Ultrastructural localization of gap junction protein connexin 43 in normal human skin, basal cell carcinoma, and squamous cell carcinoma

Lycopene enriched tomato extract suppresses chemically induced skin tumorigenesis in mice

Abstract. The present study revealed the effects of Lycopene enriched tomato extract (LycT) on chemically induced skin cancer in mice. Skin tumors were induced by topical application of 7,12-Dimethylbenz(a)anthracene (DMBA) [500 nmol/100 ul of acetone, twice a week for two weeks] and 12-O-tetradecanoyl phorbol-13-acetate (TPA) [1.7 nmol/100 ul of acetone, twice a week for eighteen weeks] and LycT (5 mg/kg b.w.) was administered orally. Male Balb/c mice were divided into four groups (n = 15 per group): control, DMBA/TPA, LycT and LycT + DMBA/TPA. The chemopreventive response of LycT to skin tumorigenesis was evident by inhibition in tumor incidence, number, size, burden and volume in LycT + DMBA/TPA group when compared to DMBA/TPA group. This was associated with inhibition of cell proliferation in LycT + DMBA/TPA group as observed by the decrease in epidermal morphometric parameters and mRNA and protein expression of proliferating cell nuclear antigen when compared to DMBA/TPA group (p ≤ 0.05). LycT decreased (p ≤ 0.05) the mRNA and protein expression of angiogenic genes (vascular endothelial growth factor, angiopoietin-2, basic fibroblast growth factor) in LycT + DMBA/TPA group, suggesting its anti-angiogenic effects. The increase (p ≤ 0.05) in protein expression of connexin-32 and 43 in LycT + DMBA/TPA group suggests improved inter cellular communication when compared to DMBA/TPA group. Histochemical studies demonstrated that the components of extracellular matrix (fibrous proteins and mucopolysaccharides) were also modulated during skin carcinogenesis and its chemoprevention by LycT. The decrease in cell proliferation parameters and expression of angiogenesis associated genes, modulation of ECM components and increase in expression of connexins suggest that LycT improved multiple dysregulated processes during chemoprevention of skin cancer.

Cx43 promotes SHF-DPCs proliferation in the hair follicle of Albas cashmere goats from anagen to telogen

Connexin 43 (Cx43), known to form gap junction transmembrane channels between the cytoplasm of two adjacent cells, plays a key role in physiological functions, such as regulating cell growth, differentiation, and maintaining tissue homeostasis. Cashmere goat is an important farm animal that provides cashmere, which was produced by secondary hair follicles (SHF), for human consumption; however, there is no report about the role of Cx43 on the growth and development of SHF in cashmere goat. In this study, we investigated the effect of Cx43 on proliferation secondary hair follicle dermal papilla cells (SHF-DPCs) in Albas cashmere goat. In SHF-DPCs, Cx43 overexpression promoted cell proliferation and upregulated the expression of IGF-1, whereas Cx43 knockdown was associated with the opposite effects. These results suggested that Cx43 may promote cell proliferation by inducing IGF-1. Overall, our research not only contributes to a better understanding of the mechanism of the growth and development of SHF in cashmere goat, but also shed light on cashmere quality control in the future.

Facets of Communication: Gap Junction Ultrastructure and Function in Cancer Stem Cells and Tumor Cells

Gap junction proteins are expressed in cancer stem cells and non-stem cancer cells of many tumors. As the morphology and assembly of gap junction channels are crucial for their function in intercellular communication, one focus of our review is to outline the data on gap junction plaque morphology available for cancer cells. Electron microscopic studies and freeze-fracture analyses on gap junction ultrastructure in cancer are summarized. As the presence of gap junctions is relevant in solid tumors, we exemplarily outline their role in glioblastomas and in breast cancer. These were also shown to contain cancer stem cells, which are an essential cause of tumor onset and of tumor transmission into metastases. For these processes, gap junctional communication was shown to be important and thus we summarize, how the expression of gap junction proteins and the resulting communication between cancer stem cells and their surrounding cells contributes to the dissemination of cancer stem cells via blood or lymphatic vessels. Based on their importance for tumors and metastases, future cancer-specific therapies are expected to address gap junction proteins. In turn, gap junctions also seem to contribute to the unattainability of cancer stem cells by certain treatments and might thus contribute to therapeutic resistance.

Characterisation of Peptide5 systemic administration for treating traumatic spinal cord injured rats

Systemic administration of a Connexin43 mimetic peptide, Peptide5, has been shown to reduce secondary tissue damage and improve functional recovery after spinal cord injury (SCI). This study investigated safety measures and potential off-target effects of Peptide5 systemic administration. Rats were subjected to a mild contusion SCI using the New York University impactor. One cohort was injected intraperitoneally with a single dose of fluorescently labelled Peptide5 and euthanised at 2 or 4 h post-injury for peptide distribution analysis. A second cohort received intraperitoneal injections of Peptide5 or a scrambled peptide and was culled at 8 or 24 h post-injury for the analysis of connexin proteins and systemic cytokine profile. We found that Peptide5 did not cross the blood-spinal cord barrier in control animals, but reached the lesion area in the spinal cord-injured animals without entering non-injured tissue. There was no evidence that the systemic administration of Peptide5 modulates Connexin43 protein expression or hemichannel closure in the heart and lung tissue of SCI animals. The expression levels of other major connexin proteins including Connexin30 in astrocytes, Connexin36 in neurons and Connexin47 in oligodendrocytes were also unaltered by systemic delivery of Peptide5 in either the injured or non-injured spinal cords. In addition, systemic delivery of Peptide5 had no significant effect on the plasma levels of cytokines, chemokines or growth factors. These data indicate that the systemic delivery of Peptide5 is unlikely to cause any off-target or adverse effects and may thus be a safe treatment option for traumatic SCI.

