CONNEXINS AND CELL SIGNALING IN DEVELOPMENT AND DISEASE

A protein kinase A-ezrin complex regulates connexin 43 gap junction communication in liver epithelial cells

Communication between adjacent cells can occur via gap junctions (GJ) composed of connexin (Cx) hexamers that allow passage of small molecules. One of the most widely and highly expressed Cxs in human tissues is Cx43, shown to be regulated through phosphorylation by several kinases including PKA. Ezrin is a membrane associated protein that can serve as an A-kinase anchoring protein (AKAP) and hold an anchored pool of PKA. Here, we used the liver epithelial cell line IAR20, which expresses Cx43 as the predominant GJ protein, to test the hypothesis that Ezrin may associate with Cx43 in cell types that form stable GJs and serve as an AKAP. Our biochemical and proteomics data indicate that Ezrin associates with Cx43 in epithelial cells. Analyses by confocal immunofluorescence microscopy and proximity ligation assays demonstrate that Ezrin and Cx43 co-localize, together with zonula occludens-1 (ZO-1) and PKA RIα and RIIα, at the cell membrane. Quantitative gap-FRAP experiments show increased GJ intercellular communication after cAMP stimulation. Moreover, loading of cells with the Ht31 peptide that displaces both PKA RIα and RIIα from the AKAP or a peptide that disrupts the Cx43-Ezrin interaction reverts the effect and reduces the level of communication, supporting the hypothesis that in IAR20 cells Ezrin associates with Cx43 (in complex with ZO-1) which places PKA in proximity to Cx43, enabling its phosphorylation and GJ opening.

Influence of vascular endothelial growth factor and radiation on gap junctional intercellular communication in glioblastoma multiforme cell lines

Glioblastoma multiforme (GBM) is a highly aggressive glial brain tumor with an unfavorable prognosis despite all current therapies including surgery, radiation and chemotherapy. One characteristic of this tumor is a strong synthesis of vascular endothelial growth factor (VEGF), an angiogenesis factor, followed by pronounced vascularization. VEGF became a target in the treatment of GBM, for example with bevacizumab or the tyrosine kinase inhibitor axitinib, which blocks VEGF receptors. To improve patients’ prognosis, new targets in the treatment of GBM are under investigations. The role of gap junctions in GBM remains unknown, but some experimental therapies affect these intercellular channels to treat the tumor. Gap junctions are composed of connexins to allow the transport of small molecules between adjacent cells through gap junctional intercellular communication (GJIC). Based on data derived from astrocytes in former studies, which show that VEGF is able to enhance GJIC, the current study analyzed the effects of VEGF, radiation therapy and VEGF receptor blockade by axitinib on GJIC in human GBM cell lines U-87 and U-251. While VEGF is able to induce GJIC in U-251 cells but not in U-87 cells, radiation enhances GJIC in both cell lines. VEGF receptor blockade by axitinib diminishes radiation induced effects in U-251 partially, while increases GJIC in U-87 cells. Our data indicate that VEGF and radiation are both modifying components of GJIC in pathologic brain tumor tissue.

Parallels between Tooth Development and Repair: Conserved Molecular Mechanisms following Carious and Dental Injury

The reparative mechanisms that operate following carious and traumatic dental injury are critical for pulp survival and involve a series of highly conserved processes. It appears that these processes share genetic programs—linked to cytoskeletal organization, cell movement, and differentiation—that occur throughout embryogenesis. Reactionary dentin is secreted by surviving odontoblasts in response to moderate stimuli, leading to an increase in metabolic activity. In severe injury, necrotic odontoblasts are replaced by other pulp cells, which are able to differentiate into odontoblast-like cells and produce a reparative dentin. This complex process requires the collaborative efforts of cells of different lineage. The behavior of each of the contributing cell types during the phases of proliferation, migration, and matrix synthesis as well as details of how growth factors control wound cell activities are beginning to emerge. In this review, we discuss what is known about the molecular mechanisms involved in dental repair.

Influence of gap junction intercellular communication composed of connexin 43 on the antineoplastic effect of adriamycin in breast cancer cells

Gap junctions (GJs) serve the principal role in the antineoplastic (cytotoxicity and induced apoptosis) effect of chemical drugs. The aim of the present study was to determine the effect of GJ intercellular communication (GJIC) composed of connexin 43 (Cx43) on adriamycin cytotoxicity in breast cancer cells. Four cell lines (Hs578T, MCF-7, MDA-MB-231 and SK-BR-3) with different degree of malignancy were used in the study. The results of western blotting and immunofluorescence revealed that, in Hs578T and MCF-7 cells, which have a low degree of malignancy, the expression levels of Cx43 and GJIC were higher than those in MDA-MB-231 and SK-BR-3 cells (which have a high degree of malignancy). In Hs578T and MCF-7 cells, where GJ could be formed, the function of GJ was modulated by a pharmacological potentiators [retinoid acid (RA)]/inhibitors [oleamide and 18-α-glycyrrhetinic acid (18-α-GA)] and small interfering RNA (siRNA). In high-density cells (where GJ was formed), enhancement of GJ function by RA increased the cytotoxicity of adriamycin, while inhibition of GJ function by oleamide/18-α-GA and siRNA decreased the cytotoxicity caused by adriamycin. Notably, the modulation of GJ did not affect the survival of cells treated with adriamycin when cells were in low density (no GJ was formed). The present study illustrated the association between GJIC and the antitumor effect of adriamycin in breast cancer cells. The cytotoxicity of adriamycin on breast cancer cells was increased when the function of gap junctions was enhanced.

Mitotic cells form actin-based bridges with adjacent cells to provide intercellular communication during rounding

In order to achieve accurate chromosome segregation, eukaryotic cells undergo a dramatic change in morphology to obtain a spherical shape during mitosis. Interphase cells communicate directly with each other by exchanging ions and small molecules via gap junctions, which have important roles in controlling cell growth and differentiation. As cells round up during mitosis, the gap junctional communication between mitotic cells and adjacent interphase cells ceases. Whether mitotic cells use alternative mechanisms for mediating direct cell-cell communication during rounding is currently unknown. Here, we have studied the mechanisms involved in the remodeling of gap junctions during mitosis. We further demonstrate that mitotic cells are able to form actin-based plasma membrane bridges with adjacent cells during rounding. These structures, termed “mitotic nanotubes,” were found to be involved in mediating the transport of cytoplasm, including Rab11-positive vesicles, between mitotic cells and adjacent cells. Moreover, a subpool of the gap-junction channel protein connexin43 localized in these intercellular bridges during mitosis. Collectively, the data provide new insights into the mechanisms involved in the remodeling of gap junctions during mitosis and identify actin-based plasma membrane bridges as a novel means of communication between mitotic cells and adjacent cells during rounding.

