The potential prognostic value of connexin 26 and 46 expression in neoadjuvant-treated breast cancer

Software BreastAnalyser for the semi-automatic analysis of breast cancer immunohistochemical images

Breast cancer is the most diagnosed cancer worldwide and represents the fifth cause of cancer mortality globally. It is a highly heterogeneous disease, that comprises various molecular subtypes, often diagnosed by immunohistochemistry. This technique is widely employed in basic, translational and pathological anatomy research, where it can support the oncological diagnosis, therapeutic decisions and biomarker discovery. Nevertheless, its evaluation is often qualitative, raising the need for accurate quantitation methodologies. We present the software BreastAnalyser, a valuable and reliable tool to automatically measure the area of 3,3'-diaminobenzidine tetrahydrocholoride (DAB)-brown-stained proteins detected by immunohistochemistry. BreastAnalyser also automatically counts cell nuclei and classifies them according to their DAB-brown-staining level. This is performed using sophisticated segmentation algorithms that consider intrinsic image variability and save image normalization time. BreastAnalyser has a clean, friendly and intuitive interface that allows to supervise the quantitations performed by the user, to annotate images and to unify the experts' criteria. BreastAnalyser was validated in representative human breast cancer immunohistochemistry images detecting various antigens. According to the automatic processing, the DAB-brown area was almost perfectly recognized, being the average difference between true and computer DAB-brown percentage lower than 0.7 points for all sets. The detection of nuclei allowed proper cell density relativization of the brown signal for comparison purposes between the different patients. BreastAnalyser obtained a score of 85.5 using the system usability scale questionnaire, which means that the tool is perceived as excellent by the experts. In the biomedical context, the connexin43 (Cx43) protein was found to be significantly downregulated in human core needle invasive breast cancer samples when compared to normal breast, with a trend to decrease as the subtype malignancy increased. Higher Cx43 protein levels were significantly associated to lower cancer recurrence risk in Oncotype DX-tested luminal B HER2- breast cancer tissues. BreastAnalyser and the annotated images are publically available https://citius.usc.es/transferencia/software/breastanalyser for research purposes.

Mapping the Anti-Cancer Activity of α-Connexin Carboxyl-Terminal (aCT1) Peptide in Resistant HER2+ Breast Cancer

Connexin 43 (Cx43) is a protein encoded by the GJA1 gene and is a component of cell membrane structures called gap junctions, which facilitate intercellular communication. Prior evidence indicates that elevated GJA1 expression in the HER2-positive (HER2+) subtype of breast cancer is associated with poor prognosis. Prior evidence also suggests that HER2+ breast cancers that have become refractory to HER2-targeted agents have a loss of Cx43 gap junction intercellular communication (GJIC). In this study, a Cx43-targeted agent called alpha-connexin carboxyl-terminal peptide (aCT1) is examined to determine whether GJIC can be rescued in refractory HER2+ breast cancer cells. A proposed mechanism of action for aCT1 is binding to the tight junction protein Zonal Occludens-1 (ZO-1). However, the true scope of activity for aCT1 has not been explored. In this study, mass spectrometry proteomic analysis is used to determine the breadth of aCT1-interacting proteins. The NanoString nCounter Breast Cancer 360 panel is also used to examine the effect of aCT1 on cancer signaling in HER2+ breast cancer cells. Findings from this study show a dynamic range of binding partners for aCT1, many of which regulate gene expression and RNA biology. nCounter analysis shows that a number of pathways are significantly impacted by aCT1, including upregulation of apoptotic factors, leading to the prediction and demonstration that aCT1 can boost the cell death effects of cisplatin and lapatinib in HER2+ breast cancer cells that have become resistant to HER2-targeted agents.

Targeting NANOG and FAK via Cx26-derived Cell-penetrating Peptides in Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) represents the most lethal and treatment-resistant breast cancer subtype with limited treatment options. We previously identified a protein complex unique to TNBC composed of the gap junction protein connexin 26 (Cx26), the pluripotency transcription factor NANOG, and focal adhesion kinase (FAK). We sought to determine whether a peptide mimetic of the interaction region of Cx26 attenuated tumor growth in preclinical models. We designed peptides based on Cx26 juxtamembrane domains and performed binding experiments with NANOG and FAK using surface plasmon resonance. Binding studies revealed that the Cx26 C-terminal tail and intracellular loop bound to NANOG and FAK with submicromolar-to-micromolar affinity and that a 5-amino acid sequence in the C-terminal tail of Cx26 (RYCSG) was sufficient for binding. Peptides with high affinity were engineered with a cell-penetrating antennapedia sequence and assessed in functional assays including cell proliferation, tumorsphere formation, and in vivo tumor growth, and downstream signaling changes were measured. The cell-penetrating Cx26 peptide (aCx26-pep) disrupted self-renewal while reducing nuclear FAK and NANOG and inhibiting NANOG target gene expression in TNBC cells but not luminal mammary epithelial cells. In vivo, aCx26-pep reduced tumor growth and proliferation and induced cell death. Here, we provide proof-of-concept that a Cx26 peptide-based strategy inhibits growth and alters NANOG activity specifically in TNBC, indicating the therapeutic potential of this targeting approach.

Connexins in Cancer, the Possible Role of Connexin46 as a Cancer Stem Cell-Determining Protein

Cancer is a widespread and incurable disease caused by genetic mutations, leading to uncontrolled cell proliferation and metastasis. Connexins (Cx) are transmembrane proteins that facilitate intercellular communication via hemichannels and gap junction channels. Among them, Cx46 is found mostly in the eye lens. However, in pathological conditions, Cx46 has been observed in various types of cancers, such as glioblastoma, melanoma, and breast cancer. It has been demonstrated that elevated Cx46 levels in breast cancer contribute to cellular resistance to hypoxia, and it is an enhancer of cancer aggressiveness supporting a pro-tumoral role. Accordingly, Cx46 is associated with an increase in cancer stem cell phenotype. These cells display radio- and chemoresistance, high proliferative abilities, self-renewal, and differentiation capacities. This review aims to consolidate the knowledge of the relationship between Cx46, its role in forming hemichannels and gap junctions, and its connection with cancer and cancer stem cells.

The relationship between connexin-43 expression and Ki67 in non-glial central nervous system tumors

BACKGROUND

Advanced intercellular communication is a known oncogenic factor. In the central nervous system, Connexin-43 (Cx43) forms this junctional networking. Moreover, it correlates with the proliferation rate, and thus behavior, of gliomas. We assessed the expression of Cx43 and its relationship to Ki67 in other common central nervous system tumors.