Connexin 43: Key roles in the skin

Gap junctions are tightly packed intercellular channels that serve a common purpose of allowing the intercellular exchange of small metabolites, second messengers and electrical signals. Connexins (Cxs) are gap junction proteins. Currently, 20 and 21 members of Cxs have been characterized in mice and humans, respectively. Connexin 43 (Cx43) is the most ubiquitously expressed type of Cx in the skin. It is produced by various different types of skin cell, such as keratinocytes, fibroblasts, endothelial and basal cells, melanocytes and dermal papilla cells. At present, more evidence indicates that Cx43 has an important role in skin repair and skin tumor development, as well as in skin cell invasion and metastasis. In this review, current knowledge regarding the regulation and function of Cx43 is summarized and the therapeutic potential of regulating Cx43 activity is discussed.

Melanoma's connections to the tumour microenvironment

SUMMARY

Melanoma cells interact with and depend on seemingly normal cells in their tumour microenvironment to allow the acquisition of the hallmarks of solid cancer. In general, there are three types of interaction of melanoma cells with their microenvironment. First, there is bilateral communication between melanoma cells and the stroma, which includes fibroblasts, endothelial cells, immune cells, soluble molecules, and the extracellular matrix. Second, while under normal conditions keratinocytes control localisation and proliferative behaviour of melanocytes in the epidermis, once this balance is disturbed and a melanoma has developed, melanoma cells may take over the control of their epidermal tumour microenvironment. Finally, there are subcompartments within tumours with different microenvironmental milieu defined by their access to oxygen and nutrients. Therefore, different melanoma cells within a tumour face different microenvironments. Interactions between melanoma cells among each other and with the cell types in their microenvironment happen through endocrine and paracrine communication and/or through direct contact via cell-cell and cell-matrix adhesion, and gap junctional intercellular communication (GJIC). Connexins have been identified as key molecules for direct cell-cell communication and are also thought to be important for the release of signalling molecules from cells to the microenvironment. In this review we provide an update of the alterations in cell-cell communication in melanoma and the tumour microenvironment associated with melanoma development and progression.

Membrane connexin 43 acts as an independent prognostic marker in oral squamous cell carcinoma

The aim of the present study was to evaluate the expression and localization of connexin (Cx) 26, -43 and -45 in a group of 35 patients with primary oral squamous cell carcinoma (OSCC) with the objective of making a more accurate disease prognosis. We analysed the expression of connexins in tissue samples of primary OSCC, matching oral mucosa free of dysplasia, and its associated lymph node metastases (LNM) by semi-quantitative immunohistochemistry of membrane, cytoplasmic and nuclear connexin expression. The levels of expression were correlated with the overall survival time (OS). Cx43 was overexpressed in tumour cells compared to epithelia in dysplasia-free mucosa. High membrane expression of Cx43 on tumour cells was the only statistically significant and independent prognostic factor of short OS (P=0.0088). Membrane expression of Cx43 in matching dysplasia-free mucosa acted similarly, but did not reach statistical significance (P=0.059). No correlation was found between the Cx26, Cx45 expression and OS. We conclude that Cx43 expression in dysplasia-free mucosa may indicate a very early stage of tumour promotion. Although overexpression of Cx43 is found in invasive tumours we only found membrane Cx43 expression to correlate with OS. This observation suggests that cytoplasmic Cx43 serves as storage and only membrane translocation may promote the formation of gap junctions and gap junctional intercellular communication (GJIC) with prognostic relevance.

Genetics of basal cell carcinoma

Basal cell carcinoma is the most common human malignancy in populations of European origin, and Australia has the highest incidence of basal cell carcinoma in the world. Great advances in the understanding of the genetics of this cancer have occurred in recent years. Mutations of the patched 1 gene (PTCH1) lead to basal cell carcinoma predisposition in Gorlin syndrome. PTCH1 is part of the hedgehog signalling pathway, and derangements within this pathway are now known to be important in the carcinogenesis of many different cancers including sporadic basal cell carcinoma. The molecular biology of the hedgehog pathway is discussed, and mouse models of basal cell carcinoma based on this pathway are explored. New developments in non-surgical treatment of basal cell carcinoma are based on this knowledge. Other genes of importance to basal cell carcinoma development include the tumour suppressor gene P53 and the melanocortin-1 receptor gene. In addition, we discuss molecules of possible importance such as the glutathione-S-transferases, DNA repair genes, cyclin-dependent kinase inhibitor 2A, Brahma and connexins. Evidence of familial aggregation of this cancer is explored and supports the possibility of genetic predisposition to this common malignancy.

Gap and tight junctions in the formation of feather branches: A descriptive ultrastructural study

The present study has focused on the distribution and ultrastructure of gap and tight junctions responsible for the formation of the barb/barbule branching in developing feathers using immunocytochemical detection. Apart from desmosomes, both tight and gap junctions are present between differentiating barb/barbule cells and during keratinization. While gap junctions are rare along the perimeter of these cells, tight junctions tend to remain localized in nodes joining barbule cells and between barb cells of the ramus. Occludin and connexin-26 but not connexin-43 have been detected between barb medullary, barb cortical and barbule cells during formation of barbs. Gap junctions are present in supportive cells located in the vicinity of barbule cells and destined to degenerate, but no close junctions are present between supportive and barb/barbule cells. Close junctions mature into penta-laminar junctions that are present between mature barb/barbule cells. Immunolabeling for occludin and Cx26 is rare along these cornified junctions. The junctions allow barb/barbule cells to remain connected until feather-keratin form the mature corneous syncytium that constitutes the barbs. A discussion of the role of gap and tight junctions during feather morphogenesis is presented.

