Activation of transcription factor NF-κB is suppressed by curcumin (diferuloylmethane)
J Biol Chem. 1995;270(42):24995-25000.
Transcription factors such as NF-κB are proteins which play an important role in a variety of responses leading to host defence, activating a rapid progression of gene expression by binding to specific DNA sequence. Expression of various cytokines and major histocompatibility complex genes, which are the part of immune system are regulated by NF-κB. Hence, diverse pathological conditions ranging from inflammation to toxic/septic shock to cancer have been associated with irregulation in NF-κB activity. This is why NF-κB has been considered an essential target for therapeutic intervention in a wide variety of disease conditions.
Curcumin, a major active component of turmeric ((Curcuma longa)), has been shown to block many reactions in which NF-κB plays a major role. It has been observed in several studies that Curcumin produces anticancer activity by inhibiting NF-κB activation by blocking tumor initiation and tumor promotion steps.
To evaluate the inhibitory effects of curcumin on NF-κB activation induced by various agents.
The cell line ML-1a, a human myelomonoblastic leukemia cell line, was grown in RPMI 1640 medium supplemented with glutamine, gentamicin and fetal bovine serum. The cell lines were maintained and checked for contamination and were treated with different concentration of activators and incubated. The nuclear extracts were obtained and following assays were conducted.
- Electrophoretic mobility shift assays (EMSA) were performed to check the binding specificity of the activators.
- Western blotting was conducted to determine p65 levels from nuclear and cytoplasmic extracts.
Results and Discussion:
- Electrophoretic mobility shift assay indicated that 40-60 μM curcumin inhibited most of the TNF response, however, it did not activate NF-κB by itself
- A test performed to understand the kinetics of inhibition revealed that TNF response was inhibited only when cells were pretreated with Curcumin, whereas no effect was observed when cells were co-treated with TNF and curcumin
- Agents like the phorbol ester (PMA), and hydrogen peroxide (H2O2) induce NF-κB activation. When the effect of curcumin on activation of this transcription factor by PMA and H2O2 was tested it was found that curcumin completely blocked PMA and H2O2-induced activation of NF-κB, indicating that curcumin is a general suppressor of NF-κB activation
- Curcumin Inhibited TNF-dependent phosphorylation and degradation of IkBα and hence, translocation of p65 subunit of NF-κB to the nucleus
Curcumin is a pharmacologically safe and potent agent useful in modulating expression of genes regulated byNF-κB and thus effective in a targeting a wide variety of pathological conditions.