Biology subjects

Hollenhorst, P. C.

Publications and source records attributed to Hollenhorst, P. C..

4 recordsLinked to original sources

bioRxiv2026

Oncogenic ETS factors expressed from fusion genes utilize EWSR1 to associate with the paraspeckle and regulate transcription.

ETS family transcription factors are aberrantly expressed in prostate cancer and Ewing sarcoma due to chromosomal rearrangements resulting in fusion genes, most commonly TMPRSS2::ERG and EWSR1::FLI1, respectively. The products of these gene fusions regulate transcription together with the intrinsically disordered protein EWSR1. However, the role of EWSR1 as a transcriptional co-regulator is not fully understood. EWSR1 can undergo liquid-liquid phase separation. We found that ERG could integrate into EWSR1 phase separated droplets. We then tested the role of the paraspeckle, a nuclear membraneless organelle known to regulate transcription and include EWSR1. Both ERG and EWSR1::FLI1 associated with the paraspeckle scaffold long non-coding RNA NEAT1_2. Disruption of paraspeckles in prostate cancer and Ewing sarcoma cell lines resulted in disruption of oncogenic phenotypes mimicking the loss of oncogenic ETS factors. In Ewing sarcoma cells paraspeckle disruption promoted similar transcriptional profiles as loss of EWSR1::FLI1. Further, loss of EWSR1::FLI1 reduced the association of a paraspeckle component with EWSR1::FLI1 target genomic loci. In TMPRSS2::ERG positive prostate cancer cells paraspeckle disruption correlated with ERG-mediated transcriptional repression. These findings suggest that the paraspeckle is an important transcriptional regulator in cancers with ETS gene fusions and provides a potential target for further mechanistic understanding and drug development.

cancer biology↗

bioRxiv2026

Activation of vitamin D signaling suppresses platinum-induced ovarian cancer stem cell plasticity

Advanced-stage high grade serous ovarian cancer (HGSC) initially responds to platinum-based chemotherapy; however, most HGSC tumors recur and develop chemotherapy-resistance, making recurrent ovarian cancer (OC) a fatal disease. Ovarian cancer stem cells (OCSCs), a subpopulation of cells capable of surviving treatment and repopulating tumors, contribute to disease relapse, and understanding the mechanisms(s) responsible for OCSC survival is critical for developing strategies to overcome acquired resistance and prevent tumor recurrence. However, whether platinum-induced OCSC enrichment results from the selection of pre-existing OCSCs or chemotherapy-induced cellular plasticity, and the molecular mechanisms underlying these processes, remain poorly understood. Here, we demonstrated that cisplatin treatment not only enriched for OCSCs but promoted the conversion of ALDH- cells to ALDH+ cells, revealing chemotherapy-induced plasticity as a potential mechanism for OCSC expansion. This conversion was associated with nuclear receptor signaling pathways, vitamin D receptor signaling (VDR/RXR) and retinoic acid receptor signaling (RAR/RXR). Importantly, activation of VDR/RXR signaling with vitamin D reduced stemness phenotypes and the cisplatin induced conversion to ALDH+ cells. In addition, vitamin D combined with cisplatin decreased tumor volume in vivo compared to either treatment alone. In contrast, cisplatin treatment increased RAR/RXR signaling, supporting an associative role for ligand-dependent nuclear receptor signaling in OCSC plasticity. Together, these findings reveal that platinum chemotherapy can actively promote the acquisition of stem-like properties and identifies VDR/RXR signaling as a potential regulatory mechanism of OCSC plasticity. Targeting this pathway with vitamin D may provide a therapeutic strategy to target OCSCs and improve responses to platinum-based chemotherapy.

cancer biology↗

bioRxiv2020

Androgen signaling connects short isoform production to breakpoint formation at Ewing sarcoma breakpoint region 1 via an R-loop-dependent mechanism

Ewing sarcoma breakpoint region 1 (EWSR1) encodes a multifunctional protein that can cooperate with the transcription factor ERG to promote prostate cancer. The EWSR1 gene is also commonly involved in oncogenic gene rearrangements in Ewing sarcoma. Despite the cancer relevance of EWSR1, its regulation is poorly understood. Here we find that in prostate cancer, androgen signaling upregulates a 5 EWSR1 isoform by promoting usage of an intronic polyadenylation site. This isoform encodes a cytoplasmic protein that can strongly promote cell migration and clonogenic growth. Deletion of an Androgen Receptor (AR) binding site near the 5 EWSR1 polyadenylation site abolished androgen-dependent upregulation. This polyadenylation site is also near the Ewing sarcoma breakpoint hotspot, and androgen signaling promoted R-loop and breakpoint formation. RNase H overexpression reduced breakage and 5 EWSR1 isoform expression suggesting an R-loop dependent mechanism. These data suggest that androgen signaling can promote R-loops internal to the EWSR1 gene leading to early transcription termination and breakpoint formation.

cancer biology↗

bioRxiv2018

Electrostatic repulsion causes anticooperative DNA binding between tumor suppressor ETS transcription factors and JUN-FOS at composite DNA sites

Many transcription factors regulate gene expression in a combinatorial fashion often by binding in close proximity on composite cis-regulatory DNA elements. Here we investigate the molecular basis by which ETS transcription factors bind with AP1 transcription factors JUN-FOS at composite DNA-binding sites. The ability to bind to DNA with JUN-FOS correlates with the phenotype of these proteins in prostate cancer: the oncogenic ERG and ETV1/4/5 subfamilies co-occupy ETS-AP1 sites with JUN-FOS in vitro, whereas JUN-FOS robustly inhibits DNA binding by the tumor suppressors EHF and SPDEF. EHF binds to ETS-AP1 DNA with tighter affinity than ERG in the absence of JUN-FOS, which may enable EHF to compete with ERG and JUN-FOS for binding to ETS-AP1 sites. Genome-wide mapping of EHF and ERG binding sites in a prostate epithelial cell line reveal that EHF is preferentially excluded from closely spaced ETS-AP1 DNA sequences. Structural modeling and mutational analyses indicate that adjacent positively-charged surfaces from EHF and JUN-FOS disfavor simultaneous DNA binding due to electrostatic repulsion. The conservation of positively charged residues on the JUN-FOS interface identified ELF1 as an additional ETS factor that exhibits anticooperative DNA binding, and we present evidence that ELF1 is frequently downregulated in prostate cancer. In summary, the divergence of electrostatic features of ETS factors at their JUN-FOS interface enables distinct binding events at ETS-AP1 DNA sequences. We propose that this mechanism can drive unique targeting of ETS transcription factors, thereby facilitating distinct transcriptional programs.

biochemistry↗