Cohesin-independent STAG proteins interact with RNA and R-loops and promote complex loading.

Area of Science:

• Molecular Biology
• Epigenetics
• Cancer Biology

Background:

• Cohesin complexes are essential for genome stability and gene regulation.
• Stromalin Antigen (SA) proteins are traditionally viewed as integral components of the cohesin ring.

Purpose of the Study:

• To investigate the functional role of SA proteins beyond their structural integration within the cohesin complex.
• To elucidate the mechanisms by which SA proteins contribute to cohesin localization and function.
• To explore the potential link between SA proteins, RNA, and R-loops in cellular processes and disease.

Main Methods:

• Depletion of RAD21 to study SA protein behavior in cohesin-depleted cells.
• Chromatin immunoprecipitation and 3D clustering analysis.
• Interaction studies with CTCF, RNA-binding proteins, RNA, and R-loops.

Main Results:

• SA proteins remain chromatin-bound and cluster in 3D upon RAD21 depletion.
• SA proteins interact with CTCF and various RNA-binding proteins involved in RNA processing.
• SA proteins bind to RNA and R-loops independently of cohesin.
• SA1 facilitates cohesin loading independently of NIPBL, suggesting a novel loading mechanism.

Conclusions:

• SA proteins play an active role in directing cohesin to specific genomic locations and biological processes.
• SA1 acts as a key regulator of cohesin loading, potentially utilizing R-loop structures.
• These findings have significant implications for understanding SA protein function in cancer and disease, given their role as pan-cancer targets and the involvement of R-loops in cancer biology.