Loss of PRKACB facilitates metastasis of diffuse-type gastric cancer through RhoA signaling activation.

Diffuse-type gastric cancer (DGC) is characterized by strong invasiveness and poor prognosis, frequently associated with peritoneal metastasis. Dysregulation of protein kinase A catalytic subunit beta (PRKACB) has been implicated in various cancers, but its role in DGC remains unclear. This study investigates the expression, function, and molecular mechanisms of PRKACB in DGC metastasis. PRKACB expression was analyzed by immunohistochemistry in tissue samples from DGC and intestinal-type gastric cancer (IGC) patients. Functional assays and a mouse peritoneal metastasis model were employed to evaluate the impact of PRKACB on metastasis. The interaction between PRKACB and RhoA was explored using co-immunoprecipitation, GST pull-down assays, and in situ proximity ligation assays. PRKACB expression was significantly lower in DGC tissues compared to IGC and adjacent non-tumor tissues. Multivariate Cox regression analysis identified low PRKACB expression as an independent prognostic factor for poor overall survival. In DGC cell lines, PRKACB knockdown enhanced cell migration, invasion, pseudopodia formation, and epithelial-mesenchymal transition (EMT), while PRKACB overexpression suppressed these activities. In vivo experiments demonstrated that PRKACB knockdown promoted earlier onset of peritoneal metastasis. Mechanistically, PRKACB interacted with RhoA and promoted its phosphorylation at S188, thereby inhibiting RhoA signaling and its downstream effectors ROCK1 and FAK. Common RhoA mutations in DGC (V38G and N41K) weakened its interaction with PRKACB, leading to reduced phosphorylation and enhanced metastatic potential. Importantly, RhoA inhibitor treatment reversed the pro-metastatic effects induced by low PRKACB expression. In conclusion, low PRKACB expression promotes DGC metastasis through activation of RhoA signaling, and PRKACB downregulation combined with functional RhoA mutations contributes to the aggressive phenotype of DGC. These findings provide new insights into DGC progression and suggest that PRKACB may serve as both a prognostic biomarker and a potential therapeutic target for DGC patients.