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Background: Esophageal squamous cell carcinoma (ESCC) is the most common histological subtype of esophageal cancer, accounting for approximately 80% of cases, and is associated with a poor prognosis: less than 20% of patients survive beyond 5 years. ESCC exhibits high heterogeneity, with TP53 mutations being the only consistently observed genomic alteration. However, our group recently identified PIK3R3 overexpression (a regulatory subunit of PI3K) in ESCC through DNA microarray analysis of 15 paired tumor and non-tumor tissue samples from patients treated at the National Cancer Institute (INCA). PIK3R3 overexpression increased AKT phosphorylation, revealing a novel activation mechanism of the PI3K/AKT pathway, and was an independent variable associated with a poor prognosis. Objective: The aim of this project is to evaluate the functional role of PIK3R3 and the PI3K/AKT pathway in ESCC progression, as well as their potential as a therapeutic target. Methods: Using specific shRNA or transfection with an expression vector, we promoted the silencing or overexpression of PIK3R3 in TE-1 and TE-13 cells, derived from human ESCC, to evaluate migration, proliferation, clonogenic potential, and spheroid formation capacity. The morphology and cell cycle of these cells were also analyzed. In silico correlation analyses, using microarray data, were conducted to identify genes potentially activated by or co-expressed by PIK3R3, contributing to an aggressive phenotype. Results: In vitro functional assays demonstrated that PIK3R3 silencing reduced proliferation, migration, clonogenicity, and spheroid formation, while its overexpression promoted opposite effects in both TE-1 and TE-13 cell lines. Furthermore, PIK3R3 silencing induced increased cell size and cell cycle arrest in the G1 phase, while its overexpression increased progression to the S phase of the cell cycle. In silico analysis of genes correlated with PIK3R3 identified associations with a senescent phenotype, and highlighted RGS-5 and HEY-1, the genes most strongly correlated and differentially expressed in tumors, as possible regulators of PI3K/AKT signaling. Conclusion: Taken together, our findings demonstrate that PIK3R3 drives ESCC aggressiveness through activation of the PI3K/AKT pathway, modulation of cell cycle progression, and promotion of tumorigenic phenotypes, positioning PIK3R3 as an important biomarker and also a promising therapeutic target for ESCC, opening new perspectives for precision oncology approaches.
Keywords: Esophageal cancer; PIK3R3; Tumor Progression
Supported by: Instituto Nacional de Câncer, Ministério da Saúde, CAPES, FAPERJ, CNPq, and Swiss Bridge Foundation.
Research area: Molecular Biology