The tumor-suppressive function of Connexin43 in keratinocytes is mediated in part via interaction with caveolin-1

Connexin43 (Cx43) is known to have tumor-suppressive effects, but the underlying mechanisms are still poorly understood. In keratinocytes, we previously showed that the COOH-terminal domain of Cx43 directly interacts with the tumor suppressor Cav-1. We now show that rat epidermal keratinocytes (REK) that are reduced in Cx43 present features of epithelial-to-mesenchymal transition and are more invasive than their control counterparts, whereas overexpression of Cx43 inhibited the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)- and epidermal growth factor (EGF)-induced invasive properties. Carbenoxolone did not alter the inhibitory effect of Cx43 against TPA- and EGF-induced cell invasion, indicating the involvement of a gap junctional intercellular communication-independent mechanism. Interestingly, the association of Cx43 with Cav-1 was found to be reduced after TPA and EGF treatment. Accordingly, the colocalization of Cx43 with Cav-1 was diminished in cells from a human epidermal squamous cell carcinoma, as well as in sections from human keratinocyte tumors, suggesting that Cx43/Cav-1 interaction plays a protective role against keratinocyte transformation. As opposed to cells that overexpress Cx43-GFP, invasion could be induced in rat epidermal keratinocytes that overexpressed a GFP-tagged truncated mutant of Cx43 (Delta244-GFP) that we previously showed not to interact with Cav-1, as well as in cells that overexpressed Cx43-GFP but were reduced in Cav-1. Our data show that Cx43 possesses tumor-suppressive properties in keratinocytes and provide the first evidence that the Cx43/Cav-1 interaction is altered in keratinocyte transformation processes, as well as in human keratinocyte tumors, and that this association might play a role in Cx43-mediated tumor suppression.

Melanoma progression exhibits a significant impact on connexin expression patterns in the epidermal tumor microenvironment

Melanoma depends on, interacts with and reacts to the stroma in which it is embedded, including fibroblasts, extracellular matrix, endothelial cells and immune cells. However, the impact of melanoma on the epidermal tumor microenvironment-the multilayered epithelium of the skin-is poorly understood. Gap junctions are essential for intercellular communication and involved in proliferation, differentiation and homeostasis of keratinocytes. We have shown previously that the gap junction proteins connexin 26 and 30 (Cx26 and Cx30) are induced in the epidermal tumor microenvironment of skin cancers including melanoma. This study compares the extent of Cx26, Cx30 and Cx43 expression in the epidermal microenvironment of melanocytic nevi and melanomas and its association with melanoma thickness, proliferative index of the tumor and its microenvironment, and with 5-year metastasis and survival. We found that induction of Cx26 and Cx30 cell-cell border expression in the epidermal tumor microenvironment correlates to malignancy. Importantly, there was a significant correlation of tumor thickness with the vertical epidermal Cx26 and Cx30 expression pattern and the horizontal Cx26 dissemination. Furthermore, horizontal Cx26 expression correlated with metastasis. Vertical epidermal expression patterns of Cx26 and Cx30 significantly correlated with the proliferative index in the epidermal tumor microenvironment but not with the proliferative index in the tumor. In contrast, Cx43 did not correlate with malignancy, thickness or proliferative index. In summary, here we show for the first time a significant association between the progression of melanoma and alterations in its epithelial tumor microenvironment.

Connexin43 phosphorylation: structural changes and biological effects

Vertebrate gap junctions, composed of proteins from the connexin gene family, play critical roles in embryonic development, co-ordinated contraction of excitable cells, tissue homoeostasis, normal cell growth and differentiation. Phosphorylation of connexin43, the most abundant and ubiquitously expressed connexin, has been implicated in the regulation of gap junctional communication at several stages of the connexin 'life cycle', including hemichannel oligomerization, export of the protein to the plasma membrane, hemichannel activity, gap junction assembly, gap junction channel gating and connexin degradation. Consistent with a short (1-5 h) protein half-life, connexin43 phosphorylation is dynamic and changes in response to activation of many different kinases. The present review assesses our current understanding of the effects of phosphorylation on connexin43 structure and function that in turn regulate gap junction biology, with an emphasis on events occurring in heart and skin.

Cochlear implantation and connexin expression in the child with keratitis-ichthyosis-deafness syndrome

We report one child with keratitis-ichthyosis-deafness (KID) syndrome. The child showed sparse, short scalp and body hairs, ichthyotic skin, bilateral sensorineural hearing loss, and visual loss. These are associated with a nucleotide substitution, 148G>A, which results in amino acid change in codon 50 of gap junctional protein connexin (Cx) 26. Immunohistochemistry of skins showed up-regulation of Cx26 and down-regulation of Cx43. He has benefited from cochlear implantation for hearing even though low visual function and skin problems with high risk of infections. This is the very rare report about Cx expression in skins and cochlear implantation in KID syndrome.

Caveolin-1 and -2 interact with connexin43 and regulate gap junctional intercellular communication in keratinocytes

Connexin43 (Cx43) has been reported to interact with caveolin (Cav)-1, but the role of this association and whether other members of the caveolin family bind Cx43 had yet to be established. In this study, we show that Cx43 coimmunoprecipitates and colocalizes with Cav-1 and Cav-2 in rat epidermal keratinocytes. The colocalization of Cx43 with Cav-1 was confirmed in keratinocytes from human epidermis in vivo. Our mutation and Far Western analyses revealed that the C-terminal tail of Cx43 is required for its association with Cavs and that the Cx43/Cav-1 interaction is direct. Our results indicate that newly synthesized Cx43 interacts with Cavs in the Golgi apparatus and that the Cx43/Cavs complex also exists at the plasma membrane in lipid rafts. Using overexpression and small interfering RNA approaches, we demonstrated that caveolins regulate gap junctional intercellular communication (GJIC) and that the presence of Cx43 in lipid raft domains may contribute to the mechanism modulating GJIC. Our results suggest that the Cx43/Cavs association occurs during exocytic transport, and they clearly indicate that caveolin regulates GJIC.

