VEGF contributes to mammary tumor growth in transgenic mice through paracrine and autocrine mechanisms.
Vascular endothelial growth factor (VEGF) has been identified as a vascular permeability factor, angiogenic cytokine, and a survival factor. To address its role in mammary carcinogenesis, we used transgenic mice with human VEGF(165) targeted to mammary epithelial cells under the control of the mouse mammary tumor virus (MMTV) promoter. Metastatic mammary carcinomas were induced by mating the MMTV-VEGF mice with MMTV-polyoma virus middle T-antigen (MT) mice to generate VEGF/MT mice. Tumor latency was decreased in the VEGF/MT mice, which developed mammary carcinomas with increased vasodilatation at 4 weeks of age. There was increased incidence, multiplicity, and weight of the mammary tumors in 6- and 8-week-old VEGF/MT mice, compared to their MT-only littermates. Macro- and microscopic lung metastases were detected in the VEGF/MT mice but not the MT mice at 6 and 8 weeks of age. Enhanced tumor growth was attributed to increased microvascular density (MVD), as well as increased tumor cell proliferation and survival. Angiogenesis array analysis showed that 24 of 25 differentially expressed genes were upregulated in the VEGF/MT tumors. In vitro studies revealed increased proliferative activity and upregulation of Flk-1 in the VEGF/MT tumor cells, compared with the MT-only tumor cells. Moreover, there was decreased proliferative activity with downregulation of Flk-1 in tumor cells isolated from conditional knockout (VEGF(-/-)) MT-induced mammary carcinomas. The slow growing VEGF(-/-) tumor cells were accumulated in the G(1)/G(0) phase of the cell cycle and this was associated with stimulation of p16(ink4a) and p21(WAF1). Similarly, p16(ink4a) was stimulated in VEGF(lox/lox)/MT mammary tumor cells following Adeno-cre-mediated VEGF gene inactivation. Collectively, the data from these transgenic models indicate that VEGF contributes to mammary tumor growth through increased neovascularization, as well as autocrine stimulation of growth and inhibition of apoptosis.
Schoeffner
Daniel J
DJ
Laboratory of Cellular Carcinogenesis and Tumor Promotion, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Matheny
Shannon L
SL
Akahane
Takemi
T
Factor
Valentina
V
Berry
Adam
A
Merlino
Glenn
G
Thorgeirsson
Unnur P
UP
D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000556:secondary; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D015152:Blotting, Northern; D018797:Cell Cycle Proteins / Q000235:genetics; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21; D005260:Female; D019942:Genes, p16; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000556:secondary; D008297:Male; D015674:Mammary Neoplasms, Animal / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000378:metabolism; D012334:RNA, Neoplasm / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics* / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000235:genetics / Q000378:metabolism
C493957:Cdkn1a protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D040301:Vascular Endothelial Growth Factor Receptor-2