Desmoglein-1/Erbin interaction suppresses ERK activation to support epidermal differentiation
Robert M. Harmon, … , Eli Sprecher, Kathleen J. Green
Robert M. Harmon, … , Eli Sprecher, Kathleen J. Green
Published March 25, 2013
Citation Information: J Clin Invest. 2013;123(4):1556-1570. https://doi.org/10.1172/JCI65220.
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Desmoglein-1/Erbin interaction suppresses ERK activation to support epidermal differentiation

Abstract

Genetic disorders of the Ras/MAPK pathway, termed RASopathies, produce numerous abnormalities, including cutaneous keratodermas. The desmosomal cadherin, desmoglein-1 (DSG1), promotes keratinocyte differentiation by attenuating MAPK/ERK signaling and is linked to striate palmoplantar keratoderma (SPPK). This raises the possibility that cutaneous defects associated with SPPK and RASopathies share certain molecular faults. To identify intermediates responsible for executing the inhibition of ERK by DSG1, we conducted a yeast 2-hybrid screen. The screen revealed that Erbin (also known as ERBB2IP), a known ERK regulator, binds DSG1. Erbin silencing disrupted keratinocyte differentiation in culture, mimicking aspects of DSG1 deficiency. Furthermore, ERK inhibition and the induction of differentiation markers by DSG1 required both Erbin and DSG1 domains that participate in binding Erbin. Erbin blocks ERK signaling by interacting with and disrupting Ras-Raf scaffolds mediated by SHOC2, a protein genetically linked to the RASopathy, Noonan-like syndrome with loose anagen hair (NS/LAH). DSG1 overexpression enhanced this inhibitory function, increasing Erbin-SHOC2 interactions and decreasing Ras-SHOC2 interactions. Conversely, analysis of epidermis from DSG1-deficient patients with SPPK demonstrated increased Ras-SHOC2 colocalization and decreased Erbin-SHOC2 colocalization, offering a possible explanation for the observed epidermal defects. These findings suggest a mechanism by which DSG1 and Erbin cooperate to repress MAPK signaling and promote keratinocyte differentiation.

Authors

Robert M. Harmon, Cory L. Simpson, Jodi L. Johnson, Jennifer L. Koetsier, Adi D. Dubash, Nicole A. Najor, Ofer Sarig, Eli Sprecher, Kathleen J. Green

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Figure 2

DSG1 colocalizes with and binds Erbin in human keratinocytes.

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DSG1 colocalizes with and binds Erbin in human keratinocytes. (A) Immuno...
(A) Immunofluorescent staining of ectopic DSG1 and endogenous Erbin in cultured normal NHEKs. Scale bars: 10 μm. (B) Structured illumination microscopy (SIM) of ectopic DSG1 (red) and Erbin (green) in cultured NHEKs. Scale bars: 2 μm. (C) Staining of endogenous Erbin and DSG1 in human skin. The dotted line approximates the basement membrane. Scale bars: 20 μm. (D) SIM of DSG1 (red) and Erbin (green) in suprabasal keratinocytes of human skin. Arrowheads indicate sites where Erbin and DSG1 stains overlap. Scale bars: 1 μm. (E) DSG1 constructs used in immunoprecipitation studies. (F and G) Lysates from NHEKs transduced with retrovirus (RV) carrying GFP or DSG1 constructs were incubated with M2 (anti-FLAG) beads to precipitate ectopic DSG1 and associated proteins, followed by Western blot analysis. Stars mark putative degradation products. (H) Densitometric quantitation of G. Normalized to FLAG-tagged DSG1 input, Erbin precipitation with ectopic DSG1 is represented as fold change with respect to the amount precipitated with Δ381(WT). Blue samples represent data points from separate experiments. P values (Student’s t test) are indicated; mean ± SEM. EC, extracellular domain; TM, transmembrane domain; FLD, full-length DSG1; Δ381(WT), truncated DSG1 mimicking the exfoliative toxin cleavage product; Δ381(AAA), Pg binding-deficient version of Δ381(WT); Δ569, encodes only the DSG1 cytoplasmic domain; CoIP, coimmunoprecipitation.