Cullin-9 (CUL9)

Cullin-9 (CUL9), also known as PARC or H7AP1, is a member of the cullin-RING E3 ubiquitin ligase family, and is the largest human cullin protein. Unlike canonical cullins, CUL9 carries an additional RING-between-RING (RBR) domain and does not use the typical substrate-recruiting adaptors, making it a structurally and functionally unique E3 ligase[1][3][4]. CUL9 forms a complex with RBX1 and mediates the ubiquitination of substrates such as survivin (BIRC5) and p53 (TP53), promoting proteasomal degradation of survivin and monoubiquitylation (but not degradation) of p53. CUL9 is highly expressed in the brain, influences neuronal differentiation, and is implicated in maintaining genome integrity, mitotic division, and cytoskeletal organization. Although CUL9 knockout mice are viable, they display neural and behavioral abnormalities, suggesting the protein's importance in brain structure and function[1][2][4][5]. CUL9 is involved in pathways related to metabolism, transcriptional regulation, and cell survival, particularly in postmitotic neurons. Emerging data support roles in cancer (tumor suppression) and psychiatric/neurodevelopmental disease, but the physiological and pathological consequences of CUL9 modulation are incompletely understood. No approved drugs specifically target CUL9, and the mechanism of its E3 ligase activity is an active area of research[1][3][4][5].

Other names

CUL9PARCH7AP1KIAA0708UbcH7-associated protein 1p53-associated parkin-like cytoplasmic proteinparkin-like cytoplasmic p53 binding proteinCullin-9

Drugs targeting E3 ubiquitin ligases like Cullin-9 would theoretically act by modulating ubiquitination of substrates, leading to either their degradation or altered protein interactions. No specific mechanisms are described for Cullin-9 due to lack of known drug modulators[1][4].