Cx26 knockout predisposes the mammary gland to primary mammary tumors in a DMBA-induced mouse model of breast cancer

Down-regulation of the gap junction protein connexin26 (Cx26) is an early event following breast cancer onset and has led to Cx26 being classically described as a tumor suppressor. Interestingly, mutations in theCx26 gene (GJB2) reduce or ablate Cx26 gap junction channel function and are the most common cause of genetic deafness. It is unknown if patients with loss-of-function GJB2 mutations have a greater susceptibility to breast tumorigenesis or aggressive breast cancer progression. To investigate these possibilities, 7, 12-dimethylbenz[α]anthracene (DMBA)-induced tumor development was evaluated in BLG-Cre; Cx26^fl/fl mice expressing Cre under the β-Lactoglobulin promoter (Cre+) compared to Cx26^fl/fl controlmice (Cre-) following pituitary isograft driven Cx26 knockout. A significantly increased number of DMBA-treated Cre+ mice developed primary mammary tumors, as well as developed multiple tumors, compared to Cre- mice. Primary tumors of Cre+ mice were of multiple histological subtypes and had similar palpable tumour onset and growth rate compared to tumors from Cre- mice. Lungs were evaluated for evidence of metastases revealing a similar percentage of lung metastases in Cre+ and Cre- mice. Together, our results suggest that loss of Cx26 predisposes the mammary gland to chemically induced mammary tumour formation which may have important implications to patients with GJB2 mutations.

Connexins: substrates and regulators of autophagy

Connexins mediate intercellular communication by assembling into hexameric channel complexes that act as hemichannels and gap junction channels. Most connexins are characterized by a very rapid turn-over in a variety of cell systems. The regulation of connexin turn-over by phosphorylation and ubiquitination events has been well documented. Moreover, different pathways have been implicated in connexin degradation, including proteasomal and lysosomal-based pathways. Only recently, autophagy emerged as an important connexin-degradation pathway for different connexin isoforms. As such, conditions well known to induce autophagy have an immediate impact on the connexin-expression levels. This is not only limited to experimental conditions but also several pathophysiological conditions associated with autophagy (dys)function affect connexin levels and their presence at the cell surface as gap junctions. Finally, connexins are not only substrates of autophagy but also emerge as regulators of the autophagy process. In particular, several connexin isoforms appear to recruit pre-autophagosomal autophagy-related proteins, including Atg16 and PI3K-complex components, to the plasma membrane, thereby limiting their availability and capacity for regulating autophagy.

Molecular mechanisms regulating formation, trafficking and processing of annular gap junctions

Internalization of gap junction plaques results in the formation of annular gap junction vesicles. The factors that regulate the coordinated internalization of the gap junction plaques to form annular gap junction vesicles, and the subsequent events involved in annular gap junction processing have only relatively recently been investigated in detail. However it is becoming clear that while annular gap junction vesicles have been demonstrated to be degraded by autophagosomal and endo-lysosomal pathways, they undergo a number of additional processing events. Here, we characterize the morphology of the annular gap junction vesicle and review the current knowledge of the processes involved in their formation, fission, fusion, and degradation. In addition, we address the possibility for connexin protein recycling back to the plasma membrane to contribute to gap junction formation and intercellular communication. Information on gap junction plaque removal from the plasma membrane and the subsequent processing of annular gap junction vesicles is critical to our understanding of cell-cell communication as it relates to events regulating development, cell homeostasis, unstable proliferation of cancer cells, wound healing, changes in the ischemic heart, and many other physiological and pathological cellular phenomena.

Evaluation of electrocardiographic parameters in patients with hearing loss genotyped for the connexin 26 gene (GJB2) mutations

Introduction

Several studies have associated congenital sensorineural hearing loss in children with prolongation of the cardiac parameter QTc. The cause of this association is unknown. At the same time, mutations in GJB2, which encodes connexin 26, are the most common cause of congenital hearing impairment.

Objective

To compare electrocardiographic parameters (PR interval, QRS complex, and QTc interval) in patients with hearing loss who were tested for mutations in GJB2 and GJB6 to investigate whether these mutations affect electrical activity of the heart.

Methods

346 patients (176 males, 170 females) with sensorineural hearing loss of 30 dB HL or more, aged 21.8 ± 19.9 years (including 147 children <14 years), underwent both genetic study for GJB2 and GJB6 mutations and electrocardiography.

Results

Mutations in GJB2, including homozygotes and heterozygotes, were found in 112 (32%) patients. There were no significant differences in ECG parameters between groups of patients with and without mutations in GJB2. No differences were observed either in men (mean PR with mutation: 155 ± 16.6 vs. 153.6 ± 30.1 without; QRS: 99.9 ± 9.9 vs. 101.1 ± 15.4; QTc: 414.9 ± 29.9 vs. 412.4 ± 25.7) or women (mean PR with: 148.7 ± 21 vs. 143.8 ± 22.8 without; QRS: 94.8 ± 7.6 vs. 92.9 ± 9.6; QTc: 416.8 ± 20.6 vs. 424.9 ± 22.8). In similar fashion, we did we find any significant differences between groups of children with and without GJB2 mutations (mean PR with: 126.3 ± 19.6 vs. 127 ± 19.7 without; QRS: 80.7 ± 9.5 vs. 79.4 ± 11.6; QTc: 419.7 ± 23.5 vs. 419.8 ± 24.8).

Conclusion

No association was found between the presence of GJB2 mutations encoding connexin 26 in patients with hearing loss and their ECG parameters (PR, QRS, QTc).

Cx43-Dependent Skeletal Phenotypes Are Mediated by Interactions between the Hapln1a-ECM and Sema3d during Fin Regeneration

Skeletal development is a tightly regulated process and requires proper communication between the cells for efficient exchange of information. Analysis of fin length mutants has revealed that the gap junction protein Connexin43 (Cx43) coordinates cell proliferation (growth) and joint formation (patterning) during zebrafish caudal fin regeneration. Previous studies have shown that the extra cellular matrix (ECM) protein Hyaluronan and Proteoglycan Link Protein1a (Hapln1a) is molecularly and functionally downstream of Cx43, and that hapln1a knockdown leads to reduction of the glycosaminoglycan hyaluronan. Here we find that the proteoglycan aggrecan is similarly reduced following Hapln1a knockdown. Notably, we demonstrate that both hyaluronan and aggrecan are required for growth and patterning. Moreover, we provide evidence that the Hapln1a-ECM stabilizes the secreted growth factor Semaphorin3d (Sema3d), which has been independently shown to mediate Cx43 dependent phenotypes during regeneration. Double knockdown of hapln1a and sema3d reveal synergistic interactions. Further, hapln1a knockdown phenotypes were rescued by Sema3d overexpression. Therefore, Hapln1a maintains the composition of specific components of the ECM, which appears to be required for the stabilization of at least one growth factor, Sema3d. We propose that the Hapln1a dependent ECM provides the required conditions for Sema3d stabilization and function. Interactions between the ECM and signaling molecules are complex and our study demonstrates the requirement for components of the Hapln1a-ECM for Sema3d signal transduction.

