Abstract B48: Regulation of mutant KRAS protein stability via SMURF2:UBCH5 complex mediated degradation of beta-TrCP1

Attempts to target mutant KRAS have been unsuccessful. Most of the current therapeutic approaches are indirect, mainly via inhibiting KRAS down-stream signaling, which have been marginally successful. Here we report the identification of Smad ubiquitination regulatory factor 2 (SMURF2), a HECT-type ubiquitin ligase (E3) as a critical regulator of mutant KRAS protein stability. We show that the loss of SMURF2 either by si-/sh-RNA mediated gene silencing or by overexpression of a catalytically inactive SMURF2 Cys716Ala (CA) mutant, can cause lysosome-mediated KRAS degradation; whereas, overexpression of wild type SMURF2 enhances KRAS protein stability. Most importantly, we found that mutant KRAS protein is more susceptible to SMURF2 alterations in that mutant protein half-life decreased from >12h in control siRNA-treated cells to <3h with Smurf2 siRNA treatment, whereas only marginal differences were noted for wild-type KRAS protein upon similar treatments. Importantly, this loss of mutant KRAS protein could be rescued by overexpressing a siRNA-resistant (si-R) wild type SMURF2. Our data further show that SMURF2 along with an ubiquitin conjugating enzyme (E2), UBCH5, poly-ubiquitinates and degrades a Ras family E3, beta-Transducing Repeat Containing Protein 1 (beta-TrCP1). Conversely, beta-TrCP1 is accumulated upon the loss of SMURF2, leading to its increased binding and degradation of KRAS. Therefore, as expected, beta-TrCP1 knockdown following Smurf2 siRNA treatment res...

Source: Molecular Cancer Research - February 5, 2015 Category: Cancer & Oncology Authors: Shukla, S., Allam, U. S., Ahsan, A., Chen, G., Beer, D. G., Lawrence, T. S., Nyati, M. K., Ray, D. Tags: RAS Targeting: Poster Presentations - Proffered Abstracts Source Type: research