The phorbol ester, phorbol myristate acetate (PMA), induces myeloid cells to differentiate towards the macrophage lineage. Polyclonal antibodies to the urokinase plasminogen activator (u-PA) interfere with this process as defined by the inability of U937 cells to adhere on tissue culture surfaces. This block in differentiation is overcome by a 21 amino acid synthetic peptide from the u-PA growth factor domain which has residues of the receptor binding sequence. Moreover, a 40 amino acid peptide from the u-PA growth factor domain is more potent and enhances by 4-fold the PMA stimulated adhesion of a similar cell line, HL60. These observations indicate that the growth factor domain of u-PA plays an important role in PMA mediated myeloid cell differentiation and adhesion.
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