Identification of transcriptional activation domain of TREB5, a CREB/ATF family protein that binds to HTLV-1 enhancer

Topoisomerase 1 Promoter Variants and Benefit from Irinotecan in Metastatic Colorectal Cancer Patients

OBJECTIVE

Topoisomerase 1 (topo-1) is an important target for the treatment of metastatic colorectal cancer (CRC). The aim of the present study was to evaluate the correlation between topo-1 single-nucleotide polymorphisms (SNPs) and clinical outcome in metastatic CRC (mCRC) patients.

METHODS

With the use of specific software (PROMO 3.0), we performed an in silico analysis of topo-1 promoter SNPs; the rs6072249 and rs34282819 SNPs were included in the study. DNA was extracted from 105 mCRC patients treated with FOLFIRI ± bevacizumab in the first line. SNP genotyping was performed by real-time PCR. Genotypes were correlated with clinical parameters (objective response rate, progression-free survival, and overall survival).

RESULTS

No single genotype was significantly associated with clinical variables. The G allelic variant of rs6072249 topo-1 SNP is responsible for GC factor and X-box-binding protein transcription factor binding. The same allelic variant showed a nonsignificant trend toward a shorter progression-free survival (GG, 7.5 months; other genotypes, 9.3 months; HR 1.823, 95% CI 0.8904-3.734; p = 0.1).

CONCLUSION

Further analyses are needed to confirm that the topo-1 SNP rs6072249 and transcription factor interaction could be a part of tools to predict clinical outcome in mCRC patients treated with irinotecan-based regimens.

An EZH2 polymorphism is associated with clinical outcome in metastatic colorectal cancer patients

BACKGROUND

Despite therapeutic innovations, metastatic colorectal cancer (mCRC) is still characterized by poor prognosis and few molecular markers predict the risk of progression. Polycomb group genes (PcGs) are epigenetic modifiers involved in tumor suppressor gene silencing. PcG member EZH2 mediates gene silencing through histone-H3 lysine-27 methylation. In colorectal cancer (CRC), EZH2 overexpression predicts shorter survival. Recently, four EZH2 single-nucleotide polymorphisms (SNPs) have been described. The present study was aimed at evaluating the correlation between EZH2 SNPs and outcome parameters in mCRC patients.

PATIENTS AND METHODS

DNA was extracted from blood samples of 110 mCRC patients treated with first-line 5-fluorouracil, folinic acid, irinotecan (FOLFIRI) and bevacizumab. Genotyping was carried out by real-time PCR. Genotype was used to predict objective response, progression-free survival (PFS) and overall survival (OS). EZH2 messenger RNA levels were evaluated on lymphocytes of a parallel cohort of 50 CRC patients.

RESULTS

One allelic variant (rs3757441 C/C versus C/T or T/T) was significantly associated with shorter PFS and OS (P < 0.01 and P < 0.05, respectively). At multivariate analysis, the same variant resulted an independent predictor of PFS and OS (P < 0.05). The C/C variant was associated with significantly higher EZH2 expression (P < 0.05).

CONCLUSION

An EZH2 SNP may be useful to predict clinical outcome in mCRC patients.

Apoptosis in human reproductive tissues: emerging concepts

In summary, apoptosis is an important concept in understanding many facets of human reproduction. Recent advances in the understanding of molecular mechanisms of apoptosis will allow us to understand this physiologically important process. How can the modulation of this process be applied to human reproduction? Studies to further understand the abnormalities of apoptosis, either too much or too little, may lead to a better understanding of the clinical problems in human reproduction.

We summarize future directions towards further understanding the roles of apoptotic processes in human reproduction in Table 3. The diseases listed in Table 3 are problems which could be approached from the apoptosis point of view. With further study using this concept as the lens, new diagnostic tools or therapies may be developed for these problems.

