The p53 response: emerging levels of co-factor complexity

Unraveling the signaling mechanism behind astrocytoma and possible therapeutics strategies: A comprehensive review

BACKGROUND

A form of cancer called astrocytoma can develop in the brain or spinal cord and sometimes causes death. A detailed overview of the precise signaling cascade underlying astrocytoma formation has not yet been revealed, although various factors have been investigated. Therefore, our objective was to unravel and summarize our current understanding of molecular genetics and associated signaling pathways with some possible therapeutic strategies for astrocytoma.

RECENT FINDINGS

In general, four different forms of astrocytoma have been identified in individuals, including circumscribed, diffuse, anaplastic, and multiforme glioblastoma, according to a recent literature review. All types of astrocytoma have a direct connection with some oncogenic signaling cascade. Common signaling is MAPK cascade, including Ras-Raf-ERK, up-regulated with activating EGFR/AKT/PTEN/mTOR and PDGFR. Recent breakthrough studies found that BRAF mutations, including KIAA1549: BRAF and BRAF V600E are responsible for astrocytoma progression. Additionally, cancer progression is influenced by mutations in some tumor suppressor genes, such as the Tp53/ATRX and MGMT mutant. As synthetic medications must cross the blood-brain barrier (BBB), modulating signal systems such as miRNA is the primary option for treating patients with astrocytoma. However, available surgery, radiation therapy, and experimental therapies such as adjuvant therapy, anti-angiogenic therapy, and EGFR-targeting antibody drug are the usual treatment for most types of astrocytoma. Similar to conventional anticancer medications, some phytochemicals slow tumor growth by simultaneously controlling several cellular proteins, including those involved in cell cycle regulation, apoptosis, metastatic spread, tyrosine kinase, growth factor receptor, and antioxidant-related proteins.

CONCLUSION

In conclusion, cellular and molecular signaling is directly associated with the development of astrocytoma, and a combination of conventional and alternative therapies can improve the malignancy of cancer patients.

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

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

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

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

Weighted miRNA co-expression network reveals potential roles of apoptosis related pathways and crucial genes in thoracic aortic aneurysm

Background

Thoracic aortic aneurysm (TAA) is a potentially life-threatening disease for which few medical therapies are available. Thus, it is critically important to investigate the underlying molecular mechanisms of TAA, and identify potential targets for TAA treatment.

Methods

Differentially expressed miRNAs (DEMs) and differentially expressed genes (DEGs) were screened, and a weighted correlation network analysis (WGCNA) was employed to construct a weighted miRNA co-expression network using GSE110527. The DEMs were then mapped into the whole co-expression network of all samples, and a DEM coexpression network was created. Molecular Complex Detection (MCODE) was used to identify crucial miRNAs. Target genes were predicted using the miRTarbase database, and further screened by identifying genes that overlapped with the DEGs of GSE26155. The screened target genes were validated using GSE9106, and the successfully validated genes were considered as crucial genes. Finally, a miRNA risk score for diagnosing TAA was calculated by undertaking a least absolute shrinkage and selection operator (LASSO) regression.

Results

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) signaling pathway was found in DEM functional enrichment. Crucial miRNAs were identified and target genes were predicted and associated with the regulation of the TRAIL signaling pathway. Next, 113 important target genes were identified as overlapping with the DEGs of GSE26155. These genes were further validated, and 5 successfully validated genes were considered as crucial genes. Finally, the miRNA risk score calculated by the LASSO regression was shown to have potential diagnostic value.

Conclusions

We performed a WGCNA analysis to construct a weighted miRNA co-expression network, predicted target genes of crucial miRNAs, identified crucial genes, and finally calculated a miRNA risk score. The results showed that pathways and genes associated with apoptosis appear to play an important role in TAA pathogenesis, and that medications targeting apoptosis might slow TAA progression. Future in vitro and in vivo experimental studies need to be undertaken to further validate our findings and investigate the mechanistic details of these crucial miRNAs and crucial genes.

The role of MiRNA-21 in gliomas: Hope for a novel therapeutic intervention?

Gliomas are the most common primary brain tumors in adults. They are generally very resistant to treatment and are therefore associated with negative outcomes. MicroRNAs (miRNAs) are small, non-coding RNA molecules that affect many cellular processes by regulating gene expression and, post-transcriptionally, the translation of mRNAs. MiRNA-21 has been consistently shown to be upregulated in glioma and research has shown that it is involved in a wide variety of biological pathways, promoting tumor cell survival and invasiveness. Furthermore, it has been implicated in resistance to treatment, both against chemotherapy and radiotherapy. In this review, we gathered the existent data on miRNA-21 and gliomas, in terms of its expression levels, association with grade and prognosis, the pathways it involves and its targets in glioma, and finally how it leads to treatment resistance. Furthermore, we discuss how this knowledge could be applied in clinical practice in the years to come. To our knowledge, this is the first review to assess in extent and depth the role of miRNA-21 in gliomas.

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

Objective

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

Methods

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

Results

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

Conclusion

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

Recent Trends of microRNA Significance in Pediatric Population Glioblastoma and Current Knowledge of Micro RNA Function in Glioblastoma Multiforme

Central nervous system tumors are a significant problem for modern medicine because of their location. The explanation of the importance of microRNA (miRNA) in the development of cancerous changes plays an important role in this respect. The first papers describing the presence of miRNA were published in the 1990s. The role of miRNA has been pointed out in many medical conditions such as kidney disease, diabetes, neurodegenerative disorder, arthritis and cancer. There are several miRNAs responsible for invasiveness, apoptosis, resistance to treatment, angiogenesis, proliferation and immunology, and many others. The research conducted in recent years analyzing this group of tumors has shown the important role of miRNA in the course of gliomagenesis. These particles seem to participate in many stages of the development of cancer processes, such as proliferation, angiogenesis, regulation of apoptosis or cell resistance to cytostatics.

