Increased expression of Dsg2 in malignant skin carcinomas: A tissue-microarray based study

Cell cycle- and cancer-associated gene networks activated by Dsg2: evidence of cystatin A deregulation and a potential role in cell-cell adhesion

Cell-cell adhesion is paramount in providing and maintaining multicellular structure and signal transmission between cells. In the skin, disruption to desmosomal regulated intercellular connectivity may lead to disorders of keratinization and hyperproliferative disease including cancer. Recently we showed transgenic mice overexpressing desmoglein 2 (Dsg2) in the epidermis develop hyperplasia. Following microarray and gene network analysis, we demonstrate that Dsg2 caused a profound change in the transcriptome of keratinocytes in vivo and altered a number of genes important in epithelial dysplasia including: calcium-binding proteins (S100A8 and S100A9), members of the cyclin protein family, and the cysteine protease inhibitor cystatin A (CSTA). CSTA is deregulated in several skin cancers, including squamous cell carcinomas (SCC) and loss of function mutations lead to recessive skin fragility disorders. The microarray results were confirmed by qPCR, immunoblotting, and immunohistochemistry. CSTA was detected at high level throughout the newborn mouse epidermis but dramatically decreased with development and was detected predominantly in the differentiated layers. In human keratinocytes, knockdown of Dsg2 by siRNA or shRNA reduced CSTA expression. Furthermore, siRNA knockdown of CSTA resulted in cytoplasmic localization of Dsg2, perturbed cytokeratin 14 staining and reduced levels of desmoplakin in response to mechanical stretching. Both knockdown of either Dsg2 or CSTA induced loss of cell adhesion in a dispase-based assay and the effect was synergistic. Our findings here offer a novel pathway of CSTA regulation involving Dsg2 and a potential crosstalk between Dsg2 and CSTA that modulates cell adhesion. These results further support the recent human genetic findings that loss of function mutations in the CSTA gene result in skin fragility due to impaired cell-cell adhesion: autosomal-recessive exfoliative ichthyosis or acral peeling skin syndrome.

Desmosome regulation and signaling in disease

Desmosomes are cell-cell adhesive organelles with a well-known role in forming strong intercellular adhesion during embryogenesis and in adult tissues subject to mechanical stress, such as the heart and skin. More recently, desmosome components have also emerged as cell signaling regulators. Loss of expression or interference with the function of desmosome molecules results in diseases of the heart and skin and contributes to cancer progression. However, the underlying molecular mechanisms that result in inherited and acquired disorders remain poorly understood. To address this question, researchers are directing their studies towards determining the functions that occur inside and outside of the junctions and the extent to which functions are adhesion-dependent or independent. This review focuses on recent discoveries that provide insights into the role of desmosomes and desmosome components in cell signaling and disease; wherever possible, we address molecular functions within and outside of the adhesive structure.

Discordant expression of desmoglein 2 and 3 at the mRNA and protein levels in nodular and superficial basal cell carcinoma revealed by immunohistochemistry and fluorescent in situ hybridization

BACKGROUND

Basal cell carcinoma (BCC) is the most common human cancer. It is thought that skewed expression of desmogleins (Dsgs) in BCC may promote tumourigenesis.

AIM

To comparatively examine expression of Dsg2/Dsg3, using fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC) in BCC subtypes.

METHODS

In total, 84 frozen sections from patients with various clinical or histological subtypes of BCC were analyzed. Expressions of Dsg2/Dsg3 protein and Dsg2/Dsg3 mRNA were evaluated using IHC and FISH, respectively, in BCC nests and BCC-free epidermis, and then quantitatively measured.

RESULTS

There was loss of correlation between Dsg2 and Dsg3 (IHC) in nodular and superficial BCC (nBCC, sBCC), and significant correlation between Dsg2 and Dsg3 (FISH) in BCC, but not nBCC and sBCC.

CONCLUSIONS

Because more prominent aberrations of Dsg2/Dsg3 expression were seen at the protein than at the mRNA level in BCC, these comparative observations indicate greater importance of events at the proteome level than those at the genome level in tumour functional compartments. Different Dsg2/Dsg3 expression in sBCC and nBCC might corroborate the possibility that sBCC and nBCC are separate conditions. These results may contribute to better understanding of the biological behaviour of BCC.

Desmoglein 3: a help or a hindrance in cancer progression?

