Polyethylene Nanoplastic Promotes Tumor Progression in Canine Mammary Tumor U27 Cells

The canine mammary tumor cell line CMT-U27 (CRL-3456, ATCC, USA) was maintained in RPMI-1640 medium supplemented with 10% fetal bovine serum and 1% Penicillin-Streptomycin-Gentamicin solution, with routine passaging every 3 days. For transcriptomic analysis, cells were treated for 48 h under two conditions: the Control group received culture medium only, whereas the PE group was exposed to 0.25 mg/mL of 50-nm spherical polyethylene nanoplastics (PE-NPs; ZKKY-PE-0005, Zhongkekeyou, China). The PE-NPs were supplied as a 2.5% (w/v) aqueous stock suspension, which was diluted to the working concentration in culture medium and vortexed for 15 min immediately before use to ensure dispersion and minimize aggregation.