AKR1B1 promotes canine mammary tumorigenesis via activation of PI3K/AKT signaling and acts as a serum biomarker

Aldo-keto reductase 1B1 (AKR1B1), also named as aldose reductase, is an enzyme implicated in metabolic regulation and signaling transduction in human cancers, but little is known in canine mammary tumors (CMTs). This study investigated expression in CMT tissues, functional role in tumor progression, and potential of AKR1B1 as a circulating biomarker. AKR1B1 expression was evaluated by immunohistochemistry in paired CMT and adjacent normal mammary tissues, and CMT-U27 cells with lentiviral AKR1B1 overexpression or shRNA-mediated AKR1B1 knockdown were used for investigation of cell proliferation, migration, and Western blot analysis of PI3K/AKT signaling and cell-cycle regulators. Results showed that AKR1B1 was markedly overexpressed in CMT tissues compared to adjacent normal glands. Targeted expression of AKR1B1 in CMT-U27 cells promoted proliferation, migration, accompanied by increase of phosphorylated AKT (Thr308) and downregulation of P21 and P27, whereas AKR1B1 knockdown led to opposite effects. Magnetic-particle chemiluminescence immunoassay was developed to measure serum AKR1B1 concentrations, and results showed serum AKR1B1 was significantly higher in Canines with CMT (4.65 ± 0.37 ng/mL; n = 50) than in healthy controls (2.27 ± 0.15 ng/mL; n = 56). Receiver operating characteristic analysis demonstrated impressive diagnostic performance with AUC = 0.8386 (95% CI 0.7597-0.9174), sensitivity at 74.0% and specificity at 83.9% at a cutoff of 3.08 ng/mL. These findings indicate that AKR1B1 acts as a tumorigenic driver via PI3K/AKT-mediated oncogenesis in CMT and a serum biomarker for non-invasive diagnosis of CMT and monitoring of disease progression.