Background and purpose: Peroxisome proliferator-activated receptor-g (PPAR-g), COX-2 and 15-lipoxygenase (LOX)-1 have been shown to be involved in tumour growth. However, the roles of PPAR-g, COX-2 or 15-LOX-1 in gastric tumourigenesis remain unclear. Here, we investigate the role of 15-LOX-1 induction by honokiol, a small-molecular weight natural product, in PPAR-g and COX-2 signalling during gastric tumourigenesis. Experimental approach: Human gastric cancer cell lines (AGS, MKN45, N87 and SCM-1) were cultured with or without honokiol. Gene and protein expressions were analysed by RT-PCR and Western blotting respectively. Small interfering RNAs (siRNAs) for COX-2, PPAR-g and 15-LOX-1 were used to interfere with the expressions of these genes. A xenograft gastric tumour model in mouse was used for in vivo study. Key results: PPAR-g and COX-2 proteins were highly expressed in gastric cancer cells. Inhibitors, or siRNA for COX-2 or PPAR-g, significantly decreased cell viability. Honokiol markedly inhibited PPAR-g and COX-2 expressions in gastric cancer cells and tumours of xenograft mice, and induced apoptosis and cell death. Honokiol markedly activated cellular 15-LOX-1 expression and 13-S-hydroxyoctadecadienoic acid (a primary product of 15-LOX-1 metabolism of linoleic acid) production. 15-LOX-1 siRNA could reverse the honokiol-induced down-regulation of PPAR-g and COX-2, and cell apoptosis. 15-LOX-1 was markedly induced in tumours of xenograft mice treated with honokiol. Conclusions and implications: These findings suggest that induction of 15-LOX-1-mediated down-regulation of a PPAR-g and COX-2 pathway by honokiol may be a promising therapeutic strategy for gastric cancer.
N(ε)-carboxymethyllysine (CML), a major advanced glycation end product, plays a crucial role in diabetes-induced vascular injury. The roles of protein tyrosine phosphatases and vascular endothelial growth factor (VEGF) receptors in CML-related endothelial cell injury are still unclear. Human umbilical vein endothelial cells (HUVECs) are a commonly used human EC type. Here, we tested the hypothesis that NADPH oxidase/reactive oxygen species (ROS)-mediated SH2 domain-containing tyrosine phosphatase-1 (SHP-1) activation by CML inhibits the VEGF receptor-2 (VEGFR-2, KDR/Flk-1) activation, resulting in HUVEC injury. CML significantly inhibited cell proliferation and induced apoptosis and reduced VEGFR-2 activation in parallel with the increased SHP-1 protein expression and activity in HUVECs. Adding recombinant VEGF increased forward biological effects, which were attenuated by CML. The effects of CML on HUVECs were abolished by SHP-1 siRNA transfection. Exposure of HUVECs to CML also remarkably escalated the integration of SHP-1 with VEGFR-2. Consistently, SHP-1 siRNA transfection and pharmacological inhibitors could block this interaction and elevating [(3)H]thymidine incorporation. CML also markedly activated the NADPH oxidase and ROS production. The CML-increased SHP-1 activity in HUVECs was effectively attenuated by antioxidants. Moreover, the immunohistochemical staining of SHP-1 and CML was increased, but phospho-VEGFR-2 staining was decreased in the aortic endothelium of streptozotocin-induced and high-fat diet-induced diabetic mice. We conclude that a pathway of tyrosine phosphatase SHP-1-regulated VEGFR-2 dephosphorylation through NADPH oxidase-derived ROS is involved in the CML-triggered endothelial cell dysfunction/injury. These findings suggest new insights into the development of therapeutic approaches to reduce diabetic vascular complications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.