Adenovirus 12 E4orf6 inhibits ATR activation by promoting TOPBP1 degradation

Abstract

Activation of the cellular DNA damage response is detrimental to adenovirus (Ad) infection. Ad has therefore evolved a number of strategies to inhibit ATM-and ATR-dependent signaling pathways during infection. Recent work suggests that the Ad5 E4orf3 protein prevents ATR activation through its ability to mislocalize the MRN complex. Here we provide evidence to indicate that Ad12 has evolved a different strategy from Ad5 to inhibit ATR. We show that Ad12 utilizes a CUL2/RBX1/elongin C-containing ubiquitin ligase to promote the proteasomal degradation of the ATR activator protein topoisomerase-IIβ-binding protein 1 (TOPBP1). Ad12 also uses this complex to degrade p53 during infection, in contrast to Ad5, which requires a CUL5-based ubiquitin ligase. Although Ad12-mediated degradation of p53 is dependent upon both E1B-55K and E4orf6, Ad12-mediated degradation of TOPBP1 is solely dependent on E4orf6. We propose that Ad12 E4orf6 has two principal activities: to recruit the CUL2-based ubiquitin ligase and to act as substrate receptor for TOPBP1. In support of the idea that Ad12 E4orf6 specifically prevents ATR activation during infection by targeting TOPBP1 for degradation, we demonstrate that Ad12 E4orf6 can inhibit the ATR-dependent phosphorylation of CHK1 in response to replication stress. Taken together, these data provide insights into how Ad modulates ATR signaling pathways during infection.DNA damage | cullin-RING ubiquitin ligases | DNA damage | proteasome

Adenovirus E4orf3 Targets Transcriptional Intermediary Factor 1γ for Proteasome-Dependent Degradation during Infection

“…It has been determined, for in-stance, that Ad12 and Ad40 E1B-55K and E4orf6 utilize exclusively the CUL2-containing CRL2 to promote the degradation of p53 during infection, while Ad16 can utilize either CRL2 or CRL5 (10,22). Further investigation has revealed that different Ad serotypes have evolved different strategies in order to neutralize the DNA damage response during infection such that the cohort of substrates targeted for degradation varies between viral serotypes (22,32).…”

Downregulation of Mdm2 and Mdm4 enhances viral gene expression during adenovirus infection

“…5,6,9 Similarly, Cul5 NTD expression failed to stabilize Mdm2 and Mdm4 in Ad12-infected cells. In contrast, in Ad5-infected cells, Cul5 NTD expression resulted in reduced levels of Mdm2 (Fig.…”

“…DNA ligase IV (lig4) 8 and TOPBP1, 6 have been identified, although precise biochemical mechanisms of substrate ubiquitination and degradation for these cellular proteins may differ. 6,9 Mdm2 is RING domain-containing E3 ubiquitin ligase that binds to p53 and mediates its ubiquitination and degradation.…”

“…For example, E1B-55K and E4orf6-34K proteins assemble an E3 ligase complex with cullin 2 or 5 (Cul2 or Cul5), Elongins B and C and RING box protein 1 or 2 (Rbx1 or 2). [3][4][5][6] A number of Successful viral replication entails elimination or bypass of host antiviral mechanisms. Here, we show that shRNAmediated knockdown of murine double minute (Mdm2) and its paralog Mdm4 enhanced the expression of early and late viral gene products during adenovirus (HAdV) infection.…”

“…6,9 Mdm2 is RING domain-containing E3 ubiquitin ligase that binds to p53 and mediates its ubiquitination and degradation. [10][11][12] This mechanism is essential for mouse embryonic development, as homozygous Mdm2 knockout is lethal, and simultaneous deletion of p53 rescues this phenotype.…”