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Regulation of vascular endothelial growth factor expression in human colon carcinoma cells by activity of src kinase
R Y Fleming1, L M Ellis, N U Parikh
1Department of Surgical Oncology, University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Background:
The c-src protooncogene encodes a protein tyrosine kinase, pp60c-src, that is a mediator in many signal transduction pathways. One pathway in which pp60c-src protein tyrosine kinase activity is implicated involves regulation of vascular endothelial growth factor (VEGF), an angiogenic factor important to neovascularization of growing tumors. Recently we demonstrated that decreased activity of pp60c-src in colon tumor cells contributes to decreased expression of VEGF. This study examined the relationship between pp60c-src activation, cell density, and VEGF production in a colon tumor cell line.
Methods:
Parental HT-29 colon adenocarcinoma cells and stable subclones created by transfection with c-src antisense and sense (control) expression vectors were plated under sparse (2 x 10(4) cells/cm2) and confluent (20 x 10(4) cells/cm2) conditions and grown for 36 hours. Protein and RNA were extracted from cells to determine pp60c-src levels, c-Src tyrosine kinase activity, and VEGF mRNA expression.
Results:
The pp60c-src kinase activity of HT-29 cells and control sense-transfected clones grown under confluent conditions was increased threefold to fivefold compared with cells grown under sparse conditions. In contrast, the ability of confluent culture conditions to increase pp60c-src activity was blunted in antisense transfectants. By regression analysis, VEGF expression was found to vary directly with pp60c-src levels (r2 = 0.886).
Conclusions:
Cell density contributes to the regulation of c-src kinase activity and VEGF expression in HT-29 cells. When the steady-state level of pp60c-src is reduced in antisense transfectants, not only is the steady-state level of VEGF reduced, but the ability of confluence to stimulate pp60c-src activity and VEGF production is too. These data suggest that c-src may be an intermediary of both constitutive and inducible pathways for VEGF production in colon tumor cells.
Insights
Cell density influences c-src kinase activity and vascular endothelial growth factor (VEGF) production in colon tumor cells. Reducing c-src levels impairs both basal and induced VEGF expression, suggesting c-src's role in tumor angiogenesis.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- The c-src protooncogene encodes pp60c-src, a protein tyrosine kinase involved in signal transduction.
- pp60c-src activity regulates vascular endothelial growth factor (VEGF), crucial for tumor neovascularization.
- Previous studies indicated decreased pp60c-src activity correlates with reduced VEGF expression in colon tumors.
Purpose of the Study:
- To investigate the relationship between pp60c-src activation, cell density, and VEGF production in a colon tumor cell line.
- To understand how cell density affects c-src kinase activity and subsequent VEGF expression.
Main Methods:
- HT-29 colon adenocarcinoma cells and c-src antisense/sense transfectants were cultured under sparse and confluent conditions.
- Protein and RNA were extracted to measure pp60c-src levels, kinase activity, and VEGF mRNA expression.
Main Results:
- Confluent conditions significantly increased pp60c-src kinase activity (3-5 fold) in HT-29 and sense transfectants compared to sparse conditions.
- This density-dependent increase in pp60c-src activity was blunted in antisense transfectants.
- VEGF expression showed a direct correlation with pp60c-src levels (r² = 0.886).
Conclusions:
- Cell density is a regulatory factor for c-src kinase activity and VEGF expression in colon tumor cells.
- Reduced steady-state pp60c-src levels diminish both basal VEGF and the response to confluence-induced stimulation.
- c-src acts as an intermediary in both constitutive and inducible VEGF production pathways in colon tumors.