Correlation between the activation of Neu tyrosine kinase and promotion of foci formation induced by selected organochlorine compounds in the MCF-7 model system

Exposure to Organochlorine Pesticides and Female Breast Cancer Risk According to Molecular Receptors Expression: a Systematic Review and Meta-analysis of Epidemiological Evidence

PURPOSE OF REVIEW

Organochlorine pesticides (OCP) have been proposed as potential mammary carcinogens since they interact with steroid signaling pathways. However, the epidemiological results are not conclusive. Most studies have evaluated breast cancer (BC) as a single entity without considering the different molecular expressions, including estrogen receptor (ER), progesterone receptor (PR), and HER2, that could differ in their association with these contaminants. Hence, we assessed the association between biological concentration of OCP and BC, according to its molecular receptor expression, based on a systematic review and meta-analysis.

RECENT FINDINGS

Of the 141 articles eligible for full-text review, nine met the inclusion criteria. The way in which molecular expression was reported was heterogeneous; therefore, the inclusion of studies in the meta-analysis was limited to eight articles. A negative association was identified for β-hexachlorocyclohexane and trans-nonachlor with ER + tumors and between hexachlorobenzene and ER - tumors. No associations were observed for p,p'-dichlorodiphenyldichloroethylene, cis-nonachlor, and dieldrin, and it was not possible to evaluate the associations between OCP with HER2 expression or triple-negative tumors due to lack of data. The results suggest that some OCP might be associated with BC depending on the expression of ER. However, the evidence is not conclusive due to the scarce data. We identified several methodological aspects to fill the gaps in knowledge and increase the comparability among studies.

Breast and prostate glands affected by environmental substances (Review)

Environmental endocrine disruptor chemicals are substances that can alter the homeostasis of the endocrine system in living organisms. They can be released from several products used in daily activities. Once in the organism, they can disrupt the endocrine function by mimicking or blocking naturally occurring hormones due to their similar chemical structure. This endocrine disruption is the most important cause of the well‑known hormone‑associate types of cancer. Additionally, it is decisive to determine the susceptibility of each organ to these compounds. Therefore, the present review aimed to summarize the effect of different environmental substances such as bisphenol A, dichlorodiphenyltrichloroethane and polychlorinated biphenyls in both the mammary and the prostate tissues. These organs were chosen due to their association with the hormonal system and their common features in carcinogenic mechanisms. Outcomes derived from the present review may provide evidence that should be considered in future debates regarding the effects of endocrine disruptors on carcinogenesis.

Timing of Environmental Exposures as a Critical Element in Breast Cancer Risk

OBJECTIVE

The role of the chemical environment in disease initiation or progression is becoming more evident. Endocrine disruption via environmental chemicals is now well documented in humans, rodent research models, and wildlife. Breast cancer is an endocrine-based disease whose risk may be modified by environmental exposures. Our purpose is to encourage more investigation into early life environmental exposures as they relate to breast cancer risk factors and disease over a lifetime.

EVIDENCE

The 2009 President's Cancer Panel, 2012 Institute of Medicine, 2013 Interagency Breast Cancer and the Environment Research Coordinating Committee reports, and research publications dated ≥2012 in PubMed were used to inform our perspective.

CONSENSUS PROCESS

Literature was reviewed and evidence gathered on the effects of the environment on risk of breast cancer or mammary tumor development in animal research models as it pertained to the influence of timing of exposure on later-life outcomes.

CONCLUSIONS

Evidence has accumulated for several chemicals that environmental factors have a stronger effect on breast cancer risk when exposure occurred early in life. The insecticide, dichlorodiphenyltrichloroethane, is an excellent example and is just one of several chemicals for which there seems to be both animal and human evidence for the developmental basis of adult disease. The developing breast undergoes many changes in early life, leaving it vulnerable to the effects of epigenetic marks, endocrine disruption, and carcinogens. More research is needed in the area of early beginnings of breast cancer, with prevention of the disease as the ultimate goal.

DDT Exposure in Utero and Breast Cancer

CONTEXT

Currently no direct evidence links in utero dichlorodiphenyltrichloroethane (DDT) exposure to human breast cancer. However, in utero exposure to another xenoestrogen, diethylstilbestrol, predicts an increased breast cancer risk. If this finding extends to DDT, it could have far-reaching consequences. Many women were heavily exposed in utero during widespread DDT use in the 1960s. They are now reaching the age of heightened breast cancer risk. DDT exposure persists and use continues in Africa and Asia without clear knowledge of the consequences for the next generation.

