The dynamic architecture of Map1- and NatB-ribosome complexes coordinates the sequential modifications of nascent polypeptide chains.

Cotranslational modification of the nascent polypeptide chain is one of the first events during the birth of a new protein. In eukaryotes, methionine aminopeptidases (MetAPs) cleave off the starter methionine, whereas N-acetyl-transferases (NATs) catalyze N-terminal acetylation. MetAPs and NATs compete with other cotranslationally acting chaperones, such as ribosome-associated complex (RAC), protein targeting and translocation factors (SRP and Sec61) for binding sites at the ribosomal tunnel exit. Yet, whereas well-resolved structures for ribosome-bound RAC, SRP and Sec61, are available, structural information on the mode of ribosome interaction of eukaryotic MetAPs or of the five cotranslationally active NATs is only available for NatA. Here, we present cryo-EM structures of yeast Map1 and NatB bound to ribosome-nascent chain complexes. Map1 is mainly associated with the dynamic rRNA expansion segment ES27a, thereby kept at an ideal position below the tunnel exit to act on the emerging substrate nascent chain. For NatB, we observe two copies of the NatB complex. NatB-1 binds directly below the tunnel exit, again involving ES27a, and NatB-2 is located below the second universal adapter site (eL31 and uL22). The binding mode of the two NatB complexes on the ribosome differs but overlaps with that of NatA and Map1, implying that NatB binds exclusively to the tunnel exit. We further observe that ES27a adopts distinct conformations when bound to NatA, NatB, or Map1, together suggesting a contribution to the coordination of a sequential activity of these factors on the emerging nascent chain at the ribosomal exit tunnel.

Reduction of Tat-interacting Protein 30 Expression Could be a Prognostic Marker in Bladder Urothelial Cancer.

BACKGROUND: Tat-interacting protein 30 (TIP30) has been reported to be a tumor suppressor, with reduced or absent expression in various tumors. However, its role in bladder urothelial cancer (BUC) has not been investigated. Therefore, herein, we investigated the expression of TIP30 protein in BUC and normal bladder mucosa and the clinical significance of TIP30 expression in the prognosis of BUC. METHODS: We reviewed data from 79 cases of BUC and 15 adjacent tissue samples from 79 patients treated at our institution between 2004 and 2007. TIP30 expression was examined by immunohistochemistry. The relationship between TIP30 expression and tumor stage, histological grade, and survival was analyzed. Differences between groups were evaluated using the t-test or matched-pairs test, and differences in the survival rates were analyzed with the log-rank test. RESULTS: TIP30 protein expression was significantly reduced in BUC tissue (t = -6.91, P < 0.05) compared with normal tissue samples, and in invasive bladder cancer (t = 10.89, P < 0.05) compared with superficial bladder cancer. TIP30 protein expression differed significantly among different differentiated groups classified either according to the World Health Organization (2004, F = 17.48, P < 0.01) or World Health Organization (1973, F = 10.68, P < 0.01). TIP30 protein expression was significantly reduced in high-grade papillary urothelial carcinoma compared with papillary urothelial neoplasm of low malignant potential (P < 0.05) and low-grade papillary urothelial carcinoma (P < 0.05). Meanwhile, TIP30 protein expression was significantly reduced in Grade III BUC, compared with Grade I (P < 0.05) and Grade II (P < 0.05). Patients with low TIP30 expression showed a higher incidence of disease progression than those with high TIP30 expression (t = 2.63, P < 0.05). Kaplan-Meier survival analysis showed a strong positive relationship between TIP30 expression and overall survival (OS) (χ2 = 17.29, P < 0.05). CONCLUSIONS: TIP30 expression was associated with clinical tumor stage in BUC, suggesting that it might play an important role in disease progression. Furthermore, TIP30 might predict postoperative OS. Thus, its evaluation might be useful for predicting prognosis.

Identification of biomarkers and pathway-related modules involved in ovarian cancer based on topological centralities.