Novel genes exhibiting DNA methylation alterations in Korean patients with chronic lymphocytic leukaemia: a methyl-CpG-binding domain sequencing study

Chronic lymphocytic leukaemia (CLL) exhibits differences between Asians and Caucasians in terms of incidence rate, age at onset, immunophenotype, and genetic profile. We performed genome-wide methylation profiling of CLL in an Asian cohort for the first time. Eight Korean patients without somatic immunoglobulin heavy chain gene hypermutations underwent methyl-CpG-binding domain sequencing (MBD-seq), as did five control subjects. Gene Ontology, pathway analysis, and network-based prioritization of differentially methylated genes were also performed. More regions were hypomethylated (2,062 windows) than were hypermethylated (777 windows). Promoters contained the highest proportion of differentially methylated regions (0.08%), while distal intergenic and intron regions contained the largest number of differentially methylated regions. Protein-coding genes were the most abundant, followed by long noncoding and short noncoding genes. The most significantly over-represented signalling pathways in the differentially methylated gene list included immune/cancer-related pathways and B-cell receptor signalling. Among the top 10 hub genes identified via network-based prioritization, four (UBC, GRB2, CREBBP, and GAB2) had no known relevance to CLL, while the other six (STAT3, PTPN6, SYK, STAT5B, XPO1, and ABL1) have previously been linked to CLL in Caucasians. As such, our analysis identified four novel candidate genes of potential significance to Asian patients with CLL.

SETD3 is a positive regulator of DNA-damage-induced apoptosis

SETD3 is a member of the protein lysine methyltransferase (PKMT) family, which catalyzes the addition of methyl group to lysine residues. However, the protein network and the signaling pathways in which SETD3 is involved remain largely unexplored. In the current study, we show that SETD3 is a positive regulator of DNA-damage-induced apoptosis in colon cancer cells. Our data indicate that depletion of SETD3 from HCT-116 cells results in a significant inhibition of apoptosis after doxorubicin treatment. Our results imply that the positive regulation is sustained by methylation, though the substrate remains unknown. We present a functional cross-talk between SETD3 and the tumor suppressor p53. SETD3 binds p53 in cells in response to doxorubicin treatment and positively regulates p53 target genes activation under these conditions. Mechanistically, we provide evidence that the presence of SETD3 and its catalytic activity is required for the recruitment of p53 to its target genes. Finally, Kaplan-Meier survival analysis, of two-independent cohorts of colon cancer patients, revealed that low expression of SETD3 is a reliable predictor of poor survival in these patients, which correlates with our findings. Together, our data uncover a new role of the PKMT SETD3 in the regulation of p53-dependent activation of apoptosis in response to DNA damage.

The Role of JMY in p53 Regulation

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

The induction of tumour suppressor protein P53 limits the entry of cells into the pluripotent inner cell mass lineage in the mouse embryo

The early preimplantation embryo is susceptible to a range of exogenous stresses which result in their reduced long-term developmental potential. The P53 tumour suppressor protein is normally held at low levels in the preimplantation embryo and we show that culture stress induces the expression of a range of canonical P53-response genes (Mdm2, Bax and Cdkn1a). Culture stress caused a P53-dependent loss of cells from resulting blastocysts, and this was most evident within the inner cell mass population. Culture stress increased the proportion of cells expressing active caspase-3 and undergoing apoptosis, while inhibition of caspase-3 increased the number of cells within the inner cell mass. The P53-dependent loss of cells from the inner cell mass was accompanied by a loss of NANOG-positive epiblast progenitors. Pharmacological activation of P53 by the MDM2 inhibitor, Nutlin-3, also caused increased P53-dependent transcription and the loss of cells from the inner cell mass. This loss of cells could be ameliorated by simultaneous treatment with the P53 inhibitor, Pifithrin-α. Culture stress causes reduced signalling via the phosphatidylinositol-3-kinase signalling pathway, and blocking this pathway caused P53-dependent loss of cells from the inner cell mass. These results point to P53 acting to limit the accumulation and survival of cells within the pluripotent lineage of the blastocyst and provide a molecular framework for the further investigation of the factors determining the effects of stressors on the embryo's developmental potential.

Depletion of UBA protein 2-like protein inhibits growth and induces apoptosis of human colorectal carcinoma cells

Ubiquitin-proteasome system regulates cell proliferation, apoptosis, angiogenesis, and motility, which are processes with particular importance for carcinogenesis. UBA protein 2-like protein (UBAP2L) was found to be associated with proteasome; however, its biological function is largely unknown. In this study, the mRNA levels of UBAP2L in human normal and colorectal carcinoma tissues were analyzed using the datasets from the publicly available Oncomine database ( www.oncomine.org ) and found UBAP2L was overexpressed in colorectal carcinoma tissues. Furthermore, we elucidated the role of UBAP2L in human colorectal cancer via an RNA interference lentivirus system in three colorectal carcinoma cell lines HCT116, SW1116, and RKO. Knockdown of UBAP2L led to suppressed cell proliferation and impaired colony formation. UBAP2L depletion in HCT116 and RKO cells also induced cell cycle arrest as well as apoptosis. Moreover, the phosphorylation of PRAS40, Bad, and the cleavage of PARP were remarkably increased after UBAP2L knockdown by Intracellular signaling array and also the activation of P38 was obviously decreased and the cleavage of Caspase 3 and Bax were increased after UBAP2L silencing by western blot assay, indicated that UBAP2L might be involved in the cell growth by the regulation of apoptosis-related proteins. Our findings indicated that UBAP2L may be essential for colorectal carcinoma growth and survival. Lentivirus-mediated small interfering RNA against UBAP2L might serve as a potential therapeutic approach for the treatment of colorectal cancer.

Negative regulation of the p300-p53 interplay by DDX24

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

Protein arginine methyltransferase 5 catalyzes substrate dimethylation in a distributive fashion

Protein arginine methyltransferase 5 (PRMT5) is a histone-modifying enzyme whose activity is aberrantly upregulated in various cancers and thereby contributes to a progrowth phenotype. Indeed, knockdown of PRMT5 leads to growth arrest and apoptosis, suggesting that inhibitors targeting this enzyme may have therapeutic utility in oncology. To aid the development of inhibitors targeting PRMT5, we initiated mechanistic studies geared to understand how PRMT5 selectively catalyzes the symmetric dimethylation of its substrates. Toward that end, we characterized the regiospecificity and processivity of bacterially expressed Caenorhabditis elegans PRMT5 (cPRMT5), insect cell-expressed human PRMT5 (hPRMT5), and human PRMT5 complexed with methylosome protein 50 (MEP50), i.e., the PRMT5·MEP50 complex. Our studies confirm that arginine 3 is the only site of methylation in both histone H4 and H4 tail peptide analogues and that sites distal to the site of methylation promote the efficient symmetric dimethylation of PRMT5 substrates by increasing the affinity of the monomethylated substrate for the enzyme. Additionally, we show for the first time that both cPRMT5 and the hPRMT5·MEP50 complex catalyze substrate dimethylation in a distributive manner, which is assisted by long-range interactions. Finally, our data confirm that MEP50 plays a key role in substrate recognition and activates PRMT5 activity by increasing its affinity for protein substrates. In total, our results suggest that it may be possible to allosterically inhibit PRMT5 by targeting binding pockets outside the active site.

