Vorinostat (SAHA) Inhibits STAT6 Phosphorylation and Transcription, Downregulates Bcl-xL, and Induces Apoptosis in Hodgkin Lymphoma (HL) Cell Lines.

Vorinostat (SAHA) Inhibits STAT6 Phosphorylation and Transcription, Downregulates Bcl-xL, and Induces Apoptosis in Hodgkin Lymphoma (HL) Cell Lines. Although the malignant Hodgkin and Reed Sternberg (HRS) cells of HL are of B-cell origin, they infrequently express B-cell antigens. Recent studies demonstrated that several B-cell specific genes are silenced in HRS cells by epigenetic mechanism, suggesting that this process may be reversible and could be explored therapeutically with deacetylase (DAC) inhibitors or hypomethylating agents. Pan-DAC and isotype-selective DAC inhibitors have shown promising activity in vitro and in vivo in a variety of lymphoid malignancies, including HL. However, the mechanisms of antiproliferative action of DAC inhibitors in HL remain unknown. In this study, we examined the antiproliferative effects of the pan-DAC inhibitor vorinostat (inhibits class I and class II DACs) on HL cell lines and determined its effect on signaling mechanisms that are known to promote HRS cell survival, including STAT3, STAT6, Akt, and ERK pathways. Vorinostat inhibited DACs as evident by the increase in histone-3 acetylation as early as 30 minutes of incubation. Furthermore, vorinostat induced the expression of the cell cycle regulatory protein p21 which was associated with an early increase in the G2M cell cycle fraction in HL cells. Vorinostat had no inhibitory effect on SATA3 or ERK, but inhibited STAT6 phosphorylation and transcription in a dose and time dependant manner. This effect was associated with a decrease in Akt phosphorylation on Ser473 residue. Because STAT6 has been reported to transcriptionally regulate Bcl-XL and Thymus and activation-regulated chemokines (TARC), we examined the effect of vorinostat on these two targets in HL cells. TARC has been shown to play an important role in attracting Th2-type T cells and T-regulatory (T-reg) cells, and to be elevated in sera from patients with HL. Vorinostat downregulated the mRNA expression of TARC in a dose dependent manner, suggesting that it may have a role in regulating chemotaxis of reactive T cells and T-reg cells to HL microenvironment in vivo. Moreover, vorinostat reduced the cellular level of the antiapoptotic protein Bcl-xL which was associated with activation of the caspase pathway, and induction of apoptosis in HL cells. Collectively, these data suggest that DAC inhibition in HL by vorinostat may induce cell death by inhibiting STAT6 and downregulating its antiapoptotic target bcl-xL protein. Furthermore, our data suggest that DAC inhibition may have an added effect in vivo on the cellular component in HL microenvironment by inhibiting TARC.