EHF/ESE3 transcription factor as a regulator of prostate epithelial cell differentiation and stem cell properties

Prostate cancer is a leading cause of cancer-related mortality. Androgen deprivation therapy is the first-line treatment option for locally advanced and metastatic PC patients. However, many patients progress to castration-resistant prostate cancer (CRPC), which is refractory to ADT and AR-pathway inhibitors (ARPI) and represents the main barrier to effectively controlling the disease. ETS transcription factors (TFs), are nodal points in multiple signaling pathways and have a prominent role in prostate cancer. Increased expression of ETS factors, like ERG, caused by TMPRSS2:ERG gene translocation, is the most common genetic rearrangement in prostate cancer. However, the oncogenic potential of ERG is strictly dependent on the crosstalk with other oncogenic factors. Our laboratory was the first to point out that another member of the ETS family, EHF/ESE3 (EHF) is one of the most expressed TF in the normal prostate epithelial cells and, unlike ERG, has a tumor suppressor role. Notably, we reported that over 50% of prostate cancers exhibited downregulation of EHF and that depletion of EHF in prostate epithelial cells induced a stem cell-like phenotype and mesenchymal and tumorigenic properties. We have proposed that EHF is a critical factor in epithelial cell differentiation and an essential barrier to malignant transformation and tumor progression. We have generated and characterized mouse models with prostate-specific EHF knockout with and without TMPRSS2:ERG gene fusion knock-in to date. The results of these studies sustain our original hypothesis, demonstrating the critical role of EHF as a lineage-specific TF that prevents malignant transformation and phenotypic plasticity in the prostate by preserving epithelial lineage integrity, also in the context of the TMPRSS2:ERG translocation. Specifically, genomic analyses of prostate-specific EHF knockout mouse models coupled to functional assays in mouse-derived organoids and allografts showed that EHF loss promotes an ambiguous transcriptional program with epithelial cells acquiring a stem cell-like and pan-plastic state leading to increased propensity to gain aberrant features of other cell lineages, like mesenchymal and endothelial cell features. In addition to the described changes in the epithelial cell compartment, another relevant aspect that emerged from studying these models is the impact of EHF loss on the tumor microenvironment.

Accordingly, in these studies, we propose that the disruption of lineage integrity consequent to EHF loss contributes to the evolution of primary PC toward metastatic clinically aggressive CRPC subtypes by activating alternative androgen-indifferent pathways. Furthermore, the newly acquired capabilities can modify the interactions of the malignant epithelial cells with the tissue microenvironment at primary and metastatic sites. Finally, we found that EHF loss in mouse and human tumors activates in the transformed epithelial cells, multiple signaling pathways that can be targeted pharmacologically to revert cell plasticity and tumor progression. Collectively, these data encourage further testing of the role of EHF in prostate tumorigenesis, integrating studies on our mouse models with human and murine cell cultures and organoids, and patient-derived xenografts.

Our specific aims are to investigate:

Aim 1. EHF control of phenotypic plasticity and tumor evolution.

Aim 2. EHF control of the tumor ecosystem.

Aim 3. Therapeutic strategies to revert aberrant phenotypic features linked to EHF loss.

We believe that the studies proposed in this application will lead to a deeper understanding of prostate cancer's biology and disease progression mechanisms. Our models will provide a robust preclinical platform for gaining mechanistic insights and discovering innovative therapeutic strategies for arresting cancer cell lineage plasticity and preventing PC progression.