CHFR is negatively regulated by SUMOylation-mediated ubiquitylation

Kaposi's sarcoma-associated herpesvirus processivity factor (PF-8) recruits cellular E3 ubiquitin ligase CHFR to promote PARP1 degradation and lytic replication

Kaposi’s sarcoma–associated herpesvirus (KSHV), which belongs to the gammaherpesvirus subfamily, is associated with the pathogenesis of various tumors. Nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1) catalyzes the polymerization of ADP-ribose units on target proteins. In KSHV-infected cells, PARP1 inhibits replication and transcription activator (RTA), a molecular switch that initiates lytic replication, through direct interaction. Thus, for efficient replication, KSHV has to overcome the molecular barrier in the form of PARP1. Previously, we have demonstrated that KSHV downregulates the expression of PARP1 through PF-8, a viral processivity factor. PF-8 induces ubiquitin–proteasome system–mediated degradation of PARP1 via direct physical association and enhances RTA transactivation activity. Here, we showed that dimerization domains of PF-8 are crucial not only for PARP1 interaction and degradation but also for enhancement of the RTA transactivation activity. PF-8 recruited CHFR for the PARP1 degradation. A knockdown of CHFR attenuated the PF-8–induced PARP1 degradation and enhancement of the RTA transactivation activity, leading to reduced KSHV lytic replication. These findings reveal a mechanism by which KSHV PF-8 recruits a cellular E3 ligase to curtail the inhibitory effect of PARP1 on KSHV lytic replication.

Kaposi’s sarcoma–associated herpesvirus (KSHV), a member of the gammaherpesvirus subfamily, is associated with the pathogenesis of various tumors. Poly(ADP-ribose) polymerase 1 (PARP1), which is involved in various cellular functions, restricts lytic replication of oncogenic gammaherpesviruses by inhibiting replication and transcription activator (RTA), a molecular switch that activates the viral lytic replication. To abrogate the inhibitory effect of PARP1, reactivated KSHV promotes PARP1 degradation via direct interaction between PARP1 and PF-8, a viral processivity factor. Dimerization domains of PF-8 were found to be critical for PARP1 interaction and degradation and for enhancing the RTA transactivation activity. Furthermore, we found that CHFR, an E3 ubiquitin ligase, is required for PF-8–induced PARP1 degradation and efficient lytic replication of KSHV. This is the first study to show the role of CHFR in viral replication or pathogenicity. This study revealed a molecular mechanism via which gammaherpesviruses overcome the PARP1-mediated inhibitory effect on viral replication: by means of PF-8, which recruits a cellular E3 ubiquitin ligase.

Toward understanding ubiquitin-modifying enzymes: from pharmacological targeting to proteomics

Ubiquitination is a highly conserved post-translational modification that regulates protein trafficking, function, and turnover. Ubiquitin ligases (E3s) conjugate ubiquitin polypeptides on substrates, whereas deubiquitnases (DUBs) reverse ubiquitination. Engineering of chemical antagonists and inhibitors of ubiquitin ligases and DUBs has considerably aided the study of enzymes that participate in ubiquitin modification of substrates. In addition, proteomic tools have been developed to characterize the enzymes, substrates, and modifications regulated by DUBs and E3s. Here we review inhibitors and antagonists that have been developed against DUBs and E3s, focusing on enzymes that participate in ubiquitin editing or in the reciprocal ubiquitin regulation of substrates. We outline the cellular biology that is regulated by these DUBs and E3s and highlight how the inhibitory compounds have improved our understanding of these pathways. Finally, we discuss the challenges and future directions for pharmacologically targeting ubiquitin-modifying enzymes, as well as the development of proteomic methods to evaluate ubiquitin modification of substrates.