PURPOSE: The present study was designed to explore the significant biomarkers and pathway-related modules for predicting the effects of eribulin relative to paclitaxel in ovarian cancer. METHODS: The gene expression data E-GEOD-50831 were downloaded from the European Bioinformatics Institute (EBI) database. Differentially expressed genes (DEGs) were screened. Subsequently, differential coexpression network was constructed. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and pathway-related modules mining were conducted. Topological centralities (degree, betweenness, closeness and stress) analyses for coexpression network and pathway-related modules were performed to explore hub genes and the most significant pathways. Then, we verified our findings in an independent sample set via RT-PCR and Western blotting. RESULTS: Centralities results of ESCO1, CDC27and MCM4 ranked the top five. Moreover, among the top 10% hub genes, CDC27, MCM4 and SOS1 were pathway-enriched genes in two networks. A total of 5 and 6 pathway-related modules were obtained under two drugs treatment. Based analyses of degree, betweenness and other centralities, DNA replication pathway-related module was the most significant under paclitaxel treatment, while cell cycle pathway-related module was the most significant under eribulin treatment. RT-PCR and Western blotting results were consistent with the bioinformatics results. The expression level of MCM4 was remarkably decreased under eribulin treatment relative to paclitaxel. CONCLUSIONS: The inhibition of ovarian cancer growth by paclitaxel and eribulin might be connected with downregulation of cell cycle and DNA replication pathway. Moreover, MCM4 signature might be a potential biomarker to predict the effect of eribulin in ovarian cancer.

Homocysteine induces glyceraldehyde-3-phosphate dehydrogenase acetylation and apoptosis in the neuroblastoma cell line Neuro2a.

High plasma levels of homocysteine (Hcy) promote the progression of neurodegenerative diseases. However, the mechanism by which Hcy mediates neurotoxicity has not been elucidated. We observed that upon incubation with Hcy, the viability of a neuroblastoma cell line Neuro2a declined in a dose-dependent manner, and apoptosis was induced within 48 h. The median effective concentration (EC50) of Hcy was approximately 5 mM. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) nuclear translocation and acylation has been implicated in the regulation of apoptosis. We found that nuclear translocation and acetylation of GAPDH increased in the presence of 5 mM Hcy and that higher levels of acetyltransferase p300/CBP were detected in Neuro2a cells. These findings implicate the involvement of GAPDH in the mechanism whereby Hcy induces apoptosis in neurons. This study highlights a potentially important pathway in neurodegenerative disorders, and a novel target pathway for neuroprotective therapy.

Homocysteine induces glyceraldehyde-3-phosphate dehydrogenase acetylation and apoptosis in the neuroblastoma cell line Neuro2a

High plasma levels of homocysteine (Hcy) promote the progression of neurodegenerative diseases. However, the mechanism by which Hcy mediates neurotoxicity has not been elucidated. We observed that upon incubation with Hcy, the viability of a neuroblastoma cell line Neuro2a declined in a dose-dependent manner, and apoptosis was induced within 48 h. The median effective concentration (EC50) of Hcy was approximately 5 mM. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) nuclear translocation and acylation has been implicated in the regulation of apoptosis. We found that nuclear translocation and acetylation of GAPDH increased in the presence of 5 mM Hcy and that higher levels of acetyltransferase p300/CBP were detected in Neuro2a cells. These findings implicate the involvement of GAPDH in the mechanism whereby Hcy induces apoptosis in neurons. This study highlights a potentially important pathway in neurodegenerative disorders, and a novel target pathway for neuroprotective therapy.

Relevance of histone marks H3K9me3 and H4K20me3 in cancer.

