Sp1 and Sp3 regulate basal transcription of the human CYP2F1 gene

Sp1 mediated the inhibitory effect of glutamate on pulmonary surfactant synthesis

BACKGROUND

Studies have shown that the release of endogenous glutamate (Glu) participates in lung injury by activating N-methyl-D-aspartate receptor (NMDAR), but the mechanism is still unclear. This study was to investigate the effects and related mechanisms of Glu on the lipid synthesis of pulmonary surfactant (PS) in isolated rat lung tissues.

METHODS

The cultured lung tissues of adult SD rats were treated with Glu. The amount of [3H]-choline incorporation into phosphatidylcholine (PC) was detected. RT-PCR and Western blot were used to detect the changes of mRNA and protein expression of cytidine triphosphate: phosphocholine cytidylyltransferase alpha (CCTα), a key regulatory enzyme in PC biosynthesis. Western blot was used to detect the expression of NMDAR1, which is a functional subunit of NMDAR. Specific protein 1 (Sp1) expression plasmids were used. After transfected with Sp1 expression plasmids, the mRNA and protein levels of CCTα were detected by RT-PCR and Western blot in A549 cells. After treated with NMDA and MK-801, the mRNA and protein levels of Sp1 were detected by RT-PCR and Western blot in A549 cells.

RESULTS

Glu decreased the incorporation of [3H]-choline into PC in a concentration- and time- dependent manner. Glu treatment significantly reduced the mRNA and protein levels of CCTα in lungs. Glu treatment up-regulated NMDAR1 protein expression, and the NMDAR blocker MK-801 could partially reverse the reduction of [3H]-choline incorporation induced by Glu (10-4 mol/L) in lungs. After transfected with Sp1 plasmid for 30 h, the mRNA and protein expression levels of CCTα were increased and the protein expression of Sp1 was also up-regulated. After A549 cells were treated with NMDA, the level of Sp1 mRNA did not change significantly, but the expression of nucleus protein in Sp1 was significantly decreased, while the expression of cytoplasmic protein was significantly increased. However, MK-801could reverse these changes.

CONCLUSIONS

Glu reduced the biosynthesis of the main lipid PC in PS and inhibited CCTα expression by activating NMDAR, which were mediated by the inhibition of the nuclear translocation of Sp1 and the promoter activity of CCTα. In conclusion, NMDAR-mediated Glu toxicity leading to impaired PS synthesis may be a potential pathogenesis of lung injury.

Xenobiotica-metabolizing enzymes in the lung of experimental animals, man and in human lung models

The xenobiotic metabolism in the lung, an organ of first entry of xenobiotics into the organism, is crucial for inhaled compounds entering this organ intentionally (e.g. drugs) and unintentionally (e.g. work place and environmental compounds). Additionally, local metabolism by enzymes preferentially or exclusively occurring in the lung is important for favorable or toxic effects of xenobiotics entering the organism also by routes other than by inhalation. The data collected in this review show that generally activities of cytochromes P450 are low in the lung of all investigated species and in vitro models. Other oxidoreductases may turn out to be more important, but are largely not investigated. Phase II enzymes are generally much higher with the exception of UGT glucuronosyltransferases which are generally very low. Insofar as data are available the xenobiotic metabolism in the lung of monkeys comes closed to that in the human lung; however, very few data are available for this comparison. Second best rate the mouse and rat lung, followed by the rabbit. Of the human in vitro model primary cells in culture, such as alveolar macrophages and alveolar type II cells as well as the A549 cell line appear quite acceptable. However, (1) this generalization represents a temporary oversimplification born from the lack of more comparable data; (2) the relative suitability of individual species/models is different for different enzymes; (3) when more data become available, the conclusions derived from these comparisons quite possibly may change.

Apoptotic effects of 7,8-dihydroxyflavone in human oral squamous cancer cells through suppression of Sp1

7,8-Dihydroxyflavone (7,8-DHF) is a member of the flavonoid family and has recently been identified as a brain-derived neurotrophic factor mimetic that selectively activates tropomyosin-receptor kinase B with high affinity. The antioxidant and anticancer effects of 7,8-DHF have been reported. However, the pharmacological mechanisms of 7,8-DHF in oral cancer are unclear. Thus, we investigated the mechanisms of the antiproliferative action of 7,8-DHF on HN22 and HSC4 oral squamous cell carcinoma cell lines. We demonstrated that 7,8-DHF decreased cell growth and induced apoptosis in the HN22 and HSC4 cells through regulation of specificity protein 1 (Sp1) using the MTS assay, DAPI staining, Annexin V, propidium iodide staining, reverse transcription-polymerase chain reaction, immunocytochemistry, pull-down assay and western blot analysis. The results showed that the Sp1 protein bound with 7,8-DHF in the HN22 and HSC4 cells. Taken together, the results suggest that 7,8-DHF could modulate Sp1 transactivation and induce apoptotic cell death by regulating the cell cycle and suppressing antiapoptotic proteins. Furthermore, 7,8-DHF may be valuable for cancer prevention and better clinical outcomes.

