NRF2 Enables EGFR Signaling in Melanoma Cells.

Julia Katharina Charlotte Kreß,Anita Hufnagel,André Marquardt,Christina Jessen,Svenja Meierjohann

doi:10.3390/ijms22083803

Abstract

Receptor tyrosine kinases (RTK) are rarely mutated in cutaneous melanoma, but the expression and activation of several RTK family members are associated with a proinvasive phenotype and therapy resistance. Epidermal growth factor receptor (EGFR) is a member of the RTK family and is only expressed in a subgroup of melanomas with poor prognosis. The insight into regulators of EGFR expression and activation is important for the understanding of the development of this malignant melanoma phenotype. Here, we describe that the transcription factor NRF2, the master regulator of the oxidative and electrophilic stress response, mediates the expression and activation of EGFR in melanoma by elevating the levels of EGFR as well as its ligands EGF and TGFα. ChIP sequencing data show that NRF2 directly binds to the promoter of EGF, which contains a canonical antioxidant response element. Accordingly, EGF is induced by oxidative stress and is also increased in lung adenocarcinoma and head and neck carcinoma with mutationally activated NRF2. In contrast, regulation of EGFR and TGFA occurs by an indirect mechanism, which is enabled by the ability of NRF2 to block the activity of the melanocytic lineage factor MITF in melanoma. MITF effectively suppresses EGFR and TGFA expression and therefore serves as link between NRF2 and EGFR. As EGFR was previously described to stimulate NRF2 activity, the mutual activation of NRF2 and EGFR pathways was investigated. The presence of NRF2 was necessary for full EGFR pathway activation, as NRF2-knockout cells showed reduced AKT activation in response to EGF stimulation compared to controls. Conversely, EGF led to the nuclear localization and activation of NRF2, thereby demonstrating that NRF2 and EGFR are connected in a positive feedback loop in melanoma. In summary, our data show that the EGFR-positive melanoma phenotype is strongly supported by NRF2, thus revealing a novel maintenance mechanism for this clinically challenging melanoma subpopulation.

Highlights

Cutaneous melanomas are mainly driven by oncogenic mutations in BRAF, NRAS, and NF1, which efficiently activate the MEK/ERK1/2 pathway [1,2]
In contrast to non-small cell lung cancer (NSCLC), Epidermal growth factor receptor (EGFR) is not mutated in melanoma, but is rather induced, e.g., as a result from therapy stress
EGFR expression has been connected to the activity of the transcription factor sexdetermining region Y-box 10 (SOX10) [43]

Summary

Introduction

Cutaneous melanomas are mainly driven by oncogenic mutations in BRAF, NRAS, and NF1, which efficiently activate the MEK/ERK1/2 pathway [1,2]. As an overactivation of the pathway is deleterious for cancer cells, mutations in these oncogenes usually exclude each other and only occur under therapy stress, e.g., when the pathway is blocked by BRAF and/or MEK inhibitors [1,2,3,4,5,6,7,8,9]. The activity of receptor tyrosine kinases including EGFR, another efficient MEK/ERK1/2 activator, is suppressed in melanoma under normal circumstances. This is in part attributed to the ERK1/2-driven expression of the SPRED and SPRY feedback inhibitors, which block EGFR/RAS signaling [10,11]. If expressed, EGFR correlates with melanoma invasiveness and pro-metastatic features [13,14]

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Conclusion