Apoptin induces apoptosis in human transformed and malignant cells but not in normal cells

Abstract

The chicken anemia virus protein apoptin induces a p53-independent, Bcl-2-insensitive type of apoptosis in various human tumor cells. Here, we show that, in vitro, apoptin fails to induce programmed cell death in normal lymphoid, dermal, epidermal, endothelial, and smooth-muscle cells. However, when normal cells are transformed they become susceptible to apoptosis by apoptin. Long-term expression of apoptin in normal human fibroblasts revealed that apoptin has no toxic or transforming activity in these cells. In normal cells, apoptin was found predominantly in the cytoplasm, whereas in transformed and malignant cells it was located in the nucleus, suggesting that the localization of apoptin is related to its activity. These properties make apoptin a potential agent for the treatment of a large number of tumors, also those lacking p53 and͞or overexpressing Bcl-2.Apoptosis (or programmed cell death) is an active and programmed physiological process for eliminating superfluous, altered, or malignant cells (1). Apoptosis is characterized by shrinkage of cells, segmentation of the nucleus, condensation, and cleavage of DNA into domain-sized fragments in most cells followed by internucleosomal degradation. Finally, the apoptotic cells fragment into membrane-enclosed bodies, which are rapidly phagocytosed by neighboring cells (2-4).The apoptotic process can be initiated by a variety of regulatory stimuli (5, 6). Changes in cell-survival rate play an important role in human pathogenesis, e.g. in cancer development, which is caused by enhanced cell proliferation but also by decreased cell death (7-10). A variety of chemotherapeutic agents and radiation have been demonstrated to induce apoptosis in tumor cells, in many instances via the action of wild-type p53 (11-15). Most tumors, however, acquire a mutation in p53 during their development, often correlated with poor response to cancer therapy (16)(17)(18). In several leukemias a high expression level of the proto-oncogene Bcl-2 is associated with a strong resistance to various apoptosis-inducing chemotherapeutic agents (19)(20)(21)(22). Apoptin, a 14-kDa basic and proline-rich protein (23) derived from the chicken anemia virus, can induce apoptosis in chicken and human malignant cell lines (24,25). We have established that apoptosis induced by apoptin is p53-independent (26) and cannot be blocked by 28). Therefore, apoptin is a potential antitumor agent. To explore this possibility further, we have examined the in vitro apoptotic activity of apoptin in normal human cells versus transformed human cells. MATERIALS AND METHODSCell Culture. Human primary T cells were isolated from six normal blood donors by Ficol centrifugation and grown in RPMI medium 1640 containing 6% human serum and 0.8 g͞ml phytohemagglutinin. After 3 days, the medium was changed, and 300 units͞ml of interleukin-2 were added (29). Human umbilical-cord vascular endothelial cells (HUVEC) and smooth-muscle cells (HSMC) were isolated from umbilical cords as described (30). HUVEC were grown in M199 ...

Activation of the Chicken Anemia Virus Apoptin Protein by Chk1/2 Phosphorylation Is Required for Apoptotic Activity and Efficient Viral Replication

“…Subcellular localization has been implicated as the main characteristic contributing to the selective mechanism of action of apoptin (9,19). Although the importance of apoptin localization in apoptosis has been well characterized, the mechanism of regulation and how it relates to viral replication has yet to be addressed.…”

“…Interestingly, this inhibitory interaction has been shown to mediate p53-independent G 2 /M cell cycle arrest and apoptosis in cancer cells by means of APC/C dissociation and degradation within PML nuclear bodies (PML-NB) (17,18). The differential subcellular localization of apoptin has been implicated as the major mechanism mediating tumor-specific cytotoxicity (9,19). In transformed cells, apoptin predominantly localizes to the nucleus, whereas this accumulation is impaired in normal cells.…”

Enhanced tumour cell nuclear targeting in a tumour progression model

“…In most cases, Apoptin can also elicit apoptosis in cancer cells [11,13], whereas nuclear translocation of Apoptin does not appear to be sufficient to mediate apoptosis in normal cells [14]. Interestingly, Apoptin nuclear translocation can be triggered in response to DNA damage in normal cells, while blocking these pathways in transformed cells can rescue them from Apoptin-induced cell death [13].…”

Experimental research Therapeutic anti-tumor effect of exogenous apoptin driven by human survivin gene promoter in a lentiviral construct

“…The specificity will ensure the killing of malignant cells while not hurting normal cells. Apoptin, a chicken anemia virus-derived protein, can specifically induce apoptosis of various tumor cells by translocating to the nucleus of tumor cells, and targeting DEDAF, Nur77, Nmi, Hippi and APC1 [1–3]. Cellular associations through apoptin and its binding partners impulse the death signal to different signal transduction pathways and finally lead to the death of the host cancer cells [4, 5].…”