XBP-1, a novel human T-lymphotropic virus type 1 (HTLV-1) tax binding protein, activates HTLV-1 basal and tax-activated transcription

X-box binding protein 1 (XBP-1), a basic leucine zipper transcription factor, plays a key role in the cellular unfolded protein response (UPR). There are two XBP-1 isoforms in cells, spliced XBP-1S and unspliced XBP-1U. XBP-1U has been shown to bind to the 21-bp Tax-responsive element of the human T-lymphotropic virus type 1 (HTLV-1) long terminal repeat (LTR) in vitro and transactivate HTLV-1 transcription. Here we identify XBP-1S as a transcription activator of HTLV-1. Compared to XBP-1U, XBP-1S demonstrates stronger activating effects on both basal and Tax-activated HTLV-1 transcription in cells. Our results show that both XBP-1S and XBP-1U interact with Tax and bind to the HTLV-1 LTR in vivo. In addition, elevated mRNA levels of the gene for XBP-1 and several UPR genes were detected in the HTLV-1-infected C10/MJ and MT2 T-cell lines, suggesting that HTLV-1 infection may trigger the UPR in host cells. We also identify Tax as a positive regulator of the expression of the gene for XBP-1. Activation of the UPR by tunicamycin showed no effect on the HTLV-1 LTR, suggesting that HTLV-1 transcription is specifically regulated by XBP-1. Collectively, our study demonstrates a novel host-virus interaction between a cellular factor XBP-1 and transcriptional regulation of HTLV-1.

A Zn-finger/FH2-domain containing protein, FOZI-1, acts redundantly with CeMyoD to specify striated body wall muscle fates in theCaenorhabditis eleganspostembryonic mesoderm

Striated muscle development in vertebrates requires the redundant functions of multiple members of the MyoD family. Invertebrates such as Drosophila and Caenorhabditis elegans contain only one MyoD homolog in each organism. Earlier observations suggest that factors outside of the MyoD family might function redundantly with MyoD in striated muscle fate specification in these organisms. However, the identity of these factors has remained elusive. Here, we describe the identification and characterization of FOZI-1, a putative transcription factor that functions redundantly with CeMyoD(HLH-1) in striated body wall muscle (BWM) fate specification in the C. elegans postembryonic mesoderm. fozi-1 encodes a novel nuclear-localized protein with motifs characteristic of both transcription factors and actin-binding proteins. We show that FOZI-1 shares the same expression pattern as CeMyoD in the postembryonic mesodermal lineage, the M lineage, and that fozi-1-null mutants exhibit similar M lineage-null defects to those found in animals lacking CeMyoD in the M lineage (e.g. loss of a fraction of M lineage-derived BWMs). Interestingly, fozi-1-null mutants with a reduced level of CeMyoD lack most, if not all, M lineage-derived BWMs. Our results indicate that FOZI-1 and the Hox factor MAB-5 function redundantly with CeMyoD in the specification of the striated BWM fate in the C. elegans postembryonic mesoderm, implicating a remarkable level of complexity for the production of a simple striated musculature in C. elegans.

Role of T-box gene tbx-2 for anterior foregut muscle development in C. elegans

During organogenesis, pluripotent precursor cells acquire a defined identity such as muscle or nerve. The transition from naïve precursor towards the differentiated state is characterized by sequential waves of gene expression that are determined by regulatory transcription factors. A key question is how transcriptional circuitry dictates the succession of events that accompanies developmental competence, cell fate specification and differentiation. To address this question, we have examined how anterior muscles are established within the Caenorhabditis elegans foregut (pharynx). We find that the T-box transcription factor tbx-2 is essential to form anterior pharyngeal muscles from the ABa blastomere. In the absence of tbx-2 function, ABa-derived cells initiate development normally: they receive glp-1/Notch signaling cues, activate the T-box gene TBX-38 and express the organ selector gene PHA-4/FoxA. However, these cells subsequently arrest development, extinguish PHA-4 and fail to activate PHA-4 target genes. tbx-2 mutant cells do not undergo apoptosis and there is no evidence for adoption of an alternative fate. TBX-2 is expressed in ABa descendants and depends on activation by pha-4 and repression by components of glp-1/Notch signaling. Our analysis suggests that a positive feedback loop between tbx-2 and pha-4 is required for ABa-derived precursors to commit to pharyngeal muscle fate.

