Control of cyclooxygenase-2 expression and tumorigenesis by endogenous 5-methoxytryptophan

Abstract

Cyclooxygenase-2 (COX-2) expression is induced by mitogenic and proinflammatory factors. Its overexpression plays a causal role in inflammation and tumorigenesis. COX-2 expression is tightly regulated, but the mechanisms are largely unclear. Here we show the control of COX-2 expression by an endogenous tryptophan metabolite, 5-methoxytryptophan (5-MTP). By using comparative metabolomic analysis and enzyme-immunoassay, our results reveal that normal fibroblasts produce and release 5-MTP into the extracellular milieu whereas A549 and other cancer cells were defective in 5-MTP production. 5-MTP was synthesized from L-tryptophan via tryptophan hydroxylase-1 and hydroxyindole O-methyltransferase. 5-MTP blocked cancer cell COX-2 overexpression and suppressed A549 migration and invasion. Furthermore, i.p. infusion of 5-MTP reduced tumor growth and cancer metastasis in a murine xenograft tumor model. We conclude that 5-MTP synthesis represents a mechanism for endogenous control of COX-2 overexpression and is a valuable lead for new anti-cancer and anti-inflammatory drug development.tumor suppression | tryptophan metabolism | inflammation control C yclooxygenase-2 (COX-2) is a rate-limiting enzyme in the production of diverse prostanoids with potent biological activities. It is involved in multiple physiological functions and triggers key pathological processes, such as tumorigenesis and inflammation (1, 2). COX-2 is constitutively overexpressed in a wide variety of human cancers and is enhanced by proinflammatory stimuli (3, 4). There is convincing evidence for a causal role of COX-2 in tumorigenesis. Inhibition of COX-2 activities was reported to control human colorectal cancer (5-8). COX-2 induces tumorigenesis by promoting important cellular functions including cell proliferation, migration, and resistance to apoptosis (9-11). The induced COX-2 expression by proinflammatory and mitogenic factors in normal cells is tightly controlled (12) whereas its overexpression in cancer cells is attributed to dysregulated transcription (13). The endogenous control mechanisms for COX-2 expression in normal cells and the mechanisms underlying the dysregulation in cancer cells are poorly understood. We previously identified in the conditioned medium of human fibroblasts small molecules (named cytoguardins) that suppress COX-2 expression induced by proinflammatory mediators (14). NMR analysis of a semipurified fraction revealed compounds with indole moieties (14). However, the exact chemical structures remain elusive. In this study, we elucidated the structure of cytoguardins by comparing the metabolomic profiles between normal and cancer cells. ResultsCytoguardins Inhibit Cancer Cell COX-2. To determine that fibroblast factors are capable of suppressing cancer cell COX-2 expression, we cocultured human Hs68 foreskin fibroblasts (HsFb) with A549 lung cancer cells in a Boyden chamber for 24 h. A549 cells were removed and treated with phorbol 12-myristate 13-acetate (PMA) for 4 h, and COX-2 proteins were analyzed. HsFb suppressed A549 ...

Inhibition of tumor cell proliferation and motility by fibroblasts is both contact and soluble factor dependent

“…In addition, other groups showed that CM from CAFs has a growth-promoting effect on tumor cells due to factors secreted in the culture medium (14,15). Among these factors, IL-6, TGFbeta, COX-2, and CXCL14 have already been mentioned (16)(17)(18)(19)(20). Interestingly, we show that our results are in accordance with Erez et al in that the proinflammatory gene signature was up-regulated in our fibroblasts in vitro as well, except for SPP1, which showed down-regulation upon tumor cell confrontation (21).…”

Endothelium-Derived 5-Methoxytryptophan Is a Circulating Anti-Inflammatory Molecule That Blocks Systemic Inflammation

“…29,33,34 On cellular activation, activated NF-κB (p65/ p50) binds to the functional binding sites on the promoter/ enhancer region of diverse genes such as COX-2, iNOS, and proinflammatory cytokines and chemokines. 14,23,25,26,[35][36][37] We show that 5-MTP blocks NF-κB activation that could account for its broad inhibitory actions on the proinflammatory cytokines and mediators. It has been shown that the inhibition of NF-κB is significantly correlated with improvement of survival from endotoxin shock and sepsis.…”

“…We previously reported that tryptophan hydroxylase 1 (TPH-1) is a key enzyme in 5-MTP synthesis and TPH-1 silencing with siRNA causes reduction of 5-MTP. 14 We wondered whether lipopolysaccharide suppresses 5-MTP through inhibition of TPH-1 expression. TPH-1 proteins were detected in HUVECs that were reduced by lipopolysaccharide in a concentration-dependent manner ( Figure 1F).…”

“…14 We postulated that human ECs produce and release tryptophan metabolite such as 5-MTP to modulate inflammatory responses and protect against systemic inflammation and sepsis. By using metabolomic analysis coupled with enzyme immunoassay and immunohistochemistry, we identified 5-MTP as a novel class of endothelial protective molecules.…”

Enrichment and characterization of cancer stem cells from a human non-small cell lung cancer cell line

“…The cell invasion assay was performed using 24 Transwell chambers (Corning Inc., Corning, NY, USA) as previously described (14). The single cells were suspended in serum-free RPMI-1640 medium at the concentration of 3x10 5 cells/ml.…”