Chicken Anemia Virus: Induction of Apoptosis by a Single Protein of a Single-Stranded DNA Virus

Chicken anemia virus (CAV) is a globally distributed avian pathogen. CAV has a circular single-stranded DNA of 2.3 kb and constitutes a unique type in the newly described virus family ofCircoviridae.The CAV genome contains three partially or completely overlapping genes. CAV causes fatal cytopathogenic effects in chicken thymocytes and cultured transformed mononuclear cells via apoptosis. In transformed (chicken) cells, the synthesis of the VP3 gene product apoptin alone mimics this CAV-induced apoptosis, which is p53 independent and cannot be inhibited by the apoptosis-inhibiting proteins Bcl-2 and CrmA. Apoptin induces apoptosis in human tumor cells but, interestingly, not in normal cells. These properties suggest that apoptin may have potential medical applications.