Phosphorylation of YBX1 in the Kidneys is Altered in Legumain Knockout-Mice

Protein phosphorylation is a common post-translational modification that plays a crucial role in cellular signal transduction. Disruptions in this process can lead to phenotypic deviations in healthy organisms. Legumain is a cysteine proteinase present in plants and animals. Legumain is involved in the regulation of kidney and hematopoietic homeostasis, as well as immune response. Its dysregulation is associated with various types of cancers and neurodegenerative diseases. Legumain knockout mice generally exhibit a normal phenotype, except for altered kidney function, hemophagocytic syndrome, and extramedullary hematopoiesis. In this study, we analyzed the changes in protein phosphorylation in legumain knockout mice compared to their wild-type counterparts to elucidate how legumain deficiency affects protein phosphorylation and related cell signaling. Phosphopeptides from the kidney and liver samples were enriched and analyzed using mass spectrometry and validated with Western blot and immunohistochemistry. Several phosphorylation sites on the RNA- and DNA-binding protein Y-box binding protein 1 were identified. A site on the serine 100 residue was found to activate the NF-κB pathway in legumain knockout mice, resulting in an enhanced inflammatory response. This was supported by the increased expression of several NF-κB genes. Overall, this study provides valuable insights into the role of legumain and its impact on various cellular processes.