Modulation of gap junction expression during transient hyperplasia of rat epidermis

IL-22 Down-Regulates Cx43 Expression and Decreases Gap Junctional Intercellular Communication by Activating the JNK Pathway in Psoriasis

The roles of IL-22 in the pathomechanisms of psoriasis have been well demonstrated. Gap junctional intercellular communication (GJIC) is widely known for its involvement in multiple biological and pathological processes such as growth-related events, cell differentiation, and inflammation. Here, we show that IL-22 significantly decreased GJIC and down-regulated Cx43 expression in HaCaT cells. Cx43 overexpression markedly inhibited the proliferation of and increased GJIC in HaCaT cells, but the silencing of Cx43 exerted the opposite effects. Additionally, Cx43 overexpression effectively rescued the IL-22-induced decrease in GJIC in HaCaT cells. The IL-22-induced down-regulation of Cx43 expression and decrease in GJIC can be significantly blocked by the JNK inhibitor SP600125 and by the overexpression of IL-22RA2 (which specifically binds to IL-22 and inhibits its activity), but not by the NF-κB inhibitor BAY11-7082, in HaCaT cells. Furthermore, the IL-22-induced down-regulation of Cx43 expression mediated by the JNK signaling pathway was confirmed in a mouse model of IL-22-induced psoriasis-like dermatitis. Similarly, Cx43 expression was significantly lower in the lesional skin than in the nonlesional skin of patients with psoriasis. These results suggest that IL-22 decreases GJIC by activating the JNK signaling pathway, which down-regulates Cx43 expression; this process is a possible pathomechanism of keratinocyte hyperproliferation in psoriasis.

Evaluation of WO2013076170: the use of a dihydroorotate dehydrogenase inhibitor for the treatment of psoriasis

Inhibition of dihydroorotate dehydrogenase (DHODH) modulates pyrimidine biosynthesis. Effective inhibitors are immunomodulatory drugs clinically useful in the treatment of diseases such as rheumatoid arthritis, psoriatic arthritis and multiple sclerosis. There is limited evidence of their potential utility in treating psoriasis. This patent application claims topical formulations of the non-hepatotoxic DHODH inhibitor 2-[(3,5-difluoro-3'-methoxy-1,1'-biphenyl-4-yl)amino]nicotinic acid for use in the treatment of psoriasis. This inhibitor had previously been claimed to be useful in treating various autoimmune disease.

All-trans retinoic Acid regulates cx43 expression, gap junction communication and differentiation in primary lens epithelial cells

PURPOSE

To examine the effect of all-trans retinoic acid (ATRA) treatment on connexin 43 (Cx43) expression, gap junction intercellular communication (GJIC), and cellular differentiation in primary canine lens epithelial cells (LEC).

METHODS AND MATERIALS

Dose and time-dependent effects of ATRA on Cx43 protein, mRNA and GJIC, were assessed by immunoblotting, quantitative reverse transcription polymerase chain reaction (qRT-PCR), and scrape loading/dye transfer assays, respectively. Expression of beta crystallin was evaluated by immunoblotting.

RESULTS

Treatment with ATRA at non-cytotoxic concentrations significantly increased Cx43 protein, mRNA and GJIC in primary canine LEC. Treatment with ATRA for five and seven days increased levels of beta crystallin, a protein marker of LEC differentiation. Inhibition of GJIC via pre-treatment with a synthetic inhibitor, 18-alpha glycyrrethinic acid (AGA), reduced ATRA-induced increases in Cx43 and GJIC and partially blocked ATRA-induced beta crystallin protein.

CONCLUSIONS

Treatment with ATRA significantly increased Cx43 expression and GJIC in canine LEC, and these effects were associated with increased LEC differentiation. Results from this study suggest that functional gap junctions may play a role in the modulation of cellular differentiation in primary canine LEC.

Association of Shh and Ptc with keratin localization in the initiation of the formation of circumvallate papilla and von Ebner's gland

The development of gustatory papillae in mammalian embryos requires the coordination of a series of morphological events, such as proliferation, differentiation and innervation. In mice, the circumvallate papilla (CVP) is a specialized structure that develops in a characteristic spatial and temporal pattern in the posterior region of the tongue dorsal surface. The distinct expression patterns of Shh and Ptc, which play important roles in the development of other epithelial appendages, have been localized in the trench wall that gives rise to von Ebner's gland (VEG). To define the cellular mechanisms responsible for morphogenesis and differentiation during early development of CVP and VEG, the localization patterns of keratins (cytokeratins) K7, K8, K18, K19, K14 and connexin-43, which are dependent on Shh expression in other developmental systems, have been examined in detail. The distinct localization of keratins K7, K8, K18, K19, K14 and connexin-43 in the epithelium giving rise to the CVP and VEG suggests that cytodifferentiation is established prior to morphological changes. Interestingly, the localization of proliferating cell nuclear antigen, a marker for cell proliferation, is similar to that of Shh. An understanding of the regulatory roles of cell-cell interactions and signalling molecules in orchestrating a mutual network will bring us nearer to defining the molecular and cellular mechanisms underlying morphogenesis in mammalian taste bud development.

