Src: coordinating metabolism in cancer

Metabolism must be tightly regulated to fulfil the dynamic requirements of cancer cells during proliferation, migration, stemness and differentiation. Src is a node of several signals involved in many of these biological processes, and it is also an important regulator of cell metabolism. Glucose uptake, glycolysis, the pentose-phosphate pathway and oxidative phosphorylation are among the metabolic pathways that can be regulated by Src. Therefore, this oncoprotein is in an excellent position to coordinate and finely tune cell metabolism to fuel the different cancer cell activities. Here, we provide an up-to-date summary of recent progress made in determining the role of Src in glucose metabolism as well as the link of this role with cancer cell metabolic plasticity and tumour progression. We also discuss the opportunities and challenges facing this field

Connexin43 Region 266–283, via Src Inhibition, Reduces Neural Progenitor Cell Proliferation Promoted by EGF and FGF-2 and Increases Astrocytic Differentiation

Neural progenitor cells (NPCs) are self-renewing cells that give rise to the major cells in the nervous system and are considered to be the possible cell of origin of glioblastoma. The gap junction protein connexin43 (Cx43) is expressed by NPCs, exerting channel-dependent and -independent roles. We focused on one property of Cx43-its ability to inhibit Src, a key protein in brain development and oncogenesis. Because Src inhibition is carried out by the sequence 266-283 of the intracellular C terminus in Cx43, we used a cell-penetrating peptide containing this sequence, TAT-Cx43266-283, to explore its effects on postnatal subventricular zone NPCs. Our results show that TAT-Cx43266-283 inhibited Src activity and reduced NPC proliferation and survival promoted by epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2). In differentiation conditions, TAT-Cx43266-283 increased astrocyte differentiation at the expense of neuronal differentiation, which coincided with a reduction in Src activity and β-catenin expression. We propose that Cx43, through the region 266-283, reduces Src activity, leading to disruption of EGF and FGF-2 signaling and to down-regulation of β-catenin with effects on proliferation and differentiation. Our data indicate that the inhibition of Src might contribute to the complex role of Cx43 in NPCs and open new opportunities for further research in gliomagenesis.FEDER RTI2018-099873-B-I00/Ministerio de Ciencia, Innovación y Universidades Rocío Talaverón fellowship/Fundación Científica Asociación Española Contra el Cáncer PGC20185-094654-B-100/Ministerio de Ciencia, Innovación y Universidade

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

Targeting metabolic plasticity in glioma stem cells in vitro and in vivo through specific inhibition of c-Src by TAT-Cx43266-283

Background: Glioblastoma is the most aggressive primary brain tumour and has a very poor prognosis. Inhibition of c-Src activity in glioblastoma stem cells (GSCs, responsible for glioblastoma lethality) and primary glioblastoma cells by the peptide TAT-Cx43266-283 reduces tumorigenicity, and boosts survival in preclinical models. Because c-Src can modulate cell metabolism and several reports revealed poor clinical efficacy of various antitumoral drugs due to metabolic rewiring in cancer cells, here we explored the inhibition of advantageous GSC metabolic plasticity by the c-Src inhibitor TAT-Cx43266-283. Methods: Metabolic impairment induced by the c-Src inhibitor TAT-Cx43266-283 in vitro was assessed by fluorometry, western blotting, immunofluorescence, qPCR, enzyme activity assays, electron microscopy, Seahorse analysis, time-lapse imaging, siRNA, and MTT assays. Protein expression in tumours from a xenograft orthotopic glioblastoma mouse model was evaluated by immunofluorescence. Findings: TAT-Cx43266-283 decreased glucose uptake in human GSCs and reduced oxidative phosphorylation without a compensatory increase in glycolysis, with no effect on brain cell metabolism, including rat neurons, human and rat astrocytes, and human neural stem cells. TAT-Cx43266-283 impaired metabolic plasticity, reducing GSC growth and survival under different nutrient environments. Finally, GSCs intracranially implanted with TAT-Cx43266-283 showed decreased levels of important metabolic targets for cancer therapy, such as hexokinase-2 and GLUT-3. Interpretation: The reduced ability of TAT-Cx43266-283-treated GSCs to survive in metabolically challenging settings, such as those with restricted nutrient availability or the ever-changing in vivo environment, allows us to conclude that the advantageous metabolic plasticity of GSCs can be therapeutically exploited through the specific and cell-selective inhibition of c-Src by TAT-Cx43266-283.Spanish Ministerio de Economía y Competitividad (FEDER BFU2015-70040-R and FEDER RTI2018-099873-B-I00), Fundación Ramón Areces. Fellowships from the Junta de Castilla y León, European Social Fund, Ministerio de Ciencia and Asociación Española Contra el Cáncer (AECC)