BACKGROUND: Circulating nucleosomes are valuable biomarkers for therapy monitoring and estimation of prognosis in cancer disease. While epigenetic and genetic modifications of DNA have been reported in blood of cancer patients, little is known about modifications of histones on circulating nucleosomes. PATIENTS AND METHODS: Sera of 45 cancer patients (21 colorectal, 4 pancreatic, 15 breast, 5 lung cancer), 12 patients with benign gastrointestinal and inflammatory diseases, and 28 healthy individuals were investigated. Histone modifications were detected by chromatin-immunoprecipitation (ChIP) using antibodies for triple histone methylations at sites H3K9me3 and H4K20me3 and subsequent real-time polymerase chain reaction using primers for the centromeric satellites SAT2. Additionally, the amount of circulating nucleosomes, as well as of carcino-embryonic antigen (CEA) and cancer antigen (CA) 19-9 were measured. RESULTS: Levels of SAT2 on H3K9me3 (median 0.507 ng/ml) and on H4K20me3 (0.292 ng/ml) were elevated in sera of patients with breast cancer when compared with healthy controls (0.049 and 0.035 ng/ml), but were lower in patients with colorectal cancer (0.039 and 0.027 ng/ml). Both histone marks were correlated with each other but did not correlate with CEA or CA 19-9 in cancer patients. When H3K9me3 and H4K20me3 were normalized to nucleosome content in sera, ratios were significantly higher in all types of cancer as well as in colorectal and breast subtypes when compared with healthy controls. Best discrimination was achieved by normalized H4K20me3 reaching areas under the curves (AUC) of 79.1%, 90.4% and 81.2% in receiver operating characteristic (ROC) curves of these three comparisons. CONCLUSION: SAT2 levels on H3K9me3 and H4K20me3 are up-regulated in breast cancer and down-regulated in colorectal cancer. Normalization to total nucleosome content enables better discrimination between cancer and control groups.

Genetic analysis of genes involved in synthesis of modified 4-amino-4,6-dideoxyglucose in flagellin of Pseudomonas syringae pv. tabaci.

Glycosylation of flagellin contributes to swimming and swarming motilities, adhesion ability, and consequently virulence in Pseudomonas syringae pv. tabaci 6605. Glycans attached to six serine residues are located in the central region of the flagellin polypeptide. The glycan structure at position Ser 201 was recently revealed to consist of two L-rhamnoses and one modified 4-amino-4,6-dideoxyglucose (viosamine). To clarify the mechanisms for glycosylation of modified viosamine, genes encoding dTDP-viosamine aminotransferase (vioA), dTDP-viosamine acetyltransferase (vioB), and viosamine-derivative transferase (vioT) were isolated and defective mutants were generated. MALDI-TOF-MS analysis of a lysyl endopeptidase-digested peptide including all six glycosylation sites from each flagellin indicated that the molecular masses of the three flagellin mutants were reduced with highly heterogeneous patterns at regular intervals of 146 Da in the mass range from m/z 13,819 to 15,732. The data indicated that the glycopeptides obtained from mutants had glycans consisting only of deoxyhexose instead of the flagellin glycans including the viosamine derivatives determined previously. The motility and virulence on host tobacco leaves were strongly impaired in the Delta vioA mutant and were weakly reduced in the Delta vioB and Delta vioT mutant strains. These results suggest that the genes vioA, vioB, and vioT are essential for glycosylation of flagellin, and accordingly are required for bacterial virulence.

Decreased expression of germinal center-associated nuclear protein is involved in chromosomal instability in malignant gliomas.

Malignant glioma (MG) is highly proliferative and invasive, with the malignant characteristics associated with aneuploidy and chromosomal instability (CIN). Here, we found that the level of germinal center-associated nuclear protein (GANP), a mammalian homologue of yeast Sac3, was markedly decreased in MGs with a poor prognosis; and thus we explored the effect of its decrease on cell-cycle progression of MG cell lines. Glioblastomas showed a significantly lower level of ganp mRNA than anaplastic astrocytomas, as measured by real-time reverse transcription-PCR, in 101 cases of adult MG. MGs of ganp(Low) expression displayed more malignant characteristics, with loss of heterozygosity on chromosome 10, epidermal growth factor receptor gene amplification, and significantly poorer prognosis than the ganp(High) group. Human diploid fibroblasts depleted of ganp mRNA by the RNA interference (RNAi) method showed a decreased percentage of S-phase cells and a cellular-senescence phenotype. MG cell lines harboring abnormalities of various cell-cycle checkpoint molecules displayed slippage of mitotic checkpoints and an increased proportion of hyperploid cells after ganp RNAi-treatment. These results suggest that GANP protects cells from cellular senescence caused by DNA damage and that a significant decrease in GANP expression leads to malignancy by generating hyperploidy and CIN.

