Suppression of acetylpolyamine oxidase by selected AP-1 members regulates DNp73 abundance: mechanistic insights for overcoming DNp73-mediated resistance to chemotherapeutic drugs

Abstract

Enhanced resistance to chemotherapy has been correlated with high levels of Delta-Np73 (DNp73), an anti-apoptotic protein of the p53 tumor-suppressor family which inhibits the pro-apoptotic members such as p53 and TAp73. Although genotoxic drugs have been shown to induce DNp73 degradation, lack of mechanistic understanding of this process precludes strategies to enhance the targeting of DNp73 and improve treatment outcomes. Antizyme (Az) is a mediator of ubiquitin-independent protein degradation regulated by the polyamine biosynthesis pathway. We show here that acetylpolyamine oxidase (PAOX), a catabolic enzyme of this pathway, upregulates DNp73 levels by suppressing its degradation via the Az pathway. Conversely, downregulation of PAOX activity by siRNA-mediated knockdown or chemical inhibition leads to DNp73 degradation in an Az-dependent manner. PAOX expression is suppressed by several genotoxic drugs, via selected members of the activator protein-1 (AP-1) transcription factors, namely c-Jun, JunB and FosB, which are required for stress-mediated DNp73 degradation. Finally, chemical-and siRNA-mediated inhibition of PAOX significantly reversed the resistant phenotype of DNp73-overexpressing cancer cells to genotoxic drugs. Together, these data define a critical mechanism for the regulation of DNp73 abundance, and reveal that inhibition of PAOX could widen the therapeutic index of cytotoxic drugs and overcome DNp73-mediated chemoresistance in tumors.

SMYD2 lysine methyltransferase regulates leukemia cell growth and regeneration after genotoxic stress

“…In this study we utilized a genome-wide functional screen to rapidly enrich for shRNAs that confer relative regenerative advantage to leukemia cells after repetitive DNA damage insults. In addition to SMYD2, whose role in AML sensitivity to DNA damage is novel and discussed below, our top list shRNAs included several well-annotated (p53 and CHK2) and proposed (PAOX [46]) determinants of cellular resistance to stress. Beyond these genes, our functional screen also identified numerous radiation resistance conferring shRNA clones that target genes previously unconnected with DNA damage response and that await experimental validation.…”

A balancing act: orchestrating amino-truncated and full-length p73 variants as decisive factors in cancer progression

“…In addition, genotoxic stress induces members of the AP-1 transcription factor family, which suppress the transactivation of the polyamine catabolic enzyme PAOX. 134 The result is that polyamines are synthesized to induce the expression of antizyme AZ1, which in turn mediates degradation of DNp73. 135 Recently, another degradation-dependent mechanism was identified that differentially regulates TP73 protein isoforms.…”

Amino-terminal p53 mutations lead to expression of apoptosis proficient p47 and prognosticate better survival, but predispose to tumorigenesis

“…In essence, clinical samples obtained with SingHealth Centralized Institutional Review Board B ethics approval were used for p53EII transcript analyses and determination of p53 mutation status by standard sequencing and PCR, and also for immunoblot and immunohistochemical analyses, as described in detailed in SI Appendix. All cell culture and biochemical work, transfections, target gene analysis by quantitative real-time PCR, and chromatin immunoprecipitations were performed as described (28,38,39).…”