Induction of Apoptosis by PQ1, a Gap Junction Enhancer that Upregulates Connexin 43 and Activates the MAPK Signaling Pathway in Mammary Carcinoma Cells

The mechanism of gap junction enhancer (PQ1) induced cytotoxicity is thought to be attributed to the change in connexin 43 (Cx43) expression; therefore, the effects of Cx43 modulation in cell survival were investigated in mammary carcinoma cells (FMC2u) derived from a malignant neoplasm of a female FVB/N-Tg(MMTV-PyVT)634Mul/J (PyVT) transgenic mouse. PQ1 was determined to have an IC₅₀ of 6.5 µM in FMC2u cells, while inducing an upregulation in Cx43 expression. The effects of Cx43 modulation in FMC2u cell survival was determined through transfection experiments with Cx43 cDNA, which induced an elevated level of protein expression similar to that seen with PQ1 exposure, or siRNA to silence Cx43 protein expression. Overexpression or silencing of Cx43 led to a reduction or an increase in cell viability, respectively. The mitogen-activated protein kinase (MAPK) family has been implicated in the regulation of cell survival and cell death; therefore, the gap junctional intercellular communication (GJIC)-independent function of PQ1 and Cx43 in the Raf/Mitogen-activated protein kinase/ERK kinase/extracellular-signal-regulated kinase (Raf-MEK-ERK) cascade of cellular survival and p38 MAPK-dependent pathway of apoptosis were explored. PQ1 treatment activated p44/42 MAPK, while the overexpression of Cx43 resulted in a reduced expression. This suggests that PQ1 affects the Raf-MEK-ERK cascade independent of Cx43 upregulation. Both overexpression of Cx43 and PQ1 treatment stimulated an increase in the phosphorylated form of p38-MAPK, reduced levels of the anti-apoptotic protein Bcl-2, and increased the cleavage of pro-caspase-3. Silencing of Cx43 protein expression led to a reduction in the phosphorylation of p38-MAPK and an increase in Bcl-2 expression. The mechanism behind PQ1-induced cytotoxicity in FMC2u mammary carcinoma cells is thought to be attributed to the change in Cx43 expression. Furthermore, PQ1-induced apoptosis through the upregulation of Cx43 may depend on p38 MAPK, highlighting that the effect of PQ1 on gap junctions as well as cellular survival via a MAPK-dependent pathway.

Chemokines in Wound Healing and as Potential Therapeutic Targets for Reducing Cutaneous Scarring

Significance: Cutaneous scarring is an almost inevitable end point of adult human wound healing. It is associated with significant morbidity, both physical and psychological. Pathological scarring, including hypertrophic and keloid scars, can be particularly debilitating. Manipulation of the chemokine system may lead to effective therapies for problematic lesions. Recent Advances: Rapid advancement in the understanding of chemokines and their receptors has led to exciting developments in the world of therapeutics. Modulation of their function has led to clinically effective treatments for conditions as diverse as human immunodeficiency virus and inflammatory bowel disease. Potential methods of targeting chemokines include monoclonal antibodies, small-molecule antagonists, interference with glycosaminoglycan binding and the use of synthetic truncated chemokines. Early work has shown promising results on scar development and appearance when the chemokine system is manipulated. Critical Issues: Chemokines are implicated in all stages of wound healing leading to the development of a cutaneous scar. An understanding of entirely regenerative wound healing in the developing fetus and how the expression of chemokines and their receptors change during the transition to the adult phenotype is central to addressing pathological scarring in adults. Future Directions: As our understanding of chemokine/receptor interactions and scar formation evolves it has become apparent that effective therapies will need to mirror the complexities in these diverse biological processes. It is likely that sophisticated treatments that sequentially influence multiple ligand/receptor interactions throughout all stages of wound healing will be required to deliver viable treatment options.

The action of mimetic peptides on connexins protects fibroblasts from the negative effects of ischemia reperfusion

Connexins have been proposed as a target for therapeutic treatment of a variety of conditions. The main approaches have been by antisense or small peptides specific against connexins. Some of these peptides enhance communication while others interfere with connexin binding partners or bind to the intracellular and extracellular loops of connexins. Here, we explored the mechanism of action of a connexin mimetic peptide by evaluating its effect on gap junction channels, connexin protein levels and hemichannel activity in fibroblast cells under normal conditions and following ischemia reperfusion injury which elevates Cx43 levels, increases hemichannel activity and causes cell death. Our results showed that the effects of the mimetic peptide were concentration-dependent. High concentrations (100-300 μM) significantly reduced Cx43 protein levels and GJIC within 2 h, while these effects did not appear until 6 h when using lower concentrations (10-30 μM). Cell death can be reduced when hemichannel opening and GJIC were minimised.

Summary: Connexin mimetic peptides can reduce the levels of connexin proteins in cells and can prevent the spread of cell death that occurs following ischemia reperfusion injury, which has therapeutic potential.

Drosophila eye size is determined by Innexin 2-dependent Decapentaplegic signalling

Organogenesis relies on specific genetic and molecular programmes, which orchestrate growth and cellular differentiation over developmental time. This is particularly important during Drosophila eye development in which cell-cell inductive events and long-range signalling have to be integrated to regulate proper cell proliferation, differentiation and morphogenesis. How these processes are coordinated is still not very well understood. Here we identify the gap junction protein Innexin2 (Inx2) as an important regulator of eye development. Depleting inx2 during eye development reduces eye size whereas elevating inx2 levels increases eye size. Loss- and gain-of-function experiments demonstrate that inx2 is required functionally in larval eye disc cells where it localises apico-laterally. inx2 regulates disc cell proliferation as well as morphogenetic furrow movement and as a result the amount of differentiated photoreceptors. inx2 interacts genetically with the Dpp pathway and we find that proper activation of the Dpp pathway transducer Mad at the furrow and expression of Dpp receptors Thickveins and Punt in the anterior disc compartment require inx2. We further show that inx2 is required for the transcriptional activation of dpp and punt in the eye disc. Our results highlight the crucial role of gap junction proteins in regulating morphogen-dependent organ size determination.

Connexin 43 expression predicts poor progression-free survival in patients with non-muscle invasive urothelial bladder cancer

Objectives

To evaluate the protein expression of connexin 43 (Cx43) in primary urothelial bladder cancer and test its association with the histopathological characteristics and clinical outcome.

Methods

A tissue microarray containing 348 tissue samples from 174 patients with primary urothelial carcinomas of the bladder was immunohistochemically stained for Cx43. The intensity of staining was semiquantitatively evaluated (score 0, 1+, 2+), and the association with clinicopathological features was assessed. Univariable and multivariable analyses were performed to identify predictors for progression-free survival (PFS).