The X-box binding protein-1 transcription factor is required for plasma cell differentiation and the unfolded protein response

X-box binding protein-1 (XBP-1) is a transcription factor essential for plasma cell differentiation. XBP-1 transcripts are found at high levels in plasma cells from rheumatoid synovium and myeloma cell lines. Lymphoid chimeras deficient in XBP-1 have a profound defect in plasma cell differentiation, with few plasma cells in their periphery and severely reduced serum immunoglobulin levels. When introduced into B-lineage cells, XBP-1 initiates plasma cell differentiation. XBP-1 is also the mammalian homologue of the yeast transcription factor Hac1p, an important component of the unfolded protein response (UPR). The UPR allows cells to tolerate conditions of endoplasmic reticulum (ER) stress caused by misfolded proteins. Studies examining the relationship between plasma cell differentiation, XBP-1, and the UPR demonstrate that this novel signaling system is vital for plasma cell differentiation. Signals that induce plasma cell differentiation and the UPR cooperate via XBP-1 to induce terminal B-cell differentiation. Additionally, XBP-1 plays an important role in the regulation of interleukin-6 production, a cytokine essential for plasma cell survival.

Expression of OASIS, a CREB/ATF family transcription factor, in CNS lesion and its transcriptional activity

We reported the expression patterns of a novel member of the CREB/ATF family, OASIS, in central nervous system (CNS) lesions and its transcriptional activity. OASIS gene expression was upregulated in the stab-injured spinal cord. Double labeling experiments revealed that the distribution of OASIS mRNA-positive cells overlapped with a population of GFAP-immunoreactive cells. This finding suggested that OASIS might regulate expression of important downstream molecules in certain subset of the reactive astrocytes (e.g. inhibitory substances in injured brain). In gel shift assays, OASIS was able to specifically bind to CRE as CREB family members were. We then examined transcriptional activity of full-length OASIS with GAL4-UAS-luciferase reporter assay in COS7 cells. OASIS protein activated transcription, but did not inhibit basal transcription driven by AdML promoter. To determine critical portion(s) of the OASIS protein in transcriptional activation, we examined the activity of various deletion constructs of OASIS gene. The assay revealed that a strong transcriptional activation domain lay in the N-terminal region where acidic amino acids clustered and a possible repression domain, which had not been reported for other CREB/ATF family members, lay in the more C-terminal region. We therefore proposed that OASIS protein positively regulated gene transcription in a subset of reactive astrocytes, and thereby influenced the reaction of injured CNS tissues.

Increased expression of mXBP-1 (TREB-5) in thymic B cells in New Zealand mice

New Zealand Black mice as well as several other murine models of murine lupus are well known for premature degeneration of thymus and development of autoimmunity. To focus on molecular events unique to murine lupus, we performed differential display using arbitrary primer pairs to distinguish NZB versus BALB/c thymus at 5 weeks of age. Following an extensive analysis of DNA bands that were either consistently up or downregulated and from studies of expression pattern of thymic genes by in situ nucleic acid hybridization, we focused on one clone that was consistently differentially expressed between NZB and BALB/c thymus. This clone was isolated, sequenced, and identified as the murine homologue of the human X box binding protein (hXBP-1), also known as TREB 5. mXBP-1 was found to be consistently upregulated in B cells in the thymic cortex of NZB and (NZBxNZW)F1, but not BALB/c, C3H/HeJ or C57BL/6 mice. In addition, it was dramatically elevated in MRL/ lpr but not MRL/++ mice; similarly, it was increased in BXSB/ Yaa male but not BXSB female thymic cortex. Of particular interest was an absence of mXBP-1 expression in the thymus of NZB/ Bln- Igh6(null)homozygotes. mXBP-1 has several putative functions, including the regulation of MHC class II expression and by virtue of its ability to recognize CRE-like elements shown to be involved in HTLV-1 transcription.

ATF6 activated by proteolysis binds in the presence of NF-Y (CBF) directly to the cis-acting element responsible for the mammalian unfolded protein response

Transcription of genes encoding molecular chaperones and folding enzymes in the endoplasmic reticulum (ER) is induced by accumulation of unfolded proteins in the ER. This intracellular signaling, known as the unfolded protein response (UPR), is mediated by the cis-acting ER stress response element (ERSE) in mammals. In addition to ER chaperones, the mammalian transcription factor CHOP (also called GADD153) is induced by ER stress. We report here that the transcription factor XBP-1 (also called TREB5) is also induced by ER stress and that induction of CHOP and XBP-1 is mediated by ERSE. The ERSE consensus sequence is CCAAT-N(9)-CCACG. As the general transcription factor NF-Y (also known as CBF) binds to CCAAT, CCACG is considered to provide specificity in the mammalian UPR. We recently found that the basic leucine zipper protein ATF6 isolated as a CCACG-binding protein is synthesized as a transmembrane protein in the ER, and ER stress-induced proteolysis produces a soluble form of ATF6 that translocates into the nucleus. We report here that overexpression of soluble ATF6 activates transcription of the CHOP and XBP-1 genes as well as of ER chaperone genes constitutively, whereas overexpression of a dominant negative mutant of ATF6 blocks the induction by ER stress. Furthermore, we demonstrated that soluble ATF6 binds directly to CCACG only when CCAAT exactly 9 bp upstream of CCACG is bound to NF-Y. Based on these and other findings, we concluded that specific and direct interactions between ATF6 and ERSE are critical for transcriptional induction not only of ER chaperones but also of CHOP and XBP-1.

