Study On The Role Of PTEN In Proliferation And Metastasis Of Murine Breast Cancer And Malignant Melanoma

Background The invasion and metastasis are the leading causes of death in malignant tumors.Breast cancer and malignant melanoma are the most common highly aggressive metastatic tumors.The abundant studies have shown that the mutation or loss of tumor suppressor gene PTEN significantly enhances the proliferation,invasion and metastasis of malignant tumor cells,similarly,the functional status of PTEN of tumor microenvironment stromal cells also greatly controls the occurrence,development,invasion and metastasis of cancers.So far,whether the loss or decrease of overall PTEN of tumor-bearing host promotes the proliferation,distant metastasis and metastatic carcinoma is barely,if ever,reported.Objective To investigate the effects of PTEN on the proliferation,migration,invasion and metastasis of mouse breast cancer cells and malignant melanoma cells,and whether the loss or inhibition of PTEN function of host promotes the growth and distant metastasis of mouse breast cancer and malignant melanoma.Methods The mouse breast cancer 4T1 cells and malignant melanoma B16 cells were treated with PTEN-specific inhibitor VO-Ohpic.MTT colorimetric and colony forming methods were employed to detect cell proliferation activity,cell scratch healing and Transwell experiments were used to determine cell migration and invasion ability,the phase distribution of the cell cycle was examined by flow cytometry,real-time quantitative RT-PCR and western blotting assay were used for detecting the mRNA and protein expression of PTEN and other related genes.The 4T1 cells and B16 cells were transplanted into BALB/c mice and C57BL/6J mice,respectively,to establish the orthotopic and metastatic models of breast cancer and malignant melanoma.The in-vivo growth and metastasis of 4T1 cells and B16 cells were observed via the animal optical in vivo imaging system.Results1 VO-Ohpic could effectively inhibit the expression of PTEN mRNAs and proteins of breast cancer 4T1 cells and malignant melanoma B16 cells.2 The proliferation activities of 4T1 cells and B16 cells were significantly increased after treatment with different concentrations of VO-Ohpic.As the concentration of VO-Ohpic over 800 nmol/L,its effect on the cells went gradually from enhancing to inhibiting.After treatment with 200 nmol/L and 500 nmol/L vo-ohpic,the wound healing and Transwell assays showed that the mobility and invasion of 4T1 cells and B16 cells obviously increased.Meanwhile,the significant heightening of AKT and PI3 K phosphorylation indicated that the PI3K-AKT signaling pathway was activated by inhibition of PTEN.3 After VO-Ohpic inhibiting PTEN expression,the growth of the VO-Ohpic-treated 4T1 cells and B16 cells in vivo obviously strengthened,and the metastasis capacity of the cells was increased and the metastases were found in mouse lung,liver and intestine.4 After intraperitoneal injection of 10 μg/kg or 20 μg/kg VO-Ohpic,the PTEN levels of the lung,liver and intestinal tissues of the mice were greatly decreased.The orthotopic implanted 4T1 breast cancer and B16 malignant melanoma grew rapidly,and the cancer cells metastasized to the lung,liver and intestine to form metastatic carcinoma.The metastasis intensity in lung,liver and intestine was negatively correlated with the PTEN level of the same organs.The similar reduction of PTEN mRNA and protein expression was also observed in the transplanted orthotopic tumor tissues.Conclusions1 The inhibition of the tumor suppressor gene PTEN significantly enhances the proliferation,invasion and metastasis abilities of breast cancer 4T1 cells and malignant melanoma B16 cells.2 The growth of orthotopic tumor and the formation of metastatic carcinoma in distant organs in tumor-bearing mice are significantly promoted as the decrease of PTEN function of the whole-body or specific organs.3 The regulation of PTEN on the proliferation,invasion and metastasis behaviours of mouse breast cancer cells and malignant melanoma is mediated by the PI3K-AKT signaling pathway.