Involvement of different nuclear hormone receptors in butyrate-mediated inhibition of inducible NF kappa B signalling.

BACKGROUND: NF kappa B plays a major role in the control of immune responses and inflammation. Recently, butyrate has not only been demonstrated to suppress NF kappa B activation in colorectal cancer cells, but also to modulate the activity and expression of the Peroxisome-Proliferator-Activated-Receptor gamma (PPAR gamma) and the vitamin D receptor (VDR). Therefore, we investigated a putative involvement of both receptors in butyrate-mediated inhibition of inducible NF kappa B signalling.
RESULTS: Treatment of HT-29 cells with butyrate attenuated basal p50 as well as TNFalpha- and LPS-induced p50 and p65 NF kappa B dimer activity in the nucleus as measured by transcription factor assay. Cytosolic expression of I kappa B alpha protein was reduced by butyrate, and TNFalpha but not by LPS. Challenge of cells with the VDR antagonist ZK191732 up-regulated basal NF kappa B activity by decreasing I kappa B alpha simultaneously, while basal signalling was not influenced by the PPAR gamma inhibitor GW9662. Pre-treatment with ZK191732 reduced the inhibitory effect of butyrate on NF kappa B activation caused by TNFalpha whereas no activation was noted in transfected dominant-negative PPAR gamma mutant vector cells. Adversely, the inhibitory effect of butyrate on NF kappa B activity induced by LPS was almost reversed in dominant-negative PPAR gamma mutant cells while pre-incubation of ZK191732 did not affect butyrate-mediated attenuation of LPS-induced NF kappa B signalling.
CONCLUSION: These findings provide evidence for the involvement of the nuclear hormone receptors PPAR gamma and VDR in butyrate-mediated inhibition of inducible NF kappa B activation dependent on the stimulated signalling pathway. Moreover, VDR appears to play an inhibitory role in the regulation of basal NF kappa B signalling.