Desmoglein 3 is one of seven desmosomal cadherins that mediate cell-cell adhesion in desmosomes. Desmosomes are the intercellular junctional complexes that anchor the intermediate filaments of adjacent cells and confer strong cell adhesion thus are essential in the maintenance of tissue architecture and structural integrity. Like adherens junctions, desmosomes function as tumour suppressors and are down regulated in the process of epithelial-mesenchymal transition and in tumour cell invasion and metastasis. However, recently several studies have shown that various desmosomal components, including desmoglein 3, are up-regulated in cancer with increased levels of expression correlating with the clinical stage of malignancy, implicating their potentiality to serve as a diagnostic and prognostic marker. Furthermore, in vitro studies have demonstrated that overexpression of desmoglein 3 in cancer cell lines activates several signal pathways that have an impact on cell morphology, adhesion and locomotion. These additional signalling roles of desmoglein 3 may not be associated to its adhesive function in desmosomes but rather function outside of the junctions, acting as a key regulator in the control of actin based cellular processes. This review will discuss recent advances which support the role of desmoglein 3 in cancer progression.

Desmosomal defects in acantholytic squamous cell carcinomas

BACKGROUND

Acantholytic squamous cell carcinoma (Acantholytic SCC) are epithelial tumors characterized by a loss of cell adhesion between neoplastic keratinocytes. The mechanism underlying loss of cell-cell adhesion in these tumors is not understood.

METHODS

A retrospective analysis of acantholytic SCC (n = 17) and conventional SCC (n = 16, controls not showing acantholysis) was conducted using a set of desmosomal and adherens junction protein antibodies. Immunofluorescence microscopy was used to identify tumors with loss of adhesion protein expression.

RESULTS

The vast majority of acantholytic SCC (89%) showed focal loss of at least one desmosomal cell adhesion protein. Most interestingly, 65% of these tumors lost expression of two or more desmosomal proteins.

CONCLUSIONS

Loss of cell adhesion in acantholytic SCC is most likely linked to the focal loss of desmosomal protein expression, thus providing potential mechanistic insight into the patho-mechanism underlying this malignancy.

Desmosomes: regulators of cellular signaling and adhesion in epidermal health and disease

Desmosomes are intercellular junctions that mediate cell-cell adhesion and anchor the intermediate filament network to the plasma membrane, providing mechanical resilience to tissues such as the epidermis and heart. In addition to their critical roles in adhesion, desmosomal proteins are emerging as mediators of cell signaling important for proper cell and tissue functions. In this review we highlight what is known about desmosomal proteins regulating adhesion and signaling in healthy skin-in morphogenesis, differentiation and homeostasis, wound healing, and protection against environmental damage. We also discuss how human diseases that target desmosome molecules directly or interfere indirectly with these mechanical and signaling functions to contribute to pathogenesis.

Altered expression and localization of desmoglein 3 in esophageal squamous cell carcinoma

Desmoglein 3 (DSG3), a transmembrane cadherin of the desmosomal cell-cell adhesion structure, plays vital roles in the maintenance of normal epithelial tissue architecture. Reports implicating a role for DSG3 expression in cancer are few and contradictory. In this study, immunohistochemical staining was employed to investigate DSG3 expression and subcellular localization in esophageal squamous cell carcinoma (ESCC), and to correlate changes with clinical characteristics. Results indicate that in normal squamous cell epithelia, strong DSG3 immunoreactivity was observed in the Stratum spinosum, and localization occurred only at the cell membrane. In ESCC, DSG3 immunoreactivity displayed an abnormal cytoplasmic localization that was correlated with cell differentiation (P=0.018). Most strikingly, in 74.1% of the tumors, DSG3 expression was up-regulated and correlated with regional lymph node metastasis (P=0.036). Moreover, in patients without lymph node metastasis, cytoplasmic localization of DSG3 correlated with poor prognosis (P=0.044). These results suggest that DSG3 is involved in the development of ESCC and imply that DSG3 overexpression is likely to be an essential contributor to the aggressive features of esophageal cancer.

Aberrant expression and altered cellular localization of desmosomal and hemidesmosomal proteins are associated with aggressive clinicopathological features of oral squamous cell carcinoma

