UBB (ubiquitin B) is a highly conserved protein modifier that functions as the core component of the ubiquitin-proteasome system, existing either as free ubiquitin or covalently conjugated to target proteins via isopeptide bonds. UBB serves diverse cellular functions depending on the specific lysine linkage: Lys-48-linked chains direct proteins for proteasomal degradation, Lys-63-linked chains regulate endocytosis and NF-κB signaling, and Lys-11-linked chains control endoplasmic reticulum-associated degradation and cell-cycle progression [UniProt annotation]. UBB dysfunction contributes to multiple diseases. In Alzheimer's disease, a UBB frameshift variant (UBB+1) accumulates in extracellular plaques and is secreted via unconventional autophagosome-mediated pathways, potentially spreading pathogenic aggregates while relieving cellular stress 1. In cancer biology, UBB downregulation in clear cell renal cell carcinoma potentiates VEGFA-dependent angiogenesis through SP1 interaction, mediating resistance to antiangiogenic therapy 2, while UBB hypermethylation creates dependency on UBC in certain cancer cell lines 3. In chr17 pulmonary diseases, elevated ubiquitination including UBB correlates with pulmonary fibrosis pathogenesis in COPD and IPF, suggesting ubiquitin dysregulation drives pathological remodeling 4. These findings establish UBB as a critical regulator of protein homeostasis with significant implications for cancer progression, neurodegeneration, and inflammatory disease.