Transcriptional activation of the c-Ha-ras protooncogene in vascular smooth muscle cells by benzo(a)pyrene

Sulfur dioxide and benzo(a)pyrene modulates CYP1A and tumor-related gene expression in rat liver

Sulfur dioxide (SO(2)) and benzo(a)pyrene (B(a)P) are common industrial and environmental contaminants. However, few data are available on the effects of SO(2) on proto-oncogenes and tumor suppressor genes, as well as the interactions between SO(2) and other xenobiotics regulating proto-oncogenes or tumor suppressor genes expression. To investigate the interactions between SO(2) and B(a)P, male Wistar rats were exposed to intratracheally instilled with B(a)P or SO(2) inhalation alone or together. We detected mRNA expression of CYP1A1 and 1A2, 7-ethoxyresorufin O-deethylase (EROD), and methoxyresorufin O-demethylase (MROD) activities in livers. The mRNA and protein levels of several cancer-related genes were analyzed in livers by real-time RT-PCR and Western blot, respectively. The EROD/MROD activities and CYP1A1/2 expression were down-regulated by SO(2) but up-regulated by B(a)P alone. Exposure of SO(2) alone induced c-fos, c-jun, c-myc, H-ras, and p53 expression, and depressed p16 and Rb expression in livers. The effects of B(a)P on the above gene were similar to SO(2) except c-fos expression. Furthermore, SO(2) + B(a)P exposure increased the expression of c-fos, c-jun, c-myc, and p53, and decreased p16 and Rb expression in livers compared with exposed to SO(2) or B(a)P alone. However, no synergistic effects were observed on H-ras and CYP1A1/2 after SO(2) + B(a)P exposure. Our findings indicate that multiple cell cycle regulatory proteins play key roles in the toxicity of SO(2) and B(a)P in livers. It might involve the activation of c-fos, c-jun, c-myc, and p53. And p16-Rb pathway might also participate in the progress. Although the gene products we studied are classed as oncogenes and tumor suppressor genes, their functions actually relate to more general processes of control of cell proliferation, survival, and/or apoptosis.

Redox regulation of c-Ha-ras and osteopontin signaling in vascular smooth muscle cells: implications in chemical atherogenesis

Reduction/oxidation (redox) reactions play a central role in the regulation of vascular cell functions. Recent studies in this laboratory have identified c-Ha-ras and osteopontin genes as critical molecular targets during oxidant-induced atherogenesis. This review focuses on the deregulation of gene transcription by redox-activated trans-acting factors after benzo(a)pyrene challenge and the modulation of extracellular matrix signaling in vascular smooth muscle cells by allylamine-induced oxidative injury. The induction of atherogenic vascular smooth muscle cell phenotypes by chemical injury exhibits remarkable parallels with those seen in other forms of atherogenesis.

Benzo(a)pyrene-induced alterations in growth-related gene expression and signaling in precision-cut adult rat liver and kidney slices

Benzo(a)pyrene (BaP) and related aromatic hydrocarbons are suspected carcinogens; however, the molecular basis underlying tumorigenesis remains unclear. To identify acute molecular targets of BaP within the liver and kidney, precision-cut slices harvested from naive, adult female Sprague-Dawley rats were challenged with BaP (0.3-30 microM) for 0.5 to 24 h. BaP did not elicit cytotoxicity, as assessed by intracellular K+ and ATP content and histological evaluation over the 24-h period. To determine if molecular signaling pathways were maintained in precision-cut slices, induction of the aryl hydrocarbon receptor (AhR) pathway was assessed following BaP challenge. Induction of cytochrome P450IA1 (P450IA1) mRNA and protein expression was observed in both liver and kidney slices. c-fos and c-Ha-ras gene expression was enhanced in liver, but not kidney, slices by BaP. c-jun mRNA levels were decreased in liver and kidney slices, although the effect was earlier (0.5 h) in liver slices compared to kidney slices. BaP increased the DNA binding of nuclear proteins to the AP-1 consensus recognition element in liver, but decreased DNA binding in kidney slices. In contrast, DNA binding of NF-kappa B was not affected by BaP in either liver or kidney slices. These results suggest that acute BaP challenge is associated with altered expression of several growth-related genes and AP-1 signaling and establish precision-cut slices as a useful in vitro system to investigate the molecular basis of BaP-induced tumorigenesis, including organ-specific differences.