METHODS

The expression of Cx43 and Ki67 were assessed in formalin-fixed paraffin embedded samples of human brain metastases, meningiomas, and neurinomas using immunohistochemistry. Neurinomas and meningiomas were jointly evaluated due to similar non-malignant behavior.

RESULTS

A total of 14 metastases of different extracerebral carcinomas, 6 meningiomas, and 10 neurinomas were evaluated. Five (36%) metastases and 5 (31%) meningiomas/neurinomas showed minor expression, whereas 6 (43%) metastases and 2 (13%) meningiomas/neurinomas showed no Cx43 expression at all. In 3 (21%) metastases and 9 (56%) meningiomas/neurinomas, moderate or strong expression of Cx43 was identified. The higher expression of Cx43 in meningiomas and neurinomas directly correlated with Ki67, r = 0.53 (P = 0.034). For metastases no significant correlation was found. Mitotic index in meningiomas/neurinomas correlated with Ki67 expression, r = 0.74 (P < 0.001), but did not show statistically significant correlation with Cx43 expression in these tumors.

CONCLUSIONS

The expression of Cx43 as a marker of cell-to-cell networking exposed a significant correlation with the Ki67-defined proliferation index in case of primary central nervous system neuroectodermal neoplasms. However, it does not seem to play a comparable role in metastases with extracerebral origin.

The role of Connexin26 regulated by MiR-2114-3p in the pathogenesis of ovarian cancer

OBJECTIVES

The purpose of our research was to determine the expression of Cx26 and miR-2114-3p, and their effects on proliferation, migration, and invasion in ovarian cancer and their mechanisms.

MATERIALS AND METHODS

Transcriptome sequencing was performed and differentially expressed Cx26 was screened. The mRNA and protein levels of Cx26 in EOC and normal ovarian tissues were verified. The relationship between Cx26 levels and prognostics was analyzed. Cx26 Lentiviral vectors were constructed to detect its effect on ovarian cancer. WB verified that PI3K/AKT pathway was the possible signal pathway regulated by Cx26. The interaction between miR-2114-3p and Cx26 was detected by double luciferase reporter assay and qrt-PCR. CCK8, clone formation, transwell, and flow cytometry assays were conducted in cells transfected miR-2114-3p plasmids. The vivo experiment investigated the effects of Cx26 on subcutaneous tumor growth, PI3K expression, proliferation proteins Ki67 and PCNA.

RESULTS

Cx26 was up-regulated in EOC tissue and cell lines, and was associated with poor prognosis of ovarian cancer, while miR-2114-3p was down-regulated in EOC cell lines. Cx26 was a direct target of miR-2114-3p. Cx26 overexpression and miR-2114-3p inhibition promoted the growth, motility, invasiveness, and S phase arrest of EOC cells. Additionally, Cx26 could activated PI3K pathway whatever in vivo and in vitro.

CONCLUSIONS

Dysregulation of Cx26 is critical in EOC patients. Manipulation of this mechanism may influence the survival of EOC patients. MiR-2114-3p regulates the tumor-promoting activity of Cx26 in EOC. By inhibiting the PI3K pathway or knocking down Cx26 effectively inhibits tumor growth in EOC cells and Nude mouse model.

Connexins and Glucose Metabolism in Cancer

Connexins are a family of transmembrane proteins that regulate diverse cellular functions. Originally characterized for their ability to mediate direct intercellular communication through the formation of highly regulated membrane channels, their functions have been extended to the exchange of molecules with the extracellular environment, and the ability to modulate numerous channel-independent effects on processes such as motility and survival. Notably, connexins have been implicated in cancer biology for their context-dependent roles that can both promote or suppress cancer cell function. Moreover, connexins are able to mediate many aspects of cellular metabolism including the intercellular coupling of nutrients and signaling molecules. During cancer progression, changes to substrate utilization occur to support energy production and biomass accumulation. This results in metabolic plasticity that promotes cell survival and proliferation, and can impact therapeutic resistance. Significant progress has been made in our understanding of connexin and cancer biology, however, delineating the roles these multi-faceted proteins play in metabolic adaptation of cancer cells is just beginning. Glucose represents a major carbon substrate for energy production, nucleotide synthesis, carbohydrate modifications and generation of biosynthetic intermediates. While cancer cells often exhibit a dependence on glycolytic metabolism for survival, cellular reprogramming of metabolic pathways is common when blood perfusion is limited in growing tumors. These metabolic changes drive aggressive phenotypes through the acquisition of functional traits. Connections between glucose metabolism and connexin function in cancer cells and the surrounding stroma are now apparent, however much remains to be discovered regarding these relationships. This review discusses the existing evidence in this area and highlights directions for continued investigation.

The prognostic value and biological significance of gap junction beta protein 2 (GJB2 or Cx26) in cervical cancer

Objective

To evaluate the prognostic value and explore the biological significance of gap junction protein beta 2 (GJB2 or Cx26) in cervical cancer (CC).

Methods

We first compared GJB2 expression between CC and normal tissues using public databases and immunohistochemistry (IHC). Based on The Cancer Genome Atlas data (TCGA cohort, n = 304) and tissue microarray samples (OBC cohort, n = 111), we explored the prognostic value of GJB2 for CC patients using bioinformatics analysis and IHC scoring. To explore the biological significance of GJB2, Gene set enrichment analysis (GSEA) and Gene Ontology (GO) were performed. The impact of GJB2 on the immune microenvironment was analyzed by CIBERSORTx and ESTIMATE algorithms. We finally investigated the relationship between GJB2 and drug sensitivity based on the Genomics of Drug Sensitivity in Cancer (GDSC).

Results

The expression of GJB2 was significantly increased in CC over normal tissues. Both the TCGA and OBC cohort found that patients with high GJB2 expression had shorter overall survival (OS) time, and high GJB2 expression was the independent risk factor for prognosis (TCGA: HR, 2.566; 95% CI, 1.066–6.180; p = 0.036; OBC: HR, 2.198; 95% CI, 1.019–4.741; p = 0.045). GJB2 was correlated with patient clinical factors such as tumor size and differentiation grade. The p53 signaling pathway and toll-like receptor pathway may be regulated by GJB2. The abundance of various immune cells was significantly different between the low and high GJB2 expression groups. The ImmuneScore was significantly increased in the high GJB2 expression group. In addition, the expression level of GJB2 was positively correlated with the natural log of the half-maximal inhibitory concentration (LN_IC50) value of cisplatin/paclitaxel (Spearman r = 0.238/0.153, p &lt; 0.001).

