Diversity of Intercellular Communication Modes: A Cancer Biology Perspective.

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Cell Death, by Any Other Name .

Studies trying to understand cell death, this ultimate biological process, can be traced back to a century ago. Yet, unlike many other fashionable research interests, research on cell death is more alive than ever. New modes of cell death are discovered in specific contexts, as are new molecular pathways. But what is "cell death", really? This question has not found a definitive answer yet. Nevertheless, part of the answer is irreversibility, whereby cells can no longer recover from stress or injury. Here, we identify the most distinctive features of different modes of cell death, focusing on the executive final stages. In addition to the final stages, these modes can differ in their triggering stimulus, thus referring to the initial stages. Within this framework, we use a few illustrative examples to examine how intercellular communication factors in the demise of cells. First, we discuss the interplay between cell-cell communication and cell death during a few steps in the early development of multicellular organisms. Next, we will discuss this interplay in a fully developed and functional tissue, the gut, which is among the most rapidly renewing tissues in the body and, therefore, makes extensive use of cell death. Furthermore, we will discuss how the balance between cell death and communication is modified during a pathological condition, i.e., colon tumorigenesis, and how it could shed light on resistance to cancer therapy. Finally, we briefly review data on the role of cell-cell communication modes in the propagation of cell death signals and how this has been considered as a potential therapeutic approach. Far from vainly trying to provide a comprehensive review, we launch an invitation to ponder over the significance of cell death diversity and how it provides multiple opportunities for the contribution of various modes of intercellular communication.

The Value of EphB2 Receptor and Cognate Ephrin Ligands in Prognostic and Predictive Assessments of Human Breast Cancer.

Cell-cell communication proteins Eph and ephrin constitute the largest family of receptor tyrosine kinases (RTKs). They are distinguished by the fact that both receptors and ligands are membrane-bound, and both can drive intracellular signaling in their respective cells. Ever since these RTKs have been found to be involved in cancer development, strategies to target them therapeutically have been actively pursued. However, before this goal can be rationally achieved, the contributions of either Eph receptors or their ephrin ligands to cancer development and progression should be scrutinized in depth. To assess the clinical pertinence of this concern, we performed a systematic review and meta-analysis of the prognostic/predictive value of EphB2 and its multiple cognate ephrin ligands in breast cancer. We found that EphB2 has prognostic value, as indicated by the association of higher EphB2 expression levels with lower distant metastasis-free survival (DMFS), and the association of lower EphB2 expression levels with poorer relapse-free survival (RFS). We also found that higher EphB2 expression could be a prognostic factor for distant metastasis, specifically in the luminal subtypes of breast cancer. EFNB2 showed a marked correlation between higher expression levels and shorter DMFS. EFNA5 or EFNB1 overexpression is correlated with longer RFS. Increased EFNB1 expression is correlated with longer OS in lymph node (LN)-negative patients and the luminal B subtype. Higher levels of EFNB2 or EFNA5 are significantly correlated with shorter RFS, regardless of LN status. However, while this correlation with shorter RFS is true for EFNB2 in all subtypes except basal, it is also true for EFNA5 in all subtypes except HER2+. The analysis also points to possible predictive value for EphB2. In systemically treated patients who have undergone either endocrine therapy or chemotherapy, we found that higher expression of EphB2 is correlated with better rates of RFS. Bearing in mind the limitations inherent to any mRNA-based profiling method, we complemented our analysis with an immunohistochemical assessment of expression levels of both the EphB2 receptor and cognate ephrin ligands. We found that the latter are significantly more expressed in cancers than in normal tissues, and even more so in invasive and metastatic samples than in ductal carcinoma in situ (DCIS). Finally, in an in vitro cellular model of breast cancer progression, based on H-Ras-transformation of the MCF10A benign mammary cell line, we observed dramatic increases in the mRNA expression of EphB2 receptor and EFNB1 and EFNB2 ligands in transformed and invasive cells in comparison with their benign counterparts. Taken together, these data show the clinical validity of a model whereby EphB2, along with its cognate ephrin ligands, have dual anti- and pro-tumor progression effects. In so doing, they reinforce the necessity of further biological investigations into Ephs and ephrins, prior to using them in targeted therapies.