HYPOTHESIS

In utero exposure to DDT is associated with an increased risk of breast cancer.

DESIGN

This was a case-control study nested in a prospective 54-year follow-up of 9300 daughters in the Child Health and Development Studies pregnancy cohort (n = 118 breast cancer cases, diagnosed by age 52 y and 354 controls matched on birth year).

SETTING AND PARTICIPANTS

Kaiser Foundation Health Plan members who received obstetric care in Alameda County, California, from 1959 to 1967, and their adult daughters participated in the study.

MAIN OUTCOME MEASURE

Daughters' breast cancer diagnosed by age 52 years as of 2012 was measured.

RESULTS

Maternal o,p'-DDT predicted daughters' breast cancer (odds ratio fourth quartile vs first = 3.7, 95% confidence interval 1.5-9.0). Mothers' lipids, weight, race, age, and breast cancer history did not explain the findings.

CONCLUSIONS

This prospective human study links measured DDT exposure in utero to risk of breast cancer. Experimental studies are essential to confirm results and discover causal mechanisms. Findings support classification of DDT as an endocrine disruptor, a predictor of breast cancer, and a marker of high risk.

Antiestrogenic activity of flavonoid phytochemicals mediated via the c-Jun N-terminal protein kinase pathway. Cell-type specific regulation of estrogen receptor alpha

Flavonoid phytochemicals act as both agonists and antagonists of the human estrogen receptors (ERs). While a number of these compounds act by directly binding to the ER, certain phytochemicals, such as the flavonoid compounds chalcone and flavone, elicit antagonistic effects on estrogen signaling independent of direct receptor binding. Here we demonstrate both chalcone and flavone function as cell type-specific selective ER modulators. In MCF-7 breast carcinoma cells chalcone and flavone suppress ERα activity through stimulation of the stress-activated members of the mitogen-activated protein kinase (MAPK) family: c-Jun N-terminal kinase (JNK)1 and JNK2. The use of dominant-negative mutants of JNK1 or JNK2 in stable transfected cells established that the antiestrogenic effects of chalcone and flavone required intact JNK signaling. We further show that constitutive activation of the JNK pathway partially suppresses estrogen (E2)-mediated gene expression in breast, but not endometrial carcinoma cells. Our results demonstrate a role for stress-activated MAPKs in the cell type-specific regulation of ERα function.

Cross-talk between non-genomic and genomic signalling pathways--distinct effect profiles of environmental estrogens

Estrogen receptor (ER) transcriptional cross-talk after activation by 17beta-estradiol (E2) has been studied in considerable detail, but comparatively little is known about the ways in which synthetic estrogen-like chemicals, so-called xenoestrogens, interfere with these signalling pathways. E2 can stimulate rapid, non-genomic signalling events, such as activation of the Src/Ras/Erk signalling pathway. We investigated how activation of this pathway by E2, the estrogenic environmental contaminants o,p'-DDT, beta-HCH and p,p'-DDE, and epidermal growth factor (EGF) influences the expression of ER target genes, such as TFF1, ER, PR, BRCA1 and CCND1, and the proliferation of breast cancer cells. Despite commonalities in their estrogenicity as judged by cell proliferation assays, the environmental contaminants exhibited striking differences in their non-genomic and genomic signalling. The gene expression profiles of o,p'-DDT and beta-HCH resembled the effects observed with E2. In the case of beta-HCH this is surprising, considering its reported lack of affinity to the "classical" ER. The expression profiles seen with p,p'-DDE showed some similarities with E2, but overall, p,p'-DDE was a fairly weak transcriptional inducer of TFF1, ER, PR, BRCA1 and CCND1. We observed distinct differences in the non-genomic signalling of the tested compounds. p,p'-DDE was unable to stimulate Src and Erk1/Erk2 activations. The effects of E2 on Src and Erk1/Erk2 phosphorylation were transient and weak when compared to EGF, but beta-HCH induced strong and sustained activation of all tested kinases. Transcription of TFF1, ER, PR and BRCA1 by E2, o,p'-DDT and beta-HCH could be suppressed partially by inhibiting the Src/Ras/Erk pathway with PD 98059. However, this was not seen with p,p'-DDE. Our investigations show that the cellular activities of estrogens and xenoestrogens are the result of a combination of extranuclear (non-genomic) and nuclear (genomic) events and highlight the need to take non-genomic effects and signalling cross-talk into consideration, when screening for environmental estrogens. Otherwise, chemicals devoid of ER affinity, such as beta-HCH, but with an effect profile otherwise similar to estrogens might be overlooked in safety testing.