Reduced expression of multiple gap junction proteins is a feature of cervical dysplasia

Cervical dysplasia is a premalignant lesion associated with human papillomavirus (HPV) infection which, over time, can turn cancerous. Previous studies have indicated that loss of gap junctions may be a feature of cervical cancer and premalignant dysplasia. Loss of the gap junction protein connexin43 has been demonstrated in dysplastic cervix, but other connexins have not been investigated. In contrast we previously showed that HPV-associated cutaneous warts – and other hyperproliferative skin conditions – display a dramatic upregulation of certain connexins, in particular connexin26. By performing immunofluorescence staining after antigen retrieval of paraffin-embedded cervical tissue samples, this study reports for the first time that connexin26 and connexin30, in addition to connexin43, are expressed in differentiating cells of normal human cervical epithelia. Moreover, in dysplastic ectocervix, all connexins studied display a dramatic loss of expression compared to adjacent normal epithelia. The role of connexins in keratinocyte differentiation and carcinogenesis is discussed.

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.

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.

Functional Domain Mapping and Selective Trans-dominant Effects Exhibited by Cx26 Disease-causing Mutations

Mutations in Cx26 are a major cause of autosomal dominant and recessive forms of sensorineural deafness. Some mutations in Cx26 are associated not only with deafness but also with skin disease. We examined the subcellular localization and function of two green fluorescent protein (GFP)-tagged Cx26 point mutants that exhibit both phenotypes, G59A-GFP and D66H-GFP. D66H-GFP was retained within the brefeldin A-insensitive trans-Golgi network, whereas a population of G59A-GFP was transported to the cell surface. Neither G59A nor D66H formed gap junctions that were permeable to small fluorescent dyes, suggesting they are loss-of-function mutations. When co-expressed with wild-type Cx26, both G59A and D66H exerted dominant-negative effects on Cx26 function. G59A also exerted a trans-dominant negative effect on co-expressed wild type Cx32 and Cx43, whereas D66H exerted a trans-dominant negative effect on Cx43 but not Cx32. We propose that the severity of the skin disease is dependent on the specific nature of the Cx26 mutation and the trans-dominant selectivity of the Cx26 mutants on co-expressed connexins. Additional systematic mutations at residue D66, in which the overall charge of this motif was altered, suggested that the first extracellular loop is critical for Cx26 transport to the cell surface as well as function of the resulting gap junction channels.

The relationship between connexins, gap junctions, tissue architecture and tumour invasion, as studied in a novel in vitro model of HPV-16-associated cervical cancer progression

Disruption of gap junctional intercellular communication (GJIC) and/or connexins (gap junction proteins) is frequently reported in malignant cell lines and tumours. Certain human papillomaviruses (HPV) associated with the development of cancers, especially of the cervix, have previously been reported to downregulate GJIC in vitro. There is also evidence for reduced gap junctions in cervical dysplasia. However, many squamous hyperproliferative conditions, including HPV-induced warts, often show extensive upregulation of certain connexins. The association between HPV and GJIC, and the mechanism and consequence of deregulated GJIC in cervical tumour progression, remains unclear. Therefore, using a variety of nonmalignant and malignant cell lines and an organotypic raft-culture system, we investigated the relationship between HPV, gap junctions and tumour progression. Established cervical tumour cell lines carrying HPV were unable to communicate via gap junctions (when assayed by dye-transfer techniques). This correlated with lack of connexin protein expression, while transfection with connexins 26 or 43 led to functional gap junction membrane plaques. On the other hand, immortal but nonmalignant cell lines that contained episomal or integrated HPV-16, but required feeder-layer and growth-factor support, were consistently well coupled, and expressed multiple connexins at membrane junctions. In vitro selection of feeder-layer and growth-factor-independent variants eventually lead to loss of GJIC, which correlated with loss of membrane and increased cytoplasmic connexin 43 localization. However, this was preceded by loss of differentiation and stromal invasion, as assayed on the organotypic raft-culture model. Using this model, a comparison between noncoupled, well-coupled and connexin-transfected cell lines revealed no firm correlation between GJIC and dysplasia, but GJIC appeared to favour increased stratification. These findings demonstrate that loss of GJIC is frequent, but appears to occur more as a consequence of, rather than being the cause of, epithelial dysplasia, and may be influenced by, but is not directly attributable to, HPV.

