HSP90AA1 inhibits autophagy to promote tumor growth: A novel therapeutic target in endometrial cancer.

BACKGROUND: HSP90AA1 functions as a molecular chaperone involved in stabilizing multiple oncogenic clients. Its role in endometrial cancer (EC), particularly regarding autophagy regulation, remains unclear. METHODS: HSP90AA1 expression was examined using UALCAN and Human Protein Atlas (HPA) databases, followed by immunohistochemical (IHC) validation in 80 EC tissues and 20 normal controls. Stable knockout and transient overexpression of HSP90AA1 were established in Ishikawa and HEC-1A cells. Colony formation, flow cytometry, and subcutaneous xenograft models were used to evaluate proliferation and tumor growth. Autophagic flux was assessed by detecting Beclin-1, the LC3B-II/I ratio, and p62, and was further confirmed by transmission electron microscopy (TEM) and mCherry-GFP-LC3B tandem fluorescent reporter assays. Mechanistically, the involvement of the AKT pathway was validated using the AKT activator SC79, and the functional dependence on autophagy was confirmed via chloroquine (CQ) rescue experiments. In vivo combination therapy with 17-AAG (17-allylamino-17-demethoxygeldanamycin, an HSP90 inhibitor) and rapamycin (an mTOR inhibitor and autophagy activator) was conducted in xenograft-bearing mice, with systemic safety evaluated by body weight and H&E staining of major organs. RESULTS: HSP90AA1 was significantly overexpressed in tumor tissues, and its high expression correlated with advanced International Federation of Gynecology and Obstetrics stage, lymphovascular space invasion (LVSI), lymph node metastasis, and higher tumor grade. sgHSP90AA1 suppressed colony formation and reduced xenograft tumor volume and weight, while overexpression decreased apoptosis. Mechanistic analysis showed that sgHSP90AA1 increased Beclin-1 expression, elevated the LC3B-II/I ratio, and reduced p62 levels, whereas overexpression produced opposite effects. TEM and confocal imaging revealed abundant autolysosomes and enhanced autophagic flux in knockout cells. SC79 reversed the effects of HSP90AA1 knockout, and CQ reversed its anti-proliferative effect, indicating that HSP90AA1 acts upstream of AKT to suppress autophagy. The combination of 17-AAG and rapamycin synergistically suppressed tumor growth, accompanied by decreased Ki67 and p62 expression and increased LC3B expression, without observable organ toxicity or body weight loss. CONCLUSIONS: HSP90AA1 drives tumor growth in endometrial cancer by suppressing autophagy via the AKT pathway. Concurrent inhibition of HSP90AA1 and activation of autophagy may offer an effective therapeutic approach.