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Megakaryocyte precursors, megakaryocytes and platelets express the HIV co‐receptor CXCR4 on their surface: determination of response to stromal‐derived factor‐1 by megakaryocytes and platelets
Author(s) -
Kowalska M. Anna,
Ratajczak Janina,
Hoxie James,
Brass Lawrence F.,
Gewirtz Alan,
Poncz Mortimer,
Ratajczak Mariusz Z.
Publication year - 1999
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1046/j.1365-2141.1999.01169.x
Subject(s) - megakaryocyte , platelet , biology , megakaryocytopoiesis , protease activated receptor , microbiology and biotechnology , haematopoiesis , receptor , immunology , stromal cell , platelet activation , thrombopoiesis , chemokine , thrombin , stem cell , cancer research , biochemistry
Thrombocytopenia is a late complication of human immunodeficiency virus (HIV) infection. The chemokine receptor CXCR4 has been shown to be a co‐receptor for lymphocyte‐tropic HIV‐1 strains. CXCR4 is also a natural receptor for the chemokine SDF‐1. We have previously shown that CXCR1 and CXCR2 are present on megakaryocytes and platelets. Although interleukin‐8 (IL‐8) and other chemokines that bind to these two receptors do not activate platelets, they are able to inhibit megakaryocytopoiesis, presumably through these receptors. We therefore examined whether CXCR4 is present on developing and mature megakaryocytes and on platelets. Reverse transcription‐polymerase chain reaction (RT‐PCR) demonstrated the presence of CXCR4 message. Immature and mature αIIbβ3 + megakaryocytes, and platelets were also positive for CXCR4 by flow cytometric studies using a CXCR4‐specific antibody. We then tested whether SDF‐1 can affect the biology of these cells. CD34 + cells and immature αIIbβ3 + cells responded to SDF‐1 as indicated by Ca 2+ mobilization and chemotaxis. However, mature megakaryocytes failed to demonstrate either of these responses, in spite of their continued ability to bind 125 I‐SDF‐1. Further, SDF‐1 failed to inhibit megakaryocyte colony growth. Platelets bound 125 I‐SDF‐1 with a K D similar to the affinity seen for CXCR4 on other cells, yet SDF‐1 did not aggregate washed platelets nor augment aggregation by low‐dose ADP or thrombin. SDF‐1 also failed to stimulate Ca 2+ mobilization, granular release or expression of P‐selectin in platelets. Accordingly, although our studies demonstrate that CD34 + precursors, megakaryocytes and platelets all express CXCR4 and bind SDF‐1, biological effects were only demonstrable of SDF‐1 on CD34 + precursors. The potential biological implications of CXCR4 expression on maturing megakaryocytes and platelets in normal individuals and following HIV infection are discussed.