Regeneration of rabbit cornea following excimer laser photorefractive keratectomy: a study on gap junctions, epithelial junctions and epidermal growth factor receptor expression in correlation with cell proliferation

Corneal wound repair was investigated in rabbits following excimer laser ablation of a 6 mm diameter and 90 microm deep disc. In the healing process particular attention was focused on the epithelium where gap junction expression and the rearrangement of desmosomes and hemidesmosomes were correlated with cell proliferation and epidermal growth factor receptor expression. Immunofluorescence-based confocal laser scanning microscopy, semithin resin section morphology and electron microscopy were utilized. In resting cornea two isotypes of gap junctions, confined to different regions in the same basal epithelial cells, were detected. Particulate connexin43 (alpha1) immunostaining was concentrated on the apical while the connexin26 type (beta2) in the baso-lateral cell membranes. This is the first report of connexin26 in the cornea. Connexin43 was found also in corneal keratocytes and endothelial cell. Since the two connexins do not form functioning heteromeric channels and have selective permeabilities they may serve alternative pathways for direct cell-cell communication in the basal cell layer. During regeneration both connexins were expressed throughout the corneal epithelium including the migrating cells. They also showed transient up-regulation 24 hr after wounding in the form of overlapping relocation to the upper cell layers. At this time, basal epithelial cells at the limbal region, adjacent to the wound and those migrating over the wounded area all expressed membrane bound epidermal growth factor receptor and they were highly proliferating. In conclusion, like in other stratified epithelia connexin26 is also expressed in the cornea. Transient up-regulation and relocation of connexins within the regenerating epithelium may reflect the involvement of direct cell-cell communication in corneal wound healing. Mitotic activity in the migrating corneal epithelial cells is also a novel finding which is probably the sign of the excessive demand for new epithelial cells in larger wounds not met alone by the proliferating limbal stock.

Differential expression of connexins during stratification of human keratinocytes

To assess whether gap junctions and connexins change during keratinocyte differentiation, we have studied epidermal equivalents obtained in organotypic cultures of keratinocytes from the outer root sheath of human hair follicles. These reconstituted tissues exhibit a number of differentiation and proliferation markers of human epidermis, including gap junctions, connexins, and K6 and Ki67 proteins. Immunostaining and northern blots showed that gap junctions of the epidermal equivalents were made of Cx26 and Cx43. Cx26 was expressed in all keratinocyte layers, throughout the development of the epidermal equivalents. In contrast, Cx43 was initially observed only in the basal layer of keratinocytes and became detectable in the stratum spinosum and granulosum only after the epidermal equivalents had thickened. The levels of Cx26 and its transcript markedly increased as a function of stratification of the epidermal equivalents, whereas those of Cx43 remained almost constant. Microinjection of Lucifer Yellow into individual keratinocytes showed that gap junctions were similarly permeable at all stages of development of the epidermal equivalents. The data show that epidermal equivalents (i) feature a pattern of connexins typical of an actively renewing human interfollicular epidermis, and (ii) provide a model that reproduces the tridimensional organization of intact epidermis and that is amenable for experimentally testing the function of junctional communication between human keratinocytes.

Connexin43 gene expression and regulation in the rodent seminiferous epithelium

Connexin43 (Cx43) is one of the most predominant gap junction proteins found in the testis. We used in situ hybridization and indirect immunofluorescence to study the distribution of Cx43 mRNA and protein in the rodent seminiferous epithelium. During mouse testis maturation, Cx43 mRNA and its corresponding protein were first detected in the adluminal compartment of the growing seminiferous tubules (early postnatal age: Day 12) to become progressively located in the basal compartment at later ages (Days 16, 19, 27). In seminiferous tubules of sexually mature animals, the intensity of the hybridization signal was stage-dependent, with a maximum at Stage VII compared with Stages V and IX of the spermatogenic cycle (p<0.05). The highest expression of Cx43 mRNA was observed in the supporting Sertoli cells and, to a lesser extent, in the most basally located and less mature germ cells (spermatogonia and spermatocytes). Consistent with these observations, in situ dye coupling was observed between Sertoli cells and basal germ cells. In a mutant mouse deficient for the retinoid X receptor beta, which exhibited abnormal spermatogenesis due to altered Sertoli cell function, Cx43 transcripts were markedly decreased in the seminiferous epithelium (p<0.01). The immunoreactive signal for Cx43 was significantly reduced in seminiferous tubules of the 3-month-old mutant mice (p<0.05) and undetectable in older animals. These data provide new information about the precise localization of Cx43 mRNA and protein in seminiferous tubules of immature and mature rodent testes. Moreover, they suggest that retinoids, through the RXRbeta receptors, could be involved in the control of Cx43 gene expression in Sertoli cells.

