Megakaryocyte synthesis is the source of epidermal growth factor in human platelets

Epidermal growth factor (EGF) is known to be present in the alpha granules of human platelets; however the source of this EGF, ie, whether it is taken up by the platelets from the circulation, or whether it is packaged into the platelets from the megakaryocyte during thrombopoiesis, is unknown. To determine whether EGF is taken up by platelets, platelets for EGF receptors were assayed and it was attempted to detect uptake of EGF by the platelets from culture medium. Platelets were found to lack EGF receptors, and no uptake of EGF from the culture medium was detected. To assess whether EGF is packaged into platelets from the megakaryocyte, megakaryocytes in frozen section bone marrow cores were stained for EGF protein by immunohistochemistry, and it was demonstrated that EGF is present in megakaryocytes. In addition, staining of megakaryocytes by in situ hybridization for EGF mRNA demonstrated its presence in these cells. Therefore it is concluded that the source of EGF in human platelets is the megakaryocyte and that this EGF is synthesized in the megakaryocyte rather than being taken up from its environment.