Biology subjects

Yildiz, U.

Publications and source records attributed to Yildiz, U..

7 recordsLinked to original sources

bioRxiv2024

PRDX6 contributes to selenocysteine metabolism and ferroptosis resistance

Selenocysteine (Sec) metabolism is crucial for cellular function and ferroptosis prevention and has traditionally been thought to begin with the uptake of the Sec carrier selenoprotein P (SELENOP). Following uptake, Sec released from SELENOP undergoes metabolisation via selenocysteine lyase (SCLY), producing selenide, a substrate used by selenophosphate synthetase 2 (SEPHS2), which provides the essential selenium donor - selenophosphate - for the biosynthesis of the selenocysteine tRNA. Here, we report the discovery of an alternative pathway mediating Sec metabolisation that is independent of SCLY and mediated by peroxiredoxin 6 (PRDX6). Mechanistically, we demonstrate that PRDX6 can readily react with selenide and interact with SEPHS2, potentially acting as a selenium delivery system. Moreover, we demonstrate the presence and functional significance of this alternative route in cancer cells where we reveal a notable association between elevated expression of PRDX6 with a highly aggressive neuroblastoma subtype. Altogether, our study sheds light on a previously unrecognized aspect of Sec metabolism and its implications in ferroptosis, offering new avenues for therapeutic exploitation.

cell biology↗

bioRxiv2024

Functional phenotyping of genomic variants using multiomic scDNA-scRNA-seq

Genomic variation ranging from single nucleotide polymorphisms to structural variants can impact gene function and expression, contributing to disease mechanisms such as cancer progression. The systematic study of this variation is hindered by inefficient precision editing tools making it challenging to confidently link genotype and gene expression in pooled screens. Additionally, assessing heterogenous variants in primary tumor samples at scale is difficult with current single-cell technologies. We developed droplet-based multiomic targeted scDNA-scRNAseq (SDR-seq) to precisely link genotypes with gene expression profiles in high-throughput. SDR-seq simultaneously assesses up to 480 RNA and gDNA targets with high coverage and sensitivity across thousands of cells. Using SDR-seq, we associate coding and non-coding variants with distinct gene expression profiles in human iPSCs. Furthermore, we demonstrate that in primary B-cell lymphoma samples, cells with a higher mutational burden exhibit elevated B-cell receptor signaling and tumorigenic gene expression. SDR-seq has broad potential for gaining functional insights into regulatory mechanisms encoded by genetic variants at diverse loci, advancing our ability to study gene expression regulation and its implications for disease.

molecular biology↗

bioRxiv2023

Scalable ultra-high-throughput single-cell chromatin and RNA sequencing reveals gene regulatory dynamics linking macrophage polarization to autoimmune disease

Enhancers and transcription factors (TFs) are crucial in regulating cellular processes, including disease-associated cell states. Current multiomic technologies to study these elements in gene regulatory mechanisms lack multiplexing capability and scalability. Here, we present SUM-seq, a cost-effective, scalable Single-cell Ultra-high-throughput Multiomic sequencing method for co-assaying chromatin accessibility and gene expression in single nuclei. SUM-seq enables profiling hundreds of samples at the million cell scale and outperforms current high-throughput single-cell methods. We applied SUM-seq to dissect the gene regulatory mechanisms governing macrophage polarization and explored their link to traits from genome-wide association studies (GWAS). Our analyses confirmed known TFs orchestrating M1 and M2 macrophage programs, unveiled key regulators, and demonstrated extensive enhancer rewiring. Integration with GWAS data further pinpointed the impact of specific TFs on a set of immune traits. Notably, inferred enhancers regulated by the STAT1/STAT2/IRF9 (ISGF3) complex were enriched for genetic variants associated with Crohns disease, ulcerative colitis and multiple sclerosis, and their target genes included known drug targets. This highlights the potential of SUM-seq for dissecting molecular disease mechanisms. SUM-seq offers a cost-effective, scalable solution for ultra-high-throughput single-cell multiomic sequencing, excelling in unraveling complex gene regulatory networks in cell differentiation, responses to perturbations, and disease studies.

