The Study On Moleculard Mechanism Of Inhibiting Cell Growth By Trastuzumab In MCF-7 Cells

Breast cancer is the most common malignant tumors in women, and its incidence is 7%-10% from all the tumors. There are about 40,000 peoples dying of breast cancer in China. There are many factors contributing to breast cancer. The exact molecular mechanism on breast cancer is still unknown. At the present, the methods using for breast cancer treatment include surgery, chemotherapy, radiotherapy and biological therapy. These therapeutic methods are strictly limited due to the side effect. It is necessary for improving clinical therapy and prognosis to further study the molecular mechanisms on breast cancer. Trastuzumab is used for treat human epithelial growth factor receptor 2 (HER2)-positive breast cancer. The research on the new molecular mechanisms on breast cancer by using trastuzumab will provide basic theory for exploring new target.Thioredoxin is one of the important redox proteins. It exists in many different prokaryotes and eukaryotes. Thioredoxin has various biological activities, such as activation of transcription factors, antioxidant, anti-apoptosis, growth promotion and inflammation regulation. Thioredoxin binding protein-2 is a negative regulatory protein of thioredoxin. It interacts with the activity site of thioredoxin, and inhibits the redox activity of thioredoxin. Thioredoxin is over-expression in various cancer tissues. However, the expression of thioredoxin binding protein-2 is decreased. Cyclin D1 is one of the important proteins in regulating cell cycle progression. Cyclooxygenase 2 (COX-2) is a rate-limiting enzyme which catalyzes the metabolism of arachidonic acid. It inhibits cell apoptosis and up-regulates vascular endothelial growth factor. It has been reported that the level of cyclin D1 and cyclooxygenase 2(COX-2) is increased in many tumor tissues. Caspase-9, a cysteine protease, is an initial caspase in the mitochondria apoptosis cascade.In our study, the HER2-positive MCF-7 cell was treated with different dose of trastuzumab, and then the expression of thioredoxin, thioredoxin binding protein-2, cyclin D1, CDK5, pro-caspase-9 and COX-2 were detected by Western Blot and RT-PCR. We found that the protein and mRNA level of thioredoxin were down-regulated by trastuzumab. Thioredoxin binding protein-2 mRNA level was not increased. We also found that the expression of cyclin Dl, pro-caspase-9 and COX-2 decreased after trastuzumab treatment. However, the CDK5 and COX-2 expression was not affected by trastuzumab. The results indicated that thioredoxin, cyclin D1 and pro-caspase-9 are involved in molecular mechanisms on trastuzumab.Our study showed new molecular mechanisms on trastuzumab inhibiting MCF-7 proliferation. It could provide basic target for breast cancer treatment.