Tony Tao

S100 proteins represent a new class of chemoattractants. Here we extend earlier evidence for the proinflammatory properties of human S100A12. A12 induced migration of monocytoid cells, with optimal activity at 10(-10) M and potency of >10(-9) M C5a. Neutrophils were poorly responsive, and lymphocyte migration was not affected. Actin polymerization in monocytoid cells was accompanied by a sustained [Ca(2+)]i flux of a magnitude comparable with C5a. A12 elicited a transient infiltration of neutrophils (4-8 h) and more delayed recruitment of monocytes (8-24 h) in vivo. A12 (approximately 70 nM) was present in synovial fluid (SF) from rheumatoid arthritis patients, and synovium contained A12-positive neutrophils in the sublining and interstitial region, often surrounding the perivasculature but rarely in the synovial lining layer, although some macrophages were positive. The A12 gene was transiently up-regulated in monocytes by tumor necrosis factor alpha (6 h); induction by lipopolysaccharide (LPS) was sustained (12-48 h). A12 may contribute to leukocyte migration in chronic inflammatory responses.

Human S100A12 (extracellular newly identified RAGE (receptor for advanced glycosylation end products)-binding protein), a new member of the S100 family of EF-hand calcium-binding proteins, was chemically synthesised using highly optimised 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate/tert-butoxycarbonyl in situ neutralisation solid-phase chemistry. Circular dichroism studies indicated that CaCl(2) decreased the helical content by 27% whereas helicity was marginally increased by ZnCl(2). The propensity of S100A12 to dimerise was examined by electrospray ionisation time-of-flight mass spectrometry which clearly demonstrated the prevalence of the non-covalent homodimer (20890 Da). Importantly, synthetic human S100A12 in the nanomolar range was chemotactic for neutrophils and macrophages in vitro.