A novel protein encoded by circIMP3 promotes prostate cancer progression by regulating alternative splicing and tumor microenvironment.

Introduction: Prostate cancer (PC) is one of the most prevalent malignancies in men, with rising incidence and mortality rates globally. Despite advances in therapeutic options such as androgen deprivation therapy and chemotherapy, effective cures, especially for advanced stages of the disease, remain limited. Recent research has highlighted the significant roles of alternative splicing (AS) and noncoding RNAs in tumor progression and drug resistance. This study aims to investigate the role of circIMP3, derived from the IMP3 gene, in prostate cancer development. Methods: In this study, we employed quantitative PCR, RNA sequencing, and immunoblotting to identify and characterize circIMP3 in prostate cancer tissues and patient blood samples. Functional assays, including cell proliferation and in vivo tumorigenicity assays, were conducted to assess the biological role of circIMP3 in PC cells. RNA immunoprecipitation sequencing (RIP-seq) was used to identify alternative splicing events regulated by circIMP3. Additionally, exosome isolation and uptake assays were performed to explore the paracrine signaling function of circIMP3 within the tumor microenvironment (TME). Results: We identified circIMP3, which is significantly upregulated in both prostate cancer tissues and peripheral blood of patients. CircIMP3 contains an internal ribosome entry site (IRES) and encodes a previously uncharacterized 288-amino-acid protein, circIMP3_288aa. Functional assays revealed that circIMP3_288aa promotes cell proliferation in vitro and accelerates tumor growth in vivo. Mechanistically, circIMP3_ 288aa regulates the alternative splicing of FBXW7, leading to impaired c-Myc ubiquitination and stabilization, which enhances oncogenic signaling. RIP-seq analysis identified over 2,000 alternative splicing events regulated by IMP3, with a notable enrichment in pathways related to ubiquitin-mediated proteolysis. Furthermore, circIMP3 is secreted into the TME via exosomes, where it is taken up by recipient cells, contributing to their proliferation. Discussion: Our findings demonstrate that circIMP3 acts as a key regulator of both intracellular alternative splicing and extracellular paracrine signaling within the TME. The ability of circIMP3 to influence FBXW7 splicing and stabilize c-Myc provides a mechanistic basis for its role in promoting oncogenesis in prostate cancer. Clinically, high expression levels of circIMP3 correlate with poorer event-free survival in prostate cancer patients, suggesting its potential as a prognostic biomarker. Additionally, the detection of circIMP3 in peripheral blood positions it as a promising target for liquid biopsy applications in PC diagnosis and monitoring.