HDAC3 ensures stepwise epidermal stratification via NCoR/SMRT-reliant mechanisms independent of its histone deacetylase activity

Abstract

Chromatin modifiers play critical roles in epidermal development, but the functions of histone deacetylases in this context are poorly understood. The class I HDAC, HDAC3, is of particular interest because it plays divergent roles in different tissues by partnering with tissue-specific transcription factors. We found that HDAC3 is expressed broadly in embryonic epidermis and is required for its orderly stepwise stratification. HDAC3 protein stability in vivo relies on NCoR and SMRT, which function redundantly in epidermal development. However, point mutations in the NCoR and SMRT deacetylase-activating domains, which are required for HDAC3's enzymatic function, permit normal stratification, indicating that HDAC3's roles in this context are largely independent of its histone deacetylase activity. HDAC3-bound sites are significantly enriched for predicted binding motifs for critical epidermal transcription factors including AP1, GRHL, and KLF family members. Our results suggest that among these, HDAC3 operates in conjunction with KLF4 to repress inappropriate expression of Tgm1, Krt16, and Aqp3. In parallel, HDAC3 suppresses expression of inflammatory cytokines through a Rela-dependent mechanism. These data identify HDAC3 as a hub coordinating multiple aspects of epidermal barrier acquisition.

Transcriptional and signalling regulation of skin epithelial stem cells in homeostasis, wounds and cancer

“…94 ZNF750 promotes epidermal differentiation by closely associating with Krüppel-like factor 4 (KLF4), 93,95,96 which is critical for skin barrier formation. 97,98 Of note, mutations of ZNF750 99 and KLF4 100 have been linked to psoriasis, an inflammatory skin disease strongly associated with defects in innate immunity and skin barrier function. These studies share a common theme in which germline mutations of squamous lineage TFs are frequently found in an overlapping spectrum of human ectodermal diseases, suggesting that these TFs are instrumental for early ectoderm specification and subsequently are repurposed to regulate squamous differentiation.…”

“…307,308 Similarly, HDAC3 governs skin barrier formation by interacting with KLF4, although, interestingly, HDAC3's histone deacetylase activity is dispensable in this particular context. 98 Indeed, a reiterative theme arises upon study of squamous lineage TF function. The interactions of these TFs with epigenetic regulators significantly impact epidermal differentiation and cSCC tumorigenesis.…”

“…Another squamous lineage TFs integrated into the stratification programme is zinc finger protein 750 (ZNF750), 93 which is down‐regulated in human patients with cleft palate syndrome harbouring mutant p63 94 . ZNF750 promotes epidermal differentiation by closely associating with Krüppel‐like factor 4 (KLF4), 93,95,96 which is critical for skin barrier formation 97,98 . Of note, mutations of ZNF750 99 and KLF4 100 have been linked to psoriasis, an inflammatory skin disease strongly associated with defects in innate immunity and skin barrier function.…”

“…In contrast, the de novo DNA methyltransferases DNMT3a/b are required for epidermal differentiation, and their loss promotes cSCC 307,308 . Similarly, HDAC3 governs skin barrier formation by interacting with KLF4, although, interestingly, HDAC3's histone deacetylase activity is dispensable in this particular context 98 …”

YAP1-TAZ/TEAD transcriptional networks restrain differentiation downstream of oncogenic Hedgehog-SMO activity

“…In order to validate the core function of KLF4 in BCC keratinocyte differentiation, we utilized available information on KLF4 chromatin immunoprecipitation analysis from mouse epidermis (ChIP-seq) 25 .…”