Dysfunctional KEAP1–NRF2 Interaction in Non-Small-Cell Lung Cancer

Abstract

BackgroundNuclear factor erythroid-2 related factor 2 (NRF2) is a redox-sensitive transcription factor that positively regulates the expression of genes encoding antioxidants, xenobiotic detoxification enzymes, and drug efflux pumps, and confers cytoprotection against oxidative stress and xenobiotics in normal cells. Kelch-like ECH-associated protein 1 (KEAP1) negatively regulates NRF2 activity by targeting it to proteasomal degradation. Increased expression of cellular antioxidants and xenobiotic detoxification enzymes has been implicated in resistance of tumor cells against chemotherapeutic drugs.Methods and FindingsHere we report a systematic analysis of the KEAP1 genomic locus in lung cancer patients and cell lines that revealed deletion, insertion, and missense mutations in functionally important domains of KEAP1 and a very high percentage of loss of heterozygosity at 19p13.2, suggesting that biallelic inactivation of KEAP1 in lung cancer is a common event. Sequencing of KEAP1 in 12 cell lines and 54 non-small-cell lung cancer (NSCLC) samples revealed somatic mutations in KEAP1 in a total of six cell lines and ten tumors at a frequency of 50% and 19%, respectively. All the mutations were within highly conserved amino acid residues located in the Kelch or intervening region domain of the KEAP1 protein, suggesting that these mutations would likely abolish KEAP1 repressor activity. Evaluation of loss of heterozygosity at 19p13.2 revealed allelic losses in 61% of the NSCLC cell lines and 41% of the tumor samples. Decreased KEAP1 activity in cancer cells induced greater nuclear accumulation of NRF2, causing enhanced transcriptional induction of antioxidants, xenobiotic metabolism enzymes, and drug efflux pumps.ConclusionsThis is the first study to our knowledge to demonstrate that biallelic inactivation of KEAP1 is a frequent genetic alteration in NSCLC. Loss of KEAP1 function leading to constitutive activation of NRF2-mediated gene expression in cancer suggests that tumor cells manipulate the NRF2 pathway for their survival against chemotherapeutic agents.

Nrf2, but not β‐catenin, mutation represents an early event in rat hepatocarcinogenesis

“…1A,B). Twenty-four of 25 Nrf2 mutations were located in the Nrf2 regions coding for either the LxxQDxDLG motif (spanning amino acids [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] or the DxETGE motif (amino acids 77-82) (Fig. 1C).…”

Redox-based regulation of signal transduction: Principles, pitfalls, and promises

“…Thus, under homeostatic conditions, the complex of KEAP-1, Nrf2 and Cul3 ascertains rapid degradation of Nrf2 via the ubiquitin proteasome system, while under conditions of oxidative stress the associations between KEAP-1 Nrf2 and Cul2 are no longer intact, thereby preventing degradation of Nrf2 [177]. Importantly a somatic mutation of the KEAP-1 gene has been identified in lung cancer leading to a glycine to cysteine substitution in the DGR domain, which reduces KEAP-1's affinity for Nrf2, providing a structural basis for the loss of KEAP-1 function and gain of Nrf2 function [178,179]. These findings convincingly illustrate the importance of oxidation events in adaptor proteins in controlling redox signaling, and also that a disturbance in these interactions is associated with human disease.…”

The Keap1–Nrf2 pathway: promising therapeutic target to counteract ROS-mediated damage in cancers and neurodegenerative diseases

“…These conserved residues are vital for repressor activity of the kelch domain. Mutation of these residues leads to abrogation of the repression activity (Singh et al 2006). …”