Abstract 1594: Targeting UBP43 for repression destabilizes PML/RARα and inhibits acute promyelocytic leukemia growth

Abstract

Abstract All-trans-retinoic acid (RA) successfully treats acute promyelocytic leukemia (APL) at least partly through triggering degradation of the PML/RARα translocation product. Prior work revealed that the E1-like ubiquitin-activating enzyme (UBE1L) associates with the interferon-stimulated gene 15 (ISG15) to repress PML/RARα protein expression. The ubiquitin protease 43 (UBP43) removes ISG15 from conjugated proteins. We derived two different anti-human UBP43 antisera to examine UBP43 protein expression. This study explored whether RA regulates UBP43 expression and if UBP43 affects PML/RARα protein stability as well as growth or apoptosis of APL cells. Retinoid regulation of the UBE1L-ISG15-UBP43 pathway was studied in cultured NB4 APL cells, transgenic APL mice and leukemic cells harvested from APL patients. Whether the deconjugase UBP43 was a therapeutic target was determined through gain and loss of UBP43 expression experiments. This study extends prior work by reporting that RA-treatment induced UBP43 expression in RA-sensitive, but not in RA-resistant NB4 APL cells. This followed an induction of UBE1L and ISG15 expression in RA-sensitive APL cells. UBP43 functions as a negative feedback loop by reversing ISG15 conjugation of PML/RARα protein. Deregulating this loop by UBP43 knock-down repressed APL cell growth by further destabilizing the PML domain of PML/RARα protein. Notably, this triggered apoptosis in APL cells. In contrast, UBP43 over-expression stabilized PML/RARα protein and promoted APL cell growth by inhibiting apoptosis. RA-treatment of a murine transgenic APL model and of de novo cultures of APL cells from patients increased UBE1L, ISG15 and UBP43 expression. Thus, this study found that the deconjugase UBP43 was retinoid regulated in NB4 APL cells as well as in leukemic cells isolated directly from APL patients and in a mouse model for APL. Oncogenic effects of PML/RARα were reversed by UBP43 knock-down, which destabilized PML/RARα protein and triggered apoptosis in APL cells. Taken together, these findings establish UBP43 as a novel molecular pharmacologic target for APL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1594.