Abstract 5250: The effect of introducing a C118S mutation into the endogenous Kras gene on early tumorigenesis

Abstract

Abstract The Ras family of small GTPase, comprised of HRAS, NRAS, and KRAS, have been found mutated to remain in an active oncogenic state in many different human cancers, which is well established to promote tumorigenesis. All three RAS isoforms contain a conserved C118, of which the thiol group can be post-translationally modified by processes such as S-nitrosylation, which have been reported to promote RAS activation. To investigate the effect of blocking such modifications on RAS function in vivo, a C118S mutation, which lacks the reactive thiol group, was knocked into the endogenous Kras gene in mice. We now report that KrasC118S/C118S mice were born at the expected ratio with no overt phenotypes. To explore the effect of this mutation on early tumorigenesis, Kras+/+, KrasC118S/+, and KrasC118S/C118S mice were treated with the carcinogen urethane to induce oncogenic mutations in Kras and lung lesions. Interestingly, both KrasC118S/+ and KrasC118S/C118S mice developed fewer and smaller lung tumors than control Kras+/+ mice, suggesting that KrasC118S impairs lung tumorigenesis. Such a reduction in tumorigenesis could be the consequence of the C118S mutation on either the unaffected Kras allele or the Kras allele with the oncogenic mutation. To evaluate the first possibility, we tested and found that mice harboring a Cre-activated LSL-KrasG12D allele formed a similar number and size of lung tumors after activation of this allele when the remaining Kras allele was wild-type or C118S mutant. These data indicate that the reduction in tumor lesions observed in KrasC118S/+ and KrasC118S/C118S mice treated with urethane was unlikely to be the consequence of the C118S mutation on the non-oncogenic Kras allele. To evaluate the second possibility, we tested and found that oncogenic mutations occurred preferentially in the native compared to the C118S mutant Kras allele in KrasC118S/+ mice treated with urethane, suggesting a selection against oncogenic mutations on the KrasC118S allele. These results are consistent with the hypothesis that post-translational modifications such as S-nitrosylation on C118 enhance the oncogenic activity of Kras in vivo, and demonstrate for the first time that blocking the ability of a protein to be modified by processes like S-nitrosylation has a biological consequence in vivo. Citation Format: Lu Huang, Christopher M. Counter. The effect of introducing a C118S mutation into the endogenous Kras gene on early tumorigenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5250. doi:10.1158/1538-7445.AM2014-5250