cDNA cloning and promoter analysis of rat caspase-9

Oxidative stress, unfolded protein response, and apoptosis in developmental toxicity

Physiological development requires precise spatiotemporal regulation of cellular and molecular processes. Disruption of these key events can generate developmental toxicity in the form of teratogenesis or mortality. The mechanism behind many developmental toxicants remains unknown. While recent work has focused on the unfolded protein response (UPR), oxidative stress, and apoptosis in the pathogenesis of disease, few studies have addressed their relationship in developmental toxicity. Redox regulation, UPR, and apoptosis are essential for physiological development and can be disturbed by a variety of endogenous and exogenous toxicants to generate lethality and diverse malformations. This review examines the current knowledge of the role of oxidative stress, UPR, and apoptosis in physiological development as well as in developmental toxicity, focusing on studies and advances in vertebrates model systems.

Dual role of Sp3 transcription factor as an inducer of apoptosis and a marker of tumour aggressiveness

BACKGROUND

The ambiguous role of transcription factor Sp3 for tumour progression is still debated since it was described as a transcriptional repressor or activator. Here we tried to decipher the molecular mechanisms implicated in Sp3 accumulation observed in aggressive tumours.

METHODOLOGY

We generated normal and tumour cell lines conditionally expressing Sp3. Cell growth was analyzed in vitro and after inoculation in nude mice. Apoptosis was assessed by pan- caspase activity assays, by counting fragmented nuclei and by determination of caspase 9 cleavage. Gene expression was determined by quantitative PCR. Cleavage by different caspases was performed after in vitro translation of the Sp3 cDNA in the presence of [S(35)] labelled methionine. Different tumour cell lines and head and neck tumour samples were tested for the presence of Sp3 by western blots. Correlation between Sp3 expression and overall survival has been statistically determined.

PRINCIPAL FINDINGS

Conditional over-expression of Sp3 induces apoptosis and modifies expression of genes implicated in the regulation of cell cycle and pro and anti apoptotic genes. Sp3 over-expression strongly reduces the development of tumours in nude mice confirming its pro-apoptotic potential in vivo. However, cells can survive to apoptosis through selective Sp3 cleavage by caspase. Sp3 induction in established tumours resulted in transient regression then progression. Progression coincides with re-accumulation of the full length form of Sp3. Sp3 is over-expressed in tumour cell lines of different origins. The presence of high levels of the full-length form of Sp3 indicates a poor prognosis for overall survival of patients with head and neck tumours.

CONCLUSIONS

Full length Sp3 accumulation highlights bypass of tumour cell apoptotic capacities and is indicative of head and neck tumours aggressiveness.

Prodeath or prosurvival: two facets of hypoxia inducible factor-1 in perinatal brain injury

Hypoxia, which occurs in the brain when oxygen availability drops below the normal level, is a major cause of perinatal hypoxic-ischemic injury (HII). The transcriptional factor hypoxia inducible factor-1 (HIF-1) is a key regulator in the pathophysiological response to the stress of hypoxia. Genes regulated by HIF-1 are involved in energy metabolism, erythropoiesis, angiogenesis, vasodilatation, cell survival and apoptosis. Compared with the adult brain, the neonatal brain is different in physiological structure, function, cellular composition and signaling pathway related gene activation and response after hypoxia. The purpose of this review is to determine if developmental susceptibility of the brain after hypoxic/ischemic injury is related to HIF-1alpha, which also plays a pivotal role in the normal brain development. HIF-1alpha regulates both prosurvival and prodeath responses in the neonatal brain and various mechanisms underlie the apparent contradictory effects, including duration of ischemic injury and severity, cell-types, and/or dependent on the nature of the stimulus after HII. Studies report an excessive induction of HIF-1 in the immature brain, which suggests that a cell death promoting role of HIF may prevail. Inhibition of HIF-1alpha and targeted activation of its prosurvival genes appear as a favorable therapeutic strategy. However, a better understanding of multifaceted HIF-1 function during brain development is required to explore potential targets for further therapeutic interventions in the neonate.