Promotion of breast cancer by beta-hexachlorocyclohexane in MCF10AT1 cells and MMTV-neu mice

Background

Exposure to β-Hexachlorocyclohexane (β-HCH), a contaminant of the hexachlorohexane pesticide lindane, has been implicated as a risk factor in the development of breast cancers in epidemiological studies. Previous studies in our laboratory have demonstrated the ability of β-HCH to elicit its actions via a ligand-independent activation of the estrogen receptor through increased c-Neu (= erbB₂ or HER-2) expression and kinase activation in both the BG-1 and MCF-7 cell lines. In addition, long term exposure (33 passages) to β-HCH was shown to promote the selection of MCF-7 cells which exhibit a more metastatic phenotype.

Methods

In this current study, we decided to investigate the long-term effects of β-HCH in both the MCF10AT1 cell line which was derived from a normal epithelial cell line by stably transfecting a mutated c-Ha-ras and a MMTV-Neu mouse model for mammary cancer in vivo. MCF10AT1 cells were exposed for 20 passages with β-HCH, 4-OH-Tamoxifen (Tam), or 17-β-estradiol (E₂) after which cells were analyzed for proliferation rates and mRNA expression by RT-PCR. In our in vivo studies, MMTV-Neu mice were injected with β-HCH and observed for tumor formation over a 70 week period.

Results

β-HCH and Tam selected MCF10AT1 cells demonstrated increased mRNA expression of MMP-13 (collagenase-3) a marker of increased invasiveness. β-HCH treatment was also seen to increase the expression in a number of proto-oncogenes (c-Neu, Cyclin D1, p27), cell status markers (Met-1, CK19), and the inflammatory marker NFκB. Previous studies, have demonstrated the role of these markers as evidence of malignant transformations, and further illustrate the ability of β-HCH to be carcinogenic. To demonstrate β-HCH's tumorigenic properties in an in vivo system, we used an MMTV-Neu mouse model.

MMTV-Neu is a c-Neu overexpressing strain which has been shown to spontaneously develop mammary tumors at later stages of aging. In this experiment, β-HCH exposure was shown to both accelerate the appearance (~8 weeks for median tumor-free period) and incidence (~25% increase at the end of the test period) of tumors when compared to control mice receiving only the corn-oil vehicle.

Conclusion

Based upon these results, it was concluded that β-HCH does act as a breast cancer promoter which exerts its tumorigenic activity via increased c-Neu expression.

Estrogenic effect of procymidone through activation of MAPK in MCF-7 breast carcinoma cell line

Procymidone modifies sexual differentiation in vitro and induces estrogenic activity in primary cultured rainbow trout hepatocytes, as shown by an increase in the contents of vitellogenin and heat shock proteins. Since this dicarboximide fungicide is found in human tissues, it was considered of interest to investigate its ability to induce endocrine damage in the MCF-7 human cell line. The mechanism of this estrogenic action was also evaluated. Procymidone 100 microM stimulated cell growth from day 3 up to day 12 and raised the level of pS2 on day 3. Although procymidone does not bind the estrogen receptor (ER), the antiestrogen ICI 182780 inhibited its effect on cell growth and pS2 content, suggesting that the ER is involved indirectly in these effects. In exploring the mechanism of ER indirect activation we found that the antibody against c-Neu receptor (9G6) did not modify procymidone's effects on cell growth and pS2 expression. Thus, procymidone does not bind the c-Neu membrane receptor, excluding this indirect ER activation pathway. We also found that procymidone induced mitogen-activated protein kinase (MAPK) at 15 and 30 min, and that PD 98059, a MAPK (Erk1/2) inhibitor, prevented procymidone's effects on cell growth and pS2, indicating that MAPK activation is responsible for procymidone ER activation. The production of reactive oxygen species (ROS) with these times and elimination of the phenomenon by alpha-tocopherol (alpha-T), a ROS scavenger, is proof that oxygen free-radical production is at the basis of the MAPK activation by procymidone.