Identification and characterization of 5'-flanking region of the human riboflavin transporter 1 gene (SLC52A1)

The human SLC52A1 gene encodes the riboflavin transporter-1 (RFVT-1), a plasma membrane protein that transports vitamin B2 (riboflavin, RF) into cells, and thus, plays a role in controlling cellular homeostasis of RF in those tissues that express the carrier protein (e.g. placenta and intestine). Currently, there is nothing known about transcriptional regulation of the SLC52A1 gene, therefore, we aimed to clone and characterize its 5'-flanking region. Using rapid amplification of the cDNA ends (5'-RACE), we identified one transcription start site (TSS). A 579 bp segment of the 5'-flanking region of this gene was cloned which exhibited robust promoter activity upon transfection in human intestinal epithelial cells. Deletion analysis revealed that the core promoter activity to be embedded in a region between -234 and -23 that lacked TATA element, was GC-rich, and harbored several putative cis-regulatory sites including KLFs, AP-2, EGRF and Sp-1. Mutating each of these sites led to a significant decrease in promoter activity (which was highest for the Sp-1 site), suggesting their possible involvement in regulating SLC52A1 transcription. Focusing on the Sp-1 site, EMSA, super-shift and ChIP analysis was performed that established the interaction of the Sp-1 transcription factor with the SLC52A1 promoter; also, co-transfection of the minimal SLC52A1 promoter with an Sp-1 containing vector in Drosophila SL-2 cells led to significant promoter activation. These results are the first to reveal the identity of the minimal SLC52A1 promoter and to establish an important role for Sp-1 in its activity.

Specificity protein 1 is a novel target of 2,4-bis (p-hydroxyphenyl)-2-butenal for the suppression of human oral squamous cell carcinoma cell growth

Background

The Maillard reaction is a chemical reaction occurring between a reducing sugar and an amino acid, generally requiring thermal processing. Maillard reaction products (MRPs) have antioxidant, antimutagenic, and antibacterial effects though 2,4-bis (p-hydroxyphenyl)-2-butenal (HPB242), a fructose-tyrosine MRP, appears to inhibit proliferation of cancer cells, its mechanism of action has not been studied in detail. The purpose of this study was to investigate the anti-proliferative effects of 2,4-bis (p-hydroxyphenyl)-2-butenal (HPB242) on two oral squamous cell carcinoma (OSCC) cell lines, HN22 and HSC4, through regulation of specificity protein 1 (Sp1).

Results

HPB242 treatment dramatically reduced the cell growth rate and apoptotic cell morphologies. Sp1 was significantly inhibited by HPB242 in a dose-dependent manner. Furthermore, cell cycle regulating proteins and anti-apoptotic proteins, which are known as Sp1 target genes, were altered at the molecular levels. The key important regulators in the cell cycle such as p27 were increased, whereas cell proliferation- and survival-related proteins such as cyclin D1, myeloid leukemia sequence 1 (Mcl-1) and survivin were significantly decreased by HPB242 or suppressed Sp1 levels, however pro-apoptotic proteins caspase3 and PARP were cleaved in HN22 and HSC4.

Conclusions

HPB242 may be useful as a chemotherapeutic agent for OSCC for the purpose of treatment and prevention of oral cancer and for the improvement of clinical outcomes.

Role of transcription factor Sp1 in the quercetin-mediated inhibitory effect on human malignant pleural mesothelioma

Quercetin (Qu) is found in plants, including red onions and in the skins of red apples, and induces the apoptosis of certain malignant cells. However, no report has been issued on the apoptotic effect of Qu on human malignant pleural mesothelioma. In the present study, it was found that MSTO-211H mesothelioma cell viability was reduced and apoptotic cell death was increased by Qu (20-80 µM), which was found to have an IC₅₀ of 58 µM. In addition, Qu increased the sub-G₁ cell population, and was found to interact with specificity protein 1 (Sp1) and significantly suppressed its expression at the protein and mRNA levels. Furthermore, Qu modulated the levels of Sp1 regulatory genes, such as cyclin D1, myeloid cell leukemia (Mcl)-1 and survivin in MSTO-211H cells. Apoptotic signaling cascades were activated by the cleavage of Bid, caspase-3 and PARP, and by the downregulation of Bcl-xL and the upregulation of Bax in MSTO-211H cells. Our results strongly suggest that Sp1 be considered as a novel molecular target of Qu in human malignant pleural mesothelioma.

