Biology subjects

Gillis, N. E.

Publications and source records attributed to Gillis, N. E..

5 recordsLinked to original sources

bioRxiv2026

Depletion of BRCA1 Potentiates Progestin-Induced Cytoskeletal Changes in an Ovarian Cancer Cell Model

Individuals with Hereditary Breast and Ovarian Cancer (HBOC) syndrome carry BRCA1/2 mutations that predispose them to various cancers. Notably, this condition increases the risk of developing an aggressive ovarian cancer (OC) subtype known as high-grade serous ovarian cancer (HGSOC). The impact of progesterone (P4) on the development of OC subtypes remains unclear. Research suggests a potential interplay between Progesterone Receptor (PR) signaling and BRCA1/2 actions. BRCA1 regulates PR expression and transcriptional activity, while P4 can drive estrogen receptor/PR complexes to BRCA1 DNA binding motifs. Normal fallopian tube tissues from healthy BRCA1/2 carriers (the cells of origin for HGSOC) exhibit gene signatures similar to those in HGSOC only during the luteal phase of the menstrual cycle, when circulating P4 levels are elevated. This implies a potential role for PR/BRCA complexes in modulating OC initiation and progression. To explore this interaction, BRCA1 was depleted in an ES-2 PR-B+ OC cell models using CRISPR-mediated gene editing. We hypothesized that BRCA1 depletion would alter PR-mediated signaling and reveal novel regulatory mechanisms. Depletion of BRCA1 led to increased total basal PR protein levels and site-specific hyperphosphorylation at S294 and S81 following R5020 (synthetic progestin) treatment. RNA sequencing of NE-1 and KO-BRCA1 pools treated with R5020 identified a high-confidence set of BRCA1-dependent, R5020-induced genes predominately involved with migration and cytoskeletal organization. Transwell assays revealed that R5020 treatment stimulates migration, an effect amplified upon BRCA1 depletion. Inhibition of PIP5K1C using UNC3230 blocked R5020-induced migration in one of the KO-BRCA1 cell pools with pan-Rho inhibitor CT04 showing similar results. The Rac1 inhibitor EHT-1864 suppressed all R5020-induced migration. In contrast, co-treatment with a pan-ROCK1/2 inhibitor Y-27632 resulted in an increase in R5020-induced migration, which was further enhanced with BRCA1 depletion. Overall, these findings establish a crosstalk between BRCA1 and PR signaling, where BRCA1 depletion sensitizes OC cells to progestin-induced migration by altering PR phosphorylation and remodeling cytoskeletal organization via PIP5K1C, Rho-GTPase, and Rac1-dependent mechanisms.

cancer biology↗

bioRxiv2025

Progesterone receptors drive advanced breast cancer phenotypes including circulating tumor- and stem-like cell expansion in the context of ESR1 mutation

Endocrine therapy resistance remains a major challenge in the treatment of advanced estrogen receptor positive (ER+) breast cancer. This can be driven by acquired mutations in the estrogen receptor gene (ESR1), such as Y537S or D538G, that primarily emerge in patients with prior aromatase inhibitor therapy and results in constitutive estrogen-independent ER activity. Progesterone receptors (PR) are important modifiers of ER activity, in part via direct binding. We previously showed that PR mediates expansion of cancer stem-like cell (CSC) populations and promotes tamoxifen resistance in nuclear ER/PR transcriptional complexes. In this study, we sought to define whether PR function changes in the context of ESR1 mutations. PR readily interacted with wild type (WT), but not Y537S or D538G ERs. RNA-seq and ChIP-seq studies demonstrated that ER+ breast cancer models expressing Y537S ER exhibited a distinct response to progesterone. CSC populations were enhanced in Y537S ER+ cells compared to WT ER+ cells. PR knockdown demonstrated that this property required PR expression but was unresponsive to antiprogestins. Moreover, we identified PR-dependent transcriptional programs such as the unfolded protein response (UPR) that can be leveraged to target CSC populations in Y537S ESR1-mutant breast cancer. The UPR activator ErSO, but not UPR inhibitors, blocked expansion of CSCs in WT as well as Y537S ER+ models. Together, our findings demonstrate a critical interplay between PR and mutant ER function and provide insight into PR-driven pathways including hyperactivation of the stress-sensing UPR that can be exploited as potential therapeutic avenues in advanced ER+ breast cancer.

