Melatonin suppresses Akt/mTOR/S6K activity, induces cell apoptosis, and synergistically inhibits cell growth with sunitinib in renal carcinoma cells via reversing Warburg effect.

BACKGROUND: Metabolic alteration drives renal cell carcinoma (RCC) development, while the impact of melatonin (MLT), a neurohormone secreted during darkness, on RCC cell growth and underlying mechanisms remains unclear. METHODS: We detected concentration of metabolites through metabolomic analyses using UPLC-MS/MS, and the oxygen consumption rate was determined using the Seahorse Extracellular Flux analyzer. RESULTS: We observed that MLT effectively inhibited RCC cell growth both in vitro and in vivo. Additionally, MLT increased ROS levels, suppressed antioxidant enzyme activity, and induced apoptosis. Furthermore, MLT treatment upregulated key TCA cycle metabolites while reducing aerobic glycolysis products, leading to higher oxygen consumption rate, ATP production, and membrane potential. Moreover, MLT treatment suppressed phosphorylation of Akt, mTOR, and p70 S6 Kinase as well as the expression of HIF-1α/VEGFA in RCC cells; these effects were reversed by NAC (ROS inhibitors). Conversely, MLT synergistically inhibited cell growth with sunitinib and counteracted the Warburg effect induced by sunitinib in RCC cells. CONCLUSIONS: In conclusion, our results indicate that MLT treatment reverses the Warburg effect and promotes intracellular ROS production, which leads to the suppression of Akt/mTOR/S6K signaling pathway, induction of cell apoptosis, and synergistically inhibition of cell growth with sunitinib in RCC cells. Overall, this study provides new insights into the mechanisms underlying anti-tumor effect of MLT in RCC cells, and suggests that MLT might be a promising therapeutic for RCC.

HOTAIR and androgen receptor synergistically increase GLI2 transcription to promote tumor angiogenesis and cancer stemness in renal cell carcinoma.

Tumor angiogenesis is a major characteristic of renal cell carcinoma (RCC). Herein, we report a novel mechanism of how lncRNA and androgen receptor (AR) drive the Hedgehog pathway to promote tumor angiogenesis in RCC. We found that the high expression of lncRNA HOTAIR in RCC is associated with poor prognosis. Moreover, HOTAIR and AR form a feedback loop to promote the expression of each other. Interestingly, we also found that in RCC, HOTAIR is associated with the Hedgehog pathway, especially GLI2, via bioinformatics analysis. Furthermore, HOTAIR promotes GLI2 expression in the presence of AR. Mechanistically, HOTAIR interacts with AR and they cooperatively bind to GLI2 promoter and increase its transcription activity. We further confirmed how HOTAIR-AR axis regulates GLI2 expression by analyzing its function in RCC cells and found that HOTAIR and AR synergistically enhanced the expression of GLI2 downstream genes, such as VEGFA, PDGFA, and cancer stem cell transcription factors, and promoted tumor angiogenesis and cancer stemness in RCC cells both in vitro and in tumor xenografts. Overall, these findings suggest that HOTAIR and GLI2 could be novel therapeutic targets against RCC.

KLF5 inhibits STAT3 activity and tumor metastasis in prostate cancer by suppressing IGF1 transcription cooperatively with HDAC1.

KLF5 is frequently deleted and downregulated in prostate cancer, and recently it has been reported that KLF5 loss is enriched in the aggressive branches of prostate cancer evolution. However, why KLF5 loss is associated with prostate cancer aggressiveness is still not clear. Herein, we analyzed KLF5 expression in TCGA and GEO database, as well as prostate cancer tissue microarray, and found that KLF5 expression significantly decreased in prostate cancer accompanying with tumor progression; moreover, KLF5 downregulation was associated with shorter survival of patients. Interestingly, we also found that KLF5 expression was obviously lower in prostate cancer metastases than in localized tissues, indicating that KLF5 downregulation is associated with prostate cancer invasion and metastasis. To assess this effect of KLF5, we knocked down KLF5 in prostate cancer cells and found that KLF5 knockdown promoted invasive ability of prostate cancer cells in vitro and in vivo. Moreover, we found that KLF5 downregulation enhanced the expression of IGF1 and STAT3 phosphorylation, while block of IGF1 with antibody decreased the enhancement of STAT3 activity and prostate cancer cell invasive ability by KLF5 knockdown, indicating that KLF5 inhibits prostate cancer invasion through suppressing IGF1/STAT3 pathway. Mechanistically, we found that KLF5 interacted with deacetylase HDAC1 and KLF5 is necessary for the binding of HDAC1 on IGF1 promoter to suppress IGF1 transcription. Taken together, our results indicate that KLF5 could be an important suppressor of prostate cancer invasion and metastasis, because KLF5 could suppress the transcription of IGF1, a tumor cell autocrine cytokine, and its downstream cell signaling to inhibit cell invasive ability, and reveal a novel mechanism for STAT3 activation in prostate cancer. These findings may provide evidence for the precision medicine in prostate cancer.

Downregulation of Collagen COL4A6 Is Associated with Prostate Cancer Progression and Metastasis.

Aims: To determine the association between collagen type IV alpha 6 (COL4A6) expression levels and prostate cancer invasion and metastasis. Methods: We analyzed three Gene Expression Omnibus (GEO) datasets through the GEO2R online tool to obtain the set of differentially expressed genes (DEGs) between malignant and nonmalignant prostate tissues, and further analyzed the COL4A6 gene's expression in databases. Western blot assays, real-time quantitative polymerase chain reaction analysis, and immunofluorescence staining were used to detect COL4A6 gene expression. Wound healing assays and cell invasion transwell assays were performed to measure cell invasion and siRNA was used to knock down COL4A6 gene expression. Results: Through the use of bioinformatic tools we showed that the COL4A6 gene is one of the highly downregulated genes in prostate cancer; additionally, hypermethylation of the COL4A6 promoter in prostate cancer is correlated with lower expression levels. We also showed that downregulation of COL4A6, which activates the p-FAK/MMP-9 signaling pathway in prostate cancer cells, is associated with prostate cancer cell metastasis based on data retrieved from The Cancer Genome Atlas (TCGA) and GEO databases. Finally, we found that the COL4A6 protein is localized extracellularly and its expression is positively correlated with disease-free survival of prostate cancer patients. Conclusion: Our results indicate that downregulation of COL4A6 may promote prostate cancer progression and invasion. Additionally, COL4A6 and its promoter methylation status could be valuable markers for prostate cancer prognoses.