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-1β, 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.This work was supported in part through funding from the Spanish Society for Rheumatology (SER; FER 2013) and Spanish Foundation for Research on Bone and Mineral Metabolism (FEIOMM), grant PRECIPITA-2015-000139 from the FECYT-Ministry of Economy and Competitiveness (to M.D.M.), grant PI16/00035 from the Health Institute ‘Carlos III’ (ISCIII, Spain), the European Regional Development Fund, ‘A way of making Europe’ from the European Union (to M.D.M.) and a grant from Xunta de Galicia IN607B 2017/21 (to M.D.M.) and pre-doctoral fellowship to M.V.-E. T.A. acknowledges support from Instituto de Salud Carlos III grants PI16/00772 and CPII16/00042, co-financed by the European Regional Development Fund (ERDF)S

HIF-1 and c-Src Mediate Increased Glucose Uptake Induced by Endothelin-1 and Connexin43 in Astrocytes

In previous work we showed that endothelin-1 (ET-1) increases the rate of glucose uptake in astrocytes, an important aspect of brain function since glucose taken up by astrocytes is used to supply the neurons with metabolic substrates. In the present work we sought to identify the signalling pathway responsible for this process in primary culture of rat astrocytes. Our results show that ET-1 promoted an increase in the transcription factor hypoxia-inducible factor-1α (HIF-1α) in astrocytes, as shown in other cell types. Furthermore, HIF-1α-siRNA experiments revealed that HIF-1α participates in the effects of ET-1 on glucose uptake and on the expression of GLUT-1, GLUT-3, type I and type II hexokinase. We previously reported that these effects of ET-1 are mediated by connexin43 (Cx43), the major gap junction protein in astrocytes. Indeed, our results show that silencing Cx43 increased HIF-1α and reduced the effect of ET-1 on HIF-1α, indicating that the effect of ET-1 on HIF-1α is mediated by Cx43. The activity of oncogenes such as c-Src can up-regulate HIF-1α. Since Cx43 interacts with c-Src, we investigated the participation of c-Src in this pathway. Interestingly, both the treatment with ET-1 and with Cx43-siRNA increased c-Src activity. In addition, when c-Src activity was inhibited neither ET-1 nor silencing Cx43 were able to up-regulate HIF-1α. In conclusion, our results suggest that ET-1 by down-regulating Cx43 activates c-Src, which in turn increases HIF-1α leading to the up-regulation of the machinery required to take up glucose in astrocytes. Cx43 expression can be reduced in response not only to ET-1 but also to various physiological and pathological stimuli. This study contributes to the identification of the signalling pathway evoked after Cx43 down-regulation that results in increased glucose uptake in astrocytes. Interestingly, this is the first evidence linking Cx43 to HIF-1, which is a master regulator of glucose metabolism

Connexin43-Src interacting sequence as a cell-penetrating peptide to study human primary glioma stem cells invasion

Resumen del trabajo presentado al XXXXVIII Congreso de la Sociedad Española de Bioquímica y Biología Molecular (SEBBM), celebrado en Valencia del 7 al 10 de septiembre de 2015.Connexin43 (Cx43) is the main gap junction channel-forming protein in astrocytes, the most abundant glial cells in central nervous system. This protein is downregulated in brain tumours called gliomas. Tumour initiation, relapse, and therapeutic resistance in gliomas is attributed to Glioma Stem Cells (GSCs). Interestingly, several cell-penetrating peptides (CPPs) containing different regions of Cx43 involved in c-Src interaction reverse Glioma Stem Cells (GSCs) phenotype and reduce the rate of cell growth. Considering the controversial Cx43 migration properties and the infi ltrative nature of these tumours, we have investigated the role of these CPPs in human primary GSC migration and invasion. Human primary GSCs were obtained from fresh tumour biopsies and were treated with CPPs. Human GSCs G166 were treated with CPPs. Migration was studied using tiny-tumour cultures, Time-Lapse live-cell Imaging and Immunocytochemistry. Invasion was studied using 8.0 μM pore transwell inserts with or without Matrigel. The mechanism involved in migration was studied by Western blot, evaluating the activity of Focal Adhesion Kinase (FAK). Our findings indicate that our CPPs reduced the rate of human primary GSCs and G166 GSCs migration and invasion. In addition, CPPs inhibited c-Src activity in these cells and consequently decreased FAK phosphorylation necessary to establish adequate focal adhesions in order to migrate. It should be mentioned that FAK is activated by Src-mediated phosphorylation. In conclusion, our results show that c-Src plays an essential role in the effects of Cx43 on migration and suggest these CPPs by inhibiting migration and invasion could be the basis for promising therapies.Peer reviewe

