Abstract
Since the human breast carcinoma MCF-7 cells lack caspase-3 to play as an important factor in apoptosis, the loss of this protein is considerd to be involved in the radioresistance in MCF-7 cells. In this study, we have reported that the overexpression of caspase-3 enhance radiation-induced apoptosis. Furthermore, the involvements of other caspase and the apoptotic pathway through mitochondria and/or TNFα-family in this radiation-induced apoptosis were examined.
The cDNAs of caspase-3 were inserted in the mammalian expression vector, pCI-neo. This plasmid was transfected into MCF-7 cells. After irradiation, the apoptotic cells were evaluated by morphological change by using PI staining.
The overexpression of caspase-3 did not increase a number of apoptotic cells without irradiation. However, X-irradiation significantly induced apoptosis in the caspase-3-overexpressed cells in comparison with that in the mock cells. This result suggest that caspase-3 acts as an important role for the radioresistance of radiation-induced apoptosis in the MCF-7 cells. Moreover, to examine whether other caspases were involved in this apoptotic induction, inhibitory peptides against caspase-8 (Ac-IETD-CHO) and caspase-9 (Ac-LETD-CHO) were utilized. Not only Ac-LETD-CHO but also Ac-IETD-CHO suppressed the enhancement of radiation-induced apoptosis in the caspase-3-overexpressed cells. This fact suggested that the radiation-induced apoptosis was associated with both apoptotic signal transduction pathways through mitochondria and TNFα-family.
