선행연구에서 본 연구자는 IEX-1 단백질이 난소 암세포에서 세포사멸(apoptosis)을 유도하는 기능을 수행함을 확인하였으나, 세포사멸과 세포생존의 여러 단계에서 어떠한 신호전달 체계로 IEX-1이 작용하는지는 정확히 알지 못하고 있다. 따라서 IEX-1 단백질과 결합하는 새로운 단백질을 찾기 위해 yeast two-hybrid system을 이용하였다. 그 결과 IEX-1이 여러 다양한 인간 암 세포에서 세포사멸을 유도하는 CATHEPSIN B 단

Previously, we identified that the overexpression of IEX-1 induces apoptosis in ovarian cancer cells. Herein we report a new binding partner of IEX-1, CATHEPSIN B, as a lysosomal enzyme which contributes to the various apoptotic signaling in tumor cells. To investigate how IEX-1 regulates cellular survival and death event, we performed yeast two-hybrid screening of rat ovarian cDNA library using IEX-1 as the bait and found CATHEPSIN B. In the present study, CATHEPSIN B and IEX-1 proteins were overexpressed in 293T cells and their specific association was determined by immunoprecipitation and immunoblot analysis. In addition, the endogenous interaction between CATHEPSIN B and IEX-1 was confirmed in HeLa cells. The current finding of lysosomal CATHEPSIN B as the IEX-1-binding partner implies that IEX-1 may involve in lysosome-mediated apoptotic signaling pathways.

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