genomics↗

bioRxiv2023

HIPSD&R-seq enables scalable genomic copy number and transcriptome profiling

Single-cell DNA-sequencing (scDNA-seq) enables decoding somatic cancer variation. Existing methods are hampered by low throughput or cannot be combined with transcriptome sequencing in the same cell. We propose HIPSD&R-seq (HIgh-throughPut Single-cell Dna and Rna-seq), a scalable yet simple assay to profile low-coverage DNA and RNA in thousands of cells in parallel. Our approach builds on an accessible modification of the 10X Genomics platform for scATAC and multiome profiling. In applications to human cell models and primary tissue, we demonstrate the feasibility to detect rare clones and we combine the assay with combinatorial indexing to profile over 16,000 cells.

cancer biology↗

bioRxiv2023

Histone H3.3 lysine 9 and 27 control repressive chromatin states at cryptic cis-regulatory elements and bivalent promoters in mouse embryonic stem cells

Histone modifications are associated with distinct transcriptional states, but it is unclear whether they instruct gene expression. To investigate this, we mutated histone H3.3 K9 and K27 residues in mouse embryonic stem cells (mESCs). Here, we find that H3.3K9 is essential for controlling specific distal intergenic regions and for proper H3K27me3 deposition at promoters. The H3.3K9A mutation resulted in decreased H3K9me3 at regions encompassing endogenous retroviruses and induced a gain of H3K27ac and nascent transcription. These changes in the chromatin environment unleashed cryptic enhancers, resulting in the activation of distinctive transcriptional programs and culminating in protein expression normally restricted to specialized immune cell types. The H3.3K27A mutant disrupted deposition and spreading of the repressive H3K27me3 mark, particularly impacting bivalent genes with higher basal level of H3.3 at promoters. Therefore, H3.3K9 and K27 crucially orchestrate repressive chromatin states at cis-regulatory elements and bivalent promoters, respectively, and instruct proper transcription in mESCs.

genomics↗

bioRxiv2023

Low level of antioxidant capacity biomarkers but not target overexpression predicts vulnerability to ROS-inducing drugs

Despite a strong rationale for why cancer cells are susceptible to redox-targeting drugs, such drugs often face tumor resistance or dose-limiting toxicity in preclinical and clinical studies. An important reason is the lack of specific biomarkers to better select susceptible cancer entities and stratify patients. Using a large panel of lung cancer cell lines, we identified a set of "antioxidant-capacity" biomarkers (ACB), which were tightly repressed, partly by STAT3 and STAT5A/B in sensitive cells, rendering them susceptible to multiple redox-targeting and ferroptosis-inducing drugs. Contrary to expectation, constitutively low ACB expression was not associated with an increased steady state level of reactive oxygen species (ROS) but a high level of nitric oxide, which is required to sustain high replication rates. Using ACBs, we identified cancer entities with a high percentage of patients with favorable ACB expression pattern, making it likely that more responders to ROS-inducing drugs could be stratified for clinical trials.

cancer biology↗

bioRxiv2022

Selenocysteine metabolism is a targetable vulnerability in MYCN-amplified cancers

Understanding the operational molecular, and metabolic networks that determine the balance between pro- and anti-ferroptotic regulatory pathways could unravel unique vulnerabilities to be exploited for cancer therapy. Here we identify the selenoprotein P (SELENOP) receptor, LRP8, as a key determinant protecting MYCN-amplified neuroblastoma cells from ferroptosis in vitro and in orthotopic neuroblastoma mouse models. Specifically, the exquisite dependency on LRP8-mediated selenocysteine import is caused by the failure of MYCN-amplified cells to efficiently utilize alternative forms of selenium/selenocysteine based uptake necessary for selenoprotein biosynthesis. Increased activity of one of such transporters, SLC7A11, in MYCN-amplified cells leads to cysteine overload, progressive mitochondrial decline and impaired proliferation. These data reveal in LRP8 a targetable, and specific vulnerability of MYCN-amplified neuroblastoma cells and disclose a yet-unaccounted mechanism for selective ferroptosis induction that has the potential to become an important therapeutic entry point for MYCN-amplified neuroblastoma. Statement of significanceGiven the largely unsuccessful repurposing of adult oncology drugs for the treatment of neuroblastoma, our discoveries pave the way for novel ferroptosis based strategies for this entity. Specifically, targeting of LRP8 may offer novel therapeutic and safer opportunities for a number of pediatric malignancies and MYCN driven cancers.

cancer biology↗