Advertisement

Cleavage Isn't Everything

Potential Novel Mechanisms of Exfoliative Toxin-Mediated Blistering
      This Commentary describes breakthroughs in understanding the interactions between desmoglein 1 and plakogloben in staphylococcal-mediated blistering skin diseases.
      Bullous impetigo and staphylococcal scalded skin syndrome are blistering skin diseases caused by infection with strains of Staphylococcus aureus that elaborate exfoliative toxins, resulting in the cleavage of the keratinocyte cell adhesion protein desmoglein 1.
      • Stanley JR
      • Amagai M
      Pemphigus, bullous impetigo, and the staphylococcal scalded-skin syndrome.
      Desmoglein 1 is a desmosomal cadherin expressed in the superficial epidermis and is the target of antibodies in the autoimmune blistering skin disease pemphigus foliaceus. Skin histology is often indistinguishable between the autoimmune and staphylococcal-mediated conditions, as both exhibit loss of intercellular adhesion in the superficial layer of keratinocytes. In pemphigus foliaceus, the autoimmune nature of the disease can be distinguished by immunofluorescence studies that detect the binding of patient autoantibodies to the cell surface of skin keratinocytes. In contrast, immunofluorescence findings are negative in staphylococcal-mediated disease. Bullous impetigo represents a localized skin infection with S. aureus, resulting in superficial blisters that quickly break open, leaving classic “honey crust” erosions. Rarely, localized infections with S. aureus can progress to bacteremia or sepsis with more widespread blistering due to systemic elaboration of toxin in staphylococcal scalded skin syndrome; in these cases, bacterial cultures of blister fluid are usually negative for growth of S. aureus. In this issue of The American Journal of Pathology, Simpson et al shed light on the cellular mechanism leading to loss of cutaneous integrity in bullous impetigo and staphylococcal scalded-skin syndrome.

      Pemphigus Neonatorum: Identification as a Desmosomal Disease

      The first cases of staphylococcal-mediated blistering disease appeared in the literature as early as 1773 and were astutely termed pemphigus neonatorum by 19th century physicians.
      • Foerster OH
      Pemphigus neonatorum, or bullous impetigo contagiosa of the newborn.
      • Lyell A
      The staphylococcal scalded skin syndrome in historical perspective: emergence of dermopathic strains of Staphylococcal aureus and discovery of the epidermolytic toxin.
      In 1878, Gottfried Ritter von Rittershain published the largest series of patients to date with staphylococcal scalded skin syndrome.
      • von Rittershain GR
      Die exfolitive dermatitis jungener senglinge.
      He described a nearly 50% mortality rate among 279 patients, thereby distinguishing “Ritter's disease” from the more benign course associated with localized disease. In the 1970s, Marian Melish and Lowell Glasgow isolated staphylococcal exfoliative toxin and demonstrated it was the causative agent of bullous impetigo and staphylococcal scalded skin syndrome.
      • Melish ME
      • Glasgow LA
      The staphylococcal scalded-skin syndrome. Development of an experimental model.
      • Melish ME
      • Glasgow LA
      • Turner MD
      The staphylococcal scalded-skin syndrome: isolation and partial characterization of the exfoliative toxin.
      • Melish ME
      • Glasgow LA
      • Turner MD
      • Lillibridge CB
      The staphylococcal epidermolytic toxin: its isolation, characterization, and site of action.
      Subsequently, the genes for exfoliative toxins A and B were cloned,
      • O'Toole PW
      • Foster TJ
      Nucleotide sequence of the epidermolytic toxin A gene of Staphylococcus aureus.
      • Lee CY
      • Schmidt JJ
      • Johnson-Winegar AD
      • Spero L
      • Iandolo JJ
      Sequence determination and comparison of the exfoliative toxin A and toxin B genes from Staphylococcus aureus.
      • Jackson MP
      • Iandolo JJ
      Cloning and expression of the exfoliative toxin B gene from Staphylococcus aureus.
      and the crystal structure of exfoliative toxin A (ETA) suggested its function as an atypical serine protease.
      • Vath GM
      • Earhart CA
      • Rago JV
      • Kim MH
      • Bohach GA
      • Schlievert PM
      • Ohlendorf DH
      The structure of the superantigen exfoliative toxin A suggests a novel regulation as a serine protease.
      In 2000, desmoglein 1 was identified as a target of exfoliative toxin proteolytic cleavage.
      • Amagai M
      • Matsuyoshi N
      • Wang ZH
      • Andl C
      • Stanley JR
      Toxin in bullous impetigo and staphylococcal scalded-skin syndrome targets desmoglein 1.
      Further studies showed that exfoliative toxins cleave the desmoglein 1 ectodomain after glutamic acid residue 381, leaving a truncated transmembrane protein lacking the trans-adhesive interface.
      • Hanakawa Y
      • Schechter N
      • Lin C
      • Garza L
      • Li H
      • Yamaguchi T
      • Fudaba Y
      • Nishifuji K
      • Sugai M
      • Amagai M
      • Stanley JR
      Molecular mechanisms of blister formation in bullous impetigo and staphylococcal scalded skin syndrome.
      Collectively, these studies described staphylococcal exfoliative toxin as a novel virulence factor that cleaves off the desmoglein 1 adhesive ectodomain, thereby disrupting cell-cell adhesion. The resulting skin blister creates a portal of entry for S. aureus to access the superficial epidermis where it can further proliferate. Thus, more than two centuries after the first descriptions of disease, the molecular pathogenesis of bullous impetigo and staphylococcal scalded skin syndrome appeared to be solved. There is beauty in simplicity. But is that all there is to the story?

