical type tumor suppressors. Mutant p53 acts as the dominant-negative inhibitor toward wild-type p53. Indeed, mutant p53 has an oncogenic potential. In some cases, malignant cancer cells bearing p53 mutations display a chemo-resistant phenotype. In response to a variety of cellular stresses such as DNA damage, p53 is induced to accumulate in cell nucleus to exert its pro-apoptotic function. Activated p53 promotes cell cycle arrest to allow DNA repair and/or apoptosis to prevent the propagation of cells with serious DNA damage through the transactivation of its target genes implicated in the induction of cell cycle arrest and/or apoptosis. Thus, the DNA-binding activity of p53 is tightly linked to its tumor suppressive function. In the present review article, we describe the regulatory mechanisms of p53 and also p53-mediated therapeutic strategies to cure malignant cancers.

p53: the attractive tumor suppressor in the cancer research field

p53 is one of the most studied tumor suppressors in the cancer research field. Of note, over 50% of human tumors carry loss of function mutations, and thus p53 has been considered to be a classical Knudson-type tumor suppressor. From the functional point of view, p53 is a nuclear transcription factor to transactivate a variety of its target genes implicated in the induction of cell cycle arrest, DNA repair, and apoptotic cell death. In response to cellular stresses such as DNA damage, p53 is activated and promotes cell cycle arrest followed by the replacement of DNA lesions and/or apoptotic cell death. Therefore, p53 is able to maintain the genomic integrity to prevent the accumulation of genetic alterations, and thus stands at a crossroad between cell survival and cell death. In this paper, we describe a variety of molecular mechanisms behind the regulation of p53.

Mediator of DNA damage checkpoint protein 1 (MDC1) expression as a prognostic marker for nodal recurrence in early-stage breast cancer patients treated with breast-conserving surgery and radiation therapy

The mediator of DNA damage checkpoint protein 1 (MDC1) regulates cell cycle checkpoints and recruits repair proteins to sites of double-stranded DNA damage using its BRCA1 carboxy-terminal (BRCT) domains. MDC1 under-expression has been associated with radiosensitivity in cells. The purpose of this study was to evaluate the clinico-pathologic and prognostic significance of MDC1 expression in a cohort of early-stage breast cancer patients treated with breast conservation therapy. Paraffin specimens from 489 women with early-stage breast cancer treated with breast conservation therapy were constructed into tissue microarrays. The arrays were stained for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and MDC1. This was correlated with clinico-pathologic factors and outcomes. MDC1 expression was evaluable in 351 cases (72%). Decreased MDC1 expression was found to be correlated with nodal failure (P = 0.05), but not ipsilateral breast relapse-free survival (IBRFS), distant metastasis-free survival (DMFS), or overall survival (OS). Subset analysis in node-negative patients revealed that decreased MDC1 expression predicted for nodal failure (P < 0.01). Our study is the first to assess the clinico-pathologic and prognostic significance of MDC1 expression in patients with early-stage breast cancer treated with lumpectomy and radiotherapy. MDC1 under-expression predicted for nodal failure, but not for IBRFS, DM, or OS. The role of other proteins involved in the DNA damage repair pathway and their effects on MDC1 expression, as well as the level of MDC1 expression in patients with BRCA1 mutations warrant further investigation.

Growth inhibition, morphology change, and cell cycle alterations in NFBD1-depleted human esophageal cancer cells

NFBD1/MDC1 is a large nuclear protein mainly participating in DNA damage response, indicating its therapeutic potential as a radio-/chemosensitizer target in cancer field. Esophageal cancer ranks among one of the most frequent cause of cancer death in the world. In this study, we used three representative esophageal cancer cell lines to investigate the effects of NFBD1 silencing on cell proliferation, cell morphology, and cell cycle distribution. Synthetic small interfering RNA (siRNA) duplexes against NFBD1 were introduced into three esophageal cancer cell lines, which subsequently resulted in a significant inhibition in NFBD1 expression in the cells. Our results have shown that a targeted siRNA depletion of NFBD1 resulted in a significant growth inhibition, morphology change, and cell cycle alterations in esophageal cancer cells. Furthermore, NFBD1 depletion also sensitized all the three esophageal cancer cell lines to chemotherapeutic agents including adriamycin and cisplatin. Taken together, our study strongly suggested that NFBD1 may serve as a potential therapeutic target in human esophageal cancer.

Regulation of p53--insights into a complex process

The p53 protein is one of the most important tumor suppressor proteins. Normally, the p53 protein is in a latent state. However, when its activity is required, e.g. upon DNA damage, nucleotide depletion or hypoxia, p53 becomes rapidly activated and initiates transcription of pro-apoptotic and cell cycle arrest-inducing target genes. The activity of p53 is regulated both by protein abundance and by post-translational modifications of pre-existing p53 molecules. In the 30 years of p53 research, a plethora of modifications and interaction partners that modulate p53's abundance and activity have been identified and new ones are continuously discovered. This review will summarize our current knowledge on the regulation of p53 abundance and activity.

