Connexin expression in mouse lung tumor

Multi-omics analysis of expression profile and prognostic values of connexin family in LUAD

PURPOSE

Our study first explored the expression differences and prognostic significance of Cx genes in pan-cancer and then focused on LUAD. Our objectives were to conducted a comprehensive analysis of the expression profile, prognostic significance, genetic alterations, potential biological functions and drug sensitivity of the Connexin gene family in LUAD.

METHODS

We developed a comprehensive prognostic model for LUAD by combining risk scores with clinical features and created a nomogram to predict 1-, 3-, and 5-year overall survival. Using single-cell sequencing, we examined the expression and biological functions of the identified prognostic markers.

RESULTS

Our risk model revealed that GJB2-5 play a critical role in the prognosis of LUAD patients, associated with many biological processes such as cell cycle, DNA damage, EMT, hypoxia, invasion, and metastasis. Furthermore, the connexin gene family is linked to transcriptional mechanisms such as the extracellular matrix (ECM), migration, mobility, angiogenesis, and the epithelial-mesenchymal transition (EMT) genetic program.

CONCLUSION

The risk model can be used as a potential prognostic factor for LUAD patients and may provide new insights into cancer treatment from perspective of the expression of Cx genes.

Connexins in Lung Cancer and Brain Metastasis

Connexins (Cxs) are involved in the brain metastasis of lung cancer cells. Thus, it is necessary to determine whether gap junction-forming Cxs are involved in the communication between lung cancer cells and the host cells, such as endothelial cells, forming the brain–blood-barrier, and cells in the central nervous system. Data from multiple studies support that Cxs function as tumor suppressors during lung cancer occurrence. However, recent evidence suggests that during metastasis to the brain, cancer cells establish communication with the host. This review discusses junctional or non-junctional hemichannel studies in lung cancer development and brain metastasis, highlighting important unanswered questions and controversies.

A novel role of Cx43-composed GJIC in PDT phototoxicity: an implication of Cx43 for the enhancement of PDT efficacy

In spite of initially promising responses, 5-year recurrence after photodynamic therapy (PDT) sustains high level and an increase in PDT effectiveness is needed. It has been demonstrated that gap junctional intercellular communication (GJIC) formed by Connexin (Cx)43 could improve the transfer of "death signal" between cells, thereby causing the enhancement of cytotoxicity of chemotherapeutics and suicide gene therapy. Nevertheless, whether Cx43-composed GJIC has an effect on PDT phototoxicity remains unknown. This study showed that Cx43-formed GJIC could improve PDT phototoxicity to tumor cells in vitro and in vivo. Specifically, Cx43-formed GJIC under the condition of high cellular density could improve PDT phototoxicity in Cx43-transfected HeLa cells and Cx43-expressing U87 glioma cells. This effect was remarkably inhibited when Cx43 was not expressed or Cx43-formed GJ channels were prohibited. Additionally, the presence of Cx43-mediated GJIC could decrease the mean RTV and tumor weights of xenografts after Photofrin-PDT. The improved PDT efficacy by Cx43-composed GJIC was correlated with stress signaling pathways mediated by ROS, calcium and lipid peroxide. The present study demonstrates the presence of Cx43-composed GJIC improves PDT phototoxicity and suggests that therapeutic strategies designed to upregulate the expression of Cx43 or enhance Cx43-mediated GJIC function may increase the sensitivity of malignant cell to PDT, leading to the increment of PDT efficacy. Oppositely, factors that retard Cx43 expression or prohibit the function of Cx43-mediated GJIC may cause insensitivity of malignant cells to PDT, leading to PDT resistance.

Connexin subtype expression during oral carcinogenesis: A pilot study in patients with oral squamous cell carcinoma

Gap junctional intercellular communication (GJIC) and connexin (Cx) expression were reported in association with carcinogenesis in various types of tumours. In an earlier histomorphometric study, the protein levels of Cx subtypes 26, 43 and 45 were differentially expressed in oral squamous cell carcinoma (OSCC), corresponding lymph node metastases and dysplasia-free oral mucosa. Moreover, membrane Cx43 acted as an independent prognostic marker in OSCC tissues. This study aimed to confirm the expression of described Cx subtypes at the mRNA level. Hence, a reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis of Cx26, Cx43 and Cx45 gene expressions was performed in paired carcinoma and mucosa samples of 15 OSCC patients. Additionally, we assessed the interaction between Cx subtype expression and clinicopathological routine parameters. The RT-qPCR analysis revealed that Cx26 was downregulated in OSCC (P=0.01), while Cx43 was marginally upregulated in cancer tissue (P=0.04). Cx45 was significantly overexpressed in OSCC tissue compared with the intraoral mucosa controls (P<0.01), and remained unchanged at different tumour stages. No significant interactions between differential Cx subtype expression and clinicopathological routine parameters were observed. In conclusion, Cx regulation at the transcriptional level appears to be an early event during the initiation and development of OSCC, and is maintained during further progression. However, the mRNA-protein correlation is variable. This may be indicative of post-transcriptional, translational and degradation regulations being associated with the determination of Cx protein concentration during oral carcinogenesis.