Senolytic activity of small molecular polyphenols from olive restores chondrocyte redifferentiation and promotes a pro-regenerative environment in osteoarthritis.

Articular cartilage and synovial tissue from patients with osteoarthritis (OA) show an overactivity of connexin43 (Cx43) and accumulation of senescent cells associated with disrupted tissue regeneration and disease progression. The aim of this study was to determine the effect of oleuropein on Cx43 and cellular senescence for tissue engineering and regenerative medicine strategies for OA treatment. Oleuropein regulates Cx43 promoter activity and enhances the propensity of hMSCs to differentiate into chondrocytes and bone cells, reducing adipogenesis. This small molecule reduce Cx43 levels and decrease Twist-1 activity in osteoarthritic chondrocytes (OACs), leading to redifferentiation, restoring the synthesis of cartilage ECM components (Col2A1 and proteoglycans), and reducing the inflammatory and catabolic factors mediated by NF-kB (IL-1ß, IL-6, COX-2 and MMP-3), in addition to lowering cellular senescence in OACs, synovial and bone cells. Our in vitro results demonstrate the use of olive-derived polyphenols, such as oleuropein, as potentially effective therapeutic agents to improve chondrogenesis of hMSCs, to induce chondrocyte re-differentiation in OACs and clearing out senescent cells in joint tissues in order to prevent or stop the progression of the disease.

Isolation and characterization of a CD34+ sub-clone in B-cell lymphoma.

Non-Hodgkin's lymphoma (NHL) is the most common hematological malignancy in the US. Many types remain incurable despite response to initial therapy and achievement of complete remission (CR). Advanced laboratory techniques like multicolor flow cytometry (FCM) and polymerase chain reaction (PCR) have demonstrated persistence of rare malignant cell population post therapy. However, the functional and biological characteristics of this population have not been elucidated. Established B-lymphoma cell lines (B-NHL) and patient-derived samples (PDS) were analyzed using 8-color FCM. CD34+ sub-population was enriched using in vitro exposure to 2-chlorodeoxyadenosine (2-CdA) and by CD34 magnetic beads. Genetic analysis of cell fractions was done by karyotyping and array comparative genomic hybridization (aCGH). Sensitivity to chemotherapy was assayed by short-term in vitro exposure to chemotherapy. Clonogenicity was determined by soft agar colony formation assay, and proliferation was determined using DNA staining with propidium iodide and FCM. FCM demonstrated the presence of a minute sub-clone of monotypic B-cells that express CD34 in B-NHL cell lines (3 of 3) and in PDS (8 of 8). This sub-population enriched up to 50 fold in vitro by exposure to 2-CdA and up to 80% purity by CD34 magnetic bead column isolation. Except for CD34 expression, this population expressed identical phenotype and genotype to parent cells, but was more proliferative, Hoechst 33342-positive, clonogenic, and resistant to chemotherapy compared with the CD34- population. The isolated CD34+ monotypic B-cells may contribute to resistance of certain NHL to treatment and should be targeted by potential new drugs for NHL.

Targeting of chondrocyte plasticity via connexin43 modulation attenuates cellular senescence and fosters a pro-regenerative environment in osteoarthritis.

Osteoarthritis (OA), a chronic disease characterized by articular cartilage degeneration, is a leading cause of disability and pain worldwide. In OA, chondrocytes in cartilage undergo phenotypic changes and senescence, restricting cartilage regeneration and favouring disease progression. Similar to other wound-healing disorders, chondrocytes from OA patients show a chronic increase in the gap junction channel protein connexin43 (Cx43), which regulates signal transduction through the exchange of elements or recruitment/release of signalling factors. Although immature or stem-like cells are present in cartilage from OA patients, their origin and role in disease progression are unknown. In this study, we found that Cx43 acts as a positive regulator of chondrocyte-mesenchymal transition. Overactive Cx43 largely maintains the immature phenotype by increasing nuclear translocation of Twist-1 and tissue remodelling and proinflammatory agents, such as MMPs and IL-1ß, which in turn cause cellular senescence through upregulation of p53, p16INK4a and NF-κB, contributing to the senescence-associated secretory phenotype (SASP). Downregulation of either Cx43 by CRISPR/Cas9 or Cx43-mediated gap junctional intercellular communication (GJIC) by carbenoxolone treatment triggered rediferentiation of osteoarthritic chondrocytes into a more differentiated state, associated with decreased synthesis of MMPs and proinflammatory factors, and reduced senescence. We have identified causal Cx43-sensitive circuit in chondrocytes that regulates dedifferentiation, redifferentiation and senescence. We propose that chondrocytes undergo chondrocyte-mesenchymal transition where increased Cx43-mediated GJIC during OA facilitates Twist-1 nuclear translocation as a novel mechanism involved in OA progression. These findings support the use of Cx43 as an appropriate therapeutic target to halt OA progression and to promote cartilage regeneration.