Dynamics of cell interactions and communications during melanoma development

Melanoma development not only involves genetic and epigenetic changes that take place within the cell, but also involves processes determined collectively by micro-environmental factors, including cell-cell interactions and communications. During the transition from normal cells to benign and malignant lesions, and subsequently to metastatic cancer, stepwise changes in intercellular communications provide tumor cells with the ability to overcome cell-cell adhesion and micro-environmental controls from the host and to invade surrounding tissues and disperse to distant locations. Cadherins are major cell-cell adhesion molecules involved in the development and maintenance of skin. E-cadherin expressed in normal melanocytes mediates growth and invasion control by keratinocytes. Progressive loss of E-cadherin and gain of N-cadherin during melanoma development not only free melanoma cells from control by keratinocytes, but also provide new adhesion properties, resulting in switched partnerships with fibroblasts and vascular endothelial cells. The cadherin subtype switching also dictates gap junctional specificity in melanocytic cells during tumor development. This selective intercellular communication may contribute to the regulation of cell growth, differentiation, apoptosis, and migration of melanocytic cells in both physiologic and pathologic conditions. Abnormal up-regulation of the immunoglobin repeat-containing cell adhesion molecules Mel-CAM and L1-CAM potentiates invasion and migration of melanoma. Thus, abnormal expression of intercellular adhesion receptors and dysregulated intercellular communication underlies melanoma development and progression.

A prospective, randomized, placebo-controlled, double-blinded, and split-face clinical study on LED phototherapy for skin rejuvenation: clinical, profilometric, histologic, ultrastructural, and biochemical evaluations and comparison of three different treatment settings

Light-emitting diodes (LEDs) are considered to be effective in skin rejuvenation. We investigated the clinical efficacy of LED phototherapy for skin rejuvenation through the comparison with three different treatment parameters and a control, and also examined the LED-induced histological, ultrastructural, and biochemical changes. Seventy-six patients with facial wrinkles were treated with quasimonochromatic LED devices on the right half of their faces. All subjects were randomly divided into four groups treated with either 830nm alone, 633nm alone, a combination of 830 and 633nm, or a sham treatment light, twice a week for four weeks. Serial photography, profilometry, and objective measurements of the skin elasticity and melanin were performed during the treatment period with a three-month follow-up period. The subject's and investigator's assessments were double-blinded. Skin specimens were evaluated for the histologic and ultrastructural changes, alteration in the status of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs), and the changes in the mRNA levels of IL-1ss, TNF-alpha, ICAM-1, IL-6 and connexin 43 (Cx43), by utilizing specific stains, TEM, immunohistochemistry, and real-time RT-PCR, respectively. In the results, objectively measured data showed significant reductions of wrinkles (maximum: 36%) and increases of skin elasticity (maximum: 19%) compared to baseline on the treated face in the three treatment groups. Histologically, a marked increase in the amount of collagen and elastic fibers in all treatment groups was observed. Ultrastructural examination demonstrated highly activated fibroblasts, surrounded by abundant elastic and collagen fibers. Immunohistochemistry showed an increase of TIMP-1 and 2. RT-PCR results showed the mRNA levels of IL-1ss, TNF-alpha, ICAM-1, and Cx43 increased after LED phototherapy whereas that of IL-6 decreased. This therapy was well-tolerated by all patients with no adverse effects. We concluded that 830 and 633nm LED phototherapy is an effective approach for skin rejuvenation.

Erythrokeratoderma variabilis successfully treated with topical tazarotene

Erythrokeratoderma variabilis, also known as Mendes da Costa syndrome, is a genodermatosis belonging to the group of diseases known as the erythrokeratodermias. Erythrokeratoderma variabilis is characterized by two distinctive manifestations: well-demarcated, variable, transient, figurate patches of erythema, and localized or generalized hyperkeratotic plaques. Treatments include topical retinoic acid, salicylic acid, and alpha-hydroxy acid in petrolatum, but all have been reported to have limited, variable success rates. We report a child with erythrokeratoderma variabilis with no family history of this entity, successfully treated with topical tazarotene.

Inhibition of JNK promotes differentiation of epidermal keratinocytes

In inflamed tissue, normal signal transduction pathways are altered by extracellular signals. For example, the JNK pathway is activated in psoriatic skin, which makes it an attractive target for treatment. To define comprehensively the JNK-regulated genes in human epidermal keratinocytes, we compared the transcriptional profiles of control and JNK inhibitor-treated keratinocytes, using DNA microarrays. We identified the differentially expressed genes 1, 4, 24, and 48 h after the treatment with SP600125. Surprisingly, the inhibition of JNK in keratinocyte cultures in vitro induces virtually all aspects of epidermal differentiation in vivo: transcription of cornification markers, inhibition of motility, withdrawal from the cell cycle, stratification, and even production of cornified envelopes. The inhibition of JNK also induces the production of enzymes of lipid and steroid metabolism, proteins of the diacylglycerol and inositol phosphate pathways, mitochondrial proteins, histones, and DNA repair enzymes, which have not been associated with differentiation previously. Simultaneously, basal cell markers, including integrins, hemidesmosome and extracellular matrix components, are suppressed. Promoter analysis of regulated genes finds that the binding sites for the forkhead family of transcription factors are over-represented in the SP600125-induced genes and c-Fos sites in the suppressed genes. The JNK-induced proliferation appears to be secondary to inhibition of differentiation. The results indicate that the inhibition of JNK in epidermal keratinocytes is sufficient to initiate their differentiation program and suggest that augmenting JNK activity could be used to delay cornification and enhance wound healing, whereas attenuating it could be a differentiation therapy-based approach for treating psoriasis.

