Complex Determinants in Specific Members of the Mannose Receptor Family Govern Collagen Endocytosis

• Published in: The Journal of biological chemistry 2014-03, Vol.289 (11), p.7935-7947
• Main Authors: Jürgensen, Henrik J., Johansson, Kristina, Madsen, Daniel H., Porse, Astrid, Melander, Maria C., Sørensen, Kristine R., Nielsen, Christoffer, Bugge, Thomas H., Behrendt, Niels, Engelholm, Lars H.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Cancer Invasion; Cell Line; Collagen; Collagen - chemistry; Drosophila; Endocytosis; Extracellular Matrix; Fibroblasts - metabolism; Glycobiology and Extracellular Matrices; HEK293 Cells; HeLa Cells; Humans; Insecta; Intracellular Collagen Degradation; Lectins, C-Type - chemistry; Ligands; Mannose Receptor; Mannose Receptor Family; Mannose-Binding Lectins - chemistry; Membrane Glycoproteins - chemistry; Mice; Molecular Sequence Data; Plasmids - metabolism; Protein Binding; Protein Chimeras; Protein Structure, Tertiary; Receptor Structure-Function; Receptors, Cell Surface - chemistry; Receptors, Mitogen - chemistry; Sequence Homology, Amino Acid; Structure-Activity Relationship; uPARAP/Endo180
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.512780

Members of the well-conserved mannose receptor (MR) protein family have been functionally implicated in diverse biological and pathological processes. Importantly, a proposed common function is the internalization of collagen for intracellular degradation occurring during bone development, cancer invasion, and fibrosis protection. This functional relationship is suggested by a common endocytic capability and a candidate collagen-binding domain. Here we conducted a comparative investigation of each member's ability to facilitate intracellular collagen degradation. As expected, the family members uPARAP/Endo180 and MR bound collagens in a purified system and internalized collagens for degradation in cellular settings. In contrast, the remaining family members, PLA2R and DEC-205, showed no collagen binding activity and were unable to mediate collagen internalization. To pinpoint the structural elements discriminating collagen from non-collagen receptors, we constructed a series of receptor chimeras and loss- and gain-of-function mutants. Using this approach we identified a critical collagen binding loop in the suggested collagen binding region (an FN-II domain) in uPARAP/Endo180 and MR, which was different in PLA2R or DEC-205. However, we also found that an active FN-II domain was not a sufficient determinant to allow collagen internalization through these receptors. Nevertheless, this ability could be acquired by the transfer of a larger segment of uPARAP/Endo180 (the Cys-rich domain, the FN-II domain and two CTLDs) to DEC-205. These data underscore the importance of the FN-II domain in uPARAP/Endo180 and MR-mediated collagen internalization but at the same time uncover a critical interplay with flanking domains. Background: Mannose receptor family members are candidate mediators of intracellular collagen degradation. Results: Despite common candidate collagen-binding domains and endocytic capacity throughout the family, only uPARAP/Endo180 and MR internalize collagens. Conclusion: A multi-domain interplay in the active receptors governs collagen endocytosis. Significance: Identification of the principal collagen receptors allows elucidation of the biological importance of intracellular collagen degradation.