Modifying chromatin and concepts of cancer

Combining Oncolytic Viruses and Small Molecule Therapeutics: Mutual Benefits

The focus of treating cancer with oncolytic viruses (OVs) has increasingly shifted towards achieving efficacy through the induction and augmentation of an antitumor immune response. However, innate antiviral responses can limit the activity of many OVs within the tumor and several immunosuppressive factors can hamper any subsequent antitumor immune responses. In recent decades, numerous small molecule compounds that either inhibit the immunosuppressive features of tumor cells or antagonize antiviral immunity have been developed and tested for. Here we comprehensively review small molecule compounds that can achieve therapeutic synergy with OVs. We also elaborate on the mechanisms by which these treatments elicit anti-tumor effects as monotherapies and how these complement OV treatment.

KDELR2 promotes breast cancer proliferation via HDAC3-mediated cell cycle progression

Background

Histone deacetylases (HDACs) engage in the regulation of various cellular processes by controlling global gene expression. The dysregulation of HDACs leads to carcinogenesis, making HDACs ideal targets for cancer therapy. However, the use of HDAC inhibitors (HDACi) as single agents has been shown to have limited success in treating solid tumors in clinical studies. This study aimed to identify a novel downstream effector of HDACs to provide a potential target for combination therapy.

Methods

Transcriptome sequencing and bioinformatics analysis were performed to screen for genes responsive to HDACi in breast cancer cells. The effects of HDACi on cell viability were detected using the MTT assay. The mRNA and protein levels of genes were determined by quantitative reverse transcription‐PCR (qRT‐PCR) and Western blotting. Cell cycle distribution and apoptosis were analyzed by flow cytometry. The binding of CREB1 (cAMP‐response element binding protein 1) to the promoter of the KDELR (The KDEL (Lys‐Asp‐Glu‐Leu) receptor) gene was validated by the ChIP (chromatin immunoprecipitation assay). The association between KDELR2 and protein of centriole 5 (POC5) was detected by immunoprecipitation. A breast cancer‐bearing mouse model was employed to analyze the effect of the HDAC3‐KDELR2 axis on tumor growth.

Results

KDELR2 was identified as a novel target of HDAC3, and its aberrant expression indicated the poor prognosis of breast cancer patients. We found a strong correlation between the protein expression patterns of HADC3 and KDELR2 in tumor tissues from breast cancer patients. The results of the ChIP assay and qRT‐PCR analysis validated that HDAC3 transactivated KDELR2 via CREB1. The HDAC3‐KDELR2 axis accelerated the cell cycle progression of cancer cells by protecting the centrosomal protein POC5 from proteasomal degradation. Moreover, the HDAC3‐KDELR2 axis promoted breast cancer cell proliferation and tumorigenesis in vitro and in vivo.

Conclusion

Our results uncovered a previously unappreciated function of KDELR2 in tumorigenesis, linking a critical Golgi‐the endoplasmic reticulum traffic transport protein to HDAC‐controlled cell cycle progression on the path of cancer development and thus revealing a potential therapeutical target for breast cancer.

Characteristics and outcome of patients with acute myeloid leukaemia and t(8;16)(p11;p13): results from an International Collaborative Study

In acute myeloid leukaemia (AML) t(8;16)(p11;p13)/MYST3-CREBBP is a very rare abnormality. Previous small series suggested poor outcome. We report on 59 patients with t(8;16) within an international, collaborative study. Median age was 52 (range: 16-75) years. AML was de novo in 58%, therapy-related (t-AML) in 37% and secondary after myelodysplastic syndrome (s-AML) in 5%. Cytogenetics revealed a complex karyotype in 43%. Besides MYST3-CREBBP, whole-genome sequencing on a subset of 10 patients revealed recurrent mutations in ASXL1, BRD3, FLT3, MLH1, POLG, TP53, SAMD4B (n = 3, each), EYS, KRTAP9-1 SPTBN5 (n = 4, each), RUNX1 and TET2 (n = 2, each). Complete remission after intensive chemotherapy was achieved in 84%. Median follow-up was 5·48 years; five-year survival rate was 17%. Patients with s-/t-AML (P = 0·01) and those with complex karyotype (P = 0·04) had an inferior prognosis. Allogeneic haematopoietic cell transplantation (allo-HCT) was performed in 21 (36%) patients, including 15 in first complete remission (CR1). Allo-HCT in CR1 significantly improved survival (P = 0·04); multivariable analysis revealed that allo-HCT in CR1 was effective in de novo AML but not in patients with s-AML/t-AML and less in patients exhibiting a complex karyotype. In summary, outcomes of patients with t(8;16) are dismal with chemotherapy, and may be substantially improved with allo-HCT performed in CR1.

Preclinical evaluation and molecular docking of 1,3-benzodioxole propargyl ether derivatives as novel inhibitor for combating the histone deacetylase enzyme in cancer

Even after huge strides in medicine, cancer continues to be a formidable disease, which is slated to become the leading cause of death worldwide. The present study investigates the 1,3-benzodioxole and its propargyl ether derivatives as a novel histone deacetylase enzyme inhibitor in order to cure cancer, as aberrant expression of histone deacetylases (HDACs) is associated with carcinogenesis. Bioinformatics approaches were employed to carry out preclinical and pharmacological evaluations of designed benzodioxole derivatives. Furthermore, their interaction with HDAC-1 enzyme was studied through computational methods for their specific inhibitory effects and evaluated for their LD50 (oral rat acute toxicity) value. In addition to this work, three-dimensional (3D) structure of HDAC-1 enzyme was extracted and evaluated using various parameters including Ramachandran plot and molecular docking stimulation. In our study, we found that compound 7 and compound 9 have higher binding score than approved drugs (SAHA, TSA and VPA). Importantly, these compounds were found to possess good pharmacological and pharmacokinetic properties and can be considered as potent novel compound to combat the HDAC-1 enzyme to cure cancer. Compounds were also analyzed and validated with parameters like absorption, metabolism, excretion, toxicity and synthetic accessibility during the preclinical evaluation. This study paves way to search for novel and potent small chemical compounds for inhibiting HDAC-1 enzyme and in particular to combat the cancer progression by interrupting the cell cycle.