Correction to: Dying to communicate: apoptotic functions of Eph/Ephrin proteins.

The original version of this article contained a mistake in reference. The references in Table 1 are incorrect. The corrected Table with proper citation is given below. The field codes ADDIN REFMGR.CITE inadvertently appeared along the article. This was overlooked during the process.

Dying to communicate: apoptotic functions of Eph/Ephrin proteins.

The Erythropoietin-producing human hepatocellular carcinoma (Eph) receptors constitute the largest family of receptor tyrosine kinases and interact with a group of ligands called Ephrins. An essential feature of the Eph receptors and Ephrin ligands is that both are membrane-bound and, upon cell-cell interaction, initiate a bidirectional signaling involving both the receptor (forward signaling) and the ligand (reverse signaling). They regulate a large set of pleiotropic functions in virtually every tissue and physiological system. In vitro as well as in vivo data support a role for Eph and Ephrin molecules in cellular processes such as proliferation, cell-cell attraction and repulsion, motility and sorting. An increasing amount of evidence supports a role for these molecules in apoptosis and, although this function in cell death has been barely examined, the available information warrants a global consideration, to identify unmet needs and potential research avenues. Here we propose a comprehensive analysis of the data available regarding the importance of Ephs and Ephrins in cell death mechanisms throughout a large array of physiological systems.

Unintended target effect of anti-BCL-2 DNAi.

INTRODUCTION: Previous research suggested that a novel compound PNT2258 inhibits B-cell lymphoma 2 (BCL-2) transcription by DNA interference (DNAi) and demonstrated its activity in preclinical xenograft models and in a pilot Phase II clinical trial in non-Hodgkin's lymphoma (NHL). While the drug downregulates BCL-2 at the promoter, mRNA, and protein levels, there is a significant homology (13-16 bases) between PNT100 and a number of promoters of genes involved in cell cycle regulation and survival. In this study, we identify cyclin-dependent kinase-4 (CDK4) as an unintended target gene of PNT2258 and examine its relevance to NHL. METHODS: We performed a Basic Local Alignment Search Tool (BLAST) homology search using PNT100 DNAi sequences. Also, we conducted CDK4 promoter assay in K562 cells and studied the protein expression of CDK4 in Wayne State University (WSU)-follicular small cleaved cell lymphoma (FSCCL), WSU-diffuse large cell lymphoma, and WSU-Waldenström's macroglobulinemia (WM) lymphoma cells. RESULTS: BLAST homology search showed that PNT100 completely binds to BCL-2 gene as expected. However, there was 100% homology in a stretch of 14 bases (8-21) between PNT100 and CDK4. PNT2258 strongly inhibited CDK4 promoter activity in K562 cells. Moreover, CDK4 protein expression was significantly downregulated by PNT2258 in WSU-FSCCL and WSU-WM cell lines. DISCUSSION: DNAi may work not only through knocking down the intended gene but also by knocking down other genes. PNT2258 affects CDK4 expression and promoter activity. Results of the present study suggest a broader mechanism of action for DNAi targeting both intended (BCL-2) and unintended (CDK4) genes.

TGF-ß/SMAD3 Pathway Stimulates Sphingosine-1 Phosphate Receptor 3 Expression: IMPLICATION OF SPHINGOSINE-1 PHOSPHATE RECEPTOR 3 IN LUNG ADENOCARCINOMA PROGRESSION.

