Expression of platelet glycoprotein Ib by cultured human megakaryocytes: ultrastructural localization and biosynthesis

Abstract

Glycoprotein Ib (GPIb), the receptor for von Willebrand factor, is a two-chain member constituent of the platelet/megakaryocytic lineage. Studies on its expression have been hampered by the difficulties in obtaining purified megakaryocytes in a sufficient number. We report a suspension liquid culture procedure that allowed isolation of more than 1 x 10(6) megakaryocytes with a purity ranging from 3% to 88% from the blood of patients with chronic myeloid leukemia, from fetal liver or from normal human bone marrow. GPIb was detected on the plasma membrane of all maturing megakaryocytes and also of promegakaryoblasts devoid of demarcation membranes. GPIb was detected on demarcation membranes of maturing megakaryocytes but was absent from all other organelles, including alpha granules. Biosynthesis of 35S-methionine labeled megakaryocytes showed that GPIb with similar electrophoretic mobility to the platelet molecule was synthesized and that it was also composed of two chains, since its molecular weight shifted in reducing conditions from 170 Kd to 145 Kd. The beta chain remained undetectable after methionine metabolic labeling, but it was immunoprecipitated after 3H-leucine metabolic labeling, confirming that this subunit is devoid of methionine. GPIb was associated with GPIX, as it is in platelets, since anti-GPIb antibodies coprecipitated a 17 Kd polypeptide.

Effect of YAP/TAZ on megakaryocyte differentiation and platelet production

“…A significant reduction of YAP was observed in YAP-knockdown cells, and reduction of both YAP and TAZ was observed when a plasmid targeting both YAP and TAZ (shYAP/TAZ) was introduced into these cells ( Figure 1 A,B). CD41, which is a common marker for megakaryocyte and platelets, is expressed on the plasma membrane of mature megakaryocyte cells prior to platelet release [ 10 , 11 ]. Our previous work and other studies demonstrated that 20–40% of a population of MEG-01 cells is made up of CD41 + cells, and MEG-01 cells can produce platelet-like particles (PLPs) either spontaneously or upon treatment with platelet induction agents, such as valproic acid (VPA) [ 4 , 12 ].…”

Pathogenic Effects of Anti-Glycoprotein Ib Antibodies on Megakaryocytes and Platelets

“…This receptor is normally expressed on the platelet plasma membrane at an average copy number of 25,000 per platelet. During thrombopoiesis GPIb is expressed as early as the megakaryoblast (4). Under normal physiologic conditions, resting platelets do not adhere to each other or to leukocytes and endothelial cells (5).…”

Lateral Mobility of Integrin αIIbβ3 (Glycoprotein IIb/IIIa) in the Plasma Membrane of a Human Megakaryocyte

“…Upon stimulation with platelet agonists, megakaryocytes aggregate and start secretion, which is accompanied by Ca2+ oscillations [14]. Their plasma membrane has the same proportion of phospholipids and fatty acids [15, 161 and contains glycoproteins IbIIX [17] and a,,,P, [18, 191. The results reveal heterogeneity in P3 mobility both in resting megakaryocytes and during stimulation.…”