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Allele-Specific Mechanisms of Activation of MEK1 Mutants Determine Their Properties.

ABSTRACT: Mutations at multiple sites in MEK1 occur in cancer, suggesting that their mechanisms of activation might be different. We analyzed 17 tumor-associated MEK1 mutants and found that they drove ERK signaling autonomously or in a RAS/RAF-dependent manner. The latter are sensitive to feedback inhibition of RAF, which limits their functional output, and often cooccur with RAS or RAF mutations. They act as amplifiers of RAF signaling. In contrast, another class of mutants deletes a hitherto unrecognized negative regulatory segment of MEK1, is RAF- and phosphorylation-independent, is unaffected by feedback inhibition of upstream signaling, and drives high ERK output and transformation in the absence of RAF activity. Moreover, these RAF-independent mutants are insensitive to allosteric MEK inhibitors, which preferentially bind to the inactivated form of MEK1. All the mutants are sensitive to an ATP-competitive MEK inhibitor. Thus, our study comprises a novel therapeutic strategy for tumors driven by RAF-independent MEK1 mutants.Significance: Mutants with which MEK1 mutants coexist and their sensitivity to inhibitors are determined by allele-specific properties. This study shows the importance of functional characterization of mutant alleles in single oncogenes and identifies a new class of MEK1 mutants, insensitive to current MEK1 inhibitors but treatable with a new ATP-competitive inhibitor. Cancer Discov; 8(5); 648-61. ©2018 AACR.See related commentary by Maust et al., p. 534This article is highlighted in the In This Issue feature, p. 517.

SUBMITTER: Gao Y

PROVIDER: S-EPMC6112572 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Allele-Specific Mechanisms of Activation of MEK1 Mutants Determine Their Properties.

Gao Yijun Y Chang Matthew T MT McKay Daniel D Na Na N Zhou Bing B Yaeger Rona R Torres Neilawattie M NM Muniz Keven K Drosten Matthias M Barbacid Mariano M Caponigro Giordano G Stuart Darrin D Moebitz Henrik H Solit David B DB Abdel-Wahab Omar O Taylor Barry S BS Yao Zhan Z Rosen Neal N

Cancer discovery 20180226 5

Mutations at multiple sites in MEK1 occur in cancer, suggesting that their mechanisms of activation might be different. We analyzed 17 tumor-associated MEK1 mutants and found that they drove ERK signaling autonomously or in a RAS/RAF-dependent manner. The latter are sensitive to feedback inhibition of RAF, which limits their functional output, and often cooccur with RAS or RAF mutations. They act as amplifiers of RAF signaling. In contrast, another class of mutants deletes a ...[more]

PMID: 29483135

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Project description:Autoantibodies against leucine-rich glioma inactivated 1 (LGI1) are found in patients with limbic encephalitis and focal seizures. Here, we generate patient-derived monoclonal antibodies (mAbs) against LGI1. We explore their sequences and binding characteristics, plus their pathogenic potential using transfected HEK293T cells, rodent neuronal preparations, and behavioural and electrophysiological assessments in vivo after mAb injections into the rodent hippocampus. In live cell-based assays, LGI1 epitope recognition was examined with patient sera (n = 31), CSFs (n = 11), longitudinal serum samples (n = 15), and using mAbs (n = 14) generated from peripheral B cells of two patients. All sera and 9/11 CSFs bound both the leucine-rich repeat (LRR) and the epitempin repeat (EPTP) domains of LGI1, with stable ratios of LRR:EPTP antibody levels over time. By contrast, the mAbs derived from both patients recognized either the LRR or EPTP domain. mAbs against both domain specificities showed varied binding strengths, and marked genetic heterogeneity, with high mutation frequencies. LRR-specific mAbs recognized LGI1 docked to its interaction partners, ADAM22 and ADAM23, bound to rodent brain sections, and induced internalization of the LGI1-ADAM22/23 complex in both HEK293T cells and live hippocampal neurons. By contrast, few EPTP-specific mAbs bound to rodent brain sections or ADAM22/23-docked LGI1, but all inhibited the docking of LGI1 to ADAM22/23. After intrahippocampal injection, and by contrast to the LRR-directed mAbs, the EPTP-directed mAbs showed far less avid binding to brain tissue and were consistently detected in the serum. Post-injection, both domain-specific mAbs abrogated long-term potentiation induction, and LRR-directed antibodies with higher binding strengths induced memory impairment. Taken together, two largely dichotomous populations of LGI1 mAbs with distinct domain binding characteristics exist in the affinity matured peripheral autoantigen-specific memory pools of individuals, both of which have pathogenic potential. In human autoantibody-mediated diseases, the detailed characterization of patient mAbs provides a valuable method to dissect the molecular mechanisms within polyclonal populations.

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Allele-Specific Mechanisms of Activation of MEK1 Mutants Determine Their Properties.

Publications

Allele-Specific Mechanisms of Activation of MEK1 Mutants Determine Their Properties.

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