RAS proteins are frequently mutated in cancer (~30% of all human tumors) and an estimated worldwide death toll of RAS-associated cancers exceeds 2 million/yr. Despite enormous efforts in RAS research over three decades, there is no clinically approved RAS inhibitor and the RAS protein remains a challenging target for cancer therapy development. In order to overcome this challenge, we sought to better understand how RAS functions under physiologic conditions and alters related signaling pathways in the mutant RAS-driven tumors. Fully matured protein K-RAS4B, the major target for cancer therapeutics, is prenylated and methylated at the carboxy-terminus, which enables K-RAS4B to anchor to the plasma membrane where it receives an upstream signal and transmits the signal to a number of downsteam pathways. There is, however, a large gap in our understanding of how the matured K-RAS4B protein functions at the surface of the plasma membrane. As a first step, we sought to develop new conformational and functional assays for the RAS protein on lipid bilayers (i.e., nanodiscs) using various biochemical and biophysical techniques. We elucidated how the membrane environment dictates the conformation of K-RAS4B and how oncogenic mutations influence the membrane-dependent conformational states of the protein (Mazhab-Jafari et al., PNAS 2015). More recently, we have been investigating multiple aspects of K-RAS4B functions and I will discuss (i) how the biologic membrane influences K-RAS4B interaction with a binding domain of RAF kinases and (ii) how we could inhibit K-RAS4B at the membrane surface by small molecules (Fang et al., Cell Chem Biol 2018) and an engineered protein. Supported by CCS, CIHR, CFI and PMCF.

Citation Format: Mitsu Ikura. Targeting K-RAS4B on biologic membranes [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr IA09.