Impairment of Autophagic Flux Participates in the Antitumor Effects of TAT-Cx43266-283 in Glioblastoma Stem Cells

Autophagy is a physiological process by which various damaged or non-essential cytosolic components are recycled, contributing to cell survival under stress conditions. In cancer, autophagy can have antitumor or protumor effects depending on the developmental stage. Here, we use Western blotting, immunochemistry, and transmission electron microscopy to demonstrate that the antitumor peptide TAT-Cx43266-283, a c-Src inhibitor, blocks autophagic flux in glioblastoma stem cells (GSCs) under basal and nutrient-deprived conditions. Upon nutrient deprivation, GSCs acquired a dormant-like phenotype that was disrupted by inhibition of autophagy with TAT-Cx43266-283 or chloroquine (a classic autophagy inhibitor), leading to GSC death. Remarkably, dasatinib, a clinically available c-Src inhibitor, could not replicate TAT-Cx43266-283 effect on dormant GSCs, revealing for the first time the possible involvement of pathways other than c-Src in TAT-Cx43266-283 effect. TAT-Cx43266-283 exerts an antitumor effect both in nutrient-complete and nutrient-deprived environments, which constitutes an advantage over chloroquine and dasatinib, whose effects depend on nutrient environment. Finally, our analysis of the levels of autophagy-related proteins in healthy and glioma donors suggests that autophagy is upregulated in glioblastoma, further supporting the interest in inhibiting this process in the most aggressive brain tumor and the potential use of TAT-Cx43266-283 as a therapy for this type of cancer

The invasion of glioblastoma stem cells is reduced by the sequence of the connexin43 that interacts with c-Src

Resumen del póster presentado al XXXIX Congreso de la Sociedad Española de Bioquímica y Biología Molecular, celebrado en Salamanca del 5 al 8 de septiembre de 2016.Glioblastoma stem cells (GSC) constitute a niche of cells with self-renewal ability and resistance to conventional therapies. Thus, they are responsible for relapse in these aggressive brain tumors when their resection is not complete. The expression of connexin43 (Cx43), the main gap junction channel-forming protein, and c-Src, a non receptor tyrosine kinase, is inversely related in glioblastoma cells. Interestingly, restoring Cx43 in GSC reverses GSC phenotype. The sequence responsible for this effect is the region that interacts with c-Src (amino acids 266-283). The Focal Adhesion Kinase (FAK) requires the c-Src-mediated phosphorylation in tyrosines 576 and 577 in order to be fully active and promote cell migration. In this study, fresh human tumour biopsies were disaggregated to obtain human primary GSCs. These cells were treated with a cell-penetrating peptide containing the Cx43-Src interacting sequence (Tat-Cx43266-283). The migration was analyzed by tracking individual cell trajectories in cultures recorded by Time-Lapse Live-cell Imaging. Matrigel-treated transwell inserts were used to analyze the invasion and the levels of phosphorylation of FAK tyrosines 576 and 577 were evaluated by western Blot. Our results showed that Tat-Cx43266-283 reduced the migration and invasion of human primary GSC. The analysis of c-Src and FAK proteins suggests that the mechanism by which this reduction takes place includes the inhibition of c-Src/FAK axis. In conclusion, Tat-Cx43266-283 inhibits c-Src with the subsequent reduction in FAK phosphorylation required to establish appropriate focal adhesions for migration. All together, these results indicate an important antivasive role of the sequence of Cx43 that interacts with c-Src in glioma stem cells.Peer reviewe