Reduced HRAS^G12V-Driven Tumorigenesis of Cell Lines Expressing KRAS^C118S

<div><p>In many different human cancers, one of the <i>HRAS</i>, <i>NRAS</i>, or <i>KRAS</i> genes in the RAS family of small GTPases acquires an oncogenic mutation that renders the encoded protein constitutively GTP-bound and thereby active, which is well established to promote tumorigenesis. In addition to oncogenic mutations, accumulating evidence suggests that the wild-type isoforms may also be activated and contribute to oncogenic RAS-driven tumorigenesis. In this regard, redox-dependent reactions with cysteine 118 (C118) have been found to promote activation of wild-type HRAS and NRAS. We sought to determine if this residue is also important for the activation of wild-type KRAS and promotion of tumorigenesis. Thus, we mutated C118 to serine (C118S) in wild-type KRAS to block redox-dependent reactions at this site. We now report that this mutation reduced the level of GTP-bound KRAS and impaired RAS signaling stimulated by the growth factor EGF. With regards to tumorigenesis, we also report that oncogenic HRAS-transformed human cells in which endogenous KRAS was knocked down and replaced with KRAS^C118S exhibited reduced xenograft tumor growth, as did oncogenic HRAS-transformed <i>Kras^C118S/C118S</i> murine cells in which the C118S mutation was knocked into the endogenous <i>Kras</i> gene. Taken together, these data suggest a role for redox-dependent activation of wild-type KRAS through C118 in oncogenic HRAS-driven tumorigenesis.</p>