Cloning, characterization and computational analysis of the 5' regulatory region of ovine glucose 6-phosphate dehydrogenase gene

To better understand the structure and the function of ovine glucose 6-phosphate dehydrogenase (G6PD) promoter region, a genome-walking procedure was followed to isolate and sequence a 1628 bp fragment, containing the 5' regulatory region of the G6PD gene. In silico analysis of the sequence showed many conserved blocks and features with other known mammalian G6PD promoter regions. The analysis also revealed the presence of one TATA box, three GC boxes, two E-boxes and several binding sites for Stimulating Protein 1 (Sp1) and Activator Protein 2 (AP2). Moreover, elements involved in the regulation of lipogenesis like USF (Upstream stimulating factor), HSF (Heat Shock Factor), F2F (Prolactin receptor), RAR (Retinoid Acid Receptor), STRE (STress Response Element), RORa (Retinoid related Orphan Receptor alpha), GATA (GATA binding factor), RFX (Regulatory Factor X), SREBP (Sterol Regulatory Element Binding Protein), MEP (Metal Element Protein), CREB (insulin receptor), PRE (Progesterone receptor), and HNF4 (Hepatic Nuclear Factor 4) were detected. The most important regulatory motifs were found to be conserved as compared to those in human and mouse counterparts. However, some differences were noted, likely indicating differences in the transcription regulation of G6PD gene between ruminant and non-ruminant species.

Evidence of HIF-1 functional binding activity to caspase-3 promoter after photothrombotic cerebral ischemia

Hypoxia-inducible factor 1 alpha (HIF-1alpha) is a transcription factor that was suggested in vitro to promote cell death by modulation of proapoptotic genes. In this report, we tested the hypothesis of an in vivo proapoptotic role of HIF-1alpha after an ischemic insult. For this purpose, HIF-1alpha and procaspase-3 mRNA and protein expressions were examined in rat brain subjected to 12- and 24-h permanent focal ischemia and the presence of an HIF-1 binding activity to the caspase-3 gene promoter was explored. The results showed that HIF-1alpha and procaspase-3 expressions increased with a similar pattern in response to ischemia. In addition, caspase-3 activation was observed in cells that express HIF-1alpha. Moreover, electrophoretic mobility assay revealed a specific HIF-1 binding activity to the caspase-3 gene promoter. Altogether the present data provide strong arguments for a causative relationship between HIF-1alpha and caspase-3 inductions through a functional binding activity to the caspase-3 gene promoter.

First molecular cloning and characterisation of caspase-9 gene in fish and its involvement in a gram negative septicaemia

Caspase-9 is an initiator caspase in the apoptotic process whose function is to activate effector caspases that are downstream in the mitochondrial pathway of apoptosis. This work reports for the first time the complete sequencing and characterisation of caspase-9 in fish. A 1924bp cDNA of sea bass caspase-9 was obtained, consisting of 1308bp open reading frame coding for 435 amino acids, 199bp of the 5'-UTR and 417bp of the 3'-UTR including a canonical polyadenilation signal 10 nucleotides upstream the polyadenilation tail. The sequence retains the pentapeptide active-site motif (QACGG) and the putative cleavage sites at Asp(121), Asp(325) and Asp(343). The sequence of sea bass caspase-9 exhibits a very close homology to the sequences of caspase-9 from other vertebrates, particularly with the putative caspases-9 of Danio rerio and Tetraodon nigroviridis (77.5 and 75.4% similarity, respectively), justifying the fact that the phylogenetic analysis groups these species together with sea bass. The sea bass caspase-9 gene exists as a single copy gene and is organised in 9 introns and 10 exons. The sea bass caspase-9 showed a basal expression in all the organs analysed, although weaker in spleen. The expression of sea bass caspase-9 in the head kidney of sea bass infected with the Photobacterium damselae ssp. piscicida (Phdp) strain PP3, showed increased expression from 0 to 12h returning to control levels at 24h. Caspase-9 activity was detected in Phdp infected sea bass head kidney from 18 to 48h post-infection, when the fish were with advanced septicaemia.