Results

Membranous Cx43 immunoreactivity was detected in 118 (67.8%) of 174 analysable urothelial carcinomas, of which 31 (17.8%) showed even a strong (score 2+) and mainly homogeneous staining. Strong expression levels of Cx43 (score 2+) were associated with higher tumour grade, multiplicity and increased proliferation (all p<0.05). In the subgroup of patients with stage pTa and pT1 bladder tumours (n=158), strong Cx43 expression (p<0.001), solid growth pattern (p<0.001) and increased Ki-67 proliferation fraction (p<0.05) were significantly associated with shorter PFS in an univariable Cox regression analysis. In multivariable Cox regression models, Cx43 immunoreactivity and histological growth pattern remained highly significant and adverse risk factors for PFS.

Conclusions

The expression levels of Cx43 are frequent in non-muscle invasive bladder cancer (NMIBC), with high expression levels being associated with poor prognosis. Routine assessment of Cx43 expression may improve the identification of high-risk NMIBC.

Connexin 43 mediates PFOS-induced apoptosis in astrocytes

Perfluorooctane sulfonate (PFOS) is a man-made environmental pollutant that is toxic to mammals. However, the neurotoxic effects of PFOS remain largely unexplored. In this study, we determined the role of an astrocyte specific gap junction protein, connexin 43 (Cx43), in PFOS-induced apoptosis. The rate of astrocyte apoptosis was higher in cortex astrocytes after PFOS treatment. These astrocytes also showed up-regulated expression of Cx43 and higher levels of cleaved caspase-3. Elevated ROS accumulation and decreased ΔΨm also confirmed the presence of PFOS-induced apoptosis. However, the exposure of astrocytes to PFOS together with carbenoxolone (CBX) significantly reduced both Cx43 and cleaved caspase-3 levels. These results indicate that Cx43 plays a proapoptotic role in PFOS-induced apoptosis in cortex astrocyte cells.

Connexin hemichannels influence genetically determined inflammatory and hyperproliferative skin diseases

Connexin mutations underlie numerous human genetic diseases. Several connexin genes have been linked to skin diseases, and mechanistic studies have indicated that a gain of abnormal channel function may be responsible for pathology. The topical accessibility of the epidermal connexins, the existence of several mouse models of human skin disease, and the ongoing identification of pharmacological inhibitors targeting connexins provide an opportunity to test new therapeutic approaches.

Insights into the role of connexins in mammary gland morphogenesis and function

Gap junctions formed of connexin subunits link adjacent cells by direct intercellular communication that is essential for normal tissue homeostasis in the mammary gland. The mammary gland undergoes immense remodeling and requires exquisite regulation to control the proliferative, differentiating, and cell death mechanisms regulating gland development and function. The generation of novel genetically modified mice with reduced or ablated connexin function within the mammary gland has advanced our understanding of the role of gap junctions during the complex and dynamic process of mammary gland development. These studies have revealed an important stage-specific role for Cx26 (GJA1) and Cx43 (GJB2), while Cx30 (GJB6) and Cx32 (Gjb1) can be eliminated without compromising the gland. Yet, there remain gaps in our understanding of the role of mammary gland gap junctions.

Extracellular matrix, gap junctions, and retinal vascular homeostasis in diabetic retinopathy

The vascular basement membrane (BM) contains extracellular matrix (ECM) proteins that assemble in a highly organized manner to form a supportive substratum for cell attachment facilitating myriad functions that are vital to cell survival and overall retinal homeostasis. The BM provides a microenvironment in which bidirectional signaling through integrins regulates cell attachment, turnover, and functionality. In diabetic retinopathy, the BM undergoes profound structural and functional changes, and recent studies have brought to light the implications of such changes. Thickened vascular BM in the retinal capillaries actively participate in the development and progression of characteristic changes associated with diabetic retinopathy. High glucose (HG)-induced compromised cell-cell communication via gap junctions (GJ) in retinal vascular cells may disrupt homeostasis in the retinal microenvironment. In this review, the role of altered ECM synthesis, compromised GJ activity, and disturbed retinal homeostasis in the development of retinal vascular lesions in diabetic retinopathy are discussed.

Differential regulation of Connexin50 and Connexin46 by PI3K signaling

Gap junction channels can modify their activity in response to cell signaling pathways. Here, we demonstrate that Connexin50 (Cx50) coupling, but not Connexin46 (Cx46), increased when co-expressed with a constitutively active p110α subunit of PI3K in Xenopus oocytes. In addition, inhibition of PI3K signaling by blocking p110α, or Akt, significantly decreased gap junctional conductance in Cx50 transfected HeLa cells, with no effect on Cx46. Alterations in coupling levels were not a result of reduced Cx50 unitary conductance, suggesting that changes in the number of active channels were responsible. These data indicate that Cx50 is specifically regulated by the PI3K signaling pathway.

Differential connexin function enhances self-renewal in glioblastoma

The coordination of complex tumor processes requires cells to rapidly modify their phenotype and is achieved by direct cell-cell communication through gap junction channels composed of connexins. Previous reports have suggested that gap junctions are tumor suppressive based on connexin 43 (Cx43), but this does not take into account differences in connexin-mediated ion selectivity and intercellular communication rate that drive gap junction diversity. We find that glioblastoma cancer stem cells (CSCs) possess functional gap junctions that can be targeted using clinically relevant compounds to reduce self-renewal and tumor growth. Our analysis reveals that CSCs express Cx46, while Cx43 is predominantly expressed in non-CSCs. During differentiation, Cx46 is reduced, while Cx43 is increased, and targeting Cx46 compromises CSC maintenance. The difference between Cx46 and Cx43 is reflected in elevated cell-cell communication and reduced resting membrane potential in CSCs. Our data demonstrate a pro-tumorigenic role for gap junctions that is dependent on connexin expression.

Biology-Driven Gene-Gene Interaction Analysis of Age-Related Cataract in the eMERGE Network

Bioinformatics approaches to examine gene-gene models provide a means to discover interactions between multiple genes that underlie complex disease. Extensive computational demands and adjusting for multiple testing make uncovering genetic interactions a challenge. Here, we address these issues using our knowledge-driven filtering method, Biofilter, to identify putative single nucleotide polymorphism (SNP) interaction models for cataract susceptibility, thereby reducing the number of models for analysis. Models were evaluated in 3,377 European Americans (1,185 controls, 2,192 cases) from the Marshfield Clinic, a study site of the Electronic Medical Records and Genomics (eMERGE) Network, using logistic regression. All statistically significant models from the Marshfield Clinic were then evaluated in an independent dataset of 4,311 individuals (742 controls, 3,569 cases), using independent samples from additional study sites in the eMERGE Network: Mayo Clinic, Group Health/University of Washington, Vanderbilt University Medical Center, and Geisinger Health System. Eighty-three SNP-SNP models replicated in the independent dataset at likelihood ratio test P < 0.05. Among the most significant replicating models was rs12597188 (intron of CDH1)-rs11564445 (intron of CTNNB1). These genes are known to be involved in processes that include: cell-to-cell adhesion signaling, cell-cell junction organization, and cell-cell communication. Further Biofilter analysis of all replicating models revealed a number of common functions among the genes harboring the 83 replicating SNP-SNP models, which included signal transduction and PI3K-Akt signaling pathway. These findings demonstrate the utility of Biofilter as a biology-driven method, applicable for any genome-wide association study dataset.

