IRF6 is a mediator of Notch pro-differentiation and tumour suppressive function in keratinocytes

Abstract

While the pro‐differentiation and tumour suppressive functions of Notch signalling in keratinocytes are well established, the underlying mechanisms remain poorly understood. We report here that interferon regulatory factor 6 (IRF6), an IRF family member with an essential role in epidermal development, is induced in differentiation through a Notch‐dependent mechanism and is a primary Notch target in keratinocytes and keratinocyte‐derived SCC cells. Increased IRF6 expression contributes to the impact of Notch activation on growth/differentiation‐related genes, while it is not required for induction of ‘canonical’ Notch targets like p21WAF1/Cip1, Hes1 and Hey1. Down‐modulation of IRF6 counteracts differentiation of primary human keratinocytes in vitro and in vivo, promoting ras‐induced tumour formation. The clinical relevance of these findings is illustrated by the strikingly opposite pattern of expression of Notch1 and IRF6 versus epidermal growth factor receptor in a cohort of clinical SCCs, as a function of their grade of differentiation. Thus, IRF6 is a primary Notch target in keratinocytes, which contributes to the role of this pathway in differentiation and tumour suppression.

Notch1 controls development of the extravillous trophoblast lineage in the human placenta

“…An analogous mechanism could regulate p63 in vCTBs, because IRF6 rapidly increased after N1ICD expression. Also, ChIP analyses showed that N1ICD interacts with two RBPJκ cognate sequences, recently identified in the proximal IRF6 promoter region (33). Moreover, silencing of IRF6 in vCTBs impaired N1ICD-dependent suppression of ΔNp63.…”

“…In contrast to myc, N1ICD was recently shown to indirectly suppress p63. N1ICD binds to the IRF6 gene in keratinocytes and activates its expression (33). In turn, IRF6 promotes proteasomal degradation of p63 (30).…”

“…MYC PROM primers were designed to span the region harboring a putative RBPJκ DNA binding motif (CTGCGGGAA) identified by Transfac Patch 1.0 at −3.060 bp, which differs by one nucleotide from the consensus sequence CTGTGGGAA. MYC NDME-c1, MYC NDME-c2, IRF6 PROM-1, and IRF6 PROM-2 primers were published elsewhere (31,33). The following primer sequences were used: MYC PROM (229 bp): forward 5′-ATGAGGTCAAGCTGGACCTAC-3′ and reverse 5′-TGACGGTGTCTGATCACTTA-3′; MYC NDME-c1 (200 bp): forward 5′-GCTGCCACATGCTGATGAAC-3′ and reverse 5′-CCAGGTAGGGGCATTACGTC-3′; MYC NDME-c2 (174 bp): forward 5′-GAG-GCCCCCATTCATTACCC-3′ and reverse 5′-GCAGTTCTTCCTACGCTGGT-3′; IRF6 PROM-1: forward 5′-ACCCTCCCAGCTTGAGTTTT-3′ and reverse 5′-AAACCCCA-GTGGCATACAAG-3′ (142 bp); IRF6 PROM-2: forward 5′-TCAATGGAGGGCAA-AATGAT-3′ and reverse 5′-ACGCCTCATCTGCTTGATCT-3′ (162 bp); human RPL30 (control) (Cell Signaling, 7014).…”

“…5H and SI Appendix, Fig. S9), previously delineated in keratinocytes (33). Notch1 intracellular domain represses p63 through IRF6 in vCTBs.…”

Distinct requirements for wnt9a and irf6 in extension and integration mechanisms during zebrafish palate morphogenesis

“…Expression of irf6 in zebrafish has been reported in the pharyngeal arches and oral epithelium, and its embryonic requirement has been examined using dominant-negative mRNA overexpression that resulted in epiboly arrest, precluding analysis of its potential role in palatogenesis (Ben et al, 2005;Sabel et al, 2009). The function of Irf6 has been described for epithelial development in murine and zebrafish models, but whether and how this gene may directly regulate palatal fusion remains unclear (Sabel et al, 2009;Restivo et al, 2011;de la Garza et al, 2012).…”