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Lack of K140 immunoreactivity in junctional epidermolysis bullosa skin and keratinocytes associates with misfolded laminin epidermal growth factor‐like motif 2 of the β3 short arm
Author(s) -
Condorelli A.G.,
Fortugno P.,
Cianfarani F.,
Proto V.,
Di Zenzo G.,
Didona B.,
Zambruno G.,
Castiglia D.
Publication year - 2018
Publication title -
british journal of dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.304
H-Index - 179
eISSN - 1365-2133
pISSN - 0007-0963
DOI - 10.1111/bjd.15690
Subject(s) - laminin , biology , missense mutation , junctional epidermolysis bullosa (veterinary medicine) , microbiology and biotechnology , epitope , exon , er retention , endoplasmic reticulum , epidermal growth factor , structural motif , mutant , mutation , gene , immunology , antibody , genetics , biochemistry , cell culture , extracellular matrix
Summary Recessive mutations in the LAMA 3 , LAMB 3 and LAMC 2 genes that encode laminin‐332 ( LM 332) (α3a, β3 and γ2 chains, respectively) cause different junctional epidermolysis bullosa ( JEB ) subtypes. Biallelic truncating mutations in any of these three genes usually lead to lack of protein expression resulting in the severe generalized JEB subtype, while missense or splice‐site mutations in at least one allele lead to reduced expression typical of JEB generalized intermediate ( JEB ‐gen intermed) or localized. Here, we molecularly characterized an adult patient with JEB showing negative skin staining for the anti‐β3 chain monoclonal antibody K140. This antibody recognizes an as yet unidentified epitope within the laminin β3 short arm. The patient harbours a homozygous splice‐site mutation resulting in highly aberrant transcripts with partial skipping of the LAMB 3 exon that encodes the laminin epidermal growth factor‐like motif 2 of the β3 short arm (β3‐ LE 2). At the protein level, mutation consequences predict a misfolded β3‐ LE 2 motif and, indeed, we found that LM 332 is correctly assembled but retained in the endoplasmic reticulum ( ER ) where it colocalizes with the lumenal ER chaperone protein BiP, leading to dramatically reduced secretion. Lack of K140 reactivity to mutant LM 332 was confirmed by immunoprecipitation and Western blot analyses. Our findings not only identify the β3‐ LE 2 subdomain as the region recognized by K140, but also show that misfolding of LM 332 structural motifs and subsequent protein retention in the ER is a common pathomechanism in JEB ‐gen intermed. In addition to its usefulness in antigen mapping diagnosis of JEB subtypes, this knowledge is relevant to the design of therapeutic strategies aimed at releasing ER ‐retained LM 332 in JEB .