Down-regulation of connexin43 and connexin32 in keratocystic odontogenic tumours: potential association with clinical features

AIMS

The objective of this study was to explore the potential involvement of connexin43 (Cx43) and connexin32 (Cx32), two vital members of the connexin families, in the pathogenesis of keratocystic odontogenic tumours (KCOT).

METHODS AND RESULTS

The expression levels of Cx43 and Cx32 in human KCOT and normal oral mucosa (OM) tissues were measured using immunohistochemistry and real-time quantitative polymerase chain reaction (qPCR). The relationship between Cx43 and Cx32 expression and markers of proliferation [proliferating cell nuclear antigen (PCNA), cyclin D1], anti-apoptosis [B cell lymphoma 2 (Bcl-2)] and autophagy [light chain 3 (LC3), Sequestosome 1 p62 (p62)] was then investigated in the KCOT samples. The results showed that Cx43 and Cx32 expression was down-regulated significantly in KCOT samples relative to OM samples. Meanwhile, the expression levels of Cx43 and Cx32 were correlated negatively with the expression levels of PCNA, cyclin D1, Bcl-2, LC3 and p62, as confirmed further by double-labelling immunofluorescence analyses.

CONCLUSIONS

This study reveals for the first time that Cx43 and Cx32 are down-regulated in KCOT and suggests an association with growth regulation, anti-apoptosis and autophagy in KCOT.

Effect of enhanced expression of connexin 43 on sunitinib-induced cytotoxicity in mesothelioma cells

Connexin (Cx) makes up a type of intercellular channel called gap junction (GJ). GJ plays a regulatory role in cellular physiology. The Cx expression level is often decreased in cancer cells compared to that in healthy ones, and the restoration of its expression has been shown to exert antiproliferative effects. This work aims to evaluate the effect of the restoration of connexin 43 (Cx43) (the most ubiquitous Cx subtype) expression on sunitinib (SU)-induced cytotoxicity in malignant mesothelioma (MM) cells. Increased Cx43 expression in an MM cell line (H28) improved the ability of SU to inhibit receptor tyrosine kinase (RTK) signaling. Moreover, higher Cx43 expression promoted SU-induced apoptosis. The cell viability test revealed that Cx43 enhanced the cytotoxic effect of SU in a GJ-independent manner. The effect of Cx43 on a proapoptotic factor, Bax, was then investigated. The interaction between Cx43 and Bax was confirmed by immunoprecipitation. Furthermore, higher Cx43 expression increased the production of a cleaved (active) form of Bax during SU-induced apoptosis with no alteration in total Bax expression. These findings indicate that Cx43 most likely increases sensitivity to SU in H28 through direct interaction with Bax. In conclusion, we found that Cx43 overcame the chemoresistance of MM cells.

The carboxyl tail of connexin32 regulates gap junction assembly in human prostate and pancreatic cancer cells

Connexins, the constituent proteins of gap junctions, are transmembrane proteins. A connexin (Cx) traverses the membrane four times and has one intracellular and two extracellular loops with the amino and carboxyl termini facing the cytoplasm. The transmembrane and the extracellular loop domains are highly conserved among different Cxs, whereas the carboxyl termini, often called the cytoplasmic tails, are highly divergent. We have explored the role of the cytoplasmic tail of Cx32, a Cx expressed in polarized and differentiated cells, in regulating gap junction assembly. Our results demonstrate that compared with the full-length Cx32, the cytoplasmic tail-deleted Cx32 is assembled into small gap junctions in human pancreatic and prostatic cancer cells. Our results further document that the expression of the full-length Cx32 in cells, which express the tail-deleted Cx32, increases the size of gap junctions, whereas the expression of the tail-deleted Cx32 in cells, which express the full-length Cx32, has the opposite effect. Moreover, we show that the tail is required for the clustering of cell-cell channels and that in cells expressing the tail-deleted Cx32, the expression of cell surface-targeted cytoplasmic tail alone is sufficient to enhance the size of gap junctions. Our live-cell imaging data further demonstrate that gap junctions formed of the tail-deleted Cx32 are highly mobile compared with those formed of full-length Cx32. Our results suggest that the cytoplasmic tail of Cx32 is not required to initiate the assembly of gap junctions but for their subsequent growth and stability. Our findings suggest that the cytoplasmic tail of Cx32 may be involved in regulating the permeability of gap junctions by regulating their size.

Regulation of FAK Activity by Tetraspan Proteins: Potential Clinical Implications in Cancer

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that regulates multiple cell signaling pathways in both physiological and pathological conditions. Overexpression and activation of FAK is associated with many advanced stage cancers through promoting cancer cell tumorigenicity and progression as well as by regulating the tumor microenvironment. FAK has multiple binding partners through which FAK exerts its functions including RhoGEF, Src family, talin, cortactin, and paxilin. Over the last few years, it has been proposed that a novel group of four transmembrane proteins can interact with FAK and regulate its activity. These include select tetraspanins such as CD151 and CD9 as well as the GAS3 family members epithelial membrane protein-2 (EMP2) and peripheral myelin protein-22 (PMP22). In this review, we discuss the current knowledge of the interaction between FAK and tetraspan proteins in physiological and pathological conditions, with an emphasis on the potential of tetraspan family members as therapeutic targets in cancer.

Fluoride alters connexin expression in rat incisor pulp

OBJECTIVE

Connexins (Cxs) are important to control growth and cell differentiation of dental tissues. The aim of the present study was to assess the impact of chronic exposure to sodium fluoride (NaF) on Cxs expression and alkaline phosphatase (ALP) activity in dental pulp, and on morphometric parameters of adult rat mandible and incisors.

DESIGN

Three groups of male Wistar rats (22 days-old) were given water containing: (a) 0.3 mg/L (Control), (b) 10 mg/L and (c) 50 mg/L of NaF for eight weeks. Incisor pulp homogenates were prepared for determination of Cx32, Cx43 and Cx45 gene expression, using semi-quantitative RT-PCR, and of ALP activity. Morphometric parameters of mandible and incisors were determined on radiographs.