      A Role for Plakoglobin in Staphylococcal-Mediated Blistering Disease

      Simpson et al
      • Simpson CL
      • Kojima S
      • Getsios S
      • Green KJ
      Plakoglobin resuces adhesive defects induced by ectodomain truncation of the desmosomal cadherin, desmoglein 1: implications for exfoliative toxin-mediated skin blistering.
      now propose an additional mechanism for exfoliative toxin-mediated blistering through sequestration of plakoglobin by ectodomain-truncated desmoglein 1. Plakoglobin, also known as γ-catenin, is a cytoplasmic plaque protein that can associate with cadherins in both desmosomes and adherens junctions. Demonstrating its predominant role in desmosomes, plakoglobin is required to confer strong desmosomal but not adherens junction adhesion on otherwise nonadherent fibroblasts,
      • Marcozzi C
      • Burdett ID
      • Buxton RS
      • Magee AI
      Coexpression of both types of desmosomal cadherin and plakoglobin confers strong intercellular adhesion.
      and plakoglobin-null keratinocytes demonstrate delayed desmosome formation, leaving adherens junctions relatively unaffected.
      • Yin T
      • Getsios S
      • Caldelari R
      • Godsel LM
      • Kowalczyk AP
      • Muller EJ
      • Green KJ
      Mechanisms of plakoglobin-dependent adhesion: desmosome-specific functions in assembly and regulation by epidermal growth factor receptor.
      Plakoglobin's essential role in human desmosome biology is evidenced by Naxos disease, characterized by wooly hair, palmoplantar keratoderma, and potentially fatal arrhythmogenic right ventricular cardiomyopathy due to decreased adhesion of cardiac myocytes leading to ventricular rupture. In pemphigus vulgaris, an autoimmune blistering disease characterized by autoantibodies to the desmosomal cadherin desmoglein 3, plakoglobin remains associated with internalized desmoglein 3, which is ultimately targeted for lysosomal degradation.
      • Calkins CC
      • Setzer SV
      • Jennings JM
      • Summers S
      • Tsunoda K
      • Amagai M
      • Kowalczyk AP
      Desmoglein endocytosis and desmosome disassembly are coordinated responses to pemphigus autoantibodies.
      Previously, it was shown that mice expressing a mutant desmoglein 3 lacking the adhesive extracellular domain exhibit defective desmosomes that are reduced in number, aberrant membrane clusters of plakoglobin, and hyperproliferation and abnormal differentiation of the epidermis.
      • Allen E
      • Yu QC
      • Fuchs E
      Mice expressing a mutant desmosomal cadherin exhibit abnormalities in desmosomes, proliferation, and epidermal differentiation.
      Based on these studies, the authors sought to determine whether pathophysiologic mechanisms of exfoliative toxin-cleaved desmoglein 1 may extend beyond simple ectodomain cleavage.
      The authors expressed a mutant desmoglein 1 protein lacking the amino-terminal 381 amino acid residues (Δ381-Dsg1) in primary human keratinocytes to mimic the exfoliative toxin-cleaved protein. Ectodomain-truncated desmoglein 1 localized to the keratinocyte cell surface, disrupted the keratinocyte cell surface staining of the desmosomal proteins desmocollin 3 and desmoplakin, reduced desmocollin 3 protein levels in whole cell lysates, and compromised the adhesive strength of keratinocytes in a cultured cell dissociation assay. Because plakoglobin has been shown to regulate levels of desmosomal cadherins in plakoglobin-deficient keratinocytes,
      • Yin T
      • Getsios S
      • Caldelari R
      • Godsel LM
      • Kowalczyk AP
      • Muller EJ
      • Green KJ
      Mechanisms of plakoglobin-dependent adhesion: desmosome-specific functions in assembly and regulation by epidermal growth factor receptor.
      the authors hypothesized that the negative effects of ectodomain-truncated desmoglein 1 on cell adhesion were due to sequestration of plakoglobin. Consistent with this hypothesis, a triple point mutation of the cytoplasmic plakoglobin binding site of Δ381-Dsg1 abolished its interaction with plakoglobin and rescued defects in desmosomal protein levels and cell adhesion. Interestingly, expression of the desmoglein 1 cytoplasmic domain alone, or a chimeric protein combining the extracellular and transmembrane domains of the interleukin 2 receptor with the cytoplasmic domain of desmoglein 1, did not compromise cell adhesion, suggesting that desmosomal localization is necessary for the dominant negative effect.
      As an alternative strategy to rescue desmosomal adhesion, exogenous expression of plakoglobin restored cell surface localization of desmosomal proteins in keratinocytes expressing ectodomain-truncated or toxin-cleaved desmoglein 1, and in part rescued the cell adhesion defects. Recent studies have indicated that plakoglobin mRNA and protein levels are up-regulated in epithelial cells after histone deacetylase inhibition.
      • Canes D
      • Chiang GJ
      • Billmeyer BR
      • Austin CA
      • Kosakowski M
      • Rieger-Christ KM
      • Libertino JA
      • Summerhayes IC
      Histone deacetylase inhibitors upregulate plakoglobin expression in bladder carcinoma cells and display antineoplastic activity in vitro and in vivo.
      • Winn RA
      • Bremnes RM
      • Bemis L
      • Franklin WA
      • Miller YE
      • Cool C
      • Heasley LE
      γ-Catenin expression is reduced or absent in a subset of human lung cancers and re-expression inhibits transformed cell growth.
      To determine whether histone deacetylase inhibitors similarly up-regulate plakoglobin in human keratinocytes, the authors treated primary keratinocytes with trichostatin A. Trichostatin A slightly up-regulated plakoglobin expression, but more significantly up-regulated protein levels of desmoglein 1 and desmocollin 3 in human keratinocytes. Trichostatin A also rescued the adhesive defects in primary keratinocytes expressing Δ381-Dsg1 or treated with exfoliative toxin.

