Pattern of cell-to-cell transfer of microRNA by gap junction and its effect on the proliferation of glioma cells

Role of miR-93-5p and Its Opposing Effect of Ionizing Radiation in Non-Small Cell Lung Cancer

Background

Radiation therapy is an effective local therapy for lung cancer. However, the interaction between genes and radiotherapy is multifaceted and intricate. Therefore, we explored the role of miR-93-5p in the proliferation, apoptosis, and migration abilities of A549 cells. Simultaneously, we also investigated the interactions between miR-93-5p and ionizing radiation (IR).

Methods

Cell Counting Kit-8, transwell, and apoptotic assay were performed to measure the proliferation, migration, and apoptosis abilities. The expression levels of miR-93-5p and its target gene in lung cancer were predicted using starBase v3.0. Then, data were validated using qPCR and western blot.

Results

miR-93-5p significantly promoted the proliferation (P < 0.01) and migration abilities (P < 0.001) of A549 cells. Gasdermin E (GSDME) was identified to be a putative target of miR-93-5p and had a negative correlation with miR-93-5p (P < 0.001). Overexpression of miR-93-5p significantly decreased GSDME in A549 (P < 0.001). Interestingly, miR-93-5p decreased cell proliferation (P < 0.01) and cell migration (P < 0.01) and increased apoptosis (P < 0.01) in A549 cells after exposure to IR.

Conclusions

miR-93-5p is presumed to play an oncogenic role in lung cancer by enhancing A549 cell proliferation and migration. It can enhance the sensitivity of radiotherapy under IR conditions. We speculate that the miR-93-5p/GSDME pathway was inhibited, activating the GSDME-related pyroptosis pathway when the cells were exposed to IR. Therefore, miR-93-5p can overcome resistance to radiotherapy and improve the efficacy of radiotherapy.

MiR-23b-3p Improves Brain Damage after Status Epilepticus by Reducing the Formation of Pathological High-Frequency Oscillations via Inhibition of cx43 in Rat Hippocampus

In order to investigate the effectiveness and safety of miR-23b-3p in anti-seizure activity and to elucidate the regulatory relationship between miR-23b-3p and Cx43 in the nervous system, we have established a lithium chloride-pilocarpine (PILO) status epilepticus (SE) model. Rats were randomly divided into the following groups: seizure control (PILO), valproate sodium (VPA+PILO), recombinant miR-23b-3p overexpression (miR+PILO), miR-23b-3p sponges (Sponges+PILO), and scramble sequence negative control (Scramble+PILO) (n = 6/group). After experiments, we got the following results. In the acute phase, the time required for rats to reach stage IV after PILO injection was significantly longer in VPA+PILO and miR+PILO. In the chronic phase after SE, the frequency of spontaneous recurrent seizures (SRSs) in VPA+PILO and miR+PILO was significantly reduced. At 10 min before seizure cessation, the average energy expression of fast ripples (FRs) in VPA+PILO and miR+PILO was significantly lower than in PILO. After 28 days of seizure, Cx43 expression in PILO was significantly increased, and Beclin1expression in all groups was significantly increased. After 28 days of SE,the number of synapses in the CA1 region of the hippocampus was significantly higher in the VPA+PILO and miR+PILO groups compared to that in the PILO group. After 28 days of SE ,hippocampal necrotic cells in the CA3 region were significantly lower in the VPA+PILO and miR+PILO groups compared to those in the PILO group. There were no significant differences in biochemical indicators among the experimental group rats 28 days after SE compared to the seizure control group. Based on the previous facts, we can reach the conclusion that MiR-23b-3p targets and blocks the expression of hippocampal Cx43 which can reduce the formation of pathological FRs, thereby alleviating the severity of seizures, improving seizure-induced brain damage.

Expression profile and gap-junctional transfer of microRNAs in the bovine cumulus-oocyte complex

MicroRNAs (miRNA) are important regulators of oocyte maturation, playing a key role in modulating gene expression both in a temporal- and spatial-specific manner. These small non-coding RNAs are involved in important processes during oocyte maturation, acting as messengers between the oocyte and its surrounding cumulus cells. Despite its significance, the bidirectional communication mechanism is still unknown. To test miRNA communication between oocyte and surrounding cumulus cells through the gap junctions the gap junctions were either blocked with carbenoxolone or not. MiRNA sequencing of oocytes at 1, 6, and 22 h of in vitro maturation was then performed. Among the differentially expressed miRNAs, bta-miR-21-5p, a regulator of cumulus cell viability and oocyte maturation, was the only previously known miRNA. Furthermore, by labeling a bta-miR-21-5p mimic with FAM, crossing of this miRNA through the gap junctions within the cumulus-oocyte complex could be visualized and internalization in the oocyte was confirmed by RT-qPCR. In conclusion, this study provides, for the first time, evidence that miRNA communication within the bovine cumulus-oocyte complex is enabled through the gap junctional network.

