Apoptin induces apoptosis by changing the equilibrium between the stability of TAp73 and ΔNp73 isoforms through ubiquitin ligase PIR2.

Head and Neck Oncology Group, King's College London Dental Institute, Floor 28 Tower Wing, Guy's Hospital Campus, London, SE1 9RT, UK.
Apoptosis (Impact Factor: 4.07). 04/2012; 17(8):762-76. DOI: 10.1007/s10495-012-0720-7
Source: PubMed

ABSTRACT Apoptin, a protein derived from the chicken anaemia virus, induces cell death in various cancer cells but shows little or no cytotoxicity in normal cells. The mechanism of apoptin-induced cell death is currently unknown but it appears to induce apoptosis independent of p53 status. Here we show that p73, a p53 family member, is important in apoptin-induced apoptosis. In p53 deficient and/or mutated cells, apoptin induced the expression of TAp73 leading to the induction of apoptosis. Knockdown of p73 using siRNA resulted in a significant reduction in apoptin-induced cytotoxicity. The p53 and p73 pro-apoptotic target PUMA plays an important role in apoptin-induced cell death as knockdown of PUMA significantly reduced cell sensitivity to apoptin. Importantly, apoptin expression resulted in a marked increase in TAp73 protein stability. Investigation into the mechanisms of TAp73 stability showed that apoptin induced the expression of the ring finger domain ubiquitin ligase PIR2 which is involved in the degradation of the anti-apoptotic ∆Np73 isoform. Collectively, our results suggest a novel mechanism of apoptin-induced apoptosis through increased TAp73 stability and induction of PIR2 resulting in the degradation of ∆Np73 and activation of pro-apoptotic targets such as PUMA causing cancer cell death.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: ΔNp63 is a transcription factor that is critical for the development of stratified epithelia and is overexpressed or amplified in >80% of squamous cell carcinomas (SCCs). We identified the RING finger E3 ubiquitin ligase PIR2/Rnf144b as a direct transcriptional target of ΔNp63α and showed that its expression parallels that of ΔNp63α in keratinocytes, SCC cell lines and SCCs. We used primary keratinocytes as a model system to investigate the function of PIR2/Rnf144b in stratified epithelia. Depletion of PIR2/Rnf144b severely impaired keratinocyte proliferation and differentiation, associated with accumulation of p21WAF1/CIP1; a known target of PIR2/Rnf144b. More importantly, we found that PIR2/Rnf144b binds and mediates proteasomal degradation of ΔNp63α, generating a hitherto unknown auto-regulatory feedback loop. These findings substantiate PIR2/Rnf144b as a potentially critical component of epithelial homeostasis, acting downstream of ΔNp63α to regulate cellular levels of p21WAF1/CIP1 and ΔNp63α.
    Oncogene 11/2012; 32(40):4758-4765. · 8.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The use of anticancer therapeutic agents is limited largely by their severe toxicity to normal tissues. The development of novel agents with tumor-specific cell-killing and effective gene delivery properties is thus very desirable. We used human adenovirus serotype 5 (AdHu5) as a vehicle to deliver the apoptin gene to specifically target gastric cancer in a recombinant gene delivery approach. AdHu5-apoptin is a safe and efficacious agent for the treatment of gastric cancer (GC). Our results show that apoptin protein encoded by the apoptin gene delivered via AdHu5 significantly inhibited the proliferation of SGC-7901 GC cells. Apoptin reduced the clone number by more than 75 % and resulted in cell cycle arrest in the G2/M phase for 48 % of the GC cells. It also induced cleavage of caspase-3, caspase-7, and caspase-9 in the GC cells. Intratumoral and peritumoral in vivo injection of AdHu5-apoptin significantly suppressed tumor growth and induced apoptosis in xenogeneic tumors in mice. The apoptosis induced by AdHu5-apoptin was independent of anti-apoptotic Bcl-2 and Bcl-xL proteins and the p53 pathway. Taken together, our results show that AdHu5-apoptin has great potential as a therapeutic agent for effective treatment of gastric tumors.
    Tumor Biology 06/2013; · 2.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The RBR (RING-BetweenRING-RING) or TRIAD [two RING fingers and a DRIL (double RING finger linked)] E3 ubiquitin ligases comprise a group of 12 complex multidomain enzymes. This unique family of E3 ligases includes parkin, whose dysfunction is linked to the pathogenesis of early-onset Parkinson's disease, and HOIP (HOIL-1-interacting protein) and HOIL-1 (haem-oxidized IRP2 ubiquitin ligase 1), members of the LUBAC (linear ubiquitin chain assembly complex). The RBR E3 ligases share common features with both the larger RING and HECT (homologous with E6-associated protein C-terminus) E3 ligase families, directly catalysing ubiquitin transfer from an intrinsic catalytic cysteine housed in the C-terminal domain, as well as recruiting thioester-bound E2 enzymes via a RING domain. Recent three-dimensional structures and biochemical findings of the RBRs have revealed novel protein domain folds not previously envisioned and some surprising modes of regulation that have raised many questions. This has required renaming two of the domains in the RBR E3 ligases to more accurately reflect their structures and functions: the C-terminal Rcat (required-for-catalysis) domain, essential for catalytic activity, and a central BRcat (benign-catalytic) domain that adopts the same fold as the Rcat, but lacks a catalytic cysteine residue and ubiquitination activity. The present review discusses how three-dimensional structures of RBR (RING1-BRcat-Rcat) E3 ligases have provided new insights into our understanding of the biochemical mechanisms of these important enzymes in ubiquitin biology.
    Biochemical Journal 03/2014; 458(3):421-37. · 4.65 Impact Factor


Available from
Jun 2, 2014