Biology subjects

Hofmann, T. G.

Publications and source records attributed to Hofmann, T. G..

4 recordsLinked to original sources

bioRxiv2026

HIPK2 regulates homology-directed DNA repair and PARP inhibitor sensitivity

Repair of DNA double-strand breaks (DSBs) by homologous recombination (HR) counteracts genome instability and carcinogenesis. Cancer cells frequently show defects in HR which can be therapeutically exploited by hypersensitivity to poly(ADP-ribose) polymerase inhibitor (PARPi) treatment. Here we identify an unforeseen function of HIPK2 in HR repair and PARPi sensitivity. HIPK2 accumulates at DSBs and associates with DSB repair factors at DNA damage foci. DSB recruitment of HIPK2 requires checkpoint kinase ATM activity. DNA repair pathway analysis revealed that HIPK2 depletion specifically impairs HR. Mechanistically, we found that HIPK2 binds BRCA1 and phosphorylates BRCA1 at Ser1191, a site that regulates damage-induced BRCA1 protein stability. Consistently, HIPK2 depletion or pharmacological inhibition of HIPK2 results in reduced BRCA1 protein levels, and sensitizes BRCA1-proficient cancer cells to IR damage and PARPi treatment. In sum, our results identify a role for HIPK2 in HR through regulating BRCA1 protein levels, and propose HIPK2 inhibition as a novel strategy to sensitize BRCA1-proficient cancer cells to PARPi treatment.

cell biology↗

bioRxiv2026

Role of a childhood cancer-linked BRIP1/FANCJ germline variant in genomic instability and cancer cell vulnerability

Childhood cancer is frequently associated with inherited pathogenic variants of cancer predisposition genes. Using Whole-Exome Sequencing, we identified an inherited, monoallelic pediatric cancer-linked germline variant of DNA helicase FANCJ/BRIP1, BRIP1R162Q of unclear clinical significance. Intriguingly, in vitro helicase assays demonstrated that BRIP1R162Q encodes a hyperactive DNA helicase. In cells, stable expression of BRIP1R162Q in BRIP1-proficient cells selectively sensitized to ectopic DNA replication stress. Moreover, BRIP1R162Q expressing cells showed chronic, steady-state activation of DNA replication stress indicated by decreased fork speed, fork stalling and impaired fork symmetry. Moreover, BRIP1R162Q expression triggered genomic instability indicated by elevated {gamma}H2AX foci numbers and chromosomal aberrations, suggesting BRIP1R162Q as a variant driving genomic instability. Mechanistically, BRIP1R162Q mislocalizes upon replication stress, and leads to accumulation of DNA secondary G-quadruplex (G4) structures and R-loops. RNaseH1 expression, which resolves R-loops, also reduced G4 levels and relieved BRIP1R162Q-induced replication stress. Finally, BRIP1R162Q introduces exploitable vulnerabilities for targeted therapies using G4-ligand Pyridostatin and DNA damage kinase ATR and DNA-PK inhibition. Our findings propose a mechanistic framework of how a childhood cancer-linked monoallic, hypermorphic BRIP1 germline variant participates in cancer development, and suggest potential therapeutic treatment strategies.

cancer biology↗

bioRxiv2023

Novel hydroxamic acid derivative induces apoptosis and constrains autophagy in leukemic cells

IntroductionPosttranslational modification of proteins by reversible acetylation regulates key biological processes. Histone deacetylases (HDACs) catalyze protein deacetylation and are frequently dysregulated in tumors. This has spurred the development of HDAC inhibitors (HDACi). Such epigenetic drugs modulate protein acetylation, eliminate tumor cells, and are approved for the treatment of blood cancers. ObjectivesWe aimed to identify novel, nanomolar HDACi with increased potency over existing agents and selectivity for the cancer-relevant class I HDACs (HDAC1/-2/-3/-8). Moreover, we wanted to define how such drugs control the apoptosis-autophagy interplay. As test systems, we used human leukemic cells and embryonic kidney-derived cells. MethodsWe synthesized novel pyrimidine-hydroxamic acid HDACi (KH9/KH16/KH29) and performed in vitro activity assays and molecular modeling of their direct binding to HDACs. We analyzed how these HDACi affect leukemic cell fate, acetylation, and protein expression with flow cytometry and immunoblot. The publicly available DepMap database of CRISPR-Cas9 screenings was used to determine sensitivity factors across human leukemic cells. ResultsNovel HDACi show nanomolar activity against class I HDACs. These agents are superior to the clinically used hydroxamic acid HDACi vorinostat. Within the KH-series of compounds, KH16 (yanostat) is the most effective inhibitor of HDAC3 (IC50 = 6 nM) and the most potent inducer of apoptosis (IC50 = 110 nM; p<0.0001) in leukemic cells. KH16 though spares embryonic kidney-derived cells. Global data analyses of knockout screenings verify that HDAC3 is a dependency factor in human blood cancer cells of different lineages, independent of mutations in the tumor suppressor p53. KH16 alters pro- and anti-apoptotic protein expression, stalls cell cycle progression, and induces a caspase-dependent processing of the autophagy proteins ULK1 and p62. ConclusionThese data reveal that HDACs are required to stabilize autophagy proteins through a suppression of apoptosis in leukemic cells. HDAC3 appears as a valid anti-cancer target for pharmacological intervention. HighlightsO_LINovel HDACi with nanomolar activity against leukemic cells were synthesized. C_LIO_LIHDACi of the KH-series are superior to a clinical grade HDACi. C_LIO_LIHDACi of the KH-series modulate acetylation and phosphorylation of proteins. C_LIO_LIThe new HDACi KH16 regulates cell cycle arrest, apoptosis, and autophagy. C_LIO_LIApoptosis acts upstream of autophagy in KH16-treated cells. C_LI

pharmacology and toxicology↗

bioRxiv2021

Multi-layered chromatin proteomics identifies cell vulnerabilities in DNA repair

The DNA damage response (DDR) is essential to maintain genome stability, and its deregulation predisposes to carcinogenesis while encompassing attractive targets for cancer therapy. Chromatin governs the DDR via the concerted interplay among different layers, including DNA, histone post-translational modifications (hPTMs), and chromatin-associated proteins. Here we employ multi-layered proteomics to characterize chromatin-mediated functional interactions of repair proteins, signatures of hPTMs, and the DNA-bound proteome during DNA double-strand break (DSB) repair at high temporal resolution. Our data illuminate the dynamics of known and novel DDR-associated factors both at chromatin and at DSBs. We functionally attribute novel chromatin-associated proteins to repair by non-homologous end-joining (NHEJ), homologous recombination (HR) and DSB repair pathway choice. We reveal histone reader ATAD2, microtubule organizer TPX2 and histone methyltransferase G9A as regulators of HR and PARP-inhibitor sensitivity. Furthermore, we distinguish hPTMs that are globally induced by DNA damage from those specifically acquired at sites flanking DSBs ({gamma}H2AX foci-specific), and profiled their dynamics during the DDR. Integration of complementary chromatin layers implicates G9A-mediated monomethylation of H3K56 at DSBs in HR. Our data provide a dynamic chromatin-centered view of the DDR that can be further mined to identify novel mechanistic links and cell vulnerabilities in DSB repair.

cancer biology↗