MicroRNAs mediated interaction of tumor microenvironment cells with breast cancer cells during bone metastasis

Breast cancer (BC) bone metastasis is primarily osteolytic and has limited therapeutic options. Metastasized BC cells prime the secondary environment in bone by forming a tumor niche, which favors their homing and colonization. The tumor microenvironment (TME) is primarily generated by the cancer cells. Bone TME is an intricate network of multiple cells, including altered bone, tumor, stromal, and immune cells. Recent findings highlight the significance of small non-coding microRNAs (miRNAs) in influencing TME during tumor metastasis. MiRNAs from TME-resident cells facilitate the interaction between the tumor and its microenvironment, thereby regulating the biological processes of tumors. These miRNAs can serve as oncogenes or tumor suppressors. Hence, both miRNA inhibitors and mimics are extensively utilized in pre-clinical trials for modulating the phenotypes of tumor cells and associated stromal cells. This review briefly summarizes the recent developments on the functional role of miRNAs secreted directly or indirectly from the TME-resident cells in facilitating tumor growth, progression, and metastasis. This information would be beneficial in developing novel targeted therapies for BC.

Modulation of the Cellular microRNA Landscape: Contribution to the Protective Effects of High-Density Lipoproteins (HDL)

High-density lipoproteins (HDL) play an established role in protecting against cellular dysfunction in a variety of different disease contexts; however, harnessing this therapeutic potential has proved challenging due to the heterogeneous and relative instability of this lipoprotein and its variable cargo molecules. The purpose of this study is to examine the contribution of microRNA (miRNA; miR) sequences, either delivered directly or modulated endogenously, to these protective functions. This narrative review introduces the complex cargo carried by HDL, the protective functions associated with this lipoprotein, and the factors governing biogenesis, export and the uptake of microRNA. The possible mechanisms by which HDL can modulate the cellular miRNA landscape are considered, and the impact of key sequences modified by HDL is explored in diseases such as inflammation and immunity, wound healing, angiogenesis, dyslipidaemia, atherosclerosis and coronary heart disease, potentially offering new routes for therapeutic intervention.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Downregulation of connexin 43-based gap junctions underlies propofol-induced excessive relaxation in hypertensive vascular smooth muscle cells

BACKGROUND

Postinduction hypotension caused by propofol remains a non-negligible problem for anesthesiologists, and is especially severe in chronic hypertensive patients with long-term vasoconstriction and decreased vascular elasticity. The functional change in gap junctions composed of Cx43 (Cx43-GJs) is reported as the biological basis of synchronized contraction or relaxation of blood vessels. Thus, we investigated the role of Cx43-GJs in propofol-induced dramatic blood pressure fluctuations in chronic hypertensive patients, and their internal mechanisms.

METHODS

Human umbilical artery smooth muscle cells (HUASMCs) were pretreated with long-term angiotensin II (Ang II), with or without propofol, to simulate the contraction and relaxation of normal and hypertensive VSMCs during anesthesia induction. The levels of F-actin polymerization and MLC2 phosphorylation were used as indicators to observe the contraction and relaxation of HUASMCs. Different specific activators, inhibitors and siRNAs were used to explore the role of Cx43-GJs and Ca²⁺ as well as the RhoA/ LIMK2/cofilin and RhoA/MLCK signaling pathways in the contraction and relaxation of normal and hypertensive HUASMCs.

RESULTS

Both F-actin polymerization and MLC2 phosphorylation were significantly enhanced in Ang II-pretreated HUASMCs, along with higher expression of Cx43 protein and stronger function of Cx43-GJs than in normal HUASMCs. However, with propofol administration, similar to Gap26 and Cx43-siRNA, the function of Cx43-GJs in Ang II-pretreated HUASMCs was inhibited compared with that in normal HUASMCs, accompanied by a larger decrease in intracellular Ca²⁺ and the RhoA/LIMK2/cofilin and RhoA/MLCK signaling pathways. Eventually F-actin polymerization and MLC2 phosphorylation were more dramatically decreased. However, these effects could be reversed by RA with enhanced Cx43-GJ function.

