Effect Of Genistein On Telomerase Activity Of The Human Breast Cancer Cell Lines And Its Mechanism

Breast cancer is a malignant tumor of the highest morbility among women now,about 1.2million new cases and 0.5million death cases happened every year.Nutrition,which is important for the development of breast cancer,has become one of the efficient protective strategies of breast cancer.A great quantity of studies indicated that,Genistein(GEN),as the most abandunt isoflavone present in soybean,which contains Genistein, daidzein,glycitein and so on,has anti-tumor effect.And it acts not only estrogen-liked effect,but also anti-estrogen effect.In addition,it could inhibit the proliferaton,induce apoptosis,and inhibit angiogenesis.But its mechanism is not fully understood now.Telomere is a special structure at the end of the chromosomes in eukaryote. Progressive shortening with each cell division ultimately results in cell death. Telomerase is a special ribonucleoprotein complex to retain the length of telomere. While telomerase activity is not detected in the majority of somatic cells,high level has been detected in a stem and germline cells,especially in the cancer cells.The human telomerase complex is compose of humam telomerase RNA(hTR),telomerase associated protein1(TP1)and human telomerase reverse transcriptase(hTERT).A number of studies showed that,the activation of telomerase,especially hTERT,is the key point in the development of tumor.The transcriptional and posttranslational regulation(phosphorylation and translocation) of hTERT is very important to telomerase activity.Telomerase has become a therapic target of breast cancer.As there were a few researches on the relationship between GEN's anti-tumor effect and telomerase activity,at first we investigated the effects of GEN in different dose and E2,alone or in combination, on the proliferation and telomerase activity of ER+ MCF-7 and ER- MDA-MB-231 cells using MTT ,TRAP-ELISA,and then the mechanism were studied using RT-PCR, western-blot and immunocytochemistry methods.The main results and conclusions were summarized as follow:1.For ER+ MCF-7 cells,10-9 mol/L E2 promoted the cell proliferation and telomerase activity obviously;GEN alone in low dose(5×10-6 mol/L) is similar to E2,promoting the cell proliferation and telomerase activity,but in combination with E2 had no effect on the cell proliferation and telomerase activity (p >0.05);GEN in high dose(40,80×10-6 mol/L) alone or in combination with E2,could inhibit the proliferation and telomerase activity (p <0.01).For ER- MDA-MB-231 cells, E2 had no effect on the cell proliferation and telomerase activity (p >0.05),and GEN in different dose alone or in combination with E2 could inhibit the proliferation and telomerase activity obviously on dose manners of GEN.The results indicated that ,the change of cell proliferation is coherent with the change of telomerase activity,GEN and E2 could regulate the telomerse activity to control cell proliferation.2.For ER+ MCF-7 cells,10-9 mol/L E2 increased the expression of hTERT mRNA and protein obviously;GEN alone in low dose(5×10-6 mol/L) is similar to E2, increasing the expression of hTERT mRNA and protein,but in combination with E2 had no effect on the expression of hTERT mRNA and protein(p >0.05);GEN in high dose(40×10-6 mol/L) alone or in combination with E2,could decrease the expression of hTERT mRNA and protein (p <0.01).For ER- MDA-MB-231 cells, E2 had no effect on the expression of hTERT mRNA and protein (p >0.05),and GEN in different dose alone or in combination with E2 could decrease the expression of hTERT mRNA and protein obviously.The results indicated that,GEN and E2 could regulate the expression of hTERT to change the telomerase activity.3.For ER+ MCF-7 cells,10-9 mol/L E2 increased the expression of p-Akt protein, enhanced the nuclear translocation of NF-κB p65 and HSP90;GEN alone in low dose(5×10-6 mol/L) is similar to E2,increasing the expression of p-Akt protein, enhanced the nuclear translocation of NF-κB p65 and HSP90,but in combination with E2 had no effect on the expression of p-Akt protein,nuclear tanslocation of NF-κB p65 and HSP90(p >0.05);GEN in high dose(40×10-6 mol/L) alone or in combination with E2,could decrease the expression of p-Akt protein,inhibited the nuclear translocation of NF-κB p65 and HSP90(p <0.01).For ER- MDA-MB-231 cells,E2 had no effect on the expression of p-Akt protein,nuclear translocation of NF-κB p65 and HSP90(p >0.05),and GEN in different dose alone or in combination with E2 could decrease the expression of p-Akt protein, inhibited the nuclear translocation of NF-κB p65 and HSP90.The results indicated that,GEN and E2 could regulate the expression of p-Akt,nuclear translocation of NF-κB and HSP90 to regulate the telomerase activity.In summary,GEN and E2 could regulate the expression of hTERT,phosphorylation and nuclear translocation to regulate the telomerase activity,ultimately to control the cell proliferation.The different effects of GEN on the two breast cancer cells are related to its dosage, the status of ER expression and the presence or absence of estrogen.For ER+ breast cancer cells,GEN in low dose,with the absence of estrogen,could bind the ER to induce the estrogen-liked effect,while with the presence of estrogen,has anti-estrogen effect.GEN in high dose with the absence or presence of estrogen,could down-regulate the telomerase activity to inhibit the cell proliferation.But for ER- breast cancer cells,GEN in different dose with the absence or presence of estrogen,could down-regulate telomerase activity.All the results indicated that,GEN in physiological dose,with the absence of endogenous estrogen,could up-regulate the telomerase activity to promote the ER+ breast cancer cells,which is a side effect to post-menopause patients of ER+ breast cancer.