Induction of cell proliferation, micronuclei and hyperdiploidy/polyploidy in the mammary cells of DDT- and DMBA-treated pubertal rats

The environmental estrogen, dichlorodiphenyltrichloroethane (DDT), and its metabolites have been implicated in the development of breast cancer through mechanisms that remain to be elucidated. It has been hypothesized that exposure to DDT and its metabolites, during critical periods of development, can contribute to an elevated risk for breast cancer in adults. In the present study, we have investigated the effect of o,p'-DDT on mammary gland cell proliferation and chromosomal alterations, in a rat mammary cancer model (commonly used to study human cancer), to gain insights into its potential role in the development of breast cancer. Twenty-one-day-old female Sprague-Dawley (SD) rats were administered o,p'-DDT, 7,12-dimethylbenz[a]anthracene (DMBA), genistein, DDT+DMBA, or DDT+DMBA+genistein, over a 14-day period. To determine changes in chromosome number and structure, we used the micronucleus assay as well as multicolor fluorescence in situ hybridization (FISH) region-specific DNA probes for rat chromosomes 4 and 19. Cell proliferation was evaluated using 5-bromo-2'-deoxyuridine (BrdU). Significant increases in BrdU-incorporated cells were seen in the rats treated with DDT+DMBA. Although micronucleus frequencies were somewhat elevated in several of the treatment groups, significant increases were not seen in any of them. Significant increases in numerical chromosomal aberrations were detected in all of the DDT- and DMBA-treated groups. Genistein significantly reduced BrdU incorporation and polyploidy in the DDT+DMBA-treated rats. These initial studies indicate that DDT and DMBA can induce cellular and chromosomal alterations in the rat mammary gland, which is consistent with the hypothesis that these agents can induce early events in mammary carcinogenesis.

Xenobiotic-induced TNF-alpha expression and apoptosis through the p38 MAPK signaling pathway

Some xenobiotics, such as dichlorodiphenyltrichloroethane (DDT), bind to and activate estrogen receptors (ERs), eliciting estrogenic effects in both wildlife and humans. However, our laboratory and others have demonstrated that DDT and DDT-like compounds target non-ER pathways. In search for a molecular mechanism we recently established that DDT and its metabolites stimulate activator protein-1 (AP-1)-mediated gene expression through the p38 mitogen-activated protein kinase (MAPK) cascade. Here, we determined that DDT-induced p38 activity produces a novel environmental signaling pathway in endometrial Ishikawa and human embryonic kidney (HEK) 293 cells. Xenobiotic exposure stimulates expression of the death ligand, tumor necrosis factor-alpha (TNF-alpha) as demonstrated using RT-PCR and reporter gene assays. Furthermore, DDT-induced p38 activity led to the release of cytochrome c from the mitochondria and activation of caspase-3/7. Ultimately, DDT-treated cells underwent cell death. Taken together, these data demonstrate DDT induces both the expression of the death ligand TNF-alpha and apoptosis through a p38 MAPK-dependent mechanism.

Age at natural menopause and exposure to organochlorine pesticides in Hispanic women

A cross-sectional study was conducted to evaluate the relationship between exposure to selected organochlorine pesticides (OCP) (p,p'-DDT, p',p'-DDE, dieldrin, hexachlorobenzene, beta-hexachlorocyclohexane [beta-HCH], oxychlordane, trans' nonachlor) and age at natural menopause in a sample of 219 menopausal women participating in the Hispanic Health and Nutrition Examination Survey in 1982-1984. Information on age at menopause, reproductive history, demographic variables, and potential confounding variables was collected via interview. Analysis of variance was employed to compare adjusted mean age at natural menopause among women by category of serum OCP level. Serum levels of p,p'-DDT, p,p'-DDE, beta-HCH, and trans-nonachlor were associated with a younger age at menopause. In particular, women with exposure levels in the highest exposure categories (serum p,p'-DDT > or = 6ppb, beta-HCH > or = 4ppb, or trans-nonachlor > or = 2ppb) had an adjusted mean age at menopause on average 5.7, 3.4, and 5.2 yr earlier, respectively, than women with serum levels of these pesticides below the detection limit. Women with serum p,p'-DDE levels greater than 23.6 ppb (highest quintile) had an adjusted mean age at menopause 1.7 yr earlier than women with serump,p'-DDE levels less than 5.5 ppb (lowest quintile). However, no consistent dose-response effect was apparent across low, medium, and high exposure categories. Interactions were detected for p,p'-DDT in combination with beta-HCH, trans-nonachlor, or oxychlordane, as well as beta-HCH in combination with oxychlordane.

