Interaction of the bullous pemphigoid antigen 1 (BP230) and desmoplakin with intermediate filaments is mediated by distinct sequences within their COOH terminus

The bullous pemphigoid antigen 1 (BP230) and desmoplakin (DP) are members of the plakin protein family of cytolinkers. Despite their homology, their COOH termini selectively bind distinct intermediate filaments (IFs). We studied sequences within their COOH termini required for their interaction with the epidermal keratins K5/K14, the simple epithelial keratins K8/K18, and type III IF vimentin by yeast three-hybrid, cell transfection, and overlay assays. The results indicate that BP230 interacts with K5/K14 but not with K8/K18 or vimentin via a region encompassing both the B and C subdomains and the COOH extremity, including a COOH-terminal eight-amino-acid stretch. In contrast, the C subdomain with the COOH-terminal extremity of DP interacts with K5/K14 and K8/K18, and its linker region is able to associate with K8/K18 and vimentin. Furthermore, the potential of DP to interact with IF proteins in yeast seems to be regulated by phosphorylation of Ser 2849 within its COOH terminus. Strikingly, BP230 and DP interacted with cytokeratins only when both type I and type II keratins were present. The head and tail domains of K5/K14 keratins were dispensable for their interaction with BP230 or DP. On the basis of our findings, we postulate that (1) the binding specificity of plakins for various IF proteins depends on their linker region between the highly homologous B and C subdomains and their COOH extremity and (2) the association of DP and BP230 with both epidermal and simple keratins is critically affected by the tertiary structure induced by heterodimerization and involves recognition sites located primarily in the rod domain of these keratins.     

Probable interaction between S100A7 and E-FABP in the cytosol of human keratinocytes from psoriatic scales

The overexpression of E-FABP and S100A7 in lesional psoriatic skin suggests a possible link with this hyperproliferative skin disease. In order to investigate a role for the proteins in this disease, the purifications for both proteins were re-analyzed. Moreover, a specific antiserum directed against purified human S100A7 was generated. By SDS-PAGE immunoblotting we show that E-FABP and S100A7 are expressed in cultured human differentiating keratinocytes and confirm their overexpression in psoriatic scales. Gel filtration and non-denaturing PAGE revealed that S100A7 co-purified with E-FABP, indicating an association between the two proteins. Ion-exchange chromatography resulted in the dissociation of the complex. Finally, immunoprecipitations using antiserum against E-FABP revealed that S100A7 co-immunoprecipitated with E-FABP from protein extracts of psoriatic scales. These data indicate that E-FABP and S100A7 might form a complex in the cytosol of human keratinocytes.     

Synergistic effect of hyaluronate fragments in retinaldehyde-induced skin hyperplasia which is a Cd44-dependent phenomenon

Background

CD44 is a polymorphic proteoglycan and functions as the principal cell-surface receptor for hyaluronate (HA). Heparin-binding epidermal growth factor (HB-EGF) activation of keratinocyte erbB receptors has been proposed to mediate retinoid-induced epidermal hyperplasia. We have recently shown that intermediate size HA fragments (HAFi) reverse skin atrophy by a CD44-dependent mechanism.

Methodology and Principal Findings

Treatment of primary mouse keratinocyte cultures with retinaldehyde (RAL) resulted in the most significant increase in keratinocyte proliferation when compared with other retinoids, retinoic acid, retinol or retinoyl palmitate. RAL and HAFi showed a more significant increase in keratinocyte proliferation than RAL or HAFi alone. No proliferation with RAL was observed in CD44^−/− keratinocytes. HA synthesis inhibitor, 4-methylumbelliferone inhibited the proliferative effect of RAL. HB-EGF, erbB1, and tissue inhibitor of MMP-3 blocking antibodies abrogated the RAL- or RAL- and HAFi-induced keratinocyte proliferation. Topical application of RAL or RAL and HAFi for 3 days caused a significant epidermal hyperplasia in the back skin of wild-type mice but not in CD44^−/− mice. Topical RAL and HAFi increased epidermal CD44 expression, and the epidermal and dermal HA. RAL induced the expression of active HB-EGF and erbB1. However, treatment with RAL and HAFi showed a more significant increase in pro-HB-EGF when compared to RAL or HAFi treatments alone. We then topically applied RAL and HAFi twice a day to the forearm skin of elderly dermatoporosis patients. After 1 month of treatment, we observed a significant clinical improvement.

Conclusions and Significance

Our results indicate that (i) RAL-induced in vitro and in vivo keratinocyte proliferation is a CD44-dependent phenomenon and requires the presence of HA, HB-EGF, erbB1 and MMPs, (ii) RAL and HAFi show a synergy in vitro and in vivo in mouse skin, and (iii) the combination of RAL and HAFi seems to have an important therapeutic effect in dermatoporosis.     

Production of the bullous pemphigoid antigen 230 (BP230) by Saccharomyces cerevisiae and Pichia pastoris

BP230 is a cytoskeletal linker protein of 2649 amino acids originally identified as the target autoantigen in bullous pemphigoid, a potentially devastating autoimmune skin blistering disorder. To better define its function, we sought to generate recombinant forms of BP230 in both Saccharomyces cerevisiae and Pichia pastoris after cloning its entire cDNA. By immunoblot analysis, full-length BP230 was not found in extracts of P. pastoris, whereas minor amounts of degraded BP230 were detected in extracts of S. cerevisiae. In contrast, both S. cerevisiae and P. pastoris were able to produce the 770-amino acid COOH-terminal domain of BP230. Furthermore, the production level of the recombinant BP230 tail in S. cerevisiae was significantly higher than that observed in P. pastoris and that of endogenous BP230 in cultured human keratinocytes. Finally, 12 of 17 (71%) BP sera recognized the recombinant BP230 protein in yeast extracts. Our results indicate that S. cerevisiae occasionally constitutes a better tool for recombinant protein production than P. pastoris. Although both its large size and poor solubility limit production of BP230, the developed yeast system provides cellular fractions enriched in BP230 recombinant proteins that constitute useful tools for the diagnosis of bullous pemphigoid.     

Intracellular localization of keratinocyte Fas ligand explains lack of cytolytic activity under physiological conditions

Acquired Fas ligand (FasL)-mediated cytolytic activity of human keratinocytes causes the massive keratinocyte cell death that occurs during toxic epidermal necrolysis, a deadly adverse drug eruption. Under normal conditions keratinocyte apoptosis is a rare event in the epidermis although keratinocytes express the death receptor Fas and its ligand. Here we have investigated why this is so. We show that Fas, FasL, Fas-associated death domain, and caspase-8 mRNA are detectable in the epidermis, primary keratinocyte cultures, and keratinocyte cell line and that Fas protein is expressed in keratinocytes of all subcorneal layers of the epidermis, whereas FasL is only expressed in the basal and first suprabasal layers. Coexpression of Fas and FasL therefore occurs in basal and suprabasal keratinocytes. In vitro, keratinocytes are killed by recombinant FasL in a dose-dependent manner, but they are unable to kill Fas-sensitive target cells despite FasL expression. Analysis of keratinocyte culture supernatants and treatment of keratinocytes with metalloproteinase inhibitors excluded cell surface expression of FasL and rapid metalloproteinase-mediated cleavage of cell surface FasL. Fluorescence-activated cell sorter, confocal microscopical, and electron microscopical analysis revealed that keratinocyte FasL is localized intracellularly predominantly associated to intermediate filaments. These data suggest that the observed inability of keratinocyte FasL to induce apoptosis under physiological conditions is due to its cellular localization and also indicate that intermediate filaments may be involved in regulating the subcellular localization of FasL.