Our laboratory has recently demonstrated a
melatonin MT1 receptor-mediated antiproliferative signaling mechanism in
androgen receptor (AR)-positive prostate epithelial cells which involves up-regulation of p27(Kip1) through dual activation of Gα(s)/
protein kinase A (PKA) and Gα(q)/
protein kinase C (PKC) in parallel, and down-regulation of activated AR signaling via PKC stimulation. The aim of the present investigation was to identify the
transcription factor that mediates
melatonin's up-regulatory effect on p27(Kip1) in LNCaP and 22Rv1
prostate cancer cells. Deletion mapping and reporter assays of the p27(Kip1) promoter revealed that the putative
melatonin-responsive
transcription factor binds to a 116 base-pair region of the promoter sequence, which contains a potential
nuclear factor kappa B (NF-κB) binding site. When the NF-κB binding site was abolished by site-directed mutagenesis, the stimulatory effect of
melatonin on p27(Kip1) promoter activity was mitigated. Notably,
melatonin inhibited the
DNA binding of activated NF-κB via
MT1 receptor-induced PKA and PKC stimulation. Furthermore,
melatonin's up-regulatory effect on p27(Kip1) transcription and consequent cell antiproliferation were abrogated by NF-κB activator but mimicked by NF-κB inhibitor. The results indicate that inhibition of constitutively active NF-κB via
melatonin MT1 receptor-induced dual activation of (Gα(s)) PKA and (Gα(q)) PKC can de-repress the p27(Kip1) promoter leading to transcriptional up-regulation of p27(Kip1).
MT1 receptor-mediated inhibition of activated NF-κB signaling provides a novel mechanism supporting the use of
melatonin in
prostate cancer chemoprevention and
therapy.