Identity between rat htf and human xbp-1 genes: determination of gene structure, target sequence, and transcription promotion function for HTF

Hepatocarcinogenesis-related transcription factor (HTF) was originally isolated from rats in which the expression was enhanced in hepatocellular carcinomas. Rat HTF (rHTF) is structurally similar to human X-box-binding protein-1 (hXBP-1), and both factors are unique in respective genomes. A previous study showed that hXBP-1 mRNA is detectable ubiquitously but is enriched in the human liver as rHTF. In this study, we demonstrated the analogous exon-intron organization and significant sequence homology for rhtf and hxbp-1 genes. Alignment of amino acid sequences of rHTF and hXBP-1 revealed that all the characteristic motifs in rHTF were conserved in hXBP-1. Moreover, Southern blotting patterns provided with the rHTF and hXBP-1 probes were basically the same. These two genes were thus thought to belong to the same evolutional lineage. We determined the consensus binding sequence (CRCGTCA) for rHTF by CASTing, and it was found to be nearly the same as that for hXBP-1. Transactivation ability of rHTF was also demonstrated. The rhtf gene generates two types of mRNAs (2.0 kb and 2.5 kb), both of which encode identical rHTF protein. These transcripts had distinct transcription initiation sites. The 2.0 kb promoter, that was revealed by the transient luciferase assay, contained GC-box and CAAT-box. Sequences around the transcription initiation site for the 2.0 kb transcript were similar in rhtf and hxbp-1 genes. Our observations suggest that HTF is a rat homolog of hXBP-1.

Targeted disruption of CRE-binding factor TREB5 gene leads to cellular necrosis in cardiac myocytes at the embryonic stage

TREB5 (hXBP-1) is a basic region leucine zipper protein which binds to a CRE-like element in both human T-cell leukemia virus type 1 and MHC class II genes. To study the function(s) of TREB5 in normal development, we have generated TREB5 deficient mice by gene targeting. Heterozygous mutant mice have not exhibited any obvious abnormalities; however, homozygous mutant embryos die between embryonic days 10.5 and 14.5. The major defect responsible for lethality is cellular necrosis of cardiac myocytes located at the atrium and the truncus arteriosus with its following ventricle. Necrotic alteration was not observed in either the endocardial cushion or the conotruncal ridge. These results indicate that TREB5 plays an essential role in maintenance and/or growth of cardiac myocytes during cardiogenesis.

Hamster adapt78 mRNA is a Down syndrome critical region homologue that is inducible by oxidative stress

We are using the technique of mRNA differential display to identify RNAs that may be important in protecting cells against the damaging effects of oxidative stress. For these studies, we utilize a so-called "adaptive response" model system in which hamster HA-1 cells respond to a minimally toxic "pretreatment" dose of hydrogen peroxide by synthesizing RNAs and proteins that protect them against subsequent exposure to a highly cytotoxic concentration of hydrogen peroxide. Using this approach, we have recently reported several novel RNAs whose levels are increased under conditions of adaptive response. Here we report a new RNA, designated adapt78, whose steady-state level is significantly induced by a pretreatment dose of hydrogen peroxide. adapt78 mRNA was calculated to be 2.35 kb in size and inducible by the standard pretreatment dose of 4 micromol H2O2/10(7) cells. It was induced as early as 90 min after peroxide exposure and maximally at 5 h. Induction was strongly dependent upon calcium. Cloning and sequencing revealed a large predicted open reading frame of 197 amino acids. In vitro transcription and translation generated a protein of 25,000 Da. GenBank homology analysis revealed that much of adapt78 is strongly homologous to a sequence that has been mapped to the Down syndrome critical region (Fuentes et al., Hum. Mol. Genet. 4, 1935-1944, 1995). However, both the 5' and the 3' ends of adapt78 show no homology to any previously reported complete sequence. adapt78 represents a new oxidant-inducible RNA and marker of cellular oxidative stress and may provide new insight into our understanding of oxidant-related disorders and neural degeneration.