Disruption of cell adhesion plays a central role in dedifferentiation, invasion, and metastasis of various cancers. The desmosome and hemidesmosome are anchoring junctions that control cell-cell and cell-matrix adhesion, respectively. To clarify their contributions in mediating the biological properties of oral cancer, we immunohistochemically examined the expression of desmoglein 1 (DSG1), DSG2, DSG3, desmocollin 2 (DSC2), integrin beta 4 (ITGB4), laminin gamma chain 2 (LAMC2), and collagen type 17 alpha 1 (COL17A1) in 51 cases of oral squamous cell carcinoma. On normal oral epithelial cells, DSG1, DSG3, DSC2, and COL17A1 were expressed on the plasma membrane, while ITGB4 and mature LAMC2 were present at the basement membrane. In cancer, the expression of DSG1, DSG3, DSC2, and COL17A1 decreased and internalized to the cytoplasm. Cytoplasmic expression of DSG2, ITGB4, and LAMC2 was induced in the cancer cells facing to the stroma. We scored immunohistochemical expression and correlated this to clinicopathological parameters including histologic differentiation, pattern of invasion, and presence of lymph node metastasis. Decrease of DSG3 and DSC2 expression correlated with a more aggressive cancer phenotype: less differentiated and more invasive histologic features and a higher incidence of nodal metastasis. Lower COL17A1 and higher LAMC2 expression were also associated with a more aggressive phenotype. The present study demonstrates that aberrant expression and altered cellular localization of desmosomal and hemidesmosomal proteins are associated with aggressive clinicopathological features of oral cancer. This reinforces the notion that disturbance of the keratin-associated anchoring junctions confers aggressive features to cancer cells.

Desmoglein 2 compensates for desmoglein 3 but does not control cell adhesion via regulation of p38 mitogen-activated protein kinase in keratinocytes

Desmosomal cadherins are transmembrane adhesion molecules that provide cell adhesion by interacting in the intercellular space of adjacent cells. In keratinocytes, several desmoglein (Dsg1-4) and desmocollin (Dsc1-3) isoforms are coexpressed. We have shown previously that Dsg2 is less important for keratinocyte cohesion compared with Dsg3 and that the latter forms a complex with p38 MAPK. In this study, we compared the involvement of Dsg2 and Dsg3 in the p38 MAPK-dependent regulation of keratinocyte cohesion. We show that loss of cell adhesion and keratin filament retraction induced by Dsg3 depletion is ameliorated by specific p38 MAPK inhibition. Furthermore, in contrast to depletion of Dsg2, siRNA-mediated silencing of Dsg3 induced p38 MAPK activation, which is in line with immunoprecipitation experiments demonstrating the interaction of activated p38 MAPK with Dsg3 but not with Dsg2. Cell fractionation into a cytoskeleton-unbound and a cytoskeleton-anchored desmosome-containing pool revealed that Dsg3, in contrast to Dsg2, is present in relevant amounts in the unbound pool in which activated p38 MAPK is predominantly detectable. Moreover, because loss of cell adhesion by Dsg3 depletion was partially rescued by p38 MAPK inhibition, we conclude that, besides its function as an adhesion molecule, Dsg3 is strengthening cell cohesion via modulation of p38 MAPK-dependent keratin filament reorganization. Nevertheless, because subsequent targeting of Dsg3 in Dsg2-depleted cells led to drastically enhanced keratinocyte dissociation and Dsg2 was enhanced at the membrane in Dsg3 knockout cells, we conclude that Dsg2 compensates for Dsg3 loss of function.

iRHOM2-dependent regulation of ADAM17 in cutaneous disease and epidermal barrier function

iRHOM2 is a highly conserved, catalytically inactive member of the Rhomboid family, which has recently been shown to regulate the maturation of the multi-substrate ectodomain sheddase enzyme ADAM17 (TACE) in macrophages. Dominant iRHOM2 mutations are the cause of the inherited cutaneous and oesophageal cancer-susceptibility syndrome tylosis with oesophageal cancer (TOC), suggesting a role for this protein in epithelial cells. Here, using tissues derived from TOC patients, we demonstrate that TOC-associated mutations in iRHOM2 cause an increase in the maturation and activity of ADAM17 in epidermal keratinocytes, resulting in significantly upregulated shedding of ADAM17 substrates, including EGF-family growth factors and pro-inflammatory cytokines. This activity is accompanied by increased EGFR activity, increased desmosome processing and the presence of immature epidermal desmosomes, upregulated epidermal transglutaminase activity and heightened resistance to Staphylococcal infection in TOC keratinocytes. Many of these features are consistent with the presence of a constitutive wound-healing-like phenotype in TOC epidermis, which may shed light on a novel pathway in skin repair, regeneration and inflammation.

Different roles of cadherins in the assembly and structural integrity of the desmosome complex

Adhesion between cells is established by the formation of specialized intercellular junctional complexes, such as desmosomes. Desmosomes contain isoforms of two members of the cadherin superfamily of cell adhesion proteins, desmocollins (Dsc) and desmogleins (Dsg), but their combinatorial roles in desmosome assembly are not understood. To uncouple desmosome assembly from other cell-cell adhesion complexes, we used micro-patterned substrates of Dsc2aFc and/or Dsg2Fc and collagen IV; we show that Dsc2aFc, but not Dsg2Fc, was necessary and sufficient to recruit desmosome-specific desmoplakin into desmosome puncta and produce strong adhesive binding. Single-molecule force spectroscopy showed that monomeric Dsc2a, but not Dsg2, formed Ca(2+)-dependent homophilic bonds, and that Dsg2 formed Ca(2+)-independent heterophilic bonds with Dsc2a. A W2A mutation in Dsc2a inhibited Ca(2+)-dependent homophilic binding, similar to classical cadherins, and Dsc2aW2A, but not Dsg2W2A, was excluded from desmosomes in MDCK cells. These results indicate that Dsc2a, but not Dsg2, is required for desmosome assembly through homophilic Ca(2+)- and W2-dependent binding, and that Dsg2 might be involved later in regulating a switch to Ca(2+)-independent adhesion in mature desmosomes.

