Abstract
Histone deacetylases (HDACs) catalyze the removal of acetyl groups from histones and contribute to transcriptional repression. In addition, the HDAC inhibitors induce apoptosis in cancer cells through alterations in histone acetylation and activation of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) apoptotic pathway. Lysophosphatidic acid (LPA) is a growth factor that promotes survival of cancer cells through activation of G protein-coupled receptors. Here we show that HDAC inhibitors can induce apoptosis through activation of the TRAIL apoptotic pathway, and LPA prevented HDAC inhibitor-induced apoptosis and increased TRAIL receptor DR4 (death receptor 4) protein expression. This was associated with increased HDAC1 recruitment to the DR4 promoter following LPA treatment and a reduction in HDAC inhibitor-induced histone acetylation in the DR4 promoter. In addition, LPA induces HDAC enzyme activity in a dose- and time-dependent manner, and this is associated with HDAC1 activation and increased binding of HDAC1 to HDAC2. Reducing the expression of HDAC1 significantly lowered LPA-induced HDAC activity and increased histone acetylation. LPA induction of HDAC activity was blocked by the LPA receptor antagonist, Ki16425, or by inhibiting receptor activation with pertussis toxin. Reducing the expression of the LPA receptor LPA(1) also blocked LPA-induced HDAC activation. In addition, LPA reduced histone acetyltransferase enzymatic activity. Finally, LPA attenuated the ability of the HDAC inhibitor to reduce HDAC activity. Thus, LPA enhances survival of cancer cells by increasing HDAC activity and reducing histone acetylation.
Highlights
Transcription in eukaryotic cells is influenced by the chromatin structure within which DNA is tightly packaged [1]
To confirm that HDAC inhibitors (HDIs)-induced apoptosis was blocked by Lysophosphatidic acid (LPA), we examined the effect of valproic acid (VPA) alone or in combination with LPA on caspase-8 activation as described under “Experimental Procedures.”
Environmental and endogenous factors up-regulating cellular histone deacetylases (HDACs) activity have not been described despite the existence of many natural and synthetic inhibitors of HDAC that are empirically being tested in clinical trials on a variety of cancers [4]
Summary
Materials—LPA (18:1) was purchased from Sigma and dissolved in phosphate-buffered saline containing 0.1% fatty acidfree bovine serum albumin. Nuclear extracts (10 g) from the cells treated with LPA (10 M) were assayed for HDAC activity. Nuclear extracts (50 g) from the cells treated with LPA (10 M) were assayed for HAT activity. 1 mg/ml protein from each pre-cleared cell lysate was incubated with 4 g of anti-HDAC1 or anti-HDAC2 antibody overnight at 4 °C, and 50 l of protein A-Sepharose beads was added and incubated for an additional 2 h. Assessment of Cell Surface Receptor Expression—Cells were resuspended in blocking buffer (10% normal goat serum in PBS), incubated for 30 min on ice to block nonspecific binding, and incubated with anti-TRAIL-R1/DR4 fluorescein isothiocyanate-conjugated antibody (Alexis) or an isotopematched control antibody (Pharmingen) for 1 h on ice. The samples were washed twice by centrifugation at 1200 rpm for 5 min with ice-cold PBS and resuspended in PBS and analyzed immediately by flow cytometry. The criterion for statistical significance was p Ͻ 0.05
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