Modulation of coupling between retinal horizontal cells by retinoic acid and endogenous dopamine

The regulation of electrical coupling between retinal neurons appears to be an important component of the neuronal mechanism of light adaptation, which enables the retina to operate efficiently over a broad range of light intensities. The information about the ambient light conditions has to be transmitted to the neuronal network of the retina and previous evidence has indicated that dopamine is an important neurochemical signal. In addition, recent studies suggest that another important chemical signal is retinoic acid, which is a light-correlated byproduct of the phototransduction cycle. This review summarizes the latest findings about the effects of dopamine and retinoic acid on gap junctional coupling in the retinas of mouse, rabbit and fish.

Retinoic acid modulates gap junctional permeability between horizontal cells of the mammalian retina

In the retina, all-trans retinoic acid (at-RA) could function as a light signal because its production increases with the level of illumination. Given the well-established effects of retinoic acid on cell coupling in other tissues, it is possible that the changing levels of at-RA modulate the gap junctional permeability between retinal neurons. This study examines the effects of retinoic acid on horizontal cell coupling, which is known to be modulated by the ambient light level. Single horizontal cells were injected under visual control with either Neurobiotin (mouse retina) or Lucifer yellow (rabbit retina) and the extent of tracer coupling or dye coupling was used to monitor the gap junctional permeability. In the mouse retina, the injection of Neurobiotin revealed a network of approximately 150-250 tracer-coupled horizontal cells. The tracer coupling was completely abolished by incubating the retina in 150 microM at-RA for 35 min. In the rabbit retina, the injection of Lucifer yellow into A-type horizontal cells revealed networks of approximately 15-30 dye-coupled horizontal cells. Incubation in 150 microM at-RA reduced the dye coupling within 12 min and complete uncoupling was achieved after 35 min. The uncoupling effects of at-RA in the mouse and rabbit retinas were concentration- and time-dependent and they were reversible after washout. The coupling was not affected by either the 9-cis form of retinoic acid or by at-RA that had been isomerized by intensive light. The uncoupling effect of at-RA persisted following treatment with a D1 receptor antagonist and thus was dopamine-independent. This study has established that at-RA is able to modulate the gap junctional permeability between horizontal cells in the mammalian retina, where its light-dependent release has already been demonstrated.

Upregulation of connexin 26 is a feature of keratinocyte differentiation in hyperproliferative epidermis, vaginal epithelium, and buccal epithelium

In epidermis, it has been suggested, intercellular communication through gap junctions is important in coordinating cell behavior. The connexins, may facilitate selective assembly or permeability of gap junctions, influencing the distribution of metabolites between cells. Using immunohistochemistry, we have compared the distribution of connexins 26 and 43 with that of proliferating cells (Ki67 labeling) in normal epidermis, hyperplastic epidermis (tape-stripped epidermis, psoriatic lesions, and viral warts), and vaginal and buccal epithelia. Connexin 43 was abundant in spinous layers of all epidermal specimens and in vaginal and buccal epithelia. Connexin 26 was absent from the interfollicular and interductal epidermis of normal hair-bearing skin, and nonlesional psoriatic epidermis but present at very low levels in plantar epidermis. Connexin 26 was prominent in lesional psoriatic epidermis and viral warts and in vaginal and buccal epithelia. In three independent experiments connexin 26 appeared in a patchy intercellular distribution in the basal epidermis within 24 h of tape stripping, proceeding to more extensive distribution in basal and suprabasal layers by 48 h. The increase in connexin 26 preceded that in cell proliferation. In vaginal epithelium, buccal epithelium, and viral warts connexin 26 was restricted mainly to suprabasal, nonproliferating cells. In psoriatic lesional epidermis connexin 26 was also located mainly in suprabasal, nonproliferating cells. Connexin 26 was present in a patchy distribution in the basal layer of psoriatic lesional epidermis, but double labeling for connexin 26 and Ki67 showed that many connexin 26 positive basal cells were nonproliferative, suggesting that connexin 26 may be related to differentiation rather than to proliferation. These observations would be consistent with a role for connexin 26 containing gap junctions during both early and later stages of keratinocyte differentiation in hyperplastic epidermis and in vaginal and buccal epithelia.