ABSTRACT: Activation of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or NRF2) transcription factor is a critical and evolutionarily conserved cellular response to oxidative stress, metabolic stress, and xenobiotic insult. Whereas NRF2 deficiency results in hypersensitivity to a variety of stressors, its aberrant activation contributes to several cancer types, most commonly squamous cell carcinomas of the oesophagus, oral cavity, bladder and lung. Between 10-35% of patients with squamous cell carcinomas display hyperactive NRF2 signaling, harboring activating mutations and copy number amplifications of the NFE2L2 oncogene or inactivating mutations or deletions of KEAP1 or CUL3, which co-complex to ubiquitylate and degrade NRF2 protein. To better understand the role of NRF2 in tumorigenesis and more broadly in development, we engineered the endogenous Nfe2l2 genomic locus to create a conditional mutant LSL-Nrf2E79Q mouse model. The NRF2E79Q mutant protein does not undergo KEAP1/CUL3-dependent degradation, resulting in its constitutive activity. The E79Q mutation is also one of the most commonly observed NRF2-activating mutations in human squamous cancers. Expression of NRF2E79Q protein in keratin 14 (Krt14)-positive murine tissues resulted in a stunted body axis, decreased weight, decreased adipocyte size, and hyperplasia of squamous cell tissues of the tongue, forestomach, and oesophagus. RNAseq profiling and follow-up validation studies of cultured Nrf2E79Q murine esophageal epithelial cells revealed known and novel NRF2-regulated transcriptional programs, including genes associated with squamous cell carcinoma (e.g. Myc), lipid and cellular metabolism (Hk2, Ppard), and growth factors (Areg, Bmp6, Vegfa). These data suggest that in addition to decreasing adipogenesis, KRT14 restricted NRF2 activation leads to hyperplasia of the oesophagus, forestomach and tongue, but notably is not sufficient to drive formation of squamous cell carcinoma.
