Dual structural requirements for multilineage hematopoietic-suppressive activity of chemokine-derived peptides

Many chemokines have direct suppressive activity in vitro and in vivo on pr imitive hematopoietic cells. However, few chemokine-derived peptides have s hown a significant activity in inhibiting hematopoiesis. Interestingly, a p eptide derived from the 34-58 sequence of the CXC chemokine platelet factor 4 (PF4) produced a 30-40% inhibition of proliferation of murine hematopoie tic progenitors (CFU-MK, CFU-GM, and BFU-E) in vitro, at concentrations of 30-60-fold lower than PF4. The aim of the present work was to define the st ructural parameters and motifs involved in conferring biological activity t o the peptide PF4(34-58). Both structural predictions and determinations re vealed a new helical motif that was further localized between residues 38 a nd 46. This helix was necessary for binding of the peptide and for permitti ng the functional DLQ motif at position 54-56 to activate the putative rece ptor site. Peptides lacking either the helical or the DLQ motif were devoid of inhibitory activity on the hematopoietic progenitors in vitro. However, among inactive peptides, only those having the helical motif counteracted the inhibition induced by the active peptide PF4(34-58). This suggested tha t the helix might be required for peptide interactions with a putative rece ptor site, whereas the DLQ motif would be implicated in the activation of t his receptor. These results identify for the first time the dual requiremen ts for the design of chemokine-derived peptides with high suppressive activ ity on hematopoiesis, as well as for the design of molecules with antagonis tic action.