Taku Kato

Prospero homeobox protein 1 (PROX1) is aberrantly expressed in tumors, including neuroendocrine neoplasms (NENs); however, the detailed expression pattern remains elusive. This study aimed to immunohistochemically assess PROX1 expression. Immunohistochemistry (IHC) for PROX1 was performed on tissue microarrays of normal tissues (n = 107), NENs (n = 152) (small cell lung carcinoma [SCLC], lung carcinoid [LC], gastroenteropancreatic-NEN [GEP-NEN], esophageal neuroendocrine carcinoma [ENEC], medullary thyroid carcinoma [MTC], neuroblastoma [NB], and pheochromocytoma [PHEO]), and non-NENs (n = 469). In normal tissues, PROX1 was expressed in lymphatic endothelial cells and a subset of epithelial cells in the gastrointestinal tract and the distal convoluted tubules. In NENs, the positive expression was observed in the nucleus of tumor cells in 19/26 SCLC (73.1%), 13/16 LC (81.3%), 10/15 GEP-NEN (66.7%), 2/2 ENEC (100%), 17/43 MTC (39.5%), 1/25 NB (4.0%), and 0/25 PHEO (0%). Although PROX1 was negative in many non-NENs, our analysis revealed high expression in certain cases with medulloblastoma and one case with juvenile granulosa cell tumor. PROX1 was expressed in specific cases with epithelial NENs and some cases with non-NENs. Analysis of PROX1 should provide insights into the molecular characteristics of distinct tumors.

BACKGROUND: Androgen receptor signaling inhibitors(ARSIs) have been used to treat patients with metastatic prostate cancer (PC) and castration-resistant prostate cancer (CRPC). In this study, we aimed to identify novel serum extracellular vesicle (EV)-based biomarkers to diagnose ARSI-resistance and therapeutic targets for ARSI-resistant CRPC. METHODS: Total RNA contained in serum EVs from 5 cases of CRPC before ARSI treatment and after acquiring ARSI-resistance was subjected to RNA-sequencing. The expression changes of selected RNAs contained in EVs were confirmed in 48 cases of benign prostatic hyperplasia (BPH) and 107 PC using reverse transcription-quantitative PCR (RT-qPCR) and compared with tissue RNA expression using public datasets. RESULTS: RNA-sequencing revealed that mitochondrial oxidative phosphorylation (OXPHOS)-related genes were increased in EVs after acquiring ARSI-resistance. Among them, RT-qPCR and datasets analysis demonstrated that SDHB mRNA was upregulated after acquiring ARSI-resistance in EVs and ARSI-exposed PC tissue compared to ARSI-naïve EVs and tissue, respectively. SDHB mRNA levels both in EVs and tissue were increased in localized PC compared with BPH and decreased in advanced PC. Tissue expression of SDHB mRNA was significantly correlated with those of other OXPHOS-related genes. SDHB mRNA in EVs (EV-SDHB) was elevated among 3 out of 7 ARSI-treating patients with stable PSA levels who later progressed to ARSI-resistant CRPC. CONCLUSIONS: The levels of OXPHOS-related mRNAs in EVs correlated with those in PC tissue, among which SDHB mRNA was found to be a novel biomarker to diagnose ARSI-resistance. EV-SDHB may be useful for early diagnosis of ARSI-resistance.

Lung neuroendocrine neoplasms (NENs) are a diverse group of tumors characterized by neuroendocrine (NE) differentiation. Among lung NENs, lung carcinoid (LC) is a rare tumor with unique characteristics. Recent research has highlighted the importance of transcription factors (TFs) in establishing gene expression programs in lung NENs such as small cell lung carcinoma. However, the TFs that control the gene expression of LC are largely unknown. In this study, we report the expression and potential function of a TF called Prospero homeobox protein1 (PROX1) in LC. Publicly available transcriptome data suggested that PROX1 was highly expressed in LC tissues, which was confirmed by immunohistochemical analysis on a tissue microarray. Knockdown of PROX1 did not impact the cellular viability of an LC-derived cell line, NCI-H727. Meanwhile, transcriptome analysis revealed that PROX1 knockdown altered the expression of genes involved in NE differentiation. ASCL1, CHGA, CALCA, and LINC00261 were suggested as downstream genes of PROX1. These findings indicate that PROX1 may play an important role in the NE identity of LC by regulating the expression of key target genes.