Desmoglein 2 depletion leads to increased migration and upregulation of the chemoattractant secretoneurin in melanoma cells

During development and progression of malignant melanoma, an important role has been attributed to alterations of cell-cell adhesions, in particular, to a “cadherin switch” from E- to N-cadherin. We have previously shown that a subtype of melanoma cells express the desmosomal cadherin desmoglein 2 as non-junction-bound cell surface protein in addition to classical cadherins. To study the role of desmoglein 2 in melanoma cells, melanoma lines containing high endogenous amounts of desmoglein 2 were depleted of the protein by RNA interference. Transwell migration and scratch wounding assays showed markedly increased migration upon desmoglein 2 suppression whereas proliferation and viability remained unaltered. In gene expression profiles, desmoglein 2 depletion was associated with overexpression of migration-related genes. Strongest overexpression was found for secretogranin II which has not been reported in melanoma cells before. The bioactive peptide derived from secretogranin II, secretoneurin, is known to exert chemoattractive functions and was demonstrated here to stimulate melanoma cell migration. In summary, we show that desmoglein 2 expression attenuates migration of melanoma cells. The mechanism of desmoglein 2 impaired cell migration is mediated by downregulation of secretogranin II. Loss of desmoglein 2 increases expression of secretogranin II, followed by an enhanced migratory activity of melanoma cells. Our data add a new pathway of regulating melanoma cell migration related to a desmoglein 2 – secretogranin II axis.

Beyond E-cadherin: roles of other cadherin superfamily members in cancer

Loss of cadherin 1 (CDH1; also known as epithelial cadherin (E-cadherin)) is used for the diagnosis and prognosis of epithelial cancers. However, it should not be ignored that the superfamily of transmembrane cadherin proteins encompasses more than 100 members in humans, including other classical cadherins, numerous protocadherins and cadherin-related proteins. Elucidation of their roles in suppression versus initiation or progression of various tumour types is a young but fascinating field of molecular cancer research. These cadherins are very diverse in both structure and function, and their mutual interactions seem to influence biological responses in complex and versatile ways.

Prognostic significance of desmoglein 2 and desmoglein 3 in esophageal squamous cell carcinoma

OBJECTIVE

Desmogleins (DSGs) are major members among the desmosomal cadherins critically involved in cell-cell adhesion and the maintenance of normal tissue architecture in epithelia. Reports exploring links of DSG family member expression with cancers are few and vary. The aim of this study was to investigate the ratio of DSG2 and DSG3 mRNA expression in esophageal squamous cell carcinoma (ESCC) tissue to normal tissue (T/N ratio) and evaluate correlations with clinical parameters.

METHODS

The mRNA expression of DSGs, as well as γ-catenin and desmoplakin, was detected by real-time quantitative RT-PCR in 85 cases of ESCC tissue specimens.

RESULTS

The expression level of DSG3 mRNA was significantly higher than that of DSG2 in ESCC specimens (p = 0.000). DSG3 mRNA expression highly correlated with histological grade (p = 0.009), whereas that of DSG2 did not significantly relate to any clinicopathologic parameter. Kaplan-Meier survival analysis showed that only DSG3 expression had an impact on the survival curve, with negative DSG3 expression indicating worse survival (p = 0.038). Multivariate Cox regression analysis demonstrated DSG3 to be an independent prognostic factor for survival. Furthermore, correlation analysis demonstrated the mRNA level of DSG3 to highly correlate with those of γ-catenin and desmoplakin in ESCC samples (p=0.000), implying that the expression of desmosomal components might be regulated by the same upstream regulatory molecules.

CONCLUSIONS

Our findings suggest that DSG3 may be involved in the progression of ESCC and serve as a prognostic marker, while expression of DSG2 cannot be used as a predictor of ESCC patient outcome.

