Molecular mechanisms for the regulation of Nrf2-mediated cell proliferation in non-small-cell lung cancers

Abstract

We previously demonstrated that the transcription factor NF-E2-related factor2 (Nrf2), expressed abundantly in non-small-cell lung cancer (NSCLC) cells, plays a pivotal role in the proliferation and chemoresistance of NSCLC. Here we show that Nrf2-mediated NSCLC cell proliferation is dually regulated by epidermal growth factor receptor (EGFR) signaling and an Nrf2 repressor protein Keap1 (Kelch-like ECH-associated protein-1). NSCLC cells expressing wild-type EGFR and Keap1 genes show enhanced proliferation on stimulation with EGFR ligand under non-stress conditions. Exposure to cigarette smoke extract (CSE) enhanced cell proliferation by modification of the Nrf2/Keap1 interaction. Although EGFR-tyrosine kinase inhibitor (TKI) inhibited the proliferation of these cells, exposure to CSE attenuated its efficacy. In NSCLC cells with Keap1 gene mutations, Nrf2 was constitutively activated owing to dysfunction of Keap1 and cells proliferated independently of EGFR signaling. Furthermore, EGFR-TKI was unable to inhibit their proliferation. In NSCLC cells with EGFR gene mutations, Nrf2 was constitutively activated by EGFR signaling. In these cells, proliferation was largely dependent on the EGFR signaling pathway. Although these cells were highly sensitive to EGFR-TKI, exposure to CSE or knockdown of Keap1 mRNA reduced sensitivity to EGFR-TKI. We found a case of NSCLC showing resistance to EGFR-TKI despite having EGFR-TKI-sensitive EGFR gene mutation because of dysfunctional mutation in Keap1 gene. Results indicate that oxidative stress reduces the anticancer effects of EGFR-TKI in wild-type Keap1 NSCLC cells. Analysis of Keap1 dysfunction may become a novel molecular marker to predict resistance to EGFR-TKI in NSCLC cells having EGFR-TKI-sensitive EGFR mutations. Finally, as the downstream molecule of both EGFR and Keap1 signaling, Nrf2 is an important molecular target for the treatment of NSCLC, where cells have mutations in EGFR, KRAS or Keap1 genes.

Characterization of a Novel Long Noncoding RNA, SCAL1, Induced by Cigarette Smoke and Elevated in Lung Cancer Cell Lines

“…Previously reports suggested that cells with KEAP1-inactivating mutations such as A549 (24) and HCC-827 (36) may have high levels of basal NRF2 activation (24,37). Intriguingly, NRF2 can also be constitutively activated by excessive EGFR activation (38,39), which is common in lung cancer and present in cell lines such as PC9, HCC-827, and NCI-1975 (38, 40). In contrast, NCI-H292 has been shown to have low levels of NRF2 activation (38).…”

“…Intriguingly, NRF2 can also be constitutively activated by excessive EGFR activation (38,39), which is common in lung cancer and present in cell lines such as PC9, HCC-827, and NCI-1975 (38, 40). In contrast, NCI-H292 has been shown to have low levels of NRF2 activation (38). Although only correlative, these expression results are consistent with the siRNA knockdown results in Figure 2, suggesting that cancer cells may also up-regulate SCAL1 expression through an NRF2-based mechanism.…”

Rac1 and Cdc42 Differentially Modulate Cigarette Smoke–Induced Airway Cell Migration through p120-Catenin–Dependent and –Independent Pathways

“…This smoke closely mimicked cigarette smoke extracts used routinely by other investigators. 24,25 Aliquots of the smoke condensate (93 mg/ m 3 of total suspended particulate matter) were stored at À80 C until use. The cells were starved in basal medium without growth factors for 1 hour, followed by incubation in smoke-free medium (Ctrl) or Smk 48 mg/m 3 of total suspended particulate matter) for the time points indicated in the text.…”

“…Realizing that cancer is a multistep process requiring numerous chemically mediated insults, we mimicked the exposure of airway epithelial cells to smoke using an established model of smoke-conditioned medium (Smk). 24,25 Primary HBE cells exposed to Smk medium underwent malignant transformation in 8 days, demonstrating rapid proliferation, anchorage-independent growth, and tumorigenesis in nude mice. 26 With this approach, we discovered p120ctn-dependent and p120ctn-independent pathways mediating cell migration provoked by cigarette smoke.…”

SNAILs promote G1 phase in selected cancer cells

“…In order to maximally avoid the interference caused by genomic mutation (genomic instability), H292 cell line was used to establish stable cell lines. In the known non-small cell lung cancer cell lines, we found only H292 cells possess the relatively stable genome (with wild-type KRAS/TP53/EGFR/ERCC1/Keap1/ Nrf2) (28)(29)(30)(31)(32)(33)(34)(35)(36).…”