Class A scavenger receptor-mediated adhesion and internalization require distinct cytoplasmic domains

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Class A scavenger receptors (SR-A) are transmembrane glycoproteins involved in ligand internalization and cell adhesion.
• Previous research identified cytoplasmic tail amino acids regulating SR-A internalization, but their role in cell adhesion remained unclear.

Purpose of the Study:

• To investigate the function of cytoplasmic domains in SR-A-mediated cell adhesion.
• To determine if SR-A adhesion and internalization pathways require distinct cytoplasmic domains.

Main Methods:

• Stable expression of various SR-A constructs in human embryonic kidney (HEK 293) cells.
• Analysis of receptor protein abundance, cell surface localization, and ligand internalization (acetylated low-density lipoprotein).
• Assessment of cell spreading and adhesion in cells expressing different SR-A variants.

Main Results:

• Deleting the SR-A cytoplasmic tail reduced receptor abundance; retaining the six membrane-proximal amino acids restored it.
• The SR-A construct with only membrane-proximal amino acids (SR-A Delta 1-49) localized to the cell surface but failed ligand internalization.
• Cells expressing SR-A Delta 1-49 exhibited increased spreading and adhesion, indicating these amino acids suffice for SR-A-mediated adhesion.

Conclusions:

• Specific membrane-proximal amino acids are critical for SR-A trafficking from the endoplasmic reticulum to the Golgi.
• SR-A-mediated cell adhesion and ligand internalization are regulated by distinct cytoplasmic domains.
• The membrane-proximal region of the SR-A cytoplasmic tail is sufficient for mediating SR-A-dependent cell adhesion.