Competitive inhibition of the transcription of rabbit CYP1A1 gene by upstream stimulatory factor 1 (USF1)

PM2.5 leads to adverse pregnancy outcomes by inducing trophoblast oxidative stress and mitochondrial apoptosis via KLF9/CYP1A1 transcriptional axis

Epidemiological studies have demonstrated that fine particulate matter (PM2.5) is associated with adverse obstetric and postnatal metabolic health outcomes, but the mechanism remains unclear. This study aimed to investigate the toxicological pathways by which PM2.5 damaged placental trophoblasts in vivo and in vitro. We confirmed that PM2.5 induced adverse gestational outcomes such as increased fetal mortality rates, decreased fetal numbers and weight, damaged placental structure, and increased apoptosis of trophoblasts. Additionally, PM2.5 induced dysfunction of the trophoblast cell line HTR8/SVneo, including in its proliferation, apoptosis, invasion, migration and angiogenesis. Moreover, we comprehensively analyzed the transcriptional landscape of HTR8/SVneo cells exposed to PM2.5 through RNA-Seq and observed that PM2.5 triggered overexpression of pathways involved in oxidative stress and mitochondrial apoptosis to damage HTR8/SVneo cell biological functions through CYP1A1. Mechanistically, PM2.5 stimulated KLF9, a transcription factor identified as binding to CYP1A1 promoter region, which further modulated the CYP1A1-driven downstream phenotypes. Together, this study demonstrated that the KLF9/CYP1A1 axis played a crucial role in the toxic progression of PM2.5 induced adverse pregnancy outcomes, suggesting adverse effects of environmental pollution on pregnant females and putative targeted therapeutic strategies.

AhR regulates the expression of human cytochrome P450 1A1 (CYP1A1) by recruiting Sp1

Cytochrome P450 1A1 (CYP1A1) is abundant in the kidney, liver, and intestine and is involved in the phase I metabolism of numerous endogenous and exogenous compounds. Therefore, exploring the regulatory mechanism of its basal expression in humans is particularly important to understand the bioactivation of several procarcinogens to their carcinogenic derivatives. Site-specific mutagenesis and deletion of the transcription factor binding site determined the core cis-acting elements in the human CYP1A1 proximal and distal promoter regions. The proximal promoter region [overlapping xenobiotic-responsive element (XRE) and GC box sequences] determined the basal expression of CYP1A1. In human hepatocellular carcinoma cells (HepG2) with aryl hydrocarbon receptor (AhR) or specificity protein 1 (Sp1) knockdown, we confirmed that AhR and Sp1 are involved in basal CYP1A1 expression. In HepG2 cells overexpressing either AhR or Sp1, AhR determined the proximal transactivation of basal CYP1A1 expression. Via DNA affinity precipitation assays and ChIP, we found that AhR bound to the promoter and recruited Sp1 to transactivate CYP1A1 expression. The coordinated interaction between Sp1 and AhR was identified to be DNA mediated. Our work revealed a basal regulatory mechanism of an interesting human gene by which AhR interacts with Sp1 through DNA and recruits Sp1 to regulate basal CYP1A1 expression.

Characterization of the 5'‐regulatory regions of the rat and human apelin genes and regulation of breast apelin by USF

Apelin, a peptide widely expressed in the body, is the endogenous ligand for the APJ receptor. To investigate how the apelin gene is regulated transcriptionally, we cloned and characterized approximately 3000 and approximately 4000 bp 5'-upstream fragments of the rat and human apelin genes. Putative CAAT-like box, but not TATA-box sites were identified. The rat (-207/-1 bp) and human (-100/+74 bp) core promoter sequences contain putative binding sites for upstream stimulatory factor (USF)-1/-2. Mutagenesis and overexpression assays showed that USF up-regulates basal and inducible apelin transcription. EMSA and supershift experiments indicated binding of USF-1/-2 to the rat (-114/-109 bp) and human (-84/-79 bp) apelin promoters. ChIP experiments show that USF is recruited to the putative USF binding site in the human apelin promoter in cultured breast cells. In concert with increased breast apelin expression during pregnancy and lactation in rats, EMSAs demonstrate an elevated binding of pregnant and lactating rat breast nuclear proteins to a consensus USF oligonucleotide. In vivo ChIP assays verified increased USF binding to the apelin promoter in breast of lactating rats. Together, our findings show that USF exerts a stimulatory role in regulation of breast apelin expression during pregnancy and lactation.