Discovery and optimization of small-molecule ligands for the CBP/p300 bromodomains

Small-molecule inhibitors that target bromodomains outside of the bromodomain and extra-terminal (BET) sub-family are lacking. Here, we describe highly potent and selective ligands for the bromodomain module of the human lysine acetyl transferase CBP/p300, developed from a series of 5-isoxazolyl-benzimidazoles. Our starting point was a fragment hit, which was optimized into a more potent and selective lead using parallel synthesis employing Suzuki couplings, benzimidazole-forming reactions, and reductive aminations. The selectivity of the lead compound against other bromodomain family members was investigated using a thermal stability assay, which revealed some inhibition of the structurally related BET family members. To address the BET selectivity issue, X-ray crystal structures of the lead compound bound to the CREB binding protein (CBP) and the first bromodomain of BRD4 (BRD4(1)) were used to guide the design of more selective compounds. The crystal structures obtained revealed two distinct binding modes. By varying the aryl substitution pattern and developing conformationally constrained analogues, selectivity for CBP over BRD4(1) was increased. The optimized compound is highly potent (K_d = 21 nM) and selective, displaying 40-fold selectivity over BRD4(1). Cellular activity was demonstrated using fluorescence recovery after photo-bleaching (FRAP) and a p53 reporter assay. The optimized compounds are cell-active and have nanomolar affinity for CBP/p300; therefore, they should be useful in studies investigating the biological roles of CBP and p300 and to validate the CBP and p300 bromodomains as therapeutic targets.

Proline, glutamic acid and leucine-rich protein-1 is essential for optimal p53-mediated DNA damage response

Proline-, glutamic acid- and leucine-rich protein-1 (PELP1) is a scaffolding oncogenic protein that functions as a coregulator for a number of nuclear receptors. p53 is an important transcription factor and tumor suppressor that has a critical role in DNA damage response (DDR) including cell cycle arrest, repair or apoptosis. In this study, we found an unexpected role for PELP1 in modulating p53-mediated DDR. PELP1 is phosphorylated at Serine1033 by various DDR kinases like ataxia-telangiectasia mutated, ataxia telangiectasia and Rad3-related or DNAPKc and this phosphorylation of PELP1 is important for p53 coactivation functions. PELP1-depleted p53 (wild-type) breast cancer cells were less sensitive to various genotoxic agents including etoposide, camptothecin or γ-radiation. PELP1 interacts with p53, functions as p53-coactivator and is required for optimal activation of p53 target genes under genomic stress. Overall, these studies established a new role of PELP1 in DDRs and these findings will have future implications in our understanding of PELP1's role in cancer progression.

Classification of a frameshift/extended and a stop mutation in WT1 as gain-of-function mutations that activate cell cycle genes and promote Wilms tumour cell proliferation

The WT1 gene encodes a zinc finger transcription factor important for normal kidney development. WT1 is a suppressor for Wilms tumour development and an oncogene for diverse malignant tumours. We recently established cell lines from primary Wilms tumours with different WT1 mutations. To investigate the function of mutant WT1 proteins, we performed WT1 knockdown experiments in cell lines with a frameshift/extension (p.V432fsX87 = Wilms3) and a stop mutation (p.P362X = Wilms2) of WT1, followed by genome-wide gene expression analysis. We also expressed wild-type and mutant WT1 proteins in human mesenchymal stem cells and established gene expression profiles. A detailed analysis of gene expression data enabled us to classify the WT1 mutations as gain-of-function mutations. The mutant WT1^Wilms2 and WT1^Wilms3 proteins acquired an ability to modulate the expression of a highly significant number of genes from the G2/M phase of the cell cycle, and WT1 knockdown experiments showed that they are required for Wilms tumour cell proliferation. p53 negatively regulates the activity of a large number of these genes that are also part of a core proliferation cluster in diverse human cancers. Our data strongly suggest that mutant WT1 proteins facilitate expression of these cell cycle genes by antagonizing transcriptional repression mediated by p53. We show that mutant WT1 can physically interact with p53. Together the findings show for the first time that mutant WT1 proteins have a gain-of-function and act as oncogenes for Wilms tumour development by regulating Wilms tumour cell proliferation.

A case report and genetic characterization of a massive acinic cell carcinoma of the parotid with delayed distant metastases

We describe the presentation, management, and clinical outcome of a massive acinic cell carcinoma of the parotid gland. The primary tumor and blood underwent exome sequencing which revealed deletions in CDKN2A as well as PPP1R13B, which induces p53. A damaging nonsynonymous mutation was noted in EP300, a histone acetylase which plays a role in cellular proliferation. This study provides the first insights into the genetic underpinnings of this cancer. Future large-scale efforts will be necessary to define the mutational landscape of salivary gland malignancies to identify therapeutic targets and biomarkers of treatment failure.

Associations of genetic variants in the transcriptional coactivators EP300 and PCAF with hepatocellular carcinoma

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is a common cause of death by cancer worldwide. In Morocco, HCC is characterized by few mutations and a mild chromosome instability suggesting that epigenetic changes may represent the driving force of tumorigenesis in the region. Recently, three studies looked for an association between EP300 or PCAF polymorphisms and cancer but there is a conspicuous lack of data regarding these histone acetyltransferase (HAT) variants and HCC development. The aim of the current study was to assess the impact of the Ile997Val in EP300 and Asn386Ser in PCAF polymorphisms on the risk of HCC.

MATERIALS AND METHODS

We performed a case-control study comparing 94 cases with HCC and 220 matching controls. Sequencing methods were used to determine the genotype at the Ile997Val and Asn386Ser on EP300 and PCAF.

