Blockade of the Ubiquitin Protease UBP43 Destabilizes Transcription Factor PML/RARα and Inhibits the Growth of Acute Promyelocytic Leukemia

Abstract

More effective treatments for acute promyelocytic leukemia (APL) are needed. APL cell treatment with all-trans-retinoic acid (RA) degrades the chimeric, dominant-negative-acting transcription factor promyelocytic leukemia gene (PML)/RARa, which is generated in APL by chromosomal translocation. The E1-like ubiquitinactivating enzyme (UBE1L) associates with interferon-stimulated gene ISG15 that binds and represses PML/ RARa protein. Ubiquitin protease UBP43/USP18 removes ISG15 from conjugated proteins. In this study, we explored how RA regulates UBP43 expression and the effects of UBP43 on PML/RARa stability and APL growth, apoptosis, or differentiation. RA treatment induced UBE1L, ISG15, and UBP43 expression in RA-sensitive but not RA-resistant APL cells. Similar in vivo findings were obtained in a transgenic mouse model of transplantable APL, and in the RA response of leukemic cells harvested directly from APL patients. UBP43 knockdown repressed PML/RARa protein levels and inhibited RA-sensitive or RA-resistant cell growth by destabilizing the PML domain of PML/RARa. This inhibitory effect promoted apoptosis but did not affect the RA differentiation response in these APL cells. In contrast, elevation of UBP43 expression stabilized PML/RARa protein and inhibited apoptosis. Taken together, our findings define the ubiquitin protease UBP43 as a novel candidate drug target for APL treatment. Cancer Res; 70(23); 9875-85. Ó2010 AACR.

The ISG15-specific protease USP18 regulates stability of PTEN

“…Both ISG15 [36] and USP18 [19] are deregulated in different cancers, consistent with an important functional role for this DUB in homeostasis of growth-regulatory proteins. This view is supported by our prior work that established ISGylation affects stability of key growth-regulatory proteins in acute promyelocytic leukemia (APL) and lung cancer [16, 17, 19, 20]. Improved understanding of the functional roles played by ISGylation should advance our knowledge of protein destabilization pathways that control oncogenesis by precisely regulating intracellular oncoprotein or tumor suppressor proteins.…”

“…The major deubiquitinating enzyme ubiquitin specific peptidase 18 (USP18) can remove ISG15 from its target proteins, reversing effects of ISGylation [15]. Studies showed that ISGylation results in destabilization of specific protein substrates [16–20]. The precise consequences of ISGylation are being elucidated, but there is growing evidence that this pathway has specialized functions [18].…”

“…The precise consequences of ISGylation are being elucidated, but there is growing evidence that this pathway has specialized functions [18]. We previously showed that engineered loss of USP18 results in the destabilization of specific oncoproteins [19–20 and LM Mustachio personal communication]. Recent work also uncovered a potential tumor suppressive role for USP18 in FVB-Usp18 knockout mice [21].…”

Retinoids and rexinoids in cancer prevention: from laboratory to clinic

“…Preclinical investigations revealed that atRA induces terminal differentiation in the leukemic cells by promoting the degradation of the fusion protein through the action of the UBE1L ubiquitin-activating enzyme [56]. Recent studies identified the ubiquitin-specific protease UBP43, an antagonist of UBE1L, as an antineoplastic target whose inhibition destabilizes the t(15;17) PML/RARα fusion protein and induces apoptosis of APL cells [57]. The causative role of a single molecular defect paved the way for differentiation-based therapy and led to successful clinical application of atRA and 13- cis -RA for the treatment of APL (Table 2) [58].…”

PMLRARα binds to Fas and suppresses Fas-mediated apoptosis through recruiting c-FLIP in vivo

“…[14][15][16][17][18] Purification and identification of Fas-associated proteins BJAB cells were screened for potential binding modulators of Fas as described in supplemental Methods.…”