VEGF-A promotes lymphoma tumour growth by activation of STAT proteins and inhibition of p27(KIP1) via paracrine mechanisms.
Increased levels of circulating VEGF-A have been demonstrated in patients with non-Hodgkin lymphoma (NHL) and are associated with progressive disease and poor clinical outcome. We investigated the role of VEGF-A in lymphoma tumour growth on a molecular level in order to identify the mechanism of VEGF-A-promoted tumour growth and to identify the potential targets for therapy. We used a model in which Daudi (human Burkitt lymphoma) tumour cells were transduced with VEGF-A165 or an empty vector (negative control) and subcutaneously injected in NOD/SCID mice. The weight of tumours overexpressing VEGF-A was increased 4-fold compared to that of control tumours (p<0.0001), whereas no in vitro growth advantage was demonstrated upon VEGF-A overexpression. VEGF-A-tumours were associated with increased microvessel densities (p=0.004) and increased tumour cell proliferation (Ki67; p<0.001) compared to control tumours. VEGF-A-tumours were characterised by upregulation of phosphorylated STAT-4 and STAT-6 and downregulation of phospho-p27(KIP1), a crucial cell cycle inhibitor (p<0.05). This was accompanied by increased levels of phosphorylated receptor tyrosine kinases, including EGFR (ErbB-2 and ErbB-4, p<0.05), an upstream regulator of STAT proteins. We demonstrated that various mouse-derived cytokines produced by mouse-derived tumour stromal cells are upregulated in VEGF-A-tumours compared to control tumours (p<0.05). These results indicate an important role for the tumour microenvironment in paracrine promotion of lymphoma tumour growth in response to tumour-derived VEGF-A. In conclusion, lymphoma-derived VEGF-A promoted lymphoma tumour growth in a paracrine loop by activation of tumour stromal cells. Our study reveals VEGF-A and STAT proteins as potential additional targets in the treatment of lymphoma.
Roorda
Berber D
BD
Division of Pediatric Oncology/Hematology, Department of Pediatrics, University Medical Center Groningen, University of Groningen, Hanzeplein 1, P.O. Box 30.001, 9700 RB Groningen, The Netherlands.
Ter Elst
Arja
A
Scherpen
Frank J G
FJ
Meeuwsen-de Boer
Tiny G J
TG
Kamps
Willem A
WA
de Bont
Eveline S J M
ES
D000818:Animals; D002051:Burkitt Lymphoma / Q000378:metabolism* / Q000473:pathology; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016207:Cytokines / Q000096:biosynthesis; D004195:Disease Models, Animal; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D009363:Neoplasm Proteins / Q000378:metabolism*; D019899:Paracrine Communication; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D050791:STAT Transcription Factors / Q000378:metabolism*; D017154:Stromal Cells; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D016207:Cytokines; D009363:Neoplasm Proteins; D050791:STAT Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D050760:Cyclin-Dependent Kinase Inhibitor p27; D020794:Receptor Protein-Tyrosine Kinases