STAT1 activation regulates proliferation and differentiation of renal progenitors

We have shown previously that activation of STAT1 contributes to the pathogenesis of Wilms tumor. This neoplasm caricatures metanephric development and is believed to originate from embryonic renal mesenchymal progenitors that lose their ability to undergo mesenchymal-epithelial transition (MET). Therefore, we hypothesized that STAT1 is also activated and functional during metanephric development. Here we have demonstrated that both STAT1 and STAT3 are activated during normal development of the embryonic kidney. Furthermore, activation of STAT1 stimulated the proliferation of metanephric mesenchymal cells, but it prevented MET and tubulogenesis induced by leukemia inhibitory factor, which preferentially activates STAT3. Consistent with its negative regulation of metanephric mesenchymal differentiation, inhibition of STAT1 activation with protein kinase CK2 inhibitor TBB or RNAi-mediated knockdown of STAT1 promoted differentiation of metanephric progenitors and abolished the effect of cytokine-induced STAT1 activation in these cells. Additionally, a cell-permeable peptide that inhibits STAT1-mediated transactivation by targeting the STAT1 N-domain also blocked cytokine-induced STAT1-dependent proliferation in metanephric progenitors and promoted LIF-induced MET and tubulogenesis. Finally, the STAT1 peptide inhibitor caused the down regulation of survival/anti-apoptotic factors, Mcl-1 and Hsp-27, and induced apoptosis in renal tumor cells with constitutively active STAT1, indicating that STAT1 is required for these cells to survive. These findings show that both metanephric progenitors and renal tumor cells utilize a STAT1-dependent mechanism for growth or survival.

Abstract 489: Selective inhibitor of STAT1 sensitizes breast cancer cells to radiation therapy

About 70% of breast cancer patients with progressive disease are resistant to conventional cancer treatments such as adjuvant chemotherapy and/or radiation therapy. Recently, the STAT1 signaling pathway has been identified as a predictive marker of poor outcome in breast cancer patients and as a factor responsible for radiation and chemotherapy resistance. STAT1 was initially considered as a tumor suppressor, since it causes growth arrest and apoptosis after stimulation with interferons and in response to DNA damage. However, constitutive activation/overexpression of STAT1 results in pro-survival cellular signaling via enhancement of expression of pro-survival proteins Mcl-1 and Hsp27 that might be responsible for observed radiation resistance of breast cancer cells. It may therefore be beneficial to sensitize patients with resistant disease to radiation or chemotherapy by inhibiting STAT1 signaling, yet there has been little effort to develop direct inhibitors of STAT1.

We have recently developed a selective inhibitor ST1-Hel2A-2 that directly binds to the N-terminal domain of STAT1, but not other STAT family members, and inhibits STAT1 transcriptional activity (ACS Chem Biol, 2007. 2(12): 799). The inhibitor kills breast cancer cells at nanomolar concentrations but does not effect survival of normal mammary epithelial cells. We have now found that inhibition of STAT1 N-domain can further sensitize breast cancer cells to ionizing radiation. The mechanism for observed sensitization at least partially depends on down-regulation of STAT1 target genes, including pro-survival Hsp27. In addition, ST1-Hel2A-2 is capable of disrupting the STAT1 N-domain protein-protein interactions. Yeast two-hybrid screening has revealed that the STAT1 N-domain associates with double-stranded RNA-activated protein kinase (PKR) and DNA glycosylase NEIL1. Both PKR and NEIL1 facilitate DNA repair after ionizing radiation and protect mammalian cells from radiation-mediated cell death. ST1-Hel2A-2 disrupts STAT1 interactions with both proteins resulting in a reduced DNA repair capacity.

Our data suggest that a novel inhibitor of STAT1 decreases radiation resistance of breast cancer cells through downregulation of pro-survival genes and inhibition of DNA repair. Inhibition of STAT1 signaling appears to be a promising strategy in overcoming radiation resistance and can be used as an effective treatment of metastatic breast cancer when combined with conventional therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 489.