      From Bench to Bedside

      Simpson et al provide convincing evidence that adhesive defects caused by ectodomain-truncated desmoglein 1 are dependent on plakoglobin sequestration. Increasing the level of cellular plakoglobin rescues desmosome organization and cell adhesion defects caused by ectodomain-truncated or toxin-cleaved desmoglein 1, potentially through up-regulation of desmocollin 3 expression. These findings add to the complexity of exfoliative toxin-induced pathology and provide scientific support for novel therapeutic strategies. As with all good lines of inquiry, the study highlights several avenues for further investigation.
      One issue relevant to the pathophysiology of staphylococcal scalded skin syndrome is whether the ectodomain-truncated desmoglein 1 accurately reflects the fate of exfoliative toxin-cleaved desmoglein 1 in vivo. The authors show that in organotypic raft cultures, exfoliative toxin-cleaved desmoglein 1 is internalized together with plakoglobin and desmocollin 1, although desmoglein 1 in the basal, nonblistered layers of the epidermis remains detectable at the cell surface. Previous studies have also suggested that acutely toxin-cleaved desmoglein 1 is internalized.
      • Amagai M
      • Matsuyoshi N
      • Wang ZH
      • Andl C
      • Stanley JR
      Toxin in bullous impetigo and staphylococcal scalded-skin syndrome targets desmoglein 1.
      A recent study examined the localization of desmosomal proteins in the skin of patients with staphylococcal scalded skin syndrome, including the desmoglein 1 ectodomain and endodomain.
      • Aalfs AS
      • Oktarina DM
      • Diercks GF
      • Jonkman MF
      • Pas HH
      Staphylococcal scalded skin syndrome: loss of desmoglein 1 in patient skin.
      In nonlesional skin, cell surface desmoglein 1 endodomain staining was preserved, even in areas where ectodomain staining was lost. However, nearer to the blister, disruption of both cell surface ectodomain and endodomain staining occurred. No changes in desmocollin 3, desmoglein 3, or plakoglobin localization were observed. Further studies are necessary to clarify the fate of the desmoglein 1 endodomain in vivo.
      Whether histone deacetylase inhibition can be used effectively as adjunctive therapy for staphylococcal mediated blistering disease, or autoimmune blistering disease, is an intriguing concept. Traditional therapy for staphylococcal scalded skin syndrome uses double antibiotic coverage including the bacterial protein synthesis inhibitor clindamycin, which interferes with toxin production. Several histone deacetylase inhibitors currently in clinical use, such as vorinostat and romidepsin, are associated with significant side effects including immune suppression, which would be undesirable in cases of fulminant infection. However, other classes of histone deacetylase inhibitors, such as valproic acid and nicotinamide, are not associated with significant immune suppression. Vorinostat has been effective in treating the autoimmune blistering disease bullous pemphigoid.
      • Gardner JM
      • Evans KG
      • Goldstein S
      • Kim EJ
      • Vittorio CC
      • Rook AH
      Vorinostat for the treatment of bullous pemphigoid in the setting of advanced refractory cutaneous T-cell lymphoma.
      There is also anecdotal support for the use of nicotinamide, either topical or oral, as an adjunctive therapy for pemphigus.
      • Chaffins ML
      • Collison D
      • Fivenson DP
      Treatment of pemphigus and linear IgA dermatosis with nicotinamide and tetracycline: a review of 13 cases.
      • Alpsoy E
      • Yilmaz E
      • Basaran E
      • Yazar S
      • Cetin L
      Is the combination of tetracycline and nicotinamide therapy alone effective in pemphigus?.
      • Iraji F
      • Banan L
      The efficacy of nicotinamide gel 4% as an adjuvant therapy in the treatment of cutaneous erosions of pemphigus vulgaris.
      Future studies may further delineate the specific protein targets of the different histone deacetylase inhibitors, leading to more effective and potentially safer therapies for these life-threatening skin diseases.