Characterization of cell clones stably transfected with short form caspase-9: apoptotic resistance and Bcl-XL expression

Caspases play important roles in the initiation and progression of apoptosis. In experimental models of ATP depletion, we have demonstrated the activation of caspase-9, -8, and -3, which is followed by the development of apoptotic morphology. To determine the specific contribution of caspase-9 to ATP depletion-induced apoptosis, we transfected renal epithelial cells with its endogenous dominant-negative inhibitor caspase-9S. Two cell clones with stable transfection were obtained. These clones expressed caspase-9S, and the cytosol isolated from these cells was resistant to cytochrome c-induced caspase activation in vitro. The clones were then examined for ATP depletion-induced apoptosis. Compared with the wild-type cells, the caspase-9S clones were markedly resistant to apoptosis in this model. Caspase activation was also inhibited. Surprisingly, these clones also showed significantly less cytochrome c release during ATP-depletion. Moreover, Bax translocation to mitochondria was inhibited, suggesting that these clones were resistant to apoptosis not only at the cytosolic caspase activation level but also at the upstream mitochondrial level. To gain insights into the mitochondrial resistance, we analyzed the expression of Bcl-2 family proteins. While the expression of Bax, Bak, and Bcl-2 was comparable to the wild-type cells, the selected clones showed specific up-regulation of Bcl-XL, an anti-apoptotic protein. We conclude that the selected clones were resistant to apoptosis at two levels. In the cytosol, they expressed dominant negative caspase-9, and at the mitochondria they up-regulated Bcl-XL.

Involvement of the mitochondrial ATP-sensitive potassium channel in the neuroprotective effect of hyperbaric oxygenation after cerebral ischemia

In the present study, we investigated whether activation of mitochondrial ATP-sensitive potassium channel is involved in the neuroprotective effect offered by early hyperbaric oxygenation after cerebral ischemia. The selective mitochondrial ATP-sensitive potassium channel antagonist 5-hydroxydecanoate was infused intracerebroventricularly before hyperbaric oxygenation treatment initiated 3 h after middle cerebral artery occlusion for 90 min. Neurological status was evaluated and brains were removed for the measurement of infarct size and immunohistochemical evaluation of apoptosis 24 h after middle cerebral artery occlusion. Early hyperbaric oxygenation treatment improved neurologic deficits and reduced infarct volume, while these effects were reversed by the administration of 5-hydroxydecanoate. Furthermore, early hyperbaric oxygenation significantly decreased the number of apoptotic cells in the peri-infarct cortex 24 h after ischemic insult and this effect was also blocked by 5-hydroxydecanoate. The present findings suggest that early hyperbaric oxygenation therapy prevents apoptosis and promotes neurologic functional recovery after focal cerebral ischemia, and the opening of mitochondrial ATP-sensitive potassium channel plays a role in this antiapoptotic effect of early hyperbaric oxygenation.

Multiple effects of hyperbaric oxygen on the expression of HIF-1 alpha and apoptotic genes in a global ischemia-hypotension rat model

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor specifically activated by hypoxia. Activation of proapoptotic caspase-9 and caspase-3 pathways, by binding with tumor suppressor p53, HIF-1alpha could lead to harmful actions such as apoptosis. We examined whether increasing oxygen levels by hyperbaric oxygen (HBO) offers neuroprotection, at least partially by suppression of HIF-1alpha and apoptotic genes. Male SD rats (n = 78) were randomly divided into 13 groups: 1 sham group, 6 groups of global ischemia-hypotension (GI), and 6 groups of HBO treatment after global ischemia-hypotension (GI + HBO). HBO (3 ATA for 2 h) was applied at 1 h after global ischemia-hypotension. Rats were sacrificed at 6, 12, 24, 48, and 96 h and 7 days. Global ischemia-hypotension (10 min ischemia, 30-35 mm Hg) produced a marked increase of HIF-1alpha expressions in the hippocampus and cortex at 6 h and peaked at 48-96 h. The expressions of p53, caspase-9, and caspase-3 were all increased in a similar time course. These molecular changes were accompanied by massive cell loss in the hippocampal regions and to a lesser degree in the cortex, with features of apoptosis. HBO treatment reduced expressions of HIF-1alpha, p53, caspase-9, and caspase-3 and decreased cell death. The protein levels of proapoptotic caspase-8 and antiapoptotic bcl-2 were increased after global ischemia-hypotension and HBO potentiated the expression of caspase-8 and decreased expression of bcl-2. These results indicate that HBO has multiple actions on apoptotic genes even though the overall effect of HBO was decreased HIF-1alpha expression and reduced apoptosis after global ischemia-hypotension.

