Somatic mutations in IRE1α regulate keratinocyte migration and survival by differentially activating Rho GTPases.

Abstract

IRE1α is an Endoplasmic Reticulum (ER) transmembrane protein with cytoplasmic kinase and endoribonuclease (RNase) domains. Under ER stress, IRE1α can splice Xbp1 mRNA enabling translation of this Unfolded Protein Response transcription factor or mediate sequence-specific degradation of mRNAs through Regulated IRE1α-Dependent Decay (RIDD). Somatic mutations in IRE1α occur in many different human cancers including non-melanoma skin cancers (NMSC). To understand their role in skin cancer pathogenesis, we generated immortalized primary mouse keratinocytes inducibly expressing multiple engineered and cancer-associated mutations, including those present in NMSC. All NMSC mutations tested were activating mutations with elevated autophosphorylation and enhanced RIDD activity relative to Xbp1 splicing. Pathway analysis of RNA-Seq data and in vitro studies showed that RNase-impaired mutations enhanced cell migration due to increased levels of active RhoA and a RIDD target, Angptl4. In contrast, activating mutations exhibited elevated Rac1 activation, enrichment of genes involved in DNA repair, increased phospho-ATR levels, and improved survival in response to UVB irradiation, a critical etiological factor for sun-exposed skin cancers. Together, these results suggest divergent roles of IRE1α mutations by mediating critical tumor-promoting events in keratinocytes.