Early postnatal parathion exposure in rats causes sex-selective cognitive impairment and neurotransmitter defects which emerge in aging

Developmental exposure of rats to the organophosphate (OP) pesticides leads to altered neurobehavioral function in juvenile and young adult stages. The current study was conducted to determine whether effects of neonatal parathion exposure on cognitive performance persist in older adult and aged rats, and the relationship of behavioral changes to underlying cholinergic and serotonergic mechanisms. We administered parathion to rat pups on postnatal days 1-4, at doses spanning the threshold for the initial signs of systemic toxicity and for barely detectable cholinesterase inhibition (0.1 or 0.2 mg/kg/day). Beginning at 14 months of age and continuing until 19 months, the rats were trained in the 16-arm radial maze. Controls showed the normal sex difference in this spatial learning and memory task, with the males committing significantly fewer working memory errors than females. Neonatal parathion exposure eliminated the sex difference primarily by causing impairment in males. In association with the effects on cognitive performance, neonatal parathion exposure elicited widespread abnormalities in indices of serotonergic (5HT) and cholinergic synaptic function, characterized by upregulation of 5HT(2) receptors and the 5HT transporter, deficits in choline acetyltransferase activity and nicotinic cholinergic receptors, and increases in hemicholinium-3 binding to the presynaptic choline transporter. Within-animal correlations between behavior and neurochemistry indicated a specific correlation between working memory performance and hippocampal hemicholinium-3 binding; parathion exposure eliminated this relationship. Like the behavioral effects, males showed greater effects of parathion on neurochemical parameters. This study demonstrates the sex-selective, long-term behavioral alterations caused by otherwise nontoxic neonatal exposure to parathion, with effects increasingly expressed with aging.

Enhanced expression of SOS1 is detected in prostate cancer epithelial cells from African-American men

African-American (AA) men experience an increased risk of developing prostate cancers as well as increased mortality following treatment as compared to European-American (EA) men. The aim of our study was to identify biological factors with the potential to predispose AA men to prostate tumor progression and metastasis. To identify cancer-specific gene expression patterns in AA men, we established primary prostate cancer epithelial cells from 14 AA and 13 EA men. High-throughput microarrays were used to investigate differences in global gene expression comparing the two groups. Quantitative RT-PCR and immunohistochemistry validated mRNA and protein expression levels. RNAi knockdowns provided support for biological significance for the identified genes in prostate cancer cells. Son of sevenless homolog 1 (SOS1) was overexpressed in AA male-derived primary prostate cancer epithelial cells. Depletion of SOS1 in PC3 and DU145 prostate cancer cells resulted in decreased capacities for cell proliferation, migration and invasion, at least partially through inhibition of extracellular signal-regulated kinase 1 and 2. Tissue microarray analyses of SOS1 expression in prostate carcinomas correlated with Gleason's grades of tumors, consistent with a possible role in prostate cancer progression. Investigation of prostate cancer-derived epithelial cells has led to identification of SOS1 as a potential candidate biomarker and molecular therapeutic target in prostate cancer in AA men, consistent with the hypothesis that a biological basis exists for prostate cancer aggressiveness in AA men.

Persistent behavioral alterations in rats neonatally exposed to low doses of the organophosphate pesticide, parathion

Although developmental exposures of rats to low levels of the organophosphate pesticides (OPs), chlorpyrifos (CPF) or diazinon (DZN), both cause persistent neurobehavioral effects, there are important differences in their neurotoxicity. The current study extended investigation to parathion (PTN), an OP that has higher systemic toxicity than either CPF or DZN. We gave PTN on postnatal days (PND) 1-4 at doses spanning the threshold for systemic toxicity (0, 0.1 or 0.2 mg/kg/day, s.c.) and performed a battery of emotional and cognitive behavioral tests in adolescence through adulthood. The higher PTN dose increased time spent on the open arms and the number of center crossings in the plus maze, indicating greater risk-taking and overall activity. This group also showed a decrease in tactile startle response without altering prepulse inhibition, indicating a blunted acute sensorimotor reaction without alteration in sensorimotor plasticity. T-maze spontaneous alternation, novelty-suppressed feeding, preference for sweetened chocolate milk, and locomotor activity were not significantly affected by neonatal PTN exposure. During radial-arm maze acquisition, rats given the lower PTN dose committed fewer errors compared to controls and displayed lower sensitivity to the amnestic effects of the NMDA receptor blocker, dizocilpine. No PTN effects were observed with regard to the sensitivity to blockade of muscarinic and nicotinic cholinergic receptors, or serotonin 5HT(2) receptors. This study shows that neonatal PTN exposure evokes long-term changes in behavior, but the effects are less severe, and in some incidences opposite in nature, to those seen earlier for CPF or DZN, findings consistent with our neurochemical studies showing different patterns of effects and less neurotoxic damage with PTN. Our results reinforce the conclusion that low dose exposure to different OPs can have quite different neurotoxic effects, obviously unconnected to their shared property as cholinesterase inhibitors.

