skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Propiconazole-enhanced hepatic cell proliferation is associated with dysregulation of the cholesterol biosynthesis pathway leading to activation of Erk1/2 through Ras farnesylation

Abstract

Propiconazole is a mouse hepatotumorigenic fungicide designed to inhibit CYP51, a key enzyme in the biosynthesis of ergosterol in fungi and is widely used in agriculture to prevent fungal growth. Metabolomic studies in mice revealed that propiconazole increased levels of hepatic cholesterol metabolites and bile acids, and transcriptomic studies revealed that genes within the cholesterol biosynthesis, cholesterol metabolism and bile acid biosyntheses pathways were up-regulated. Hepatic cell proliferation was also increased by propiconazole. AML12 immortalized hepatocytes were used to study propiconazole's effects on cell proliferation focusing on the dysregulation of cholesterol biosynthesis and resulting effects on Ras farnesylation and Erk1/2 activation as a primary pathway. Mevalonate, a key intermediate in the cholesterol biosynthesis pathway, increases cell proliferation in several cancer cell lines and tumors in vivo and serves as the precursor for isoprenoids (e.g. farnesyl pyrophosphate) which are crucial in the farnesylation of the Ras protein by farnesyl transferase. Farnesylation targets Ras to the cell membrane where it is involved in signal transduction, including the mitogen-activated protein kinase (MAPK) pathway. In our studies, mevalonic acid lactone (MVAL), a source of mevalonic acid, increased cell proliferation in AML12 cells which was reduced by farnesyl transferase inhibitors (L-744,832 or manumycin) or simvastatin,more » an HMG-CoA reductase inhibitor, indicating that this cell system responded to alterations in the cholesterol biosynthesis pathway. Cell proliferation in AML12 cells was increased by propiconazole which was reversed by co-incubation with L-744,832 or simvastatin. Increasing concentrations of exogenous cholesterol muted the proliferative effects of propiconazole and the inhibitory effects of L-733,832, results ascribed to reduced stimulation of the endogenous cholesterol biosynthesis pathway. Western blot analysis of subcellular fractions from control, MVAL or propiconazole-treated cells revealed increased Ras protein in the cytoplasmic fraction of L-744,832-treated cells, while propiconazole or MVAL reversed these effects. Western blot analysis indicated that phosphorylation of Erk1/2, a protein downstream of Ras, was increased by propiconazole. These data indicate that propiconazole increases cell proliferation by increasing the levels of cholesterol biosynthesis intermediates presumably through a negative feedback mechanism within the pathway, a result of CYP51 inhibition. This feedback mechanism increases Erk1/2 signaling through mevalonate-mediated Ras activation. These results provide an explanation for the observed effects of propiconazole on hepatic cholesterol pathways and on the increased hepatic cell proliferation induced by propiconazole in mice. Highlights: ► Propiconazole increases cell proliferation in AML12 mouse hepatocytes. ► Propiconazole increases Ras farnesylation and alters Ras membrane localization. ► Propiconazole increases Erk1/2 phosphorylation. ► Dysregulation of the cholesterol biosynthesis pathway can explain these results. ► These results can explain similar effects induced by propiconazole in mice.« less

Authors:
; ;
Publication Date:
OSTI Identifier:
22215293
Resource Type:
Journal Article
Resource Relation:
Journal Name: Toxicology and Applied Pharmacology; Journal Volume: 260; Journal Issue: 2; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; BILE ACIDS; BIOSYNTHESIS; CELL MEMBRANES; CELL PROLIFERATION; CHOLESTEROL; CONCENTRATION RATIO; ENZYMES; ERGOSTEROL; IN VIVO; INHIBITION; LIVER; LIVER CELLS; METABOLISM; METABOLITES; MEVALONIC ACID; MICE; NEOPLASMS; PHOSPHORYLATION

Citation Formats

Murphy, Lynea A., Moore, Tanya, and Nesnow, Stephen, E-mail: nesnow.stephen@epa.gov. Propiconazole-enhanced hepatic cell proliferation is associated with dysregulation of the cholesterol biosynthesis pathway leading to activation of Erk1/2 through Ras farnesylation. United States: N. p., 2012. Web. doi:10.1016/J.TAAP.2012.02.003.
Murphy, Lynea A., Moore, Tanya, & Nesnow, Stephen, E-mail: nesnow.stephen@epa.gov. Propiconazole-enhanced hepatic cell proliferation is associated with dysregulation of the cholesterol biosynthesis pathway leading to activation of Erk1/2 through Ras farnesylation. United States. doi:10.1016/J.TAAP.2012.02.003.
