Biology subjects

Hacker, K.

Publications and source records attributed to Hacker, K..

3 recordsLinked to original sources

bioRxiv2024

TRIM52 is a primate-specific player in the DNA repair process under tight proteolytic control by a triad of giant E3 ligases

Tripartite motif 52 (TRIM52) exhibits strong positive selection in humans, yet is lost in many other mammals. In contrast to what one would expect for such a non-conserved factor, TRIM52 loss compromises cell fitness. We set out to determine the cellular function of TRIM52. Genetic and proteomic analyses revealed TRIM52s involvement in resolving topoisomerase 2 (TOP2)-DNA cross-links, mitigating DNA damage and preventing cell-cycle arrest. Consistent with a fitness-promoting function, TRIM52 is upregulated in various cancers, prompting us to investigate its regulatory pathways. We found TRIM52 to be targeted for ultra-rapid proteasomal degradation by the giant E3 ubiquitin ligases BIRC6, HUWE1, and UBR4/KCMF1. BIRC6 mono-ubiquitinates TRIM52, with subsequent extension by UBR4/KCMF1. These findings underscore TRIM52s pivotal role in DNA damage repair and regulation of its own abundance through multi-ligase degradation.

molecular biology↗

bioRxiv2024

Multiple ubiquitin ligases protect human genome integrity by targeting cancer-associated APOBEC3 deaminases for degradation.

HighlightsO_LIRNA-free APOBEC3 (A3) can enter the nucleus, leading to genomic mutations. C_LIO_LIThree E3 ligases specifically bind the RNA-binding domain of nuclear A3s. C_LIO_LICancer-associated A3B and A3H-I are thereby targeted for proteasomal degradation. C_LIO_LIThese E3 ligases thus act as genome guardians by limiting A3-mediated mutagenesis. C_LI APOBEC family members play crucial roles in antiviral restriction. However, certain APOBEC3 (A3) proteins drive harmful hypermutation in humans, contributing to cancer. The cancer-associated A3 proteins are capable of transiting from the cytosol to the nucleus, where they can cause genome mutations. Here, we uncover a specific set of cellular pathways that protect genomic DNA from the major cancer-associated A3 proteins. Through genetic and proteomic screening we identify UBR4, UBR5, and HUWE1 as key ubiquitin E3 ligases marking cancer-associated A3B and A3H-I for degradation, thereby limiting A3-driven hypermutation. Mechanistically, UBR5 and HUWE1 recognize unoccupied A3 RNA-binding domains, thus promoting proteasomal degradation of APOBEC3 protein that is not engaged in its antiviral cellular function. Depletion or mutation of the E3 ligases in cells and human cancer samples increases A3-driven genome mutagenesis. Our findings reveal that UBR4, UBR5, and HUWE1 are crucial factors in a ubiquitination cascade that maintains human genome stability.

cell biology↗

bioRxiv2022

HUWE1 controls tristetraprolin proteasomal degradation by regulating its phosphorylation

Tristetraprolin (TTP) is a critical negative immune regulator. It binds AU-rich elements in the untranslated-regions of many mRNAs encoding pro-inflammatory mediators, thereby accelerating their decay. A key but poorly understood mechanism of TTP regulation is its timely proteolytic removal: TTP is degraded by the proteasome through yet unidentified phosphorylation-controlled drivers. In this study, we set out to identify factors controlling TTP stability. Cellular assays showed that TTP is strongly lysine-ubiquitinated, which is required for its turnover. A genetic screen identified the ubiquitin E3 ligase HUWE1 as a strong regulator of TTP proteasomal degradation, which we found to control TTP stability indirectly by regulating its phosphorylation. Pharmacological assessment of multiple kinases revealed that HUWE1-regulated TTP phosphorylation and stability was independent of the previously characterized effects of MAPK-mediated S52/S178 phosphorylation. HUWE1 function was dependent on phosphatase and E3 ligase binding sites identified in the TTP C-terminus. Our findings indicate that while phosphorylation of S52/S178 is critical for TTP stabilization at earlier times after pro-inflammatory stimulation, phosphorylation of the TTP C-terminus controls its stability at later stages.

cell biology↗