CONCLUSION

Long-term exposure to Ang II significantly enhanced the expression of the Cx43 protein and function of Cx43-GJs in HUASMCs, resulting in the accumulation of intracellular Ca²⁺ and the activation of its downstream RhoA/LIMK2/cofilin and RhoA/MLCK signaling pathways, which maintained HUASMCs in a state of excessive-contraction. With inhibition of Cx43-GJs by propofol in Ang II-pretreated HUASMCs, intracellular Ca²⁺ and its downstream signaling pathways were dramatically inhibited, which ultimately excessively relaxed HUASMCs. This is the reason why the blood pressure fluctuation of patients with chronic hypertension was more severe after receiving propofol induction. Video Abstract.

The Multifaceted Role of Connexins in Tumor Microenvironment Initiation and Maintenance

Today's research on the processes of carcinogenesis and the vital activity of tumor tissues implies more attention be paid to constituents of the tumor microenvironment and their interactions. These interactions between cells in the tumor microenvironment can be mediated via different types of protein junctions. Connexins are one of the major contributors to intercellular communication. They form the gap junctions responsible for the transfer of ions, metabolites, peptides, miRNA, etc., between neighboring tumor cells as well as between tumor and stromal cells. Connexin hemichannels mediate purinergic signaling and bidirectional molecular transport with the extracellular environment. Additionally, connexins have been reported to localize in tumor-derived exosomes and facilitate the release of their cargo. A large body of evidence implies that the role of connexins in cancer is multifaceted. The pro- or anti-tumorigenic properties of connexins are determined by their abundance, localization, and functionality as well as their channel assembly and non-channel functions. In this review, we have summarized the data on the contribution of connexins to the formation of the tumor microenvironment and to cancer initiation and progression.

PDGF-AA promotes gap junction intercellular communication in chondrocytes via the PI3K/Akt pathway

BACKGROUND

Gap junction intercellular communication (GJIC) plays an important role in cell growth, development and homeostasis. Connexin 43 (Cx43) is an important half-channel protein responsible for gap junction formation. Platelet-derived growth factor AA (PDGF-AA) regulates the proliferation, migration, metabolism, apoptosis and cell cycle of chondrocytes. However, the role of PDGF-AA in gap junction intercellular communication in chondrocytes is not fully understood. In the current study, we performed experiments to explore the effect of PDGF-AA on GJIC and its underlying biomechanical mechanism.

METHODS

qPCR was performed to determine the expression of PDGF, PDGFR and connexin family genes in chondrocytes and/or cartilage. A scrape loading/dye transfer assay was used to determine GJIC. Western blot analysis was applied to detect the expression of Cx43 and PI3K/Akt signaling pathway proteins. Immunofluorescence staining was utilized to examine protein distribution. Scanning electron microscopy was used to delineate the morphology of chondrocytes.

RESULTS

Expression of PDGF-A mRNA was highest among the PDGF family in chondrocytes and cartilage tissues. PDGF-AA promoted functional GJIC formation in chondrocytes by upregulating the expression of Cx43. Enhanced functional GJIC formation in chondrocytes induced by PDGF-AA occurred through the activation of PI3K/Akt signaling and its nuclear accumulation.

CONCLUSION

For the first time, this study provides evidence demonstrating the role of PDGF-AA in cell-to-cell communication in chondrocytes through mediating Cx43 expression.

Active Compounds and Targets of Yuanzhi Powder in Treating Alzheimer's Disease and Its Relationship with Immune Infiltration Based on HPLC Fingerprint and Network Pharmacology

Background

Yuanzhi powder (YZP) has been extensively investigated as a natural prescription with therapeutic benefits for Alzheimer's disease (AD). However, its active compounds and underlying immune mechanism for treating AD are still unclear. This study aimed to investigate the immune mechanism of YZP against AD through high-performance liquid chromatography (HPLC)-based network pharmacology and gene chip technology.

Methods

Active components of YZP were obtained from HPLC and public databases. Subsequently, GSE5281, GSE28146, GSE29378, and GSE97760 from the Gene Expression Omnibus (GEO) database were downloaded to extract AD difference genes (DEGs). The active components-targets network and protein interaction network were then constructed by Cytoscape. The biological processes and signaling pathways, which implicate the targets of YZP for AD, were analyzed using the ClueGo Cytoscape plug-in. Molecular docking experiments were performed to verify the affinity of targets and ligands. Ultimately, the link between the hub genes and immune cell infiltration was assessed via CIBERSORT.