Murphy, Lynea A., Moore, Tanya, and Nesnow, Stephen, E-mail: nesnow.stephen@epa.gov. Sun . "Propiconazole-enhanced hepatic cell proliferation is associated with dysregulation of the cholesterol biosynthesis pathway leading to activation of Erk1/2 through Ras farnesylation". United States. doi:10.1016/J.TAAP.2012.02.003.
@article{osti_22215293,
title = {Propiconazole-enhanced hepatic cell proliferation is associated with dysregulation of the cholesterol biosynthesis pathway leading to activation of Erk1/2 through Ras farnesylation},
author = {Murphy, Lynea A. and Moore, Tanya and Nesnow, Stephen, E-mail: nesnow.stephen@epa.gov},
abstractNote = {Propiconazole is a mouse hepatotumorigenic fungicide designed to inhibit CYP51, a key enzyme in the biosynthesis of ergosterol in fungi and is widely used in agriculture to prevent fungal growth. Metabolomic studies in mice revealed that propiconazole increased levels of hepatic cholesterol metabolites and bile acids, and transcriptomic studies revealed that genes within the cholesterol biosynthesis, cholesterol metabolism and bile acid biosyntheses pathways were up-regulated. Hepatic cell proliferation was also increased by propiconazole. AML12 immortalized hepatocytes were used to study propiconazole's effects on cell proliferation focusing on the dysregulation of cholesterol biosynthesis and resulting effects on Ras farnesylation and Erk1/2 activation as a primary pathway. Mevalonate, a key intermediate in the cholesterol biosynthesis pathway, increases cell proliferation in several cancer cell lines and tumors in vivo and serves as the precursor for isoprenoids (e.g. farnesyl pyrophosphate) which are crucial in the farnesylation of the Ras protein by farnesyl transferase. Farnesylation targets Ras to the cell membrane where it is involved in signal transduction, including the mitogen-activated protein kinase (MAPK) pathway. In our studies, mevalonic acid lactone (MVAL), a source of mevalonic acid, increased cell proliferation in AML12 cells which was reduced by farnesyl transferase inhibitors (L-744,832 or manumycin) or simvastatin, an HMG-CoA reductase inhibitor, indicating that this cell system responded to alterations in the cholesterol biosynthesis pathway. Cell proliferation in AML12 cells was increased by propiconazole which was reversed by co-incubation with L-744,832 or simvastatin. Increasing concentrations of exogenous cholesterol muted the proliferative effects of propiconazole and the inhibitory effects of L-733,832, results ascribed to reduced stimulation of the endogenous cholesterol biosynthesis pathway. Western blot analysis of subcellular fractions from control, MVAL or propiconazole-treated cells revealed increased Ras protein in the cytoplasmic fraction of L-744,832-treated cells, while propiconazole or MVAL reversed these effects. Western blot analysis indicated that phosphorylation of Erk1/2, a protein downstream of Ras, was increased by propiconazole. These data indicate that propiconazole increases cell proliferation by increasing the levels of cholesterol biosynthesis intermediates presumably through a negative feedback mechanism within the pathway, a result of CYP51 inhibition. This feedback mechanism increases Erk1/2 signaling through mevalonate-mediated Ras activation. These results provide an explanation for the observed effects of propiconazole on hepatic cholesterol pathways and on the increased hepatic cell proliferation induced by propiconazole in mice. Highlights: ► Propiconazole increases cell proliferation in AML12 mouse hepatocytes. ► Propiconazole increases Ras farnesylation and alters Ras membrane localization. ► Propiconazole increases Erk1/2 phosphorylation. ► Dysregulation of the cholesterol biosynthesis pathway can explain these results. ► These results can explain similar effects induced by propiconazole in mice.},
doi = {10.1016/J.TAAP.2012.02.003},
journal = {Toxicology and Applied Pharmacology},
number = 2,
volume = 260,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2012},
month = {Sun Apr 15 00:00:00 EDT 2012}
}
