| Phycoerythrin(PE) is an important component of phycobiliproteins which can be divided into C-, B, b-andR-, according to spectral characteristics, and of all types R-PE which comes from Rhodophyceae is the most representative. Recently, there are many researches on PE anti-tumor biological activities and they are mainly divided into the following two directions.1. PE can be used as photosensitizer in photodynamic cancer therapy. Photosensitizer can be detained in tumour cells due to its higher tumour cellular affinity. After irradiation with light, photosensitizer jumped into the excited state immediately after absorbing photons, in this way can it pass the energy to the oxygen molecules around meanwhile to generate a kind of strong toxic--singlet oxygen which could kill the tumour cells. Not only does PE have natural affinity with tumour cells but it could induce apoptosis as well, therefor it has become the research focous in the exploitative of photosensitizer.2. PE has direct anti-tumor effect in vivo and vitro. The crude extract of PE could inhibit S180 sarcoma in vivo, while in vitro, PE has a stronger inhibitory effect of Hella, and however the specific mechanism is still unclear. So based on the above, this study will do futher research on the specific mechanism of PE in vitro.Methods:The inhibitory rate of MCF-7 cells was measured by MTT assay and SRB assay. The apoptotic morphology of MCF-7 cells was observed through the inverted microscope and fluorescence microscope staining by Hoechst 33258. AnnexinV-FITC/PI was used to observe the appearance of PS around outside the MCF-7 cells which is specific in the apoptosis so that apoptosis caused by PE can be determined. Apoptosis and influences on cell cycle of MCF-7 caused by PE was observed by flow cytometry (FCM).The expression of cyclinA and cyclin dependent kinase—CDK2 and CDC25A were detected by FCM.Results:The results indicated that PE could inhibit the human breast MCF-7 cells significantly. The suppression was in a dose dependent manner. MTT assay and SRB assay showed that the IC50 of 72 h was 147.82μg/mL while the GI50 was 109.76μg/mL. Compared with the normal cells, MCF-7 cells which were given different concentrations of PE had changed the optical patterns. Moreover, with the concentration of PE increased and time prolonged, more and more suspension cells appeared. After stained by Hoechst 33258, apoptotic bodies were also observed in MCF-7 through fluorescence microscope. The result of laser scanning confocal microscope showed us red nucleus and green membrane in one cell, what's more, as the dose increases, the number of apoptotic cells also increased gradually. The results of FCM showed us that PE could cause a dose-dependent apoptosis in MCF-7 cells. With regard to cell cycle, PE could increase the number of G1 and S phase cells significantly, at the same time reduce the number of G2 phase cells, which indicated that the number of DNA synthesis phase cells increased and the process of cell division accelerated, that is to say cell cycle is shortening. The expression of protein cyclinA and CDC25A were significantly increased while CDK2 were reduced, all the results showed a dose-dependent relationship according to FCM.Conclusion:The results demonstrate that PE dramatically suppresses MCF-7 cell growth by inducing apoptosis and the mechanism seems related to the increasing number of G1 and S phase cells. Through overexpression of cyclin dependent kinase CDC25A, PE made cyclinA which is the specific protein of G1 and S phase overexpressed, also reduced the correlation cyclin dependent kinase CDK2, so that it can achieve G1, S phase cycle arrest and induce apoptosis in MCF-7 cells.
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