Molecular cloning and characterization of murine caspase-12 gene promoter

The activation of caspase-12 is involved in endoplasmic reticulum-mediated apoptosis. To investigate how caspase-12 is transcriptionally and translationally regulated, we isolated and sequenced the 5'-flanking region of mouse caspase-12 gene by a PCR-mediated chromosome-walking technique, using mouse genomic DNA as a template. Two DNA fragments of 3,221 and 800 bp were isolated and cloned into pGL3 promoterless vector upstream of the luciferase gene. The small DNA fragment contains the first intron sequence located downstream of the first exon and 27 bp from the second exon, whereas the large fragment contains the small fragment and the 5'-flanking region. Reporter constructs generated from these DNA fragments showed a substantial promoter activity in mouse NIH 3T3 or human embryonic kidney 293 cells grown in the presence of 10% serum. In the absence of serum, the luciferase activity was drastically reduced. However, the luciferase mRNA was higher in serum-starved cells than in control cells, suggesting that translation of luciferase mRNA was drastically inhibited. However, Western blot analysis revealed that the quantity of procaspase-12 is actually higher in serum-starved cells relative to that cultured in the presence of 10% serum. Progressive deletion analysis of the 3,221-bp sequence revealed that the highest luciferase activity was observed with the construct containing 700 bp upstream of ATG. The transcriptional initiation site was identified by 5' RACE techniques using total RNA from NIH 3T3 cells. Our results should facilitate studies on the mechanism regulating the expression of this important gene.

Interspecies comparison of neuroglobin, cytoglobin and myoglobin: Sequence evolution and candidate regulatory elements

Neuroglobin and cytoglobin are two novel members of the vertebrate globin family. Their physiological role is poorly understood, although both proteins bind oxygen reversibly and may be involved in cellular oxygen homeostasis. Here we investigate the selective constraints on coding and non-coding sequences of the neuroglobin and cytoglobin genes in human, mouse, rat and fish. Neuroglobin and cytoglobin are highly conserved, displaying very low levels of non-synonymous nucleotide substitutions. An oxygen supply function predicts distinct modes of gene regulation, involving hypoxia-responsive transcription factors. To detect conserved candidate regulatory elements, we compared the neuroglobin and cytoglobin genes in mammals and fish. The myoglobin gene was included to test if it also contains hypoxia-responsive regulatory elements. Long conserved non-coding sequences, indicative of gene-regulatory elements, were found in the cytoglobin and myoglobin, but not in the neuroglobin gene. Sequence comparison and experimental data allowed us to delimit upstream regions of the neuroglobin and cytoglobin genes that contain the putative promoters, defining candidate regulatory regions for functional tests. The neuroglobin and the myoglobin genes both lack conserved hypoxia-responsive elements (HREs) for transcriptional activation, but contain conserved hypoxia-inducible mRNA stabilization signals in their 3' untranslated regions. The cytoglobin gene, in contrast, harbors both conserved HREs and mRNA stabilization sites, strongly suggestive of an oxygen-dependent regulation.