Expression of the gap junction proteins connexin 26 and connexin 43 in human middle ear cholesteatoma

CONCLUSION

The results of this study showed upregulated expression and a change in localization of both connexin 43 (Cx43) and Cx26 in human middle ear cholesteatoma compared to those in normal retroauricular skins (RASs) and ear canal skins (ECSs). This suggests that perturbations of intercellular communication through gap junctions may be associated with the pathology of human cholesteatomas.

OBJECTIVE

Cholesteatomas in the middle ear require intercellular signal exchange through gap junctions as well as intracellular signal pathways for the hyperproliferation and differentiation of epithelial cells. Cx is a gap junction protein involved in intercellular communication. The objective of this study was to analyze the expression and possible roles of Cx43 and Cx26 in human cholesteatoma compared to normal epithelium.

MATERIAL AND METHODS

Ten RASs, 10 ECSs and 10 cholesteatomas were obtained during middle ear operations. Immunohistochemical staining, Western blotting and reverse transcriptase polymerase chain reaction (RT-PCR) were used to detect Cx43 and Cx26. The expression patterns of Cx43 and Cx26 were also compared with that of the proliferation marker Ki67.

RESULTS

In human cholesteatomas, Cx43 was expressed in whole suprabasal layers, except in the basal layer, and Cx26 was usually expressed in the suprabasal and basal layers. However, normal RASs showed weak expression of Cx43 in the upper spinosal and granular layers (with no expression in the basal layers) and restricted localization of Cx26 in the basal layer. The expression of Cx43 and Cx26 in ECSs was weak but showed similar patterns to that of cholesteatoma. RT-PCR and Western blotting showed that the expression of Cx43 and Cx26 was higher in cholesteatoma than in RASs. Epithelial cells expressing Cx43 and Cx26 in cholesteatoma were not exactly identical to Ki67-expressing cells on immunohistochemical staining.

Defective gap junctional intercellular communication in the carcinogenic process

Gap junctions are membrane structures made of intercellular channels which permit the diffusion from cytoplasm to cytoplasm of small hydrophilic molecules. Nearly 40 years ago, the loss of functional gap junctions has been described in cancer cells and led to the hypothesis that such type of intercellular communication is involved in the carcinogenesis process. From this time, a lot of data has been accumulated confirming that gap junctions are frequently decreased or absent in cancer cells whatever their tissue and species origins. Here, we review such data by insisting on the possible links existing between altered gap-junctional intercellular communication capacity (or the altered expression of their constitutive proteins, the connexins) and the stages of cancer progression in various cancer models. Then, we analyse particular aspects of the disturbance of connexin-mediated communication in cancer such as the cytoplasmic localization of connexins, the lack of heterologous communication between cancer cells and normal cells, the role of connexin gene mutations in cancer. In a separate part of the review, we also analyse the disturbance of gap-junctional intercellular communication during the late stages of cancer (invasion and metastasis processes).

Drebrin, an Actin-Binding, Cell-Type Characteristic Protein: Induction and Localization in Epithelial Skin Tumors and Cultured Keratinocytes

Isoform E2 of drebrin, an actin-binding protein originally identified in neuronal cells, has recently been identified in diverse non-neuronal cells, mostly in association with cell processes and intercellular junctions. Here, we report on the presence of drebrin in normal human skin, epithelial skin cancers, and cultured keratinocytes. Keratinocytes of normal epidermis contain almost no drebrin but the protein is readily seen in hair follicles. By immunohistochemistry and immunoblot, basal cell carcinomas (BCC) are rich in drebrin, and confocal laser scanning and immunoelectron microscopy show accumulation at adhering junctions, in co-localization with actin and partially with plaque proteins. In squamous cell carcinomas, keratoacanthomas, and in epidermal precancers, drebrin is heterogeneously distributed, appearing as mosaics. Primary keratinocyte cultures contain significant amounts of drebrin enriched at adhering junctions. When epithelium-derived cells devoid of drebrin are transfected with drebrin-enhanced green fluorescent protein, constructs accumulate in the cell periphery, and immunoprecipitation shows complexes with actin. During epidermal growth factor induced formation of cell processes, drebrin retains this junction association, as observed by live cell microscopy. Our results suggest novel functions of drebrin such as an involvement in cell-cell adhesion and tumorigenesis and a potential value in diagnosis of BCC.

Temporal regulation of connexin phosphorylation in embryonic and adult tissues

Gap junctions, composed of proteins from the connexin family, allow for intercellular communication between cells in tissues and are important in development, tissue/cellular homeostasis, and carcinogenesis. Genome databases indicate that there are at least 20 connexins in the mouse and human. Connexin phosphorylation has been implicated in connexin assembly into gap junctions, gap junction turnover, and cell signaling events that occur in response to tumor promoters and oncogenes. Connexin43 (Cx43), the most widely expressed and abundant gap junction protein, can be phosphorylated at several different serine and tyrosine residues. Here, we focus on the dynamic regulation of Cx43 phosphorylation in tissue and how these regulatory events are affected during development, wound healing, and carcinogenesis. The activation of several kinases, including protein kinase A, protein kinase C, p34cdc2/cyclin B kinase, casein kinase 1, mitogen-activated protein kinase, and pp60src kinase, can lead to the phosphorylation of different residues in the C-terminal region of Cx43. The use of antibodies specific for phosphorylation at defined residues has allowed the examination of specific phosphorylation events both in tissue culture and in vivo. These new antibody tools and those under development will allow us to correlate specific phosphorylation events with changes in connexin function.