Previously, we showed that levels of sphingosine-1 phosphate receptor 3 (S1PR3) are increased in a panel of cultured human lung adenocarcinoma cell lines, and that S1PR3-mediated signaling pathways regulate proliferation, soft agar growth, and invasion of human lung adenocarcinoma cells in vitro In the present study, we examine S1PR3 levels in human lung adenocarcinoma specimens. cDNA array and tumor microarray analysis shows that mRNA and protein levels of S1PR3 are significantly increased in human lung adenocarcinomas when compared with normal lung epithelial cells. Promoter analysis shows 16 candidate SMAD3 binding sites in the promoter region of S1PR3. ChIP indicates that TGF-ß treatment stimulates the binding of SMAD3 to the promoter region of S1PR3. Luciferase reporter assay demonstrates that SMAD3 transactivates S1PR3 promoter. TGF-ß stimulation or ectopic expression of TGF-ß up-regulates S1PR3 levels in vitro and ex vivo Pharmacologic inhibition of TGF-ß receptor or SMAD3 abrogates the TGF-ß-stimulated S1PR3 up-regulation. Moreover, S1PR3 knockdown dramatically inhibits tumor growth and lung metastasis, whereas ectopic expression of S1PR3 promotes the growth of human lung adenocarcinoma cells in animals. Pharmacological inhibition of S1PR3 profoundly inhibits the growth of lung carcinoma in mice. Our studies suggest that levels of S1PR3 are up-regulated in human lung adenocarcinomas, at least in part due to the TGF-ß/SMAD3 signaling axis. Furthermore, S1PR3 activity promotes the progression of human lung adenocarcinomas. Therefore, S1PR3 may represent a novel therapeutic target for the treatment of deadly lung adenocarcinomas.

Spatio-temporal regulation of EGFR signaling by the Eps15 homology domain-containing protein 3 (EHD3).

The epidermal growth factor (EGF) receptor EGFR is a major receptor tyrosine kinase whose role in gliomagenesis is well established. We have recently identified EHD3 [Eps15 homology (EH) domain-containing protein 3], an endocytic trafficking regulatory protein, as a putative brain tumor suppressor. Here, we investigate the underlying mechanisms, by establishing a novel mechanistic and functional connection between EHD3 and the EGFR signaling pathway. We show that, in response to stimulation with the EGF ligand, EHD3 accelerates the rate of EGFR degradation by dramatically increasing its ubiquitination. As part of this process, EHD3 also regulates EGFR endosomal trafficking by diverting it away from the recycling route into the degradative pathway. Moreover, we found that upon EGF activation, rather than affecting the total MAPK and AKT downstream signaling, EHD3 decreases endosome-based signaling of these two pathways, thus suggesting the contribution of EHD3 in the spatial regulation of EGFR signaling. This function explains the higher sensitivity of EHD3-expressing cells to the growth-inhibitory effects of EGF. In summary, this is the first report supporting a mechanism of EHD3-mediated tumor suppression that involves the attenuation of endosomal signaling of the EGFR oncogene.

PNT2258, a novel deoxyribonucleic acid inhibitor, induces cell cycle arrest and apoptosis via a distinct mechanism of action: a new class of drug for non-Hodgkin's lymphoma.

Current therapy for BCL-2-associated tumors such as Non-Hodgkin Lymphomas (NHL) is inadequate. The DNAi PNT2258, a 24 base single-stranded phosphodiester DNA oligodeoxynucleotide (PNT100) encapsulated in a protective liposome, was precisely designed to treat cancers that over-express BCL-2. PNT2258 strongly inhibited BCL-2 promoter activity, confirming its predicted mechanism of action. BCL-2 mRNA and protein expression were significantly downregulated in a follicular small cleaved cell lymphoma (WSU-FSCCL) cell line. 2.5µM PNT2258 induced an initial S- phase arrest followed by a gradual increase in the sub-G0 (apoptosis) compartment and a reciprocal progressive decrease of the S phase. Terminal deoxynucleotidyl transferase (TdT)-positive populations and cleaved caspase-3 and PARP were also increased. The data are consistent with the idea that BCL-2 inhibition by PNT2258 activates apoptotic pathways in WSU-FSCCL cells. This is the first report to address the distinct mechanism of action underlying the anti-BCL-2 functions of PNT2258. Growth inhibition in two other cell lines, WSU-DLCL2 and WSU-WM, supports broad applicability of BCL-2 DNAi to treatment of B-cell NHL.