Natural diterpenes from coffee, cafestol and kahweol induce apoptosis through regulation of specificity protein 1 expression in human malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is a highly aggressive cancer with a very poor prognosis. Several clinical studies such as immunotherapy, gene therapy and molecular targeting agents have been tried for treatment of malignant mesothelioma, however, there is no application for effective clinical treatment. Coffee has various biological functions such as anti-oxidant, anti-inflammatory, anti-mutagenic and anti-carcinogenic activities. The therapeutic activities of the bioactive compounds in coffee was sugested to influence intracellular signaling of MPM. Regarding to the cancer-related functions, In this study, suppression of Sp1 protein level followed by induction of MSTO-211H cell apoptosis by cafestol and kahweol were investigated in oreder to determine Sp1's potential as a significant target for human MPM therapy as well.

Methods

Cells were treated separately with final concentration of cafestol and kahweol and the results were analyzed by MTS assay, DAPI staining, PI staining, luciferase assay, RT-PCR, and immunoblotting.

Results

Viability of MSTO-211H and H28 cells were decreased, and apoptotic cell death was increased in MSTO-211H as a result of cafestol and kahweol treatment. Cafestol and kahweol increased Sub-G₁ population and nuclear condensation in MSTO-211H cells. Roles of Sp1 in cell proliferation and apoptosis of the MSTO-211H cells by the Sp1 inhibitor of Mithramycin A were previously confirmed. Cafestol and kahweol significantly suppressed Sp1 protein levels. Kahweol slightly attenuated Sp1 mRNA, while Cafestol did not affect in MSTO-211H cells. Cafestol and kahweol modulated the promoter activity and protein expression level of the Sp1 regulatory genes including Cyclin D1, Mcl-1, and Survivin in mesothelioma cells. Apoptosis signaling cascade was activated by cleavages of Bid, Caspase-3, and PARP with cafestol and by upregulation of Bax, and downregulation of Bcl-_xl by kahweol.

Conclusions

Sp1 can be a novel molecular target of cafestol and kahweol in human MPM.

Cytochrome P450-mediated pulmonary metabolism of carcinogens: regulation and cross-talk in lung carcinogenesis

Lung cancer is strongly associated with exogenous risk factors, in particular tobacco smoking and asbestos exposure. New research data are accumulating about the regulation of the metabolism of tobacco carcinogens and the metabolic response to oxidative stress. These data provide mechanistic details about why well known risk factors cause lung cancer. The purpose of this review is to evaluate the present knowledge of the role of cytochrome P450 (CYP) enzymes in the metabolism of tobacco carcinogens and associations with tobacco and asbestos carcinogenesis. Major emphasis is placed on human data and regulatory pathways involved in CYP regulation and lung carcinogenesis. The most exciting new research findings concern cross-talk of the CYP-regulating aryl hydrocarbon receptor with other transcription factors, such as nuclear factor-erythroid 2-related factor 2, involved in the regulation of xenobiotic metabolism and antioxidant enzymes. This cross-talk between transcription factors may provide mechanistic evidence for clinically relevant issues, such as differences in lung cancers between men and women and the synergism between tobacco and asbestos as lung carcinogens.

Critical appraisal of the expression of cytochrome P450 enzymes in human lung and evaluation of the possibility that such expression provides evidence of potential styrene tumorigenicity in humans

Styrene is widely used with significant human exposure, particularly in the reinforced plastics industry. In mice it is both hepatotoxic and pneumotoxic, and this toxicity is generally thought to be associated with its metabolism to styrene oxide. Styrene causes lung tumors in mice but not in rats. The question is how the tumorigenic effect in mouse lung may relate to the human. This review examines the comparison of the metabolic activation rates (1) between the liver and lung and (2) for the lung, between the rodent and human. Emphasis is placed on the specific cytochromes P450 present in the lungs of humans and what role they might play in the bioactivation of styrene and other compounds. In general, pulmonary metabolism is very slow compared to hepatic metabolism. Furthermore, metabolic rates in humans are slow compared to those in rats and mice. There is a wide difference in what specific cytochromes P450 investigators have reported as being present in human lung which makes comparisons, both inter-species and inter-organ, difficult. The general low activity for cytochrome P450 activity in the lung, especially for CYP2F1, the human homolog for CYP2F2 which has been identified in mice as being primarily responsible for styrene metabolism, argues against the hypothesis that human lung would produce enough styrene oxide to damage pulmonary epithelial cells leading to cell death, increased cell replication and ultimately tumorigenicity, the presumed mode of action for styrene in the production of the mouse lung tumors.