Long-term exposure to beta-hexachlorocyclohexane (beta-HCH) promotes transformation and invasiveness of MCF-7 human breast cancer cells

Due to its lipophilicity and persistence, an organochlorine compound, beta-hexachlorocyclohexane (beta-HCH), is known to frequently accumulate in human adipose and breast tissues. An epidemiological study has indicated that exposure to beta-HCH could be one of the significant environmental risk factors for the development of human breast cancers. Additionally, beta-HCH has recently been identified as an environmental estrogen capable of activating estrogen receptor (ER) through a ligand-independent pathway. In the present investigation, we examined the impact of long-term in vitro exposure to beta-HCH on cell transformation and the metastatic potentials of MCF-7 cells. We found that continuous exposure of MCF-7 cells to beta-HCH at 100 nM and 1 microM or to 17beta-estradiol (E(2)) at 1 nM for up to 13 months (33 passages) not only enhanced their transformation tendencies but also promoted their invasiveness. Western blot analysis revealed that beta-HCH induced transformation-related biochemical changes in MCF-7 cells, such as a decline in the levels of ERalpha and p44/42 MAP kinase and a significant increase in expression of c-ErbB2 and MMP-9 levels. In contrast, long-term E(2) treatment resulted in the downregulation of ERalpha and p44/42 MAP kinase and upregulation of MMP-9 only, but no changes in c-ErbB2. Together, these results indicate that these biochemical changes induced by beta-HCH are consistent with the events taking place in these cells to promote the phenotypical expression of transformed cells. Our results provide the in vitro mechanistic basis supporting the hypothesis that beta-HCH is one of the epigenetic risk factors assisting the progression of breast cancer cells to an advanced state of malignancy.

Comparison of the characteristic of estrogenic action patterns of beta-HCH and heregulin beta1 in MCF-7 human breast cancer cells

In this study, we compared the estrogenic action pattern of beta-HCH to another ErbB2 activating agent, heregulin beta1 (HRG), along with 17beta-estradiol and epidermal growth factor, to understand the similarities and differences of their action mechanisms. Not surprisingly, most of the initial test results indicated that the two agents, beta-HCH and HRG, are remarkably similar in several estrogenicity tests. However, in-depth biochemical studies revealed that there are some distinct differences between these two compounds in affecting ErbB2 and ErbB3 at early stages of their action. Immunocoprecipitation and Western blot studies indicated that beta-HCH mainly promotes dimerization of ErbB2 and ErbB3 at early time points, whereas HRG causes their dimerization with a rapid and significant rise in their tyrosine phosphorylation levels. These results indicate that, while both beta-HCH and HRG act through ErbB2, their initial actions differ. To understand the long-term consequence of such differential actions of these two agents, we tested the effect of a number of standard pathway specific inhibitors on their actions to induce foci formation after 2 weeks of exposure. The most conspicuous difference between beta-HCH and HRG in MCF-7 foci formation test was their response to 4-hydroxytamoxifen and LY294002, a PI3K inhibitor, i.e., the action of beta-HCH was inhibited by 4-hydroxytamoxifen but stimulated by LY294002, whereas that of heregulin was suppressed by LY294002 but stimulated by 4-hydroxytamoxifen. It appears, therefore, that the action of the latter relies more heavily on the PI3K route as compared to that of the former which has been shown to mainly act through p42/44 MAPK. These differences may account for their differential sensitivities to 4-hydroxytamoxifen.

Effects of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (p,p'-DDT) on 3T3-L1 and 3T3-F442A adipocyte differentiation