RESULTS

We found an overall association between genotypes Val/Val in EP300 and HCC risk (OR, 3.03; 95% CI, 1.08-8.47; P=0.028). Population stratifications revealed a trend or significantly higher risks of HCC development for women and HCV-negative patients carrying the EP300 Val/Val genotype (OR, 4.06; 95% CI, 0.71-23.36; P=0.09 and OR, 4.48; 95% CI, 1.04-19.14; P=0.02, respectively). The PCAF Ser/Ser genotype at codon 386 was more frequent in HCC cases than in control group (P=0.03). We observed trends for higher risk of HCC among men and/or HCV-negative patients carrying Ser/Ser genotype when compared with controls (OR, 10.62; 95% CI, 0.50-225.13 and OR, 11.78; 95% CI, 0.47-295.56, respectively).

CONCLUSION

It appears that variants of the transcriptional coactivator genes (EP300 and PCAF) may influence HCC risk in populations with low mutations or chromosomal instability rates. Additional surveys are warranted to confirm this first report.

The p53 cofactor Strap exhibits an unexpected TPR motif and oligonucleotide-binding (OB)-fold structure

Activation of p53 target genes for tumor suppression depends on the stress-specific regulation of transcriptional coactivator complexes. Strap (stress-responsive activator of p300) is activated upon DNA damage by ataxia telangiectasia mutated (ATM) and Chk2 kinases and is a key regulator of the p53 response. In addition to antagonizing Mdm2, Strap facilitates the recruitment of p53 coactivators, including JMY and p300. Strap is a predicted TPR-repeat protein, but shows only limited sequence identity with any protein of known structure. To address this and to elucidate the molecular mechanism of Strap activity we determined the crystal structure of the full-length protein at 2.05 Å resolution. The structure of Strap reveals an atypical six tetratricopeptide repeat (TPR) protein that also contains an unexpected oligonucleotide/oligosaccharide-binding (OB)-fold domain. This previously unseen domain organization provides an extended superhelical scaffold allowing for protein-protein as well as protein-DNA interaction. We show that both of the TPR and OB-fold domains localize to the chromatin of p53 target genes and exhibit intrinsic regulatory activity necessary for the Strap-dependent p53 response.

Oral contraceptive and progestin-only use correlates to tissue tumor marker expression in women with cervical intraepithelial neoplasia

BACKGROUND

The study was conducted to investigate correlations between combined oral contraceptive (COC), any progestin-only contraceptive, medicated intrauterine device (MID) or systemic progestin-only (Syst-P) use and tumor marker expression in cervical intraepithelial neoplasia compared to nonusers.

STUDY DESIGN

One-hundred ninety-five women of fertile age with cervical biopsies ranging histologically from normal epithelium to carcinoma in situ were recruited consecutively. Combined oral contraceptive, Syst-P and MID users were investigated according to the expression of 11 tumor markers.

RESULTS

Overexpression of cyclooxygenase-2 (Cox-2) was observed in COC users, while interleukin 10 was underexpressed. When users of progestogen-only contraceptives were analyzed, there was a lower expression of cytokeratin 10 and interleukin 10. When only MID users were analyzed, a high expression of p53 was found. Expression of Cox-2, p53 and retinoblastoma protein differed between COC and MID users.

CONCLUSION

The study showed molecular alterations, which, in general, have not been studied previously in COC users and have never been studied in progestogen-only users. These biological events might be involved in epidemiological correlations found between hormonal contraceptive use and cervical neoplasms.

Role of p53 serine 46 in p53 target gene regulation

The tumor suppressor p53 plays a crucial role in cellular growth control inducing a plethora of different response pathways. The molecular mechanisms that discriminate between the distinct p53-responses have remained largely elusive. Here, we have analyzed the p53-regulated pathways induced by Actinomycin D and Etoposide treatment resulting in more growth arrested versus apoptotic cells respectively. We found that the genome-wide p53 DNA-binding patterns are almost identical upon both treatments notwithstanding transcriptional differences that we observed in global transcriptome analysis. To assess the role of post-translational modifications in target gene choice and activation we investigated the genome-wide level of phosphorylation of Serine 46 of p53 bound to DNA (p53-pS46) and of Serine 15 (p53-pS15). Interestingly, the extent of S46 phosphorylation of p53 bound to DNA is considerably higher in cells directed towards apoptosis while the degree of phosphorylation at S15 remains highly similar. Moreover, our data suggest that following different chemotherapeutical treatments, the amount of chromatin-associated p53 phosphorylated at S46 but not at pS15 is higher on certain apoptosis related target genes. Our data provide evidence that cell fate decisions are not made primarily on the level of general p53 DNA-binding and that post-translationally modified p53 can have distinct DNA-binding characteristics.

Double null cells reveal that CBP and p300 are dispensable for p53 targets p21 and Mdm2 but variably required for target genes of other signaling pathways

The histone acetyltransferase coactivators CBP (CREBBP) and p300 (EP300) have more than 400 described protein interaction partners and are implicated in numerous transcriptional pathways. We have shown previously that CBP and p300 double knockout mutations in mouse embryonic fibroblasts (dKO MEFs) result in mixed effects on cAMP-inducible gene expression, with many CREB target genes requiring CBP/p300 for full expression, while others are unaffected or expressed better in their absence. Here we used CBP and p300 dKO MEFs to examine gene expression in response to four other signals: DNA damage (via p53), double-stranded RNA, serum, and retinoic acid. We found that while retinoic acid-inducible gene expression tends to be uniformly dependent on CBP/p300, dsRNA- and serum-inducible genes displayed non-uniform requirements for CBP/p300, with the dsRNA-inducible expression of Ifnb1 (interferon-β) being particularly dependent on CBP/p300. Surprisingly, the p53-dependent genes Cdkn1a (p21/CIP/WAF) and Mdm2 did not require CBP/p300 for their expression. As with cAMP-responsive CREB targets, we propose that the signal-responsive recruitment of CBP and p300 does not necessarily indicate a requirement for these coactivators at a locus. Rather, target gene context (e.g. DNA sequence) influences the extent to which transcription requires CBP/p300 versus other coactivators, which may not be HATs.

