SOSSB1 and SOSSB2 mutually regulate protein stability through competitive binding of SOSSA

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Human single-stranded DNA-binding proteins hSSB1 (SOSSB1) and hSSB2 (SOSSB2) are crucial for genome stability as part of the sensor of single-stranded DNA (SOSS) complex.
• The precise mechanisms governing the mutual expression and regulation of SOSSB1 and SOSSB2 have remained largely unelucidated.

Purpose of the Study:

• To investigate the mutual regulatory relationship between SOSSB1 and SOSSB2 protein expression.
• To elucidate the molecular mechanisms underlying the stability and degradation of SOSSB1 and SOSSB2.
• To determine the functional consequences of SOSSB1 and SOSSB2 loss on DNA repair and cellular response to damage.

Main Methods:

• Depletion studies using cell models to assess protein stability.
• Co-immunoprecipitation assays to analyze protein-protein interactions.
• Proteasome inhibition assays to investigate degradation pathways.
• Assessment of DNA repair efficiency, radiosensitivity, and apoptosis.

Main Results:

• Depletion of SOSSB1 increases SOSSB2 protein stability, and vice versa, indicating mutual stabilization.
• SOSSB1 and SOSSB2 levels are regulated by competitive binding to SOSSA, which interacts with conserved OB-fold domains.
• Destabilized SOSSB1 and SOSSB2 are degraded through the proteasome pathway.
• Simultaneous loss of SOSSB1 and SOSSB2 exacerbates homologous recombination (HR) DNA repair defects, increases radiosensitivity, and promotes apoptosis.

Conclusions:

• SOSSB1 and SOSSB2 positively regulate HR-mediated DNA repair.
• The interaction of SOSSA with SOSSB1 or SOSSB2 prevents their proteasomal degradation, thereby maintaining genome stability.
• This study reveals a novel mechanism of mutual protein regulation essential for DNA repair and cellular survival.