Endoplasmic reticulum exit sites are segregated for secretion based on cargo size

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• TANGO1, TANGO1-Short, and cTAGE5 proteins form complexes at endoplasmic reticulum exit sites (ERES).
• These complexes are crucial for the export of bulky cellular cargoes.
• The C-terminal proline-rich domain (PRD) of these proteins interacts with Sec23A, influencing COPII coat assembly.

Purpose of the Study:

• To investigate the role of TANGO1-Short in cargo export using a light-inducible system.
• To understand how controlling the interaction between TANGO1-Short and Sec23A affects ERES organization and function.
• To determine if ERES handle cargoes based on size.

Main Methods:

• Engineered TANGO1-Short by replacing its PRD with light-responsive domains in U2OS cells.
• Utilized light activation to induce and control the binding of modified TANGO1-Short to Sec23A.
• Observed ERES localization, cargo export dynamics, and effects on Golgi organization using microscopy.

Main Results:

• Light activation rapidly and reversibly recruited TANGO1-ShortΔPRD to ERES by binding Sec23A.
• Prolonged Sec23A-TANGO1-Short binding led to ERES aggregation near the nucleus, blocking cargo export.
• Bulky cargoes (collagen VII, collagen I) were retained at fewer stalled ERES compared to small cargo molecules.

Conclusions:

• ERES may be functionally segregated to accommodate cargoes of different sizes.
• This size-based segregation facilitates simultaneous and optimal trafficking of diverse cargo types for secretion.
• The light-inducible system provides a novel tool to dissect ERES dynamics and cargo export mechanisms.