The lung communication network

The different types of cells in the lung, from the conducting airway epithelium to the alveolar epithelium and the pulmonary vasculature, are interconnected by gap junctions. The specific profile of gap junction proteins, the connexins, expressed in these different cell types forms compartments of intercellular communication that can be further shaped by the release of extracellular nucleotides via pannexin1 channels. In this review, we focus on the physiology of connexins and pannexins and describe how this lung communication network modulates lung function and host defenses in conductive and respiratory airways.

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.

Connexin32 inhibits gastric carcinogenesis through cell cycle arrest and altered expression of p21Cip1 and p27Kip1

Gap junctions and their structural proteins, connexins (Cxs), have been implicated in carcinogenesis. To explore the involvement of Cx32 in gastric carcinogenesis, immunochemical analysis of Cx32 and proliferation marker Ki67 using tissue-microarrayed human gastric cancer and normal tissues was performed. In addition, after Cx32 overexpression in the human gastric cancer cell line AGS, cell proliferation, cell cycle analyses, and p21(Cip1) and p27(Kip1) expression levels were examined by bromodeoxyuridine assay, flow cytometry, real-time RT-PCR, and western blotting. Immunohistochemical study noted a strong inverse correlation between Cx32 and Ki67 expression pattern as well as their location. In vitro, overexpression of Cx32 in AGS cells inhibited cell proliferation significantly. G1 arrest, up-regulation of cell cycle-regulatory proteins p21(Cip1) and p27(Kip1) was also found at both mRNA and protein levels. Taken together, Cx32 plays some roles in gastric cancer development by inhibiting gastric cancer cell proliferation through cell cycle arrest and cell cycle regulatory proteins.

Higher susceptibility of spontaneous and NNK-induced lung neoplasms in connexin 43 deficient CD1 × AJ F1 mice: paradoxical expression of connexin 43 during lung carcinogenesis

Connexins (Cxs) are proteins that form the communicating gap junctions, and reportedly have a role in carcinogenesis. Here, we evaluated the importance of Connexin43 (Cx43) in spontaneous and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung carcinogenesis. Male wild-type (Cx43(+/+) ) and hemizygote (Cx43(+/-) ) CD1 × AJ F1 mice were injected with NNK or saline. After 60 weeks mice were euthanized; lung nodules were counted, measured, and fixed in formalin or snap frozen. Immunohistochemistry for Cx43 and Beta-catenin (β-catenin) was performed and Cx43 mRNA expression was evaluated by real-time PCR. Cx43 deletion significantly increased the incidence and number of spontaneous nodules in the CD1 × AJ F1 mice and the number of gross lesions and the aggressiveness of lesions in NNK-treated mice. Cx43 mRNA increased significantly and was correlated with the aggressiveness of tumors, although lesions from Cx43(+/-) mice expressed less Cx43 RNAm than their counterparts. Lung parenchyma presented a Cx43 immunostaining pattern with points or plaques between cells. In hyperplasias and adenomas, Cx43 was found in the membrane and in cytoplasm. Malignant lesions presented increased Cx43 in cytoplasm and a few membrane spots of immunostaining. β-catenin was weakly expressed in lung parenchyma. Though hyperplasias presented some cells with nuclear β-catenin, NNK-induced tumors contained a higher number of this staining pattern. Also, no difference in β-catenin occurred between both genotypes independently of the histological grade. In summary, our results indicate that Cx43 acts as a tumor suppressor gene in early lung tumorigenesis and loses this property in advanced carcinogenesis. Therefore, Cxs are better classified as conditional tumor suppressors.

Connexins as therapeutic targets in lung disease

INTRODUCTION

The lung is a mechanically active system exposed to the external environment and is particularly sensitive to injury and inflammation. Studies have identified intercellular communication pathways that promote proper lung function in response to injury and disease. These pathways involve connexins (Cxs) and gap junctional intercellular communication (GJIC).

