The Potential Roles Of TGIF In Cd Exposure-induced Breast Cancer Cell Migration And Invasion

Cadmium(Cd)is a toxic heavy metal pollutant,which exists widely in nature in the form of compounds.Cd is one of the hazardous substances with known health effects on multiple organs and systems,owing partly to its low excretion rate with elimination half-time of 10-30 years.The principal sources of Cd exposure in population are occupational exposure or contaminated air,food,water,and tobacco smoke.In 1993,the International Agency for Research on Cancer(IARC)has classified cadmium and its compounds as a human carcinogen.Previous studies have demonstrated that Cd is associated with the formation and development of a variety of cancers,including breast cancer.TG-interacting factor(TGIF)is a transcriptional repressor.Emerging studies have indicated that abnormal TGIF expression is related to tumor formation and progression.TGIF also plays a pivotal role in the initiation of breast cancer and is implicated in the invasion and migration of breast cancer cells.However,it is not clear whether TGIF is involved in the migration and invasion of human breast cancer cells induced by exposure to Cd.ObjectiveThe aim of this study was to investigate the potential roles of TGIF in Cd exposure-induced breast cancer cell migration and invasion.Moreover,since matrix metalloproteinase-2(MMP2)and N-cadherin were involved in breast cancer cell migration and invasion,we tentatively investigated whether these proteins are the downstream targets in cadmium-upregulated TGIF expression to promote breast cancer cell invasion and migration.This might provide new insights into understanding the precise molecular mechanisms of breast cancer cell invasion and migration induced by exposure to Cd.Methods1.The human breast cancer cell lines(MCF-7 and MDA-MB-231)were used as experimental models.Cells were exposed to Cd(0,0.5,or 1.0 μM)for eight weeks.Western blot and quanlitative real-time polymerase chain reaction(q RT-PCR)assays were carried out to determine the expression of TGIF protein and m RNA,respectively.2.Wound-healing assay and cell invasion assay were performed on the human breast cancer cell lines of MCF-7 and MDA-MB-231 exposed to Cd(0,0.5,or 1.0μM)for eight weeks to assess the effects of Cd exposure on breast cancer cell migration and invasion.3.The human breast cancer cell lines of MCF-7 and MDA-MB-231 were transiently transfected with TGIF-si RNA or control-si RNA.To detect the interfering efficiency of TGIF-si RNA transfection,Western blot and q RT-PCR assays were carried out to determine the expression of TGIF protein and m RNA,respectively.4.Wound-healing assay and cell invasion assay were carried out to explore the effects of TGIF silencing on Cd exposure-induced migration and invasion of the human breast cancer cell lines of MCF-7 and MDA-MB-231.5.Quantitative RT-PCR was used to detect the effects of TGIF silencing on Cd exposure-induced the expression of MMP2 and N-cadherin m RNA in the human breast cancer cell lines of MCF-7 and MDA-MB-231.Results1.The expression of TGIF protein and m RNA were markedly increased in Cd-exposed MCF-7 cells and Cd-exposed MDA-MB-231 cells compared to solvent control(0 μM),respectively.This observation suggested that Cd exposure up-regulated TGIF expression in human breast cancer cells.2.The relative ability of cell migration and invasion were significantly increased in Cd-exposed MCF-7 cells and Cd-exposed MDA-MB-231 cells compared to solvent control(0 μM),respectively.This observation verified that exposure to Cd for eight weeks increased the ability of migration and invasion in human breast cancer cells.3.The expression of TGIF protein and m RNA was markedly decreased in TGIF-si RNA-transfected MCF-7 cells and TGIF-si RNA-transfected MDA-MB-231 cells compared to those transfected with control-si RNA,respectively.This observation suggested that TGIF-silenced MCF-7 cells and TGIF-silenced MDA-MB-231 cells were successfully established.4.The relative ability of cell migration and invasion were significantly increased in Cd-exposed MCF-7 cells and Cd-exposed MDA-MB-231 cells compared to solvent control cells(0 μM)when intact TGIF existed.However,there were no significant difference in the relative ability of cell migration and invasion between Cd-exposed MCF-7 cells and Cd-exposed MDA-MB-231 cells and control cells when TGIF was silenced by si RNA.5.The expression of MMP2 m RNA was significantly increased in Cd-exposed MCF-7 cells compared to solvent control cells when intact TGIF existed.However,the expression of MMP2 m RNA was significantly decreased in Cd-exposed MCF-7cells transfected with TGIF-si RNA compared to Cd-exposed MCF-7 cells transfected with Control-si RNA.The similar results were observed in MDA-MB-231 cells.Cd exposure-induced up-regulation of N-cadherin m RNA expression was not affected by TGIF-si RNA transfection in both MCF-7 cells and MDA-MB-231 cells.This observation suggested that MMP2 might be a downstream molecular of TGIF in Cd exposure-promoted breast cancer cell migration and invasion.ConclusionIn conclusion,our findings suggested that Cd exposure promoted breast cancer cell migration and invasion by upregulating TGIF,which might enrich our understanding of the molecular mechanisms of Cd exposure-promoted breast cancer progression and further provide the clue in the prevention of environmental exposure to Cd-caused breast cancer metastasis.