Conclusion

GJB2 can serve as a potential prognostic marker of poor survival and a therapeutic target in CC. Moreover, GJB2 may affect the immune microenvironment and is correlated with chemoresistance.

Connexin Expression in Pituitary Adenomas and the Effects of Overexpression of Connexin 43 in Pituitary Tumor Cell Lines

Gap junction intercellular communication (GJIC) is considered a key mechanism in the regulation of tissue homeostasis. GJIC structures are organized in two transmembrane channels, with each channel formed by connexins (Cxs). GJIC and Cxs expression alterations are related to the process of tumorigenesis in different cell types. Pituitary neuroendocrine tumors (PitNETs) represent 15–20% of intracranial neoplasms, and usually display benign behavior. Nevertheless, some may have aggressive behavior, invading adjacent tissues, and featuring a high proliferation rate. We aimed to assess the expression and relevance of GJIC and Cxs proteins in PitNETs. We evaluated the mRNA expression levels of Cx26, 32, and 43, and the protein expression of Cx43 in a series of PitNETs. In addition, we overexpressed Cx43 in pituitary tumor cell lines. At the mRNA level, we observed variable expression of all the connexins in the tumor samples. Cx43 protein expression was absent in most of the pituitary tumor samples that were studied. Moreover, in vitro studies revealed that the overexpression of Cx43 decreases cell growth and induces apoptosis in pituitary tumor cell lines. Our results indicate that the downregulation of Cx43 protein might be involved in the tumorigenesis of most pituitary adenomas and have a potential therapeutic value for pituitary tumor therapy.

TOPK: A new predictor of the therapeutic response to neoadjuvant chemotherapy and prognosis in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) has a high probability of relapse and poor overall survival. Neoadjuvant chemotherapy (NACT) is currently a routine treatment strategy for TNBC, but some patients do not respond well. T-LAK cell-originated protein kinase (TOPK) is highly expressed in breast cancer cells and contributes to cancer cell proliferation. The present study aimed to investigate the correlation of TOPK expression with NACT treatment response and prognosis in TNBC.

METHODS

We collected 66 pairs of TNBC samples before and after NACT with docetaxel+ epirubicin+ cyclophosphamide (TEC). The Miller-Payne (MP) system was used to assess the therapeutic response to NACT in TNBC patients.

RESULTS

Immunohistochemistry analysis showed that TNBC patients with high TOPK expression before NACT had a poor treatment response and a poor prognosis. The expression of TOPK after NACT was significantly higher than that before NACT in patients with MP grade 1-3. In contrast, patients with MP grade 4-5 had significantly lower TOPK expression after NACT than before NACT, and the expression change in Ki-67 in patients with MP grade 4-5 exhibited the same trend. Survival analysis revealed that patients with TNBC accompanied by elevated TOPK expression before NACT had a worse prognosis than those with lower TOPK expression.

CONCLUSION

TOPK may be a novel predictor for the therapeutic response to NACT and prognosis for patients with TNBC.

Differential Expression of BOC, SPOCK2, and GJD3 Is Associated with Brain Metastasis of ER-Negative Breast Cancers

Simple Summary

Brain metastasis is diagnosed in 30–50% of metastatic breast cancer patients with currently limited treatment strategies and usually short survival rates. In the present study, we aim to identify genes specifically associated with the development of brain metastasis in breast cancer. Therefore, we compared RNA expression profiles from two groups of patients with metastatic breast cancer, with and without brain involvement. Three genes BOC, SPOCK2, and GJD3 were overexpressed in the group of primary breast cancers which developed brain metastasis. Expression profiles were confirmed in an independent breast cancer cohort for both BOC and SPOCK2. In addition, differential overexpression of SPOCK2 and GJD3 mRNA levels were found to be associated with the development of brain metastasis in an external online database of 204 primary breast cancers. Verification of these genes as biomarkers for brain metastasis development in primary breast cancer is warranted.

Abstract

Background: Brain metastasis is considered one of the major causes of mortality in breast cancer patients. To invade the brain, tumor cells need to pass the blood-brain barrier by mechanisms that are partially understood. In primary ER-negative breast cancers that developed brain metastases, we found that some of the differentially expressed genes play roles in the T cell response. The present study aimed to identify genes involved in the formation of brain metastasis independently from the T cell response. Method: Previously profiled primary breast cancer samples were reanalyzed. Genes that were found to be differentially expressed were confirmed by RT-PCR and by immunohistochemistry using an independent cohort of samples. Results: BOC, SPOCK2, and GJD3 were overexpressed in the primary breast tumors that developed brain metastasis. BOC expression was successfully validated at the protein level. SPOCK2 was validated at both mRNA and protein levels. SPOCK2 and GJD3 mRNA overexpression were also found to be associated with cerebral metastasis in an external online database consisting of 204 primary breast cancers. Conclusion: The overexpression of BOC, SPOCK2, and GJD3 is associated with the invasion of breast cancer into the brain. Further studies to determine their specific function and potential value as brain metastasis biomarkers are required.

Connexin 32 induces pro-tumorigenic features in MCF10A normal breast cells and MDA-MB-231 metastatic breast cancer cells

Connexins (Cx), the basic subunit of gap junctions, play important roles in cell homeostasis, and their abnormal expression and function are associated with human hereditary diseases and cancers. In tumorigenesis, connexins were observed to have both anti-tumorigenic and pro-tumorigenic roles in a context- and stage-dependent manner. Initially, Cx26 and Cx43 were thought to be the only connexins involved in normal breast homeostasis and breast cancer. Later on, association of Cx32 expression with lymph node metastasis of breast cancer and subsequent demonstration of its expression in normal breast tissue suggested that Cx32 contributes to breast tissue homeostasis. Here, we aimed to determine the effects of Cx32 on normal breast cells, MCF10A, and on breast cancer cells, MDA-MB-231. Cx32 overexpression had profound effects on MCF10A cells, decreasing cell proliferation by increasing the doubling time of MCF10A. Furthermore, MCF10A cells acquired mesenchymal-like appearance upon Cx32 expression and had increased migration capacity and expression of both E-cadherin and vimentin. In contrast, Cx32 overexpression altered the EMT markers of MDA-MB-231 by increasing the expression of mesenchymal markers, such as slug and vimentin, and decreasing E-cadherin expression without affecting their proliferation and morphology. Our results indicate, for the first time in the literature, that Cx32 has tumor-promoting roles in MCF10A and MDA-MB-231 cells.

