Ubiquitin ligase ARF-BP1/Mule modulates base excision repair

Abstract

Base excision repair (BER) is the major cellular pathway involved in removal of endogenous/spontaneous DNA lesions. Here, we study the mechanism that controls the steady-state levels of BER enzymes in human cells. By fractionating human cell extract, we purified the E3 ubiquitin ligase Mule (ARF-BP1/HectH9) as an enzyme that can ubiquitylate DNA polymerase b (Pol b), the major BER DNA polymerase. We identified lysines 41, 61 and 81 as the major sites of modification and show that replacement of these lysines to arginines leads to increased protein stability. We further show that the cellular levels of Pol b and its ubiquitylated derivative are modulated by Mule and ARF and siRNA knockdown of Mule leads to accumulation of Pol b and increased DNA repair. Our findings provide a novel mechanism regulating steady-state levels of BER proteins.

Short Communication Huwe1 as a therapeutic target for neural injury

“…Recently, Parsons et al (2009) provided a new mechanism underlying the cellular response to DNA damage. It is known that base excision repair (BER) is the major cellular system involved in the removal of DNA lesions induced by endogenous and exogenous DNA damaging agents.…”

“…The regulation of cellular Pol β levels is vital, as under or overproduction of Pol β leads to deficient repair or an increased rate of mutagenesis, respectively, and both have been linked to increased cancer susceptibility (Matsuda et al, 2003). Parsons et al (2009) conceived that the dynamics of cellular Pol β are controlled by Huwe1 and ARF, which determine the fate of the newly synthesized cytoplasmic Pol β. Huwe1 is predominantly a cytoplasmic protein, whereas ARF is located in the nucleoli. In response to DNA damage, ARF is released from the nucleoli, allowing it to interact with Huwe1 and inhibiting its ubiquitin ligase activity, which restrains the degradation of Pol β by Huwe1 (Parsons et al, 2009).…”

“…Parsons et al (2009) conceived that the dynamics of cellular Pol β are controlled by Huwe1 and ARF, which determine the fate of the newly synthesized cytoplasmic Pol β. Huwe1 is predominantly a cytoplasmic protein, whereas ARF is located in the nucleoli. In response to DNA damage, ARF is released from the nucleoli, allowing it to interact with Huwe1 and inhibiting its ubiquitin ligase activity, which restrains the degradation of Pol β by Huwe1 (Parsons et al, 2009). These results provide a molecular link between DNA damage and Huwe1 activity.…”

Mule determines the apoptotic response to HDAC inhibitors by targeted ubiquitination and destruction of HDAC2

“…Mule was first identified as a ubiquitin ligase for an anti-apoptotic Bcl-2 family protein, Mcl-1 (Zhong et al 2005). Mule is also known as ARF-BP1, Ureb1, LASU1, HUWE1, or HectH9, and promotes ubiquitin-proteasomal degradation of multiple substrates, including p53, c-Myc, Cdc6, histones, N-Myc, Miz1, TopBP1, and Polb (Adhikary et al 2005;Chen et al 2005;Zhong et al 2005;Hall et al 2007;Liu et al 2007;Herold et al 2008;Zhao et al 2008;Parsons et al 2009;Yang et al 2010). However, whether any of these existing or unidentified substrates mediate the major function of Mule in the DNA damage response remains elusive.…”

Dichotomous role of pancreatic HUWE1/MULE/ARF-BP1 in modulating beta cell apoptosis in mice under physiological and genotoxic conditions

“…Among them, p53, MCL1 and DNA polymerase beta are better characterised [16,20,33]. Intriguingly, p53 induces apoptosis while MCL-1 and DNA polymerase inhibit the apoptotic pathway.…”