Cholangiocarcinomas associated with long-term inflammation express the activation-induced cytidine deaminase and germinal center-associated nuclear protein involved in immunoglobulin V-region diversification.

Cholangiocarcinoma (CCA) represents a model of tumor development after long-term inflammation which causes DNA damage or impairs DNA repair mechanism. AID and GANP, both appearing in antigen-driven B cells, are involved in affinity maturation of the immunoglobulin V-region with increased somatic mutation. A normal cholangiocyte line showed the induction of AID transcripts after stimulation with TNF-alpha, whereas ganp transcripts appeared constitutively in this cell line. Next, we examined the expression of AID and GANP in clinical CCA specimens to obtain information whether their expression levels are associated with the malignant grade of CCA. AID expression was similarly detected in the clinical cases of both well-differentiated and poorly-differentiated CCAs. On the contrary, GANP expression was detected in CCA cells at a higher level in the nucleus of poorly-differentiated CCAs with shorter survivals than in that of well-differentiated CCAs. The high and low cases of nuclear GANP expression showed no change in the frequency of the TP53 mutations, however, further investigation by in vitro experiment demonstrated that the high GANP expression caused the increased number of gammaH2AX foci after DNA damage by ionizing-irradiation. These results suggest that GANP is involved in regulation of DNA repair mechanism and the abnormal over-expression of GANP together with AID might be associated with rigorous DNA damage, potentially causing the malignant development of CCAs during long-term inflammation.

Immunohistochemical analysis of human arrest-defective-1 expressed in cancers in vivo.

The arrest-defective-1 (ARD1) gene has been reported to be important in yeast cell cycle regulation, and recent studies have shown that human arrest-defective-1 (hARD1) is related to cancer cell proliferation. To investigate the expression pattern of hARD1 protein in cancer tissues, immunohistochemical analysis was performed to analyze the hARD1 expression pattern in 400 cases of 19 types of common cancer and 133 non-cancer samples from 11 tissue types. hARD1 protein was expressed extensively in cancer tissues including glandular carcinoma and squamous cancer, and the positive rate was 71.5% (15/20) in urinary bladder cancer, 62.5% (30/48) in breast cancer and 57.1% (8/14) in cervical carcinoma. The average hARD1-positive rate was 52.3% in cancers and 31.5% in non-cancers, for which the difference was significant (p<0.005). Comparing the staining intensity of different fields in the same section, the hARD1 protein was highly accumulated in cancer cells when compared to the cells adjacent to cancer. The positive rate of breast and intestinal cancer was obviously higher than corresponding non-cancers (p<0.05 and 0.01). These findings suggest that the accumulation of hARD1 protein may be related to carcinogenesis of various types of cancer.

N-acetyltransferase ARD1-NAT1 regulates neuronal dendritic development.

ARD1 and NAT1 constitute an N-acetyltransferase complex where ARD1 holds the enzymatic activity of the complex. The ARD1-NAT1 complex mediates N-terminal acetylation of nascent polypeptides that emerge from ribosomes after translation. ARD1 may also acetylate the internal lysine residues of proteins. Although ARD1 and NAT1 have been found in the brain, the physiological role and substrates of the ARD1-NAT1 complex in neurons remain unclear. Here we investigated role of N-acetyltransferase activity in the process of neuronal development. Expression of ARD1 and NAT1 increased during dendritic development, and both proteins colocalized with microtubules in dendrites. The ARD1-NAT1 complex displayed acetyltransferase activity against a purified microtubule fraction in vitro. Inhibition of the complex limited the dendritic extension of cultured neurons. These findings suggest that the ARD1-NAT1 complex has acetyltransferase activity against microtubules in dendrites. Regulation by acetyltransferase activity is a novel mechanism that is required for dendritic arborization during neuronal development.

