Characterization of novel cofactors for oncogenic transcription factors Myc and FoxM1 and cytotoxic peptides derived from an essential Myc domain

Human cancer is developed as the consequence of the activation of oncogenes and inactivation of tumor suppression genes. Modern sciences has identified and characterized the functions of such genes to understand the mechanism of cancer development in order to cure cancer ultimately. In this thesis, I explored the functions of human oncogenes, Myc and FoxM1. Myc and FoxM1 are transcription factors that regulate the expression of numerous genes and their deregulation are frequently observed in human malignancy. I isolated Myc-interacting proteins by affinity-purification. LRP130 cooperates with Myc to enhance transactivation. LRP130-Myc interaction is required for proliferation, transformation. I identified PCKbeta in LRP130 complex. It was observed that the activation of PCKbeta suppresses the transactivation by Myc. I concluded that the LRP130 positively regulates Myc in normal circumstance, while it becomes opposite when PCKbeta in LRP130 complex is activated. Second, I characterized the function of TRUSS as Myc-interacting protein to recruit E3 ubiquitin ligase, which induces the rapid degradation of Myc protein. Since TRUSS is a new DCAF from this study, biochemical and cellular analysis demonstrated TRUSS is a suppressor of Myc transcription activation. Third, I investigated potential therapeutic application of MB2 peptides. MB2 peptide was shown to induce massive cell death of human cancer cell lines. I characterized the biological properties of MB2 peptide. Cell death induced by MB2 peptide is not required for the activation of caspases and p53. I suggest that MB2 peptide induced the depolarization of mitochondrial outer membrane, as potential mechanism of cell death. At last, I characterized new cofactors of cell cycle regulating transcription factor FoxM1. FoxM1 regulates G2/M transition and proper mitosis. I isolated PLK1, PP2A complex, and SF3B3 as FoxM1-interacting proteins. I demonstrated their interaction is cell-cycle specific and the association with PLK1 enhances transactivation by FoxM1. I isolated SF3B3 from Nocodazole-arrested cells. Association with SF3B3 is relevant to the phosphorylation status of FoxM1. In conclusion, I characterized interacting proteins with two important transcription factors, Myc and FoxM1 and biological significances of their interactions. Those investigations provide useful knowledge to design drugs to prevent and cure human cancers.