Regulation of vascular endothelial growth factor expression in human colon carcinoma cells by activity of src kinase.
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.
Fleming
R Y
RY
Department of Surgical Oncology, University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Ellis
L M
LM
Parikh
N U
NU
Liu
W
W
Staley
C A
CA
Gallick
G E
GE
D000230:Adenocarcinoma; D002999:Clone Cells; D003110:Colonic Neoplasms; D016373:DNA, Antisense; D016228:Endothelial Growth Factors / Q000096:biosynthesis*; D015972:Gene Expression Regulation, Neoplastic; D005822:Genetic Vectors; D006801:Humans; D007700:Kinetics; D008222:Lymphokines / Q000096:biosynthesis*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism; D051575:Proto-Oncogene Proteins c-yes; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000096:biosynthesis / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D012044:Regression Analysis; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D019061:src-Family Kinases
D016373:DNA, Antisense; D016228:Endothelial Growth Factors; D008222:Lymphokines; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D011505:Protein-Tyrosine Kinases; D051575:Proto-Oncogene Proteins c-yes; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases