E3 ubiquitin-protein ligase CHIP

STUB1 encodes E3 ubiquitin-protein ligase CHIP, a 303-amino-acid protein (UniProt: Q9UNE7) that functions as a key regulator of protein quality control. It catalyzes ubiquitin-dependent proteasomal degradation of misfolded chaperone substrates and collaborates with heat shock proteins (Hsp70, Hsc70, Hsp90) to maintain cellular proteostasis. CHIP also modulates mitochondrial function through selective autophagy of dysfunctional mitochondria and regulates diverse cellular pathways including apoptosis, transcription, and immune tolerance.

STUB1 is broadly expressed and participates in cellular stress responses across multiple tissues. UniProt lists two disease associations: spinocerebellar ataxia autosomal recessive 16 (SCAR16, MIM 615768) and spinocerebellar ataxia 48 (SCA48, MIM 618093), both characterized by progressive cerebellar neurodegeneration.

In Alzheimer's Disease, STUB1 is significantly upregulated in post-mortem AD brain tissue relative to age-matched controls (mean log2 fold-change +0.16; Chaparral AD proteomics). This elevation may reflect activation of protein quality control mechanisms in response to pathological protein accumulation characteristic of AD neurodegeneration.