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Blood, 15 February 2006, Vol. 107, No. 4, pp. 1245-1246.
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CHEMOKINES
Comment on Ottersbach et al, page 1284
A helical turn makes an attractive inhibitor
Charlie Mantel
INDIANA UNIVERSITY SCHOOL OF MEDICINE
A helical motif embedded in the tertiary structure of the chemokine, macrophage-inflammatory protein 1- (MIP-1/CCL3) has been identified as the essential structural determinant conferring hematopoietic stem/progenitor cell proliferation suppression.
MIP-1 was the first member identified in the chemokine family of proinflammatory proteins that possess potent leukocyte chemoattractant properties.1 It was subsequently found to have the ability to suppress in vitro hematopoietic colony formation, particularly colonies stimulated by synergistic combinations of growth factors that are believed to be the most primitive subsets of hematopoietic progenitors.2,3 These studies have prompted the hypothesis that deregulation of MIP-1 suppression could contribute to leukemogenesis. MIP-1 is the only  -chemokine that has hematopoietic stem/progenitor cell (HS/PC) suppressive properties along with potent proinflammatory effects, while other members, like RANTES/CCL5, only have the latter property.4 A chemokine receptor that is uniquely associated with the HS/PC inhibitory effects of MIP-1 has never been identified, but the fact that MIP-1 receptor–null bone marrow cells (CCR1-/-) are still equally sensitive to MIP-1 suppression supports such a hypothesis.
In this issue of Blood, Ottersbach and colleagues have now identified the structural domains of the MIP-1 molecule that are necessary for the MIP-1 proliferation inhibitory effects, which may provide new insights and important new tools that could begin to shed light on this situation. These investigators used a "domain-swapping" approach to construct mutant chimeric chemokines composed of different structural elements of MIP-1 and RANTES, and then assessed their biological activities. They assessed calcium flux induction, which is relevant to their chemotactic properties, and assessed their HS/PC-suppressive properties in a standard assay they had already developed and reported.5 Members of this same group were previously able to use this approach to eliminate the chemoattractant effects from MIP-1 while preserving its ability to suppress HS/PC colony formation, and thus identified the structural domains in the N- and C-terminal regions as important for MIP-1 chemoattraction as well as for proteoglycan binding and self-aggregation.
The group has now come full circle by constructing a MIP-1/RANTES chimeric molecule that has just the opposite properties: loss of HS/PC suppression while maintaining the ability to induce a calcium flux. After demonstrating that the N- and C-terminal domains were unimportant for HS/PC suppression, the authors localized the suppressive region as being between the second and fourth cysteins. They then went further to identify the 310 helical turn that precedes the first -strand of MIP-1 as crucial for suppression. Ultimately, their analysis focused on a dipeptide motif in this region that was necessary for HS/PC suppression, and could even convert the nonsuppressive RANTES molecule into a suppressive mutant by swapping this domain into the analogous region of RANTES.
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The 3-dimensional structure of murine MIP-1. The 310 helical turn is located on the loop that sits C-terminal to the first two cysteine residues. Image provided courtesy of Gerard J. Graham and Neil W. Isaacs; used with permission.
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These findings add powerful new support for the idea that the leukocyte attractant and HS/PC inhibitory effects of MIP-1 are transmitted to cells by divergent mechanisms. Armed with this new information and new tools, these investigators now seem likely to make new progress toward understanding the mechanism of MIP-1 HS/PC suppression and whether or not a unique, but unidentified, MIP-1 receptor transmits this important function. 
References
- Youn BS, Mantel C, Broxmeyer HE. Chemokines, chemokine receptors and hematopoiesis. Immunol Rev. 2000;177: 150-174.[CrossRef][Medline]
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- Graham GJ, Wright EG, Hewick R, et al. Identification and characterization of an inhibitor of haemopoietic stem cell proliferation. Nature. 1990;344: 442-444.[CrossRef][Medline]
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- Broxmeyer HE, Youn BS, Kim C, Hangoc G, Cooper S, Mantel C. Chemokine regulation of hematopoiesis and the involvement of pertussis toxin-sensitive G alpha i proteins. Ann N Y Acad Sci. 2001;938: 117-127.[Medline]
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- Ottersbach K, Cook DN, Kuziel WA, et al. Macrophage inflammatory protein-1 alpha uses a novel receptor for primitive hemopoietic cell inhibition. Blood. 2001;98: 3476-3478.[Abstract/Free Full Text]
- Graham GJ, Freshney MG. CFU-A assay for measurement of the antiproliferative effects of chemokines on murine early hemopoietic progenitors. Methods Mol Biol. 2000;138: 179-189.[Medline]
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Related Article in Blood Online:
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A310 helical turn is essential for the proliferation-inhibiting properties of macrophage inflammatory protein-1 alpha (CCL3)
- Katrin Ottersbach, John Mclean, Neil W. Isaacs, and Gerard J. Graham
Blood 2006 107: 1284-1291.
[Abstract]
[Full Text]
[PDF]
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