      References

        • Stanley JR
        • Amagai M
        Pemphigus, bullous impetigo, and the staphylococcal scalded-skin syndrome.
        N Engl J Med. 2006; 355: 1800-1810
        • Simpson CL
        • Kojima S
        • Getsios S
        • Green KJ
        Plakoglobin resuces adhesive defects induced by ectodomain truncation of the desmosomal cadherin, desmoglein 1: implications for exfoliative toxin-mediated skin blistering.
        Am J Pathol. 2010; 177: 2921-2937
        • Foerster OH
        Pemphigus neonatorum, or bullous impetigo contagiosa of the newborn.
        J Am Med Assoc. 1909; LIII: 358-362
        • Lyell A
        The staphylococcal scalded skin syndrome in historical perspective: emergence of dermopathic strains of Staphylococcal aureus and discovery of the epidermolytic toxin.
        J Am Acad Dermatol. 1983; 9: 285-294
        • von Rittershain GR
        Die exfolitive dermatitis jungener senglinge.
        Centralzt f kinderheilk. 1878; 2: 3-23
        • Melish ME
        • Glasgow LA
        The staphylococcal scalded-skin syndrome. Development of an experimental model.
        N Engl J Med. 1970; 282: 1114-1119
        • Melish ME
        • Glasgow LA
        • Turner MD
        The staphylococcal scalded-skin syndrome: isolation and partial characterization of the exfoliative toxin.
        J Infect Dis. 1972; 125: 129-140
        • Melish ME
        • Glasgow LA
        • Turner MD
        • Lillibridge CB
        The staphylococcal epidermolytic toxin: its isolation, characterization, and site of action.
        Ann N Y Acad Sci. 1974; 236: 317-343
        • O'Toole PW
        • Foster TJ
        Nucleotide sequence of the epidermolytic toxin A gene of Staphylococcus aureus.
        J Bacteriol. 1987; 169: 3910-3915
        • Lee CY
        • Schmidt JJ
        • Johnson-Winegar AD
        • Spero L
        • Iandolo JJ
        Sequence determination and comparison of the exfoliative toxin A and toxin B genes from Staphylococcus aureus.
        J Bacteriol. 1987; 169: 3904-3909
        • Jackson MP
        • Iandolo JJ
        Cloning and expression of the exfoliative toxin B gene from Staphylococcus aureus.
        J Bacteriol. 1986; 166: 574-580
        • Vath GM
        • Earhart CA
        • Rago JV
        • Kim MH
        • Bohach GA
        • Schlievert PM
        • Ohlendorf DH
        The structure of the superantigen exfoliative toxin A suggests a novel regulation as a serine protease.
        Biochemistry. 1997; 36: 1559-1566
        • Amagai M
        • Matsuyoshi N
        • Wang ZH
        • Andl C
        • Stanley JR
        Toxin in bullous impetigo and staphylococcal scalded-skin syndrome targets desmoglein 1.
        Nat Med. 2000; 6: 1275-1277
        • Hanakawa Y
        • Schechter N
        • Lin C
        • Garza L
        • Li H
        • Yamaguchi T
        • Fudaba Y
        • Nishifuji K
        • Sugai M
        • Amagai M
        • Stanley JR
        Molecular mechanisms of blister formation in bullous impetigo and staphylococcal scalded skin syndrome.
