Biology subjects

Garvin, A. J.

Publications and source records attributed to Garvin, A. J..

8 recordsLinked to original sources

bioRxiv2024

USP50 suppresses alternative RecQ helicase use and deleterious DNA2 activity during replication.

Mammalian DNA replication employs several RecQ DNA helicases to orchestrate the faithful duplication of genetic information. Helicase function is often coupled to the activity of specific nucleases, but how helicase and nuclease activities are co-directed is unclear. Here we identify the inactive ubiquitin-specific protease, USP50, as a ubiquitin-binding and chromatin-associated protein required for ongoing replication, fork restart, telomere maintenance and cellular survival during replicative stress. USP50 supports WRN:FEN1 at stalled replication forks, suppresses MUS81-dependent fork collapse and restricts double-strand DNA breaks at GC-rich sequences. Surprisingly we find that cells depleted for USP50 and recovering from a replication block exhibit increased DNA2 and RECQL4 foci and that the defects in ongoing replication, poor fork restart and increased fork collapse seen in these cells are mediated by DNA2, RECQL4 and RECQL5. These data define a novel ubiquitin-dependent pathway that promotes the balance of helicase: nuclease use at ongoing and stalled replication forks.

cancer biology↗

bioRxiv2022

Pin1-promoted SUMOylation of RNF168 restrains its chromatin accumulation.

The E3 ubiquitin ligase RNF168 is a rate-limiting component of DNA double-strand break signalling that acts to amplify histone ubiquitylation. The confining of RNF168 chromatin spreading around DNA break sites has been related to constraining its expression levels and to the removal of ubiquitin-conjugates to which it binds. Here we identify a new mechanism that suppresses RNF168 amplification at chromatin. We show that depletion of Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) or mutation of the Pin1-binding site of RNF168 increases DNA-damage site accumulation of RNF168 to supraphysiological levels without impacting RNF168 expression levels. Pin1 promotes SUMOylation of RNF168 by SUMO2/3, and a SUMO conjugation site on RNF168 is required to restrict RNF168 accumulations. We find Pin1-SUMO mediated-regulation of RNF168 is associated with cellular radioresistance. These data demonstrate that the regulation of chromatin ubiquitylation is actively suppressed by modification of RNF168 to counteract excessive RNF168-ubiquitin spreading.

molecular biology↗

bioRxiv2022

SUMO4 regulates DNA double-strand break repair independently of conjugation.

The amplitudes of small-modifier protein signalling through ubiquitin and the Small Ubiquitin-like Modifiers, SUMO1-3, are critical to the correct phasing of DNA repair protein accumulation, activity, and clearance, and for the completion of mammalian DNA double-strand break (DSB) repair. However, how SUMO-conjugate signalling in the response is delineated is poorly understood. At the same time, the role of the non-conjugated SUMO protein, SUMO4, has remained enigmatic. Here we reveal that SUMO4 is required to prevent excessive DNA-damage-induced SUMOylation and deleterious over-accumulation of RAP80. Mechanistically we show SUMO4 acts independently of its conjugation and potentiates SENP1 catalytic activity. These data identify SUMO4 as a SUMO deconjugation component and show SUMO4:SENP1 are critical regulators of DNA-damage-induced SUMO signalling. HighlightsO_LIThe roles of the SUMO family members, SUMO1-4, in DSB repair are not redundant. C_LIO_LISUMO4 conjugation is deleterious. C_LIO_LISUMO4 promotes SENP1 catalytic activity. C_LIO_LISUMO4:SENP1 restrict SUMO-signalling and accumulation of the BRCA1-A complex. C_LI

molecular biology↗

bioRxiv2022

RAD52 underlies the synthetic-lethal relationship between BRCA1/2 and 53BP1 deficiencies and DNA polymerase theta loss.

Introductory paragraphCells lacking several DNA repair proteins, including those promoting homologous recombination (HR), are sensitive to polymerase theta (Pol{theta}) repression1-4. Pol{theta} drives theta-mediated end joining (TMEJ) and suppresses HR but what mediates its synthetic lethal relationships is unclear. Here we examine murine Brca1C61G/C61G 53bp1-/-cells and find they are largely HR proficient by using RNF168 and RAD52. They exhibit no more TMEJ than 53bp1-/- cells yet are more sensitive to targeting of Pol{theta}. We find that RAD52 recruitment to damaged chromatin is increased following Pol{theta} depletion. RAD52 accumulation and cellular sensitivity to Pol{theta} repression can be curbed by the RAD51-binding regions of BARD1 and BRCA2, and sensitivity of BRCA1/2 depleted cells to Pol{theta} repression is suppressed by RAD52 inhibition. 53bp1-/- cells exhibit a smaller increase in RAD52 recruitment following Pol{theta} repression and also become resistant to Pol{theta} repression following RAD52 inhibition. Thus, RAD52 mediates sensitivity to targeting Pol{theta} in these contexts.

molecular biology↗

bioRxiv2022

SUMO monoclonal antibodies vary in sensitivity, specificity, and ability to detect SUMO conjugate types.