Eighteen New Candidate Effectors of the Phytonematode Heterodera glycines Produced Specifically in the Secretory Esophageal Gland Cells During Parasitism

Heterodera glycines, the soybean cyst nematode, is the number one pathogen of soybean (Glycine max). This nematode infects soybean roots and forms an elaborate feeding site in the vascular cylinder. H. glycines produces an arsenal of effector proteins in the secretory esophageal gland cells. More than 60 H. glycines candidate effectors were identified in previous gland-cell-mining projects. However, it is likely that additional candidate effectors remained unidentified. With the goal of identifying remaining H. glycines candidate effectors, we constructed and sequenced a large gland cell cDNA library resulting in 11,814 expressed sequence tags. After bioinformatic filtering for candidate effectors using a number of criteria, in situ hybridizations were performed in H. glycines whole-mount specimens to identify candidate effectors whose mRNA exclusively accumulated in the esophageal gland cells, which is a hallmark of many nematode effectors. This approach resulted in the identification of 18 new H. glycines esophageal gland-cell-specific candidate effectors. Of these candidate effectors, 11 sequences were pioneers without similarities to known proteins while 7 sequences had similarities to functionally annotated proteins in databases. These putative homologies provided the bases for the development of hypotheses about potential functions in the parasitism process.

MOZ and MORF acetyltransferases: Molecular interaction, animal development and human disease

Lysine residues are subject to many forms of covalent modification and one such modification is acetylation of the ε-amino group. Initially identified on histone proteins in the 1960s, lysine acetylation is now considered as an important form of post-translational modification that rivals phosphorylation. However, only about a dozen of human lysine acetyltransferases have been identified. Among them are MOZ (monocytic leukemia zinc finger protein; a.k.a. MYST3 and KAT6A) and its paralog MORF (a.k.a. MYST4 and KAT6B). Although there is a distantly related protein in Drosophila and sea urchin, these two enzymes are vertebrate-specific. They form tetrameric complexes with BRPF1 (bromodomain- and PHD finger-containing protein 1) and two small non-catalytic subunits. These two acetyltransferases and BRPF1 play key roles in various developmental processes; for example, they are important for development of hematopoietic and neural stem cells. The human KAT6A and KAT6B genes are recurrently mutated in leukemia, non-hematologic malignancies, and multiple developmental disorders displaying intellectual disability and various other abnormalities. In addition, the BRPF1 gene is mutated in childhood leukemia and adult medulloblastoma. Therefore, these two acetyltransferases and their partner BRPF1 are important in animal development and human disease.

Antitumor action of a novel histone deacetylase inhibitor, YF479, in breast cancer

Accumulating evidence demonstrates important roles for histone deacetylase in tumorigenesis (HDACs), highlighting them as attractive targets for antitumor drug development. Histone deactylase inhibitors (HDACIs), which have shown favorable anti-tumor activity with low toxicity in clinical investigations, are a promising class of anticancer therapeutics. Here, we screened our compound library to explore small molecules that possess anti-HDAC activity and identified a novel HDACI, YF479. Suberoylanilide hydroxamic acid (SAHA), which was the first approved HDAC inhibitor for clinical treatment by the FDA, was as positive control in our experiments. We further demonstrated YF479 abated cell viability, suppressed colony formation and tumor cell motility in vitro. To investigate YF479 with superior pharmacodynamic properties, we developed spontaneous and experimental breast cancer animal models. Our results showed YF479 significantly inhibited breast tumor growth and metastasis in vivo. Further study indicated YF479 suppressed both early and end stages of metastatic progression. Subsequent adjuvant chemotherapy animal experiment revealed the elimination of local-regional recurrence (LRR) and distant metastasis by YF479. More important, YF479 remarkably prolonged the survival of tumor-bearing mice. Intriguingly, YF479 displayed more potent anti-tumor activity in vitro and in vivo compared with SAHA. Together, our results suggest that YF479, a novel HDACI, inhibits breast tumor growth, metastasis and recurrence. In light of these results, YF479 may be an effective therapeutic option in clinical trials for patients burdened by breast cancer.

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.

Anacardic acid induces caspase-independent apoptosis and radiosensitizes pituitary adenoma cells

OBJECT

Pituitary adenomas, which are common intracranial tumors, are associated with significant patient morbidity due to hormone secretion or mass effect or as a complication of therapy. Epigenetic regulation has emerged as an important component of malignant tumor pathogenesis, although the contribution in the progression of benign pituitary tumors remains largely unexplored. The present study evaluates the effect of anacardic acid (6-pentadecyl salicylic acid), a natural histone acetyltransferase inhibitor, on pituitary adenoma cells.

METHODS

The concentration- and time-dependent effects of anacardic acid on the viability of GH3 and MMQ pituitary adenoma cells were determined by 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell cycle phase distribution, protein expression, and percentage of apoptotic cells were assessed by flow cytometry and Western blotting. Colony forming assays were used to study the radiosensitizing effect of anacardic acid.

RESULTS

The present study identifies a novel antiproliferative and cytotoxic effect of anacardic acid on pituitary adenoma cells. These effects were associated with an increase in poly([adenosine diphosphate]-ribose) polymerase cleavage, sub-G1 arrest, and annexin V staining, consistent with apoptotic cell death; however, the pancaspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-(O-methyl)-fluoromethylketone failed to reverse anacardic acid-induced cell death, suggesting a possible nonclassical apoptotic mechanism. Anacardic acid also reduced the expression of survivin and X-linked inhibitor of apoptosis protein, antiapoptotic proteins associated with cellular survival and radioresistance, and radiosensitized pituitary adenoma cells.

CONCLUSIONS

These findings warrant further exploration of anacardic acid as a single agent or as an adjunct to radiation therapy for the treatment of pituitary tumors.

Expression of chicken zygote arrest 1 (Zar1) and Zar1-like genes during sexual maturation and embryogenesis

Maternal mRNAs, which are expressed in oocytes, play an important role in the success of early embryo development, as they allow the first cleavages to occur. Zygote arrest 1 (Zar1) is an oocyte-specific maternal-effect gene that functions at the oocyte-to-embryo transition in many vertebrate species including human, pig, cattle, sheep, mouse, rat, frog and zebrafish. Recently, through in silico studies, a gene structurally related to Zar1, called Zar1-like has been identified in many vertebrates, including the chicken. The objectives of this study were to investigate the expression of the chicken Zar1 and Zar1-like genes in chicken tissues and embryos and to determine whether sexual maturation affects their mRNA abundance. RNA was extracted from various organs of chickens aged from one month up to two years old and from chicken embryos until day ten of embryonic development. Expression analysis of the genes was performed using RT-PCR and real-time PCR. RT-PCR analysis revealed that both genes were preferentially expressed in chicken oocytes, ovary and testes and in embryos during embryonic development. Quantitative real-time PCR analysis revealed a significant up regulation of Zar1 in the mature ovary, and also a significant up regulation of Zar1 and Zar1-like genes in the testes of sexually mature roosters, suggesting a key role of these genes in the chicken fertility. In contrast, expression of Zar1-like was not affected by age in the chicken ovary. Our results indicate that the chicken Zar1 and Zar1-like transcripts are co-expressed in high levels in the chicken gonads. In addition their expression beyond the stage of embryonic genome activation suggests an embryonic and not only a maternal origin of these transcripts.

Non-genetic cell-to-cell variability and the consequences for pharmacology

Recent advances in single-cell assays have focused attention on the fact that even members of a genetically identical group of cells or organisms in identical environments can exhibit variability in drug sensitivity, cellular response, and phenotype. Underlying much of this variability is stochasticity in gene expression, which can produce unique proteomes even in genetically identical cells. Here we discuss the consequences of non-genetic cell-to-cell variability in the cellular response to drugs and its potential impact for the treatment of human disease.

Spermidinyl-CoA-based HAT inhibitors block DNA repair and provide cancer-specific chemo- and radiosensitization

Acetyl group turnover on specific lysine epsilon-amino groups of the core chromosomal histones regulates DNA accessibility function, and the acetylating and deacetylating enzymes that govern the turnover provide important targets for the development of anti-cancer drugs. Histone deacetylase (HDAC) inhibitors have been developed and evaluated extensively in clinical trials, while the development of inhibitors of histone acetyltransferase (HAT) has proceeded more slowly. Here we have examined the cellular effects of an S-substituted coenzyme A (CoA) inhibitor of histone acetylation, consisting of spermidine (Spd) linked to the S-terminus of CoA through a thioglycolic acid linkage (adduct abbreviated as Spd-CoA), as well as the effects of a truncated Spd-CoA derivative lacking the negatively charged portion of the CoA moiety. While exposure of cancer cells to Spd-CoA has little effect on cell viability, it causes a rapid inhibition of histone acetylation that correlates with a transient arrest of DNA synthesis, a transient delay in S-phase progression, and an inhibition of nucleotide excision repair and DNA double strand break repair. These effects correlate with increased cellular sensitivity to the DNA-targeted chemotherapeutic drugs, cisplatin (Platinol()) and 5-fluorouracil, to the DNA damaging drug, camptothecin, and to UV-C irradiation. The sensitization effects of Spd-CoA are not observed in normal cells due to a barrier to uptake. The truncated Spd-CoA derivative displays similar but enhanced chemosensitization effects, suggesting that further modifications of the Spd-CoA structure could further improve potency. The results demonstrate that Spd-CoA and its truncated version are efficiently and selectively internalized into cancer cells, and suggest that the resulting inhibition of acetylation-dependent DNA repair enhances cellular sensitivity to DNA damage. These and related inhibitors of histone acetylation could therefore constitute a novel class of potent therapy sensitizers applicable to a broad range of conventional cancer treatments.

AML with translocation t(8;16)(p11;p13) demonstrates unique cytomorphological, cytogenetic, molecular and prognostic features

Balanced chromosomal rearrangements define distinct entities in acute myeloid leukemia (AML). Here, we present 13 AML cases with t(8;16)(p11;p13) with observed low incidence (13/6124 patients), but more frequent presentation in therapy-related AML than in de novo AML (7/438 versus 6/5686, P=0.00001). Prognosis was poor with median overall survival of 4.7 months. Cytomorphology was characterized by parallel positive myeloperoxidase and non-specific esterase staining, therefore, French-American-British (FAB)-classification was impossible and origin of the AML with t(8;16) from an early stem cell with myeloid and monoblastic potential is hypothesized. Erythrophagocytosis was observed in 7/13 cases. Using gene expression profiling on 407 cases, patients with t(8;16) were compared to AML FAB subtypes with normal karyotype. Principal component analyses demonstrated that AML with t(8;16) were distinct from FAB subtypes M1, M4, M5a/b. When further compared to AML showing balanced rearrangements, that is, current WHO categories t(15;17), t(8;21), inv(16) and t(11q23)/MLL, AML with t(8;16) cases were clustered close to t(11q23)/MLL sharing commonly expressed genes. Subsequently, a pairwise comparison discriminated AML with t(8;16) from AML with t(11q23)/MLL, thus defining a highly unique signature for AML with t(8;16). In conclusion, AML with t(8;16) demonstrates unique cytomorphological, cytogenetic, molecular and prognostic features and is a specific subtype of AML.

SWI/SNF: a chromatin-remodelling complex with a role in carcinogenesis

SWI/SNF is a chromatin-remodelling complex that makes DNA that has been compacted into nucleosomes accessible to transcription factors and repair enzymes. It does this by displacing DNA from the core histone surface. SWI/SNF consists of at least nine subunits, including one of two alternative ATPase subunits, BRM or BRG-1, that provide the energy for remodelling. As it regulates access to DNA it controls many aspects of normal cellular function. Limited studies have recently linked loss of function of SWI/SNF subunits to cancer development, suggesting that it may be a tumor suppressor complex. As epigenetic repression regulates SWI/SNF component expression at least in some cases, restoration of function is therapeutically promising for cancer treatment. Considerably more research is required into deregulation of SWI/SNF in cancer and determination of how this affects tumor development. This is an exciting but poorly understood molecule that may have a role in carcinogenesis.

Negative regulation of transcription coactivator p300 by orphan receptor TR3

p300 regulates the transcriptional activity of a variety of transcription factors by forming an activation complex and/or promoting histone acetylation. Here, we show a unique characteristic of orphan receptor TR3 in negatively regulating the function of p300. TR3 was found to interact with p300 and inhibited the acetylation of transcription factors induced by p300, resulting in the repression of their transcriptional activity. Further analysis revealed that both a conserved transcriptional adapter motif (TRAM) in p300 and a specific sequence FLELFIL in TR3 were critical for their interaction. TR3 binding completely covered the histone acetyltransferase (HAT) domain of p300 and resulted in suppression of the HAT activity, as the p300-induced histone H3 acetylation and transcription were inhibited with the presence TR3. Furthermore, an agonist of TR3, a natural octaketide isolated from Dothiorella sp. HTF3 of an endophytical fungus, was shown to be a potent compound for inhibiting p300 HAT activity (IC₅₀ = 1.5 μg/ml) in vivo. More importantly, this agonist could repress the transcriptional activity of transcription factors, and proliferation of cancer cells. Taken together, our results not only delineate a novel transcriptional repressor function for TR3, but also reveal its modulation on p300 HAT activity as the underlying mechanism.

The Plant Homeodomain Fingers of Fission Yeast Msc1 Exhibit E3 Ubiquitin Ligase Activity

The DNA damage checkpoint pathway governs how cells regulate cell cycle progression in response to DNA damage. A screen for suppressors of a fission yeast chk1 mutant defective in the checkpoint pathway identified a novel Schizosaccharomyces pombe protein, Msc1. Msc1 contains 3 plant homeodomain (PHD) finger motifs, characteristically defined by a C4HC3 consensus similar to RING finger domains. PHD finger domains in viral proteins and in the cellular protein kinase MEKK1 (mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase 1) have been implicated as ubiquitin E3 protein ligases that affect protein stability. The close structural relationship of PHD fingers to RING fingers suggests that other PHD domain-containing proteins might share this activity. We show that each of the three PHD fingers of Msc1 can act as ubiquitin E3 ligases, reporting for the first time that PHD fingers from a nuclear protein exhibit E3 ubiquitin ligase activity. The function of the PHD fingers of Msc1 is needed to rescue the DNA damage sensitivity of a chk1Delta strain. Msc1 co-precipitates Rhp6, the S. pombe homologue of the human ubiquitin-conjugating enzyme Ubc2. Strikingly, deletion of msc1 confers complete suppression of the slow growth phenotype, UV and hydroxyurea sensitivities of an rhp6 deletion strain and restores deficient histone H3 methylation observed in the rhp6Delta mutant. We speculate that the target of the E3 ubiquitin ligase activity of Msc1 is likely to be a chromatin-associated protein.

Gene expression profiling of acute myeloid leukemia with translocation t(8;16)(p11;p13) and MYST3-CREBBP rearrangement reveals a distinctive signature with a specific pattern of HOX gene expression

Acute myeloid leukemia (AML) with translocation t(8;16)(p11;p13) is an infrequent leukemia subtype with characteristic clinicobiological features. This translocation leads to fusion of MYST3 (MOZ) and CREBBP (CBP) genes, probably resulting in a disturbed transcriptional program of a myelomonocytic precursor. Nonetheless, its gene expression profile is unknown. We have analyzed the gene expression profile of 23 AML patients, including three with molecularly confirmed MYST3-CREBBP fusion gene, using oligonucleotide U133A arrays (Affymetrix). MYST3-CREBBP cases clustered together and clearly differentiated from samples with PML-RARalpha, RUNX1-RUNX1T1, and CBFbeta-MYH11 rearrangements. The relative expression of 46 genes, selected according to their differential expression in the high-density array study, was analyzed by low-density arrays in an additional series of 40 patients, which included 7 MYST3-CREBBP AML cases. Thus, genes such as prolactin (PRL) and proto-oncogene RET were confirmed to be specifically overexpressed in MYST3-CREBBP samples whereas genes such as CCND2, STAT5A, and STAT5B were differentially underexpressed in this AML category. Interestingly, MYST3-CREBBP AML exhibited a characteristic pattern of HOX expression, with up-regulation of HOXA9, HOXA10, and cofactor MEIS1 and marked down-regulation of other homeobox genes. This profile, with overexpression of FLT3, HOXA9, MEIS1, AKR7A2, CHD3, and APBA2, partially resembles that of AML with MLL rearrangement. In summary, this study shows the distinctive gene expression profile of MYST3-CREBBP AML, with overexpression of RET and PRL and a specific pattern of HOX gene expression.

Cloning and developmental expression of WSTF during Xenopus laevis embryogenesis

The gene WSTF is deleted in the autosomal dominant hereditary disorder Williams-Beuren syndrome. This disorder is caused by a 1.3 megabase deletion in human chromosome 7, encompassing at least 17 genes. The WSTF protein contains a bromodomain, found predominantly in chromatin-associated proteins. Reported association of WSTF with chromatin remodeling factors and functional data support a role for WSTF during chromatin remodeling. Here, we report the cloning and developmental expression pattern of Xenopus laevis WSTF. Xenopus laevis WSTF is a protein with a predicted amino acid sequence of 1441 amino acids. Three discrete domains can be identified in the Xenopus laevis WSTF protein, a PHD finger, a DDT domain and a bromodomain. Alignment of Xenopus WSTF with the corresponding orthologues from Homo sapiens, Gallus gallus, Mus musculus and Danio rerio demonstrates an evolutionary conservation of WSTF amino acid sequence and domain organization. In situ hybridization reveals a dynamic expression profile during embryonic development. WSTF is expressed differentially in neural tissue, especially during neurulae stages in the eye, in neural crest cells and the brain.

Versican: signaling to transcriptional control pathways

Versican, a chondroitin sulfate proteoglycan, is one of the main components of the extracellular matrix, which provides a loose and hydrated matrix during key events in development and disease. Versican participates in cell adhesion, proliferation, migration, and angiogenesis, and hence plays a central role in tissue morphogenesis and maintenance. In addition, versican contributes to the development of a number of pathologic processes including atherosclerotic vascular diseases, cancer, tendon remodeling, hair follicle cycling, central nervous system injury, and neurite outgrowth. Versican is a complex molecule consisting of modular core protein domains and glycosaminoglycan side chains, and there are various steps of synthesis and processes regulating them. Also, there is differential temporal and spatial expression of versican by multiple cell types and in different developmental and pathological time frames. To fully appreciate the functional roles of versican as it relates to changing patterns of expression in development and disease, an in depth knowledge of versican's biosynthetic processing is necessary. The goal of this review is to evaluate the current status of our knowledge regarding the transcriptional control of versican gene regulation. We will be focusing on the signal transduction pathways, promoter regions, cis-acting elements, and trans-factors that have been characterized.

Histone deacetylase inhibitor FK228 activates tumor suppressor Prdx1 with apoptosis induction in esophageal cancer cells

PURPOSE

The histone deacetylase inhibitor FK228 shows strong activity as a potent antitumor drug but its precise mechanism is still obscure. The purpose of this study is to reveal the effect of FK228 on gene expression in the cell and to determine the mechanism of the antitumor activity of FK228 for further clinical applications.