Loss of the desmosomal cadherin desmoglein-2 suppresses colon cancer cell proliferation through EGFR signaling

Desmosomal cadherins mediate cell-cell adhesion in epithelial tissues and have been known to be altered in cancer. We have previously shown that one of the two intestinal epithelial desmosomal cadherins, desmocollin-2 (Dsc2) loss promotes colonic epithelial carcinoma cell proliferation and tumor formation. In this study we show that loss of the other intestinal desmosomal cadherin, desmoglein-2 (Dsg2) that pairs with Dsc2, results in decreased epithelial cell proliferation and suppressed xenograft tumor growth in mice. Dsg2-deficient cells demonstrated a compensatory increase in Dsc2 expression, and small interfering RNA-mediated loss of Dsc2 restored proliferation in Dsg2-deficient cells. Dsg2 downregulation inhibited epidermal growth factor receptor (EGFR) signaling and cell proliferation through altered phosphorylation of EGFR and downstream extracellular signal-regulated kinase activation in parallel with inhibited EGFR receptor internalization. Additionally, we demonstrated a central role of Dsc2 in controlling EGFR signaling and cell proliferation in intestinal epithelial cells. Consistent with these findings, analyses of human colon cancers demonstrated increased Dsg2 protein expression. Taken together, these data demonstrate that partner desmosomal cadherins Dsg2 and Dsc2 play opposing roles in controlling colonic carcinoma cell proliferation through differential effects on EGFR signaling.

Mechanistic basis of desmosome-targeted diseases

Desmosomes are dynamic junctions between cells that maintain the structural integrity of skin and heart tissues by withstanding shear forces. Mutations in component genes cause life-threatening conditions including arrhythmogenic right ventricular cardiomyopathy, and desmosomal proteins are targeted by pathogenic autoantibodies in skin blistering diseases such as pemphigus. Here, we review a set of newly discovered pathogenic alterations and discuss the structural repercussions of debilitating mutations on desmosomal proteins. The architectures of native desmosomal assemblies have been visualized by cryo-electron microscopy and cryo-electron tomography, and the network of protein domain interactions is becoming apparent. Plakophilin and desmoplakin mutations have been discovered to alter binding interfaces, structures, and stabilities of folded domains that have been resolved by X-ray crystallography and NMR spectroscopy. The flexibility within desmoplakin has been revealed by small-angle X-ray scattering and fluorescence assays, explaining how mechanical stresses are accommodated. These studies have shown that the structural and functional consequences of desmosomal mutations can now begin to be understood at multiple levels of spatial and temporal resolution. This review discusses the recent structural insights and raises the possibility of using modeling for mechanism-based diagnosis of how deleterious mutations alter the integrity of solid tissues.

Decreased expression of intercellular adhesion molecules in acantholytic squamous cell carcinoma compared with invasive well-differentiated squamous cell carcinoma of the skin

Intercellular adhesion proteins are poorly characterized in acantholytic squamous cell carcinoma (ASCC), a more aggressive tumor than nonacantholytic invasive well-differentiated squamous cell carcinoma (SCC) of the skin. In this study we compared expression of Dsg3, E-cadherin, and syndecan-1 in ASCC and SCC. Immunohistochemical detection of Dsg3, E-cadherin, and syndecan-1 in 22 ASCCs and 22 SCCs was graded on a semiquantitative scale for intensity of staining (SI) and degree of circumferential staining (CS) about the cell membrane. Results were assessed by means of conditional logistic regression and χ(2) analysis. Dsg3 and E-cadherin expression (SI, CS) was significantly decreased (P < .05) in ASCC compared with SCC, whereas staining for syndecan-1 was similar in the 2 tumor types. Differences in expression of adhesion markers between ASCC and SCC may contribute to the development of acantholysis in ASCC and its more aggressive biologic behavior.

Desmoglein 2 is less important than desmoglein 3 for keratinocyte cohesion

Desmosomes provide intercellular adhesive strength required for integrity of epithelial and some non-epithelial tissues. Within the epidermis, the cadherin-type adhesion molecules desmoglein (Dsg) 1-4 and desmocollin (Dsc) 1-3 build the adhesive core of desmosomes. In keratinocytes, several isoforms of these proteins are co-expressed. However, the contribution of specific isoforms to overall cell cohesion is unclear. Therefore, in this study we investigated the roles of Dsg2 and Dsg3, the latter of which is known to be essential for keratinocyte adhesion based on its autoantibody-induced loss of function in the autoimmune blistering skin disease pemphigus vulgaris (PV). The pathogenic PV antibody AK23, targeting the Dsg3 adhesive domain, led to profound loss of cell cohesion in human keratinocytes as revealed by the dispase-based dissociation assays. In contrast, an antibody against Dsg2 had no effect on cell cohesion although the Dsg2 antibody was demonstrated to interfere with Dsg2 transinteraction by single molecule atomic force microscopy and was effective to reduce cell cohesion in intestinal epithelial Caco-2 cells which express Dsg2 as the only Dsg isoform. To substantiate these findings, siRNA-mediated silencing of Dsg2 or Dsg3 was performed in keratinocytes. In contrast to Dsg3-depleted cells, Dsg2 knockdown reduced cell cohesion only under conditions of increased shear. These experiments indicate that specific desmosomal cadherins contribute differently to keratinocyte cohesion and that Dsg2 compared to Dsg3 is less important in this context.