Human prolyl-4-hydroxylase alpha(I) transcription is mediated by upstream stimulatory factors

Prolyl-4-hydroxylase alpha(I) (P4Halpha(I)) is the rate-limiting subunit for P4H enzyme activity, which is essential for procollagen hydroxylation and secretion. In the current study, we have characterized the human P4Halpha(I) promoter for transcription factors and DNA elements regulating P4Halpha(I) expression. Using a progressive deletion cloning approach, we have constructed pGL3-P4Halpha(I) recombinant plasmids. We have identified a positive regulatory region at the positions of bp -184 to -97 responsible for approximately 80% of the P4Halpha(I) promoter efficiency. Three E-boxes were located within this region, and the E-box at position bp -135 explains most of the regulatory capacity. Upstream stimulatory factors (USF1/USF2) were shown to bind on the E-box using chromatin immunoprecipitation assay. Suppression of USF1 and/or USF2 using specific short interference RNA resulted in a significant reduction in P4Halpha(I) promoter activity, and overexpressed USF1 or USF2 increased P4Halpha(I) promoter activity significantly. Although transforming growth factor beta1 increased the USF1/USF2-E-box binding and P4Halpha(I) promoter activity, this up-regulatory effect can be largely prevented by USF1/USF2-specific short interference RNA. On the other hand, cigarette smoking extracts, which have been shown to suppress P4Halpha(I) expression, inhibited the binding between the USF1/USF2 and E-box, resulting in a reduced P4Halpha(I) promoter activity. Furthermore, the E-box on the P4Halpha(I) promoter appeared to indiscriminately bind with either USF1 or USF2, with a similar outcome on the promoter efficiency. In conclusion, our study shows that USF1/USF2 plays a critical role in basal P4Halpha(I) expression, and both positive (transforming growth factor beta1) and negative (cigarette smoking extract) regulators appear to influence the USF-E-box interaction and affect P4Halpha(I) expression.

Suppression of cytochrome P450 2C11 by aromatic hydrocarbons: mechanistic insights from studies of the 5'-flanking region of the CYP2C11 gene

The aromatic hydrocarbon receptor (AHR) functions as a ligand-activated transcription factor that mediates responses to aromatic hydrocarbons (AHs). Induction of cytochrome p450 1A1 (CYP1A1) is the most fully characterized response and is mediated by binding of the activated AHR complex to dioxin-responsive elements (DREs) located in the 5'-flanking region of the gene. In contrast to CYP1A1 induction, several other genes including the rat male-specific constitutive hepatic CYP2C11 are suppressed by AHs. Our aim was to determine whether CYP2C11 suppression by AHs is mediated by the AHR via interaction with DRE-like sequences. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) suppressed CYP2C11 mRNA in primary rat hepatocytes without altering the mRNA half-life. We identified five regions in the CYP2C11 5'-flank containing the DRE invariant core; electrophoretic gel retardation assays showed that at least one of these DREs is a potential binding site for the AHR. To test the function of the CYP2C11-DREs, Hepa-1, BRL 5637, and HepG2 cells were transfected with reporter constructs containing regions of the CYP2C11 5'-flank and promoter. No decrease in luciferase activity was found following TCDD treatment. In primary rat hepatocytes, the luciferase reporter vectors were suppressed by interleukin-1 beta but not by TCDD. In vitro footprinting showed protein binding at several sites in the CYP2C11 5'-flank, but the pattern was not altered by in vivo 3-methylcholanthrene treatment. These studies imply that AHs down-regulate CYP2C11 by a negative transcriptional mechanism that is not simply due to AHR binding to an identified DRE-like sequence and that is distinct from that used by inflammatory cytokines.