Results

83 YZP active compounds and 641 DEGs associated with AD, including quercetin, berberine, 3,6′-disinapoylsucrose, coptisine, and palmatine, were evaluated. We showed that FOS, CCL2, and GJA1 were the core targets and that the gap junction is an essential signaling pathway in YZP for AD. Furthermore, the AD group had a higher infiltration level of naïve B cells and resting CD4 memory T cells, as determined by the CIBERSORT. Notably, the immune cells-targets network demonstrates that GJA1 and GRM1 are intimately related to naïve B cells and plasma cells.

Conclusions

YZP may help treat AD by targeting proteins with key active compounds to regulate naïve B cells and plasma cells. Our results demonstrate a new immune mechanism for treating AD with YZP.

The intercellular communications mediating radiation-induced bystander effects and their relevance to environmental, occupational, and therapeutic exposures

PURPOSE

The assumption that traversal of the cell nucleus by ionizing radiation is a prerequisite to induce genetic damage, or other important biological responses, has been challenged by studies showing that oxidative alterations extend beyond the irradiated cells and occur also in neighboring bystander cells. Cells and tissues outside the radiation field experience significant biochemical and phenotypic changes that are often similar to those observed in the irradiated cells and tissues. With relevance to the assessment of long-term health risks of occupational, environmental and clinical exposures, measurable genetic, epigenetic, and metabolic changes have been also detected in the progeny of bystander cells. How the oxidative damage spreads from the irradiated cells to their neighboring bystander cells has been under intense investigation. Following a brief summary of the trends in radiobiology leading to this paradigm shift in the field, we review key findings of bystander effects induced by low and high doses of various types of radiation that differ in their biophysical characteristics. While notable mechanistic insights continue to emerge, here the focus is on the many means of intercellular communication that mediate these effects, namely junctional channels, secreted molecules and extracellular vesicles, and immune pathways.

CONCLUSIONS

The insights gained by studying radiation bystander effects are leading to a basic understanding of the intercellular communications that occur under mild and severe oxidative stress in both normal and cancerous tissues. Understanding the mechanisms underlying these communications will likely contribute to reducing the uncertainty of predicting adverse health effects following exposure to low dose/low fluence ionizing radiation, guide novel interventions that mitigate adverse out-of-field effects, and contribute to better outcomes of radiotherapeutic treatments of cancer. In this review, we highlight novel routes of intercellular communication for investigation, and raise the rationale for reconsidering classification of bystander responses, abscopal effects, and expression of genomic instability as non-targeted effects of radiation.

Exosomes Derived from Glioma Cells under Hypoxia Promote Angiogenesis through Up-regulated Exosomal Connexin 43

Glioblastoma multiform (GBM) is a highly aggressive primary brain tumor. Exosomes derived from glioma cells under a hypoxic microenvironment play an important role in tumor biology including metastasis, angiogenesis and chemoresistance. However, the underlying mechanisms remain to be elucidated. In this study, we aimed to explore the role of connexin 43 on exosomal uptake and angiogenesis in glioma under hypoxia. U251 cells were exposed to 3% oxygen to achieve hypoxia, and the expression levels of HIF-1α and Cx43, involved in the colony formation and proliferation of cells were assessed. Exosomes were isolated by differential velocity centrifugation from U251 cells under normoxia and hypoxia (Nor-Exos and Hypo-Exos), respectively. Immunofluorescence staining, along with assays for CCK-8, tube formation and wound healing along with a transwell assay were conducted to profile exosomal uptake, proliferation, tube formation, migration and invasion of HUVECs, respectively. Our results revealed that Hypoxia significantly up-regulated the expression of HIF-1α in U251 cells as well as promoting proliferation and colony number. Hypoxia also increased the level of Cx43 in U251 cells and in the exosomes secreted. The uptake of Dio-stained Hypo-Exos by HUVECs was greater than that of Nor-Exos, and inhibition of Cx43 by ^37,43gap27 or lenti-Cx43-shRNA efficiently prevented the uptake of Hypo-Exos by recipient endothelial cells. In addition, the proliferation and total loops of HUVECs were remarkably increased at 24 h, 48 h, and 10 h after Hypo-Exos, respectively. Notably, ^37,43gap27, a specific Cx-mimetic peptide blocker of Cx37 and Cx43, efficiently alleviated Hypo-Exos-induced proliferation and tube formation by HUVECs. Finally, ^37,43gap27 also significantly attenuated Hypo-Exos-induced migration and invasion of HUVECs. These findings demonstrate that exosomal Cx43 contributes to glioma angiogenesis mediated by Hypo-Exos, and suggests that exosomal Cx43 might serve as a potential therapeutic target for glioblastoma.