RESULTS

Cx43 gene expression increased with exposure to NaF in a dose-dependent manner. Cx32 mRNA levels were higher than controls in the 10mg/L NaF group only; Cx45 mRNA levels were lower in groups given 10 and 50mg/L of NaF than in controls. ALP activity was higher in both high-NaF dose groups compared to the control group (p<0.05). Lower incisor diameter was lower in the 50 mg/L NaF than in the control group (p<0.01). None of the mandibular growth parameters were affected by NaF treatment.

CONCLUSION

Our results showed that fluorotic alterations in rat incisor were associated with increased Cx43 expression and ALP activity, as well as with changes in the expression pattern of different Cxs in pulp tissue. The observed changes may have a stimulating effect on dentin mineralization.

Cx43 phosphorylation on S279/282 and intercellular communication are regulated by IP3/IP3 receptor signaling

Background

Inositol 1,4,5-trisphosphate receptor (IP₃R) plays a pivotal role in the Ca²⁺ release process in a variety of cell types. Additionally, IP₃R is distributed in ventricular intercalated discs, but its function(s) in this particular site remains unknown. Connexin (Cx43), the predominant gap junction (GJ) protein in ventricular myocardium, is linked to several signaling pathways that regulate Cx43 properties by (de)phosphorylation on multiple residues. Here, we investigated the regulatory role of IP₃R in cell-cell communication and the mechanism(s) underlying this effect.

Results

In neonatal rat and adult mouse ventricular myocytes IP₃R co-localized and co-immunoprecipitated with Cx43 in GJ plaques detected by immunostaining and western blot assays. Blocking IP₃R with antagonists or silencing pan-IP₃R expression with shRNA hindered the 6-carboxyfluorescein (6-CFDA) diffusion through GJs and desynchronized Ca²⁺ transients among confluent neonatal myocytes in culture, whereas stimulation of IP₃R with IP₃ ester or ATP exerted the opposite effect. Likewise, 6-CFDA propagation through GJs was modulated by IP₃R activation or inhibition in cell pairs of isolated adult cardiomyocytes. Furthermore, IP₃R activation or IP₃R suppression promoted or suppressed, respectively, Cx43 phosphorylation on S279/282. Site-directed mutagenesis indicated that expression of a mutant Cx43-S282A (alanine) inhibited S279/282 phosphorylation and GJ permeability, while the S279A mutant showed the opposite effect in ventricular myocytes. Expression of these mutants in HEK293 cells revealed that cells with a dual S279/282 mutation failed to express exogenous Cx43, whereas cells with a single S279 or S282 mutation displayed Cx43 overexpression with increased phosphorylation of S279/282 and promotion of intercellular communication.

Conclusions

These results demonstrated, for the first time, that IP₃R physically interacts with Cx43 and participates in the regulation of Cx43 phosphorylation on S279/282, thereby affecting GJ intercellular communication in ventricular myocytes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-014-0058-6) contains supplementary material, which is available to authorized users.

Vitamin D3 regulates the formation and degradation of gap junctions in androgen-responsive human prostate cancer cells

1α-25(OH)2 vitamin D3 (1-25D), an active hormonal form of Vitamin D3, is a well-known chemopreventive and pro-differentiating agent. It has been shown to inhibit the growth of several prostate cancer cell lines. Gap junctions, formed of proteins called connexins (Cx), are ensembles of cell-cell channels, which permit the exchange of small growth regulatory molecules between adjoining cells. Cell-cell communication mediated by gap junctional channels is an important homeostatic control mechanism for regulating cell growth and differentiation. We have investigated the effect of 1-25D on the formation and degradation of gap junctions in an androgen-responsive prostate cancer cell line, LNCaP, which expresses retrovirally-introduced Cx32. Connexin32 is expressed by the luminal and well-differentiated cells of normal prostate and prostate tumors. Our results document that 1-25D enhances the expression of Cx32 and its subsequent assembly into gap junctions. Our results further show that 1-25D prevents androgen-regulated degradation of Cx32, post-translationally, independent of androgen receptor (AR)-mediated signaling. Finally, our findings document that formation of gap junctions sensitizes Cx32-expressing LNCaP cells to the growth inhibitory effects of 1-25D and alters their morphology. These findings suggest that the growth-inhibitory effects of 1-25D in LNCaP cells may be related to its ability to modulate the assembly of Cx32 into gap junctions.

A Mechanically Tunable Microfluidic Cell-Trapping Device

Controlled manipulation, such as isolation, positioning and trapping of cells, is important in basic biological research and clinical diagnostics. Micro/nanotechnologies have been enabling more effective and efficient cell trapping than possible with conventional platforms. Currently available micro/nanoscale methods for cell trapping, however, still lack flexibility in precisely controlling the number of trapped cells. We exploited the large compliance of elastomers to create an array of cell-trapping microstructures, whose dimensions can be mechanically modulated by inducing uniformly distributed strain via application of external force on the chip. The device consists of two elastomer polydimethylsiloxane (PDMS) sheets, one of which bears dam-like, cup-shaped geometries to physically capture cells. The mechanical modulation is used to tune the characteristics of cell trapping to capture a predetermined number of cells, from single cells to multiple cells. Thus, enhanced utility and flexibility for practical applications can be attained, as demonstrated by tunable trapping of MCF-7 cells, a human breast cancer cell line.

The use of connexin-based therapeutic approaches to target inflammatory diseases

Alterations in Connexin43 (Cx43) expression levels have been shown to play a role in inflammatory processes including skin wounding and neuroinflammation. Cx43 protein levels increase following a skin wound and can inhibit wound healing. Increased Cx43 has been observed following stroke, epilepsy, ischemia, optic nerve damage, and spinal cord injury with gap junctional communication and hemichannel opening leading to increased secondary damage via the inflammatory response. Connexin43 modulation has been identified as a potential target for protection and repair in neuroinflammation and skin wound repair. This review describes the use of a Cx43 specific antisense oligonucleotide (Cx43 AsODN) and peptide mimetics of the connexin extracellular loop domain to modulate Cx43 expression and/or function in inflammatory disorders of the skin and central nervous system. An overview of the role of connexin43 in inflammatory conditions, how antisense and peptide have allowed us to elucidate the role of Cx43 in these diseases, create models of diseases to test interventions and their potential for use clinically or in current clinical trials is presented. Antisense oligonucleotides are applied topically and have been used to improve wound healing following skin injury. They have also been used to develop ex vivo models of neuroinflammatory diseases that will allow testing of intervention strategies. The connexin mimetic peptides have shown potential in a number of neuroinflammatory disorders in ex vivo models as well as in vivo when delivered directly to the injury site or when delivered systemically.