[hARD1 antiserum preparation and primary immunohistochemical analysis of hARD1 in tumor tissues].

Human arrest defective 1 (hARD1) is an acetyltransferase; its physiological significance remains unclear. To explore the relationship between ARD1 protein and tumors, we detected the hARD1 protein in tumor tissues in vivo. We cloned hARD1 gene from Hela cell and construct recombinant plasmid pET28b-hARD1. The recombinant plasmid was transformed into E. coli BL21 (DE3)plysS. hARD1 protein was expressed by inducing with IPTG(1 mmol/L) and purified up to 95% through Ni2+ chelation affinity chromatography. We used the purified hARD1 protein as antigen immunized the Balb/c mice and obtained the hARD1 specific polyclonal antiserum. Through immunohistochemical analysis of different tumor tissues in vivo, we found that hARD1 expressed at high frequency in breast cancer, prostate cancer and lung cancer, especially, hARD1 expression frequency in breast cancer was up to 70%, which is higher than in the other tumors. These results indicate that the high expression level of hARD1 could be an indicator of the breast cancer. This new finding would be a foundation to further explore the relationship between breast tumor and hARD1.

Implication of human N-alpha-acetyltransferase 5 in cellular proliferation and carcinogenesis.

The N-alpha-acetyltransferase NatB, composed in Saccharomyces cerevisiae by the Nat3p and Mdm20p subunits, is an important factor for yeast growth and resistance to several stress agents. However, the expression and functional role of the mammalian counterpart has not yet been analysed. Here, we report the identification of Nat3p human homologue (hNAT5/hNAT3) and the characterization of its biological function. We found that hNAT5/hNAT3 silencing in HeLa cells results in inhibition of cell proliferation and increased sensitivity to the pro-apoptotic agent MG132. Moreover, inhibition of hNAT5/hNAT3 expression induces p53 activation and upregulation of the antiproliferative protein p21(WAF1/CIP1). The changes of the cellular transcriptome after hNAT5/hNAT3 knockdown confirmed the involvement of this protein in cell growth and survival processes. Among the genes differentially expressed, we observed upregulation of several p53-dependent antiproliferative and pro-apoptotic genes. In the c-myc transgenic mice, which is a model of inducible hepatocarcinoma, we found that hNAT5/hNAT3 was upregulated when the tumour was induced. In accordance with this observation, we noticed increased hNAT5/hNAT3 protein level in neoplastic versus non-neoplastic tissue in a high proportion of patients with hepatocellular carcinoma. Consequently, our results suggest that hNAT5/hNAT3 is required for cellular proliferation and can be implicated in tumour growth.

Generation of novel monoclonal antibodies and their application for detecting ARD1 expression in colorectal cancer.

Arrest defective 1 (ARD1) is an acetyltransferase involved in cell cycle control in yeast. ARD1 interacts with human N-acetyltransferase (NATH) to form a functional N-terminal acetyltransferase complex. Recently it had been linked with proliferation and apoptosis in mammalian cells, but its function in cancer development remains unclear. To evaluate significance of ARD1 expression in human colorectal cancer, we generated a panel of monoclonal antibodies (mAbs) with high specificity and sensitivity against ARD1. All of the 10 different clones could be used in ELISA and Western blot, and clone 10C12, 13G2, and 4D10 can interact with ARD1 in eukaryotic cells by immunoprecipitation (IP). Clones of 14D4 and 10C12 were strongly reacted to ARD1 in immunocytochemistry (ICH) and immunohistochemistry (IHC). ARD1 expression was evaluated in human colorectal cancer and colitis tissues by immunohistochemical analysis with mAb 14D4. Forty-one were ARD1-positive in 50 colorectal cancer tissues and only 12 were weak positive in the 50 matched normal tissues (P < 0.001). Moreover, ARD1 expression was not detectable in 20 cases of colitis tissue (P < 0.001). Furthermore, all of the six human colorectal cancer cell lines we examined were also ARD1-positive at mRNA and protein levels. Taken together, the novel mAbs against ARD1 we generated could be good tools for both basic and clinical studies, and ARD1 could be a potential biomarker in colorectal cancer.