Unexpected repertoire of metazoan transcription factors in the unicellular holozoan Capsaspora owczarzaki

How animals (metazoans) originated from their single-celled ancestors remains a major question in biology. As transcriptional regulation is crucial to animal development, deciphering the early evolution of associated transcription factors (TFs) is critical to understanding metazoan origins. In this study, we uncovered the repertoire of 17 metazoan TFs in the amoeboid holozoan Capsaspora owczarzaki, a representative of a unicellular lineage that is closely related to choanoflagellates and metazoans. Phylogenetic and comparative genomic analyses with the broadest possible taxonomic sampling allowed us to formulate new hypotheses regarding the origin and evolution of developmental metazoan TFs. We show that the complexity of the TF repertoire in C. owczarzaki is strikingly high, pushing back further the origin of some TFs formerly thought to be metazoan specific, such as T-box or Runx. Nonetheless, TF families whose beginnings antedate the origin of the animal kingdom, such as homeodomain or basic helix-loop-helix, underwent significant expansion and diversification along metazoan and eumetazoan stems.

Adenovirus E1B 55-kilodalton protein is a p53-SUMO1 E3 ligase that represses p53 and stimulates its nuclear export through interactions with promyelocytic leukemia nuclear bodies

Oncogenic transformation by adenovirus E1A and E1B-55K requires E1B-55K inhibition of p53 activity to prevent E1A-induced apoptosis. During viral infection, E1B-55K and E4orf6 substitute for the substrate-binding subunits of the host cell cullin 5 class of ubiquitin ligases, resulting in p53 polyubiquitinylation and proteasomal degradation. Here we show that E1B-55K alone also functions as an E3 SUMO1-p53 ligase. Fluorescence microscopy studies showed that E1B-55K alone, in the absence of other viral proteins, causes p53 to colocalize with E1B-55K in promyelocytic leukemia (PML) nuclear bodies, nuclear domains with a high concentration of sumoylated proteins. Photobleaching experiments with live cells revealed that E1B-55K tethering of p53 in PML nuclear bodies decreases the in vivo nuclear mobility of p53 nearly 2 orders of magnitude. E1B-55K-induced p53 sumoylation contributes to maximal inhibition of p53 function since mutation of the major p53 sumoylation site decreases E1B-55K-induced p53 sumoylation, tethering in PML nuclear bodies, and E1B-55K inhibition of p53 activity. Mutation of the E1B-55K sumoylation site greatly inhibits E1B-55K association with PML nuclear bodies and the p53 nuclear export to cytoplasmic aggresomes observed in E1A-E1B-transformed cells. Purified E1B-55K and p53 form high-molecular-weight complexes potentially through the formation of a network of E1B-55K dimers bound to the N termini of p53 tetramers. In support of this model, a p53 mutation that prevents tetramer formation greatly reduces E1B-55K-induced tethering in PML nuclear bodies and p53 nuclear export. These data indicate that E1B-55K's association with PML nuclear bodies inactivates p53 by first sequestering it in PML nuclear bodies and then greatly facilitating its nuclear export.

Modulation of gene expression in endothelial cells by hyperlipaemic postprandial serum from healthy volunteers

A single high-fat challenge induces plasmatic pro-inflammatory and pro-oxidative responses in the postprandial state, even in healthy men. This period is also associated with vascular endothelial dysfunction, which is an early event in the development of cardiovascular diseases. However, knowledge about the mechanisms involved in postprandial hyperlipaemia-induced endothelial dysfunction is sparse. An objective of our study was to characterize the behaviour and gene expression of vascular endothelial cells exposed to postprandial hyperlipaemic sera. Human umbilical vein endothelial cells (HUVECs) were cultured in media containing 10% serum from healthy men withdrawn either before or 4 h after a high-fat challenge. Endothelial cell proliferation, adhesion and migration were then assessed. The transcriptomic profiles of endothelial cells exposed to pre and postprandial sera were also compared. Exposure to postprandial hyperlipaemic sera significantly decreased HUVEC proliferation when compared to preprandial serum (P < 0.0001), while no changes in migration or endothelial/monocyte interactions were observed. The transcriptomic analysis revealed changes in the expression of 675 genes, of which 431 have a known function. Among them, a set of differentially expressed genes was linked to cell cycle regulation and apoptosis and are regulated in favour of cell cycle arrest or death. This result was confirmed by measuring the induction of apoptosis after postprandial sera exposure (P = 0.011). Taken together, the transcriptomic results and pathway analysis showed that postprandial serum promotes apoptosis in HUVECs, potentially through the activation of the p53 network. We conclude that upon postprandial serum exposure, vascular endothelial cells transcriptionally regulate genes involved in the control of cell cycle and death to favour growth arrest and apoptosis. These findings support the hypothesis that postprandial hyperlipaemia is associated with vascular dysfunction and offer new insights into the mechanisms involved.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12263-010-0166-x) contains supplementary material, which is available to authorized users.

MSK2 inhibits p53 activity in the absence of stress

Mitogen- and stress-activated kinase 2 (MSK2) inhibits the transcription factor p53, and we investigate here the mechanisms underlying this inhibition. In the absence of stress stimuli, MSK2 selectively suppressed the expression of a subset of p53 target genes. This basal inhibition of p53 by MSK2 occurred independently of its kinase activity and of upstream mitogen-activated protein kinase signaling to MSK2. Furthermore, MSK2 interacted with and inhibited the p53 coactivator p300 and associated with the Noxa promoter. Apoptotic stimuli promoted the degradation of MSK2, thus relieving its inhibition of p53 and enabling efficient p53-dependent transactivation of Noxa, which contributed to apoptosis. Together, these findings constitute a new mechanism for the regulation of p53 transcriptional activity in response to stress.

New molecular markers in resistant B-CLL

B-chronic lymphocytic leukemia (B-CLL) is characterized by a highly variable clinical course which has long remained a stumbling block for clinicians. This variability appears to arise from complex molecular alterations identified in malignant cells from patient subsets. Recent studies have focused in particular on identifying new molecular markers to help predict the most effective and adapted treatments. In addition to the mutation status of immunoglobulin variable heavy-chain region (IgVH) genes, which is a well-established predictive factor in B-CLL, these new markers include defects of cell factors involved in the maintenance of genome stability, such as telomere function, DNA repair, ATM and p53. Other predictive factors, such as tyrosine kinase Zap-70 and soluble factors found in patient sera, may be associated with B-cell receptor signal transduction. Interestingly, an alteration of these factors fits closely, though not strikingly, with the absence of somatic mutations in IgVH genes, suggesting that the latter may be due either to epigenetic events leading to an unstable genome or to an inherited defect in the immune response of malignant B-cells. Recent lessons from Zap-70 expression/phosphorylation suggest that some of these markers may reflect the defective pathways in B-CLL cells rather than being markers of cell malignancy per se. Furthermore, specific subsets of markers are found in patient cells resistant to treatment. Current studies on gene expression profiling and proteomic analyses should soon lead to a better understanding of how these pathways are affected, especially in multi-drug resistant B-CLL.