Modulation of a cardiogenic shock inducible RNA by chemical stress: adapt73/PigHep3

BACKGROUND

Understanding how mammalian cells respond to stress is important in the study, detection, and therapy of stress-related disorders. We have been studying cellular stress response in hamster HA-1 cells by using an adaptive response model. HA-1 cells respond to a minimally toxic "pretreatment" dose of hydrogen peroxide by synthesizing RNAs and proteins that protect them against subsequent exposure to a higher cytotoxic concentration of peroxide. The purpose of our studies is to identify and partially characterize any mRNA whose steady state level is significantly modulated during adaptation.

METHODS

HA-1 cells were exposed to a pretreatment dose of hydrogen peroxide and RNA extracted. The differential display technique was used to identify modulated mRNAs. The effects of calcium ionophore A23187 and cis (II)-platinum on the modulation of mRNA from HA-1 cells and A23187 on the modulation of mRNAs from human IMR-90 cells were also determined.

RESULTS

One of the RNAs induced by a pretreatment concentration of hydrogen peroxide was designated adapt73. The size of the induced adapt73 RNA was determined to be 2.1 kb. Induction of adapt73 was maximal 5 hours after peroxide treatment, but elevated levels were still obvious at 10 hours. This induction was not specific to oxidative stress, because other stress agents including as (II)-platinum and especially calcium ionophore A23187 also induced adapt73 mRNA levels. Partial sequencing of adapt73 and a subsequent GenBank homology search revealed extensive homology to a novel RNA from pig, designated PigHep3, that was identified as a cardiogenic shock response gene from liver in pigs that were undergoing resuscitation after circulatory shock. Homology to a completely sequenced but uncharacterized human homolog was also found. Using a partially sequenced expressed sequence tag (EST) human clone to adapt73, we probed Northern blots containing RNA from IMR-90 human fibroblasts treated with A23187. A strongly induced human adapt73 mRNA homolog was observed, almost identical in size to its hamster homolog. In vitro transcription and translation of the human EST clone revealed a translatable Adapt73 protein product.

CONCLUSIONS

These data indicate that adapt73/PigHep3 RNA can be induced by multiple chemical stress, that these inductions occur under protective or adaptive response conditions, that there is an inducible human homolog to adapt73, and suggest that adapt73 may be an important physiologic mediator of organ and cellular shock response in mammals.

Physical and functional interaction between the human T-cell lymphotropic virus type 1 Tax1 protein and the CCAAT binding protein NF-Y

Tax1, a potent activator of human T-cell lymphotropic virus type 1 (HTLV-1) transcription, has been shown to modulate expression of many cellular genes. Tax1 does not bind DNA directly but regulates transcription through protein-protein interactions with sequence-specific transcription factors. Using the yeast two-hybrid system to screen for proteins which interact with Tax1, we isolated the B subunit of the CCAAT binding protein NF-Y from a HeLa cDNA library. The interaction of Tax1 with NF-YB was specific in that NF-YB did not interact with a variety of other transcription factors, including human immunodeficiency virus Tat, human papillomavirus E6, and Bicoid, or with the M7 (amino acids 29CP-AS) Tax1 mutant. However, NF-YB did interact with the C-terminal Tax1 mutants M22 (130TL-AS) and M47 (319LL-RS). We also show that in vitro-translated NF-YB specifically bound to a glutathione S-transferase-Tax1 fusion protein. Further, Tax1 coimmunoprecipitated with NF-Y from nuclear extracts of HTLV-1-transformed cells, providing evidence for in vivo interaction of Tax1 and NF-YB. We further demonstrate that Tax1 specifically activated the NF-Y-responsive DQbeta promoter, as well as a minimal promoter which contains only the Y-box element. In addition, mutation of the Y-box element alone abrogated Tax1-mediated activation. Taken together, these data indicate that Tax1 interacts with NF-Y through the B subunit and that this interaction results in activation of the major histocompatibility complex class II promoter. Through activation of this and other NF-Y driven promoters, the Tax1-NF-Y interaction may play a critical role in causing cellular transformation and HTLV-1 pathogenesis.