        J Clin Invest. 2002; 110: 53-60
        • Marcozzi C
        • Burdett ID
        • Buxton RS
        • Magee AI
        Coexpression of both types of desmosomal cadherin and plakoglobin confers strong intercellular adhesion.
        J Cell Sci. 1998; 111: 495-509
        • Yin T
        • Getsios S
        • Caldelari R
        • Godsel LM
        • Kowalczyk AP
        • Muller EJ
        • Green KJ
        Mechanisms of plakoglobin-dependent adhesion: desmosome-specific functions in assembly and regulation by epidermal growth factor receptor.
        J Biol Chem. 2005; 280: 40355-40363
        • Calkins CC
        • Setzer SV
        • Jennings JM
        • Summers S
        • Tsunoda K
        • Amagai M
        • Kowalczyk AP
        Desmoglein endocytosis and desmosome disassembly are coordinated responses to pemphigus autoantibodies.
        J Biol Chem. 2006; 281: 7623-7634
        • Allen E
        • Yu QC
        • Fuchs E
        Mice expressing a mutant desmosomal cadherin exhibit abnormalities in desmosomes, proliferation, and epidermal differentiation.
        J Cell Biol. 1996; 133: 1367-1382
        • Canes D
        • Chiang GJ
        • Billmeyer BR
        • Austin CA
        • Kosakowski M
        • Rieger-Christ KM
        • Libertino JA
        • Summerhayes IC
        Histone deacetylase inhibitors upregulate plakoglobin expression in bladder carcinoma cells and display antineoplastic activity in vitro and in vivo.
        Int J Cancer. 2005; 113: 841-848
        • Winn RA
        • Bremnes RM
        • Bemis L
        • Franklin WA
        • Miller YE
        • Cool C
        • Heasley LE
        γ-Catenin expression is reduced or absent in a subset of human lung cancers and re-expression inhibits transformed cell growth.
        Oncogene. 2002; 21: 7497-7506
        • Aalfs AS
        • Oktarina DM
        • Diercks GF
        • Jonkman MF
        • Pas HH
        Staphylococcal scalded skin syndrome: loss of desmoglein 1 in patient skin.
        Eur J Dermatol. 2010; 20: 451-456
        • Gardner JM
        • Evans KG
        • Goldstein S
        • Kim EJ
        • Vittorio CC
        • Rook AH
        Vorinostat for the treatment of bullous pemphigoid in the setting of advanced refractory cutaneous T-cell lymphoma.
        Arch Dermatol. 2009; 145: 985-988
        • Chaffins ML
        • Collison D
        • Fivenson DP
        Treatment of pemphigus and linear IgA dermatosis with nicotinamide and tetracycline: a review of 13 cases.
        J Am Acad Dermatol. 1993; 28: 998-1000
        • Alpsoy E
        • Yilmaz E
        • Basaran E
        • Yazar S
        • Cetin L
        Is the combination of tetracycline and nicotinamide therapy alone effective in pemphigus?.
        Arch Dermatol. 1995; 131: 1339-1340
        • Iraji F
        • Banan L
        The efficacy of nicotinamide gel 4% as an adjuvant therapy in the treatment of cutaneous erosions of pemphigus vulgaris.
        Dermatol Ther. 2010; 23: 308-311

      Linked Article