ADAM17/EGFR axis promotes transglutaminase-dependent skin barrier formation through phospholipase C γ1 and protein kinase C pathways

Abstract

The vitally important skin barrier is formed by extensive cross-linking activity of transglutaminases (TGs) during terminal epidermal differentiation. We have previously shown that epidermal deficiency of a disintegrin and metalloproteinase 17 (ADAM17), the principal EGFR ligand sheddase, results in postnatal skin barrier defects in mice due to impeded TG activity. However, the mechanism by which ADAM17/EGFR signalling maintains TG activity during epidermal differentiation remains elusive. Here we demonstrate that ADAM17-dependent EGFR signalling promotes TG activity in keratinocytes committed to terminal differentiation by direct induction of TG1 expression. Restored TG1 expression of EGF-stimulated differentiated Adam17−/− keratinocytes was strongly repressed by inhibitors for PLCγ1 or protein kinase C (PKC) pathways, while treatment with the PKC stimulator 12-O-tetradecanoylphorbol-13-acetate restored TG activity in the epidermis of keratinocyte-specific Adam17−/− (AD17ΔKC) mice. Further investigations emphasized the expression of PKCη, a mediator of TGM1 transcription, to be sensitive to EGFR activation. In agreement, topical skin application of cholesterol sulfate, an activator of PKCη, significantly improved TG activity in epidermis of AD17ΔKC mice. Our results suggest ADAM17/EGFR-driven PLCγ1 and PKC pathways as important promoters of TG1 expression during terminal keratinocyte differentiation. These findings may help to identify new therapeutic targets for inflammatory skin diseases related to epidermal barrier defects.

Studies on differentiation‐dependent expression and activity of distinct transglutaminases by specific substrate peptides using three‐dimensional reconstituted epidermis

“…Thus, TG1 and TG3 are indispensable enzymes for CE formation, which eventually determine the properties of the skin epidermis under several cellular signaling and regulation . Knockdown of either TG1 or TG3 in the 3D cultured cells, as expected, resulted in aberrant formation of the cornified layer as they matured to the differentiated stage in keratinocytes.…”

Loss of RHBDF2 results in an early-onset spontaneous murine colitis

“…FABP2 and TGM2 have both been implicated in the development and progression of IBD . In addition, ADAM17/EGFR signaling mechanisms have been shown to regulate TGM2 activity during epithelial cell differentiation . Transcriptional levels of FABP2 and TGM2 in Il10 −/− / Rhbdf2 −/− mice were found to be similar to that of Rhbdf2 −/− or Il10 −/− mice and WT controls, indicating that RHBDF2 may not be responsible for the regulation of FABP2 and TGM2 at the genetic level under chronic inflammation (Fig.…”

Phospholipase Cγ1 is required for normal irritant contact dermatitis responses and sebaceous gland homeostasis

“…PLCγ1 cKO mice showed normal expression of differentiation markers, namely keratin 5, keratin 1, filaggrin and loricrin (Figure B and C). Since a previous in vitro study has suggested that PLCγ1 plays a critical role in the induction of transglutaminase activity in primary keratinocytes, we examined transglutaminase activity in interfollicular epidermis. However, enzymatic activity of transglutaminase was not found to be altered in interfollicular epidermis of PLCγ1 cKO mice (Figure B).…”