The phosphorylated form of connexin43 is up-regulated in breast hyperplasias and carcinomas and in their neoformed capillaries

We applied an antiserum (SA226P) specifically recognizing the phosphorylated form of connexin43 (P-Cx43) to human breast samples including normal breast samples, with fibrocystic disease (FCD), fibroadenomas (FA), in situ and infiltrating carcinomas of all major types, and miscellaneous extramammary tumors. The findings were compared with those obtained with commercial antisera recognizing all Cx43 forms (pan-Cx43). A subset of samples was stained for Her2-neu and p44/42 to mitogen-activated protein kinase. Paraffin step sections were used. Immunoblots were performed on frozen samples of a representative subset of cases. In the normal breast, FCD, and FA, SA226P stained strongly and extensively most myoepithelial cells (MECs); luminal cells remained unstained. In proliferative FCD and some cellular FA, SA226P stained MEC and the capillary endothelium (CE). In ductal and lobular in situ carcinomas, SA226P reacted strongly and diffusely with the remaining MEC, the CE, and the transformed luminal cells. SA226P stained all infiltrating carcinomas except the tubular variant. In all breast carcinomas, the CE within and adjacent to tumors and some myofibroblasts stained with SA226P. By contrast, pan-Cx43 stained weakly and sporadically the MEC and rare samples of invasive carcinomas. Notably, Mab p44/42 reacted in parallel with the samples stained with SA226P, whereas reactions with Her2 were negative. Immunoblot findings paralleled those obtained immunohistochemically. We conclude that P-Cx43, restricted to MEC in the normal breast, is up-regulated in the same cells in hyperplasias and dysplasias and FA and is strongly up-regulated in invasive carcinomas. Notably, in some proliferative FCD and in most in situ and infiltrating carcinomas, P-Cx43 is strongly expressed in CE within and adjacent to the lesions but not away from them. These findings were paralleled by the strong nuclear reactions noted with Mab p44/42. These phenomena, although not exclusive to malignancy, are particularly conspicuous in breast carcinomas and seemingly reflect active proliferation associated with abnormal gap junctional intercellular communication.

Differential induction of connexins 26 and 30 in skin tumors and their adjacent epidermis

Gap junctions (GJs) have been shown to play a role in tumor progression including a variety of keratinocyte-derived and non-keratinocyte-derived skin tumors. Here we show that the synthesis of the GJ proteins connexin 26 and connexin 30 (Cx26 and Cx30) is induced in keratinocyte-derived epithelial skin tumors whereas there is either no change or a downregulation of Cx43. Cx26, Cx30, and Cx43 are absent in non-epithelial skin tumors. Further, Cx26 and Cx30 are induced in the epidermis adjacent to malignant melanoma but absent in the epidermis adjacent to benign non-epithelial skin lesions (melanocytic nevi and angioma). The keratinocyte-derived skin tumors are very heterogeneous regarding the Cx26/Cx30 pattern in the epidermis at the periphery of the tumors. We did not observe any difference in the localization of the very similar proteins Cx26 and Cx30 but a variation in intensity of immunoreactivity. As the staining patterns of Cx26 and Cx30 antibodies are not identical to those of CK6, a marker for hyperproliferation, and CK17, a marker for trauma, we discuss that the induction of these gap junctional proteins exceeds a reflection of reactive hyperproliferative or traumatized epidermis. We further discuss the putative roles of these gap junctional proteins in tumor progression.

Novel Connexin 43 (GJA1) mutation causes oculo-dento-digital dysplasia with curly hair

Oculo-dento-digital dysplasia (ODDD) [OMIM 164200] is a rare autosomal dominant pleiotropic disorder comprising ocular, craniofacial, and digital anomalies, caused by mutations in the gap junction alpha-1 gene (GJA1 or Connexin 43 (CX43)) [Paznekas et al., 2003]. In a Danish family affected over five generations, we found a novel mutation, 286G --> A, resulting in Val96Met. We provide an easy method for mutation detection by use of the restriction enzyme Nde1 and discuss possible pathogenetic mechanisms, arguing that loss of function cannot be excluded. This is the second article reporting ODDD mutations.

A 2-bp deletion in theGJA1 gene is associated with oculo-dento-digital dysplasia with palmoplantar keratoderma

Oculo-dento-digital dysplasia (ODDD, OMIM no. 164210) is a pleiotropic disorder characterized mainly by ocular anomalies, varying degrees of finger and toe syndactyly, and enamel defects. It is caused by missense mutations in the gene coding for the gap junction protein connexin 43 or GJA1. Other types of mutations have so far not been reported. Here we describe a Dutch kindred with ODDD showing a new symptom, palmoplantar keratoderma, and associated with a novel 2-bp deletion mutation of GJA1. The dinucleotide deletion 780_781delTG is located in the cytoplasmic C-terminal loop and leads to a frameshift. This is predicted to lead to the production of a slightly truncated protein with 46 incorrect amino acids in the C-terminal cytoplasmic loop (C260fsX307). This novel mutation may explain the presence of skin symptoms.