Molecular analysis of the CYP2F1 gene: identification of a frequent non-functional allelic variant

The CYP2F1 is a human cytochrome P450 that is selectively expressed in lung tissue and involved in the metabolism of various pneumotoxicants with potential carcinogenic effects. In the present study, we report the first systematic investigation of the genetic polymorphism of this enzyme. We analyzed the nucleotidic sequence of the CYP2F1 gene in DNA samples from 90 French Caucasians consisting in 44 patients with lung cancer and 46 control individuals, using single-strand conformation polymorphism analysis of PCR products (PCR-SSCP). We identified 24 novel mutations distributed in the promoter region of the gene, as well as in the coding regions and their flanking intronic sequences. In addition to the wild-type CYP2F1*1 allele, seven allelic variant, CYP2F1*2A, *2B, *3, *4, *5A, *5B and *6, were characterized. The most frequent allelic variant, CYP2F1*2A (25.6%), harbors a combination of 9 mutations, including 2 missense mutations (Asp218Asn and Gln266His) and a 1-bp insertion (c.14_15insC) that creates a premature stop codon in exon 2, probably leading to the synthesis of a severely truncated protein with no catalytic activity. The identification of around 7% of homozygotes for the frameshift mutation in our Caucasian population suggests the existence of an interindividual variation of the CYP2F1 activity and, consequently, the possibility of interindividual differences in the toxic response to some pneumotoxicants and in the susceptibility to certain chemically induced diseases. However, our preliminary results did not show any evidence that the CYP2F1 genetic polymorphism has implications in the pathogenesis of lung cancer.

Trichostatin A blocks TGF-beta-induced collagen gene expression in skin fibroblasts: involvement of Sp1

Transforming growth factor- beta (TGF-beta) stimulates Type I collagen synthesis by fibroblasts and is implicated in tissue fibrosis. Here, we demonstrate that histone deacetylase inhibitor Trichostatin A (TSA) suppresses the TGF-beta-induced Type I collagen synthesis but not induced PAI-1 synthesis suggesting the influence of TSA is gene specific. Results further reveal that there is no significant alteration in Smad activation and function in presence of TSA suggesting suppression of TGF-beta-induced collagen synthesis is not due to impaired Smad signaling. TGF-beta induces the levels of Sp1, an essential transcription factor of Smad-dependent stimulation of collagen synthesis. However, in presence of TSA, TGF-beta fails to induce Sp1 levels, its interaction with Smad complex and Sp1 binding site in COL1A2 promoter. Furthermore, overexpressed Sp1 reverses the TSA-mediated inhibition of TGF-beta-induced collagen gene expression. Collectively, these results suggest that TSA-mediated suppression of Smad-dependent TGF-beta-induced collagen synthesis is due to suppression of Sp1 activity in skin fibroblasts.

Molecular mechanisms regulating human CYP4B1 lung-selective expression

Lung-selective cytochrome P450 expression is well recognized; however, little is known regarding regulatory mechanisms. To address this knowledge gap, transient expression of CYP4B1/luciferase constructs was used to identify a proximal, positively acting regulatory element, position -139 to -45, that functioned in all cells examined; a negatively acting element, position -457 to -216, that only functioned in HepG2 hepatoblastoma cells; and a distal, positively acting element, position -1087 to -1008, that functioned in A549 or BEAS-2B lung-derived cells but not HepG2 cells or 293 kidney-derived cells. Competitive electrophoretic mobility shift assays further localized specific A549, but not HepG2, nuclear protein binding to two sites within the distal element, CYP4B1 position -1052 to -1042 and -1026 to -1008. Several potential lung-selective transcription factor recognition sequences were identified within these elements. However, attempts to identify specific factor(s) were unsuccessful. In contrast, in vitro DNA/protein binding assays combined with transient expression and mutagenesis studies identified two functional Sephadex protein/Krüppel-like factor families of transcription factor sites within the proximal element (position -118 to -114 and position -77 to -73) that bound both Sephadex protein 1 (Sp1) and Sephadex protein 3 (Sp3) in vitro. Furthermore, Sp1-dependent synergistic regulation was observed in A549 cells involving the proximal and distal regulatory elements. Chromatin immunoprecipitation assays demonstrated binding of neither Sp1 nor Sp3 to the CYP4B1 proximal element in human liver tissue, whereas selective Sp1 binding was observed in human lung tissue. Thus, the composite findings are consistent with both the proximal Sp1 elements and the distal regulatory element acting to synergistically control CYP4B1 lung-selective expression.