TIP30/CC3 expression in breast carcinoma: relation to metastasis, clinicopathologic parameters, and P53 expression.

Metastasis is the most frequent cause of death in patients with breast cancer. Tip30/CC3 gene is a putative metastasis suppressor gene, which was first identified by a differential display analysis of messenger RNA from the highly metastatic human variant small cell lung carcinoma (SCLC) versus less metastatic classic SCLC cell lines. The aim of this study was to analyze the relationship between expression of TIP30/CC3 and clinical prognosis in 87 patients with surgically removed breast carcinoma. Tumor tissues were stained immunohistochemically with anti-TIP30/CC3 antibody. We demonstrated that the expression of TIP30/CC3 was inversely associated with axillary lymph node metastasis (P = .0008) and vascular invasion (P = .0016). Expression of TIP30/CC3 was not correlated with tumor grade, estrogen, progesterone, and P53 expression. Inhibition of TIP30/CC3 expression by RNA-mediated interference greatly enhanced breast cancer cell invasion through the extracellular matrix, whereas overexpression of TIP30/CC3 by adenovirus vector suppressed invasion through the extracellular matrix. These data supported the theory that the expression of TIP30/CC3 had a suppressive function on tumor metastasis. In summary, the decrease in expression of TIP30/CC3 is related to metastasis and may represent a new prognosticator in breast carcinoma.

A novel mechanism for drug-induced liver failure: inhibition of histone acetylation by hydralazine derivatives.

BACKGROUND/AIMS: The aim of this study was to investigate the precise mechanism of liver failure by hydralazine derivatives, with special reference to liver regeneration failure. METHODS: Histone acetylation and proliferation of hepatocytes were evaluated by immunohistochemistry with anti-acetylated histone H4 and proliferating cell nuclear antigen (PCNA). Inhibition of histone acetylation by drugs was determined by in vitro histone acetylation assay. Mice livers fed with todralazine for 1 or 4 months were subjected to immunohistochemistry and Western blotting. Todralazine-fed mice were challenged with anti-Fas to check liver regeneration failure. RESULTS: On immunohistochemistry, histone acetylation in the hepatocytes was significantly impaired in patients with hydralazine derivatives. In an in vitro acetyl transferase assay, histone acetylation was inhibited by hydralazine derivatives in a dose-dependent manner. Mice fed with todralazine (3mg/day) for 4 months showed impairment of histone acetylation in hepatocytes whereas no inhibition was observed in mice fed with todralazine for 1 month. Anti-Fas challenge to todralazine-fed mice resulted in impairment of liver regeneration in respect of liver weight loss with impairment of histone acetylation in hepatocytes. CONCLUSIONS: Todralazine could inhibit catalysis of histone acetyltransferase and long-term administration of todralazine may impair histone acetylation of the hepatocytes, resulting in liver regeneration failure.

Establishment of sister chromatid cohesion at the S. cerevisiae replication fork.

Two identical sister copies of eukaryotic chromosomes are synthesized during S phase. To facilitate their recognition as pairs for segregation in mitosis, sister chromatids are held together from their synthesis onward by the chromosomal cohesin complex. Replication fork progression is thought to be coupled to establishment of sister chromatid cohesion, facilitating identification of replication products, but evidence for this has remained circumstantial. Here we show that three proteins required for sister chromatid cohesion, Eco1, Ctf4, and Ctf18, are found at, and Ctf4 travels along chromosomes with, replication forks. The ring-shaped cohesin complex is loaded onto chromosomes before S phase in an ATP hydrolysis-dependent reaction. Cohesion establishment during DNA replication follows without further cohesin recruitment and without need for cohesin to re-engage an ATP hydrolysis motif that is critical for its initial DNA binding. This provides evidence for cohesion establishment in the context of replication forks and imposes constraints on the mechanism involved.

