Differential Activity of The Kras Oncogene By Method of Activation: Implications For Signaling and Therapeutic Intervention

<p>Despite having been identified over thirty years ago and definitively established as having a critical role in driving tumor growth and predicting for resistance to therapy, the <em>KRAS</em> oncogene remains a target in cancer for which there is no effective treatment. KRas is activated b y mutations at a few sites, primarily amino acid substitutions at codon 12 which promote a constitutively active state. I have found that different amino acid substitutions at codon 12 can activate different KRas downstream signaling pathways, determine clonogenic growth potential and determine patient response to molecularly targeted therapies. Computer modeling of the KRas structure shows that different amino acids substituted at the codon 12 position influences how KRas interacts with its effecters.</p> <p>In the absence of a direct inhibitor of mutant KRas several agents have recently entered clinical trials alone and in combination directly targeting two of the common downstream effecter pathways of KRas, namely the Mapk pathway and the Akt pathway. These inhibitors were evaluated for efficacy against different <em>KRAS</em> activating mutations. An isogenic panel of colorectal cells with wild type KRas replaced with KRas G12C, G12D, or G12V at the endogenous loci differed in sensitivity to Mek and Akt inhibition. In contrast, screening was performed in a broad panel of lung cell lines alone and no correlation was seen between types of activating<em> KRAS</em> mutation due to concurrent oncogenic lesions.</p> <p>To find a new method to inhibit <em>KRAS</em> driven tumors, siRNA screens were performed in isogenic lines with and without active KRas. The knockdown of <em>CNKSR1</em> (CNK1) showed selective growth inhibition in cells with an oncogenic <em>KRAS</em>. The deletion of CNK1 reduces expression of mitotic cell cycle proteins and arrests cells with active KRas in the G1 phase of the cell cycle similar to the deletion of an activated<em> </em>KRas regardless of activating substitution. CNK1 has a PH domain responsible for localizing it to membrane lipids making KRas potentially amenable to inhibition with small molecules. The work has identified a series of small molecules capable of binding to this PH domain and inhibiting CNK1 facilitated KRas signaling.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2012

Author dc:creator

• Ihle, Nathan

Contributors dc:contributor

• Garth Powis
• E. Scott Kopetz
• Michael Davies

• KRAS
• RAS
• CNKSR1
• CNK1
• Biochemistry, Biophysics, and Structural Biology
• Medicine and Health Sciences
• Molecular Biology
• Systems Biology

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/314

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1349