The novel p53 target gene IRF2BP2 participates in cell survival during the p53 stress response

The tumor suppressor p53 contributes to the cellular fate after genotoxic insults, mainly through the regulation of target genes, thereby allowing e.g. repair mechanisms resulting in cell survival or inducing apoptosis. Unresolved so far is the issue, which exact mechanisms lead to one or the other cellular outcome. Here, we describe the interferon regulatory factor-2-binding protein-2 (IRF2BP2) as a new direct target gene of p53, influencing the p53-mediated cellular decision. We show that upregulation of IRF2BP2 after treatment with actinomycin D (Act.D) is dependent on functional p53 in different cell lines. This occurs in parallel with the down-regulation of the interacting partner of IRF2BP2, the interferon regulatory factor-2 (IRF2), which is known to positively influence cell growth. Analyzing the molecular functions of IRF2BP2, it appears to be able to impede on the p53-mediated transactivation of the p21- and the Bax-gene. We show here that overexpressed IRF2BP2 has an impact on the cellular stress response after Act.D treatment and that it diminishes the induction of apoptosis after doxorubicin treatment. Furthermore, the knockdown of IRF2BP2 leads to an upregulation of p21 and faster induction of apoptosis after doxorubicin as well as Act.D treatment.

MicroRNA-21 targets a network of key tumor-suppressive pathways in glioblastoma cells

MicroRNA dysregulation is observed in different types of cancer. MiR-21 up-regulation has been reported for the majority of cancers profiled to date; however, knowledge is limited on the mechanism of action of miR-21, including identification of functionally important targets that contribute to its proproliferative and antiapoptotic actions. In this study, we show for the first time that miR-21 targets multiple important components of the p53, transforming growth factor-beta (TGF-beta), and mitochondrial apoptosis tumor-suppressive pathways. Down-regulation of miR-21 in glioblastoma cells leads to derepression of these pathways, causing repression of growth, increased apoptosis, and cell cycle arrest. These phenotypes are dependent on two of the miR-21 targets validated in this study, HNRPK and TAp63. These findings establish miR-21 as an important oncogene that targets a network of p53, TGF-beta, and mitochondrial apoptosis tumor suppressor genes in glioblastoma cells.

Arginine methylation regulates the p53 response

Activation of the p53 tumour suppressor protein in response to DNA damage leads to apoptosis or cell-cycle arrest. Enzymatic modifications are widely believed to affect and regulate p53 activity. We describe here a level of post-translational control that has an important functional consequence on the p53 response. We show that the protein arginine methyltransferase (PRMT) 5, as a co-factor in a DNA damage responsive co-activator complex that interacts with p53, is responsible for methylating p53. Arginine methylation is regulated during the p53 response and affects the target gene specificity of p53. Furthermore, PRMT5 depletion triggers p53-dependent apoptosis. Thus, methylation on arginine residues is an underlying mechanism of control during the p53 response.

Preimplantation embryo development in the mouse requires the latency of TRP53 expression, which is induced by a ligand-activated PI3 kinase/AKT/MDM2-mediated signaling pathway

A universal response to cellular stress is the expression of transformation-related protein 53 (TRP53). This transcription factor reduces cell proliferation and/or survival and is classed as a tumour suppressor protein. Several stresses (including culture) cause increased TRP53 expression in blastocysts and their reduced long-term developmental potential. This study shows that culture from the zygote stage (but not the 2-cell stage) reduced the development of C57BL6 inbred (but not hybrid) strain mouse embryos. Reduced viability was TRP53 dependent, being partially reversed by a TRP53 inhibitor (Pifithrin-alpha). However, the presence of culture did not cause an increase in Trp53 mRNA levels (levels were reduced following culture, P < 0.001). Transformed mouse 3T3 cell double minute 2 (MDM2) causes the ubiquitination and degradation of TRP53. MDM2 activation is accompanied by phosphorylation of Ser-166, and this is commonly catalyzed by the phosphatidylinositol-3 kinase and RAC-alpha serine/threonine-protein kinase (AKT) signaling pathway. Paf is an autocrine embryotrophin that activates the phosphatidylinositol-3 kinase/AKT pathway. High levels of TRP53 expression occurred following the culture of zygotes lacking the Paf receptor (Ptafr(-/-)) and following inhibition of phosphatidylinositol-3 kinase or AKT. Inhibition of MDM2 caused a Trp53-dependent reduction in zygote development. Inbred strain embryos cultured from the zygote stage expressed less phosphorylated MDM2 than similar embryos collected from the uterus. The addition of Paf to the media caused increased phosphorylation of MDM2, and this was blocked by inhibitors of phosphatidylinositol-3 kinase and AKT. The study identifies trophic ligand signaling via the activation of phosphatidylinositol-3 kinase and AKT as a mechanism resulting in the activation of MDM2.

The ubiquitin-proteasome system in colorectal cancer

The proteasome is a multiprotein complex that regulates the stability of hundreds of cellular proteins and thus, it is implicated in virtually all cellular functions. Most of the time, to be recognized and processed by the proteasome, a protein has to be linked to a chain of ubiquitin molecules. Cell proliferation, apoptosis, angiogenesis and motility, processes with particular importance for carcinogenesis are regulated by the ubiquitin-proteasome system (UPS). In colorectal epithelium, UPS plays a role in the regulation of the Wnt/beta-catenin/APC/TCF4 signaling which regulates proliferation of colorectal epithelial cells in the bottom of the crypts and the inhibition of this proliferation as cells move towards colon villi tips. In most colorectal cancers APC (Adenomatous Polyposis Coli) disabling mutations interfere with the ability of the proteasome to degrade beta-catenin leading to uninhibited cell proliferation. Other key molecules in colorectal carcinogenesis such as p53, Smad4 and components of the k-ras pathways are also regulated by the UPS. In this review I discuss the role of UPS in colorectal carcinogenesis and colorectal cancer prognosis and aspects of its inhibition for therapeutic purposes.