The role of altered cell-cell communication in melanoma progression

Under normal homeostasis, melanocyte growth and behaviour is tightly controlled by the surrounding keratinocytes. Keratinocytes regulate melanocyte behaviour through a complex system of paracrine growth factors and cell-cell adhesion molecules. Pathological changes, leading to development of malignant melanoma, upset this delicate homeostatic balance and can lead to altered expression of cell-cell adhesion and cell-cell communication molecules. In particular, there is a switch from the E-cadherin-mediated keratinocyte-melanocyte partnership to the N-cadherin-mediated melanoma-melanoma and melanoma-fibroblast interaction. Other changes include the alteration in the gap junctions formed between the melanocyte and keratinocyte. Changes in the connexin expression, in particular the loss of connexin 43, may result in a reduction or a loss of gap junctional activity, which is thought to contribute towards tumour progression. In the current review we describe the alterations in cell-cell adhesion and communication associated with melanoma development and progression, and discuss how a greater understanding of these processes may aid the future therapy of this disease.

Functional organization of the bovine rumen epithelium

The functional organization of the bovine rumen epithelium has been examined by electron and light microscopy combined with immunocytochemistry to define a transport model for this epithelium. Expression of connexin 43, an integral component of gap junctions, the tight-junction molecules claudin-1 and zonula occludens 1 (ZO-1), and the catalytic α-subunit of Na+-K+-ATPase was demonstrated by SDS-PAGE and Western blotting. From the lumen surface, four cell layers can be distinguished: the stratum corneum, the stratum granulosum, the stratum spinosum, and the stratum basale. Both claudin-1 and ZO-1 immunostaining showed plasma membrane staining, which was present at the stratum granulosum with decreasing intensity through the stratum spinosum to the stratum basale. The stratum corneum was negative for claudin-1 immunostaining. Transmission electron microscopy confirmed that occluding tight junctions were present at the stratum granulosum. Plasma membrane connexin 43 immunostaining was most intense at the stratum granulosum and decreased in intensity through stratum spinosum and stratum basale. There was intense immunostaining of the stratum basale for Na+-K+-ATPase, with weak staining of the stratum spinosum. Both the stratum granulosum and the stratum corneum were essentially negative. Stratum basale cells also displayed a high mitochondrial density relative to more apical cell layers. We conclude that epithelial barrier function may be attributed to the stratum granulosum and that cell-cell gap junctions allow diffusion to interconnect the barrier cell layer with the stratum basale where Na+-K+-ATPase is concentrated.

Connexins 26, 30, and 43: Differences Among Spontaneous, Chronic, and Accelerated Human Wound Healing

Gap junctions (GJ) are known to be involved in spontaneous wound healing in rodent skin. We analyzed the staining patterns of the GJ proteins Cx26, Cx30, and Cx43 in human cutaneous wound healing and compared ex vivo spontaneous wound healing to non-healing wounds (chronic leg ulcers) and to ex vivo accelerated wound healing after transplantation of cultured keratinocytes. We demonstrate a loss of Cx43 staining at the wound margins during initial wound healing and after transplantation of keratinocytes. In contrast, Cx43 remains present at the margins of most non-healing wounds. We show a subsequent induction of Cx26 and Cx30 near the wound margins in spontaneous wound healing and-even earlier-after the transplantation of keratinocytes. The cells at the wound margins remain negative until the commencement of epidermal regeneration. Cx26/30 are present at the wound margins of most non-healing wounds. Cx stainings are absent in the transplanted keratinocytes during early wound healing, but there is a subsequent induction. Our results suggest that the downregulation of Cx43 is an important event in human wound healing. We discuss the assumption that direct cell-cell communication via GJ contribute to the acceleration of wound healing after the transplantation of keratinocytes.

Sequestration of connexin43 in the early endosomes: An early event of Leydig cell tumor progression

Connexins form gap junction channels that allow intercellular communication between neighboring cells. Compelling evidence has revealed that Cx are tumor-suppressor genes and reduced Cx expression has been related with uncontrolled cell growth in tumors and transformed cells. In the present study, we addressed Cx transcriptional and posttranscriptional regulations during the earlier stage of testicular tumors confined to Leydig cells in a transgenic mice model. In situ hybridization indicated that connexin43 (Cx43) mRNA was highly expressed either at early tumorogenesis (3 m) characterized by intense proliferation of Leydig cells, or at advanced tumorogenesis (6-7 m) when tumor cells completely invaded the testis. In contrast, Cx43 protein analyzed by Western blotting or classic immunohistochemical analyses was present at the beginning of tumor progression, but was dramatically reduced as tumor advanced. Application of high-resolution deconvolution microscopy to testis sections demonstrates that cells that proliferate exhibited an aberrant cytoplasmic Cx43 localization, in contrast to the expected plasma membrane Cx43 localization in normal Leydig cells. Dual immunofluorescence labeling with specific markers of cellular compartments shows that cytoplasmic Cx43 signal was mainly sequestered within early endosomes. Altogether, this study provides the first evidence that impaired Cx43 trafficking in endosomes is an early event associated with uncontrolled cell proliferation that could serve as a neoplastic marker.

Changes in gap junction distribution and connexin expression pattern during human fetal skin development

Gap junctions are intercellular channels composed of connexin subunits that mediate cell-cell communication. The functions of gap junctions are believed to be associated with cell proliferation and differentiation and to be important in maintaining tissue homeostasis. We therefore investigated the expression of connexins (Cx)26 and 43, the two major connexins in human epidermis, and examined the formation of gap junctions during human fetal epidermal development. By immunofluorescence, Cx26 expression was observed between 49 and 96 days' estimated gestational age (EGA) but was not present from 108 days' EGA onwards. Conversely, Cx43 expression was observed from 88 days' EGA onwards. Using electron microscopy, the typical structure of gap junctions was observed from 120 days' EGA. The number of gap junctions increased over time and they were more common in the upper layers, within the periderm and intermediate keratinocyte layers rather than the basal layer. Immunoelectron microscopy revealed Cx43 labeling on the gap junction structures after 105 days' EGA. Formation of gap junctions increased as skin developed, suggesting that gap junctions may play an important role in fetal skin development. Furthermore, the changing patterns of connexin expression suggest that Cx26 is important for early fetal epidermal development.