Persistent cognitive alterations in rats after early postnatal exposure to low doses of the organophosphate pesticide, diazinon

BACKGROUND

Developmental neurotoxicity of organophosphorous insecticides (OPs) involves multiple mechanisms in addition to cholinesterase inhibition. We have found persisting effects of developmental chlorpyrifos (CPF) and diazinon (DZN) on cholinergic and serotonergic neurotransmitter systems and gene expression as well as behavioral function. Both molecular/neurochemical and behavioral effects of developmental OP exposure have been seen at doses below those which cause appreciable cholinesterase inhibition.

OBJECTIVES

We sought to determine if developmental DZN exposure at doses which do not produce significant acetylcholinesterase inhibition cause persisting cognitive deficits.

METHODS

Rats were exposed to DZN on postnatal days 1-4 at doses (0.5 and 2 mg/kg/d) that span the threshold for cholinesterase inhibition. They were later examined with a cognitive battery tests similar to that used with CPF.

RESULTS

In the T-maze DZN caused significant hyperactivity in the initial trials of the session, but not later. In a longer assessment of locomotor activity no DZN-induced changes were seen over a 1-hour session. Prepulse inhibition was reduced by DZN exposure selectively in males vs. females; DZN eliminated the sex difference present in controls. In the radial maze, the lower but not higher DZN dose significantly impaired spatial learning. This type of nonmonotonic dose-effect function has previously been seen with CPF as well. The lower dose DZN group also showed significantly greater sensitivity to the memory-impairing effects of scopolamine a muscarinic acetylcholine antagonist.

CONCLUSIONS

Neonatal DZN exposure below the threshold for appreciable cholinesterase inhibition caused persisting neurocognitive deficits in adulthood. The addition of some inhibition of AChE with a higher dose reversed the cognitive impairment. This non-monotonic dose-effect function has also been seen with neurochemical effects. Some of the DZN effects on cognition resemble those seen earlier for CPF, some differ. Our data suggest that DZN and CPF affect transmitter systems supporting memory function, differently, implying participation of mechanisms other than their common inhibition of cholinesterase.

Rationally designed inhibitors identify STAT3 N-domain as a promising anticancer drug target

Activation of the signal transducer and activator of transcription 3 (STAT3) is frequently detected in many cancer types. Activated STAT3 may participate in oncogenesis by stimulating cell proliferation and resisting apoptosis, as well as promoting tumor angiogenesis, invasion, and migration. Many STAT3-dependent cellular responses are mediated through interactions with other proteins, and the amino-terminal domain (N-domain) of STAT3 was proposed to be responsible for this. Our NMR studies revealed that synthetic analogs of the STAT4 second alpha-helix bind to the N-domain and perturb its structure. Structural data available for the STAT4 N-domain was used for the rational design of STAT3 helix 2 analogs with enhanced biological activity. Cell-permeable derivatives of the STAT3 second helix were found to directly and specifically bind to STAT3 but not STAT1 as determined by FRET analysis in cells expressing GFP-STAT3 and GFP-STAT1. Furthermore, they potently induced apoptotic death in breast cancer cells but not normal breast cells or STAT3-deficient fibroblasts. The inhibitors caused significant changes in the mitochondrial potential of cancer cells, leading to cell death. These compounds not only are promising drug candidates but also offer a convenient tool for studying the mechanisms of action of STAT transcription factors and have facilitated our understanding of the crucial role of the N-domain in STAT3 function.