Mechanisms of prostate cancer cell survival after inhibition of AR expression

Recent reports have shown that the AR is the key determinant of the molecular changes required for driving prostate cancer cells from an androgen-dependent to an androgen-independent or androgen depletion-independent (ADI) state. Several recent publications suggest that down-regulation of AR expression should therefore be considered the principal strategy for the treatment of ADI prostate cancer. However, no valid data is available about how androgen-dependent prostate cancer cells respond to apoptosis-inducing drugs after knocking down AR expression and whether prostate cancer cells escape apoptosis after inhibition of AR expression. This review will focus on mechanisms of prostate cancer cell survival after inhibition of AR activity mediated either by androgen depletion or by targeting the expression of AR by siRNA. We have shown that knocking down AR expression by siRNA induced PI3K-independent activation of Akt, which was mediated by calcium/calmodulin-dependent kinase II (CaMKII). We also showed that the expression of CaMKII genes is under AR control: active AR in the presence of androgens inhibits CaMKII gene expression whereas inhibition of AR activity results in an elevated level of kinase activity and in enhanced expression of CaMKII genes. This in turn activates the anti-apoptotic PI3K/Akt pathways. CaMKII also express anti-apoptotic activity that is independent from the Akt pathway. This may therefore be an important mechanism by which prostate cancer cells escape apoptosis after androgen depletion or knocking down AR expression. In addition, we have found that there is another way to escape cell death after AR inhibition: DNA damaging agents cannot fully activate p53 in the absence of AR and as a result p53 down stream targets, for example, microRNA-34, cannot be activated and induce apoptosis. This implies that there may be a need for re-evaluation of the therapeutic approaches to human prostate cancer.

In silico analysis of phosphoproteome data suggests a rich-get-richer process of phosphosite accumulation over evolution

Recent phosphoproteome analyses using mass spectrometry-based technologies have provided new insights into the extensive presence of protein phosphorylation in various species and have raised the interesting question of how this protein modification was gained evolutionarily on such a large scale. We investigated this issue by using human and mouse phosphoproteome data. We initially found that phosphoproteins followed a power-law distribution with regard to their number of phosphosites: most of the proteins included only a few phosphosites, but some included dozens of phosphosites. The power-law distribution, unlike more commonly observed distributions such as normal and log-normal distributions, is considered by the field of complex systems science to be produced by a specific rich-get-richer process called preferential attachment growth. Therefore, we explored the factors that may have promoted the rich-get-richer process during phosphosite evolution. We conducted a bioinformatics analysis to evaluate the relationship of amino acid sequences of phosphoproteins with the positions of phosphosites and found an overconcentration of phosphosites in specific regions of protein surfaces and implications that in many phosphoproteins these clusters of phosphosites are activated simultaneously. Multiple phosphosites concentrated in limited spaces on phosphoprotein surfaces may therefore function biologically as cooperative modules that are resistant to selective pressures during phosphoprotein evolution. We therefore proposed a hypothetical model by which the modularization of multiple phosphosites has been resistant to natural selection and has driven the rich-get-richer process of the evolutionary growth of phosphosite numbers.

Promotion of cell death or neurite outgrowth in PC-12 and N2a cells by the fungal alkaloid militarinone A depends on basal expression of p53

The fungal alkaloid militarinone A (MiliA) was recently found to stimulate neuronal outgrowth in PC-12 cells by persistant activation of pathways that are also involved in NGF-mediated differentiation, namely the PI3-K/PKB and the MEK/ERK pathways. Application of equal concentrations of MiliA to other cells such as the murine neuroblastoma cell line N2a resulted in immediate onset of apoptosis by nuclear translocation of apoptosis inducing factor (AIF), activation of caspases and c-Jun/AP-1 transcription factor without an intermediate differentiated phenotype, although minor transient phosphorylation of PKB and MAPK as well as activation of NF-kappaB were also observed. Translocation of AIF was preceded by p53 phosphorylation at Ser15 and blocked by pifithrin alpha, a known inhibitor of p53-transcriptional activity. We here show that both cell types activate the same pathways albeit in different time scales. This is mainly due to contrasting basal expression levels of p53, which in turn regulates expression of AIF. In PC-12 cells, continuous activation of these pathways after prolonged treatment with 40 muM MiliA first led to up-regulation of p53, phosphorylation of p53, release of AIF from mitochondria and its translocation into the nucleus. Additionally, also activation of the c-Jun/AP-1 transcription factor was observed, and PC-12 cells subsequently underwent apoptosis 48-72 h post-treatment. We report that similar pathways working on different levels are able to initially shape very divergent cellular responses.

Sp1-mediated transcriptional regulation of NFBD1/MDC1 plays a critical role in DNA damage response pathway

NFBD1/MDC1 is a large nuclear protein with an anti-apoptotic potential which participates in DNA damage response. Recently, we have demonstrated that NFBD1 has an inhibitory effect on pro-apoptotic p53 and DNA damage-induced transcriptional repression of NFBD1 plays an important role in p53-dependent apoptotic response. In this study, we have found that NFBD1 promoter region contains canonical Sp1-, STAT-1- and NF-Y-binding sites and finally we have identified Sp1 as a transcriptional activator for NFBD1. The 5'-RACE and bioinformatic analyses revealed that NFBD1 encodes at least four transcriptional variants arising from distinct transcriptional start sites. Luciferase reporter assays using a series of NFBD1 promoter deletion mutants demonstrated that the proximal Sp1-binding site is required for the transcriptional activation of NFBD1. Indeed, the endogenous Sp1 was recruited onto the proximal Sp1-binding site as examined by chromatin immunoprecipitation (ChIP) assay and siRNA-mediated knockdown of the endogenous Sp1 in HeLa cells reduced the expression levels of NFBD1, which renders cells sensitive to adriamycin (ADR). In support of this notion, mithramycin A (MA, Sp1 inhibitor) treatment resulted in a significant down-regulation of NFBD1. Taken together, our present findings suggest that Sp1-mediated transcriptional regulation of NFBD1 plays an important role in the regulation of DNA damage response.