HERC2 inactivation abrogates nucleolar localization of RecQ helicases BLM and WRN

Abstract

The nucleolus is a nuclear structure composed of ribosomal DNA (rDNA), and functions as a site for rRNA synthesis and processing. The rDNA is guanine-rich and prone to form G-quadruplex (G4), a secondary structure of DNA. We have recently found that HERC2, an HECT ubiquitin ligase, promotes BLM and WRN RecQ DNA helicases to resolve the G4 structure. Here, we report the role of HERC2 in the regulation of nucleolar localization of the helicases. Furthermore, HERC2 inactivation enhances the effects of CX-5461, an inhibitor of RNA polymerase I (Pol I)-mediated transcription of rRNA with an intrinsic G4-stabilizing activity. HERC2 depletion or homozygous deletion of the C-terminal HECT domain of HERC2 prevented the nucleolar localization of BLM and WRN, and inhibited relocalization of BLM to replication stress-induced nuclear RPA foci. HERC2 colocalized with fibrillarin and Pol I subunit RPA194, both of which are required for rRNA transcription. The HERC2 dysfunction enhanced the suppression of pre-rRNA transcription by CX-5461. These results suggest the effect of HERC2 status on the functions of BLM and WRN on rRNA transcription in the nucleolus. Since HERC2 is downregulated in numerous cancers, this effect may be clinically relevant considering the beneficial effects of CX-5461 in cancer treatments.

Harnessing the Nucleolar DNA Damage Response in Cancer Therapy

“…APEX1 also interacts with the 47S pre-rRNA and other rRNA species, suggesting a role for APEX1 at rDNA in repairing rRNA for quality control purposes [75]. Moreover, ATM and ATR, which are PARP1 interacts with several RecQ-like helicases including Werner syndrome RecQ such as helicase (WRN) and BLM [71], which also reside in the nucleolus and are implicated in resolving G4 structures, R-loops and stalled replication forks [72]. WRN and BLM interact with Pol I and facilitate Pol I transcription, suggesting their dual role in mediating Pol I transcription as well as resolving replication and topological stress at the rDNA loci.…”

Runs of Homozygosity Revealed Reproductive Traits of Hu Sheep

“…In KEGG pathway enrichment analyses, there are five genes in breast disease pathways. LGSN , OCA2 , and HERC2 reportedly mediated resistance to breast cancers [ 34 , 35 , 36 ]. In addition, we found some candidate genes which are associated with livestock meat traits ( MICU2 , HAO1 , OCA2 , SPATA5 ) and some genes related to wool traits ( GFRA3 , CDC23 , CDC25C ).…”

The ZZ domain of HERC2 is a receptor of arginylated substrates

“…In response to DNA damage, HERC2 undergoes SUMOylation and interacts with RNF8, another E3 ubiquitin ligase, which ubiquitinates histone substrates, recruiting repair factors to DNA damage foci and promoting DNA repair 15 . HERC2 was shown to be necessary for the nucleolar localization and functions of the BML and WRN helicases 16 , 17 . However, a limited information is available regarding the function of the cytosolic pool of HERC2.…”