Separate pathways for O acetylation of polymeric and monomeric sialic acids and identification of sialyl O-acetyl esterase in Escherichia coli K1.

O acetylation at carbon positions 7 or 9 of the sialic acid residues in the polysialic acid capsule of Escherichia coli K1 is catalyzed by a phase-variable contingency locus, neuO, carried by the K1-specific prophage, CUS-3. Here we describe a novel method for analyzing polymeric sialic acid O acetylation that involves the release of surface sialic acids by endo-N-acetylneuraminidase digestion, followed by fluorescent labeling and detection of quinoxalinone derivatives by chromatography. The results indicated that NeuO is responsible for the majority of capsule modification that takes place in vivo. However, a minor neuO-independent O acetylation pathway was detected that is dependent on the bifunctional polypeptide encoded by neuD. This pathway involves O acetylation of monomeric sialic acid and is regulated by another bifunctional enzyme, NeuA, which includes N-terminal synthetase and C-terminal sialyl O-esterase domains. A homologue of the NeuA C-terminal domain (Pm1710) in Pasteurella multocida was also shown to be an esterase, suggesting that it functions in the catabolism of acetylated environmental sialic acids. Our combined results indicate a previously unexpected complexity in the synthesis and catabolism of microbial sialic and polysialic acids. These findings are key to understanding the biological functions of modified sialic acids in E. coli K1 and other species and may provide new targets for drug or vaccine development.

Purified recombinant hARD1 does not catalyse acetylation of Lys532 of HIF-1alpha fragments in vitro.

In humans, many responses to hypoxia including angiogenesis and erythropoiesis are mediated by the alpha/beta-heterodimeric transcription factor hypoxia inducible factor (HIF). The stability and/or activity of human HIF-1alpha are modulated by post-translational modifications including prolyl and asparaginyl hydroxylation, phosphorylation, and reportedly by acetylation of the side-chain of Lys532 by ARD1 (arrest defective protein 1 homologue), an acetyltransferase. Using purified recombinant human ARD1 (hARD1) we did not observe ARD1-mediated N-acetylation of Lys532 using fragments of HIF-1alpha. However, recombinant hARD1 from Escherichia coli was produced with partial N-terminal acetylation and was observed to undergo slow self-mediated N-terminal acetylation. The observations are consistent with the other data indicating that hARD1, at least alone, does not acetylate HIF-1alpha, and with reports on the N-terminal acetyltransferase activity of a recently reported heterodimeric complex comprising hARD1 and N-acetyltransferase protein.

A human T-cell lymphotropic virus type 1 enhancer of Myc transforming potential stabilizes Myc-TIP60 transcriptional interactions.

The human T-cell lymphotropic virus type 1 (HTLV-1) infects and transforms CD4+ lymphocytes and causes adult T-cell leukemia/lymphoma (ATLL), an aggressive lymphoproliferative disease that is often fatal. Here, we demonstrate that the HTLV-1 pX splice-variant p30II markedly enhances the transforming potential of Myc and transcriptionally activates the human cyclin D2 promoter, dependent upon its conserved Myc-responsive E-box enhancer elements, which are associated with increased S-phase entry and multinucleation. Enhancement of c-Myc transforming activity by HTLV-1 p30II is dependent upon the transcriptional coactivators, transforming transcriptional activator protein/p434 and TIP60, and it requires TIP60 histone acetyltransferase (HAT) activity and correlates with the stabilization of HTLV-1 p30II/Myc-TIP60 chromatin-remodeling complexes. The p30II oncoprotein colocalizes and coimmunoprecipitates with Myc-TIP60 complexes in cultured HTLV-1-infected ATLL patient lymphocytes. Amino acid residues 99 to 154 within HTLV-1 p30II interact with the TIP60 HAT, and p30II transcriptionally activates numerous cellular genes in a TIP60-dependent or TIP60-independent manner, as determined by microarray gene expression analyses. Importantly, these results suggest that p30II functions as a novel retroviral modulator of Myc-TIP60-transforming interactions that may contribute to adult T-cell leukemogenesis.