Based upon our initial observations that 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (p,p'-DDT) induces a concentration-dependent increase in 3T3-L1 adipocyte differentiation, the mechanism of the p,p'-DDT-induced adipocyte differentiation was studied, using 3T3-L1 and 3T3-F442A cells. Since, it is known that the differentiation of the 3T3-L1 adipocyte cell line involves the induction of the transcription factors CCAAT enhancer binding protein beta (C/EBPbeta), peroxisome proliferator-activated receptor gamma (PPARgamma), and C/EBPalpha, the possible role of these factors in p,p'-DDT-induced adipocyte differentiation had to be examined. It was found that p,p'-DDT-treated 3T3-L1 cells showed a concentration-dependent increase in the nuclear levels of both PPARgamma and C/EBPalpha protein. On the other hand, treatment with p,p'-DDT (20 microM) did not affect the expression pattern of C/EBPbeta protein during differentiation. Gel shift analysis of nuclear proteins for binding to the C/EBP recognition site of DNA showed an increase in binding activity at day 2 of differentiation in p,p'-DDT-treated cells. Supershift analysis revealed that this rise was caused mainly by a dramatic increase in the abundance of the C/EBPalpha-DNA complex. Similar increases were observed at days 4 and 7 after the induction of differentiation. Tumor necrosis factor alpha induced a strong inhibition of adipocyte differentiation, which was reversed by co-treatment with troglitazone, an activator of PPARgamma. p,p'-DDT was unable to reverse the inhibitory effect of tumor necrosis factor alpha on adipocyte differentiation in 3T3-L1 cells. 3T3-F442A is another preadipocyte cell line that can be induced to differentiate into adipocytes in the presence of insulin and fetal bovine serum. p,p'-DDT (20 microM) induced an alteration in the morphology of these cells at day 2 after the induction of differentiation. These cells however, were unable to become fully differentiated adipocytes. These data showed, therefore, the ability of p,p'-DDT to alter the differentiation process of adipocyte cell lines through the modification of transcription factors regulating this event.

Foci formation of MCF7 cells as an in vitro screening method for estrogenic chemicals

Previously we reported a novel phenomenon that some organochlorine compounds mainly act through activation of c-Neu tyrosine kinase without being strong agonists for the estrogen receptor. In this study we tested the possibility of developing an assay system to identify estrogenic compounds acting through this c-Neu-mediated mechanism. We describe herein an assay that utilizes foci formation of MCF7 cells as an endpoint, antibody 9G6 to neutralize the c-Neu-mediated pathway and 4-hydroxytamoxifen to block the ER. Aroclors 1242 and 1248, 2,2',3,5',6-pentachlorobiphenyl (PCB 95), 2,2'-dichlorobiphenyl (PCB), cis- and trans- permethrins, and chlorothalonil were found to render estrogenic effects through this c-Neu-mediated mechanism, while α and β- endosulfans appeared to act through a pathway independent of the c-Neu-mediated one. Pentachloronitrobenzene was found to be capable of antagonizing the 17β-estradiol effect, which has never been reported previously.

Estrogenic action of β-HCH through activation of c-Neu in MCF-7 breast carcinoma cells

β-HCH is known to be a poor agonist for the estrogen receptor (ER), and yet it has been shown to act like an estrogen in stimulating foci formation in MCF-7 cells. We investigated the reason for such an action of β-HCH, using a rat prolactin-luciferase reporter system transfected to MCF-7 cells. We found that the presence of c-Neu (erbB2), ER and ERE is needed for β-HCH to act estrogenic at the transcription activation level in this cell line. We compared the action of β-HCH to that of EGF which is known to act estrogenic without being an agonist for ER in this cell and found that their action patterns are quite similar, the only difference being that the former action is blocked by an antibody against c-Neu and the latter by both c-Neu and EGF receptor antibody. We concluded that β-HCH's estrogenic action in this cell model is mediated through "ligand-independent activation of ER pathway".

Increased ErbB-2 tyrosine kinase activity, MAPK phosphorylation, and cell proliferation in the prostate cancer cell line LNCaP following treatment by select pesticides

The oncogene erbB-2 codes for a receptor tyrosine kinase that functions as a key mitotic signal in a variety of cell types. Amplification or overexpression of erbB-2 occurs in many forms of cancer, such as of the breast, colon, and prostate, and is an indicator of poor prognosis in those diseases. In the human prostate cancer cell lines LNCaP and PC-3, erbB-2 kinase was activated by pesticides of different chemical classes: (1) the organochlorine insecticides beta-hexa-chlorocyclohexane (beta-HCH), o,p'-dichlorodiphenyltrichloroethane (o,p'-DDT), and heptachlor epoxide; (2) the pyrethroid insecticide trans-permethrin, and (3) the fungicide chlorothalonil. o,p'-DDT also causes phosphorylation of mitogen-activated protein kinase (MAPK) and cellular proliferation of the androgen-dependent LNCaP line. However, no proliferative effect was observed in the androgen-independent PC-3 line. The proliferative effect of o,p'-DDT in LNCaP could not be blocked by the androgen receptor antagonist p,p'-dichlorodiphenyldichloroethene (p,p'-DDE), indicating that this effect of o,p'-DDT does not occur through direct interaction with the androgen receptor. Together these data demonstrate a putative mechanism for the action of certain pesticides in hormonal carcinogenesis.