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Comparison of the genetic extinction of NRAS to pharmacological MEK inhibition in an inducible mouse model of melanoma

ABSTRACT: Since direct pharmacological inhibition of RAS has thus far been unsuccessful, we explored system biology approaches to identify synergistic drug combination(s) that can mimic direct RAS inhibition. Leveraging an inducible mouse model of NRAS-mutant melanoma, we compare pharmacological MEK inhibition to complete NRAS-Q61K extinction in vivo. NRAS-Q61K extinction leads to a complete and durable tumor regression by enhancing both apoptosis and cell cycle arrest. By contrast, MEK inhibition only produces tumor stasis at best and we find that it robustly activates apoptosis but does not significantly impede proliferation. We used microarrays to determine which transcripts were affected by NRAS-Q61K extinction but insufficiently by MEK inhibition. We selected a single comparative timepoint, 4 days post-treatment. Downstream analyses included GSEA and TRAP algorithms, leading to the identification of a differentially affected CDK4-driven proliferation network. Immune genes were also identified as significant, but control experiments determined these to be largely the off-target effects of doxycycline and not of NRAS-Q61K extinction.

ORGANISM(S): Mus musculus

PROVIDER: GSE39984 | GEO | 2012/08/09

SECONDARY ACCESSION(S): PRJNA172204

REPOSITORIES: GEO

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Project description:Extinction learning refers to the phenomenon that a previously learned response to an environmental stimulus, for example the expression of an aversive behavior upon exposure to a specific context, is reduced when the stimulus is repeatedly presented in the absence of a previously paired aversive event. Extinction of fear memories has been implicated with the treatment of anxiety disease but the molecular processes that underlie fear extinctionare only beginning to emerge. Here we show that fear extinction initiates up-regulation of hippocampal insulin-growth factor 2 (Igf2) and down-regulation of insulin-growth factor binding protein 7 (Igfbp7). In line with this observation we demonstrate that IGF2 facilitates fear extinction, while IGFBP7 impairs fear extinction in an IGF2-dependent manner. Furthermore, we identify one cellular substrate of altered IGF2-signaling during fear extinction. To this end we show that fear extinction-induced IGF2/IGFBP7-signaling promotes the survival of 17-19 day-old newborn hippocampal neurons. In conclusion, our data suggests that therapeutic strategies that enhance IGF2-signaling and adult neurogenesis might be suitable to treat disease linked to excessive fear memory. We employed mice to investigate fear extinction in the hippocampus-dependent contextual fear conditioning paradigm. To this end, male C57BL/6J mice were exposed to the fear conditioning box (context) followed by an electric foot-shock which elicits the acquisition of conditioned contextual fear. For extinction training animals were repeatedly reexposed to the conditioned context on consecutive days (24h interval) without receiving the footshockagain (extinction trial, E). This procedure eventually results in the decline of the aversive freezing behavior. Mice that were exposed to the conditioning context without receiving fear conditioning training served as control groups. To gain a better understanding of the molecular processes underlying fear extinction we performed a genome-wide analysis of the hippocampal transcriptome during fear extinction. In the employed paradigm fear extinction is a gradual process. To capture the longitudinal course of fear extinction we decided to perform hippocampal microarray analysis at two time points: (1) After the first extinction trial (E1) when animals display high levels of aversive freezing behavior and (2) at the extinction trial on which the freezing behavior was significantly reduced when compared to E1. This extinction trial, in the case of this experiment E5, we termed “extinction trial low freezing” (ELF). Mice that were exposed to the conditioning context without receiving fear conditioning training served as control groups (3). For all three groups we hybridized 5 samples (biological replicates).

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Comparison of the genetic extinction of NRAS to pharmacological MEK inhibition in an inducible mouse model of melanoma

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