EXPERIMENTAL DESIGN AND RESULTS

Microarray analysis was applied to verify the gene expression profiles of 4,608 genes after FK228 treatment using human esophageal squamous cell cancer cell lines T.Tn and TE2. Among them, peroxiredoxin 1 (Prdx1), a member of the peroxiredoxin family of antioxidant enzymes having cell growth suppression activity, as well as p21(WAF1), were significantly activated by FK288. In addition, FK228 strongly inhibited the cell growth of T.Tn and TE2 by the induction of apoptosis. Further, chromatin immunoprecipitation analysis revealed that FK228 induced the accumulation of acetylated histones H3 and H4 in Prdx1 promoter, including the Sp1-binding site. In mouse xenograft models of T.Tn and TE2 cells, FK228 injection resulted in significant tumor regression as well as activated Prdx1 expression in tumor tissues. Prdx1 suppression by RNA interference hindered the antitumor effect of FK228.

CONCLUSION

Our results indicate that the antitumor effect of FK228 in esophageal cancer cells is shown at least in part through Prdx1 activation by modulating acetylation of histones in the promoter, resulting in tumor growth inhibition with apoptosis induction.

SPOC1, a novel PHD-finger protein: association with residual disease and survival in ovarian cancer

We report the identification of a novel human gene (SPOC1) which encodes a protein with a PHD-finger domain. The gene is located in chromosomal region 1p36.23, a region implicated in tumor development and progression. RNA in situ hybridization experiments showed strong SPOC1 expression in some rapidly proliferating cell types, such as spermatogonia, but not in nonproliferating mature spermatocytes. In addition, high SPOC1 mRNA expression was observed in several ovarian cancer cell lines. This prompted us to systematically examine SPOC1 expression in ovarian cancer in relation to prognosis. SPOC1 mRNA expression was quantified in tumor tissue of 103 patients with epithelial ovarian cancer. Interestingly, SPOC1 was associated with residual disease, whereby patients with unresectable tumors showed higher levels compared to patients without residual tumor tissue after surgery (p = 0.029). The univariable proportional hazards model showed an association between SPOC1 expression and survival (p = 0.043, relative risk = 1.535). Median survival time was 1,596 days for patients with low SPOC1 expression vs. only 347 days for patients with high expression, using Kaplan-Meier analysis. However, SPOC1 was not associated with survival when multivariable analysis was adjusted for residual disease. This can be explained by the correlation between residual disease and SPOC1 expression. In conclusion, SPOC1 is a novel PHD-finger protein showing strong expression in spermatogonia and ovarian cancer cells. SPOC1 overexpression was associated with unresectable carcinomas and shorter survival in ovarian cancer.

Global histone modification patterns predict risk of prostate cancer recurrence

Aberrations in post-translational modifications of histones have been shown to occur in cancer cells but only at individual promoters; they have not been related to clinical outcome. Other than being targeted to promoters, modifications of histones, such as acetylation and methylation of lysine and arginine residues, also occur over large regions of chromatin including coding regions and non-promoter sequences, which are referred to as global histone modifications. Here we show that changes in global levels of individual histone modifications are also associated with cancer and that these changes are predictive of clinical outcome. Through immunohistochemical staining of primary prostatectomy tissue samples, we determined the percentage of cells that stained for the histone acetylation and dimethylation of five residues in histones H3 and H4. Grouping of samples with similar patterns of modifications identified two disease subtypes with distinct risks of tumour recurrence in patients with low-grade prostate cancer. These histone modification patterns were predictors of outcome independently of tumour stage, preoperative prostate-specific antigen levels, and capsule invasion. Thus, widespread changes in specific histone modifications indicate previously undescribed molecular heterogeneity in prostate cancer and might underlie the broad range of clinical behaviour in cancer patients.

Histone deacetylation in epigenetics: an attractive target for anticancer therapy

The reversible histone acetylation and deacetylation are epigenetic phenomena that play critical roles in the modulation of chromatin topology and the regulation of gene expression. Aberrant transcription due to altered expression or mutation of genes that encode histone acetyltransferase (HAT) or histone deacetylase (HDAC) enzymes or their binding partners, has been clearly linked to carcinogenesis. The histone deacetylase inhibitors are a new promising class of anticancer agents (some of which in clinical trials), that inhibit the proliferation of tumor cells in culture and in vivo by inducing cell-cycle arrest, terminal differentiation, and/or apoptosis. This report reviews the chemistry and the biology of HDACs and HDAC inhibitors, laying particular emphasis on agents actually in clinical trials for cancer therapy and on new potential anticancer lead compounds more selective and less toxic.

Function of the ING family of PHD proteins in cancer

The ING genes encode a family of at least seven proteins with conserved plant homeodomain (PHD)-type zinc fingers in their C-termini. The founding member, ING1, is capable of binding to and affecting the activity of histone acetyltransferase (HAT), histone deacetylase (HDAC), and factor acetyltransferase (FAT) protein complexes. Some ING proteins are involved in transcriptional regulation of genes, such as the p53-inducible genes p21 and Bax. Others have been found to affect post-translational modifications, exemplified by the ING2-induced acetylation of p53 on the same site deacetylated by the Sir2 HDAC. Upon UV irradiation, ING1 causes cell cycle arrest and interacts with proliferating cell nuclear antigen to promote DNA repair or induce apoptosis in cells to prevent tumorigenesis depending upon the severity of DNA damage. It is very likely that, by linking DNA repair, apoptosis and chromatin remodeling to the transcriptional regulation of critical genes, ING1 exerts it tumor suppressor functions by helping maintain genomic stability. Therefore, ING proteins, which are down-regulated in a broad variety of cancer types, are able to restrict cell growth and proliferation, induce apoptosis, and modulate cell cycle progression, which strongly supports the notion that ING family proteins act as class II tumor suppressors.

Mapping DNA-binding domains of the autoimmune regulator protein

The human autoimmune regulator (AIRE) gene encodes a putative DNA-binding protein, which is mutated in patients affected by the autoimmune polyglandular syndrome type 1 or autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy. We have recently reported that AIRE can bind to two different DNA sequence motifs, suggesting the existence of at least two DNA-binding domains in the AIRE protein. By expressing a series of recombinant AIRE protein fragments, we demonstrate here that the two well-known plant homeodomains (PHD) domains in AIRE can bind to the ATTGGTTA sequence motif. The first ATTGGTTA-binding domain is mapped to amino acids 299-355 and the second ATTGGTTA-binding domain to amino acids 434-475. Furthermore, the SAND domain of AIRE is shown to bind to TTATTA motif. Results presented herein show that the residues at position 189-196 of AIRE (QRAVAMSS) are required for its binding to the TTATTA motif. The required sequence for DNA binding in the SAND domain of AIRE is remarkably different from other SAND-containing proteins such as Sp-100b and NUDR. Data presented in this paper indicate that the two PHD domains contained in AIRE, in addition to the SAND domain, can bind to specific DNA sequence motifs.

