Expression of IIb3 Integrin (GPIIb-IIIa) in Myeloid Cell Lines and Normal CD34/CD33 Bone Marrow Cells Submitted 08/15/97; revised 08/22/97 (communicated by Alvin M. Mauer, M.D., 09/23/97) C. Denise Wall 1 , Pamela B. Conley 2 , Juan Armendariz-Borunda 3 , Chitra Sudarshan 3 , John E. Wagner 4 , Rajendra Raghow 3,5 , Lisa K. Jennings 1 ABSTRACT: Regulation of myeloid cell proliferation and differentiation in the bone marrow is mediated, in part, by the interaction of integrins on early myeloid cells with the extracellular matrix proteins secreted by stromal cells. To further define adhesive protein receptors of early myeloid cells, we examined the expression of the integrin GPIIb-IIIa ( IIb  3 ) in leukemic cell lines KG-1a, KG-1, and HL-60, that represent early stages of myeloid differentiation. All three cell lines expressed surface GPIIb-IIIa as measured by flow cytometry and by binding of 125 I-anti-GPIIb-IIIa monoclonal antibody. Preincubation of cells with human AB serum or platelet releasate increased GPIIb-IIIa surface expression. GPIIb transcripts were identified in all three cell lines by Northern blot analysis. Furthermore, we readily detected GPIIb transcripts in fluorescence activated cell sorted (FACS) myeloid cells from normal human bone marrow by RT-PCR. Cloning and sequencing of the PCR products established the identity of GPIIb transcripts in the leukemic cell lines and CD34+/CD33+ normal bone marrow cells. Since the normal myeloid cells also demonstrated markers corresponding to the maturational stage of KG-1a/KG-1 cells, we propose that GPIIb-IIIa may serve as a myeloid differentiation antigen and as a key integrin of myeloid precursors. Keywords: integrins, glycoprotein IIb-IIIa, myeloid precursor cell, myeloid differentiation antigen, myeloid leukemic cell lines INTRODUCTION Platelet glycoprotein IIb-IIIa (GPIIb-IIIa) (1) is a heterodimeric, transmembrane glycoprotein complex consisting of an  and subunit (1,2). This surface glycoprotein serves as a receptor for fibrinogen, fibronectin, vitronectin and von Wille- brand factor on activated platelets (3-9) and plays an essential role in platelet aggregation (10). GPIIb-IIIa is also present in membranes of - granules, which, after platelet activation, fuses with the outer membrane and leads to increased surface expression of GPIIb-IIIa (11). The importance of GPIIb-IIIa in platelet func- tion has led to an examination of other cell types for expression of this specific glycoprotein com- plex.Using platelet anti-GPIIb-IIIa antibodies as probes, the presence of GPIIb-IIIa or GPIIb-IIIa- like proteins on endothelial cells and leukocytes has been reported (12-14) . In many instances it was shown that GPIIb-IIIa antibodies were cross- reacting with other adhesive glyco-proteins that had a significant degree of amino acid sequence homology with GPIIb-IIIa (15). Further investiga- tion of these glycoproteins led to the discovery of a large family of transmembrane receptors for adhesive proteins, termed integrins (2,16). The / heterodimers have specificities for such adhe- 1 The University of Tennessee, Memphis, Department of Medicine, Memphis, TN; 2 COR Therapeutics, South San Francisco, CA; 3 Veteran Affairs Medical Center, Memphis, TN; 4 Department of Pediatrics, University of Minnesota, Minneapolis, MN; 5 The University of Tennessee, Memphis, Department of Pharmacology, Memphis, TN. Reprint request to: Lisa K. Jennings, Ph.D., Department of Medicine, Room A303, 956 Court Avenue, Memphis, Tennessee 38163. phone (901)448-5067, fax (901)448-7181, email: ljennings@utmem1.utmem.edu C.D. Wall, et al. Blood Cells, Molecules, and Diseases (1997) 23(18) Sept 30: 361–376 Article No. MD970153 1079-9796/97 $25.00 Published by Academic Press Copyright  1997 by The Blood Cells Foundation, La Jolla, California, USA Established by Springer-Verlag, Inc. in 1975 All rights of reproduction in any form reserved. 361