Soluble CD44 interacts with intermediate filament protein vimentin on endothelial cell surface

Area of Science:

• Cell Biology
• Molecular Interactions
• Cancer Research

Background:

• CD44 is a cell surface glycoprotein and hyaluronan receptor.
• Soluble CD44 (sCD44) levels increase during inflammation and in cancer.
• Previous studies showed CD44 hyaluronan binding domain (CD44HABD) inhibits tumor growth, suggesting non-hyaluronan targets.

Purpose of the Study:

• To identify novel binding partners of CD44 beyond hyaluronan.
• To investigate the interaction between CD44 and intermediate filament protein vimentin.
• To elucidate the role of vimentin in CD44 function on endothelial cells.

Main Methods:

• Utilized a non-hyaluronan-binding CD44HABD mutant (CD443MUT) to identify interaction partners.
• Co-precipitation assays to confirm CD44-vimentin interaction in HUVECs and MCF-7 cells.
• Binding kinetics (Kd) and displacement assays using recombinant vimentin.
• Internalization studies in wild-type and vimentin-knockout endothelial cells.

Main Results:

• Identified vimentin as a novel binding partner for CD44HABD and CD443MUT.
• Demonstrated that CD44 binds to the N-terminal head domain of vimentin.
• Quantified the binding affinity of CD443MUT to vimentin in solution and immobilized forms.
• Showed that vimentin mediates the internalization of CD44 into endothelial cells.

Conclusions:

• Vimentin serves as a specific binding site for soluble CD44 on endothelial cells.
• The CD44-vimentin interaction is independent of CD44's hyaluronan-binding activity.
• Vimentin plays a critical role in the cellular uptake of CD44.