MOZ-TIF2 inhibits transcription by nuclear receptors and p53 by impairment of CBP function

Chromosomal rearrangements associated with acute myeloid leukemia (AML) include fusions of the genes encoding the acetyltransferase MOZ or MORF with genes encoding the nuclear receptor coactivator TIF2, p300, or CBP. Here we show that MOZ-TIF2 acts as a dominant inhibitor of the transcriptional activities of CBP-dependent activators such as nuclear receptors and p53. The dominant negative property of MOZ-TIF2 requires the CBP-binding domain (activation domain 1 [AD1]), and coimmunoprecipitation and fluorescent resonance energy transfer experiments show that MOZ-TIF2 interacts with CBP directly in vivo. The CBP-binding domain is also required for the ability of MOZ-TIF2 to extend the proliferative potential of murine bone marrow lineage-negative cells in vitro. We show that MOZ-TIF2 displays an aberrant nuclear distribution and that cells expressing this protein have reduced levels of cellular CBP, leading to depletion of CBP from PML bodies. In summary, our results indicate that disruption of the normal function of CBP and CBP-dependent activators is an important feature of MOZ-TIF2 action in AML.

Chick Pcl2 regulates the left-right asymmetry by repressing Shh expression in Hensen's node

Asymmetric expression of sonic hedgehog (Shh) in the left side of Hensen's node, a crucial step for specifying the left-right (LR) axis in the chick embryo, is established by the repression of Shhexpression in the right side of the node. The transcriptional regulator that mediates this repression has not been identified. We report the isolation and characterization of a novel chick Polycomblike 2 gene, chick Pcl2, which encodes a transcription repressor and displays an asymmetric expression, downstream from Activin-βB and Bmp4, in the right side of Hensen's node in the developing embryo. In vitro mapping studies define the transcription repression activity to the PHD finger domain of the chick Pcl2 protein. Repression of chick Pcl2expression in the early embryo results in randomized heart looping direction,which is accompanied by the ectopic expression of Shh in the right side of the node and Shh downstream genes in the right lateral plate mesoderm (LPM), while overexpression of chick Pcl2 represses Shh expression in the node. The repression of Shh by chick Pcl2 was also supported by studies in which chick Pcl2 was overexpressed in the developing chick limb bud and feather bud. Similarly,transgenic overexpression of chick Pcl2 in the developing mouse limb inhibits Shh expression in the ZPA. In vitro pull-down assays demonstrated a direct interaction of the chick Pcl2 PHD finger with EZH2, a component of the ESC/E(Z) repressive complex. Taken together with the fact that chick Pcl2 was found to directly repress Shh promoter activity in vitro, our results demonstrate a crucial role for chick Pcl2 in regulating LR axis patterning in the chick by silencing Shh in the right side of the node.

Molecular requirements for gene expression mediated by targeted histone acetyltransferases

Histone acetyltransferases (HATs) play fundamental roles in regulating gene expression. HAT complexes with distinct subunit composition and substrate specificity act on chromatin-embedded genes with different promoter architecture and chromosomal locations. Because requirements for HAT complexes vary, a central question in transcriptional regulation is how different HAT complexes function in different chromosomal contexts. Here, we have tested the ability of targeted yeast HATs to regulate gene expression of an epigenetically silenced locus. Of a panel of HAT fusion proteins targeted to a telomeric reporter gene, Sas3p and Gcn5p selectively increased expression of the silenced gene. Reporter gene expression was not solely dependent on acetyltransferase activity of the targeted HAT. Further analysis of Gcn5p-mediated gene expression revealed collateral requirements for HAT complex subunits Spt8p and Spt3p, which interact with TATA-binding protein, and for a gene-specific transcription factor. These data demonstrate plasticity of gene expression mediated by HATs upon encountering novel promoter architecture and chromatin context. The telomeric location of the reporter gene used in these studies also provides insight into the molecular requirements for heterochromatin boundary formation and for overcoming transcriptional silencing.

The diverse superfamily of lysine acetyltransferases and their roles in leukemia and other diseases

Acetylation of the epsilon-amino group of lysine residues, or N(epsilon)-lysine acetylation, is an important post-translational modification known to occur in histones, transcription factors and other proteins. Since 1995, dozens of proteins have been discovered to possess intrinsic lysine acetyltransferase activity. Although most of these enzymes were first identified as histone acetyltransferases and then tested for activities towards other proteins, acetyltransferases only modifying non-histone proteins have also been identified. Lysine acetyltransferases form different groups, three of which are Gcn5/PCAF, p300/CBP and MYST proteins. While members of the former two groups mainly function as transcriptional co-activators, emerging evidence suggests that MYST proteins, such as Esa1, Sas2, MOF, TIP60, MOZ and MORF, have diverse roles in various nuclear processes. Aberrant lysine acetylation has been implicated in oncogenesis. The genes for p300, CBP, MOZ and MORF are rearranged in recurrent leukemia-associated chromosomal abnormalities. Consistent with their roles in leukemogenesis, these acetyltransferases interact with Runx1 (or AML1), one of the most frequent targets of chromosomal translocations in leukemia. Therefore, the diverse superfamily of lysine acetyltransferases executes an acetylation program that is important for different cellular processes and perturbation of such a program may cause the development of cancer and other diseases.

Pygopus is required for embryonic brain patterning in Xenopus

We have identified two Xenopus mRNAs that encode proteins homologous to a component of the Wnt/beta-catenin transcriptional machinery known as Pygopus. The predicted proteins encoded by both mRNAs share the same structural properties with human Pygo-2, but with Xpygo-2alpha having an additional 21 N-terminal residues. Xpygo-2alpha messages accumulate in the prospective anterior neural plate after gastrulation and then are localized to the nervous system, rostral to and including the hindbrain. Xpygo-2beta mRNA is expressed in oocytes and early embryos but declines in level before and during gastrulation. In late neurula, Xpygo-2beta mRNA is restricted to the retinal field, including eye primordia and prospective forebrain. A C-terminal truncated mutant of Xpygo-2 containing the N-terminal Homology Domain (NHD) caused both axis duplication when injected at the 2-cell stage and inhibition of anterior neural development when injected in the prospective head, mimicking the previously described effects of Wnt-signaling activators. Inhibition of Xpygo-2alpha and Xpygo-2beta by injection of gene-specific antisense morpholino oligonucleotides into prospective anterior neurectoderm caused brain defects that were prevented by coinjection of Xpygo-2 mRNA. Both Xpygo-2alpha and Xpygo-2beta morpholinos reduced the eye and forebrain markers Xrx-1, Xpax-6, and XBF-1, while the Xpygo-2alpha morpholino also eliminated expression of the mid-hindbrain marker En-2. The differential expression and regulatory activities of Xpygo-2alpha/beta in rostral neural tissue indicate that they represent essential components of a novel mechanism for Wnt signaling in regionalization of the brain.