Tight junctions and compositionally related junctional structures in mammalian stratified epithelia and cell cultures derived therefrom

The occurrence of extended tight junction (TJ) structures, including zonulae occludentes (ZO), and the spatial arrangement of TJ proteins in stratified mammalian epithelia has long been controversially discussed. Therefore, we have systematically examined the localization of TJ proteins in diverse stratified epithelial tissues (e.g., epidermis, heel pad, snout, gingiva, tongue, esophagus, exocervix, vagina, urothelium, cornea) of various species (human, bovine, rodents) as well as in human cell culture lines derived from stratified epithelia, by electron microscopy as well as by immunocytochemistry at both the light and the electron microscopic level, using antibodies to TJ proteins such as occludin, claudins 1 and 4, protein ZO-1, cingulin and symplekin. We have found an unexpected diversity of TJ-related structures of which only those showing colocalization with the most restricted transmembrane TJ marker protein, occludin, are presented here. While in epidermis and urothelium occludin is restricted to the uppermost living cell layer, TJ-related junctions are abundant in the upper third or even in the majority of the suprabasal cell layers in other stratified epithelia. Interfollicular epidermis contains, in the stratum granulosum, extended, probably continuous ZO-like structures which can also be traced at least through the Henle cell layer of hair follicles. Similar apical ZO-like structures have been seen in the upper living cell layers of all other stratified epithelia and cell cultures examined, but in most of them we have noticed, in addition, junctional regions showing relatively broad, ribbon-like membrane contacts which in cross-section often appear pentalaminar, with an electron-dense middle lamella ("lamellated TJs", coniunctiones laminosae). In suprabasal layers of several stratified epithelia we have further observed TJ protein-containing junctions of variable sizes which are characterized by a 10-30-nm dense lamina interposed between the two membranes ("sandwich junctions"; iuncturae structae). Moreover, we have often observed variously sized regions in which the intermembrane distance is rather regularly bridged by short rod-like elements ("cross-bridged cell walls"; parietes transtillati), often in close vicinity of TJ-related structures or desmosomes. The significance of these structures and their possible biological importance are discussed.

Cadherin repertoire determines partner-specific gap junctional communication during melanoma progression

Reduced gap junction activity has long been implicated in tumorigenesis. To elucidate the potential role of intercellular communication in melanoma development, we examined gap junctional capability of melanocytic cells from various stages of tumor progression in coculture models using dye transfer assays. Normal melanocytes coupled with keratinocytes by gap junctional formation, whereas melanoma cells did not. Instead, melanoma cells communicated among themselves and with fibroblasts. This switch in communication partners coincided with a shift from E-cadherin to N-cadherin expression during melanoma development. Forced expression of E-cadherin by adenoviral gene transfer in N-cadherin-expressing melanoma cells restored gap junctional compatibility with keratinocytes. Our data suggest that (1) melanocyte transformation is associated with loss of the pre-existing gap junctional activity with keratinocytes but a concomitant gain of communication with a newly juxtaposed cell type, the fibroblasts, (2) the specificity of gap junctional formation during melanoma development is determined by the cadherin profile on the melanocytic cells and (3) the overall gap junctional activity of melanocytic cells is not reduced with transformation.

Internalization of gap junctions in benign familial pemphigus (Hailey-Hailey disease) and keratosis follicularis (Darier's disease)

Hereditary skin disorders involving acantholysis, such as Hailey-Hailey disease and Darier's disease, have been genetically linked to distinct chromosomal parts which do not code for known structural proteins. Such evidence suggests that the genomic abnormalities underlying these dermatoses may concern functional/regulatory mechanisms of keratinocyte cohesion. Epidermal communication junctions (gap junctions) are responsible for direct coupling of cells and, thus, co-ordinate the behaviour of keratinocytes within the tissue. Consequently, they remain one of the potential, and poorly studied, elements in the pathogenesis of hereditary acantholytic diseases. We have investigated the distribution and fate of gap junctions during non-immune acantholysis, using fine immunolocalization methods at the light and electron microscopic levels. Our results demonstrate normal expression of epidermal gap junction proteins, connexins 26 and 43, in non-lesional skin of Hailey-Hailey and Darier's diseases. The gap junctions were not primarily dismantled during acantholysis, typical of both of the studied dermatoses, but underwent internalization and subsequent cytoplasmic dispersion in the portions of cells which were no longer attached to the rest of the tissue. In Darier's disease, perifollicular acantholysis did not specifically concern epithelium of appendages coexpressing connexin 26 in addition to connexin 43, further indicating that the observed changes in gap junction localization were secondary to the loss of cell-cell contact. We demonstrated that the sequence of changes was identical in both diseases and that the previously described putative differences were apparently related to the degree of acantholysis present in the studied biopsies. The fate of the junctional structures and proteins, documented in the present study, is most probably a form of recycling process also used by normal keratinocytes during organogenesis and tissue differentiation.

The S100 family of multipurpose calcium-binding proteins

Antibodies reactive with S100 protein are useful markers in a diagnostic immunohistochemistry laboratory dealing with cutaneous tumors. However, S100 protein is not a single protein but instead a group of S100 proteins with diverse functions. S100 proteins constitute a family of acidic calcium-binding proteins that are important in intracellular calcium metabolism. Recent evidence that some S100 proteins are secreted makes it likely that they are also involved in cell-cell interactions. The exploration of the status of the different members of the S100 family may yield not only diagnostic clues but also relevant functional information about the cells. Considerable recent progress has been made in our understanding of S100 proteins. This review surveys some of these findings that may be either directly or indirectly relevant to cutaneous pathology.