| Background:Breast cancer is the most common cancer in women around the worldwide. In recent years, with the increasing of stress in our life and the environment pollution, the incidence of breast cancer in women ranked first in cancer around the world and the mortality rate ranked second only to lung cancer. Currently, breast cancer incidence and mortality have been effectively controlled in a certain extent, but the cause of death is metastasis in almost all breast cancer patients. Therefore, clarifying the mechanism of breast cancer metastasis will contribute to the prevention and treatment of breast cancer. Wnt signaling pathway is an evolutionarily conserved signaling pathway that plays an important role in controlling enbryonic development, regulating cell growth, migration, and differentiation. The accumulation of β-catenin is the core of the abnormal Wnt signaling pathway in the cell. And the transcription of specific target gene was induced by its downstream transduction pathway. DKK1 is not only a member of the DKK family, but also inhibits the Wnt/β-catenin signaling pathway as the strongest secreted glycoprotein. DKK1, as an inhibitor of the Wnt/β-catenin signaling pathways, plays an important role in cell migration, proliferation and other characteristics. The literature has confirmed that DKK1 plays an important role in the occurrence and development of liver cancer. However, we are still unclear on the change of DKK1 expression with the relationship of the pathogenesis and metastasis in breast cancer. Moreover, it is also having no idea in the potential molecular mechanism. Objective:In this study, we will examine the expression of DKK1 in both breast cancer cell lines and clinical samples, and try to determine the potential role of DKK1 in breast cancer. Methods:RT-PCR and Western blot assay were used to detect the expression of mRNA and protein of DKK1 in breast cancer cells(MDA-MB-453, MCF-7, HCC-1937, MDA-MB-231 and primary culture cells) and breast cancer tissues. MTT assay, scratch(wound healing) experiments and Transwell experiments was used to detected breast cancer cell proliferation, migration and invasion ability in overexpression or gene knock down DKK1 of breast cancer cell lines. Western blot was used to detect the expression of β-catenin, E-caherin, MMP-7 and other related proteins in Wnt/β-catenin signaling pathway. Immunohistochemical staining was used to detect the expression of DKK1, β-catenin, MMP-7, E-caherin expression in breast cancer tissues. Results:1. Compared with the adjacent tissues, the expression of DKK1 in mRNA and protein level in breast cancer tissues was relatively low.2. There were no significant differences in the expression of DKK1 in mRNA and protein levels in four breast cancer cells and primary culture cells.3. Overexpression of DKK1 in breast cancer cell lines can significantly inhibit the proliferation, migration and invasion ability of breast cancer cells. On the contrary, DKK1 down-regulated can significantly promote the proliferation, migration and invasion ability of breast cancer cells.4. Overexpression of DKK1 can significantly reduce the expression of β-catenin in breast cancer cell line MDA-MB-231 and MMP-7 protein, and upregulate the expression of E-cadherin. On the contrary, when using short hairpin(shRNA silencing of DKK expression), β-catenin protein expression significantly increased in breast cancer cell line MCF-7, MDA-MB-231, and E-cadherin expression was significantly reduced.5. The immunohistochemical results showed that the expression of β-catenin and MMP-7 were significantly higher than that in the adjacent tissues. Furthermore, β-catenin and MMP-7 were negatively correlated with the expression of DKK1. The expression of E-cadherin in breast cancer tissues was significantly lower than that in the adjacent tissues. Moreover, E-cadherin were positively correlated with the expression of DKK1. Conclusions:1. DKK1 down-regulated promotes the proliferation and metastasis of breast cancer.2. DKK1 down-regulated leads to the activation of the Wnt/β-catenin signaling pathway in breast cancer, and then, the expression of β-catenin and its downstream protein expression of MMP-7 are increased. MMP-7 is likely to promote the proliferation and metastasis of breast cancer by hydrolysis of E-cadherin. |
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