MicroRNA-3148 inhibits glioma by decreasing DCUN1D1 and inhibiting the NF-kB pathway

Glioma, which originates in the brain, is the most aggressive tumor of the central nervous system. It has been shown that microRNA (miRNA) controls the proliferation, migration and apoptosis of glioma cells. The objective of the present study was to measure microRNA-3148 (miR-3148) expression and investigate its impact on the pathogenetic mechanism of glioma. In the present study, reverse transcription-quantitative real-time PCR was employed to detect miR-3148 expression levels in glioma tissues and cell lines. Cell Counting Kit-8 assay, 5-ethynyl-2'-deoxyuridine assay, and Transwell migration assay were performed to assess the influence of miR-3148 on the malignant biological behavior of glioma cells. The biological functions of miR-3148 in glioma were examined via a xenograft tumor growth assay. Furthermore, the association between miR-3148 and DCUN1D1 was investigated via immunohistochemistry, dual-luciferase reporter assay and western blotting. It was observed that miR-3148 was expressed at low levels in glioma cells, and this represented a poor survival rate. In addition, an increased level of miR-3148 in cells and animal models inhibited glioma cell migration and proliferation. Moreover, miR-3148 decreased DCUN1D1 and curbed the nuclear factor κ enhancer binding protein (NF-κB) signaling pathway, thus decreasing the growth of glioma. Thus, miR-3148 is expressed within glioma tissues at low levels where it suppresses glioma by curbing the NF-κB pathway and lowering DCUN1D1.

Inhibition of gap junction communication between cells can induce apoptosis of corpus cavernosum smooth muscle in guinea pigs

In this study, we aimed to investigate the effect of gap junction (GJ) on apoptosis of smooth muscle. Forty adult male guinea pigs were randomly divided into four groups with 10 guinea pigs in each group. Adeno-associated virus (AAV) and Gap27 were injected at the root of the corpus cavernosum. Two weeks later, the corpus cavernosum tissue was taken to be tested. The expression of Cx43 and α-SMC protein was detected by immunofluorescence and Western blotting. The content of corpus cavernosum smooth muscle was detected by Masson trichrome staining. Apoptosis was detected by TUNEL staining and Western blotting. The results showed that Gap27 did not affect Cx43 but decreased the expression of smooth muscle. The results of TUNEL staining and detection of apoptosis-related proteins showed that apoptosis was induced by Gap27. In addition, we found that corpus cavernosum injection of AAV could induce obvious apoptosis. In this study, we examined the effect of inhibition of gap junction on smooth muscle, and suggested that the decrease of gap junction function may be a potential mechanism of smooth muscle apoptosis.

Investigation of miR-93-5p and its effect on the radiosensitivity of breast cancer

Accumulating evidence suggests that intrinsic resistance to radiotherapy reduces the survival of patients with cancer. The present study investigated whether miR-93-5p affects proliferation, migration, apoptosis, and radiosensitivity of breast cancer (BC) cells. MDA-MB-468, MCF-7, and MDA-MB-231 BC cells were incubated with hsa-miR-93-5p mimics, hsa-miR-93-5p inhibitor, and negative control RNA with or without exposure to ionizing radiation to determine cell proliferation, migration, and apoptosis using the Cell Counting Kit-8 assay, wound healing assay and apoptotic assay, respectively. Overexpression of miR-93-5p inhibited the migratory abilities (P = 0.001) and decreased the cell proliferation (P = 0.049) of MCF-7 cells. In MCF-7 cells, a significant increase in apoptosis was detected after treatment with miR-93-5p compared with the negative control (P = 0.001) and miR-93-5p inhibitor (P = 0.004). In MDA-MB-468 cells, the proportion of apoptotic cells increased following exposure to ionizing radiation (P = 0.001). The percentage of apoptotic MDA-MB-231 cells in the miR-93-5p group was significantly increase compared with that determined in the negative control (P = 0.044) and hsa-miR-93-5p inhibitor (P = 0.046) groups. In conclusion, our findings showed that miR-93-5p reduces BC cell proliferation and migratory capacity, and increases the ratio of apoptotic cells. Overexpression of miR-93-5p could increase radiosensitivity in BC cells by increasing apoptosis. This evidence provides new insight into the treatment of BC and identifies miR-93-5p as a potential therapeutic target.