A comprehensive review of advanced biopolymeric wound healing systems

Wound healing is a complex and dynamic process that involves the mediation of many initiators effective during the healing process such as cytokines, macrophages and fibroblasts. In addition, the defence mechanism of the body undergoes a step-by-step but continuous process known as the wound healing cascade to ensure optimal healing. Thus, when designing a wound healing system or dressing, it is pivotal that key factors such as optimal gaseous exchange, a moist wound environment, prevention of microbial activity and absorption of exudates are considered. A variety of wound dressings are available, however, not all meet the specific requirements of an ideal wound healing system to consider every aspect within the wound healing cascade. Recent research has focussed on the development of smart polymeric materials. Combining biopolymers that are crucial for wound healing may provide opportunities to synthesise matrices that are inductive to cells and that stimulate and trigger target cell responses crucial to the wound healing process. This review therefore outlines the processes involved in skin regeneration, optimal management and care required for wound treatment. It also assimilates, explores and discusses wound healing drug-delivery systems and nanotechnologies utilised for enhanced wound healing applications.

Particular distribution of the GJB2/GJB6 gene mutations in Mexican population with hearing impairment

BACKGROUND

Hereditary sensorineural hearing loss (SNHL) is a genetically heterogeneous disorder worldwide. Mutations in the GJB2 gene are a frequent cause of hereditary SNHL. There is a prevalence of certain mutations in various populations which suggests that specific mutations may be influenced by ethnic background.

OBJECTIVE

To analyze the prevalence of GJB2, GJB6 mutations in several geographic areas of Mexico in patients with hereditary SNHL.

MATERIALS AND METHODS

One hundred and forty Mexican unrelated propositi with prelingual SNHL were included in the study. All patients had three previous generations born in Mexico and belonged to no specific ethnic group. Analyses of the GJB2 and GJB6 genes and mt.1555A<G were performed in all subjects.

RESULTS

Twenty-three homozygous mutations, 57 heterozygous mutations, 1 double heterozygous (GJB2/GJB6) and 59 wild-type genotypes in the GJB2 gene were observed. Three patients had the homozygous c.del35 mutation whereas 26 patients were heterozygous for this gene defect. Only one patient with the GJB6 gene deletion was present (it includes the double heterozygous GJB2/GJB6). The mt.1555A>G mutation was not detected.

CONCLUSION

We found a great variety of mutations depending on the analyzed region in patients with SNHL; 57.86% of patients had affection in one or two alleles in GJB2 or GJB6 genes whereas 42.14% were wild-type. In some cases, allele distribution depended on region. Molecular studies of more genes involved in hereditary non-syndromic SNHL are required to completely confirm the molecular basis of hearing loss in Mexican population.

Human adult stem cells as the target cells for the initiation of carcinogenesis and for the generation of "cancer stem cells"

The inference to stem cells has been found in ancient myths and the concept of stem cells has existed in the fields of plant biology, developmental biology and embryology for decades. In the field of cancer research, the stem cell theory was one of the earliest hypotheses on the origin of a cancer from a single cell. However, an opposing hypothesis had it that an adult differentiated somatic cell could "de-differentiate" to become a cancer cell. Only within the last decade, via the "cloning" of Dolly, the sheep, did the field of stem cell biology really trigger an exciting revolution in biological research. The isolation of human embryonic stem cells has created a true revolution in the life sciences that has led to the hope that these human stem cells could lead to (a) basic science understanding of gene regulation during differentiation and development; (b) stem cell therapy; (c) gene therapy via stem cells; (d) the use of stem cells for drug discovery; (e) screening for toxic effects of chemicals; and (f) understand the aging and diseases of aging processes.

Possible roles of LI-Cadherin in the formation and maintenance of the intestinal epithelial barrier

LI-cadherin belongs to the so called 7D-cadherins, exceptional members of the cadherin superfamily which are characterized by seven extracellular cadherin repeats and a small cytosolic domain. Under physiological conditions LI-cadherin is expressed in the intestine and colon in human and mouse and in the rat also in hepatocytes. LI-cadherin was shown to act as a functional Ca²⁺-dependent adhesion molecule, linking neighboring cells and a lot of biophysical and biochemical parameters were determined in the last time. It is also known that dysregulated LI-cadherin expression can be found in a variety of diseases. Although there are several hypothesis and theoretical models concerning the function of LI-cadherin, the physiological role of LI-cadherin is still enigmatic.

Connexin43 siRNA promotes HUVEC proliferation and inhibits apoptosis induced by ox-LDL: an involvement of ERK signaling pathway

Oxidized low-density lipoprotein (ox-LDL), one of the most important risk factors of atherosclerosis, is a highly antigenic, potent chemoattractant that facilitates the development of atherosclerosis. Gap junctions also play an important in the development of atherosclerosis. In this study, we investigated the effects of ox-LDL on connexin43 and the mechanisms of connexin43 siRNA-inhibited apoptosis induced by ox-LDL in human umbilical vein endothelial cell (HUVEC), to clarify the role of connexin43 in atherosclerosis. Our results showed that ox-LDL significantly inhibited the growth and promoted apoptosis of HUVEC in a dose-dependent manner. Also, ox-LDL upregulated the expression of connexin43. Furthermore, knockdown connexin43 by siRNA promoted proliferation and inhibited apoptosis in ox-LDL-stimulated HUVEC. Moreover, the level of phosphor-ERK1/2 and connexin43 was remarkably attenuated by a ERK pathway inhibitor (PD98059). These results suggest that connexin43 siRNA promotes HUVEC proliferation and inhibits apoptosis induced by ox-LDL, and ERK signaling pathway appears to be involved in these processes.

Effects of vitamin D receptor knockout on cornea epithelium gap junctions

PURPOSE

Gap junctions are present in all corneal cell types and have been shown to have a critical role in cell phenotype determination. Vitamin D has been shown to influence cell differentiation, and recent work demonstrates the presence of vitamin D in the ocular anterior segment. This study measured and compared gap junction diffusion coefficients among different cornea epithelium phenotypes and in keratocytes using a noninvasive technique, fluorescence recovery after photobleaching (FRAP), and examined the influence of vitamin D receptor (VDR) knockout on epithelial gap junction communication in intact corneas. Previous gap junction studies in cornea epithelium and keratocytes were performed using cultured cells or ex vivo invasive techniques. These invasive techniques were unable to measure diffusion coefficients and likely were disruptive to normal cell physiology.

METHODS

Corneas from VDR knockout and control mice were stained with 5(6)-carboxyfluorescein diacetate (CFDA). Gap junction diffusion coefficients of the corneal epithelium phenotypes and of keratocytes, residing in intact corneas, were detected using FRAP.

RESULTS

Diffusion coefficients equaled 18.7, 9.8, 5.6, and 4.2 μm(2)/s for superficial squamous cells, middle wing cells, basal cells, and keratocytes, respectively. Corneal thickness, superficial cell size, and the superficial squamous cell diffusion coefficient of 10-week-old VDR knockout mice were significantly lower than those of control mice (P < 0.01). The superficial cell diffusion coefficient of heterozygous mice was significantly lower than control mice (P < 0.05).

