Thymidine phosphorylase induces angiogenesis in vivo and in vitro: an evaluation of possible mechanisms

Abstract

1 Thymidine phosphorylase (TP) is elevated in the plasma of cancer patients, and has been implicated in pathophysiological angiogenesis. However, the downstream signals underlying this implication remain obscure. The purpose of the present study was to examine the effects of TP on the neovascularisation response in vitro and in vivo. 2 Both TP and its catalytic product, 2-deoxy-D-ribose-1-phosphate, and downstream 2-deoxy-Dribose (2-DDR) promoted endothelial tubulogenesis in vitro, and the regeneration of a wounded monolayer of endothelial cells without exerting any mitogenic effect. In vivo, both TP and 2-DDR promoted the development of functional vasculature into an avascular sponge. A TP inhibitor, 6-amino-5-chlorouracil, was able to partially reverse the effects of TP, but had no effect on the 2-DDRinduced angiogenesis. 3 Enhanced monolayer regeneration was observed with TP-cDNA-transfected bladder carcinoma cells. The transfection of TP-cDNA, however, did not confer any proliferative advantage. The regeneration of TP overexpressing cells was associated with a time-dependent expression of the enzyme haeme-oxygenase (HO-1). 4 The present study demonstrates that both TP and its ribose-sugar metabolites induce angiogenesis by mediating a cohesive interplay between carcinoma and endothelial cells. The induction of HO-1 in TP-transfected cells suggests that it could be a possible downstream signal for the angiogenic effects of TP. Furthermore, reducing sugars have been shown to induce oxidative stress, and ribose could be a possible cause for the upregulation of HO-1, which has been implicated in the release of angiogenic factors. Therefore, we postulate that 2-DDR could be mediating the angiogenic effects of TP possibly through an oxidative stress mechanism and additionally getting integrated in the endothelial metabolic machinery. British Journal of Pharmacology (2003) 139, 219-231. doi:10.1038/sj.bjp.0705216 Keywords: Thymidine phosphorylase; deoxy-D-Ribose; haemeoxygenase-1; angiogenesis Abbreviations: TP, thymidine phosphorylase; 2-DDR, 2-deoxy-D-ribose; 2-DLR, 2-deoxy-L-ribose; HO1, haemeoxygenase-1; TP inhibitor, 6-amino-5-chlorouracil; VEGF, vascular endothelial growth factor; CO, carbon monoxide; EBM, endothelial basal medium; EGM, endothelial growth medium IntroductionAngiogenesis or neovascularisation is finely choreographed through the interplay of the endothelial cells, angiogenic mediators, cytokines, growth factors and adhesion molecules, and can be said to involve three key events, namely migration, proliferation and maturation of the endothelial cells (Griffioen & Molema, 2000). Angiogenesis is of fundamental importance in several physiological processes including embryogenesis, wound healing and the menstrual cycle. It is however also implicated in certain pathological conditions, such as atherosclerosis, diabetic retinopathy, psoriasis and tumour growth (Griffioen & Molema, 2000). Thymidine phosphorylase (TP), which is identical to platelet-derived endothelial cell growth factor (Furukawa et a...

Accumulation of thymidine-derived sugars in thymidine phosphorylase overexpressing cells

“…dR-1-P can be isomerized to dR-5-P mediated by phosphopentomutase (E.C. 5.4.2.7) and is degraded to dR by a phosphatase [10]. dR-5-P can be split into G3P plus acetaldehyde by deoxyriboaldolase (E.C.…”

“…In various in vitro studies, TP had a chemotactic effect on endothelial cells [5,6,7,8]. In vivo, TP induced angiogenesis using various cancer cell lines that were transfected with TP [9,10]. The role of TP in angiogenesis seems evident, but its exact mechanism is still unknown and it is postulated to be related to the sugars that are formed from thymidine (TdR) degradation by TP.…”

“…The metabolite dR has previously shown angiogenic activity [6,10] and could elongate the sprouting in the aortic ring assay [19]. In addition, dR induced endothelial cell migration in various studies [5,8].…”

The Nucleoside Derivative 5′-O-Trityl-inosine (KIN59) Suppresses Thymidine Phosphorylase-triggered Angiogenesis via a Noncompetitive Mechanism of Action

“…It is assumed that the products of the enzyme reaction are angiogenic, in partic- ular 2-deoxy-D-ribose that is obtained by dephosphorylation of 2-deoxy-␣-D-ribose-1-phosphate. It has been proposed that the extracellular release of 2-deoxy-D-ribose forms a chemotactic gradient that mediates endothelial cell migration (25,28,29). Recent observations also suggest that 2-deoxy-D-ribose induces angiogenesis by generating oxygen radical species, which induce the secretion of oxidative stress-responsive angiogenic factors, like vascular endothelial cell growth factor, interleukin-8, and matrix metalloproteinase-1 (6,28).…”

“…It has been proposed that the extracellular release of 2-deoxy-D-ribose forms a chemotactic gradient that mediates endothelial cell migration (25,28,29). Recent observations also suggest that 2-deoxy-D-ribose induces angiogenesis by generating oxygen radical species, which induce the secretion of oxidative stress-responsive angiogenic factors, like vascular endothelial cell growth factor, interleukin-8, and matrix metalloproteinase-1 (6,28). Moreover, Hotchkiss et al (7) have shown that TPase and 2-deoxy-D-ribose activate specific integrins, which directly links TPase-induced endothelial cell migration to intracellular signal transduction pathways.…”