Hematologic malignancies: newer strategies to counter the BCL-2 protein.

INTRODUCTION: BCL-2 is the founding member of the BCL-2 family of apoptosis regulatory proteins that either induce (pro-apoptotic) or inhibit (anti-apoptotic) apoptosis. The anti-apoptotic BCL-2 is classified as an oncogene, as damage to the BCL-2 gene has been shown to cause a number of cancers, including lymphoma. Ongoing research has demonstrated that disruption of BCL-2 leads to cell death. BCL-2 is also known to be involved in the development of resistance to chemotherapeutic agents, further underscoring the importance of targeting the BCL-2 gene in cancer therapeutics. Thus, numerous approaches have been developed to block or modulate the production of BCL-2 at the RNA level using antisense oligonucleotides or at the protein level with BCL-2 inhibitors, such as the novel ABT737. METHODS: In this article, we briefly review previous strategies to target the BCL-2 gene and focus on a new approach to silence DNA, DNA interference (DNAi). RESULTS AND CONCLUSION: DNA interference is aimed at blocking BCL-2 gene transcription. Evaluations of this technology in preclinical and early clinical studies are very encouraging and strongly support further development of DNAi as cancer therapeutics. A pilot phase II clinical trial in patients with relapsed or refractory non-Hodgkin lymphoma, PNT2258 demonstrated clinical benefit in 11 of 13 patients with notable responses in diffuse large B cell lymphoma and follicular lymphoma. By targeting the DNA directly, the DNAi technology promises to be more effective compared with other gene-interference strategies that target the RNA or protein but leaves the dysregulated DNA functional.

Role of the EphB2 receptor in autophagy, apoptosis and invasion in human breast cancer cells.

The Eph and Ephrin proteins, which constitute the largest family of receptor tyrosine kinases, are involved in normal tissue development and cancer progression. Here, we examined the expression and role of the B-type Eph receptor EphB2 in breast cancers. By immunohistochemistry using a progression tissue microarray of human clinical samples, we found EphB2 to be expressed in benign tissues, but strongly increased in cancers particularly in invasive and metastatic carcinomas. Subsequently, we found evidence that EphB2, whose expression varies in established cell breast lines, possesses multiple functions. First, the use of a DOX-inducible system to restore EphB2 function to low expressers resulted in decreased tumor growth in vitro and in vivo, while its siRNA-mediated silencing in high expressers increased growth. This function involves the onset of apoptotic death paralleled by caspases 3 and 9 activation. Second, EphB2 was also found to induce autophagy, as assessed by immunofluorescence and/or immunoblotting examination of the LC3, ATG5 and ATG12 markers. Third, EphB2 also has a pro-invasive function in breast cancer cells that involves the regulation of MMP2 and MMP9 metalloproteases and can be blocked by treatment with respective neutralizing antibodies. Furthermore, EphB2-induced invasion is kinase-dependent and is impeded in cells expressing a kinase-dead mutant EphB2. In summary, we identified a mechanism involving a triple role for EphB2 in breast cancer progression, whereby it regulates apoptosis, autophagy, and invasion.

Ehd3, a regulator of vesicular trafficking, is silenced in gliomas and functions as a tumor suppressor by controlling cell cycle arrest and apoptosis.

EHD3 [Eps15 homology (EH) domain-containing protein 3] is a protein that resides in tubular and vesicular membrane structures and participates in endocytic recycling, although all its functions are unknown. Since Ehd3 is most abundantly expressed in brain tissues, we examined its role in brain cancer progression. Using immunohistochemistry, we report loss of EHD3 expression in gliomas, including low-grade astrocytomas, suggesting that this is an early event in gliomagenesis. EHD3 expression is also very low in most of glioma cell lines tested. In two cell lines, a bisulfite sequencing method identifies promoter hypermethylation as a mechanism of Ehd3 silencing, and its expression was restored by the demethylating agent 5-Azacytidine. Doxycycline-inducible restoration of EHD3 expression to glioma cells decreases their growth and invasiveness and induces cell cycle arrest and apoptosis. Furthermore, shRNA-mediated Ehd3 silencing increases cell growth. Using a xenograft model, we demonstrate Ehd3 growth inhibitory functions in glioma cells in vivo. We suggest that Ehd3 functions as a tumor suppressor gene and loss of its expression is a very common event in gliomas. This is the first study to highlight the importance of a member of the C-terminal EHD proteins in cancer and to link their functions to the cell cycle and apoptosis.

Post-transcriptional regulation of connexin43 in H-Ras-transformed cells.

Connexin43 (Cx43) expression is lost in cancer cells and many studies have reported that Cx43 is a tumor suppressor gene. Paradoxically, in a cellular NIH3T3 model, we have previously shown that Ha-Ras-mediated oncogenic transformation results in increased Cx43 expression. Although the examination of transcriptional regulation revealed essential regulatory elements, it could not solve this paradox. Here we studied post-transcriptional regulation of Cx43 expression in cancer using the same model in search of novel gene regulatory elements. Upon Ras transformation, both Cx43 mRNA stability and translation efficiency were increased. We investigated the role of Cx43 mRNA 3' and 5'Untranslated regions (UTRs) and found an opposing effect; a 5'UTR-driven positive regulation is observed in Ras-transformed cells (NIH-3T3(Ras)), while the 3'UTR is active only in normal NIH-3T3(Neo) cells and completely silenced in NIH-3T3(Ras) cells. Most importantly, we identified a previously unknown regulatory element within the 3'UTR, named S1516, which accounts for this 3'UTR-mediated regulation. We also examined the effect of other oncogenes and found that Ras- and Src-transformed cells show a different Cx43 UTRs post-transcriptional regulation than ErbB2-transformed cells, suggesting distinct regulatory pathways. Next, we detected different patterns of S1516 RNA-protein complexes in NIH-3T3(Neo) compared to NIH-3T3(Ras) cells. A proteomic approach identified most of the S1516-binding proteins as factors involved in post-transcriptional regulation. Building on our new findings, we propose a model to explain the discrepancy between the Cx43 expression in Ras-transformed NIH3T3 cells and the data in clinical specimens.

Platelet-type 12-lipoxygenase induces MMP9 expression and cellular invasion via activation of PI3K/Akt/NF-κB.

Prostate cancer is the most frequently diagnosed cancer and the second leading cause of death in males in the United States. Using human prostate cancer specimens, the authors have previously shown that elevated expression levels of 12-lipoxygenase (12-LOX) occurred more frequently in advanced stage, high-grade prostate cancer, suggesting that 12-LOX expression is associated with carcinoma progression and invasion. Previous reports from their group and others have shown that 12-LOX is a positive modulator of invasion and metastasis; however, the mechanism remains unclear. In this work, a new link between 12-LOX and the matrix metalloproteinase 9 (MMP9) in prostate cancer angiogenesis is reported. This study demonstrated that overexpression of 12-LOX in prostate cancer PC-3 cells resulted in elevated expression of MMP9 mRNA, protein and secretion. Exogenous addition of 12(S)-hydroxy eicosatetraenoic acid, the sole and stable end product of arachidonic acid metabolism by 12-LOX, is able to increase MMP9 expression in wild-type PC-3 cells. Furthermore, using pharmacological and genetic inhibition approaches, it was found that 12-LOX activates phosphoinositol 3 kinase (PI3K)/Akt, which results in nuclear factor-kappa B (NF-κB)-driven MMP9 expression, ensuing in enhanced chemoattraction of endothelial cells. Specific inhibitors of 12-LOX, PI3K or NF-κB inhibited MMP9 expression in 12-LOX-expressing PC-3 cells and resulted in the blockade of the migratory ability of endothelial cells. In summary, the authors have identified a new pathway by which overexpression of 12-LOX in prostate cancer cells leads to augmented production of MMP9 via activation of PI3K/Akt/NF-κB signaling. The role of 12-LOX-mediated MMP9 secretion in endothelial cell migration may account for the proangiogenic function of 12-LOX in prostate cancer.

Exogenous CXCL12 activates protein kinase C to phosphorylate connexin 43 for gap junctional intercellular communication among confluent breast cancer cells.

