Histone deacetylase 6 (HDAC6) is a multi-substrate cytoplasmic enzyme that regulates many important biological processes. Recently, some reports have implicated HDAC6 in viral infection. However, nothing is known about its regulation in virus-infected cells. The data presented here for the first time demonstrate the caspase-3-mediated cleavage of HDAC6 in influenza A virus (IAV)-infected cells. HDAC6 polypeptide contains the caspase-3 cleavage motif DMAD-S at the C-terminus, and is a caspase-3 substrate. The cleavage removes most of the C-terminal ubiquitin-binding zinc finger domain from HDAC6, which could be significant for HDAC6's role in IAV-induced apoptosis in infected cells. © 2009 Federation of European Biochemical Societies.