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Microenvironment changes (in pH) affect VEGF alternative splicing.

Elias AP, Dias S - Cancer Microenviron (2008)

Bottom Line: Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors.SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production.Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

View Article: PubMed Central - PubMed

Affiliation: Angiogenesis Laboratory, Centro de Investigação em Patobiologia Molecular (CIPM), Instituto Português de Oncologia de Francisco Gentil, Lisboa, Portugal.

ABSTRACT
Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors. Although the relative contribution of the VEGF isoforms has been studied in tumor angiogenesis, little is known about the mechanisms that regulate the alternative splicing process. Here, we tested microenvironment cues that might regulate VEGF alternative splicing. To test this, we used endometrial cancer cells that produce all VEGF isoforms as a model, and exposed them to varying pH levels, hormones, glucose and CoCl(2) (to mimic hypoxia). Low pH had the most consistent effects in inducing variations in VEGF splicing pattern (VEGF121 increased significantly, p < 0.001, when compared to VEGF145, 165 or 189). This was accompanied by activation of the p38 stress pathway and SR proteins (splicing factors) expression and phosphorylation. SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production. Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

No MeSH data available.


Related in: MedlinePlus

VEGF isoforms that result from pre-mRNA alternative splicing. These isoforms differ in the presence or absence of exons 6 and 7 that codes for heparin-binding domains and in the presence of exon 8a or 8b that induce antagonist effects of VEGF. The localization of the probes and primers used to amplify the different isoforms of VEGF are indicated by a line or an arrow, respectively. The lines and arrows in blue represent the probes and primers used to amplify either VEGF165+VEGF165b or VEGF189+VEGF189b
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Fig1: VEGF isoforms that result from pre-mRNA alternative splicing. These isoforms differ in the presence or absence of exons 6 and 7 that codes for heparin-binding domains and in the presence of exon 8a or 8b that induce antagonist effects of VEGF. The localization of the probes and primers used to amplify the different isoforms of VEGF are indicated by a line or an arrow, respectively. The lines and arrows in blue represent the probes and primers used to amplify either VEGF165+VEGF165b or VEGF189+VEGF189b

Mentions: The VEGF-A gene undergoes alternative splicing between exons 5 and 8 (Fig. 1) [5]. This mechanism results in the predominant production of four isoforms, which differ in molecular weight, and are thus known as VEGF121, 165, 189, and 145. VEGF165 is the predominant secreted isoform, produced by most cell types (and most tumors), and although it is a diffusible protein, a significant fraction binds to the extracellular matrix (ECM). In contrast, VEGF121 is a freely diffusible isoform that does not bind to heparin, while VEGF189 binds strongly to heparin and therefore is completely sequestered in the ECM. The isoform 145 of VEGF is observed preferentially in carcinomas of the female reproductive system [6]. The importance of selective VEGF isoform secretion by tumors has been demonstrated [7]. In detail, tumors that secrete predominantly the VEGF121 isoform have increased dilated and peripheral blood vessels, while tumors overexpressing VEGF189, had highly branched and internal neo-vasculature [8]. More recently, increased ratio of VEGF121 versus the 165 or 189 isoforms was shown to be critical for the angiogenic phenotype of prostate cancers [9].Fig. 1


Microenvironment changes (in pH) affect VEGF alternative splicing.

Elias AP, Dias S - Cancer Microenviron (2008)

VEGF isoforms that result from pre-mRNA alternative splicing. These isoforms differ in the presence or absence of exons 6 and 7 that codes for heparin-binding domains and in the presence of exon 8a or 8b that induce antagonist effects of VEGF. The localization of the probes and primers used to amplify the different isoforms of VEGF are indicated by a line or an arrow, respectively. The lines and arrows in blue represent the probes and primers used to amplify either VEGF165+VEGF165b or VEGF189+VEGF189b
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2654355&req=5

Fig1: VEGF isoforms that result from pre-mRNA alternative splicing. These isoforms differ in the presence or absence of exons 6 and 7 that codes for heparin-binding domains and in the presence of exon 8a or 8b that induce antagonist effects of VEGF. The localization of the probes and primers used to amplify the different isoforms of VEGF are indicated by a line or an arrow, respectively. The lines and arrows in blue represent the probes and primers used to amplify either VEGF165+VEGF165b or VEGF189+VEGF189b
Mentions: The VEGF-A gene undergoes alternative splicing between exons 5 and 8 (Fig. 1) [5]. This mechanism results in the predominant production of four isoforms, which differ in molecular weight, and are thus known as VEGF121, 165, 189, and 145. VEGF165 is the predominant secreted isoform, produced by most cell types (and most tumors), and although it is a diffusible protein, a significant fraction binds to the extracellular matrix (ECM). In contrast, VEGF121 is a freely diffusible isoform that does not bind to heparin, while VEGF189 binds strongly to heparin and therefore is completely sequestered in the ECM. The isoform 145 of VEGF is observed preferentially in carcinomas of the female reproductive system [6]. The importance of selective VEGF isoform secretion by tumors has been demonstrated [7]. In detail, tumors that secrete predominantly the VEGF121 isoform have increased dilated and peripheral blood vessels, while tumors overexpressing VEGF189, had highly branched and internal neo-vasculature [8]. More recently, increased ratio of VEGF121 versus the 165 or 189 isoforms was shown to be critical for the angiogenic phenotype of prostate cancers [9].Fig. 1

Bottom Line: Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors.SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production.Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

View Article: PubMed Central - PubMed

Affiliation: Angiogenesis Laboratory, Centro de Investigação em Patobiologia Molecular (CIPM), Instituto Português de Oncologia de Francisco Gentil, Lisboa, Portugal.

ABSTRACT
Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors. Although the relative contribution of the VEGF isoforms has been studied in tumor angiogenesis, little is known about the mechanisms that regulate the alternative splicing process. Here, we tested microenvironment cues that might regulate VEGF alternative splicing. To test this, we used endometrial cancer cells that produce all VEGF isoforms as a model, and exposed them to varying pH levels, hormones, glucose and CoCl(2) (to mimic hypoxia). Low pH had the most consistent effects in inducing variations in VEGF splicing pattern (VEGF121 increased significantly, p < 0.001, when compared to VEGF145, 165 or 189). This was accompanied by activation of the p38 stress pathway and SR proteins (splicing factors) expression and phosphorylation. SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production. Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

No MeSH data available.


Related in: MedlinePlus