Unimpaired skin carcinogenesis in Desmoglein 3 knockout mice

The contribution of adherens junction inactivation, typically by downregulation or mutation of the transmembrane core component E-cadherin, to cancer progression is well recognized. In contrast, the role of the desmosomal cadherin components of the related cell-cell adhesion junction, the desmosome, in cancer development has not been well explored. Here, we use mouse models to probe the functional role of desmosomal cadherins in carcinogenesis. Because mice lacking the desmosomal cadherin Desmoglein 3 (Dsg3) have revealed a crucial role for Dsg3 in cell-cell adhesion in stratified epithelia, we investigate the consequence of Dsg3 loss in two models of skin carcinogenesis. First, using Dsg3−/− keratinocytes, we show that these cells display adhesion defects in vitro and compromised tumor growth in allograft assays, suggesting that Dsg3 enables tumor formation in certain settings. In contrast, using an autochthonous model for SCC development in response to chronic UVB treatment, we discover a surprising lack of enhanced tumorigenesis in Dsg3−/− mice relative to controls, unlike mice lacking the desmosomal component Perp. Accordingly, there is no defect in the apoptotic response to UVB or enhanced immune cell infiltration upon Dsg3 loss that could promote tumorigenesis. Thus, Dsg3 does not display a clear function as a tumor suppressor in these mouse skin cancer models. Continued unraveling of the roles of Dsg3 and other desmosomal constituents in carcinogenesis in different contexts will be important for ultimately improving cancer diagnosis, prognostication, and treatment.

Hailey-Hailey disease and tight junctions: Claudins 1 and 4 are regulated by ATP2C1 gene encoding Ca(2+) /Mn(2+) ATPase SPCA1 in cultured keratinocytes

Mutations in the ATP2C1 gene encoding Ca(2+) /Mn(2+) ATPase SPCA1 cause Hailey-Hailey disease (HHD, OMIM 16960). HHD is characterized by epidermal acantholysis. We attempted to model HHD using normal keratinocytes, in which the SPCA1 mRNA was down-regulated with the small inhibitory RNA (siRNA) method. SiRNA inhibition significantly down-regulated the SPCA1 mRNA, as demonstrated by qPCR, and decreased the SPCA1 protein beyond detectable level, as shown by Western analysis. The expression of selected desmosomal, adherens and tight junction (TJ) proteins was then studied in the SPCA1-deficient and control keratinocytes cultured in low (0.06 mm) or high (1.2 mm) calcium concentration. The mRNA and protein levels of most TJ components were up-regulated in non-treated control keratinocyte cultures upon switch from low to high calcium concentration. In contrast, SPCA1-deficient keratinocytes displayed high levels of TJ proteins claudins 1 and 4 even in low calcium. ZO-1 did not, however, follow similar expression patterns. Protein levels of occludin, beta-catenin, E-cadherin, desmoplakin, desmogleins 1-3, desmocollin 2/desmocollin 3 and plakoglobin did not show marked changes in SPCA1-deficient keratinocytes. Indirect immunofluorescence labelling revealed delayed translocation of desmoplakin and desmoglein 3 in desmosomes and increased intracellular pools of TJ and desmosomal components in SPCA1-inhibited keratinocytes. The results show that SPCA1 regulates the levels of claudins 1 and 4, but does not affect desmosomal protein levels, indicating that TJ proteins are differently regulated. The results also suggest a potential role for claudins in HHD.

Immunotherapy in nonmelanoma skin cancer

Nonmelanoma skin cancer is the most common type of cancer in humans. The role of the immune system in the prevention and regression of cancer is significant. UV radiation, being the most important risk factor in the development of skin cancer, has a suppressive effect on local and systemic immune effectors. Different immunotherapeutic approaches have been used for the treatment of nonmelanoma skin cancer including adoptive T-cell therapies, vaccine-based strategies, cytokines and monoclonal antibodies. The most important advancement with promising effects in the field of nonmelanoma skin cancer immunotherapy is the topical immune response modifier imiquimod. In addition, immunoprevention has been successfully applied for autosomal dominant basal cell nevus syndrome. Immunotherapeutic approaches provide a new modality for the treatment of recurrent or multiple nonmelanoma skin tumors.

