POSTTRANSLATIONAL MODIFICATIONS AFFECT THE ACTIVITY OF THE HUMAN MONOCYTE CHEMOTACTIC PROTEINS MCP-1 AND MCP-2 - IDENTIFICATION OF MCP-2(6-76) AS A NATURAL CHEMOKINE INHIBITOR

Chemokines are important mediators in infection and inflammation, The monocyte chemotactic proteins (MCPs) form a subclass of structurally r elated C-C chemokines, MCPs select specific target cells due to bindin g to a distinct set of chemokine receptors, Recombinant and synthetic MCP-1 variants have been shown to function as chemokine antagonists, I n this study, posttranslationally modified immunoreactive MCP-1 and MC P-2 were isolated from mononuclear cells, Natural forms of MCP-1 and M CP-2 were biochemically identified by Edman degradation and mass spect rometry and functionally characterized in chemotaxis and Ca2+-mobiliza tion assays. Glycosylated MCP-1 (12 and 13.5 kDa) mas found to be two- to threefold less chemotactic for monocytes and THP-1 cells than nong lycosylated MCP-1 (10 kDa), Natural, NH2-terminally truncated MCP-1(5- 76) and MCP-1(6-76) were practically devoid of bioactivity, whereas CO OH-terminally processed MCP-1(1-69) fully retained its chemotactic and Ca2+ inducing rapacity, The capability of naturally modified MCP-1 fo rms to desensitize the Ca2+ response induced by intact MCP-1 in THP-1 cells correlated with their agonistic potency, In contrast, naturally modified MCP-2(6-76) was devoid of activity, but could completely bloc k the chemotactic effect of intact MCP-2 as well as that of MCP-1, MCP -3, and RANTES. Carboxyl-terminally processed MCP-2(1-74) did retain i ts chemotactic potency, Although comparable as a chemoattractant, natu ral intact MCP-2 was found to be 10-fold less potent than MCP-1 in ind ucing an intracellular Ca2+ increase, It can be concluded that under p hysiologic or pathologic conditions, posttranslational modification af fects chemokine potency and that natural MCP-2(6-76) is a functional C -C chemokine inhibitor that might be useful as an inhibitor of inflamm ation.