Zygote arrest 1 (Zar1) is an evolutionarily conserved gene expressed in vertebrate ovaries

Zygote arrest 1 (ZAR1) is an ovary-specific maternal factor that plays essential roles during the oocyte-to-embryo transition. In mice, the Zar1 mRNA is detected as a 1.4-kilobase (kb) transcript that is synthesized exclusively in growing oocytes. To further understand the functions of ZAR1, we have cloned the orthologous Zar1 cDNA and/or genes for mouse, rat, human, frog, zebrafish, and pufferfish. The entire mouse Zar1 gene and a related pseudogene span approximately 4.0 kb, contain four exons, and map to adjacent loci on mouse chromosome 5. The human ZAR1 orthologous gene similarly consists of four exons and resides on human chromosome 4p12, which is syntenic with the mouse Zar1 chromosomal locus. Rat (Rattus norvegicus) and pufferfish (Fugu rubripes) Zar1 genes were recognized by database mining and deduced protein alignment analysis. The rat Zar1 gene also maps to a region that is syntenic with the mouse Zar1 gene locus on rat chromosome 14. Frog (Xenopus laevis) and zebrafish (Danio rerio) Zar1 orthologs were cloned by reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends analysis of ovarian mRNA. Unlike mouse and human, the frog Zar1 is detected in multiple tissues, including lung, muscle, and ovary. The Zar1 mRNA appears in the cytoplasm of oocytes and persists until the tailbud stage during frog embryogenesis. Mouse, rat, human, frog, zebrafish, and pufferfish Zar1 genes encode proteins of 361, 361, 424, 295, 329, and 320 amino acids, respectively, and share 50.8%-88.1% amino acid identity. Regions of the N-termini of these ZAR1 orthologs show high sequence identity among these various proteins. However, the C-terminal 103 amino acids of these proteins, encoded by exons 2-4, contain an atypical eight-cysteine Plant Homeo Domain motif and are highly conserved, sharing 80.6%-98.1% identity among these species. These findings suggest that the carboxyl-termini of these ZAR1 proteins contain an important functional domain that is conserved through vertebrate evolution and that may be necessary for normal female reproduction in the transition from oocyte to embryonic life.

Assessment of protein expression by means of 2-D gel electrophoresis with and without mass spectrometry

Careful examination of current literature, particularly over the last 5 years, reveals a wide range of approaches for the relative quantification of protein expression in cells, tissues, and body fluids. In view of such an observation, it is reasonable to ask whether researchers need new methods, or whether it is more productive to optimize and tune already existing ones. It is generally agreed that none of the existing methodologies on its own can give a full account of protein expression in a complex medium; this limitation, however, has not prevented the use of existing methods to provide valuable information on a wide range of proteins, where their expression has been correlated to certain pathologies and/or to pharmacological, genetic, or environmental factors. In the present work, an attempt is made to review the application of one of these methodologies, namely two-dimensional polyacrylamide gel electrophoresis on its own or in conjunction with mass spectrometry, to assess protein expression, particularly when such expression can be correlated to certain pathologies.

A Paradigm for Gene Regulation: Inflammation, NF-κB and PPAR

The onset of inflammatory gene expression is driven by the transcription factor NF-kappaB, whose transcriptional activity is regulated at multiple levels. First, NF-kappaB activity is regulated by cytoplasmic degradation of the IkappaB inhibitor and nuclear translocation. Second, the nuclear p65 transactivation potential can be further influenced by posttranslational modifications, such as phosphorylation and/or acetylation. The p65 phosphorylation is a process highly regulated by both cell- and stimulus-dependent activating kinases. Ser276 phosphorylation seems to be highly important considering its crucial role in the interaction with and the engagement of the cofactor CBP/p300. We have identified MSK1 as an acting kinase in the TNF-signalling pathway, where it is responsible for p65 phosphorylation at Ser276, as well as for H3 phosphorylation of Ser10 in IL-6 promoter-associated chromatin (Fig. 1) (Saccani et al., 2002; Vermeulen et al., 2002, 2003). To our knowledge, this was the first report that identifies one particular kinase involved in transcription factor phosphorylation and histone modification at the level of a single promoter in order to establish gene activation. The question of which element takes the initial step to recruit and to assemble the activated transcription complex still remains unanswered (Vanden Berghe et al., 2002). PPAR alpha negatively interferes with inflammatory gene expression by up-regulation of the cytoplasmic inhibitor molecule IkappaB alpha, thus establishing an autoregulatory loop (Fig. 1). This induction takes place in the absence of a PPRE, but requires the presence of NF-kappaB and Sp1 elements in the IkappaB alpha promoter sequence as well as DRIP250 cofactors. The detailed mechanism how PPAR can activate genes in a non-DNA-binding way needs further investigation; moreover, it is at present not clear whether this upregulation, unlike the inhibitory effect of glucocorticoids, is a cell type- or a PPAR-specific phenomenon.

Structural basis of ICF-causing mutations in the methyltransferase domain of DNMT3B

Mutations in the gene encoding for a de novo methyltransferase, DNMT3B, lead to an autosomal recessive Immunodeficiency, Centromeric instability and Facial anomalies (ICF) syndrome. To analyse the protein structure and consequences of ICF-causing mutations, we modelled the structure of the DNMT3B methyltransferase domain based on Haemophilus haemolyticus protein in complex with the cofactor AdoMet and the target DNA sequence. The structural model has a two-subdomain fold where the DNA-binding region is situated between the subdomains on a surface cleft having positive electrostatic potential. The smaller subdomains of the methyltransferases differ in length and sequences and therefore only the target recognition domain loop was modelled to show the location of an ICF-causing mutation. Based on the model, the DNMT3B recognizes the GC sequence and flips the cytosine from the double-stranded DNA to the catalytic pocket. The amino acids in the cofactor and target cytosine binding sites and also the electrostatic properties of the binding pockets are conserved. In addition, a registry of all known ICF-causing mutations, DNMT3Bbase, was constructed. The structural principles of the pathogenic mutations based on the modelled structure and the analysis of chi angle rotation changes of mutated side chains are discussed.

