Evidence for the Ubiquitin Protease UBP43 as an Antineoplastic Target

Abstract

New pharmacologic targets are needed for lung cancer. One candidate pathway to target is composed of the E1-like ubiquitin-activating enzyme (UBE1L) that associates with interferon-stimulated gene 15 (ISG15), which complexes with and destabilizes cyclin D1. Ubiquitin protease 43 (UBP43/USP18) removes ISG15 from conjugated proteins. This study reports that gain of UBP43 stabilized cyclin D1, but not other D-type cyclins or cyclin E. This depended on UBP43 enzymatic activity; an enzymatically inactive UBP43 did not affect cyclin D1 stability. As expected, small interfering RNAs (siRNAs) that reduced UBP43 expression also decreased cyclin D1 levels and increased apoptosis in a panel of lung cancer cell lines. Forced cyclin D1 expression rescued UBP43 apoptotic effects, which highlighted the importance of cyclin D1 in conferring this. Short hairpin RNA (shRNA)-mediated reduction of UBP43 significantly increased apoptosis and reduced murine lung cancer growth in vitro and in vivo after transplantation of these cells into syngeneic mice. These cells also exhibited increased response to all-trans-retinoic acid (RA), interferon (IFN), or cisplatin treatments. Notably, gain of UBP43 expression antagonized these effects. Normal-malignant human lung tissue arrays were examined independently for UBP43, cyclin D1, and cyclin E immunohistochemical expression. UBP43 was significantly (P < 0.01) increased in the malignant versus normal lung. A direct relationship was found between UBP43 and cyclin D1 (but not cyclin E) expression. Differential UBP43 expression was independently detected in a normal-malignant tissue array with diverse human cancers. Taken together, these findings uncovered UBP43 as a previously unrecognized anti-neoplastic target.

The ISG15-specific protease USP18 regulates stability of PTEN

“…The PTM ISG15 has distinct functions and is regulated by the DUB USP18 [15,18,35]. 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].…”

“…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].…”

Deubiquitinase USP18 Loss Mislocalizes and Destabilizes KRAS in Lung Cancer

“…We previously found that specific oncogenic proteins including PML/RARα and cyclin D1 were substrates of the ubiquitin-like interferon-stimulated gene 15 (ISG15) modification (ISGylation) pathway (6–8). This pathway engages the E1 activating enzyme UBE1L, the E2 conjugating enzyme UBCH8 and the E3 ligase that enables ISG15 to bind protein substrates and regulate their stability (9–11).…”

“…The deubiquitinating (DUB) enzyme ubiquitin-specific protease 18 (USP18) is the major enzyme involved in ISG15 removal from substrate proteins (12). USP18 activity reduces ISG15 protein conjugation and promotes tumorigenesis if an oncogenic substrate is stabilized by USP18 (6–8). USP18 also functions as a negative regulator of interferon (IFN) signaling independent of its ISG15 deconjugase activity (13).…”

Novel Protective Role for Ubiquitin-Specific Protease 18 in Pathological Cardiac Remodeling

“…5,9 The thorough dissection of USP18 unraveled its role in antiviral activity and cancer inhibition. [10][11][12] Intriguingly, the gene encoding human USP18 is located on chromosome 22q11.2 in a minimal region deleted in DiGeorge syndrome, which is characterized by immune deficiencies and congenital cardiac abnormalities. 9 Emerging evidence has shed light on the relevance of USP18 to several well-known signaling pathways that participate in cardiac remodeling, including nuclear factor κB, calcineurin-nuclear factor of activated T cells, transforming growth factor-β-activated kinase 1 (TAK1) signaling.…”