Biology subjects

Yasar, P.

Publications and source records attributed to Yasar, P..

5 recordsLinked to original sources

bioRxiv2026

Protocol for measuring endocrine disruptive effects on transcriptional bursting using single-molecule imaging in human breast cancer cells

Transcriptional bursts regulate gene expression by altering burst size or burst frequency. Here, we present a protocol that integrates fixed-cell smFISH and live-cell single-molecule imaging to analyze estrogen-responsive transcriptional bursting of the TFF1 gene in human breast cancer cell lines. This workflow enables measurement of burst size, burst initiation, and active allele frequency to determine how endocrine disruptor chemicals modulate transcriptional bursting dynamics. For complete details on the use and execution of this protocol, please refer to Day, Yasar et al.1

cell biology↗

bioRxiv2026

Layered Single-Cell Heterogeneity in Hormone Receptor Signaling Across Mouse Organoids and Human ERα+ Cancer Cells

Hormone receptor signaling is often interpreted through receptor abundance as a proxy for hormone responsiveness, yet the determinants of single-cell variability in hormone response remain unclear. Using murine mammary organoids, we mapped estrogen (E2) and progesterone (P4) responses at single-cell resolution. Despite controlled 3D culture conditions, basal cell-derived organoids exhibit striking variability in hormone-induced transcriptional responses, with ER cells varying in the fraction of responsive genes engaged. This variability is not explained by receptor abundance alone. Instead, response magnitude correlates with expression of transcriptional co-regulators including Ncoa1, Ncor1, and Ncor2, suggesting that co-regulator balance contributes to variation in endocrine response magnitude. Organoids exhibit a mixed basal-luminal enhancer landscape and growth factor-dependent remodeling of ER and PR protein abundance. MCF7 cells show delayed activation kinetics and reach a lower response plateau. Together, these findings reveal that hormone response magnitude varies independently of receptor abundance in mammary organoids and follows distinct activation dynamics in human ER+ cancer cells.

cell biology↗

bioRxiv2025

H3K27me3 chromatin heterogeneity reveals variable cell responses to estrogen and endocrine treatment

Gene expression heterogeneity generates subpopulations of tumor cells that can evade therapeutic pressure. This heterogeneity has been observed in both primary Estrogen Receptor alpha positive (ER+) breast tumors and cell lines. Therefore, understanding the mechanisms regulating expression heterogeneity is critical towards developing effective therapies. A key contributor to gene expression variability is the stochastic nature of transcription. Transcription occurs in a probabilistic, burst-like manner, in which gene activation occurs intermittently, producing RNA in pulses and interspersed with transcriptional off-periods. The estrogen-responsive gene TFF1 is expressed in the majority of ER breast tumors and exemplifies such heterogeneity, with transcriptional inactivity ranging from minutes to several days. Here, we identify the molecular mechanism underlying the wide range in TFF1 expression by analyzing cells sorted based on their TFF1 activity levels. We observed that TFF1 inactive (TFF1low) cells exhibit a repressive chromatin state marked by H3K27me3 at the TFF1 promoter and enhancer. Despite global similarity in ER binding, occupancy at the TFF1 regulatory elements was selectively reduced in TFF1low cells, resulting in fewer active alleles and diminished transcriptional bursting frequency. Conversely, TFF1high cells exhibited more active TFF1 alleles and hyperbursting. These cells also retained sensitivity to endocrine therapy, while TFF1low cells displayed reduced drug responsiveness. Genome-wide, differentially enriched H3K27me3 regions correlated with variable expression of estrogen-responsive genes, highlighting a broader regulatory mechanism that links chromatin state to expression variability. Together, our findings establish how repressive chromatin dynamics contribute to gene expression heterogeneity and endocrine resistance in ER breast cancer. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=67 SRC="FIGDIR/small/677184v1_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@1194eedorg.highwire.dtl.DTLVardef@8cb67aorg.highwire.dtl.DTLVardef@202ad9org.highwire.dtl.DTLVardef@1dd222a_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2024

CXXC5 is a ubiquitinated protein and is degraded by the ubiquitination-proteasome pathway

CXXC5 as a member of the zinc-finger CXXC family proteins interacts with unmodified CpG dinucleotides to modulate the expression of genes involved in cellular proliferation, differentiation, and death in physiology and pathophysiology. Various signaling pathways including mitogenic estrogens, particularly 17{beta}-estradiol (E2), contribute to the expression and synthesis of CXXC5. However, how signaling pathways modulate protein levels of CXXC5 in cells is largely unknown. We previously reported that some key regulators, including retinoblastoma 1 and E74 Like ETS Transcription Factor 1, of the G1 to S phase transitions are involved in the expression of CXXC5 in estrogen-responsive MCF7 cells, derived from a breast adenocarcinoma. We, therefore, predict that the synthesis of CXXC5 is regulated in a cell cycle-dependent manner. We report here that although E2 in synchronized MCF7 cells augments both transcription and synthesis of CXXC5 in the G1 phase, CXXC5 protein levels are primarily mediated by ubiquitination independently of cell cycle phases. Utilizing the bioUbiquitination approach, which is based on cellular biotinylation of ubiquitin, in HEK293FT cells derived from immortalized human embryonic kidney cells followed by sequential immunoprecipitation coupled mass spectrometry analyses, we identified multiple ubiquitinated lysine residues of CXXC5. We show in both MCF7 and HEK293FT cells that the ubiquitinated lysine residues contribute to the degradation of CXXC5 through the ubiquitin-proteasome pathway.

cell biology↗

bioRxiv2023

ERα mediated gene state switching regulates the extent of the single-cell estrogen response

Gene regulation is complex, involving the coordination of hundreds of proteins that function to control genome accessibility, mediate enhancer-promoter interactions, and initiate transcription. At individual loci, transcriptional initiation is stochastic, resulting in short periods of nascent RNA synthesis known as transcriptional bursts. To understand how altered Estrogen Receptor function and cofactor recruitment regulates transcriptional bursting, we used single molecule imaging of estrogen responsive genes in Bisphenol A (BPA) treated cells. Using live cell imaging of the estrogen responsive TFF1 gene, we observe that cells treated with BPA exhibited burst initiation kinetics and burst sizes which were indistinguishable from cells induced with Estradiol (E2). However, we observed a 50% reduction in the number of active alleles in BPA treated cells. This effect is gene specific, as GREB1 was unperturbed. Although we observed no difference in chromatin accessibility, the TFF1 promoter exhibited an altered structure which coincided with reduced ER and cofactor binding. Lastly, deletion of the enhancer locus removed the BPA effect, indicating that enhancer function was perturbed. Our results demonstrate gene specific effects of altered ER recruitment and function which lead to a reduction of transcriptionally permissive states. Our work supports the model that the early estrogen response occurs from alleles in primed transcriptionally permissive states with additional inactive alleles contributing to the response over time.

cell biology↗