Developmental diazinon neurotoxicity in rats: later effects on emotional response

Developmental exposure to the organophosphorus pesticides chlorpyrifos and diazinon (DZN) alters serotonergic synaptic function at doses below the threshold for cholinesterase inhibition, however there are some indications that the two agents may differ in several important attributes. Previously, we found that low-dose chlorpyrifos exposure in neonatal rats causes lasting changes in emotional response and in the current study we did a comparable evaluation for DZN. Male and female Sprague-Dawley rat pups (N=10-12 of each sex per treatment group) were given 0, 0.5 or 2 mg/(kg day) of DZN s.c. daily on postnatal days (PND) 1-4. These doses bracket the threshold for barely-detectable cholinesterase inhibition. Starting on PND 52, these rats began a battery of tests to assess emotional reactivity. In the elevated plus maze, there was a slight decrease in the time spent in the open arms for DZN-exposed males, while DZN-exposed females were not different from control females. In the novelty-suppressed feeding test, DZN-exposed males had significantly shorter latencies to begin eating than did control males, reducing the values to those normally seen in females. DZN-exposed rats of either sex showed reduced preference for chocolate milk in the anhedonia test that compared the consumption of chocolate milk to water. These findings show that neonatal exposures to DZN at a dose range below the threshold for cholinesterase inhibition nevertheless evokes specific, later alterations in emotional behaviors, particularly in males. The effects show not only some similarities to those of chlorpyrifos but also some differences, in keeping with neurochemical findings comparing the two agents.

ELR+-CXC chemokines and their receptors in early metanephric development

Although originally identified as mediators of inflammation, it is now apparent that chemokines play a fundamental role in tissue development. In this study, ELR(+)-CXC chemokine family members CXCL2 and CXCL7, along with their preferred receptor CXCR2, were expressed at the earliest stages of metanephric development in the rat, and signaling through this receptor was required for the survival and maintenance of the undifferentiated metanephric mesenchyme (MM). A specific antagonist of the CXCR2 receptor SB225002 induced apoptosis in this population but did not affect more mature structures or cells in the ureteric bud. CXCL7 treatment of isolated MM elicited an angiogenic response by upregulation of matrix metalloprotease 9 and endothelial and mesangial markers (platelet-endothelial cell adhesion molecule, Megsin, Thy-1, PDGF receptor alpha, and vascular alpha-actin) and induced SB225002-sensitive cell invasion through a matrix. Because Wilms' tumor cells may similarly depend on CXCR2 signaling for survival, primary tumor samples were analyzed, and 15 of 16 Wilms' tumors were found to be CXCR2 positive, whereas grossly normal kidney tissues from tumor patients or renal cell carcinomas were CXCR2 negative. Furthermore, cell lines derived from Wilms' tumors but not those from renal cell carcinomas were sensitive to SB225002-induced apoptosis. These data provide evidence for a prosurvival and proangiogenic role of ELR(+)-CXC chemokines and their receptor CXCR2 during metanephric development and suggest a novel mechanism for chemotherapeutic intervention in Wilms' tumor.

The role of ascorbate in the modulation of HIF-1alpha protein and HIF-dependent transcription by chromium(VI) and nickel(II)

Molecular oxygen is involved in hydroxylation and subsequent degradation of HIF-1alpha, a subunit of HIF-1 transcription factor; therefore oxygen shortage (hypoxia) stabilizes this protein. However, HIF-1alpha can also be stabilized by transition metal ions in the presence of oxygen, suggesting that a different mechanism is involved in metal-induced hypoxic stress. Recently, we showed that the depletion of intracellular ascorbate by metals may lead to the inhibition of hydroxylases. Because nickel(II) has similarity to iron(II), an alternative hypothesis suggests that iron substitution for nickel in the enzyme inhibits hydroxylase activity. Here we investigated the induction of HIF-1 by another metal, chromium, which cannot replace iron in the enzyme. We show that chromium(VI), but not chromium(III), can oxidize ascorbate both in cells and in a cell-free system. In agreement with these data chromium(VI) stabilizes HIF-1alpha protein in cells only until it is reduced to chromium(III). In contrast, nickel(II) was found to be a catalyst, which facilitated continuous oxidation of ascorbate by ambient oxygen. These data correlate with extended stabilization of HIF-1alpha after acute exposure to nickel(II). The HIF-1-dependent reporter assays revealed that 20-24 h was required to fully develop the HIF-1 transcriptional response, and the acute exposure to nickel(II), but not chromium(VI), meets this requirement. However, repeated (chronic) exposure to chromium(VI) can also lead to extended stabilization of HIF-1alpha. Thus, the obtained data emphasize the important role of ascorbate in regulation of HIF-1 transcriptional activity in metal-exposed human lung cells.