Despite ongoing attempts to improve the overall breast cancer (BC) survival rate, BC cells' (BCCs) predilection for metastasizing to the bone marrow has enabled BCCs to not only remain dormant, but also evade detection. BCCs are able to acquire quiescence by establishing gap junctional intercellular communication (GJIC) with the stroma through the assembly of connexins (Cxs). The chemoattractant CXCL12 also appears to play a role in GJIC based on its tendency to decrease when GJIC is formed between BCCs and bone marrow stroma. This study investigates the role CXCL12 has on Cx43 expression and PKC-mediated Cx43 phosphorylation. Cx43 gene reporter assays revealed that as the BCCs come in contact with each other and establish GJIC, there is an inverse relationship between CXCL12 level and Cx43 expression. Immunoblot analyses confirmed this relationship at the level of protein, showing decreased Cx43 and reduced Cx43 phosphorylation at higher CXCL12 concentrations. However, real-time PCR studies revealed little change in Cx43 mRNA levels, despite stimulation with different concentrations of CXCL12, indicating CXCL12's effect on Cx43 is post-translational, through phosphorylation. Immunoblot analyses and functional dye exchange studies showed activation of PKC by exogenous CXCL12 in the phosphorylation, which in turn, increased intercellular communication. These findings elucidate the importance of considering the microenvironment's role in micrometastasis in clinical studies pertaining to prospective breast cancer treatment.

The Eph/Ephrin family in cancer metastasis: communication at the service of invasion.

Cancer cells rely on intercellular communication throughout the different stages of their transformation and progression into metastasis. They do so by co-opting different processes such as cell-cell junctions, growth factors, receptors, and vesicular release. Initially characterized in neuronal and vascular tissues, Ephs and Ephrins, the largest family of receptor tyrosine kinases, comprised of two classes (i.e., A and B types), is increasingly scrutinized by cancer researchers. These proteins possess the particular features of both the receptors and ligands being membrane-bound which, via mandatory direct cell-cell interactions, undergo a bidirectional signal transduction initiated from both the receptor and the ligand. Following cell-cell interactions, Ephs/Ephrins behave as guidance molecules which trigger both repulsive and attractive signals, so as to direct the movement of cells through their immediate microenvironment. They also direct processes which include sorting and positioning and cytoskeleton rearrangements, thus making them perfect candidates for the control of the metastatic process. In fact, the role of Ephs and Ephrins in cancer progression has been demonstrated for many of the family members and they, surprisingly, have both tumor promoter and suppressor functions in different cellular contexts. They are also able to coordinate between multiple processes including cell survival, proliferation, differentiation, adhesion, motility, and invasion. This review is an attempt to summarize the data available on these Ephs/Ephrins' biological functions which contribute to the onset of aggressive cancers. I will also provide an overview of the factors which could explain the functional differences demonstrated by Ephs and Ephrins at different stages of tumor progression and whose elucidation is warranted for any future therapeutic targeting of this signaling pathway in cancer metastasis.

Gap junctions and connexins as therapeutic targets in cancer.

IMPORTANCE OF THE FIELD: Connexins (Cxs) and gap junctional intercellular communications (GJICs) play roles in cancer development, growth and metastasis. Experimental studies suggest that targeting Cxs may be a novel technique, either to inhibit tumor cell growth directly or to sensitize to various therapies. AREAS COVERED IN THIS REVIEW: A brief introduction to the role of Cxs in cancer. The focus is mainly on data available in the literature regarding therapeutic aspects. WHAT THE READER WILL GAIN: This article reviews the various strategies that take advantage of gap junctions and connexins to eliminate cancer cells, including use of the bystander effect (BE) in gene therapy, the effect of connexins on chemosensitization, the role of apoptotic processes and interactions with the microenvironment. Attempts to restore connexin expression at the transcriptional and post-transcriptional levels are described, as well as promising strategies recently explored. The potential and limitations of the approaches are discussed. TAKE HOME MESSAGE: Connexins have multiple facets, singly, in hemichannel complexes, in gap junctions or interacting with different proteins. The regulation of their expression is not fully resolved and selective manipulation of Cxs expression is therefore a challenge. Although the therapeutic potential of connexins is undeniable, more effort is needed to study the regulation and functions of these proteins.