Expression of DSG1 and DSC1 are prognostic markers in anal carcinoma patients

Background:

Our purpose was to investigate if dysregulation of cell adhesion molecules could be linked to prognosis in squamous cell carcinomas (SCCs) of the anal region.

Methods:

Protein expression of desmoglein-1 (DSG1), desmocollin-1 (DSC1) and E-cadherin was studied by immunohistochemistry in a cohort of 53 anal carcinoma patients treated by radiation alone or combined with 5-fluorouracil and mitomycin C.

Results:

Univariate analyses identified, among others, negative membranous DSG1 staining (P=0.009), negative cytoplasmic DSC1 staining (P=0.012) and negative DSG1 (membranous)+negative DSC1 (cytoplasmic) staining (P=0.004) to be associated with improved cancer-specific survival (CSS). On multivariate analyses positive DSG1 (membranous)+DSC1 (cytoplasmic) staining (HR 6.95, P=0.044), large tumour size and lymph node metastases (HR 6.44, P=0.004) and radiation without chemotherapy (HR 6.73 P=0.004) were associated with worse CSS. On univariate analysis, improved disease-free survival was associated with negative membranous staining of DSG1 (P=0.047), and negative DSG1 (membranous)+negative DSC1 (cytoplasmic) staining (P=0.025), among others.

Conclusion:

Membrane negativity for DSG1 and cytoplasmic negativity for DSC1 are favourable markers for CSS in SCCs of the anal region.

Cell-cell connectivity: desmosomes and disease

Cell-cell connectivity is an absolute requirement for the correct functioning of cells, tissues and entire organisms. At the level of the individual cell, direct cell-cell adherence and communication is mediated by the intercellular junction complexes: desmosomes, adherens, tight and gap junctions. A broad spectrum of inherited, infectious and auto-immune diseases can affect the proper function of intercellular junctions and result in either diseases affecting specific individual tissues or widespread syndromic conditions. A particularly diverse group of diseases result from direct or indirect disruption of desmosomes--a consequence of their importance in tissue integrity, their extensive distribution, complex structure, and the wide variety of functions their components accomplish. As a consequence, disruption of desmosomal assembly, structure or integrity disrupts not only their intercellular adhesive function but also their functions in cell communication and regulation, leading to such diverse pathologies as cardiomyopathy, epidermal and mucosal blistering, palmoplantar keratoderma, woolly hair, keratosis, epidermolysis bullosa, ectodermal dysplasia and alopecia. Here, as well as describing the importance of the other intercellular junctions, we focus primarily on the desmosome, its structure and its role in disease. We will examine the various pathologies that result from impairment of desmosome function and thereby demonstrate the importance of desmosomes to tissues and to the organism as a whole.

RNAi-mediated inhibition of the desmosomal cadherin (desmoglein 3) impairs epithelial cell proliferation

OBJECTIVES

  Desmoglein 3 (Dsg3) is a desmosomal adhesion protein expressed in basal and immediate suprabasal layers of skin. Importance of Dsg3 in cell-cell adhesion and maintenance of tissue integrity is illustrated by findings of keratinocyte dissociation in the autoimmune disease, pemphigus vulgaris, where autoantibodies target Dsg3 on keratinocyte surfaces and cause Dsg3 depletion from desmosomes. However, recognition of possible participation of involvement of Dsg3 in cell proliferation remains controversial. Currently, available evidence suggests that Dsg3 may have both anti- and pro-proliferative roles in keratinocytes. The aim of this study was to use RNA interference (RNAi) strategy to investigate effects of silencing Dsg3 in cell-cell adhesion and cell proliferation in two cell lines, HaCaT and MDCK.

MATERIALS AND METHODS

  Cells were transfected with siRNA, and knockdown of Dsg3 was assessed by western blotting, fluorescence-activated cell sorting and confocal microscopy. Cell-cell adhesion was analysed using the hanging drop/fragmentation assay, and cell proliferation by colony forming efficiency, BrdU incorporation, cell counts and organotypic culture.

RESULTS

  Silencing Dsg3 caused defects in cell-cell adhesion and concomitant reduction in cell proliferation in both HaCaT and MDCK cells.

CONCLUSION

  These findings suggest that Dsg3 depletion by RNAi reduces cell proliferation, which is likely to be secondary to a defect in cell-cell adhesion, an essential function required for cell differentiation and morphogenesis.