Recombinant, refolded tetrameric p53 and gonadotropin-releasing hormone-p53 slow proliferation and induce apoptosis in p53-deficient cancer cells

The p53 tumor suppressor is mutated in over 50% of human cancers. Mutations resulting in amino acid changes within p53 result in a loss of activity and consequent changes in expression of genes that regulate DNA repair and cell cycle progression. Replacement of p53 using protein therapy would restore p53 function in p53-deficient tumor cells, with a consequence of tumor cell death and tumor regression. p53 functions in a tetrameric form in vivo. Here, we refolded a wild-type, full-length p53 from inclusion bodies expressed in Escherichia coli as a stable tetramer. The tetrameric p53 binds to p53-specific DNA and, when transformed into a p53-deficient cancer cell line, induced apoptosis of the transformed cells. Next, using the same expression and refolding technology, we produced a stable tetramer of recombinant gonadotropin-releasing hormone-p53 fusion protein (GnRH-p53), which traverses the plasma membrane, slows proliferation, and induces apoptosis in p53-deficient, GnRH-receptor–expressing cancer cell lines. In addition, we showed a time-dependent binding and internalization of GnRH-p53 to a receptor-expressing cell line. We conclude that the GnRH-p53 fusion strategy may provide a basis for constructing an effective cancer therapeutic for patients with tumors in GnRH-receptor–positive tissue types. [Mol Cancer Ther 2008;7(6):1420–9]

Characterization of genome-wide p53-binding sites upon stress response

The tumor suppressor p53 is a sequence-specific transcription factor, which regulates the expression of target genes involved in different stress responses. To understand p53's essential transcriptional functions, unbiased analysis of its DNA-binding repertoire is pivotal. In a genome-wide tiling ChIP-on-chip approach, we have identified and characterized 1546 binding sites of p53 upon Actinomycin D treatment. Among those binding sites were known as well as novel p53 target sites, which included regulatory regions of potentially novel transcripts. Using this collection of genome-wide binding sites, a new high-confidence algorithm was developed, p53scan, to identify the p53 consensus-binding motif. Strikingly, this motif was present in the majority of all bound sequences with 83% of all binding sites containing the motif. In the surrounding sequences of the binding sites, several motifs for potential regulatory cobinders were identified. Finally, we show that the majority of the genome-wide p53 target sites can also be bound by overexpressed p63 and p73 in vivo, suggesting that they can possibly play an important role at p53 binding sites. This emphasizes the possible interplay of p53 and its family members in the context of target gene binding. Our study greatly expands the known, experimentally validated p53 binding site repertoire and serves as a valuable knowledgebase for future research.

A transcription cofactor required for the heat-shock response

The Stress-responsive activator of p300 (Strap) is a transcription cofactor that has an important role in the control of DNA damage response through its ability to regulate p53 activity. Here, we report that Strap is inducible by heat shock and stimulates the transcription of heat-shock genes. A chromatin-associated complex involving heat-shock factor 1 (HSF1), Strap and the p300 coactivator assembles on the heat-shock protein 70 (hsp70) promoter, and Strap augments HSF1 binding and chromatin acetylation in Hsp genes, most probably through the p300 histone acetyltransferase. Cells depleted of Strap do not survive under heat-shock conditions. These results indicate that Strap is an essential cofactor that acts at the level of chromatin control to regulate heat-shock-responsive transcription.

Skp2 suppresses p53-dependent apoptosis by inhibiting p300

The F box protein Skp2 is oncogenic, and its frequent amplification and overexpression correlate with the grade of malignancy of certain tumors. Conversely, depletion of Skp2 decreases cell growth and increases apoptosis. Here, we show that Skp2 counteracts the transactivation function of p53 and suppresses apoptosis mediated by DNA damage or p53 stabilization. We demonstrate that Skp2 forms a complex with p300 through the CH1 and the CH3 domains of p300 to which p53 is thought to bind and antagonizes the interaction between p300 and p53 in cells and in vitro. As Skp2 antagonizes the interaction between p300 and p53, Skp2 suppresses p300-mediated acetylation of p53 and the transactivation ability of p53. Conversely, ectopic expression of p300 rescues the transactivation function of p53 in cells overexpressing Skp2. Taken together, our results indicate that Skp2 controls p300-p53 signaling pathways in cancer cells, making Skp2 a potential molecular target for cancer therapy.

Roles of CREB-binding protein (CBP)/p300 in respiratory epithelium tumorigenesis

CREB-binding protein (CBP) and its homologue p300 are transcriptional co-activators of various sequence-specific transcription factors that are involved in a wide array of cellular activities, such as DNA repair, cell growth, differentiation and apoptosis. Several studies have suggested that CBP and p300 might be considered as tumour suppressors, with their prominent role being the cross-coupling of distinct gene expression patterns in response to various stimuli. They exert their actions mainly via acetylation of histones and other regulatory proteins (e.g. p53). A major paradox in CBP/p300 function is that they seem capable of contributing to various opposed cellular processes. Respiratory epithelium tumorigenesis represents a complex process of multi-step accumulations of a gamut of genetic and epigenetic aberrations. Transcription modulation through the alternate formation of activating and repressive complexes is the ultimate converging point of these derangements, and CBP/p300 represents key participants in this interplay. Thus, illumination of their molecular actions and interactions could reveal new potential targets for pharmacological interventions in respiratory epithelium carcinogenesis.

Pathogenesis of colorectal carcinoma and therapeutic implications: the roles of the ubiquitin-proteasome system and Cox-2

Pathways of the molecular pathogenesis of colorectal carcinoma have been extensively studied and molecular lesions during the development of the disease have been revealed. High up in the list of colorectal cancer lesions are APC (adenomatous polyposis coli), K-ras, Smad4 (or DPC4-deleted in pancreatic cancer 4) and p53 genes. All these molecules are part of important pathways for the regulation of cell proliferation and apoptosis and as a result perturbation of these processes lead to carcinogenesis. The ubiquitin-proteasome system (UPS) is comprised of a multi-unit cellular protease system that regulates several dozens of cell proteins after their ligation with the protein ubiquitin. Given that among these proteins are regulators of the cell cycle, apoptosis, angiogenesis, adhesion and cell signalling, this system plays a significant role in cell fate and carcinogenesis. UPS inhibition has been found to be a pre-requisite for apoptosis and is already clinically exploited with the proteasome inhibitor bortezomib in multiple myeloma. Cyclooxygenase-2 (Cox-2) is the inducible form of the enzyme that metabolizes the lipid arachidonic acid to prostaglandin H2, the first step of prostaglandins production. This enzyme is up-regulated in colorectal cancer and in several other cancers. Inhibition of Cox-2 by aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) has been found to inhibit proliferation of colorectal cancer cells and in epidemiologic studies has been shown to reduce colon polyp formation in genetically predisposed populations and in the general population. NSAIDs have also Cox-independent anti-proliferative effects. Targeted therapies, the result of increasingly understanding carcinogenesis in the molecular level, have entered the field of anti-neoplastic treatment and are used by themselves and in combination with chemotherapy drugs. Combinations of targeted drugs have started also to be investigated. This article reviews the molecular pathogenesis of colorectal cancer, the roles of UPS and Cox-2 in it and puts forward a rational for their combined inhibition in colorectal cancer treatment.