Sequential Release of Small Extracellular Vesicles from Bilayered Thiolated Alginate/Polyethylene Glycol Diacrylate Hydrogels for Scarless Wound Healing

Excessive scar formation has adverse physiological and psychological effects on patients; therefore, a therapeutic strategy for rapid wound healing and reduced scar formation is urgently needed. Herein, bilayered thiolated alginate/PEG diacrylate (BSSPD) hydrogels were fabricated for sequential release of small extracellular vesicles (sEVs), which acted in different wound healing phases, to achieve rapid and scarless wound healing. The sEVs secreted by bone marrow derived mesenchymal stem cells (B-sEVs) were released from the lower layer of the hydrogels to promote angiogenesis and collagen deposition by accelerating fibroblast and endothelial cell proliferation and migration during the early inflammation and proliferation phases, while sEVs secreted by miR-29b-3p-enriched bone marrow derived mesenchymal stem cells were released from the upper layer of the hydrogels and suppressed excessive capillary proliferation and collagen deposition during the late proliferation and maturation phases. In a full-thickness skin defect model of rats and rabbit ears, the wound repair rate, angiogenesis, and collagen deposition were evaluated at different time points after treatment with BSSPD loaded with B-sEVs. Interestingly, during the end of the maturation phase in the in vivo model, tissues in the groups treated with BSSPD loaded with sEVs for sequential release (SR-sEVs@BSSPD) exhibited a more uniform vascular structure distribution, more regular collagen arrangement, and lower volume of hyperplastic scar tissue than tissues in the other groups. Hence, SR-sEVs@BSSPD based on skin repair phases was successfully designed and has considerable potential as a cell-free therapy for scarless wound healing.

Connexins in Cancer: Jekyll or Hyde?

The expression, localization, and function of connexins, the protein subunits that comprise gap junctions, are often altered in cancer. In addition to cell-cell coupling through gap junction channels, connexins also form hemichannels that allow communication between the cell and the extracellular space and perform non-junctional intracellular activities. Historically, connexins have been considered tumor suppressors; however, they can also serve tumor-promoting functions in some contexts. Here, we review the literature surrounding connexins in cancer cells in terms of specific connexin functions and propose that connexins function upstream of most, if not all, of the hallmarks of cancer. The development of advanced connexin targeting approaches remains an opportunity for the field to further interrogate the role of connexins in cancer phenotypes, particularly through the use of in vivo models. More specific modulators of connexin function will both help elucidate the functions of connexins in cancer and advance connexin-specific therapies in the clinic.

Connexins-Therapeutic Targets in Cancers

Connexins (Cx) are members of a protein family that forms intercellular channels localised in gap junction (GJ) plaques and single transmembrane channels called hemichannels. They participate in intercellular communication or communication between the intracellular and extracellular environments. Connexins affect cell homeostasis, growth and differentiation by enabling the exchange of metabolites or by interfering with various signalling pathways. Alterations in the functionality and the expression of connexins have been linked to the occurrence of many diseases. Connexins have been already linked to cancers, cardiac and brain disorders, chronic lung and kidney conditions and wound healing processes. Connexins have been shown either to suppress cancer tumour growth or to increase tumorigenicity by promoting cancer cell growth, migration and invasiveness. A better understanding of the complexity of cancer biology related to connexins and intercellular communication could result in the design of novel therapeutic strategies. The modulation of connexin expression may be an effective therapeutic approach in some types of cancers. Therefore, one important challenge is the search for mechanisms and new drugs, selectively modulating the expression of various connexin isoforms. We performed a systematic literature search up to February 2020 in the electronic databases PubMed and EMBASE. Our search terms were as follows: connexins, hemichannels, cancer and cancer treatment. This review aims to provide information about the role of connexins and gap junctions in cancer, as well as to discuss possible therapeutic options that are currently being studied.

