Cellular adhesion mediated by factor J, a complement inhibitor. Evidence for nucleolin involvement

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Factor J (FJ) is a known inhibitor of the classical and alternative complement pathways.
• The cellular interactions and specific binding mechanisms of Factor J remain incompletely understood.

Purpose of the Study:

• To investigate the interaction between Factor J and various human cell lines.
• To identify the specific cell surface receptor mediating Factor J binding and subsequent cell adhesion.

Main Methods:

• Flow cytometry was used to assess Factor J-cell interactions with Jurkat, K562, JY, and peripheral blood lymphocytes.
• Cell adhesion assays were performed with immobilized Factor J, with inhibition studies using antibodies and glycosaminoglycans.
• Affinity chromatography and microsequence analysis were employed to identify the putative Factor J receptor, followed by immunofluorescence and Western blot validation.

Main Results:

• Factor J induced adhesion of tested cell lines to immobilized Factor J, an interaction dependent on active cell metabolism and cytoskeletal integrity.
• Adhesion was specifically blocked by anti-Factor J antibodies and soluble Factor J, and modulated by glycosaminoglycans and enzymatic treatment.
• Nucleolin was identified as the 110 kDa receptor for Factor J on the cell membrane, and its interaction with Factor J was confirmed.

Conclusions:

• Factor J mediates cell adhesion through specific binding to nucleolin on the cell surface.
• Nucleolin acts as the primary receptor, mediating the interaction between Factor J and cells, impacting cellular adhesion processes.