Macrophage Receptor with Collagenous Structure (MARCO) Is Processed by either Macropinocytosis or...

Area of Science:

• Cell Biology
• Molecular Biology
• Immunology

Background:

• The Macrophage Receptor with COllagenous structure (MARCO) is a key plasma membrane receptor involved in the uptake of un-opsonized particles by phagocytic cells.
• Understanding the internalization pathways of MARCO is crucial for elucidating its role in cellular processes and immune responses.

Purpose of the Study:

• To investigate the distinct cellular mechanisms by which MARCO is internalized in Chinese Hamster Ovary (CHO-K1) cells.
• To characterize the intracellular trafficking and molecular associations of internalized MARCO.

Main Methods:

• Stable transfection of CHO-K1 cells with GFP-MARCO.
• Microscopy to observe MARCO internalization via macropinocytosis and endocytosis.
• Co-localization studies with LC3B and lysosomes.
• Analysis of LC3-II/LC3-I ratio.
• Assessment of the role of cytoskeletal components (tubulin, actin) in MARCO trafficking.

Main Results:

• MARCO was internalized through two distinct pathways: macropinocytosis forming large vesicles and endocytosis forming amphisomes.
• Amphisomes, but not macropinosomes, co-localized with LC3B and lysosomes, indicating autophagosome involvement.
• The LC3-II/LC3-I ratio increased in the presence of specific amines, suggesting autophagy induction.
• Intracellular trafficking of MARCO-containing puncta was regulated by tubulin, not actin, with speeds up to 2-3 μm/sec.

Conclusions:

• MARCO utilizes both macropinocytic and endocytic pathways for internalization.
• Endocytosis of MARCO involves fusion with autophagosomes, forming amphisomes that traffic along microtubules.
• MARCO may function as an adhesive receptor facilitating the incorporation of extracellular materials into cells via these pathways.