Biology subjects

Mutlu, M.

Publications and source records attributed to Mutlu, M..

5 recordsLinked to original sources

bioRxiv2025

TAOK1 regulates chemo- and radiosensitivity in BRCA1/2-deficient tumors

BRCA1/2-deficient cells are hypersensitive to replication stress- and DNA-damage-inducing agents such as poly(ADP-ribose) polymerase inhibitors (PARPi), platinum drugs, and ionizing radiation (IR), largely due to impaired homologous recombination repair and replication fork (RF) protection. The precise mechanisms underlying RF vulnerability in the absence of BRCA1/2 remain incompletely understood, however. Here, we identify Thousand And One Amino Acid Kinase 1 (TAOK1) as a novel regulator of RF dynamics that sensitizes BRCA1/2-deficient cells to both PARPi and IR. Unlike established DNA repair factors, such as PARG or the 53BP1-RIF1-shieldin-CST pathway, which mediate PARPi sensitivity while protecting cells against IR, TAOK1 promotes RF degradation and suppresses post-replicative damage repair. TAOK1 depletion stabilizes RFs and reduces replication-associated DNA damage in BRCA1/2-deficient cells, thereby conferring therapy resistance. Interestingly, we found that TAOK1 functions in RF regulation to be independent of its kinase activity. Instead, it interacts with PCNA and regulates ISG15 levels and thereby affects RF stability. Our findings reveal TAOK1 as a non-canonical mediator of therapy sensitivity in BRCA1/2-deficient tumors. TeaserTAOK1 controls replication fork stability through PCNA and ISG15, affecting therapy response in BRCA1/2-deficient cancers.

cancer biology↗

bioRxiv2024

Structural basis of dual BACH1 regulation by SCFFBXO22 and SCFFBXL17

BTB and CNC homolog 1 (BACH1) is a master transcriptional regulator of the cellular oxidative stress response and pro-metastatic oncogene. Post-translational stability of BACH1 is tightly regulated by distinct F-box ubiquitin ligases, including SCFFBXO22 and SCFFBXL17. However, the molecular details have been elusive. Here, we reveal a structural switch in FBXO22 that controls the recognition of a three-dimensional degron in the BACH1 BTB domain, thus explaining its specificity for dimeric BACH1. We describe how cancer-associated mutations in FBXO22 modulate binding and ubiquitylation of BACH1. Further, we reveal that cancer-related mutations or cysteine-modifications destabilize the BTB domain and redirect BACH1 to FBXL17, where it is recognized as a monomer. This explains how complementary ligases post-translationally regulate BACH1 depending on the state of its BTB domain. Our findings provide mechanistic insights into the regulation of the oxidative stress response and may spur therapeutic strategies to targeting oxidative stress-related disorders and metastatic cancers.

biophysics↗

bioRxiv2023

A novel HERC4-dependent glue degrader targeting STING

Stimulator of interferon genes (STING) is a central component of the pathway sensing the presence of cytosolic nucleic acids, having a key role in type I interferon innate immune response. Localized at the endoplasmic reticulum (ER), STING becomes activated by cGAMP, which is generated by the intracellular DNA sensor cyclic GMP-AMP synthase (cGAS). Due to its critical role in physiological function and its involvement in a variety of diseases, STING has been a notable focus for drug discovery. Recent advances in drug discovery allow the targeting of proteins previously considered "un-druggable" by novel mechanism of actions. Molecular glue degraders are defined as the compounds leading targeted protein degradation (TPD) by creating novel ligase-substrate interactions. Here, we identified AK59 as a novel molecular glue degrader for STING. A genome-wide, CRISPR/Cas9 knockout screen showed that the compound-mediated degradation of STING by AK59 is compromised by the loss of HECT and RLD domain containing E3 ubiquitin protein ligase 4 (HERC4), ubiquitin-like modifier activating enzyme 5 (UBA5) and ubiquitin like modifier activating enzyme 6 (UBA6). While UBA5 and UBA6 could be the auxiliary factors for AK59 activity, our results indicate that HERC4 is the main E3 ligase for the observed degradation mechanism. Validation by individual CRISPR knockouts, co-immunoprecipitations, as well as proximity mediated reporter assays suggested that AK59 functions as a glue degrader by forming a novel interaction between STING and HERC4. Furthermore, our data reveals that AK59 was effective on the most common pathological STING mutations that cause STING-associated vasculopathy with onset in infancy (SAVI), suggesting a potential clinical application of this mechanism. Thus, these findings not only reveal a novel mechanism for compound-induced degradation of STING but also utilize HERC4 as potential E3 ligase that for TPD, enabling novel therapeutic applications.

molecular biology↗

bioRxiv2022

MND1 and PSMC3IP control PARP inhibitor sensitivity in mitotic cells

The PSMC3IP-MND1 heterodimer promotes RAD51 and DMC1-dependent D-loop formation during meiosis in yeast and mammalian organisms. For this purpose, it catalyzes the DNA strand exchange activities of the recombinases. Interestingly, in a panel of genome-scale CRISPR-Cas9 mutagenesis and interference screens in mitotic cells, we found that depletion of either PSMC3IP or MND1 caused sensitivity to clinical Poly (ADP-Ribose) Polymerase inhibitors (PARPi). A retroviral mutagenesis screen in mitotic cells also identified PSMC3IP and MND1 as genetic determinants of ionizing radiation sensitivity. The role PSMC3IP and MND1 play in preventing PARPi sensitivity in mitotic cells appears to be independent of a previously described role in alternative lengthening of telomeres (ALT). PSMC3IP or MND1 depleted cells accumulate toxic RAD51 foci in response to DNA damage, show impaired homology-directed DNA repair, and become PARPi sensitive, even in cells lacking both BRCA1 and TP53BP1. Although replication fork reversal is also affected, the epistatic relationship between PSMC3IP-MND1 and BRCA1/BRCA2 suggests that the abrogated D-loop formation is the major cause of PARPi sensitivity. This is corroborated by the fact that a PSMC3IP p.Glu201del D-loop formation mutant associated with ovarian dysgenesis fails to reverse PARPi sensitivity. These observations suggest that meiotic proteins such as MND1 and PSMC3IP could have a greater role in mitotic cells in determining the response to therapeutic DNA damage.

cancer biology↗

bioRxiv2022

MDC1 counteracts restrained replication fork restart and its loss causes chemoresistance in BRCA1/2-deficient mammary tumors

MDC1 is a key protein in DNA damage signaling. When DNA double-strand breaks (DSBs) occur, MDC1 localizes to sites of damage to promote the recruitment of other factors, including the 53BP1-mediated DSB repair pathway. By studying mechanisms of poly(ADP-ribose) polymerase inhibitor (PARPi) resistance in BRCA2;p53-deficient mouse mammary tumors, we identified a thus far unknown role of MDC1 in replication fork biology. MDC1 localizes at active replication forks during normal fork replication and its loss reduces fork speed. We show that MDC1 contributes to the restart of replication forks and thereby promotes sensitivity to PARPi and cisplatin. Loss of MDC1 causes MRE11-mediated resection, resulting in delayed fork restart. This improves DNA damage tolerance and causes chemoresistance in BRCA1/2-deficient cells. Hence, our results show a role for MDC1 in replication fork progression that mediates PARPi- and cisplatin-induced DNA damage, in addition to its role in DSB repair.

molecular biology↗