TY - JOUR
T1 - The Sp1 transcription factor contributes to the tumor necrosis factor-induced expression of the angiogenic factor thymidine phosphorylase in human colon carcinoma cells
AU - Zhu, Geng Hui
AU - Lenzi, Michelle
AU - Schwartz, Edward L.
N1 - Funding Information:
This study was supported by grants R01-CA54422, R01-CA89352, and P01-CA13330 from the National Cancer Institute.
PY - 2002/12/5
Y1 - 2002/12/5
N2 - Thymidine phosphorylase (TP; also known as platelet-derived endothelial cell growth factor, PD-ECGF) is an angiogenic factor that is chemotactic for endothelial cells and has been found to induce neovascularization in vivo. TP is frequently overexpressed in human solid tumors, where its expression has been correlated with increased tumor microvessel density, invasion, and metastasis, and shorter patient survival. In this report, TP activity in the WiDr colon carcinoma cell line was found to be induced 100-fold by tumor necrosis factor (TNFα), a secretory product of activated macrophages that has indirect angiogenic activities. Increased TP activity was accompanied by increased TP mRNA levels and without an increase in mRNA stability. TNFα-induced TP mRNA levels were reduced by mithramycin, a DNA-binding transcription inhibitor specific for GC-rich sequences. Transcriptional regulation by TNFα was confirmed by transient transfection of WiDr with upstream TP sequences in a luciferase reporter construct. Deletion analysis of the reporter pinpointed two regions of the TP promoter with regulatory elements for both TNFα-inducible and basal expression, and they contained, respectively, three and one consensus binding sites for the Sp1-family of transcription factors. One additional region contributed only to basal TP expression, and it contained three Sp1 sites. TNFα-induced TP expression decreased when point mutations were made in three of the four Sp1 sites postulated to contribute to both basal and TNFα-inducible expression. Electrophoretic mobility shift assays further demonstrated binding of nuclear Sp1 to these three sites. Sp1-binding activity was also increased in cells treated with TNFα. These studies establish a role for Sp1 in the regulation of expression of the angiogenic factor TP in colon cancer WiDr cells.
AB - Thymidine phosphorylase (TP; also known as platelet-derived endothelial cell growth factor, PD-ECGF) is an angiogenic factor that is chemotactic for endothelial cells and has been found to induce neovascularization in vivo. TP is frequently overexpressed in human solid tumors, where its expression has been correlated with increased tumor microvessel density, invasion, and metastasis, and shorter patient survival. In this report, TP activity in the WiDr colon carcinoma cell line was found to be induced 100-fold by tumor necrosis factor (TNFα), a secretory product of activated macrophages that has indirect angiogenic activities. Increased TP activity was accompanied by increased TP mRNA levels and without an increase in mRNA stability. TNFα-induced TP mRNA levels were reduced by mithramycin, a DNA-binding transcription inhibitor specific for GC-rich sequences. Transcriptional regulation by TNFα was confirmed by transient transfection of WiDr with upstream TP sequences in a luciferase reporter construct. Deletion analysis of the reporter pinpointed two regions of the TP promoter with regulatory elements for both TNFα-inducible and basal expression, and they contained, respectively, three and one consensus binding sites for the Sp1-family of transcription factors. One additional region contributed only to basal TP expression, and it contained three Sp1 sites. TNFα-induced TP expression decreased when point mutations were made in three of the four Sp1 sites postulated to contribute to both basal and TNFα-inducible expression. Electrophoretic mobility shift assays further demonstrated binding of nuclear Sp1 to these three sites. Sp1-binding activity was also increased in cells treated with TNFα. These studies establish a role for Sp1 in the regulation of expression of the angiogenic factor TP in colon cancer WiDr cells.
KW - Angiogenic factor
KW - Colorectal cancer
KW - Thymidine phosphorylase
KW - Transcription regulation
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U2 - 10.1038/sj.onc.1206030
DO - 10.1038/sj.onc.1206030
M3 - Article
C2 - 12466967
AN - SCOPUS:0037028218
SN - 0950-9232
VL - 21
SP - 8477
EP - 8485
JO - Oncogene
JF - Oncogene
IS - 55
ER -