Connexin-46 Contained in Extracellular Vesicles Enhance Malignancy Features in Breast Cancer Cells

Under normal conditions, almost all cell types communicate with their neighboring cells through gap junction channels (GJC), facilitating cellular and tissue homeostasis. A GJC is formed by the interaction of two hemichannels; each one of these hemichannels in turn is formed by six subunits of transmembrane proteins called connexins (Cx). For many years, it was believed that the loss of GJC-mediated intercellular communication was a hallmark in cancer development. However, nowadays this paradigm is changing. The connexin 46 (Cx46), which is almost exclusively expressed in the eye lens, is upregulated in human breast cancer, and is correlated with tumor growth in a Xenograft mouse model. On the other hand, extracellular vesicles (EVs) have an important role in long-distance communication under physiological conditions. In the last decade, EVs also have been recognized as key players in cancer aggressiveness. The aim of this work was to explore the involvement of Cx46 in EV-mediated intercellular communication. Here, we demonstrated for the first time, that Cx46 is contained in EVs released from breast cancer cells overexpressing Cx46 (EVs-Cx46). This EV-Cx46 facilitates the interaction between EVs and the recipient cell resulting in an increase in their migration and invasion properties. Our results suggest that EV-Cx46 could be a marker of cancer malignancy and open the possibility to consider Cx46 as a new therapeutic target in cancer treatment.

Connexin43 as a Tumor Suppressor: Proposed Connexin43 mRNA-circularRNAs-microRNAs Axis Towards Prevention and Early Detection in Breast Cancer

Breast cancer (BC) is a global public health burden, constituting the highest cancer incidence in women worldwide. Connexin43 (Cx43) is a member of a family of transmembrane proteins responsible in part for intercellular communication between adjacent breast epithelial cells, via gap junctions. Cx43 plays key role in mammary gland development and differentiation and its spatio-temporal perturbation contributes to tumorigenesis. Thus, Cx43 acts as a breast tumor-suppressor. Signaling pathways and phenotypes downstream of Cx43 mRNA loss/mis-localization in breast cells have been well-studied. However, axes parallel to Cx43 loss are less understood. microRNAs (miRNAs) are small endogenous non-coding RNAs that repress translation and circularRNAs (circRNAs) are a class of endogenous RNAs that originate from RNA splicing and act as miRNA "sponges". CircRNAs and miRNAs are dysregulated in cancers and are highly abundant and stable in the circulation. Thus, they present as attractive liquid biopsy cancer biomarkers. Here, an axis for Cx43 mRNA-circRNAs-miRNAs interactions along BC initiation (denoted by loss of breast epithelial polarity and development of hyperplastic phenotypes) is proposed to potentially serve as a signature biomarker toward BC early-onset detection and prevention.

Gap Junction Intercellular Communication in the Carcinogenesis Hallmarks: Is This a Phenomenon or Epiphenomenon?

If occupational tumors are excluded, cancer causes are largely unknown. Therefore, it appeared useful to work out a theory explaining the complexity of this disease. More than fifty years ago the first demonstration that cells communicate with each other by exchanging ions or small molecules through the participation of connexins (Cxs) forming Gap Junctions (GJs) occurred. Then the involvement of GJ Intercellular Communication (GJIC) in numerous physiological cellular functions, especially in proliferation control, was proven and accounts for the growing attention elicited in the field of carcinogenesis. The aim of the present paper is to verify and discuss the role of Cxs, GJs, and GJIC in cancer hallmarks, pointing on the different involved mechanisms in the context of the multi-step theory of carcinogenesis. Functional GJIC acts both as a tumor suppressor and as a tumor enhancer in the metastatic stage. On the contrary, lost or non-functional GJs allow the uncontrolled proliferation of stem/progenitor initiated cells. Thus, GJIC plays a key role in many biological phenomena or epiphenomena related to cancer. Depending on this complexity, GJIC can be considered a tumor suppressor in controlling cell proliferation or a cancer ally, with possible preventive or therapeutic implications in both cases.

Prognostic value of the mRNA expression of gap junction α members in patients with gastric cancer

Gastric cancer remains one of the primary causes of cancer-associated death worldwide. The gap junction α (GJA) family has been demonstrated to be involved in the cellular proliferation and metastasis of gastric cancer. However, the prognostic value of GJA in gastric cancer is yet to be elucidated. In the present study, the overall survival (OS) of patients with gastric cancer and the mRNA expression of GJA family members, including GJA1, GJA3, GJA4, GJA10 and GJA12, were analyzed using 593 patients with gastric cancer from the Kaplan-Meier plotter database. High GJA1 and GJA10 mRNA expression levels were associated with a poorer patient outcome (P=0.0066 and P=0.015, respectively), whereas high mRNA expression levels of GJA4 and GJA12 were associated with longer survival times (P=0.0056 and P=0.0054, respectively). Furthermore, the values of specific prognostic indicators of different subtypes of gastric cancer, including human epidermal growth factor receptor 2 status, Lauren differentiation and tumor stage, were also analyzed. The findings of the present study suggested a potential role for GJA family members in gastric cancer, which warrants further investigation.

Connexins in cancer: bridging the gap to the clinic

Gap junctions comprise arrays of intercellular channels formed by connexin proteins and provide for the direct communication between adjacent cells. This type of intercellular communication permits the coordination of cellular activities and plays key roles in the control of cell growth and differentiation and in the maintenance of tissue homoeostasis. After more than 50 years, deciphering the links among connexins, gap junctions and cancer, researchers are now beginning to translate this knowledge to the clinic. The emergence of new strategies for connexin targeting, combined with an improved understanding of the molecular bases underlying the dysregulation of connexins during cancer development, offers novel opportunities for clinical applications. However, different connexin isoforms have diverse channel-dependent and -independent functions that are tissue and stage specific. This can elicit both pro- and anti-tumorigenic effects that engender significant challenges in the path towards personalised medicine. Here, we review the current understanding of the role of connexins and gap junctions in cancer, with particular focus on the recent progress made in determining their prognostic and therapeutic potential.

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

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

All-trans retinoic acid reverses epithelial-mesenchymal transition in paclitaxel-resistant cells by inhibiting nuclear factor kappa B and upregulating gap junctions

Paclitaxel is a widely used chemotherapy drug, but development of resistance leads to treatment failure. Tumor cells that are treated with a sublethal dose of paclitaxel for a long period of time show the epithelial‐mesenchymal transition (EMT) phenotype, which leads to metastasis and resistance. All‐trans retinoic acid (ATRA) is always used in combination with paclitaxel and can reverse EMT in many types of cancer cells. The ability of ATRA to reverse EMT in chemoresistant cells is still unknown. In the present study, the ability of ATRA to reverse EMT in paclitaxel‐resistant cells was investigated. Three colorectal cancer cell lines, HCT116, LoVo and CT26, were treated with sublethal doses of paclitaxel to create resistant cell lines. Western blotting, immunocytochemistry, and “parachute” dye‐coupling assays showed that ATRA reverses EMT, inhibits nuclear factor kappa B (NF‐κΒ), and upregulates gap junctions in paclitaxel‐resistant cells. Scratch wound‐healing and Transwell assays showed that ATRA decreases the migration and invasion abilities of paclitaxel‐resistant cells. In addition, the CT26 cell line was used in the Balb/c pulmonary metastasis model to show that ATRA reduces metastasis of paclitaxel‐resistant cells in vivo. Given these data, ATRA may reverse EMT by inhibiting NF‐κΒ and upregulating gap junctions in paclitaxel‐resistant cells.

The Complex Subtype-Dependent Role of Connexin 43 (GJA1) in Breast Cancer

Gap junction transmembrane channels allow the transfer of small molecules between the cytoplasm of adjacent cells. They are formed by proteins named connexins (Cxs) that have long been considered as a tumor suppressor. This widespread view has been challenged by recent studies suggesting that the role of Connexin 43 (Cx43) in cancer is tissue- and stage-specific and can even promote tumor progression. High throughput profiling of invasive breast cancer has allowed for the construction of subtyping schemes that partition patients into at least four distinct intrinsic subtypes. This study characterizes Cx43 expression during cancer progression with each of the tumor subtypes using a compendium of publicly available gene expression data. In particular, we show that Cx43 expression depends greatly on intrinsic subtype. Tumor grade also co-varies with patient subtype, resulting in Cx43 co-expression with grade in a subtype-dependent manner. Better survival was associated with a high expression of Cx43 in unstratified and luminal tumors but with a low expression in Her2e subtype. A better understanding of Cx43 regulation in a subtype-dependent manner is needed to clarify the context in which Cx43 is associated with tumor suppression or cancer progression.

Cx26 drives self-renewal in triple-negative breast cancer via interaction with NANOG and focal adhesion kinase

Tumors adapt their phenotypes during growth and in response to therapies through dynamic changes in cellular processes. Connexin proteins enable such dynamic changes during development, and their dysregulation leads to disease states. The gap junction communication channels formed by connexins have been reported to exhibit tumor-suppressive functions, including in triple-negative breast cancer (TNBC). However, we find that connexin 26 (Cx26) is elevated in self-renewing cancer stem cells (CSCs) and is necessary and sufficient for their maintenance. Cx26 promotes CSC self-renewal by forming a signaling complex with the pluripotency transcription factor NANOG and focal adhesion kinase (FAK), resulting in NANOG stabilization and FAK activation. This FAK/NANOG-containing complex is not formed in mammary epithelial or luminal breast cancer cells. These findings challenge the paradigm that connexins are tumor suppressors in TNBC and reveal a unique function for Cx26 in regulating the core self-renewal signaling that controls CSC maintenance.

Connexin proteins are usually considered as tumor suppressors. Here, the authors show that connexin 26 (Cx26) regulates the self-renewal of breast cancer stem cells via a ternary complex with FAK and NANOG.

Dysregulated connexin 43 in HER2-positive drug resistant breast cancer cells enhances proliferation and migration

Connexin 43 (Cx43) is a gap junction protein whose function in the development of breast cancer and in breast cancer progression remains unclear. Evidence suggests that Cx43 (GJA1) mRNA and protein expression is altered in breast tumors. However, reports indicate both increased and decreased Cx43 levels in human breast cancer samples. Studies also suggest that loss of Cx43 regulated gap junction intercellular communication is a common feature of breast malignancies that potentially correlates with histological stage. Further evidence suggests that Cx43 (GJA1) mRNA expression is negatively correlated with HER2 positivity but a relationship between Cx43 and HER2 in breast cancer is not well defined. Therefore, in this study, we sought to evaluate the relationship between Cx43 activity, HER2, and drug resistance. Using HER2+ breast cancer cell lines that are sensitive or resistant to HER2 inhibitor, we evaluated Cx43 gap junction function. We found that Cx43 gap junction activity is completely lost in drug resistant HER2-positive (HER2+) breast cancer cells, whereas Cx43 gap junction activity can be restored by Cx43 overexpression in drug sensitive HER2+ cells. Moreover, the dysregulation of Cx43 resulted in increased tumorigenic and migratory capacity of the HER2+ drug resistant breast cancer cells.

Mind the Gaps in Tumor Immunity: Impact of Connexin-Mediated Intercellular Connections

Gap junctions (GJs)-mediated intercellular communications (GJICs) are connexin (Cx)-formed plasma membrane channels that allow for the passage of small molecules between adjacent cells, and are involved in several physiopathological processes, including immune responses against cancer. In general, tumor cells are poorly coupled through GJs, mainly due to low Cx expression or reduced channel activity, suggesting that Cxs may have tumor suppressor roles. However, more recent data indicate that Cxs and/or GJICs may also in some cases promote tumor progression. This dual role of Cx channels in tumor outcome may be due, at least partially, to the fact that GJs not only interconnect cells from the same type, such as cancer cells, but also promote the intercellular communication of tumor cells with different types of cells from their microenvironment, and such diverse intercellular interactions have distinctive impact on tumor development. For example, whereas GJ-mediated interactions among tumor cells and microglia have been implicated in promotion of tumor growth, tumor cells delivery to dendritic cells of antigenic peptides through GJs have been associated with enhanced immune-mediated tumor elimination. In this review, we provide an updated overview on the role of GJICs in tumor immunity, focusing on the pro-tumor and antitumor effect of GJs occurring among tumor and immune cells. Accumulated data suggest that GJICs may act as tumor suppressors or enhancers depending on whether tumor cells interact predominantly with antitumor immune cells or with stromal cells. The complex modulation of immune-tumor cell GJICs should be taken into consideration in order to potentiate current cancer immunotherapies.