Mutation analysis of EP300 in colon, breast and ovarian carcinomas

The putative tumour suppressor gene EP300 is located on chromosome 22q13 which is a region showing frequent loss of heterozygosity (LOH) in colon, breast and ovarian cancers. We analysed 203 human breast, colon and ovarian primary tumours and cell lines for somatic mutations in EP300. LOH across the EP300 locus was detected in 38% of colon, 36% of breast, and 49% of ovarian primary tumours but no somatic mutations in EP300 were identified in any primary tumour. Analysis of 17 colon, 11 breast, and 11 ovarian cancer cell lines identified truncating mutations in 4 colon cancer cell lines (HCT116, HT29, LIM2405 and LIM2412). We confirmed the presence of a previously reported frameshift mutation in HCT116 at codon 1699 and identified a second frameshift mutation at codon 1468. Bi-allelic inactivation of EP300 was also detected in LIM2405 that harbours an insC mutation at codon 927 as well an insA mutation at codon 1468. An insA mutation at codon 1468 was identified in HT29 and a CGA>TGA mutation at codon 86 was identified in LIM2412. Both these lines were heterozygous across the EP300 locus and western blot analysis confirmed the presence of an apparently wild-type protein. Our study has established that genetic inactivation of EP300 is rare in primary colorectal, breast and ovarian cancers. In contrast, mutations are common among colorectal cancer cell lines with 4/17 harbouring homozygous or heterozygous mutations. The rarity of EP300 mutations among these tumour types that show a high frequency of LOH across 22q13 may indicate that another gene is the target of the loss. It is possible that bi-allelic inactivation of EP300 is not necessary and that haploinsufficiency is sufficient to promote tumorigenesis. Alternatively, silencing of EP300 may be achieved by epigenetic mechanisms such as promoter methylation.

Ubiquitin-dependent proteolysis: its role in human diseases and the design of therapeutic strategies

Protein degradation is one of the tactics employed by the cell for irreversibly inactivating proteins. In eukaryotes, ATP-dependent protein degradation in the cytoplasm and nucleus is carried out by the 26S proteasome. Most proteins are targeted to the 26S proteasome by covalent attachment of a multi-ubiquitin chain. A key component of the enzyme cascade that results in attachment of the multi-ubiquitin chain to the target or labile protein is the ubiquitin ligase that controls the specificity of the ubiquitination reaction. Defects in ubiquitin-dependent proteolysis have been shown to result in a variety of human diseases, including cancer, neurodegenerative diseases, and metabolic disorders. This review focuses on the role of ubiquitin-dependent degradation in human disease and potential clinical applications that are being developed to exploit the cells natural proteolytic machinery to treat diseases.

A new nuclear component of the Wnt signalling pathway

The Wnt signalling pathway is pivotal in normal and malignant development. A key effector is Armadillo (Arm)/beta-catenin, which functions with TCF to transcribe Wnt target-genes. Here, we report the discovery of pygopus (pygo), whose mutant phenotypes specifically mimic loss-of-Wingless (Wg) signalling. pygo is required for dTCF-mediated transcription, but not for Wg-induced stabilization of Arm. Pygo is a nuclear protein that is found in a complex with Arm in vivo. Humans possess two Pygo proteins, both of which are required for TCF-mediated transcription in colorectal cancer cells. The presence of a PHD domain implicates Pygo proteins in a chromatin-related function, and we propose that they mediate chromatin access to TCF or Arm/beta-catenin.

The PHD domain of MEKK1 acts as an E3 ubiquitin ligase and mediates ubiquitination and degradation of ERK1/2

ERK1/2 MAP kinases are important regulators in cellular signaling, whose activity is normally reversibly regulated by threonine-tyrosine phosphorylation. In contrast, we have found that stress-induced ERK1/2 activity is downregulated by ubiquitin/proteasome-mediated degradation of ERK1/2. The PHD domain of MEKK1, a RING finger-like structure, exhibited E3 ubiquitin ligase activity toward ERK2 in vitro and in vivo. Moreover, both MEKK1 kinase activity and the docking motif on ERK1/2 were involved in ERK1/2 ubiquitination. Significantly, cells expressing ERK2 with the docking motif mutation were resistant to sorbitol-induced apoptosis. Therefore, MEKK1 functions not only as an upstream activator of the ERK and JNK through its kinase domain, but also as an E3 ligase through its PHD domain, providing a negative regulatory mechanism for decreasing ERK1/2 activity.

Epstein-Barr virus nuclear antigen 3C and prothymosin alpha interact with the p300 transcriptional coactivator at the CH1 and CH3/HAT domains and cooperate in regulation of transcription and histone acetylation

The Epstein-Barr virus nuclear antigen 3C (EBNA3C), encoded by Epstein-Barr virus (EBV), is essential for mediating transformation of human B lymphocytes. Previous studies demonstrated that EBNA3C interacts with a small, nonhistone, highly acidic, high-mobility group-like nuclear protein prothymosin alpha (ProT(alpha)) and the transcriptional coactivator p300 in complexes from EBV-infected cells. These complexes were shown to be associated with histone acetyltransferase (HAT) activity in that they were able to acetylate crude histones in vitro. In this report we show that ProT(alpha) interacts with p300 similarly to p53 and other known oncoproteins at the CH1 amino-terminal domain as well as at a second domain downstream of the bromodomain which includes the CH3 region and HAT domain. Similarly, EBNA3C also interacts with p300 at regions which include the CH1 and CH3/HAT domains, suggesting that ProT(alpha) and EBNAC3C may interact in a complex with p300. We also show that ProT(alpha) activates transcription when targeted to promoters by fusion to the GAL4 DNA binding domain and that this activation is enhanced by the addition of an exogenous source of p300 under the control of a heterologous promoter. This overall activity is down-modulated in the presence of EBNA3C. These results further establish the interaction of cellular coactivator p300 with ProT(alpha) and demonstrate that the associated activities resulting from this interaction, which plays a role in acetylation of histones and coactivation, can be regulated by EBNA3C. Furthermore, this study establishes for the first time a transcriptional role for ProT(alpha) in recruitment or stabilization of coactivator p300, as well as other basal transcription factors, at the nucleosomes for regulation of transcription.