  • Highlights: {yields} The aliphatic acetogenins [(2S,4S)-2,4-dihydroxyheptadec-16-enyl acetate] (1) and [(2S,4S)-2,4-dihydroxyheptadec-16-ynyl acetate] (2) isolated from avocado fruit inhibit phosphorylation of c-RAF (Ser338) and ERK1/2 (Thr202/Tyr204). {yields} Aliphatic acetogenin 2, but not 1, prevents EGF-induced activation of EGFR (Tyr1173). {yields} Combination of both aliphatic acetogenins synergistically inhibits c-RAF (Ser338) and ERK1/2 (Thr202/Tyr204) phosphorylation and human oral cancer cell proliferation. {yields} The potential anticancer activity of avocado fruits is due to a combination of specific aliphatic acetogenins targeting two key components of the EGFR/RAS/RAF/MEK/ERK1/2 cancer pathway. {yields} Providing a double hit on a critical cancer pathway such as EGFR/RAS/RAF/MEK/ERK1/2 by phytochemicals like thosemore » found in avocado fruit could lead to more effective approach toward cancer prevention. -- Abstract: Avocado (Persea americana) fruits are consumed as part of the human diet and extracts have shown growth inhibitory effects in various types of human cancer cells, although the effectiveness of individual components and their underlying mechanism are poorly understood. Using activity-guided fractionation of the flesh of avocado fruits, a chloroform-soluble extract (D003) was identified that exhibited high efficacy towards premalignant and malignant human oral cancer cell lines. From this extract, two aliphatic acetogenins of previously known structure were isolated, compounds 1 [(2S,4S)-2,4-dihydroxyheptadec-16-enyl acetate] and 2 [(2S,4S)-2,4-dihydroxyheptadec-16-ynyl acetate]. In this study, we show for the first time that the growth inhibitory efficacy of this chloroform extract is due to blocking the phosphorylation of EGFR (Tyr1173), c-RAF (Ser338), and ERK1/2 (Thr202/Tyr204) in the EGFR/RAS/RAF/MEK/ERK1/2 cancer pathway. Compounds 1 and 2 both inhibited phosphorylation of c-RAF (Ser338) and ERK1/2 (Thr202/Tyr204). Compound 2, but not compound 1, prevented EGF-induced activation of the EGFR (Tyr1173). When compounds 1 and 2 were combined they synergistically inhibited c-RAF (Ser338) and ERK1/2 (Thr202/Tyr204) phosphorylation, and human oral cancer cell proliferation. The present data suggest that the potential anticancer activity of avocado fruits is due to a combination of specific aliphatic acetogenins that target two key components of the EGFR/RAS/RAF/MEK/ERK1/2 cancer pathway.« less
  • Biphasic dose-response relationship induced by environmental agents is often characterized with the effect of low-dose stimulation and high-dose inhibition. Some studies showed that arsenite may induce cell proliferation and apoptosis via biphasic dose-response relationship in human cells; however, mechanisms underlying this phenomenon are not well understood. In the present study, we aimed at investigating the relationship between biphasic effect of arsenite on cell proliferation and apoptosis and activation of JNK and ERK1/2 in human embryo lung fibroblast (HELF) cells. Our results demonstrated that cell proliferation may be stimulated at lower concentrations (0.1 and 0.5 {mu}M) arsenite but inhibited at highermore » concentrations (5 and 10 {mu}M). When cell apoptosis was used as the endpoint, the concentration-response curves were changed to U-shapes. During stimulation phospho-JNK levels were significantly increased at 3, 6, and 12 h after 0.1 or 0.5 {mu}M arsenite exposure. Phospho-ERK1/2 levels were increased with different concentrations (0.1-10 {mu}M) of arsenite at 6, 12, and 24 h. Blocking of JNK pathway with 20 {mu}M SP600125 or ERK1/2 by 100 {mu}M PD98059 significantly inhibited biphasic effect of arsenite in cells. Data in the present study suggest that activation of JNK and ERK1/2 may be involved in biphasic effect of arsenite when measuring cell proliferation and apoptosis in HELF cells. JNK activation seems to play a more critical role than ERK1/2 activation in the biphasic process.« less
