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

The mode of action of different organochlorine pesticides families in mammalians

Organochlorine pesticides (OCPs) show differences in their chemical structure, mechanism of toxicity, and target organisms. However, OCPs also have some common characteristics such as high persistence in the environment, bioaccumulation, and toxicity which lead to health issues. Nowadays, the toxicity of OCPs is well known, but we still do not know all the specific molecular mechanisms leading to their toxicity in mammalians. Therefore, this review aims to collect data about the mode of action of various classes of OCPs, highlighting their differences and common behavioural reactions in the human and animal body. To discuss the OCPs molecular pathways and fate in different systems of the body, three organochlorine insecticides were selected (Dichlorodiphenyltrichloroethane, Hexachlorocyclohexane and Chlordecone), regarding to their widespread use, with consequent effects on the ecosystem and human health. Their common biological responses at the molecular scale and their different interactions in human and animal bodies were highlighted and presented.

Estrogenic evaluation and organochlorine identification in blubber of North Sea harbour porpoise (Phocoena phocoena) stranded on the North Sea coast

Thirteen individual organochlorine compounds at 3 concentrations (80, 400, and 2000 ng/mL culture medium), as well as mixtures, were assayed for the estrogen receptor (ER) activation or inhibition, using a luciferase reporter gene assay (RGA). None of the PCB 138, 153, or 180 or their mixture induced a response in the RGA. o,p′-DDT was the most potent xenoestrogen from the DDT group, inducing a response already at 80 ng/mL. From the HCH and HCB group, only β-HCH (at 400 and 2000 ng/mL) and δ-HCH (at 2000 ng/mL) displayed estrogenic activities. These 13 organochlorines were determined by GC-MS in 12 samples of North Sea harbor porpoise blubber. The PCBs were the main contaminants. Within each group, PCB 153 (6.0 × 10²~4.2 × 10⁴  μg/kg), p,p′-DDE (5.1 × 10²~8.6 × 10³  μg/kg), and HCB (7.6 × 10¹~1.5 × 10³  μg/kg) were the compounds found in highest concentrations. The hormonal activity of the porpoise blubber samples was also assayed in RGA, where two samples showed estrogenic activity, seven samples showed antiestrogenic activity, and one sample showed both estrogenic and antiestrogenic activity. Our results suggest that the 13 POPs measured by GC-MS in the samples cannot explain alone the estrogenicity of the extracts.

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.

Serum free BG-1 cell proliferation assay: A sensitive method for determining organochlorine pesticide estrogen receptor activation at the nanomolar range

Most xenobiotic estrogeniety assay methods rely on direct agonist action on the estrogen receptor (ER) to approximate activation potential. Such methods do have drawbacks since some ER activating pesticides are weak or non-agonistic in ligand-binding assays. This study discusses a method that detects pesticide estrogenic actions regardless of ER ligand binding ability. Using a serum-free BG-1 ovarian cell culture model, we investigated the ability of several organochlorine (OC) pesticides to stimulate known estrogenic actions. We observed concentration dependent ER mediated cell proliferation in BG-1 cells using heptachlor epoxide (HE), beta-hexachlorohexane (beta-HCH), and endosulfan (Endo). In addition, we observed upregulation of the ERE-dependent proteins progesterone receptor and PS2. Gel-shift/EMSA studies for ERE binding further supported these OC's ERE activating abilities. All of these effects were abolished using ICI 164,384(ICI). Using the same culture conditions, we tested the blocking action of growth factor antibodies for erbB2(9G6) and insulin-like growth factor (IGF-Ab) receptors and discovered they inhibited BG-1 proliferation (9G6: HE and beta-HCH/ IGF-Ab: Endo.) This experiment confirms the existence of a possible cross-talk between ER and growth factor receptors in OC ligand-dependent activation and also validates this sensitive method for determining both ligand-dependent and independent estrogenic activity of selected pesticides.

Estrogenic activity of procymidone in rainbow trout (Oncorhynchus mykiss) hepatocytes: a possible mechanism of action

It is known that procymidone modifies sexual differentiation in vivo and in vitro, and that it induces vitellogenin (Vtg) synthesis in primary cultured rainbow trout hepatocytes. The aim of this study was to evaluate the mechanism underlying this latter in vitro estrogenic action. The cells were treated for 24 h with procymidone 150 microM (with 17beta-estradiol [E2] 20 microM as a positive control) combined with an estrogen receptor (ER) antagonist (tamoxifen 20 microM or ICI 182,780 1 microM) or, given the drug toxic action on the production of reactive oxygen species (ROS), a free radical scavenger (alpha-tocopherol 30 microM). The results from ELISA experiments provided evidence that procymidone Vtg-induction is inhibited by ER antagonists and by alpha-tocopherol suggesting that both ER and ROS are involved in this effect. The ROS detection revealed that the treatment with alpha-tocopherol and tamoxifen completely prevented ROS induction by procymidone, that was not inhibited by ICI 182,780. In exploring the mechanism mediating these events and its timing, we found that procymidone induced mitogen-activated protein kinase (MAPK) at 30 and 60 min, and that this effect was blocked by co-treatment with alpha-tocopherol. In summary, the results of the study clearly support the idea that the estrogenic activity of procymidone in primary cultured trout hepatocytes is mediated by ROS production, and that this activity is similar to that of the ligand-independent ER activation involving MAPK.

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.

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.