AREAS COVERED IN THIS REVIEW

The functional expression of Cxs in airway epithelium and vasculature, under normal and pathological conditions, is reviewed. Inhibition of GJIC and/or silencing of Cxs have been shown to modulate the course of disease development. Cx-based channels: i) coordinate ciliary beating and fluid transport to promote clearance of particulates, ii) regulate secretion of pulmonary surfactant, in response to deep inhalation by interconnecting type I and type II alveolar epithelial cells, and iii) are key mediators of pro- and anti-inflammatory signalling by the pulmonary endothelium, in order to modulate leukocyte recruitment from the circulation.

EXPERT OPINION

Cx-based channels play several central roles in promoting a regulated inflammatory response and facilitating lung repair, thus enabling the pulmonary epithelium and vasculature to behave as integrated systems. Several pathologies can disrupt the normal communication pathways required for proper lung function, including acute lung injury, asthma, cystic fibrosis, pulmonary fibrosis and cancer.

Altered expression and localization of connexin32 in human and murine gastric carcinogenesis

BACKGROUND

Intercellular communication via gap junctions, composed of protein subunits called connexins (Cxs), plays a key role in controlling cell growth, differentiation and carcinogenesis. Impaired gap junctional intercellular communication has been reported in various cancers and diseases.

AIMS

We investigated Cx32 expression patterns and semiquantitatively assessed Cx32 expression in cancers and preneoplastic lesions. To determine if cell proliferation is correlated with Cx32 expression, we evaluated Ki67 expression in a gastric cancer mouse model.

METHODS

In human and mouse, normal stomach and gastric adenocarcinoma tissues were used for immunohistochemical analyses.

RESULTS

Cx32 was detected at cell-cell (intercellular) contact points in normal cells and exhibited punctate intercellular and intracytoplasmic staining in cancer cells. The frequency of Cx32 loss of expression was significantly higher in human adenocarcinomas than in normal stomach. As tumor cells were less differentiated, Cx32 expression levels and intercellular and intracytoplasmic staining were also significantly lower. The Cx32 expression pattern in the mouse gastric cancer model was similar in several important respects to that of human. In mucous metaplasia of the mouse stomach, Cx32 was mainly expressed in the cytoplasm of epithelial cells. There was also an inverse correlation between Cx32 expression and cell proliferation in mouse tumors. However, there was no difference in the levels of Cx32 mRNA between normal and cancerous tissues.

CONCLUSIONS

These findings suggest that altered Cx32 expression, a loss of intercellular Cx32 and a gain of intracytoplasmic Cx32 in the form of punctate "dot", plays an important role in the formation of gastric adenocarcinomas.

Inhibition of gap junctional Intercellular communication in WB-F344 rat liver epithelial cells by triphenyltin chloride through MAPK and PI3-kinase pathways

Background

Organotin compounds (OTCs) have been widely used as stabilizers in the production of plastic, agricultural pesticides, antifoulant plaints and wood preservation. The toxicity of triphenyltin (TPT) compounds was known for their embryotoxic, neurotoxic, genotoxic and immunotoxic effects in mammals. The carcinogenicity of TPT was not well understood and few studies had discussed the effects of OTCs on gap junctional intercellular communication (GJIC) of cells.

Method

In the present study, the effects of triphenyltin chloride (TPTC) on GJIC in WB-F344 rat liver epithelial cells were evaluated, using the scrape-loading dye transfer technique.

Results

TPTC inhibited GJIC after a 30-min exposure in a concentration- and time-dependent manner. Pre-incubation of cells with the protein kinase C (PKC) inhibitor did not modify the response, but the specific MEK 1 inhibitor PD98059 and PI3K inhibitor LY294002 decreased substantially the inhibition of GJIC by TPTC. After WB-F344 cells were exposed to TPTC, phosphorylation of Cx43 increased as seen in Western blot analysis.

Conclusions

These results show that TPTC inhibits GJIC in WB-F344 rat liver epithelial cells by altering the Cx43 protein expression through both MAPK and PI3-kinase pathways.