cancer biology↗

bioRxiv2025

Isoform-Specific Gene Regulation by Progesterone Receptors Drives Divergent Phenotypes in Breast Cancer Cells

Exposure to progesterone is a recognized risk factor for breast cancer, and PGR polymorphisms are associated with various malignancies. Two progesterone receptor (PR) isoforms, full length PR-B and truncated PR-A, are expressed from the PGR gene in breast tissue and play crucial roles in normal physiology and breast cancer progression. An imbalance in the expression ratio of these isoforms, favoring increased levels of PR-A, is common in breast cancer and is associated with resistance to tamoxifen in luminal A-type tumors. Notably, PRs have recently been implicated in promoting endocrine resistance and driving the expansion of cancer stem-like cell (CSC) populations. Despite this insight, the isoform-specific molecular and epigenetic mechanisms underlying PR action in estrogen receptor positive (ER+) breast cancers remain understudied. Phenotypic studies of T47D cell lines that express exclusively PR-A or PR-B showed that PR isoforms regulate divergent cell fates. PR-B-expressing cells have a higher proliferation rate, while PR-A-expressing cells produce more mammospheres. We profiled progesterone-driven gene expression in cells grown in both adherent (2D) and mammosphere (3D) growth conditions and found differential gene regulation by PR-A and PR-B that is consistent with the observed divergent phenotypes. Only the PR-A-driven gene signature of ER+ breast cancer cells maintained as non-adherent mammospheres robustly predicted poor clinical outcome in the METABRIC data set. We then performed CUT&RUN to identify the genomic binding patterns unique to each PR isoform and their suite of target genes. Our findings indicate that PR-A acts as a regulator of the cell cycle, while PR-B plays a pivotal role in metabolism and intracellular signaling. Our genomic profiling of PRs in this model system has unveiled novel isoform-specific functions of PR. This work has shifted our prior understanding of the role of PRs in gene regulation, offering potential insights for therapeutic interventions in ER+ breast cancer.

cancer biology↗

bioRxiv2021

A Thyroid Hormone Receptor Beta Specific Agonist Suppresses Anaplastic Thyroid Cancer Cell Phenotype and Increases Efficacy of Therapeutic Agents

Thyroid hormone receptor beta (TR{beta}) is a recognized tumor suppressor in numerous solid cancers. The molecular signaling of TR{beta} has been elucidated in several cancer types through re-expression models. Remarkably, the potential impact of selective activation of endogenous TR{beta} on tumor progression remains largely unexplored. We used cell-based and in vivo assays to evaluate the effects of the TR{beta} agonist Sobetirome (GC-1) on a particularly aggressive and dedifferentiated cancer, anaplastic thyroid cancer (ATC). Here we report that GC-1 reduced the tumorigenic phenotype, decreased cancer stem-like cell populations, and induced re-differentiation of the ATC cell lines with different mutational backgrounds. Of note, this selective activation of TR{beta} amplified the effects of therapeutic agents in blunting the aggressive cell phenotype and stem-cell growth. In xenograft assays, GC-1 alone inhibited tumor growth and was as effective as the kinase inhibitor, Sorafenib. These results indicate that selective activation of TR{beta} not only induces a tumor suppression program de novo but enhances the effectiveness of anti-cancer agents revealing potential novel combination therapies for ATC and other aggressive solid tumors.

cancer biology↗

bioRxiv2021

Thyroid Hormone Dependent Transcriptional Programming by TRβ Requires SWI/SNF Chromatin Remodelers

Transcriptional regulation in response to thyroid hormone (T3) is a dynamic and cell-type specific process that maintains cellular homeostasis and identity in all tissues. However, our understanding of the mechanisms of thyroid hormone receptor (TR) actions at the molecular level are actively being refined. We used an integrated genomics approach to profile and characterize the cistrome of TR{beta}, map changes in chromatin accessibility, and capture the transcriptomic changes in response to T3 in normal thyroid cells. There are significant shifts in TR{beta} genomic occupancy in response to T3, which are associated with differential chromatin accessibility, and differential recruitment of SWI/SNF chromatin remodelers. We further demonstrate selective recruitment of BAF and PBAF SWI/SNF complexes to TR{beta} binding sites, revealing novel differential functions in regulating chromatin accessibility and gene expression. Our findings highlight three distinct modes of TR{beta} interaction with chromatin and coordination of coregulator activity.

genomics↗