Connexin 43 in the development and progression of breast cancer: What's the connection? (Review)

Connexin 43 is a prominent gap junction protein within normal human breast tissue. Thus far, there have been a number of research studies performed to determine the function of connexin 43 in breast tumor formation and progression. Within primary tumors, research suggests that the level of connexin 43 expression in breast tumors is altered when compared to normal human breast tissue. While some reports indicate that connexin 43 levels decrease, other evidence suggests that connexin 43 levels are increased and protein localization shifts from the plasma membrane to the cytoplasm. In either case, the prevailing theory is that breast tumor cells have reduced gap junction intercellular communication within primary tumors. The current consensus appears to be that the loss of connexin 43 gap junction intercellular communication is an early event in malignancy, with the possibility of gap junction restoration in the event of metastasis. However, additional evidence is needed to support the latter claim. The purpose of this report is to review the connexin 43 literature that describes studies using human tissue samples, in order to evaluate the function of connexin 43 protein in normal human breast tissue as well as the role of connexin 43 in human breast tumor formation and metastatic progression.

Distinctive actions of connexin 46 and connexin 50 in anterior pituitary folliculostellate cells

Folliculostellate cell gap junctions establish a network for the transmission of information within the anterior pituitary. Connexins make up gap junction channels. Changes in connexin (Cx) turnover modify gap junction-mediated intercellular communication. We have reported that cytokines and hormones influence Cx43 turnover and coupling in folliculostellate cells and in the folliculostellate cell line TtT/GF. In addition, the expression of different connexins alters intercellular communication and connexins may have functions besides cell coupling. Here we assessed the expression, turnover and subcellular localization of Cx46 and Cx50 in the anterior pituitary and TtT/GF cells. Then, we assessed the impact of various natural (lactation, annual reproductive cycle, bFGF) and pathological (autoimmune orchitis, diabetes/obesity) conditions associated with altered anterior pituitary hormone secretion on Cx46 and Cx50. Anterior pituitary Cx46 and Cx50 expression and subcellular distribution were cell-dependent. Cx46 was expressed by folliculostellate, TtT/GF and endocrine cells. In the cytoplasm, Cx46 was chiefly associated with lysosomes. Variously sized Cx46 molecules were recovered exclusively in the TtT/GF cell nuclear fraction. In the nucleus, Cx46 co-localized with Nopp-140, a nucleolar factor involved in rRNA processing. Neither cytoplasmic nor nuclear Cx46 and Cx43 co-localized. Cx50 localized to folliculostellate and TtT/GF cells, and to the walls of blood capillaries, not to endocrine cells. Cx50 was cytoplasmic and associated with the cell membrane, not nuclear. Cx50 did not co-localize with Cx46 but it co-localized in the cytoplasm and co-immunoprecipitated with Cx43. Cx46 and Cx50 responses to various physiological and pathological challenges were different, often opposite. Cx46 and Cx43 expression and phosphorylation profiles differed in the anterior pituitary, whereas Cx50 and Cx43 were similar. The data suggest that Cx46 participates to cellular growth and proliferation and that Cx50, together with Cx43, contributes to folliculostellate cell coupling.

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.

Gap junctions and cancer: communicating for 50 years

Fifty years ago, tumour cells were found to lack electrical coupling, leading to the hypothesis that loss of direct intercellular communication is commonly associated with cancer onset and progression. Subsequent studies linked this phenomenon to gap junctions composed of connexin proteins. Although many studies support the notion that connexins are tumour suppressors, recent evidence suggests that, in some tumour types, they may facilitate specific stages of tumour progression through both junctional and non-junctional signalling pathways. This Timeline article highlights the milestones connecting gap junctions to cancer, and underscores important unanswered questions, controversies and therapeutic opportunities in the field.

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.

Connexin and pannexin channels in cancer

Communication among cells via direct cell-cell contact by connexin gap junctions, or between cell and extracellular environment via pannexin channels or connexin hemichannels, is a key factor in cell function and tissue homeostasis. Upon malignant transformation in different cancer types, the dysregulation of these connexin and pannexin channels and their effect in cellular communication, can either enhance or suppress tumorigenesis and metastasis. In this review, we will highlight the latest reports on the role of the well characterized connexin family and its ability to form gap junctions and hemichannels in cancer. We will also introduce the more recently discovered family of pannexin channels and our current knowledge about their involvement in cancer progression.

Association of STAT3 with Cx26 and Cx43 in human uterine endometrioid adenocarcinoma

Signal transducer and activator of transcription-3 (STAT3) drives endometrial carcinogenesis, while signaling via gap junctions gets weakened during cancer progression. Connexin 26 (Cx26), Cx43 and STAT3 were immunohistochemically evaluated in 78 endometrioid adenocarcinomas: Nuclear expression of STAT3 positively correlated with cytoplasmic immunoreactivity to Cx43 (P=0.004, r=0.318) and Cx26 (P=0.006, r=0.309). STAT3 correlated with Cx43 (P=0.022, r=0.411) and Cx26 (P=0.008 r=0.466) in G1 tumors. A statistically significant linkage remained in G2 cancers between STAT3 and Cx43 (P=0.061, r=0.262) and Cx26 (P=0.016, r=0.331); however, no correlations were observed in G3 tumors. STAT3 was significantly associated with Cx 43 (p=0.003, r=0.684) and Cx26 (p=0.049, r=0.500) in estrogen receptor (ER) negative adenocarcinomas. STAT3 did not correlate with Cx43 in ER positive adenocarcinomas; however, STAT3 expression remained correlated with Cx26 expression (P=0.035, r=0.268). In progesterone receptor negative tumors STAT3 was significantly associated with Cx43 (P=0.035, r=0.451) and Cx26 (P<0.0001, r=0.707). However, in PgR positive adenocarcinomas STAT3 correlated with Cx43 (P=0.03, r=0.290) but not with Cx26. Thus, it appears that hormone dependent acceleration of cancer growth breaks the association between STAT3 and Cx expression. These associations become weaker as the tumors dedifferentiate from G1 to G3 endometrioid adenocarcinomas. The present study provides evidence that the loss of correlation between STAT3 and selected Cx proteins occurs in tumors with more aggressive behavior.

