We investigated the subcellular distribution of human ZBP1, which harbors the N-terminal Z-DNA binding domains, Z alpha and Z beta. ZBP1 was distributed primarily in the cytoplasm and occasionally as nuclear foci in interferon (IFN)-treated primary hepatocellular carcinoma cells, and in several other transfected cell types. In leptomycin B (LMB)-treated cells, endogenous ZBP1 efficiently accumulated in nuclear foci, which overlapped PML oncogenic domains (PODs) or nuclear bodies (NBs). In transfection assays, the unique C-terminal region of ZBP1 was necessary for its typical cytoplasmic localization. Interestingly, the Z alpha-deleted form displayed an increased association with PODs compared to wild-type and, unlike wild-type, perfectly accumulated in PODs in LMB-treated cells, implying that the presence of Z beta domain also facilitates the cytoplasmic localization. Our results demonstrate that ZBP1 is localized primarily in the cytoplasm but also associated with nuclear PODs in IFN or LNB-treated cells. Given that about half of ZBP1 mRNA lacks exon 2 encoding the Za domain, our data also suggest that the localization of ZBP1 may be differentially regulated by the Z-DNA binding domain, Z alpha, in splice variants. (c) 2006 Elsevier Inc. All rights reserved.