Effects of emerin dysregulation on the very-small-nuclear phenotype and neuronal differentiation and its association with a clinically aggressive subtype of prostate cancer.

207 Background: Circulating tumor cells (CTCs) with a very-small-nuclear (vsn) phenotype (i.e., vsnCTCs) in prostate cancer (PCa) represent a distinct subset of CTCs characterized by nuclei smaller than 8.5 μm. Our previous studies established a link between vsnCTCs and the presence of visceral metastasis. Emerging evidence suggests that the reduction of emerin (EMD), a nuclear envelope protein, contributes to PCa metastasis and is associated with nuclear shape instability. This study aims to validate vsnCTCs as a biomarker in metastatic castration-resistant prostate cancer (mCRPC) and investigate the correlation between EMD expression and the vsnCTC phenotype. Methods: CTCs were isolated from 93 mCRPC patients using the NanoVelcro CTC assay and categorized as either vsnCTC-positive (vsnCTC+) or vsnCTC-negative (vsnCTC-). We compared overall survival (OS) and progression-free survival (PFS) between these two groups. In vitro experiments were conducted using PCa cell lines (C4-2B, 22Rv1, and DU145) with EMD knockdown via siRNA or shRNA to study its impact on cellular phenotypes. Additionally, we measured EMD expression and nuclear size in abiraterone- and enzalutamide-resistant (Abi-R/Enza-R) C4-2B cells. Results: vsnCTC+ patients had significantly worse OS and PFS compared to vsnCTC- patients. Multivariate analysis revealed that vsnCTC+ status was independently associated with poorer OS and PFS. EMD expression was markedly reduced in CTCs from vsnCTC+ patients compared to vsnCTC- patients, with a significant positive correlation between EMD expression and CTC nuclear size. EMD knockdown in PCa cells resulted in smaller nuclei, enhanced invasion, and the upregulation of genes associated with neuronal de-differentiation (e.g., SOX2, CHGA, MYCN, and AURKA). Additionally, C4-2B Abi-R/Enza-R cells had significantly smaller nuclei and lower EMD expression, consistent with our clinical observation of the vsnCTCs association with ARSI resistance. These resistant cells also demonstrated elevated expression of neuronal de-differentiation genes. Conclusions: The presence of vsnCTCs represents a novel hallmark of an aggressive subtype of mCRPC, closely linked to EMD dysregulation and neuroendocrine differentiation. These findings highlight the potential of vsnCTCs and associated biological changes as a predictive biomarker. Our findings underscore the importance of EMD in the progression and therapeutic resistance of advanced PCa.