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Down-regulation of vascular endothelial growth factor in a human colon carcinoma cell line transfected with an
1Department of Surgical Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Abstract:
Vascular endothelial growth factor (VEGF) is implicated in the angiogenesis of human colon cancer. Recent evidence suggests that factors that regulate VEGF expression may partially depend on c-src-mediated signal transduction pathways. The tyrosine kinase activity of Src is activated in most colon tumors and cell lines. We established stable subclones of the human colon adenocarcinoma cell line HT29 in which Src expression and activity are decreased specifically as a result of a transfected antisense expression vector. This study determined whether VEGF expression is decreased in these cell lines and whether the smaller size and reduced growth rate of antisense vector-transfected cell lines in vivo might result, in part, from reduced vascularization of tumors. Northern blot analysis of these cell lines revealed that VEGF mRNA expression was decreased in proportion to the decrease in Src kinase activity. Under hypoxic conditions, cells with decreased Src activity had a <2-fold increase in VEGF expression, whereas parental cells had a >50-fold increase. VEGF protein in the supernatants of cells was also reduced in antisense transfectants compared with that from parental cells. In nude mice, subcutaneous tumors from antisense transfectants showed a significant reduction in vascularity. These results suggest that Src activity regulates the expression of VEGF in colon tumor cells.
Insights
Src kinase activity regulates vascular endothelial growth factor (VEGF) expression in human colon cancer cells. Decreased Src activity reduced VEGF levels, impacting tumor vascularization and growth.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Research
Background:
- Vascular endothelial growth factor (VEGF) drives angiogenesis in human colon cancer.
- c-src-mediated signal transduction pathways are suggested to regulate VEGF expression.
- Src tyrosine kinase activity is elevated in most colon tumors.
Purpose of the Study:
- To investigate if decreased Src expression/activity impacts VEGF expression in colon cancer cells.
- To determine if reduced tumor vascularization contributes to the smaller size and slower growth of tumors with decreased Src activity.
Main Methods:
- Stable subclones of HT29 human colon adenocarcinoma cells with reduced Src expression/activity were created using antisense expression vectors.
- VEGF mRNA and protein levels were analyzed via Northern blot and supernatant collection.
- Tumor vascularity was assessed in vivo using nude mouse models.
Main Results:
- VEGF mRNA expression decreased proportionally with reduced Src kinase activity.
- Hypoxic conditions showed a significantly blunted VEGF increase in cells with decreased Src activity compared to parental cells.
- VEGF protein levels were lower in antisense transfectants.
- Tumors derived from antisense transfectants exhibited significantly reduced vascularity in vivo.
Conclusions:
- Src activity plays a regulatory role in VEGF expression within colon tumor cells.
- Targeting Src activity may represent a therapeutic strategy to inhibit colon cancer angiogenesis and growth.