CONCLUSIONS

Our results demonstrate differences in gap junction dye spread among the epithelial cell phenotypes, mirroring the epithelial developmental axis. The VDR knockout influences previously unreported cell-to-cell communication in superficial epithelium.

Connexins in colorectal cancer pathogenesis

The connexins constitute a family of integral membrane proteins that form channels between adjacent cells. These channels are assembled in plasma membrane domains known as gap junctions and enable cells to directly exchange ions and small molecules. Intercellular communication via gap junctions plays important roles in regulating cell growth and differentiation and in maintaining tissue homeostasis. This type of cell communication is often impaired during cancer development, and several members of the connexin protein family have been shown to act as tumor suppressors. Emerging evidence suggests that the connexin protein family has important roles in colorectal cancer development. In the normal colonic epithelial tissue, three connexin isoforms, connexin 26 (Cx26), Cx32 and Cx43, have been shown to be expressed at the protein level. Colorectal cancer development is associated with loss of connexin expression or relocalization of connexins from the plasma membrane to intracellular compartments. Downregulation of connexins in colorectal carcinomas at the transcriptional level involves cancer-specific promoter hypermethylation. Recent studies suggest that Cx43 may constrain growth of colon cancer cells by interfering with the Wnt/β-catenin pathway. There is also increasing evidence that the connexins may have potential as prognostic markers in colorectal cancer. This review discusses the role of connexins in colorectal cancer pathogenesis, as well as their potential as prognostic markers and targets in the prevention and treatment of the disease.

Regulation of cellular communication by signaling microdomains in the blood vessel wall

It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.

Molecular dynamics simulations highlight structural and functional alterations in deafness-related M34T mutation of connexin 26

Mutations of the GJB2 gene encoding the connexin 26 (Cx26) gap junction protein, which is widely expressed in the inner ear, are the primary cause of hereditary non-syndromic hearing loss in several populations. The deafness–associated single amino acid substitution of methionine 34 (M34) in the first transmembrane helix (TM1) with a threonine (T) ensues in the production of mutant Cx26M34T channels that are correctly synthesized and assembled in the plasma membrane. However, mutant channels overexpressed in HeLa cells retain only 11% of the wild type unitary conductance. Here we extend and rationalize those findings by comparing wild type Cx26 (Cx26WT) and Cx26M34T mutant channels in silico, using molecular dynamics simulations. Our results indicate that the quaternary structure of the Cx26M34T hemichannel is altered at the level of the pore funnel due to the disruption of the hydrophobic interaction between M34 and tryptophan 3 (W3) in the N–terminal helix (NTH). Our simulations also show that external force stimuli applied to the NTHs can detach them from the inner wall of the pore more readily in the mutant than in the wild type hemichannel. These structural alterations significantly increase the free energy barrier encountered by permeating ions, correspondingly decreasing the unitary conductance of the Cx26M34T hemichannel. Our results accord with the proposal that the mutant resides most of the time in a low conductance state. However, the small displacement of the NTHs in our Cx26M34T hemichannel model is not compatible with the formation of a pore plug as in the related Cx26M34A mutant.

CIP75 (connexin43-interacting protein of 75 kDa) mediates the endoplasmic reticulum dislocation of connexin43

The proteasomal degradation of the gap junction protein connexin43 is facilitated by its interaction with the connexin43-interacting protein of 75 kDa at the endoplasmic reticulum membrane.

Connexins: mechanisms regulating protein levels and intercellular communication

Intercellular communication can occur through gap junction channels, which are comprised of connexin proteins. Therefore, levels of connexins can directly correlate with gap junctional intercellular communication. Because gap junctions have a critical role in maintaining cellular homeostasis, the regulation of connexin protein levels is important. In the connexin life cycle, connexin protein levels can be modified through differential gene transcription or altered through trafficking and degradation mechanisms. More recently, significant attention has been directed to the pathways that cells utilize to increase or decrease connexin levels and thus indirectly, gap junctional communication. Here, we review the studies revealing the mechanisms that affect connexin protein levels and gap junctional intercellular communication.

Impact of 7,12-dimethylbenz[a]anthracene exposure on connexin gap junction proteins in cultured rat ovaries

7,12-Dimethylbenz[a]anthracene (DMBA) destroys ovarian follicles in a concentration-dependent manner. The impact of DMBA on connexin (CX) proteins that mediate communication between follicular cell types along with pro-apoptotic factors p53 and Bax were investigated. Postnatal day (PND) 4 Fisher 344 rat ovaries were cultured for 4days in vehicle medium (1% DMSO) followed by a single exposure to vehicle control (1% DMSO) or DMBA (12.5nM or 75nM) and cultured for 4 or 8days. RT-PCR was performed to quantify Cx37, Cx43, p53 and Bax mRNA level. Western blotting and immunofluorescence staining were performed to determine CX37 or CX43 level and/or localization. Cx37 mRNA and protein increased (P<0.05) at 4days of 12.5 nM DMBA exposure. Relative to vehicle control-treated ovaries, mRNA encoding Cx43 decreased (P<0.05) but CX43 protein increased (P<0.05) at 4days by both DMBA exposures. mRNA expression of pro-apoptotic p53 was decreased (P<0.05) but no changes in Bax expression were observed after 4days of DMBA exposures. In contrast, after 8days, DMBA decreased Cx37 and Cx43 mRNA and protein but increased both p53 and Bax mRNA levels. CX43 protein was located between granulosa cells, while CX37 was located at the oocyte cell surface of all follicle stages. These findings support that DMBA exposure impacts ovarian Cx37 and Cx43 mRNA and protein prior to both observed changes in pro-apoptotic p53 and Bax and follicle loss. It is possible that such interference in follicular cell communication is detrimental to follicle viability, and may play a role in DMBA-induced follicular atresia.

Interplay of mechanotransduction, FOXC2, connexins, and calcineurin signaling in lymphatic valve formation

The directional flow of lymph is maintained by hundreds of intraluminal lymphatic valves. Lymphatic valves are crucial to prevent lymphedema, accumulation of fluid in the tissues, and to ensure immune surveillance; yet, the mechanisms of valve formation are only beginning to be elucidated. In this chapter, we will discuss the main steps of lymphatic valve morphogenesis, the important role of mechanotransduction in this process, and the genetic program regulated by the transcription factor Foxc2, which is indispensable for all steps of valve development. Failure to form mature collecting lymphatic vessels and valves causes the majority of postsurgical lymphedema, e.g., in breast cancer patients. Therefore, this knowledge will be useful for diagnostics and development of better treatments of secondary lymphedema.