Dominant-negative function of the C-terminal fragments of NBR1 and SQSTM1 generated during enteroviral infection

Area of Science:

• Virology
• Cell Biology
• Molecular Biology

Background:

• Coxsackievirus infection causes ubiquitin aggregate accumulation, impairing cellular health and aiding viral pathogenesis.
• Selective autophagy, mediated by proteins like sequestosome 1 (SQSTM1) and neighbor of BRCA1 gene 1 protein (NBR1), normally clears these aggregates.
• SQSTM1 is cleaved during coxsackievirus infection, disrupting its autophagic function.

Purpose of the Study:

• To investigate if NBR1 can compensate for the loss of SQSTM1 function after coxsackievirus infection.
• To determine the mechanism and consequences of SQSTM1 and NBR1 cleavage during viral infection.
• To explore the regulatory relationship between SQSTM1 and NBR1 in the context of coxsackievirus infection.

Main Methods:

• Viral infection models (Coxsackievirus).
• Protein cleavage site mapping using viral proteases (2Apro and 3Cpro).
• Analysis of protein-protein interactions (LC3, ubiquitin binding) and functional assays (autophagy, dominant-negative effects).
• Gene knockdown and overexpression studies to assess regulatory relationships.

Main Results:

• NBR1, like SQSTM1, is cleaved at two sites by viral proteases 2Apro and 3Cpro.
• Cleaved SQSTM1 and NBR1 C-terminal fragments exhibit dominant-negative effects, inhibiting native protein function.
• A mutual regulatory relationship exists: SQSTM1 influences NBR1 expression, and vice versa, indicating no compensation.
• Viral infection disrupts ubiquitin aggregate clearance by cleaving key autophagy adaptors.

Conclusions:

• Coxsackievirus infection employs a novel mechanism involving the cleavage of SQSTM1 and NBR1.
• This cleavage leads to loss-of-function and gain-of-function toxicities, hindering aggregate clearance.
• The findings elucidate a pathway contributing to viral pathogenesis through impaired autophagy and increased ubiquitin conjugates.