Deconstructing the skin: cytoarchitectural determinants of epidermal morphogenesis

To provide a stable environmental barrier, the epidermis requires an integrated network of cytoskeletal elements and cellular junctions. Nevertheless, the epidermis ranks among the body's most dynamic tissues, continually regenerating itself and responding to cutaneous insults. As keratinocytes journey from the basal compartment towards the cornified layers, they completely reorganize their adhesive junctions and cytoskeleton. These architectural components are more than just rivets and scaffolds - they are active participants in epidermal morphogenesis that regulate epidermal polarization, signalling and barrier formation.

A role for caveolin-1 in desmoglein binding and desmosome dynamics

Desmoglein-2 (Dsg2) is a desmosomal cadherin that is aberrantly expressed in human skin carcinomas. In addition to its well-known role in mediating intercellular desmosomal adhesion, Dsg2 regulates mitogenic signaling that may promote cancer development and progression. However, the mechanisms by which Dsg2 activates these signaling pathways and the relative contribution of its signaling and adhesion functions in tumor progression are poorly understood. In this study we show that Dsg2 associates with caveolin-1 (Cav-1), the major protein of specialized membrane microdomains called caveolae, which functions in both membrane protein turnover and intracellular signaling. Sequence analysis revealed that Dsg2 contains a putative Cav-1-binding motif. A permeable competing peptide resembling the Cav-1 scaffolding domain bound to Dsg2, disrupted normal Dsg2 staining and interfered with the integrity of epithelial sheets in vitro. Additionally, we observed that Dsg2 is proteolytically processed; resulting in a 95-kDa ectodomain shed product and a 65-kDa membrane-spanning fragment, the latter of which localizes to lipid rafts along with full-length Dsg2. Disruption of lipid rafts shifted Dsg2 to the non-raft fractions, leading to the accumulation of these proteins. Interestingly, Dsg2 proteolytic products are elevated in vivo in skin tumors from transgenic mice overexpressing Dsg2. Collectively, these data are consistent with the possibility that accumulation of truncated Dsg2 protein interferes with desmosome assembly and/or maintenance to disrupt cell-cell adhesion. Furthermore, the association of Dsg2 with Cav-1 may provide a mechanism for regulating mitogenic signaling and modulating the cell-surface presentation of an important adhesion molecule, both of which could contribute to malignant transformation and tumor progression.

Characterization of full-length and proteolytic cleavage fragments of desmoglein-2 in native human colon and colonic epithelial cell lines

The desmosomal cadherin desmoglein-2 (Dsg2) is a transmembrane cell adhesion protein that is widely expressed in epithelial and non-epithelial tissues, such as the intestine, epidermis, testis, and heart. Dsg2 has been shown to regulate numerous cellular processes, including proliferation and apoptosis, and we have previously reported that intracellular fragments of Dsg2 promote apoptosis in colonic epithelial cells. While several studies have shown that both the extracellular and intracellular domains of Dsg2 can be targeted by proteases, identification of these putative Dsg2 fragments in colonic epithelial cells has not been performed. Here, we report that the mouse monoclonal antibody (mAb) AH12.2 binds to the first extracellular domain of Dsg2. Using this antibody along with previously described mAb against the extracellular (6D8) and intracellular (DG3.10) domains of Dsg2, we characterize the expression and identify the cleavage fragments of Dsg2 in colonic epithelial cells. This study provides a detailed description of the extracellular and intracellular Dsg2 cleavage fragments that are generated in the simple epithelium of the colon and will guide future studies examining the relationship of these fragments to cellular fate and disease states.

Desmosomes: new perpetrators in tumour suppression

Adherens junctions, which are intercellular adhesive complexes that are crucial for maintaining epithelial homeostasis, are downregulated in many cancers to promote tumour progression. However, the role of desmosomes - adhesion complexes that are related to adherens junctions - in carcinogenesis has remained elusive. Recent studies using mouse genetic approaches have uncovered a role for desmosomes in tumour suppression, demonstrating that desmosome downregulation occurs before that of adherens junctions to drive tumour development and early invasion, suggesting a two-step model of adhesion dysfunction in cancer progression.

The Misregulation of Cell Adhesion Components during Tumorigenesis: Overview and Commentary

Cell adhesion complexes facilitate attachment between cells or the binding of cells to the extracellular matrix. The regulation of cell adhesion is an important step in embryonic development and contributes to tissue homeostasis allowing processes such as differentiation and cell migration. Many mechanisms of cancer progression are reminiscent of embryonic development, for example, epithelial-mesenchymal transition, and involve the disruption of cell adhesion and expression changes in components of cell adhesion structures. Tight junctions, adherens junctions, desmosomes, and focal adhesion besides their roles in cell-cell or cell-matrix interaction also possess cell signaling function. Perturbations of such signaling pathways can lead to cancer. This article gives an overview of the common structures of cell adhesion and summarizes the impact of their loss on cancer development and progression with articles highlighted from the present issue.