Potential therapeutic target secretogranin II might cooperate with hypoxia-inducible factor 1α in sunitinib-resistant renal cell carcinoma.

Multitargeted receptor tyrosine kinase inhibitors, including vascular endothelial growth factor (VEGF) inhibitors, such as sunitinib, have been used as the primary targeted agents for patients with recurrent or distant metastasis of advanced renal cell carcinoma (RCC). However, endogenous or acquired sunitinib resistance has become a significant therapeutic problem. Therefore, we focused on mechanisms of sunitinib resistance in RCC. First, we undertook RNA sequencing analysis using previously established sunitinib-resistant RCC (SUR-Caki1, SUR-ACHN, and SUR-A498) cells. The results showed increased expression of secretogranin II (SCG2, chromogranin C) in SUR-RCC cells compared to parental cells. The Cancer Genome Atlas database showed that SCG2 expression was increased in RCC compared to normal renal cells. In addition, the survival rate of the SCG2 high-expression group was significantly lower than that of the RCC low-expression group. Thus, we investigated the involvement of SCG2 in sunitinib-resistant RCC. In vitro analysis showed that migratory and invasive abilities were suppressed by SCG2 knockdown SUR cells. As SCG2 was previously reported to be associated with angiogenesis, we undertook a tube formation assay. The results showed that suppression of SCG2 inhibited angiogenesis. Furthermore, coimmunoprecipitation assays revealed a direct interaction between SCG2 and hypoxia-inducible factor 1α (HIF1α). Expression levels of VEGF-A and VEGF-C downstream of HIF1α were found to be decreased in SCG2 knockdown SUR cells. In conclusion, SCG2 could be associated with sunitinib resistance through VEGF regulation in RCC cells. These findings could lead to a better understanding of the VHL/HIF/VEGF pathway and the development of new therapeutic strategies for sunitinib-resistant RCC.

Targeting of the glutamine transporter SLC1A5 induces cellular senescence in clear cell renal cell carcinoma.

In recent years, cancer metabolism has attracted attention as a therapeutic target, and glutamine metabolism is considered one of the most important metabolic processes in cancer. Solute carrier family 1 member 5 (SLC1A5) is a sodium channel that functions as a glutamine transporter. In various cancer types, SLC1A5 gene expression is enhanced, and cancer cell growth is suppressed by inhibition of SLC1A5. However, the involvement of SLC1A5 in clear cell renal cell carcinoma (ccRCC) is unclear. Therefore, in this study, we evaluated the clinical importance of SLC1A5 in ccRCC using The Cancer Genome Atlas database. Our findings confirmed that SLC1A5 was a prognosis factor for poor survival in ccRCC. Furthermore, loss-of-function assays using small interfering RNAs or an SLC1A5 inhibitor (V9302) in human ccRCC cell lines (A498 and Caki1) showed that inhibition of SLC1A5 significantly suppressed tumor growth, invasion, and migration. Additionally, inhibition of SLC1A5 by V9302 in vivo significantly suppressed tumor growth, and the antitumor effects of SLC1A5 inhibition were related to cellular senescence. Our findings may improve our understanding of ccRCC and the development of new treatment strategies for ccRCC.

Exosomal microRNA-1 and MYO15A as a target for therapy and diagnosis in renal cell carcinoma.

Exosomes are 40-100 nm nano-sized extracellular vesicles and are receiving increasing attention as novel structures that participate in intracellular communication. We previously found that miRNA-1 (miR-1) functions as a tumor suppressor in renal cell carcinoma (RCC). In this study, we investigated the function of exosomal miR-1 and the possibility that the exosome constitutes a tumor maker in RCC. First, we established the method to collect exosomes from cell lysates and human serum by a spin column-based method. Next, we assessed exosomes using Nanosight nanoparticle tracking analysis and Western blot analysis with exosome marker CD63. We confirmed that exosomes labeled with PKH26 fused with recipient cells. Moreover, miR-1 expression was elevated in RCC cells treated with exosomes derived from miR-1-transfected cells. Functional analyses showed that exosomal miR-1 significantly inhibited cell proliferation, migration and invasion compared to control treatment. Our analyses with TCGA database of RCCs showed that miR-1 expression was significantly downregulated in clinical RCC samples compared to that in normal kidney samples, and patients with low miR-1 expression had poorer overall survival in comparison to patients with high expression. Furthermore, RNA sequence analyses showed that expression levels of several genes were altered by exposure to exosomal miR-1. The analyses with TCGA database indicated that high expression of MYO15A was associated with a poorer outcome in RCC. In addition, RT-qPCR analysis of exosomes from clinical patients' sera showed that MYO15A was significantly upregulated in RCC patients compared to that in healthy controls. This study showed that treatment with exosomal miR-1 might be an effective approach to treating RCCs. In addition, exosomal MYO15A could be a diagnostic tumor marker in RCCs.

microRNA-99a-5p induces cellular senescence in gemcitabine-resistant bladder cancer by targeting SMARCD1.

Patients with advanced bladder cancer are generally treated with a combination of chemotherapeutics, including gemcitabine, but the effect is limited due to acquisition of drug resistance. Thus, in this study, we investigated the mechanism of gemcitabine resistance. First, gemcitabine-resistant cells were established and resistance confirmed in vitro and in vivo. Small RNA sequencing analyses were performed to search for miRNAs involved in gemcitabine resistance. miR-99a-5p, selected as a candidate miRNA, was downregulated compared to its parental cells. In gain-of-function studies, miR-99a-5p inhibited cell viabilities and restored sensitivity to gemcitabine. RNA sequencing analysis was performed to find the target gene of miR-99a-5p. SMARCD1 was selected as a candidate gene. Dual-luciferase reporter assays showed that miR-99a-5p directly regulated SMARCD1. Loss-of-function studies conducted with si-RNAs revealed suppression of cell functions and restoration of gemcitabine sensitivity. miR-99a-5p overexpression and SMARCD1 knockdown also suppressed gemcitabine-resistant cells in vivo. Furthermore, ß-galactosidase staining showed that miR-99a-5p induction and SMARCD1 suppression contributed to cellular senescence. In summary, tumor-suppressive miR-99a-5p induced cellular senescence in gemcitabine-resistant bladder cancer cells by targeting SMARCD1.