Differential gene expression in anticancer drug- and TRAIL-mediated apoptosis in renal cell carcinomas

Renal cell carcinomas (RCC) exhibit marked differences in susceptibility towards anticancer drug- and TRAIL-induced apoptosis. However, the underlying mechanisms determining apoptosis-sensitivity or -resistance are not well understood. The purpose of this study was to compare gene expression patterns induced by DNA-damage- and death receptor-induced apoptosis and to detect differentially expressed genes responsible for differences in apoptosis-susceptibility. Therefore, we performed a comparative cDNA-array analysis in an apoptosis-resistant and an apoptosis-sensitive RCC cell line. In the sensitive cell line an upregulation of multiple E2F1- and p53-inducible proapaptotic and cell-cycle regulating target genes by Topotecan as well as TRAIL was observed. Interestingly, several antiapoptotic NFkappaB-dependent target genes were also induced. In the resistant cell line, however, only a small number of E2F1-, p53- and NFkappaB-dependent target genes were differentially regulated. Conclusively, anticancer drug- as well as TRAIL-sensitivity go along with an upregulation of multiple proapoptotic genes. In contrast, the mechanisms of apoptosis-resistance are-at least in part-located upstream of gene induction and seem not to depend upon upregulation of de-novo-synthesized antiapoptotic genes. Conclusively, the proapoptotic stimuli are confronted with a cellular context which allows apoptosis to be conducted-in the sensitive cell line-or not-in the resistant cell line.

Histone acetylation and methylation: combinatorial players for transcriptional regulation

Post-synthetic modification of histone proteins in chromatin architecture plays a central role in the epigenetic regulation of transcription. Histone acetylation and methylation are the two major modifications that function as a specific transcription regulator in response to various cellular signals. Albeit the mechanism of action of these modifications in transcription is not well understood, recent discovery of histone acetyltransferase (HAT) and methyltransferase (HMT) activities within transcriptional regulators has an important implication for histone modification to be a key player for the precise regulation of transcription processes. Here, we discuss recent advances made on histone acetylation and methylation as a fundamental process to modulate gene transcription, with a particular emphasis on their combinatorial effects in transcriptional control.

A new p38 MAP kinase-regulated transcriptional coactivator that stimulates p53-dependent apoptosis

The p38 mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in stress-induced cell-fate decisions by orchestrating responses that go from cell-cycle arrest to apoptosis. We have identified a new p38 MAPK-regulated protein that we named p18(Hamlet), which becomes stabilized and accumulates in response to certain genotoxic stresses such as UV or cisplatin treatment. Overexpression of p18(Hamlet) is sufficient to induce apoptosis, whereas its downregulation reduces the apoptotic response to these DNA damage-inducing agents. We show that p18(Hamlet) interacts with p53 and stimulates the transcription of several proapoptotic p53 target genes such as PUMA and NOXA. This correlates with enhanced p18(Hamlet)-induced recruitment of p53 to the promoters. In proliferating cells, low steady-state levels of p18(Hamlet) are probably maintained by a p53-dependent negative feedback loop. Therefore, p18(Hamlet) is a new cell-fate regulator that links the p38 MAPK and p53 pathways and contributes to the establishment of p53-regulated stress responses.

The nuclear function of p53 is required for PUMA-mediated apoptosis induced by DNA damage

The tumor suppressor p53 can induce apoptosis by activating gene expression in the nucleus, or by directly permeabilizing mitochondria in the cytoplasm. It has been shown that PUMA, a downstream target of p53 and a BH3-only Bcl-2 family member, plays an essential role in apoptosis induced by both nuclear and cytoplasmic p53. To understand how PUMA does so, we used homologous recombination to delete the binding sites of p53 in the promoter of PUMA in human colorectal cancer cells. As a result, the induction of PUMA and apoptosis in response to p53 and DNA-damaging agents were abrogated. Transcription coactivator recruitment and histone modifications in the PUMA promoter were suppressed. However, induction of PUMA and apoptosis in response to non-DNA-damaging stimuli were unaffected. These results indicate that the binding of nuclear p53 to the specific sites within the PUMA promoter is essential for its ability to induce apoptosis and is likely to be required for its tumor suppressive capacity.

The notch regulator MAML1 interacts with p53 and functions as a coactivator

Members of the evolutionarily conserved Mastermind (MAM) protein family, including the three related mammalian Mastermind-like (MAML) proteins MAML1-3, function as crucial coactivators of Notch-mediated transcriptional activation. Given the recent evidence of cross-talk between the p53 and Notch signal transduction pathways, we have investigated whether MAML1 may also be a transcriptional coactivator of p53. Indeed, we show here that MAML1 is able to interact with p53. We show that MAML1-p53 interaction involves the N-terminal region of MAML1 and the DNA-binding domain of p53, and we use a chromatin immunoprecipitation assay to show that MAML1 is part of the activator complex that binds to native p53-response elements within the promoter of the p53 target genes. Overexpression of wild-type MAML1 as well as a mutant, defective in Notch signaling, enhanced the p53-dependent gene induction in mammalian cells, whereas MAML1 knockdown reduced the p53-dependent gene expression. MAML1 increases the half-life of p53 protein and enhances its phosphorylation/acetylation upon DNA damage of cells. Finally, RNA interference-mediated knockdown of the single Caenorhabditis elegans MAML homolog, Lag-3, led to substantial abrogation of p53-mediated germ-cell apoptotic response to DNA damage and markedly reduced the expression of Ced-13 and Egl-1, downstream pro-apoptotic targets of the C. elegans p53 homolog Cep-1. Thus, we present evidence for a novel coactivator function of MAML1 for p53, independent of its function as a coactivator of Notch signaling pathway.