Monoclonal antibodies (MAb) to members of the Small Ubiquitin-like modifier (SUMO) family are essential tools in the study of cellular SUMOylation. However, many reagents are poorly validated, and the choice of which antibody to use for which detection format is without an evidence base. Here we test twenty-four anti-SUMO monoclonal antibodies for sensitivity and specificity to SUMO1-4 in monomeric and polymeric states in dot-blots, immunoblots, immunofluorescence and immunoprecipitation. We find substantial variability between SUMO MAbs for different conjugation states, detection of increased SUMOylation in response to thirteen different stress agents and as enrichment reagents for analysis of SUMOylated RanGAP1 or KAP1. All four anti-SUMO4 monoclonal antibodies tested cross-reacted with SUMO2/3, and several SUMO2/3 monoclonal antibodies cross-reacted with SUMO4. ~10% of tested monoclonal antibodies produced specific results across multiple applications.

molecular biology↗

bioRxiv2022

Modification of the SUMO activating enzyme subunit SAE2 directs SUMO isoform bias required for mitotic fidelity.

Mammalian cells possess three conjugatable SUMO variants: SUMO1 and the largely indistinguishable SUMO2 and SUMO3 (designated SUMO2/3). Some SUMOylated substrates are modified by both SUMO1 and SUMO2/3, while others show biased modifications towards SUMO1 or SUMO2/3. How preferential SUMO protein conjugation is coordinated is poorly understood. Here, we examine a modification of the catalytic component of the human SUMO Activation Enzyme, SAE2. We observe that lysine 164 of SAE2 is deacetylated during mitosis in an HDAC6-dependent manner. We find that an acetyl-analogue mutant, SAE2-K164Q, biases the activation and conjugation of SUMO2>SUMO1 and discriminates SUMO1 and SUMO2/3 through their C-terminal tails. Complementation of SAE2-depleted or inhibited cells with SAE2-K164Q restricts mitotic SUMO1-conjugates and increases multipolar spindle formation. We confirm the SUMO E1-dependent modification of the nuclear mitotic apparatus, NuMA, and find that the mitotic defects of both SAE2-K164Q complemented cells and HDAC6-inhibitor-treated cells are corrected by either over-expression of SUMO1 or by expression of a GFP-SUMO1-NuMA-K1766R fusion protein. Our observations suggest a model in which the SAE1:SAE2 enzyme is deacetylated on early mitosis to encourage the conjugation of SUMO1 to support mitotic fidelity. These surprising data reveal that the SUMO-activating enzyme can bias SUMO variant conjugation.

molecular biology↗

bioRxiv2018

The deSUMOylase SENP2 coordinates homologous recombination and non-homologous end joining by independent mechanisms.

SUMOylation in the DNA double-strand break (DSB) response regulates recruitment, activity and clearance of repair factors. However, our understanding of a role for deSUMOylation in this process is limited. Here we identify different mechanistic roles for deSUMOylation in homologous recombination (HR) and non-homologous enjoining (NHEJ) through the investigation of the deSUMOylase SENP2. We find regulated deSUMOylation of MDC1 prevents excessive SUMOylation and its RNF4-VCP mediated clearance from DSBs, thereby promoting NHEJ. In contrast we show HR is differentially sensitive to SUMO availability and SENP2 activity is needed to provide SUMO. SENP2 is amplified as part of the chromosome 3q amplification in many cancers. Increased SENP2 expression prolongs MDC1 foci retention and increases NHEJ and radioresistance. Collectively our data reveal that deSUMOylation differentially primes cells for responding to DSBs and demonstrates the ability of SENP2 to tune DSB repair responses.

cell biology↗

bioRxiv2018

GSK3β-SCF-FBXW7 mediated phosphorylation and ubiquitination of IRF1 are required for its transcription-dependent turnover.

IRF1 (Interferon Regulatory Factor-1) is the prototype of the IRF family of DNA binding transcription factors. IRF1 protein expression is regulated by transient up-regulation in response to external stimuli followed by rapid degradation via the ubiquitin-proteasome system. Here we report that DNA bound IRF1 turnover is promoted by GSK3{beta} (Glycogen Synthase Kinase 3{beta}) via phosphorylation of the T181 residue which generates a phosphodegron for the SCF (Skp-Cul-Fbox) ubiquitin E3-ligase receptor protein Fbxw7 (F-box/WD40 7). This regulated turnover is essential for IRF1 activity, as mutation of T181 results in an improperly stabilised protein that accumulates at target promoters but fails to induce RNA-Pol-II elongation and subsequent transcription of target genes. Consequently, the anti-proliferative activity of IRF1 is lost in cell lines expressing T181A mutant. Further, cell lines with dysfunctional Fbxw7 are less sensitive to IRF1 overexpression, suggesting an important co-activator function for this ligase complex. As T181 phosphorylation requires both DNA binding and RNA-Pol-II elongation, we propose that this event acts to clear \"spent\" molecules of IRF1 from transcriptionally engaged target promoters.

molecular biology↗