Identification of benzo[a]pyrene-inducible cis-acting elements within c-Ha-ras transcriptional regulatory sequences

Previous studies in this laboratory have demonstrated that transcriptional deregulation of c-Ha-ras expression is associated with the induction and maintenance of proliferative vascular smooth muscle cell (SMC) phenotypes by benzo[a]pyrene (BaP). We examined previously undescribed cis-acting elements within the proximal 5' regulatory region of c-Ha-ras (-550 to +220) for their ability to influence BaP-induced transcription in murine SMCs. BaP-inducible DNA binding activity was demonstrated at a site located -30 relative to the major start site cluster at +1 that exhibits extensive homology to a consensus aryl hydrocarbon response element (AHRE), as well as a site located at -543 that contains a consensus electrophile response element (EpRE). In vitro cross-linking studies revealed the specific interaction of 104- and 96-kDa proteins with the putative AHRE and of an 80-kDa protein with the EpRE. The use of monoclonal antibodies to the aryl hydrocarbon receptor transcription factor in competition electrophoretic mobility shift assays indicated this protein is specifically induced by BaP to interact at the AHRE within the c-Ha-ras 5' regulatory region. Transient transfection with an Ha-ras promoter construct containing the putative AHRE but lacking the EpRE linked to the chloramphenicol acetyl transferase reporter gene, followed by challenge with BaP (0.3, 3.0, and 30 microM), revealed transcriptional activation that was not statistically significant. However, insertion of an oligonucleotide composed of the EpRE immediately upstream of basal sequences at -330 was associated with strong activation of transcription by BaP. These data indicate that c-Ha-ras gene expression is modulated by BaP via a complex mechanism that likely involves interactions among multiple regulatory elements. We conclude that c-Ha-ras expression is regulated by BaP at the transcriptional level, a response that may constitute an epigenetic basis of atherogenesis.

The induction of proliferative vascular smooth muscle cell phenotypes by benzo[a]pyrene does not involve mutational activation of ras genes

Previous studies in this laboratory have suggested that benzo[a]pyrene (BaP) challenge in vivo and in vitro induces genomic changes that result in the acquisition of proliferative vascular smooth muscle cell (SMC) phenotypes. Because this phenotypic change correlates with alterations in ras gene expression, and ras genes are known mutational targets of BaP, the present studies were conducted to determine if BaP induces activating mutation(s) or ras genes in SMCs. For in vivo studies, male Sprague-Dawley rats were given weekly injections of an atherogenic dose of BaP (10 mg/kg) or vehicle for 8 weeks and SMCs were isolated from the thoracic aorta and established in culture. For in vitro studies, naive rat aortic SMCs were challenged with 3 micro M BaP for 24 h and then subjected to nine serial passages for the induction of proliferative phenotypes. Measurements of DNA synthesis and cell numbers were conducted to define patterns of proliferative behavior in BaP and control cells. In parallel studies, exons 1 and 2 of ras genes were amplified by reverse-transcription polymerase chain reaction and sequenced to screen for activating ras mutations. BaP treatment in vivo was associated with the development of aortic wall lesions characterized by loss of endothelial integrity, fragmentation of the elastic laminae, expansion of the smooth muscle cell mass, and change in the orientation of medial SMCs. Although BaP enhanced the growth rate of vascular SMCs relative to controls, no mutations were detected in the activating regions (codons 12, 13, 60, or 61) of c-Ha-, c-Ki-, or N-ras genes. These data demonstrate that BaP-induced alterations in the proliferative potential of SMCs do not involve activating mutations in the frequently mutated regions of ras genes.