Cisplatin and oxaliplatin inhibit gap junctional communication by direct action and by reduction of connexin expression, thereby counteracting cytotoxic efficacy

Cisplatin [cis-diamminedichloroplatinum(II)]/oxaliplatin [1,2-diamminocyclohexane(trans-1)oxolatoplatinum(II)] toxicity is enhanced by functional gap junctions between treated cells, implying that inhibition of gap junctions may decrease cytotoxic activity of these platinum-based agents. This study investigates the effect of gap junction modulation by cisplatin/oxaliplatin on cytotoxicity in a transformed cell line. The effects were explored using junctional channels expressed in transfected HeLa cells and purified hemichannels. Junctional channels showed a rapid, dose-dependent decrease in dye coupling with exposure to cisplatin/oxaliplatin. With longer exposure, both compounds also decreased connexin expression. Both compounds inhibit the activity of purified connexin hemichannels, over the same concentration range that they inhibit junctional dye permeability, demonstrating that inhibition occurs by direct interaction of the drugs with connexin protein. Cisplatin/oxaliplatin reduced the clonogenic survival of HeLa cells at low density and high density in a dose-dependent manner, but to a greater degree at high density, consistent with a positive effect of gap junctional intercellular communication (GJIC) on cytotoxicity. Reduction of GJIC by genetic or pharmacological means decreased cisplatin/oxaliplatin toxicity. At low cisplatin/oxaliplatin concentrations, where effects on connexin channels are minimal, the toxicity increased with increased cell density. However, higher concentrations strongly inhibited GJIC, and this counteracted the enhancing effect of greater cell density on toxicity. The present results indicate that inhibition of GJIC by cisplatin/oxaliplatin decreases their cytotoxicity. Direct inhibition of GJIC and reduction of connexin expression by cisplatin/oxaliplatin may thereby compromise the effectiveness of these compounds and be a factor in the development of resistance to this class of chemotherapeutic agents.

Cancer genomics identifies regulatory gene networks associated with the transition from dysplasia to advanced lung adenocarcinomas induced by c-Raf-1

BACKGROUND

Lung cancer is a leading cause of cancer morbidity. To improve an understanding of molecular causes of disease a transgenic mouse model was investigated where targeted expression of the serine threonine kinase c-Raf to respiratory epithelium induced initially dysplasia and subsequently adenocarcinomas. This enables dissection of genetic events associated with precancerous and cancerous lesions.

METHODOLOGY/PRINCIPAL FINDINGS

By laser microdissection cancer cell populations were harvested and subjected to whole genome expression analyses. Overall 473 and 541 genes were significantly regulated, when cancer versus transgenic and non-transgenic cells were compared, giving rise to three distinct and one common regulatory gene network. At advanced stages of tumor growth predominately repression of gene expression was observed, but genes previously shown to be up-regulated in dysplasia were also up-regulated in solid tumors. Regulation of developmental programs as well as epithelial mesenchymal and mesenchymal endothelial transition was a hall mark of adenocarcinomas. Additionally, genes coding for cell adhesion, i.e. the integrins and the tight and gap junction proteins were repressed, whereas ligands for receptor tyrosine kinase such as epi- and amphiregulin were up-regulated. Notably, Vegfr- 2 and its ligand Vegfd, as well as Notch and Wnt signalling cascades were regulated as were glycosylases that influence cellular recognition. Other regulated signalling molecules included guanine exchange factors that play a role in an activation of the MAP kinases while several tumor suppressors i.e. Mcc, Hey1, Fat3, Armcx1 and Reck were significantly repressed. Finally, probable molecular switches forcing dysplastic cells into malignantly transformed cells could be identified.

CONCLUSIONS/SIGNIFICANCE

This study provides insight into molecular pertubations allowing dysplasia to progress further to adenocarcinoma induced by exaggerted c-Raf kinase activity.

Exogenous Cx43 expression decrease cell proliferation rate in rat hepatocarcinoma cells independently of functional gap junction

BACKGROUND

Gap junction intercellular communication (GJIC) is considered to play a role in the regulation of homeostasis because it regulates important processes, such as cell proliferation and cell differentiation. A reduced or lost GJIC capacity has been observed in solid tumors and studies have demonstrated that GJIC restoration in tumor cells contribute to reversion of the transformed phenotype. This observation supports the idea that restoration of the functional channel is essential in this process. However, in the last years, reports have proposed that just the increase in the expression of specific connexins can contribute to reversion of the malign phenotype in some tumor cells. In the present work, we studied the effects of exogenous Connexin 43 (Cx43) expression on the proliferative behavior and phenotype of rat hepatocarcinoma cells.

RESULTS

The exogenous Cx43 did not increase GJIC capacity of transfected cells, but it was critical to decrease the cell proliferation rate as well as reorganization of the actin filaments and cell flattening. We also observed more adhesion capacity to substrate after Cx43 transfection.