Critical role of gap junction communication, calcium and nitric oxide signaling in bystander responses to focal photodynamic injury

Ionizing and nonionizing radiation affect not only directly targeted cells but also surrounding “bystander” cells. The underlying mechanisms and therapeutic role of bystander responses remain incompletely defined. Here we show that photosentizer activation in a single cell triggers apoptosis in bystander cancer cells, which are electrically coupled by gap junction channels and support the propagation of a Ca²⁺ wave initiated in the irradiated cell. The latter also acts as source of nitric oxide (NO) that diffuses to bystander cells, in which NO levels are further increased by a mechanism compatible with Ca²⁺-dependent enzymatic production. We detected similar signals in tumors grown in dorsal skinfold chambers applied to live mice. Pharmacological blockade of connexin channels significantly reduced the extent of apoptosis in bystander cells, consistent with a critical role played by intercellular communication, Ca²⁺ and NO in the bystander effects triggered by photodynamic therapy.

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.

Radiological and Pathological Predictors of Response to Neoadjuvant Chemotherapy in Breast Cancer: A Brief Literature Review

BACKGROUND

Early clinical response to neoadjuvant chemotherapy (NACT) in breast cancer correlates with pathological response at surgery. A tailored approach using biomarkers to predict response to NACT has become a research priority. Predictors of response can be divided into pathological and radiological biomarkers. Advances in gene expression profiling and diffusion-weighted MRI techniques are used to predict tumour response, and combinations thereof are the future of predicting response to NACT in early-stage breast cancer.

METHODS

We searched Medline, CINAHL and Embase databases for studies on NACT. Key words used were NACT, breast cancer, pathological* complete response, primary chemotherapy, radiological*, predictor*, gene expression and biomarkers limited to the English language. Pathological markers such as tumour subtypes, topoisomerase IIα expression, Ki67, apoptosis-related markers and gene expression profiling were included.

RESULTS

From 119 articles, 42 studies were reviewed; the majority of studies identified used pathological clinical response as an end point to NACT, whilst others used complete clinical response. Despite extensive studies, results regarding long-term survival following NACT and potential predictors are inconclusive.

CONCLUSION

Future development of a predictive model combining key pathological and radiological biomarkers could provide personalised treatment regimens that improve pathological complete response rates and longer-term outcomes.

Targeting connexin 43 with α-connexin carboxyl-terminal (ACT1) peptide enhances the activity of the targeted inhibitors, tamoxifen and lapatinib, in breast cancer: clinical implication for ACT1

BACKGROUND

Treatment failure is a critical issue in breast cancer and identifying useful interventions that optimize current cancer therapies remains a critical unmet need. Expression and functional studies have identified connexins (Cxs), a family of gap junction proteins, as potential tumor suppressors. Studies suggest that Cx43 has a role in breast cancer cell proliferation, differentiation, and migration. Although pan-gap junction drugs are available, the lack of specificity of these agents increases the opportunity for off target effects. Consequently, a therapeutic agent that specifically modulates Cx43 would be beneficial and has not been tested in breast cancer. In this study, we now test an agent that specifically targets Cx43, called ACT1, in breast cancer.

METHODS

We evaluated whether direct modulation of Cx43 using a Cx43-directed therapeutic peptide, called ACT1, enhances Cx43 gap junctional activity in breast cancer cells, impairs breast cancer cell proliferation or survival, and enhances the activity of the targeted inhibitors tamoxifen and lapatinib.

RESULTS

Our results show that therapeutic modulation of Cx43 by ACT1 maintains Cx43 at gap junction sites between cell-cell membrane borders of breast cancer cells and augments gap junction activity in functional assays. The increase in Cx43 gap junctional activity achieved by ACT1 treatment impairs proliferation or survival of breast cancer cells but ACT1 has no effect on non-transformed MCF10A cells. Furthermore, treating ER+ breast cancer cells with a combination of ACT1 and tamoxifen or HER2+ breast cancer cells with ACT1 and lapatinib augments the activity of these targeted inhibitors.

CONCLUSIONS

Based on our findings, we conclude that modulation of Cx43 activity in breast cancer can be effectively achieved with the agent ACT1 to sustain Cx43-mediated gap junctional activity resulting in impaired malignant progression and enhanced activity of lapatinib and tamoxifen, implicating ACT1 as part of a combination regimen in breast cancer.

Eventual proapoptotic or anti-apoptotic impact of aberrantly expressed Cx43 and Cx26 can depend on ER-alpha overexpression in human endometrioid adenocarcinoma

Estrogen receptor (ER) and progesterone receptor (PgR) accumulations lead to impairment of gap junctional intercellular communication in endometrial cancer. The task of this study was to explore relationships of Cx26 and Cx43 with anti-apoptotic protein Bcl-xL and proapoptotic agent Bak in ER-alpha and PgR negative or variably positive endometrioid adenocarcinomas. Cx26, Cx43, Bak, Bcl-xL, PgR and ER-alpha were detected in 78 endometrioid adenocarcinomas with immunohistochemistry. There was a remarkable cellular re-distribution of Cx26 and Cx43 from normally membranous location in normal endometrium to aberrantly cytoplasmic expression in endometrioid adenocarcinomas, thus suggesting the decrease of functional membranous gap junctions in the malignancy. Bak failed to correlate with Cx43 regardless of either PgR or ER-alpha status of tumors, while Bcl-xL positively correlated with Cx43 in ER-alpha positive tumors (p = 0.001, r = 0.427) and both PgR positive (p = 0.019, r = 0.312) and negative (p = 0.015, r = 0.509) cancers. Similarly, Bcl-xL significantly associated with Cx26 in ER-alpha positive tumors (p = 0.036, r = 0.267) and both PgR positive (p = 0.026, r = 0.297) and negative (p = 0.046, r = 0.429) cancers. On the contrary, Bak exclusively correlated with Cx26 only in ER-alpha negative tumors (p = 0.027, r = 0.551). ER-alpha status of endometrioid adenocarcinomas could restrict eventual proapoptotic or anti-apoptotic impact of aberrantly expressed Cx43 and Cx26 in these tumors.

Correlations of differentially expressed gap junction connexins Cx26, Cx30, Cx32, Cx43 and Cx46 with breast cancer progression and prognosis

BACKGROUND AND AIMS

Connexins and their cell membrane channels contribute to the control of cell proliferation and compartmental functions in breast glands and their deregulation is linked to breast carcinogenesis. Our aim was to correlate connexin expression with tumor progression and prognosis in primary breast cancers.

MATERIALS AND METHODS

Meta-analysis of connexin isotype expression data of 1809 and 1899 breast cancers from the Affymetrix and Illumina array platforms, respectively, was performed. Expressed connexins were also monitored at the protein level in tissue microarrays of 127 patients equally representing all tumor grades, using immunofluorescence and multilayer, multichannel digital microscopy. Prognostic correlations were plotted in Kaplan-Meier curves and tested using the log-rank test and cox-regression analysis in univariate and multivariate models.

