Identification of a Potent Apoptotic Peptide by Fibroblasts: Studies Toward the Design of a Novel Agent for Breast Cancer Therapy

摘要

We previously showed that constitutive activation of the platelet- derived growth factor beta receptor (PDGFR) in mortal human fibroblasts (HDFs) by the bovine papillomavirus E5 or the v-Sis oncoprotein induces partial transformation of these cells. However, two weeks after they reach their peak density E5- and v-Sis-expressing HDFs secrete a small, hydrophilic peptide that induces massive apoptosis in an autocrine manner. Specifically, this peptide induces a type of caspase-independent, Bcl-2-resistant apoptosis by promoting mitochondrial dysfunction, which results in the release of the apoptotic mitochondrial protein AIF into the cytosol and its subsequent translocation to the nucleus. We hypothesize that as a negative feedback response to sustained PDGFR signaling, HDFs release a small, hydrophilic peptide that induces apoptosis by activating or sensitizing pro-apoptotic Bcl-2-related proteins such as Bax, which in turn promote mitochondrial dysfunction. The primary goal of this project is to identify this apoptotic peptide produced by partially transformed HDFs. To date, we have further characterized this peptide and are in the process of designing a scheme for purification of the peptide by ion- exchange chromatography. Furthermore, we obtained evidence that the peptide disrupts the redox homeostasis in the cells. Since this peptide can induce apoptosis of a number of different tumor cell lines including MCF-7 and MDA human breast carcinoma cells, once identified it could serve as the forerunner of a novel anti-breast cancer agent.