CONCLUSION

Cx43 expression leads to a decrease of the growth of the rat hepatocellular carcinoma cells and it contributes to the reversion of the transformed phenotype. These effects were independent of the GJIC and were probably associated with the phosphorylation pattern changes and redistribution of the Cx43 protein.

The remodeling of connexin in the hypertrophied right ventricular in pulmonary arterial hypertension and the effect of a dual ET receptor antagonist (bosentan)

Studies on the role of connexins (Cxs) in the pathogenesis of right ventricular (RV) hypertrophy in pulmonary arterial hypertension (PAH) have not been reported to date. Therefore, we established a rat model of PAH induced by monocrotaline (MCT), and they were randomized to three groups: Control, MCT, and MCT+bosentan. Through electromicroscopy, in the control group, the gap junctions were long and frequent in intercalated disks, and short and rare at the sites of side-side cell junctions. In the MCT group, the opposite distribution was detected. In the MCT+bosentan group, the distribution of gap junctions was similar to that in the control group. Using immunoconfocal microscopy, most of the Cx43 staining was aggregated at the cell termini, and staining was weak at the sites of side-side cell junctions in the control group. However, the distribution of Cx43 was opposite in the MCT group. In the MCT+bosentan group, the result was similar to that in the control group. Therefore, perturbation of connexin distribution may be associated with RV hypertrophy. Improving the distribution of Cx43 in RV myocardium may be one of the mechanisms of a dual ET receptor antagonist partly reversing the RV hypertrophy.

Connexin-43 upregulation in micrometastases and tumor vasculature and its role in tumor cell attachment to pulmonary endothelium

BACKGROUND

The modulation of gap junctional communication between tumor cells and between tumor and vascular endothelial cells during tumorigenesis and metastasis is complex. The notion of a role for loss of gap junctional intercellular communication in tumorigenesis and metastasis has been controversial. While some of the stages of tumorigenesis and metastasis, such as uncontrolled cell division and cellular detachment, would necessitate the loss of intercellular junctions, other stages, such as intravasation, endothelial attachment, and vascularization, likely require increased cell-cell contact. We hypothesized that, in this multi-stage scheme, connexin-43 is centrally involved as a cell adhesion molecule mediating metastatic tumor attachment to the pulmonary endothelium.

METHODS

Tumor cell attachment to pulmonary vasculature, tumor growth, and connexin-43 expression was studied in metastatic lung tumor sections obtained after tail-vein injection into nude mice of syngeneic breast cancer cell lines, overexpressing wild type connexin-43 or dominant-negatively mutated connexin-43 proteins. High-resolution immunofluorescence microscopy and Western blot analysis was performed using a connexin-43 monoclonal antibody. Calcein Orange Red AM dye transfer by fluorescence imaging was used to evaluate the gap junction function.

RESULTS

Adhesion of breast cancer cells to the pulmonary endothelium increased with cancer cells overexpressing connexin-43 and markedly decreased with cells expressing dominant-negative connexin-43. Upregulation of connexin-43 was observed in tumor cell-endothelial cell contact areas in vitro and in vivo, and in areas of intratumor blood vessels and in micrometastatic foci.

CONCLUSION

Connexin-43 facilitates metastatic 'homing' by increasing adhesion of cancer cells to the lung endothelial cells. The marked upregulation of connexin-43 in tumor cell-endothelial cell contact areas, whether in preexisting 'homing' vessels or in newly formed tumor vessels, suggests that connexin-43 can serve as a potential marker of micrometastases and tumor vasculature and that it may play a role in the early incorporation of endothelial cells into small tumors as seeds for vasculogenesis.

Connexin 43 expression promotes malignancy of HuH7 hepatocellular carcinoma cells via the inhibition of cell-cell communication

In normal liver, Connexin (Cx) 43 is not detected, but up-regulated in some liver cancers. We herein investigated the role of Cx43 in hepatoma cell carcinogenesis. Cx43-silenced HuH7 cells using shRNA showed lower growth and higher differentiation, and Cx43-overexpressing cells exhibited rapid growth and low differentiation. Unexpectedly, gap junctional intercellular communication (GJIC) was inversely correlated with Cx43 levels. Furthermore, the expression level and promoter activity of Cx32 was negatively regulated by the expression of Cx43. From these data, Cx43 expression may be in part responsible for the malignancy of hepatoma cells through a decrease in GJIC composed of Cx32.