Downregulation of uncoupling protein 1 by hypermethylation in gastric cancer activates Rap1 signaling.

Abstract

Background: Uncoupling protein 1 (UCP1) plays a pivotal role in modulating energy expenditure and maintaining metabolic homeostasis within brown and beige adipocytes. It has also been implicated in tumorigenesis.

Aim: To investigate the expression and function of UCP1 in gastric cancer (GC).

Methods: UCP1 protein expression in 211 GC tissues was examined using immunohistochemistry. Bisulfite sequencing PCR (BSP) was used to detect the methylation status of the UCP1 promoter in GC cell lines and tissues. The relationship between UCP1 expression and clinicopathological parameters was analyzed. CCK8, scratch, transwell, and flow cytometry assays were carried out to analyze the proliferation, migration, invasion, and apoptosis of GC cell lines after knockdown or overexpression of UCP1 in vitro. A nude mouse tumor xenograft model was used to investigate the function of UCP1 in vivo. RNA sequencing, Kyoto Encyclopedia of Genes and Genomes analysis, and Rap1 pull-down assays were performed to identify the pathway associated with UCP1.

Results: Loss of UCP1 was significantly associated with gender, poor differentiation, and advanced TNM stage of GC. Hypermethylation of UCP1 was confirmed in GC cells and tumor tissues by BSP. Overexpression of UCP1 suppressed GC cell proliferation, migration, and invasion, and it promoted apoptosis in vitro. UCP1 overexpression also suppressed GC tumor growth in vivo. Moreover, overexpression of UCP1 in GC cells resulted in a significant decrease in active Rap1 protein levels, whereas downregulation of UCP1 markedly enhanced Rap1 activity.

Conclusion: UCP1 downregulation in GC through promoter hypermethylation is related to the progression of GC, indicating that UCP1 plays a role as a tumor suppressor in GC. It regulates Rap1 signaling and may be a potential therapeutic target in GC.