The SQSTM1/p62 UBA domain regulates Ajuba localisation, degradation and NF-κB signalling function

Area of Science:

• Cellular Biology
• Molecular Biology
• Biochemistry

Background:

• The LIM-domain protein Ajuba and scaffold protein SQSTM1/p62 are key regulators of NF-κB signaling, crucial for osteoclast differentiation and survival.
• Mutations in the ubiquitin-associated domain (UBA) of SQSTM1/p62 are common in Paget's disease of bone, suggesting a role in pathogenesis.
• NF-κB signaling is implicated in bone diseases and cancer cell survival.

Purpose of the Study:

• To investigate the interaction between Ajuba and SQSTM1/p62 and its impact on NF-κB signaling.
• To determine how SQSTM1/p62 affects Ajuba stability, localization, and function.
• To explore the implications of this interaction in diseases like Paget's disease and cancer.

Main Methods:

• HEK293 cell culture and co-expression experiments.
• Analysis of NF-κB activity.
• Assessment of Ajuba protein levels and localization under various stress conditions (autophagy, proteasomal stress).
• Investigation of SQSTM1/p62 UBA domain dependency.

Main Results:

• Ajuba activates NF-κB signaling, but co-expression with SQSTM1/p62 inhibits this activation in a UBA domain-dependent manner.
• SQSTM1/p62 protects Ajuba from autophagy-mediated degradation and reduces its nuclear presence.
• Intact UBA domain of SQSTM1/p62 forms complexes with Ajuba, inhibiting signaling without targeting Ajuba for degradation.

Conclusions:

• SQSTM1/p62 modulates Ajuba's function by regulating its stability and localization, impacting NF-κB signaling.
• Altered SQSTM1/p62 levels or UBA domain mutations, as seen in Paget's disease and cancer, can disrupt this regulation, potentially driving disease pathogenesis.
• This interaction highlights a novel mechanism by which SQSTM1/p62 influences osteoclastogenesis and cancer cell survival.