Curcumin inhibits connective tissue growth factor gene expression in activated hepatic stellate cells in vitro by blocking NF-kappaB and ERK signalling.
OBJECTIVE
Gene expression of connective tissue growth factor (CTGF) is induced in activated hepatic stellate cells (HSC), the major effectors in hepatic fibrosis, and production of extracellular matrix (ECM) is consequently increased. We previously reported that curcumin, the yellow pigment in curry, suppressed ctgf expression, leading to decreased production of ECM by HSC. The purpose of this study is to evaluate signal transduction pathways involved in the curcumin suppression of ctgf expression in HSC.


METHODS
Transient transfection assays were performed to evaluate effects of activation of signalling pathways on the ctgf promoter activity. Real-time PCR and Western blotting analyses were conducted to determine expression of genes.


RESULTS
Suppression of ctgf expression by curcumin was dose-dependently reversed by lipopolysaccharide (LPS), an NF-kappaB activator. LPS increased the abundance of CTGF and type I collagen in HSC in vitro. Activation of NF-kappaB by dominant active IkappaB kinase (IKK), or inhibition of NF-kappaB by dominant negative IkappaBalpha, caused the stimulation, or suppression of the ctgf promoter activity, respectively. Curcumin suppressed gene expression of Toll-like receptor-4, leading to the inhibition of NF-kappaB. On the other hand, interruption of ERK signalling by inhibitors or dominant negative ERK, like curcumin, reduced NF-kappaB activity and in ctgf expression. In contrast, the stimulation of ERK signalling by constitutively active ERK prevented the inhibitory effects of curcumin.


CONCLUSIONS
These results demonstrate that the interruption of NF-kappaB and ERK signalling by curcumin results in the suppression of ctgf expression in activated HSC in vitro.
Chen
A
A
Department of Pathology, School of Medicine, Saint Louis University, St Louis, MO 63104, USA. achen5@slu.edu
Zheng
S
S
D000818:Animals; D015153:Blotting, Western; D055513:Connective Tissue Growth Factor; D003474:Curcumin / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors; D005786:Gene Expression Regulation / Q000187:drug effects*; D017874:Immediate-Early Proteins / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008297:Male; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D016133:Polymerase Chain Reaction; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000187:drug effects / Q000378:metabolism; D014162:Transfection
C526316:CCN2 protein, rat; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D016328:NF-kappa B; D051197:Toll-Like Receptor 4; D055513:Connective Tissue Growth Factor; D048049:Extracellular Signal-Regulated MAP Kinases; D003474:Curcumin