Hypoxic Melanoma Cells Deliver microRNAs to Dendritic Cells and Cytotoxic T Lymphocytes through Connexin-43 Channels

Alterations in microRNA (miRNA) profiles, induced by tumor microenvironment stressors, like hypoxia, allow cancer cells to acquire immune-resistance phenotypes. Indeed, hypoxia-induced miRNAs have been implicated in cancer progression through numerous cancer cell non-autonomous mechanisms, including the direct transfer of hypoxia-responsive miRNA from cancer to immune cells via extracellular vesicles. Connexin-43 (Cx43)-constituted gap junctions (GJs) have also been involved in miRNA intercellular mobilization, in other biological processes. In this report, we aimed to evaluate the involvement of Cx43-GJs in the shift of miRNAs induced by hypoxia, from hypoxic melanoma cells to dendritic cells and melanoma-specific cytotoxic T lymphocytes (CTLs). Using qRT-PCR arrays, we identified that miR-192-5p was strongly induced in hypoxic melanoma cells. Immune cells acquired this miRNA after co-culture with hypoxic melanoma cells. The transfer of miR-192-5p was inhibited when hypoxic melanoma cells expressed a dominant negative Cx43 mutant or when Cx43 expression was silenced using specific short-hairpin RNAs. Interestingly, miR-192-5p levels on CTLs after co-culture with hypoxic melanoma cells were inversely correlated with the cytotoxic activity of T cells and with ZEB2 mRNA expression, a validated immune-related target of miR-192-5p, which is also observed in vivo. Altogether, our data suggest that hypoxic melanoma cells may suppress CTLs cytotoxic activity by transferring hypoxia-induced miR-192-5p through a Cx43-GJs driven mechanism, constituting a resistance strategy for immunological tumor escape.

Antagonistic Functions of Connexin 43 during the Development of Primary or Secondary Bone Tumors

Despite research and clinical advances during recent decades, bone cancers remain a leading cause of death worldwide. There is a low survival rate for patients with primary bone tumors such as osteosarcoma and Ewing’s sarcoma or secondary bone tumors such as bone metastases from prostate carcinoma. Gap junctions are specialized plasma membrane structures consisting of transmembrane channels that directly link the cytoplasm of adjacent cells, thereby enabling the direct exchange of small signaling molecules between cells. Discoveries of human genetic disorders due to genetic mutations in gap junction proteins (connexins) and experimental data using connexin knockout mice have provided significant evidence that gap-junctional intercellular communication (Gj) is crucial for tissue function. Thus, the dysfunction of Gj may be responsible for the development of some diseases. Gj is thus a main mechanism for tumor cells to communicate with other tumor cells and their surrounding microenvironment to survive and proliferate. If it is well accepted that a low level of connexin expression favors cancer cell proliferation and therefore primary tumor development, more evidence is suggesting that a high level of connexin expression stimulates various cellular process such as intravasation, extravasation, or migration of metastatic cells. If so, connexin expression would facilitate secondary tumor dissemination. This paper discusses evidence that suggests that connexin 43 plays an antagonistic role in the development of primary bone tumors as a tumor suppressor and secondary bone tumors as a tumor promoter.

Role of ROS/RNS in Preeclampsia: Are Connexins the Missing Piece?

Preeclampsia is a pregnancy complication that appears after 20 weeks of gestation and is characterized by hypertension and proteinuria, affecting both mother and offspring. The cellular and molecular mechanisms that cause the development of preeclampsia are poorly understood. An important feature of preeclampsia is an increase in oxygen and nitrogen derived free radicals (reactive oxygen species/reactive nitrogen species (ROS/RNS), which seem to be central players setting the development and progression of preeclampsia. Cell-to-cell communication may be disrupted as well. Connexins (Cxs), a family of transmembrane proteins that form hemichannels and gap junction channels (GJCs), are essential in paracrine and autocrine cell communication, allowing the movement of signaling molecules between cells as well as between the cytoplasm and the extracellular media. GJCs and hemichannels are fundamental for communication between endothelial and smooth muscle cells and, therefore, in the control of vascular contraction and relaxation. In systemic vasculature, the activity of GJCs and hemichannels is modulated by ROS and RNS. Cxs participate in the development of the placenta and are expressed in placental vasculature. However, it is unknown whether Cxs are modulated by ROS/RNS in the placenta, or whether this potential modulation contributes to the pathogenesis of preeclampsia. Our review addresses the possible role of Cxs in preeclampsia, and the plausible modulation of Cxs-formed channels by ROS and RNS. We suggest these factors may contribute to the development of preeclampsia.

