Differential susceptibility of Cx26 mutations associated with epidermal dysplasias to peptidoglycan derived from Staphylococcus aureus and Staphylococcus epidermidis.

Mutations in Connexin26 (Cx26) give rise to a spectrum of dominantly inherited hyperproliferating skin disorders, the severest being keratitis-ichthyosis-deafness (KID) syndrome, an inflammatory skin disorder, with patients prone to opportunistic infections. We compared the effects of peptidoglycan (PGN) extracted from the skin commensal Staphylococcus epidermidis and the opportunistic pathogen Staphylococcus aureus on interleukin-6 and connexin expression in HaCaT cells (a keratinocyte cell line) and connexin channel activity in HaCaT and HeLa (connexin deficient) cells transfected to express KID and non-KID Cx26 mutations. In both cell types, PGN from S. aureus induced hemichannel activity in cells expressing KID mutants as monitored by ATP release assays following 15-min challenge, while that from S. epidermidis evoked a response in HeLa cells. In KID mutant expressing cells, ATP release was significantly higher than in cells transfected with wild-type Cx26. No ATP release was observed in non-KID mutant transfected cells or in the presence of carbenoxolone, a connexin channel blocker. PGN isolated from S. aureus but not S. epidermidis induced interleukin-6 and Cx26 expression in HaCaT cells following 6-h challenge. Challenge by PGN from S. aureus evoked a greater interleukin-6 response in cells expressing KID mutants than in cells expressing wtCx26 or non-KID mutants. This response returned to basal levels if acute KID hemichannel signalling was blocked prior to PGN challenge. Thus, KID mutants form channels that can be triggered by the pro-inflammatory mediator PGN from opportunistic pathogens but not skin commensals, providing further insight into the genotype-phenotype relationship of Cx26 disorders.

Molecular analysis of connexin26 asparagine14 mutations associated with syndromic skin phenotypes.

Mutations in connexin26, a cutaneous gap junction protein, cause a wide variety of skin disorders including keratitis-ichthyosis-deafness syndrome (KID). We previously delineated a phenotype distinct from KID, hypotrichosis-deafness syndrome, caused by the mutation p.Asn14Lys in connexin26. However, a different mutation at the same location, p.Asn14Tyr, was reported to cause a disorder similar to KID. Distinct substitutions cause different conformational changes to the protein, each with unique consequences for its behaviour. This may explain the phenotypic differences. We found the previously described mutation p.Asn14Tyr in connexin26 in two patients from Brazil and Poland, and observe quite distinct phenotypes distinguishable from classical KID syndrome. We assessed functional consequences of p.Asn14Tyr and p.Asn14Lys, using fluorescently labelled proteins and parachute assay, comparing them with the classical KID mutation p.Asp50Asn. Our analyses show that p.Asn14Tyr, p.Asn14Lys and p.Asp50Asn have different consequences for protein localization and gap junction permeability. However, the differences between the phenotypes we observed cannot be readily explained from effects on protein trafficking or gap junction permeability.

A novel missense mutation in the second extracellular domain of GJB2, p.Ser183Phe, causes a syndrome of focal palmoplantar keratoderma with deafness.

Gap junctions, which consist of connexins, are intercellular channels that mediate rapid intercellular communication. In the skin, connexins are involved in the regulation of epidermal growth and differentiation. GJB2 encodes connexin26, which is an important skin-expressed gap junction protein. Mutations in GJB2 cause a wide variety of unique disorders, but despite extensive research, their mechanisms of action are poorly understood. The identification of novel diseases caused by mutations in GJB2 may help to illuminate the genotype-phenotype correlation and elucidate the function of different regions of the protein. Here, we report the first account of a family with a GJB2 missense mutation in the second extracellular domain (p.Ser183Phe) that causes skin abnormalities in addition to sensorineural hearing loss. Using fluorescent connexin26-EGFP fusion proteins, we showed that the mutation induces a partial protein transport defect that cannot be rescued by wild-type protein. Dye-transfer experiments using a parachute assay revealed channel functionality. Although p.Ser183Phe affects the second extracellular domain, mutations in the first extracellular domain also lead to focal palmoplantar keratoderma and likewise perturb protein transport in a dominant-negative manner. Therefore, we hypothesize that focal palmoplantar keratoderma in gap junction skin disease may be specifically associated with connexin trafficking defects as well as with mutations affecting its extracellular domains, thus broadening the spectrum of GJB2-associated diseases.

Multicentric reticulohistiocytosis: case report.

A 64-year-old woman developed slowly expanding asymptomatic red bumps on the hands and in the face since 1 year. Histopathological examination showed mononucleated and multinucleated giant cells with a characteristic "ground glass" appearance. Based on the clinical and histopathological findings, we made the diagnosis of multicentric reticulohistiocytosis (MRH). This rare variant of histiocytosis was described for the first time in 1950. Clinically, the disorder is characterized by papulonodular cutaneous lesions, and a severe and often destructive arthropathy. The reticulohistiocytoses are a rare group of closely related non-Langerhans cell histiocytosis that most commonly manifest in adults. Because MRH can be associated with an underlying malignancies, and an interdisciplinary examination and regimen of these patients is advisable.