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Mol. Cell. Biol., 09 1995, 4851-4855, Vol 15, No. 9
Y Zhang and BJ Rollins
Monocyte chemoattractant protein 1 (MCP-1) is a member of the chemokine
family of proinflammatory cytokines, all of which share a high degree of
amino acid sequence similarity. Aberrant expression of chemokines occurs in
a variety of diseases that have an inflammatory component, such as
atherosclerosis. Although structural analyses indicate that chemokines form
homodimers, there is controversy about whether dimerization is necessary
for activity. To address this question for MCP-1, we obtained evidence in
four steps. First, coprecipitation experiments demonstrated that MCP-1
forms dimers at physiological concentrations. Second, chemically
cross-linked MCP-1 dimers attract monocytes in vitro with a 50% effective
concentration of 400 pM, identical to the activity of non-cross-linked
MCP-1. Third, an N- terminal deletion variant of MCP-1 (called 7ND) that
inhibits MCP-1- mediated monocyte chemotaxis specifically forms
heterodimers with wild- type MCP-1. Finally, although 7ND inhibits
wild-type MCP-1 activity, it has no effect on cross-linked MCP-1. These
results indicate that 7ND is a dominant negative inhibitor, implying that
MCP-1 activates its receptor as a dimer. In addition, chemical
cross-linking restores activity to an inactive N-terminal insertional
variant of MCP-1, further supporting the need for dimerization. Since the
reported Kd for MCP-1 monomer dissociation is much higher than its 50%
effective concentration or Kd for receptor binding, active dimer formation
may require high local concentrations of MCP-1. Our data further suggest
that the dimer interface can be a target for MCP-1 inhibitory drugs.
Copyright © 1995, American Society for Microbiology
A dominant negative inhibitor indicates that monocyte chemoattractant protein 1 functions as a dimer
Department of Medicine, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
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