RESULTS

The expression of GJA1/Cx43, GJA3/Cx46 and GJB2/Cx26 and, for the first time, GJA6/Cx30 and GJB1/Cx32 was revealed both in normal human mammary glands and breast carcinomas. Within their subfamilies these connexins can form homo- and heterocellular epithelial channels. In cancer, the array datasets cross-validated each other's prognostic results. In line with the significant correlations found at mRNA level, elevated Cx43 protein levels were linked with significantly improved breast cancer outcome, offering Cx43 protein detection as an independent prognostic marker stronger than vascular invasion or necrosis. As a contrary, elevated Cx30 mRNA and protein levels were associated with a reduced disease outcome offering Cx30 protein detection as an independent prognostic marker outperforming mitotic index and necrosis. Elevated versus low Cx43 protein levels allowed the stratification of grade 2 tumors into good and poor relapse free survival subgroups, respectively. Also, elevated versus low Cx30 levels stratified grade 3 patients into poor and good overall survival subgroups, respectively.

CONCLUSION

Differential expression of Cx43 and Cx30 may serve as potential positive and negative prognostic markers, respectively, for a clinically relevant stratification of breast cancers.

Significant association of combination of OCT4, NANOG, and SOX2 gene polymorphisms in susceptibility and response to treatment in North Indian breast cancer patients

PURPOSE

Dysregulations of regulatory genes in embryonic stem cells (ESCs) gene polymorphisms may lead to breast cancer cell growth, differentiation, and tumor metastasis.

METHODS

Polymorphisms in OCT4 (rs3130932), NANOG (rs11055786), LIN28 (rs4274112), and SOX2 (rs11915160) genes were evaluated for susceptibility in 297 breast cancer females and 273 healthy controls from north Indian population. Response to neo-adjuvant chemotherapy was followed in 128 locally advanced breast cancer patients along with clinicopathological features. Genotyping was done using TaqMan allelic discrimination assays. Statistical analysis was performed using SPSS and multifactor dimensionality reduction (MDR).

RESULTS

For OCT4 gene polymorphism, protective effect of genotypes AC [P corr = 0.031, OR = 0.63 (0.44-0.91)] and AC+CC [P corr = 0.031, OR = 0.68 (0.48-0.95)] was seen in patients. However, no association of NANOG, LIN28, and SOX2 gene polymorphisms was found with overall breast cancer susceptibility. Further, significant association of AG+GG genotype [P corr = 0.021, OR = 6.08 (1.83-20.15)] and G allele [P corr = 0.021, OR = 3.07 (1.21-7.77)] of rs4274112 polymorphism was seen with positive lymph node. For OCT4, significant association of allele C was seen with patients having negative hormone receptor [P corr = 0.021, OR = 0.51 (0.29-0.90)], but no association of any of the studied polymorphisms individually was found with response to NACT. On MDR analysis, we found combination of SNPs SOX2 rs11915160, OCT4 rs3130932, and NANOG rs11055786 to be the best interaction model for predicting breast cancer risk [p for permutation test <10(-3), OR = 2.04 (1.43-2.910] and response to NACT [p for permutation test = 0.005, OR = 2.09 (1.24-3.52)].

CONCLUSION

Combination of genetic variants of ESCs gene may have a profound effect in breast cancer risk and response to NACT.

Possible role of hemichannels in cancer

In humans, connexins (Cxs) and pannexins (Panxs) are the building blocks of hemichannels. These proteins are frequently altered in neoplastic cells and have traditionally been considered as tumor suppressors. Alteration of Cxs and Panxs in cancer cells can be due to genetic, epigenetic and post-transcriptional/post-translational events. Activated hemichannels mediate the diffusional membrane transport of ions and small signaling molecules. In the last decade hemichannels have been shown to participate in diverse cell processes including the modulation of cell proliferation and survival. However, their possible role in tumor growth and expansion remains largely unexplored. Herein, we hypothesize about the possible role of hemichannels in carcinogenesis and tumor progression. To support this theory, we summarize the evidence regarding the involvement of hemichannels in cell proliferation and migration, as well as their possible role in the anti-tumor immune responses. In addition, we discuss the evidence linking hemichannels with cancer in diverse models and comment on the current technical limitations for their study.

Stability and prognostic value of Slug, Sox9 and Sox10 expression in breast cancers treated with neoadjuvant chemotherapy

BACKGROUND

Expression of transcription-factors as Slug and Sox9 was recently described to determine mammary stem-cell state. Sox10 was previously shown to be present also in breast cancer. Protein overexpression of Slug, Sox9 and Sox10 were associated with poor overall survival and with triple-negative phenotype in breast cancer. In this study we tested the stability of Slug, Sox9 and Sox10 expression during chemotherapy and addressed their prognostic role of in neoadjuvant treated primary breast-cancer and their correlation to pathological-response and overall survival.

METHODS

We analyzed immunohistochemical expression of Slug, Sox9 and Sox10 in tissue microarrays of 96 breast cancers prior to and after neoadjuvant chemotherapy. Expression was evaluated in invasive tumor cells and in tumor stroma and scored as 0, 1+, 2+ 3+. Expression-profile prior to and after chemotherapy was correlated to overall survival (Kaplan Meier) and with established clinico-pathological parameter.

RESULTS

Sox9, Sox10 and Slug were expressed in 82-96% of the tumor cells prior to chemotherapy. Slug was expressed in 97% of the cases in tumor stroma before therapy. Change in expression-profile after chemotherapy occurred only in Slug expression in tumor-cells (decreased from 82 to 51%, p = 0.0001, Fisher's exact test). The other markers showed no significant change after chemotherapy. Stromal Sox9 expression (0 to 2+) correlated to better overall survival after chemotherapy (p = 0.004) and reached almost statistical significance prior to chemotherapy (p = 0.065). There was no correlation between Sox9 and hormone-receptor expression. In multivariate-analysis, the stromal Sox9 expression after chemotherapy proved to be an independent and better prognostic marker than hormone-receptor status. Other clinico-pathological parameter (as HER2-status or pathological-stage) showed no correlation to the analyzed markers.

CONCLUSION

Strong stromal Sox9 expression in breast cancer after chemotherapy was found to bear negative prognostic information and was associated with shortened overall survival. Slug expression was significantly changed (reduced) in samples after neoadjuvant chemotherapy.