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Substitutions in the KRas oncogene determine protein behavior: Implications for signaling and clinical outcome.

ABSTRACT: Mutant KRAS (mut-KRAS) is present in 30% of all human cancers and plays a critical role in cancer cell growth and resistance to therapy. There is evidence from colon cancer that mut-KRAS is a poor prognostic factor and negative predictor of patient response to molecularly targeted therapy. However, evidence for such a relationship in non small cell lung cancer (NSCLC) is conflicting. KRAS mutations are primarily found at codons 12 and 13, where different base changes lead to alternate amino acid substitutions that lock the protein in an active state. The patterns of mut-KRas amino acid substitutions in colon cancer and NSCLC are quite different, with aspartate (D) predominating in colon cancer (50%) and cysteine (C) in NSCLC (47%). Through an analysis of a recently completed biopsy biomarker-driven, molecularly targeted multi-arm trial of 215 evaluable patients with refractory NSCLC we show that mut-KRas-G12C/V but not total mut-KRAS predicts progression free survival for the overall group, and for the sorafenib and vandetanib treatment arms. Transcriptome microarray data shows differential expression of cell cycle genes between mut-KRas-G12C/V and G12D patient tumors. A panel of NSCLC cell lines with known mut-KRas amino acid substitutions was used to identify pathways activated by the different mut-KRas, showing that mut-KRas-G12D activates both PI-3-K and MEK signaling, while mut-KRas G12C does not, and alternatively activates RAL signaling. This finding was confirmed using immortalized human bronchial epithelial cells stably transfected with wt-KRAS and different forms of mut-KRAS. Molecular modeling studies show that the different conformation imposed by mut-KRas-G12C could lead to altered association with downstream signaling transducers compared to wild type and mut-KRas-G12D. The significance of the findings for developing mut-KRAS therapies is profound, since it suggests that not all mut-KRas amino acid substitutions signal to effectors in a similar way, and may require different therapeutic interventions.

ORGANISM(S): Homo sapiens

PROVIDER: GSE27389 | GEO | 2012/01/01

SECONDARY ACCESSION(S): PRJNA153915

REPOSITORIES: GEO

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Project description:Mutant KRAS (mut-KRAS) is present in 30% of all human cancers and plays a critical role in cancer cell growth and resistance to therapy. There is evidence from colon cancer that mut-KRAS is a poor prognostic factor and negative predictor of patient response to molecularly targeted therapy. However, evidence for such a relationship in non small cell lung cancer (NSCLC) is conflicting. KRAS mutations are primarily found at codons 12 and 13, where different base changes lead to alternate amino acid substitutions that lock the protein in an active state. The patterns of mut-KRas amino acid substitutions in colon cancer and NSCLC are quite different, with aspartate (D) predominating in colon cancer (50%) and cysteine (C) in NSCLC (47%). Through an analysis of a recently completed biopsy biomarker-driven, molecularly targeted multi-arm trial of 215 evaluable patients with refractory NSCLC we show that mut-KRas-G12C/V but not total mut-KRAS predicts progression free survival for the overall group, and for the sorafenib and vandetanib treatment arms. Transcriptome microarray data shows differential expression of cell cycle genes between mut-KRas-G12C/V and G12D patient tumors. A panel of NSCLC cell lines with known mut-KRas amino acid substitutions was used to identify pathways activated by the different mut-KRas, showing that mut-KRas-G12D activates both PI-3-K and MEK signaling, while mut-KRas G12C does not, and alternatively activates RAL signaling. This finding was confirmed using immortalized human bronchial epithelial cells stably transfected with wt-KRAS and different forms of mut-KRAS. Molecular modeling studies show that the different conformation imposed by mut-KRas-G12C could lead to altered association with downstream signaling transducers compared to wild type and mut-KRas-G12D. The significance of the findings for developing mut-KRAS therapies is profound, since it suggests that not all mut-KRas amino acid substitutions signal to effectors in a similar way, and may require different therapeutic interventions. Gene expression profiles were measured in 22 core biopsies from patients with refractory non-small cell lung cancer included in the Biomarker-integrated Approaches of Targeted Therapy for Lung Cancer Elimination (BATTLE). All tumors were KRAS mutants, but with different patterns of amino acid substitutions. Supervised analysis of transcriptome profiling was performed to compare cysteine or valine KRAS mutants with other KRAS mutants.

Project description:The small GTPase KRAS transmits signals from cell surface receptors to various downstream signaling pathways, thereby regulating a multitude of cellular processes. Activating KRAS mutations occur in approximately 30% of human cancers and contribute to malignant transformation through constitutive activation of downstream signaling cascades. These mutations cluster in several hotspots, with codons 12 and 13 being most commonly. It has been suggested that the position and type of amino acid exchange influence the transforming capacity of mutant KRAS proteins. To address this hypothesis, we used MCF10A human mammary epithelial cells to establish isogenic cell lines that express eight different cancer-associated KRAS mutations (G12C, G12D, G12V, G13C, G13D, A18D, Q61H, K117N) at physiological levels, and investigated the biochemical and functional consequences of the different KRAS variants in vitro. In addition, selected effects were evaluated in comparison to cells that overexpress mutant KRAS. The overall effects of mutants expressed at normal levels were moderate compared to overexpressed variants, but allowed delineation of biological functions that were related to specific alleles rather than KRAS expression level. None of the mutations induced morphological changes or migratory abilities. KRAS-G12D, -G12V, -G13D, and -K117N were able to mediate EGF-independent proliferation, whereas anchorage-independent growth was primarily induced by the K117N and Q61H variants. Analysis of known RAS effectors showed that none of the mutations led to increased phosphorylation of ERK, PDK1, or AKT. Both codon 13 mutations were associated with increased EGFR expression, which was not seen with other variants. Finally, comparative gene expression analysis of MCF10A-G13D versus MCF10A-G12D revealed distinct transcriptional changes, such as enhanced cytokine and p53 signaling, upon G13D expression. Together, we describe a useful resource for investigating the function of multiple KRAS mutations and provide insights into the differential effects of these variants in MCF10A cells.

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Substitutions in the KRas oncogene determine protein behavior: Implications for signaling and clinical outcome.

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