The 5′-upstream region of human programmed cell death 5 gene contains a highly active TATA-less promoter that is up-regulated by etoposide

The PDCD5 (programmed cell death 5), a novel apoptosis related gene, is functionally associated with cell apoptosis, exhibits a ubiquitous expression pattern and is up-regulated in some types of tumor cells undergoing apoptosis. To study the transcriptional regulation of the PDCD5 gene, we have cloned 1.1 kb of its 5'-upstream region. The DNA sequencing analysis revealed a major transcriptional start site at 72 base pairs in front of the ATG translational start codon. The upstream of the transcriptional start site lacks a canonical TATA box and CAAT box. Transient transfection and luciferase assay demonstrate that this region presents extremely strong promoter activity. The 5'-deleted sequences fused to a luciferase reporter gene demonstrated that the -555/-383 region from the transcription start site is crucial for transcriptional regulation, and the luciferase reporter gene's expression significantly increased in the early stage of cell apoptosis induced by etoposide. These results imply that the PDCD5 gene may be a target gene under the control of some important apoptosis-related transcriptional factors during the cell apoptosis.

Transcriptional regulation of the CRLR gene in human microvascular endothelial cells by hypoxia

Adrenomedullin is a 52 amino acid peptide that shows a remarkable range of effects on the vasculature that include inter alia, vasodilatation, regulation of permeability, inhibition of endothelial cell apoptosis, and promotion of angiogenesis. Recently the G-protein coupled receptor (GPCR) calcitonin receptor-like receptor (CRLR), and receptor activity modifying proteins (RAMPs) have become recognized as integral components of the adrenomedullin signaling system. However, mechanisms of regulation of CRLR expression are still largely unknown. This is in part due to lack of information on the gene promoter. In this study we have determined the transcriptional start of human CRLR cDNA by 5'-RACE and cloned the proximal 5'-flanking region of the gene by PCR. The 2318 bp genomic fragment contains the basal promoter of human CRLR, including potential TATA-boxes and several GC boxes. Regulatory elements binding known transcription factors, such as Sp-1, Pit-1, glucocorticoid receptor, and hypoxia-inducible factor-1 alpha (HIF-1alpha) were also identified. When cloned into reporter gene vectors, the genomic fragment showed significant promoter activity, indicating that the 5'-flanking region isolated by PCR contains the gene promoter of human CRLR. Of significance is that the cloned promoter fragments were activated by hypoxia when transfected in primary microvascular endothelial cells. Site-directed mutagenesis of the consensus hypoxia-response element (HRE) in the 5'-flanking region abolished such a response. We also demonstrated by semi-quantitative RT-PCR that transcription of the gene is activated by hypoxia in microvascular endothelial cells. In contrast, expression of RAMPs 1, 2, and 3 was unaffected by low oxygen tension. We conclude that simultaneous transcriptional up-regulation of CRLR and its ligand adrenomedullin in endothelial cells could lead to a potent survival loop and therefore might play a significant role in vascular responses to hypoxia and ischemia.

Gene promoter of apoptosis inhibitory protein IAP2: identification of enhancer elements and activation by severe hypoxia

Inhibitors of apoptosis (IAPs) antagonize cell death and regulate the cell cycle. One mechanism controlling IAP expression is translation initiation through the internal ribosome entry sites. Alternatively, IAP expression can be regulated at the transcription level. We showed recently the activation of IAP2 transcription by severe hypoxia. To pursue this regulation, we have cloned the full-length cDNA of rat IAP2, and have isolated and analysed the promoter regions of this gene. The cDNA encodes a protein of 589 amino acids, exhibiting structural features of IAP. In rat tissues, a major IAP2 transcript of approximately 3.5 kb was detected. We subsequently isolated 3.3 kb of the proximal 5'-flanking regions of this gene, which showed significant promoter activity. Of interest, 5' sequential deletion of the promoter sequence identified an enhancer of approximately 200 bp. Deletion of cAMP-response-element-binding protein (CREB) sites in the enhancer sequence diminished its activity. Finally, the IAP2 gene promoter was activated significantly by severe hypoxia and not by CoCl(2) or desferrioxamine, pharmacological inducers of hypoxia-inducible factor-1. In conclusion, in this study we have cloned the full-length cDNA of rat IAP2, and for the first time we have isolated and analysed promoter sequences of this gene, leading to the identification of enhancer elements. Moreover, we have demonstrated activation of the gene promoter by severe hypoxia, a condition shown to induce IAP2. These findings provide a basis for further investigation of gene regulation of IAP2, a protein with multiple functions.