The Effect Of Caveolin-1 In Nerve Growth Factor Signaling Pathway Of Breast Cancer

Objective:To investigate the effect of Caveolin-1 on Nerve Growth Factor signaling pathway in human breast cancer MCF-7 cells, the effect of Caveolin-1 on cell proliferation and survival in MCF-7 cells, and to find the potential therapeutic target for breast cancer.Methods:Caveolin-1 expression in several different breast cancer cell lines was mapped by Western Blotting. Caveolin-1 was forcedly expressed in MCF-7 cells by transient transfection. The proliferation rate of MCF-7 cells before/after transfection was detected by MTT assay. Cav-1 expression after transfection, apoptosis relative signal pathway and NGF signal pathway were detected via Western Blotting and Immunofluorescence.Results:Caveolin-1 only has a weak expression in 5 different breast cancer cells. MCF-7 cell line has a high proliferation rate and a high level of TrkA expression. In this cell line, natively expressed Cav-1 cannot be phosphorylated as a kinase substrate. Transiently transfected with the whole length human Caveolin-1 gene, MCF-7 expressed Caveolin-1 protein at a high level. And the protein production can be phosphorylated at Y14 site. The proliferation rate decreased dramatically after transfection. We didn't obtain any obvious difference of TrkA expression before/after transfection, but its localization was changed from nucleus to cytoplasm. Phosphorylated Erk1/2 increased after transfection, but the effect of NGF treatment on it was abolished remarkably. Meanwhile we recorded a decrease of phosphorylated form of RSK2 in cytoplasm and CREB in nucleus, respectively. And the decrease of p-CREB cannot be totally recovered by NGF treatment. In short-term observation, the quantity of phosphorylated form of P38 increased remarkably, the expression of Bax increased and Bcl-2 decreased, respectively.Conclusion:Caveolin-1 expression lost in several breast cancer cell lines. The proliferation and survival of MCF-7 cells were inhibited after transient transfection. A different cell morphology occurred after transfection. The NGF tyrosine receptor TrkA expression didn't show obvious difference after transfection, but its localization was changed from nucleus to cytoplasm. The quantity of phosphorylated RSK2 and phosphorylated CREB decreased dramatically and p-CREB quantity reduction cannot be totally recovered by NGF treatment. This result strongly indicated that Caveolin-1 inhibits the NGF self-cycling in MCF-7 cells via the regulation of TrkA function. In MCF-7/Cav-1 cells, BAX expression increased at 24 hours after transfection whereas Bcl-2 expression decreased at the same time, which suggests that Caveolin-1 can trigger cell apoptosis via Bax pathway. All these results suggest that Caveolin-1 may both inhibit the proliferation signal and trigger the apoptosis signal, and finally inhibits the cell proliferation.