FAM105A regulates the Hippo/YAP signaling pathway via deubiquitination to promote gastric cancer cell proliferation and migration.

BACKGROUND: Gastric cancer (GC) is one of the leading causes of global cancer mortality, underscoring an urgent need for novel therapeutic targets. Dysregulation of ubiquitination and deubiquitination plays a critical role in tumorigenesis. The deubiquitinating enzyme FAM105A, belonging to the OTULIN subfamily, has not yet been characterized in cancer. Preliminary bioinformatics analysis indicated that FAM105A is upregulated in gastric adenocarcinoma and positively correlates with the expression of CTGF, a downstream target of the Hippo/YAP signaling pathway, which is frequently dysregulated in GC. This study aimed to elucidate the role and mechanism of FAM105A in GC progression.

METHODS: Bioinformatics databases were used to analyze the expression of FAM105A and its clinical significance, which was further validated in clinical samples via immunohistochemistry (IHC) and Western blot (WB). In vitro and in vivo functional assays were conducted using stable FAM105A-knockdown and FAM105A-overexpressing GC cell lines. The interaction between FAM105A and YAP was investigated using co-immunoprecipitation (Co-IP), immunofluorescence, ubiquitination assays, and proximity ligation assay (PLA). The functional dependency on the Hippo pathway was assessed using the YAP inhibitor Verteporfin (VP). Domain mapping was performed by constructing truncated mutants of both FAM105A and YAP.

RESULTS: FAM105A was significantly overexpressed in GC tissues, and its high expression correlated with advanced TNM stage and poor prognosis. Functionally, FAM105A promoted GC cell proliferation, migration, and inhibited apoptosis in vitro. In vivo evaluation using xenograft models demonstrated that FAM105A-overexpressing xenografts exhibited significantly larger tumor volumes compared to controls, while FAM105A-knockdown tumors showed reduced growth. FAM105A knockdown significantly decreased final tumor weight, whereas overexpression increased tumor mass. Immunohistochemical analysis revealed that knockdown tumors exhibited consistently reduced Ki-67 immunopositivity, while overexpression samples showed enhanced proliferation signatures. Mechanistically, Co-IP experiments further confirmed that FAM105A binds to YAP via its OTU domain, whereas full-length YAP, but not its truncation variants, efficiently interacts with FAM105A. FAM105A deubiquitinates and stabilizes YAP protein, promotes its nuclear translocation, and thereby activates the Hippo/YAP signaling pathway. The oncogenic effects of FAM105A overexpression were effectively reversed by the YAP inhibitor VP.

CONCLUSION: This study provides comprehensive in vitro and in vivo evidence demonstrating that the deubiquitinating enzyme FAM105A functions as an oncogene in GC by stabilizing YAP and activating the Hippo/YAP pathway, thereby promoting tumor growth. FAM105A represents a promising prognostic biomarker and a potential therapeutic target for gastric cancer.