Ahn Rhi Lee

Therapy-induced neuroendocrine prostate cancer (t-NEPC) is a highly aggressive subtype of prostate cancer with poor patient survival. Emerging evidence indicates that t-NEPC can develop when prostate adenocarcinoma cells acquire cancer stem-like cell signaling in the presence of androgen receptor inhibition, followed by redifferentiation toward neuroendocrine lineage and subsequent t-NEPC progression. Whether the stem-like signaling is controlled by the core pluripotency stem cell genes (e.g., LIN28 and SOX2) remains unknown. Here, we report that the transcription of the LIN28B isoform and SOX2 were co-upregulated in t-NEPC patient tumors, patient-derived xenografts, transgenic mice, and cell models. Immunohistochemistry validated that LIN28B and SOX2 protein expression were elevated in t-NEPC patient biopsies. Using prostate adenocarcinoma and t-NEPC cell models, we demonstrated that LIN28B induced a stem-like gene network, neuroendocrine biomarkers, and neuroendocrine cell morphology. LIN28B depletion by CRISPR inhibited t-NEPC tumorigenesis and xenograft growth. These LIN28B functions were mediated mainly through the suppression of let-7 miRNA expression, resulting in de-repression of the transcription factor HMGA2 and HMGA2-mediated SOX2 expression. This study revealed a mechanism by which t-NEPC can develop through the LIN28B/let-7/SOX2 axis that regulates a cancer cell stem-like gene network, highlighting LIN28B as a potential therapeutic target in t-NEPC.

Potent androgen receptor pathway inhibition (ARPI) therapies have given rise to a lethal, aggressive subtype of castration‐resistant prostate cancer (CRPC) called treatment‐induced neuroendocrine prostate cancer (t‐NEPC). Now, t‐NEPC poses a major clinical problem as approximately 20% of CRPC cases bear this subtype—a rate of occurrence that is predicted to rise with the widespread use of ARPI therapies. Unfortunately, there are no targeted therapies currently available to treat t‐NEPC as the origin and molecular underpinnings of t‐NEPC development remain unclear. In the present study, we identify that RNA splicing of the G protein‐coupled receptor kinase‐interacting protein 1 (GIT1) gene is a unique event in t‐NEPC patients. Specifically, upregulation of the GIT1‐A splice variant and downregulation of the GIT1‐C variant expressions are associated with t‐NEPC patient tumors, patient‐derived xenografts, and cell models. RNA‐binding assays show that RNA splicing of GIT1 is directly driven by SRRM4 and is associated with the neuroendocrine phenotype in CRPC cohorts. We show that GIT1‐A and GIT1‐C regulate differential transcriptomes in prostate cancer cells, where GIT1‐A regulates genes associated with morphogenesis, neural function, environmental sensing via cell‐adhesion processes, and epigenetic regulation. Consistent with our transcriptomic analyses, we report opposing functions of GIT1‐A and GIT1‐C in the stability of focal adhesions, whereby GIT1‐A promotes focal adhesion stability. In summary, our study is the first to report that alternative RNA splicing of the GIT1 gene is associated with t‐NEPC and reprograms its function involving FA‐mediated signaling and cell processes, which may contribute to t‐NEPC development.

While the use of next-generation androgen receptor pathway inhibition (ARPI) therapy has significantly increased the survival of patients with metastatic prostate adenocarcinoma (AdPC), several groups have reported a treatment-resistant mechanism, whereby cancer cells can become androgen receptor (AR) indifferent and gain a neuroendocrine (NE)-like phenotype. This subtype of castration-resistant prostate cancer has been termed “treatment-induced castration-resistant neuroendocrine prostate cancer” (CRPC-NE). Recent reports indicate that the overall genomic landscapes of castration-resistant tumors with AdPC phenotypes and CRPC-NE are not significantly altered. However, CRPC-NE tumors have been found to contain a NE-specific pattern throughout their epigenome and splicing transcriptome, which are significantly modified. The molecular mechanisms by which CRPC-NE develops remain unclear, but several factors have been implicated in the progression of the disease. Recently, Ser/Arg repetitive matrix 4 (SRRM4), a neuronal-specific RNA splicing factor that is upregulated in CRPC-NE tumors, has been shown to establish a CRPC-NE-unique splicing transcriptome, to induce a NE-like morphology in AdPC cells, and, most importantly, to transform AdPC cells into CRPC-NE xenografts under ARPI. Moreover, the SRRM4-targeted splicing genes are highly enriched in various neuronal processes, suggesting their roles in facilitating a CRPC-NE program. This article will address the importance of SRRM4-mediated alternative RNA splicing in reprogramming translated proteins to facilitate NE differentiation, survival, and proliferation of cells to establish CRPC-NE tumors. In addition, we will discuss the potential roles of SRRM4 in conjunction with other known pathways and factors important for CRPC-NE development, such as the AR pathway, TP53 and RB1 genes, the FOXA family of proteins, and environmental factors. This study aims to explore the multifaceted functions of SRRM4 and SRRM4-mediated splicing in driving a CRPC-NE program as a coping mechanism for therapy resistance, as well as define future SRRM4-targeted therapeutic approaches for treating CRPC-NE or mitigating its development.

A relaxed fundus (FUN) and a contracted lower uterine segment (LUS) of human myometrium are required for maintaining pregnancy. How this regional myometrium function is regulated remains unclear. We have previously reported that the homeobox protein A13 (HoxA13) is highly expressed in the LUS and can enhance the expression of contraction-associated proteins (CAPs). Here, we show that in contrast to HoxA13, HoxA10 and HoxA11 genes are expressed at significantly higher levels in myometrium tissues and primary myocytes from the FUN. When introduced exogenously into a human myometrial cell line, HoxA10 and HoxA11 suppress the messenger RNA (mRNA) levels of several CAP genes including interleukin-1 beta (IL-1β), IL-6, connexin 43 (Cx43), and cyclooxygenase 2 (Cox2). Consistently, enhanced HoxA10 and HoxA11 expressions strongly inhibited IL-1β and Cx43 protein levels. We further confirmed that higher expression of HoxA10 and HoxA11 genes in primary myocytes from the FUN compared to that from the LUS was associated with lower expression of IL-1β, IL-6, Cox2, and Cx43 genes. We conclude that the expression patterns of HoxA10, HoxA11, and HoxA13 and their actions in regulating CAP genes in FUN and LUS create regionalized myometrium phenotypes in women that may be important to control regionalized myometrium contractility for maintaining pregnancy.

Alternative RNA splicing of the MEAF6 gene facilitates neuroendocrine prostate cancer progression Alternative RNA splicing of the MEAF6 gene facilitates neuroendocrine prostate cancer progression