Resveratrol Induces Cell Growth Arrest and Cell Death of Adult T-Cell Leukemia Cells Via Deacetylation of STAT3 by SIRT1

Abstract 2844

Adult T-cell leukemia (ATL) is an aggressive malignancy of peripheral T cells infected with human T-cell leukemia virus type 1 (HTLV-1). The prognosis of aggressive ATL patients remains poor because of its resistance to conventional chemotherapy. Therefore, new therapeutic targets should be explored. We recently reported that signal transducers, and activators of transcription 3 (STAT3)/survivin pathway is critical for cell proliferation and survival of ATL cells (Ito S. et al. Leuk Res. 2010. 34:352-357). Thus, STAT3 may be one of the therapeutic targets in ATL. Recent report suggested that acetylation in the SH2 domain of STAT3 is an important regulatory modification that influences protein-protein interaction and transcriptional regulation. Although STAT3 has been shown to interact with p300 acetyltransferase, the mechanism of deacetylation of STAT3 remains unknown. It has been recently shown that fasting-activated longevity protein sirtuin 1 (SIRT1) deacetylase/STAT3 pathway in the regulation of gluconeogenesis. We hypothesized that STAT3 deacetylation by SIRT1 may influence the cell growth and survival of ATL cells. In this study, we investigated the effects of resveratrol, an activator of SIRT1 deacetylase, on HTLV-1 infected T-cell lines, KUT1 and MT2 cells. We found that resveratrol significantly suppressed cell proliferation in a dose- and time-dependent manner by trypan blue exclusion method (P<0.01, ED50=50mM). Resveratrol also induced apoptosis in these cells by flow cytometric analysis with AnnexinV/propidium iodide staining (P<0.01). We next examined intracellular signaling in resveratrol-treated cells. Immunoblot analysis showed the suppression of constitutive phosphorylation of STAT3 at Tyr705 and IkBα at Ser32 but not JAK3 and STAT5 of both cells 24 hours after the treatment of resveratrol. Interestingly, resveratrol reduced acetylation of STAT3 at Lys685. We also observed the cleavage of caspase-3 and poly(ADP-ribose) polymerase (PARP) in resveratrol-treated cells, indicating that resveratrol induces caspase-dependent apoptosis in these cells. To better understand the mechanism by which resveratrol induces STAT3 deacetylation, we examined the relationship between SIRT1 and STAT3. SIRT1 protein expression level was elevated after the treatment of resveratrol. Immunoprecipitation assay revealed the physical interaction of STAT3 with SIRT1 in MT2 cells, suggesting that the mechanism of action of resveratrol involves the deacetylation of STAT3 through the interaction of STAT3 with SIRT1.

Our data indicate that resveratrol presents a potent anti-leukemia effect in part via the deacetylation of STAT3 in HTLV-1 infected cells. These mechanistic findings suggest that resveratrol may have a potential in the treatment of ATL.