Data from <i>BRN4</i> Is a Novel Driver of Neuroendocrine Differentiation in Castration-Resistant Prostate Cancer and Is Selectively Released in Extracellular Vesicles with <i>BRN2</i>

Abstract

<div>AbstractPurpose:<p>Neuroendocrine prostate cancer (NEPC), an aggressive variant of castration-resistant prostate cancer (CRPC), often emerges after androgen receptor–targeted therapies such as enzalutamide or <i>de novo</i>, via trans-differentiation process of neuroendocrine differentiation. The mechanistic basis of neuroendocrine differentiation is poorly understood, contributing to lack of effective predictive biomarkers and late disease recognition. The purpose of this study was to examine the role of novel proneural <u>P</u>it-<u>O</u>ct-<u>U</u>nc-domain transcription factors (TF) in NEPC and examine their potential as noninvasive predictive biomarkers.</p><p><b>Experimental Design:</b> Prostate cancer patient-derived xenograft models, clinical samples, and cellular neuroendocrine differentiation models were employed to determine the expression of TFs <i>BRN1</i> and <i>BRN4</i>. <i>BRN4</i> levels were modulated in prostate cancer cell lines followed by functional assays. Furthermore, extracellular vesicles (EV) were isolated from patient samples and cell culture models, characterized by nanoparticle tracking analyses, Western blotting, and real-time PCR.</p>Results:<p>We identify for the first time that: (i) <i>BRN4</i> is amplified and overexpressed in NEPC clinical samples and that <i>BRN4</i> overexpression drives neuroendocrine differentiation via its interplay with <i>BRN2</i>, a TF that was previously implicated in NEPC; (ii) <i>BRN4</i> and <i>BRN2</i> mRNA are actively released in prostate cancer EVs upon neuroendocrine differentiation induction; and (iii) enzalutamide treatment augments release of <i>BRN4</i> and <i>BRN2</i> in prostate cancer EVs, promoting neuroendocrine differentiation induction.</p>Conclusions:<p>Our study identifies a novel TF that drives NEPC and suggests that as adaptive mechanism to enzalutamide treatment, prostate cancer cells express and secrete <i>BRN4</i> and <i>BRN2</i> in EVs that drive oncogenic reprogramming of prostate cancer cells to NEPC. Importantly, EV-associated <i>BRN4</i> and <i>BRN2</i> are potential novel noninvasive biomarkers to predict neuroendocrine differentiation in CRPC.</p></div>