Thrombopoietin Enhances the aIIbb3-Dependent Adhesion of Megakaryocytic Cells to Fibrinogen or Fibronectin Through PI 3 Kinase

The effect of thrombopoietin (TPO) on the functional activity a5 integrins were completely ineffective, clearly indicating of surface aIIbb3 (GPIIbIIIa) was investigated in both primary that aIIbb3 participates in this association. A role for PI 3 human megakaryocytic cells, derived from peripheral blood kinase (PI 3-K) in the TPO-mediated increase in aIIbb3 funcCD34 cells, and HEL hematopoietic cell line. TPO (100 ng/ tion in megakaryocytic cells was suggested by the ability of mL) induced a sixfold to ninefold enhancement of adhesion the PI 3-K inhibitor wortmannin (100 nmol/L) and antisense of both primary megakaryocytic and HEL cells to plates oligonucleotides directed against the p85 regulatory subunit coated with either fibrinogen or fibronectin and a parallel of PI 3-K to completely block the TPO-induced increase in increase of immunoreactivity to the PAC1 monoclonal antiaIIbb3 integrin activity upon TPO stimulation. The modulabody (MoAb) and fluorescein isothiocyanate-fibrinogen, tion of adhesiveness to extracellular matrix proteins conboth of which recognize an activated state of aIIbb3 . The taining the RGD motif mediated by TPO likely plays a physioenhanced adhesion to fibrinogen or fibronectin was medilogic role in megakaryocytopoiesis, as pretreatment of ated by the Arg-Gly-Asp (RGD) recognition sequence of CD34 cells with RGDS or anti-aIIb MoAb significantly reaIIbb3 , as it was abolished by pretreatment of cells with satuduced the number of megakaryocytic colonies obtained in rating concentrations of RGDS peptide. A MoAb specific for a fibrinclot semisolid assay. the aIIb subunit of aIIbb3 also inhibited cell attachment to q 1997 by The American Society of Hematology. fibrinogen or fibronectin, while MoAb to anti-avb3 or anti-