HOXC9 promotes cell proliferation and suppresses mitochondria-dependent apoptosis through the AKT/mTOR pathway in esophageal squamous cell carcinoma.

Homeobox C9 (HOXC9) is aberrantly expressed in multiple malignancies; however, its functional role in esophageal squamous cell carcinoma (ESCC) remains elusive. This study investigated the expression, function, and underlying molecular mechanisms of HOXC9 in ESCC. HOXC9 was evaluated via immunohistochemistry in 118 ESCC and paired normal tissues. Stable cell lines with HOXC9 knockout, knockdown, and overexpression were established in KYSE70 and KYSE150 cells. Cell proliferation, apoptosis, mitochondrial membrane potential, and in vivo xenograft growth were assessed. Mechanistic studies were performed using RNA-seq, Western blotting, and PI3K inhibitor LY294002 (30 µM). IHC analysis revealed significantly elevated HOXC9 expression in ESCC versus paired adjacent normal tissues (high expression rate: 57.6% vs. 22.9%, P < 0.0001) and associated with poorer overall survival. Receiver operating characteristic (ROC) curve analysis showed favorable diagnostic value for HOXC9 (area under the curve [AUC] = 0.97). Functional assays showed that HOXC9 promoted ESCC cell proliferation and inhibited mitochondria-dependent apoptosis. Mechanistically, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment and Western blot analyses indicated that HOXC9 is associated with activation of the protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway. Pharmacological blockade and xenograft experiment further supported the involvement of this pathway in HOXC9-driven oncogenic phenotypes. This study identifies a potential mechanism by which HOXC9 contributes to ESCC progression via AKT/mTOR-mediated inhibition of mitochondria-dependent apoptosis and promotion of cell proliferation. These findings suggest HOXC9 as a candidate prognostic biomarker and preliminary therapeutic target for ESCC, requiring further validation across clinical and molecular subtypes.