CD44 is associated with a high risk of metastasis, recurrence, and drug resistance in various cancers. Here we report that platelet endothelial aggregation receptor 1 (PEAR1) is a CD44 chaperone protein that protected CD44 from endocytosis-mediated degradation and enhances cleavage of the CD44 intracellular domain (CD44-ICD). Furthermore, we found that lysyl oxidase–like protein 2 (LOXL2), an endogenous ligand of PEAR1, bound to the PEAR1-EMI domain and facilitated the interaction between PEAR1 and CD44 by inducing PEAR1 Ser891 phosphorylation in a manner that was independent of its enzyme activity. Levels of PEAR1 protein and PEAR1 phosphorylation at Ser891 were increased in patients with triple-negative breast cancer (TNBC), were positively correlated with expression of LOXL2 and CD44, and were negatively correlated with overall survival. The level of PEAR1 Ser891 phosphorylation was identified as the best independent prognostic factor in TNBC patients. The prognostic efficacy of the combination of PEAR1 phosphorylation at Ser891 and CD44 expression was superior to that of PEAR1 phosphorylation at Ser891 alone. Blocking the interaction between LOXL2 and PEAR1 with monoclonal antibodies significantly inhibited TNBC metastasis, representing a promising therapeutic strategy for TNBC.

Hyperuricemia, i.e., increased plasma uric acid concentration, is a common problem in clinical practice, leading to gout or nephrolithiasis, and is associated with other disorders, such as metabolic syndrome, cardiovascular disease, and chronic renal disease. Xanthine oxidoreductase (XOR) is a critical rate-limiting enzyme involved in uric acid synthesis and a promising target for hyperuricemia therapy. However, XOR inhibitors currently face clinical problems such as a short half-life and side effects. Here, we found that specifically targeting liver Xor with GalNAc-siRNAs had a good therapeutic effect on hyperuricemia. First, siRNAs were designed to target various sites in the homologous region between Homo sapiens and Mus musculus Xor mRNA and were screened in primary mouse hepatocytes. Then, the siRNAs were modified to increase their stability in vivo and conjugated with GalNAc for liver-specific delivery. The effects of GalNAc-siRNAs were evaluated in three hyperuricemia mouse models, including potassium oxonate and hypoxanthine administration in WT and humanized XDH mice and Uox knockout mice. Febuxostat, a specific XOR inhibitor used for hyperuricemia treatment, was used as a positive control. Targeting liver Xor with GalNAc-siRNAs by subcutaneous administration reduced plasma uric acid levels, uric acid accumulation in the kidney, renal inflammation, and fibrosis, thereby alleviating kidney damage in hyperuricemia mouse models without hepatoxicity. The results demonstrated that targeting liver Xor with GalNAc-siRNAs was a promising strategy for hyperuricemia therapy.