Thymidine catabolism promotes NADPH oxidase-derived reactive oxygen species (ROS) signalling in KB and yumoto cells

Sci Rep. 2018 Apr 30;8(1):6760. doi: 10.1038/s41598-018-25189-y.

Abstract

Thymidine phosphorylase (TP) is a rate-limiting enzyme in the thymidine catabolic pathway. TP is identical to platelet-derived endothelial cell growth factor and contributes to tumour angiogenesis. TP induces the generation of reactive oxygen species (ROS) and enhances the expression of oxidative stress-responsive genes, such as interleukin (IL)-8. However, the mechanism underlying ROS induction by TP remains unclear. In the present study, we demonstrated that TP promotes NADPH oxidase-derived ROS signalling in cancer cells. NADPH oxidase inhibition using apocynin or small interfering RNAs (siRNAs) abrogated the induction of IL-8 and ROS in TP-expressing cancer cells. Meanwhile, thymidine catabolism induced by TP increased the levels of NADPH and intermediates of the pentose phosphate pathway (PPP). Both siRNA knockdown of glucose 6-phosphate dehydrogenase (G6PD), a rate-limiting enzyme in PPP, and a G6PD inhibitor, dihydroepiandrosterone, reduced TP-induced ROS production. siRNA downregulation of 2-deoxy-D-ribose 5-phosphate (DR5P) aldolase, which is needed for DR5P to enter glycolysis, also suppressed the induction of NADPH and IL-8 in TP-expressing cells. These results suggested that TP-mediated thymidine catabolism increases the intracellular NADPH level via the PPP, which enhances the production of ROS by NADPH oxidase and activates its downstream signalling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Dihydrotestosterone / pharmacology
  • Gene Knockout Techniques
  • Glucosephosphate Dehydrogenase / antagonists & inhibitors
  • Glucosephosphate Dehydrogenase / genetics*
  • Humans
  • Interleukin-8 / genetics
  • Metabolism / genetics
  • NADPH Oxidases / genetics
  • NADPH Oxidases / metabolism*
  • Neoplasms / drug therapy
  • Neoplasms / metabolism*
  • Neoplasms / pathology
  • Pentose Phosphate Pathway / genetics
  • RNA, Small Interfering / genetics
  • Reactive Oxygen Species / metabolism
  • Thymidine / metabolism*
  • Thymidine Phosphorylase / genetics*
  • Thymidine Phosphorylase / metabolism

Substances

  • Interleukin-8
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • Dihydrotestosterone
  • Glucosephosphate Dehydrogenase
  • NADPH Oxidases
  • TYMP protein, human
  • Thymidine Phosphorylase
  • Thymidine