  • Highlights: •CDK-associated Cullin 1 (CAC1) expression increases in human lung carcinoma. •CAC1 promotes the proliferation of lung cancer A549 cells. •CAC1 promotes human lung cancer A549 cell proliferation with activation of ERK1/2. -- Abstract: Lung cancer is one of the most common causes of cancer-related death in the world, but the mechanisms remain unknown. In this study, we investigated the expression of CDK-associated Cullin 1 (CAC1) in lung cancer, the effect of CAC1 on the proliferation of human lung cancer A549 cells, and the activation of signaling pathways of mitogen-activated protein kinases (MAPKs). Results showed that CAC1 expression was highermore » levels in human lung carcinoma than normal lung tissue, and CAC1 siRNA reduced the proliferation of lung cancer A549 cells by decreasing cell activity and cell division in vitro. The proportion of cells treated with CAC1 siRNA increased in the G1 phase and decreased in the S and G2/M phase, indicative of G1 cell cycle arrest. Furthermore, the proportions of early/late apoptosis in lung cancer A549 cells were enhanced with CAC1 siRNA treatment. It was also found that activation of extracellular signal-regulated protein kinase (ERK) and p38 signaling pathways were involved in the proliferation of A549 cells. After CAC1 siRNA treatment, p-ERK1/2 levels decreased, and meanwhile p-p38 level increased, A549 cell proliferation increased when ERK1/2 signaling is activated by PMA. Our findings demonstrated that CAC1 promoted the proliferation of human lung cancer A549 cells with activation of ERK1/2 signaling pathways, suggesting a potential cure target for treatment of human lung cancer.« less
  • Highlights: •H{sub 2}O{sub 2} inhibits TGF-β1-induced cell cycle arrest. •H{sub 2}O{sub 2} induces Smad3 linker phosphorylation through Akt-ERK1/2 pathway. •H{sub 2}O{sub 2}-mediated suppression of TGF-β signal requires Smad3 linker phosphorylation. •This is a first report about interplay between H{sub 2}O{sub 2} and growth inhibition pathway. -- Abstract: Hydrogen peroxide (H{sub 2}O{sub 2}) functions as a second messenger in growth factor receptor-mediated intracellular signaling cascade and is tumorigenic by virtue of its ability to promote cell proliferation; however, the mechanisms underlying the growth stimulatory action of H{sub 2}O{sub 2} are less understood. Here we report an important mechanism for antagonistic effectsmore » of H{sub 2}O{sub 2} on growth inhibitory response to transforming growth factor-β1 (TGF-β1). In Mv1Lu and HepG2 cells, pretreatment of H{sub 2}O{sub 2} (0.05–0.2 mM) completely blocked TGF-β1-mediated induction of p15{sup INK4B} expression and increase of its promoter activity. Interestingly, H{sub 2}O{sub 2} selectively suppressed the transcriptional activation potential of Smad3, not Smad2, in the absence of effects on TGF-β1-induced phosphorylation of the COOH-tail SSXS motif of Smad3 and its nuclear translocation. Mechanism studies showed that H{sub 2}O{sub 2} increases the phosphorylation of Smad3 at the middle linker region in a concentration- and time-dependent manner and this effect is mediated by activation of extracellular signal-activated kinase 1/2 through Akt. Furthermore, expression of a mutant Smad3 in which linker phosphorylation sites were ablated significantly abrogated the inhibitory effects of H{sub 2}O{sub 2} on TGF-β1-induced increase of p15{sup INK4B}-Luc reporter activity and blockade of cell cycle progression from G1 to S phase. These findings for the first time define H{sub 2}O{sub 2} as a signaling molecule that modulate Smad3 linker phosphorylation and its transcriptional activity, thus providing a potential mechanism whereby H{sub 2}O{sub 2} antagonizes the cytostatic function of TGF-β1.« less
  • Native LDL may be a mitogenic stimulus of VSMC proliferation in lesions where endothelial disruption occurs. Recent studies have demonstrated that the mitogenic effects of LDL are accompanied by Erk1/2 activation via an unknown G-protein-coupled receptor (GPCR). In this article, we report that LDL translocated PKC{beta}{sub II} and PKC{theta} from cytosol to plasma membrane, and inhibition of PKC{beta}{sub II} and PKC{theta} decreased LDL effects via the deactivation of Erk1/2. Moreover, pertussis toxin, but not cholera toxin or heparin, inhibited LDL-induced translocation of PKC{beta}{sub II} and PKC{theta}, suggesting that Gi protein plays a role in LDL effects. Of LPA, S1P, andmore » LDL, whose signaling is conveyed via Gi/o proteins, only LDL induced translocation of PKC{beta}{sub II} and PKC{theta}. Inhibition of PKC{beta}{sub II} or PKC{theta}, as well as of Erk1/2 and GPCR, decreases LDL-induced upregulation of Egr-1, which is critical for cell proliferation. This is the first report, to our knowledge, that the participation of PKC{theta} in VSMC proliferation is unique.« less