In vertebrates p53 participates in numerous biological processes including cell cycle

In vertebrates p53 participates in numerous biological processes including cell cycle regulation apoptosis differentiation and oncogenic transformation. cycle. Regulation by p53 may be exerted by direct protein signaling and/or by its ability to transcriptionally activate other genes. p53 a sequence-specific transcriptional activator (reviewed in reference 53) has been shown to activate under physiological conditions a number of cellular genes which mediate its roles in cell cycle arrest and apoptosis. p21 is likely to be its main effector in inducing a G1 block (reviewed in reference 26) while a more recently identified target 14 has been proposed to be responsible at least in part AS703026 for its G2 arrest (22). The ability of p53 to induce apoptosis is usually more complex because in some cases the transactivation function of p53 has been shown to be required while in others a transactivation-independent function was exhibited (reviewed in reference 26). p53 target genes which play roles in apoptosis include and (reviewed in references 17 and 26). Additionally it was recently shown that a class of genes termed PIG genes some of which function in reactive oxygen species metabolism are specifically induced by p53 during the apoptotic process (43). In keeping with its function as a transcriptional activator p53 has been shown to interact with several polypeptide components of the general transcription factors TFIID and TFIIH AS703026 AS703026 (17 26 and also with the p300/CBP coactivators (3 19 32 There is evidence that p53 may interact with and regulate DNA repair and/or replication factors as well (26). The transcription-independent role of p53 in apoptosis is not fully comprehended but protein interactions with p53 may be involved. Perhaps the best-studied p53 interactor is the oncoprotein MDM2 which binds to the N terminus of p53 (9 28 39 40 42 MDM2 both inhibits the ability of p53 to activate transcription (39 40 51 and targets p53 for proteasome-mediated degradation (7 21 27 Some additional proteins which may functionally interact with p53 include the c-Abl nuclear tyrosine kinase (16) the Wilms’ AS703026 tumor suppressor protein Wt1 (35) and the p33tumor suppressor (15). Many DNA viruses encode p53 binding proteins that affect p53 function. The simian virus 40 large tumor antigen binds to the p53 central conserved region and represses its transactivation function (5 13 The adenovirus 55-kDa protein E1B binds to the p53 activation domain name in a region which overlaps the MDM2 conversation region (33) and causes p53 to repress transcription (60) while the adenovirus E4orf6 product interacts with p53 and abrogates TATA binding protein-associated factor binding (12). The conversation of the human papillomavirus E6 product with p53 leads to ubiquitin-mediated degradation of the p53 protein (24). It has also been reported that this hepatis B virus X protein (57) as well as Epstein-Barr virus-encoded EBNA-5 (49) and BZLF1 (61) can bind to p53. The fact that a number of viruses encode gene products that CCND2 can interact with p53 suggests that alteration of p53 apoptotic function is usually a prerequisite for mounting a productive viral contamination (reviewed in references 50 and 58). Baculoviruses have two classes of genes which can block apoptosis induced during viral contamination: p35-like genes and inhibitor of apoptosis (IAP) genes (reviewed in reference 11). p35 of nuclear polyhedrosis virus (AcSF-21 cells activates SF-caspase-1 (1 37 47 Whereas p35 blocks the AS703026 activity of mature SF-caspase-1 some members of the IAP family (e.g. baculovirus OpIAP) block the processing and activation of this caspase (47). The mechanism by which baculoviruses activate caspases remains unclear but it is known that baculovirus DNA replication and/or late viral gene expression are required for maximum levels of apoptosis (10 29 Overexpression of IPLB-SF21 (SF-21) (52) hsOpIAPpacR (38) and TN-368 (23) cells were maintained at 27°C in TC-100 growth medium (GIBCO BRL Gaithersburg Md.) supplemented with 10% fetal bovine serum and 0.26% tryptose broth (Difco Laboratories Inc. Detroit Mich.) as described previously (41). Plasmids. phsEHp53 was constructed by replacing the open reading frame (ORF) within the ORF. The human p53 insert was prepared by PCR using pEV55Hp53 as a.