Serine-phosphorylated STAT1 is a prosurvival factor in Wilms' tumor pathogenesis

Wilms' tumor (WT), one of the most common pediatric solid cancers, arises in the developing kidney as a result of genetic and epigenetic changes that lead to the abnormal proliferation and differentiation of the metanephric blastema. As activation of signal transducers and activators of transcription (STATs) plays an important role in the maintenance/growth and differentiation of the metanephric blastema, and constitutively activated STATs facilitate neoplastic behaviors of a variety of cancers, we hypothesized that dysregulation of STAT signaling may also contribute to WT pathogenesis. Accordingly, we evaluated STAT phosphorylation patterns in tumors and found that STAT1 was constitutively phosphorylated on serine 727 (S727) in 19 of 21 primary WT samples and two WT cell lines. An inactivating mutation of S727 to alanine reduced colony formation of WT cells in soft agar by more than 80% and induced apoptosis under conditions of growth stress. S727-phosphorylated STAT1 provided apoptotic resistance for WT cells via upregulation of expression of the heat-shock protein (HSP)27 and antiapoptotic protein myeloid cell leukemia (MCL)-1. The kinase responsible for STAT1 S727 phosphorylation in WT cells was identified based upon the use of selective inhibitors as protein kinase CK2, not p38, MAP-kinase kinase (MEK)1/2, phosphatidylinositol 3'-kinase, protein kinase C or Ca/calmodulin-dependent protein kinase II (CaMKII). The inhibition of CK2 blocked the anchorage-independent growth of WT cells and induced apoptosis under conditions of growth stress. Our findings suggest that serine-phosphorylated STAT1, as a downstream target of protein kinase CK2, plays a critical role in the pathogenesis of WT and possibly other neoplasms with similar STAT1 phosphorylation patterns.

Species-specific effects of the hepatocarcinogens 3'-methyl-4-dimethyl-aminoazobenzene and ortho-aminoazotoluene in mouse and rat liver

The effects of rat-specific hepatocarcinogen 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB), mouse-specific hepatocarcinogen ortho-aminoazotoluene (OAT), non-species-specific hepatocarcinogen diethylnitrosamine (DENA), and non-carcinogenic 4'-methyl-4-dimethylaminoazobenzene (4'-MeDAB) on glucocorticoid induction of tyrosine aminotransferase (TAT) and DNA-binding activity of hepatocyte nuclear factor 3 (HNF3) family of transcription factors were investigated with carcinogen-susceptible and -resistant animals. Species-specific hepatocarcinogens 3'-MeDAB and OAT strongly inhibited glucocorticoid induction of TAT in the liver of susceptible but not resistant animals. DENA, which is highly carcinogenic for the liver of both rats and mice inhibited glucocorticoid induction of TAT in both species, while non-carcinogenic 4'-MeDAB was absolutely ineffective both in rats and mice. The inhibition of TAT activity by the carcinogens was due to reduced levels of TAT mRNA, which is most likely to be a result of the reduced rate of transcription initiation of the TAT gene. In all cases, the TAT inhibition was accompanied by significant reduction of DNA-binding activity of the HNF3 transcription factor, which is known to be critical to glucocorticoid regulation of TAT gene. We also demonstrated that the described species-specific effects of OAT and of 3'-MeDAB on HNF3 DNA-binding activity may be initiated not only by administration in vivo, but also by their direct administration to homogenate, intact nuclei or nuclear lysate, but not to nuclear extract fraction, obtained by precipitation with 0.32 g/mL of ammonium sulfate (Fraction I). We showed, that a factor responsible for this effect might be precipitated in 0.32-0.47 g/mL interval of ammonium sulfate concentration. In contrast, non-specific hepatocarcinogen DENA was effective upon being added directly to Fraction I, implying a different mechanism of its action.

