No abstract

The p53 binding protein 2 (53BP2) has been identified as the interacting protein to p53, Bcl-2, and p65 subunit of nuclear factor κ κ κ κ B (NF-κ κ κ κ B). The TP53BP2 gene encodes two splicing variants, 53BP2S and 53BP2L, previously known as apoptosis stimulating protein 2 of p53 (ASPP2). We found that these 53BP2 proteins are located predominantly in the cytoplasm and induce apoptosis as demonstrated by cleavage of poly ADP ribose polymerase (PARP) and annexin V staining. Furthermore, we demonstrate that 53BP2 is located in the mitochondria and induces apoptosis associated with depression of the mitochondrial trans-membrane potential (∆ ∆ ∆ ∆Ψ Ψ Ψ Ψ m) and activation of caspase-9. From these findings we conclude that 53BP2 induces apoptosis through the mitochondrial death pathway.

The transcription factor NF-kB is a positive transcription factor for a number of genes and has been recognized as an anti-apoptotic regulator. However, the mechanism by which NF-kB blocks apoptosis is still controversial. Here, we demonstrate the evidence that NF-kB could attenuate the TNF-a-induced apoptosis without de novo protein synthesis using human pancreatic cancer cell lines, MIA PaCa-2 and Capan-2. The TNF-a-induced apoptosis was blocked by IL-1b, a potent inducer of NF-kB activation. This inhibitory eect of IL-1b was evident when cells were treated with protein synthesis inhibitors such as cycloheximide (CHX). Moreover, NF-kB decoy oligonucleotides could not block the anti-apoptotic eect of IL-1b at doses sucient to block the NF-kB-dependent transcription induced by IL-1b. To con®rm the role of NF-kB in blocking apoptosis, we generated stable cell lines expressing IkBDN, a highly stable form of IkBa, a cytoplasmic inhibitor of NF-kB. In these stable transfectants, the antiapoptotic eect of IL-1b was totally abolished, indicating that the anti-apoptotic action of IL-1b could be ascribed to the NF-kB action. These ®ndings show that de novo protein synthesis is dispensable for anti-apoptotic eects of NF-kB and support the possibility that NF-kB could exert its anti-apoptotic action through protein-protein interaction.

The p53 binding protein 2 (53BP2) has been identified independently as the interacting protein to p53, Bcl-2, and p65 subunit of nuclear factor κ κ κ κ B (NF-κ κ κ κ B). It was demonstrated that overexpression of 53BP2 (renamed as 53BP2S) induces apoptotic cell death. In this study we explored the effect of NF-κ κ κ κ B activation elicited by a physiological NF-κ κ κ κ B inducer, interleukin-1β β β β (IL-1β β β β ), and anti-apoptotic Bcl-2 family proteins on the 53BP2S-mediated apoptosis. We found that both NF-κ κ κ κ B activation and Bcl-2 family proteins could prevent the 53BP2S-mediated depression of mitochondrial transmembrane potential, activation of caspase-9, cleavage of poly ADP ribose polymerase (PARP), and cell death. These observations suggested that 53BP2S/Bbp and its directly or indirectly interacting proteins might play crucial roles in the regulation of apoptosis and contribute to carcinogenesis. It is also suggested that 53BP2S/Bbp induces apoptosis through the mitochondrial death pathway presumably by counteracting the actions of anti-apoptotic Bcl-2 family proteins. The regulatory network of the 53BP2S-mediated apoptosis cascade including its interacting proteins is discussed.