Keap1 inhibition sensitizes head and neck squamous cell carcinoma cells to ionizing radiation via impaired non-homologous end joining and induced autophagy

Sara Sofia Deville,Maria Kaufmann,Nils Cordes,Susanne Luft

doi:10.1038/s41419-020-03100-w

Abstract

The function of Keap1 (Kelch-like ECH-associated protein 1), a sensor of oxidative and electrophilic stress, in the radiosensitivity of cancer cells remains elusive. Here, we investigated the effects of pharmacological inhibition of Keap1 with ML344 on radiosensitivity, DNA double-strand break (DSB) repair and autophagy in head and neck squamous cell carcinoma (HNSCC) cell lines. Our data demonstrate that Keap1 inhibition enhances HNSCC cell radiosensitivity. Despite elevated, Nrf2-dependent activity of non-homologous end joining (NHEJ)-related DNA repair, Keap1 inhibition seems to impair DSB repair through delayed phosphorylation of DNA-PKcs. Moreover, Keap1 inhibition elicited autophagy and increased p62 levels when combined with X-ray irradiation. Our findings suggest HNSCC cell radiosensitivity, NHEJ-mediated DSB repair, and autophagy to be co-regulated by Keap1.

Highlights

Survival rates of patients with head and neck squamous cell carcinomas (HNSCC) remain to be optimized[1,2,3]
A previously published whole-exome sequencing in a panel of HNSCC cell lines revealed a high mutational rate of the KEAP1 gene putatively resulting in alterations in protein characteristics[4]
Keap[1] was identified in a high-throughput screen in HNSCC cells as novel target critically involved in radioresistance and DNA repair processes[22]

Summary

Introduction

Survival rates of patients with head and neck squamous cell carcinomas (HNSCC) remain to be optimized[1,2,3]. In a high-throughput screen in three-dimensionally grown HNSCC cell lines, we recently identified Keap[1] (Kelch-like ECH-associated protein (1) as critical regulator of cellular radiosensitivity[4]. The Keap1/Nrf[2] (Nuclear factor (erythroid-derived-2)like (2) signaling axis senses free radicals and protects the cell during excessive oxidative and electrophilic conditions[5]. The Keap1/Nrf[2] axis has been reported to be involved in various cell functions such as DNA repair or autophagy[9]. Cells comprise two major cellular machineries to repair these DNA lesions, i.e., nonhomologous end joining (NHEJ) and homologous recombination (HR)[11,12]. After DSB recognition by the DNA damage response (DDR) proteins Mre[11], Rad[50], Official journal of the Cell Death Differentiation Association

Methods

Results

Conclusion