Potassium channels and their role in glioma: A mini review

K⁺ channels regulate a multitude of biological processes and play important roles in a variety of diseases by controlling potassium flow across cell membranes. They are widely expressed in the central and peripheral nervous system. As a malignant tumor derived from nerve epithelium, glioma has the characteristics of high incidence, high recurrence rate, high mortality rate, and low cure rate. Since glioma cells show invasive growth, current surgical methods cannot completely remove tumors. Adjuvant chemotherapy is still needed after surgery. Because the blood-brain barrier and other factors lead to a lower effective concentration of chemotherapeutic drugs in the tumor, the recurrence rate of residual lesions is extremely high. Therefore, new therapeutic methods are needed. Numerous studies have shown that different K⁺ channel subtypes are differentially expressed in glioma cells and are involved in the regulation of the cell cycle of glioma cells to arrest them at different stages of the cell cycle. Increasing evidence suggests that K⁺ channels express in glioma cells and regulate glioma cell behaviors such as cell cycle, proliferation and apoptosis. This review article aims to summarize the current knowledge on the function of K⁺ channels in glioma, suggests K⁺ channels participating in the development of glioma.

The Roles of miRNA in Glioblastoma Tumor Cell Communication: Diplomatic and Aggressive Negotiations

Glioblastoma (GBM) consists of a heterogeneous collection of competing cellular clones which communicate with each other and with the tumor microenvironment (TME). MicroRNAs (miRNAs) present various exchange mechanisms: free miRNA, extracellular vesicles (EVs), or gap junctions (GJs). GBM cells transfer miR-4519 and miR-5096 to astrocytes through GJs. Oligodendrocytes located in the invasion front present high levels of miR-219-5p, miR-219-2-3p, and miR-338-3p, all related to their differentiation. There is a reciprocal exchange between GBM cells and endothelial cells (ECs) as miR-5096 promotes angiogenesis after being transferred into ECs, whereas miR-145-5p acts as a tumor suppressor. In glioma stem cells (GSCs), miR-1587 and miR-3620-5p increase the proliferation and miR-1587 inhibits the hormone receptor co-repressor-1 (NCOR1) after EVs transfers. GBM-derived EVs carry miR-21 and miR-451 that are up-taken by microglia and monocytes/macrophages, promoting their proliferation. Macrophages release EVs enriched in miR-21 that are transferred to glioma cells. This bidirectional miR-21 exchange increases STAT3 activity in GBM cells and macrophages, promoting invasion, proliferation, angiogenesis, and resistance to treatment. miR-1238 is upregulated in resistant GBM clones and their EVs, conferring resistance to adjacent cells via the CAV1/EGFR signaling pathway. Decrypting these mechanisms could lead to a better patient stratification and the development of novel target therapies.

Pattern of cell-to-cell transfer of microRNA by gap junction and its effect on the proliferation of glioma cells

MicroRNA is expected to be a novel therapeutic tool for tumors. Gap junctions facilitate the transfer of microRNA, which exerts biological effects on tumor cells. However, the length of microRNA that can pass through certain gap junctions composed of specific connexin remains unknown. To address this question, the present study investigated the permeability of gap junctions composed of various connexins, including connexin 43, connexin 32 or connexin 37, to microRNAs consisting of 18-27 nucleotides in glioma cells and cervical cancer cells. Results indicated that all of the microRNAs were able to be transferred from donor glioma cells to neighboring cells through the connexin 43 composed gap junction, but not the gap junctions composed of connexin 32 or connexin 37, in cervical cancer cells. Downregulation of the function of gap junctions comprising connexin 43 by pharmacological inhibition and shRNA significantly decreased the transfer of these microRNAs. In contrast, gap junction enhancers and overexpression of connexin 43 effectively increased these transfers. In glioma cells, cell proliferation was inhibited by microRNA-34a. Additionally, these effects of microRNA-34a were significantly enhanced by overexpression of connexin 43 in U251 cells, indicating that gap junctions play an important role in the antitumor effect of microRNA by transfer of microRNA to neighboring cells. Our data are the first to clarify the pattern of microRNA transmission through gap junctions and provide novel insights to show that antitumor microRNAs should be combined with connexin 43 or a connexin 43 enhancer, not connexin 32 or connexin 37, in order to improve the therapeutic effect.