Study On The Effects Of Octylphenol And 17beta-estadiol On Apoptosis And Bcl-2 Family In Human Breast Cancer Cells

It has been indicated recently that apoptosis may play a critical role in the generation and progression of cancer, and apoptosis can be regulated in hormone-responsive tissues, especially in mammary epithelial cells by estrogen, which has a paradoxical effect on the expressions of Bcl-2 gene family ---a group of important regulators in the apoptotic pathways.In the environment, there exist many endocrine-disrupting chemicals. Some of them can mimic the function or activity of the endogenous estrogen 17beta-estradiol (E2) and have the influences on the development of sexual characteristics and cancers of hormone-responsive tissues. It has been shown that alkylphenols (APs), the degradation products of the widely used alkylphenol ethoxylates surfactants, is one kind of such chemicals. Although the chemical structures and characteristics of APs are far from those of the 17beta-estradiol, it can also bind the estrogen receptor(ER) and induce the proliferation of the estrogen sensitive human breast cancer cell line MCF-7. We suggest that APs, the environmental estrogen, can act as endogenous estrogen to inhibit tumor necrosis factor ((TNF-()-induced apoptosis and regulate the expessions of bcl-2 family in ER-positive breast cancer cells.In vitro the MCF-7 cells were pretreated with E2 and octylphenol(OP), whose estrogenicity is strongest in APs. The apoptotic cells induced by TNF-( were detected by TdT-mediated d-UTP nick end labeling ((TUNEL). The mRNA and protein changes of Bcl-2, Bax, Bcl-x and Bak were determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) andprotein bloting immune action (Western-Blot) respectively. The results were described as following: 1. OP, as well as E2, could affect the apoptotic pathway in MCF-7 cells. Apoptosis of the cells induced by TNF-( could be inhibited after being pretreated with OP or E2. OP could only mimic the apoptosis function of E2 in a short term treatment, as the inhibition effects disappeared when the pretreating time was prolonged to 120 hours. It was quite different from that of E2 and suggested the complexity effects of OP. 2. OP could change the expressions of Bcl-2, Bax, Bcl-xl, Bak protien in MCF-7 cells. Both OP and E2 had paradoxical regulation effects on Bcl-2 family proteins. Protein Bcl-2 and Bak increased while Bcl-xl decreased and Bax did not change after being treated with OP and E2. The expressions of the family members were different with the concentraions and the stimulating time of OP and E2. The effect of OP could be blocked by the anti-estrogen drug tamoxifen, indicating that the environmental estrogen inhibited apoptosis through estrogenic pathways. In general, the OP effects were quite similar to those of E2, but weaker than the later. When cells were treated with OP for more than 120 hours, the pro-apoptotic protein Bax increased a lot, which might contribute to the disappearing of the inhibition effects on apoptosis.3. We also found that OP resulted in an increasing of Bcl-2 and Bak, but with no change in Bax in mRNA level in MCF-7 cells. It was in consistent with protein level that OP mimiced the transcription function of E2 in Bcl-2 family members. Changes in mRNAs were more obvious than those in proteins. The time-depended changes of mRNAs were different from those of the proteins. The results suggested that the banance among the Bcl-2 family members might exist and could be disrupted by OP or E2. Those confirmed the suggestion that OP act like endogenous E2 on the process of apoptosis through Bcl-2 family...