[Activity of lectins of winter wheat seedlings infected with mycoplasma and treated with salicylic acid]

Changes in activity of soluble and cell wall lectins have been revealed in seedlings of winter wheat Triticum aestivum L. cultivar Mironovskaya 808 after infection with mycoplasma Acholeplasma laidlawii 118. The protective effect of salicylic acid was manifested as negating the bursts of lectin activity induced by mycoplasma infection.

o-Aminoazotoluene does induce the enzymes of its own mutagenic activation in mouse liver

The objective of this study was to investigate the CYP1A1 and CYP1A2 mRNAs and enzyme activities in mouse liver during induction with o-aminoazotoluene (OAT) as well as the capability of the hepatic S9-fraction from OAT-treated mice to induce its own activation to mutagens in the Ames test using S. typhymurium strain TA98. The data obtained indicate that when used at appropriate doses, OAT is a PAH-type inducer of mouse hepatic microsomal monooxygenases, which activity is not less than that of the known inducer 3,4-benzo[alpha]pyrene. In the absence of S9-fraction enzymes no OAT-mediated mutagenicity was observed in the Ames test. In the presence of the S9-fraction from OAT-pretreated mice, OAT induced as high revertant numbers, as it did in the presence of the S9 fraction from the liver of Aroclor 1254-treated mice. Thus, OAT does induce the enzymes of its own mutagenic activation in mouse liver.

[Lectin and mitotic activities in root meristems of winter wheat under oryzalin effect]

The effect of oryzalin, a microtubule polymerization inhibitor (10 MM), on lectin and mitotic activities (mitotic index and duration of mitotic phases) was studied in unhardened (23 degrees C) and hardened (7 days, 2-3 degrees C) winter wheat seedlings. Three wheat cultivars differing in their frost tolerance were compared. Oryzalin treatment (3 h) decreased activity of soluble lectins, increased activity of cell wall lectin mitotic index. Under these conditions, prolongation of anaphases and disappearance of telophases were detected. Plant hardening reduced the sensitivity of cell wall lectins and mitotic activity to the cytoskeleton inhibitor due, presumably, to the appearance of cold-stable microtubules. Plant growing and hardening with oryzalin stopped mitoses and caused the appearance of polyploid cells and cells with micronuclei. These abnormalities were preserved after hardening. The results obtained demonstrate an important role of microtubules in adaptation of plants to low temperature.

[Change in lectin specificity of winter wheat seedlings in the course of infection with mycoplasms]

The activity of soluble lectins in leaves and roots of seedlings of winter wheat (Triticum aestivum L.) cultivar Mironovskaya 808 increased 1 day and 2 days, respectively, after infection with the mycoplasma Acholeplasma laidlawii 118. Analysis of acid-soluble proteins of wheat leaves by PAGE revealed the appearance of 22- and 20-kDa polypeptides, the disappearance of a 14-kDa polypeptide, and an increase in the content of polypeptides with molecular weights of 76, 48, 25, and 18 kDa. The 18-kDa polypeptide is a subunit of wheat germ agglutinin. A change in the activity of lectins may be a nonspecific response of plants to infection with the pathogen.

STRA13 Interacts with STAT3 and Modulates Transcription of STAT3-dependent Targets

STRA13 is a pVHL-dependent bHLH transcription factor up-regulated on the mRNA level in multiple cancer cell lines and implicated recently in the regulation of immune cell homeostasis and autoimmunity. In searching for STRA13-interacting proteins with oncogenic potential by the yeast two-hybrid screening, we identified STAT3 beta as a STRA13-binding partner. We showed that STRA13 binds predominantly to phosphorylated (active) STAT3 alpha and beta isoforms via its HLH and C-terminal regions. We also found that STRA13 was able to activate transcription from STAT-dependent cis-elements. Expression of endogenous STRA13 was shown to be cytokine-inducible, consistent with STRA13 involvement in STAT-dependent transcription regulation. We demonstrated that the STAT3-regulated promoter of the pro-apoptotic Fas gene was activated upon STRA13 over-expression and that co-expression of STRA13 with STAT3 beta or STAT3 alpha modulated the transcriptional outcome. Forced expression of STRA13 induced apoptosis, in agreement with the STRA13 activation effect on the Fas promoter. Simultaneous expression of STRA13 and STAT3 beta resulted in alleviation of the STRA13 pro-apoptotic effect. Thus, for the first time, we identify STRA13 as a STAT3 partner and provide a consistent line of evidence for STRA13 involvement into regulation of apoptosis via the STAT pathways.

