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HIF-1 and c-Src mediate increased glucose uptake induced by endothelin-1 and connexin43 in astrocytes.

Valle-Casuso JC, González-Sánchez A, Medina JM, Tabernero A - PLoS ONE (2012)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Bioquímica y Biología Molecular, Instituto de Neurociencias de Castilla y León (INCYL), Universidad de Salamanca, Salamanca, Spain.

ABSTRACT
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.

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Proposed mechanism.Since Cx43 inhibits c-Src activity [43], it could be proposed that ET-1 by reducing Cx43 activates c-Src, which in turn increases HIF-1α. HIF-1α dimerizes with HIF-1ß and translocates to the nucleus. The transcriptional activity of HIF induces the synthesis of the machinery required to augment the rate of glucose uptake in astrocytes, i.e., the glucose transporters, GLUT-1 and GLUT-3 and the enzymes required for glucose phosphorylation, type I and type II hexokinase (Hx-1 and Hx-2).
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pone-0032448-g008: Proposed mechanism.Since Cx43 inhibits c-Src activity [43], it could be proposed that ET-1 by reducing Cx43 activates c-Src, which in turn increases HIF-1α. HIF-1α dimerizes with HIF-1ß and translocates to the nucleus. The transcriptional activity of HIF induces the synthesis of the machinery required to augment the rate of glucose uptake in astrocytes, i.e., the glucose transporters, GLUT-1 and GLUT-3 and the enzymes required for glucose phosphorylation, type I and type II hexokinase (Hx-1 and Hx-2).

Mentions: As mentioned above, endothelins are involved in several pathologies of the CNS such as gliomas [11]. It should be mentioned that reduced expression of Cx43 [58], [59], [60], [61], high c-Src activity [62] and activation of the HIF-1 pathway [63] are all common features of gliomas. In addition, glioma cells, like many other cancer cells adapt their metabolism to the tumour environment, a process known as “Warburg Effect” that begins by an increase in the rate of glucose uptake and a metabolic shift to aerobic glycolysis, which is associated with a survival advantage as well as the generation of substrates necessary in rapidly proliferating cells [64]. For instance, enzymes such as Hx-2 are key mediators of aerobic glycolisis and promote tumour growth in gliomas [65]. In this study, we suggest that these events could be linked in a common pathway. Thus, our results suggest that ET-1 by down-regulating Cx43 activates c-Src, which in turn up-regulates HIF-1α leading to the transcription of the machinery required to increase the rate of glucose uptake in astrocytes (Figure 8). These metabolic changes are probably designed to sustain the higher rate of cell proliferation observed under these circumstances [66]. ET-1 participates in the progression of different tumours [67], however, whether the presence of ET-1 in gliomas [11] activates the pathway reported in this study (Figure 8) to promote the growth and progression of these tumours remains to be elucidated and warrant further exploration.


HIF-1 and c-Src mediate increased glucose uptake induced by endothelin-1 and connexin43 in astrocytes.

Valle-Casuso JC, González-Sánchez A, Medina JM, Tabernero A - PLoS ONE (2012)

Proposed mechanism.Since Cx43 inhibits c-Src activity [43], it could be proposed that ET-1 by reducing Cx43 activates c-Src, which in turn increases HIF-1α. HIF-1α dimerizes with HIF-1ß and translocates to the nucleus. The transcriptional activity of HIF induces the synthesis of the machinery required to augment the rate of glucose uptake in astrocytes, i.e., the glucose transporters, GLUT-1 and GLUT-3 and the enzymes required for glucose phosphorylation, type I and type II hexokinase (Hx-1 and Hx-2).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3285680&req=5

pone-0032448-g008: Proposed mechanism.Since Cx43 inhibits c-Src activity [43], it could be proposed that ET-1 by reducing Cx43 activates c-Src, which in turn increases HIF-1α. HIF-1α dimerizes with HIF-1ß and translocates to the nucleus. The transcriptional activity of HIF induces the synthesis of the machinery required to augment the rate of glucose uptake in astrocytes, i.e., the glucose transporters, GLUT-1 and GLUT-3 and the enzymes required for glucose phosphorylation, type I and type II hexokinase (Hx-1 and Hx-2).
Mentions: As mentioned above, endothelins are involved in several pathologies of the CNS such as gliomas [11]. It should be mentioned that reduced expression of Cx43 [58], [59], [60], [61], high c-Src activity [62] and activation of the HIF-1 pathway [63] are all common features of gliomas. In addition, glioma cells, like many other cancer cells adapt their metabolism to the tumour environment, a process known as “Warburg Effect” that begins by an increase in the rate of glucose uptake and a metabolic shift to aerobic glycolysis, which is associated with a survival advantage as well as the generation of substrates necessary in rapidly proliferating cells [64]. For instance, enzymes such as Hx-2 are key mediators of aerobic glycolisis and promote tumour growth in gliomas [65]. In this study, we suggest that these events could be linked in a common pathway. Thus, our results suggest that ET-1 by down-regulating Cx43 activates c-Src, which in turn up-regulates HIF-1α leading to the transcription of the machinery required to increase the rate of glucose uptake in astrocytes (Figure 8). These metabolic changes are probably designed to sustain the higher rate of cell proliferation observed under these circumstances [66]. ET-1 participates in the progression of different tumours [67], however, whether the presence of ET-1 in gliomas [11] activates the pathway reported in this study (Figure 8) to promote the growth and progression of these tumours remains to be elucidated and warrant further exploration.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Bioquímica y Biología Molecular, Instituto de Neurociencias de Castilla y León (INCYL), Universidad de Salamanca, Salamanca, Spain.

ABSTRACT
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.

Show MeSH