Background: The epigenetic combinations of DNA demethylating agents and histone
deacetylase (HDAC) inhibitors have demonstrated clinical benefits for non-small cell lung cancer
(NSCLC) treatment, however, there are few studies uncovering the underlying molecular mechanism
of the combinations. Our previous study showed that DNA demethylating agent Azacitidine (Aza)
demethylated CpG sites in paired box gene 5 (pax5) promoter region, but did not induce pax5 mRNA
or protein expression.
Methods: In this study we used epigenetic combination of Aza and HDAC inhibitor Vorinostat (SAHA)
to treat NSCLC cells and to elucidate the underlying molecular mechanism. We treated pax5-
silenced NSCLC H460 cells with Aza+SAHA combination at sub-toxic concentration and detected
the re-expression of pax5 mNRA and protein.
Results: The results showed demethylation of CpG sites in pax5 promoter region by Aza treatment
and increased DNA accessibility for protein binding by SAHA treatment. The combination of
Aza+SAHA significantly increased p53 protein binding to DNA in pax5 promoter region (p<0.01).
More efficient binding of the transcription factor p53 to pax5 promoter region is likely because SAHA
increased accessibility of the chromatin conformation and Aza-demethylated DNA was more
permissive, allowing transcription factors to bind.
Conclusion: Our study not only explained an underlying mechanism, that pax5 re-expression was induced
by Aza+SAHA combination in H460 cells via p53, but also demonstrated a pattern showing
that the combination of demethylating agent and HDAC inhibitor can re-activate tumor suppressor
gene (TSG) which is associated with the enhancement of transcription factors binding to the promoter
region of the TSG.