[Different sensitivity of inbred mice to hepatocarcinogen ortho-aminoazotoluene may be due to differences in the negative control mechanisms of hepatocyte proliferation]

A most convenient model to study mechanisms of live organism response to chemical carcinogens is tumor induction in murine liver by aminoazodyes, in particular by ortho-aminoazotoluene (OAT). We studied both early and late stages of hepatocarcinogenesis on several lines of inbred mice differing in sensibility to OAT. By means of autoradiography, we examined proliferative activity of hepatocytes obtained from the liver of sensitive (A/He, DD, SWR) and resistant to OAT AKR, CC57Br, BALB/c lines of mice, which were injected carcinogen. The level of p53, p21Cip1, bax, mdm2, cyclin G, gadd45 genes expression in the liver of mice of different lines given OAT injection was studied by multiplex PCR method. Carcinogen caused a decrease of hepatocyte proliferative activity induced by partial hypatectomy (PHE), and an increase in p53, p21Cip, bax, mdm2, and cyclin G genes within mice of A/He, DD and SWR lines. Cell fusion experiments on hepatocytes obtained from regenerating murine liver sensitive to A/He line carcinogen and given long-time OAT administrations with resting and proliferating fibroblasts of NIH 3T3 mice revealed no obvious suppression of DNA synthesis in heterokaryons. Unlike, in fusion experiments on serum-stimulated fibroblasts with hepatocytes obtained from the liver of BALB/c line mice also given OAT suppression of DNA synthesis in stimulated fibroblasts in heterokaryons was observed 15 days following PHE. These results enable us to conclude that OAT administrations break negative endogenous mechanisms of hepatocyte proliferation control in the liver of mice sensitive to carcinogenes.

[mRNA level and cytochrome P450 1A activity in the liver of C57BL mice induced by various xenobiotics]

The rate of hepatic cytochrome P450 Cypla1 and Cyp1a2 induction was investigated in C57BL male mice during induction with o-aminoazotoluene (OAT), benzo[a]pyrene (BP) and 1,4-dihydroxyanthraquinone (AQ). The Cypla1 mPNA level determined by quantitative RT-competitive PCR increased more than three orders of magnitude during induction with OAT and BP compared with untreated animals and remained unchanged during induction with AQ. The Cypla2 mRNA level was only 8.5, 18.7 and 1.9 times higher during induction with OAT, BP and AQ respectively than in untreated mice. At the same time 7-Ethoxyresorufin-O-deethylase (EROD) and 7-Methoxyresorufin-O-demethylase (MROD) activities of Cypla were also investigated in liver. The increase of Cypla1 mRNA level correlated with the increase of EROD activity. This suggests involvement of the transcriptional mechanism of the inducibility of this enzyme. In the case of Cypla2 there was insignificant increase of its mRNA level but high catalytic activity registered in liver in response to injection of the inductor of MR metabolism. This can imply the posttranscriptional mechanism of Cypla2 regulation. During induction with AQ the Cypla1 mRNA level remained unchanged, but the EROD activity increased almost 20-fold. The latter suggests insufficient specificity of this substrate for Cypla1. Thus, on the basis of the data obtained, the mRNA level can be considered as more accurate estimation of Cypla1 and Cypla2 inducibility, than the determination of the enzyme activity.

Species specific hepatocarcinogen inhibition of the glucocorticoid induction of tyrosine aminotransferase gene in mouse and rat liver

3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB) is a potent hepatocarcinogen in rats and a weak carcinogen in mice, whereas o-aminoazotoluene (OAT) is a potent hepatocarcinogen in mice but weak hepatocarcinogen in rats. They significantly suppress glucocorticoid induction of tyrosine aminotransferase (TAT) in the liver of sensitive animals and have minor effect on the induction of this enzyme in the liver of resistant animals (3'-MeDAB-treated mice and OAT-treated rats). The inhibitory effect of these carcinogens is realized at the level of gene transcription (decreased accumulation of TAT mRNA). This effect is mediated via reduction of DNA-binding activity of transcription factor HNF3 (without decrease of its content) without any involvement of the glucocorticoid receptor. It was shown that carcinogens influence DNA-binding activity of HNF3 via an unknown nuclear factor.