Megakaryocyte maturation is associated with expression of the CXC chemokine connective tissue-activating peptide CTAP III

Connective tissue-activating peptide III (CTAP III), a CXC chemokine derive d from the chemokine precursor platelet basic protein (PBP) by proteolytic cleavage, has been identified in platelets, activated macrophages, neutroph ils and T lymphocytes. CTAP III can support stem cell-derived haematopoiesi s yet inhibits the proliferation of committed megakaryocyte (MK) progenitor s. This investigation was aimed at characterizing CTAP III expression in hu man MKs and determining it's role in MK differentiation. We report high exp ression of CTAP III in mature human bone marrow (BM) MKs and megakaryoblast cell lines following differentiation induction with phorbol eater 12-myris tate 13-acetate (PMA). Immunostaining with anti-CTAP III antibodies demonst rated its prominent presence in platelet producing zones in the cytoplasm a nd intense staining around the periphery of the large BM MKs. In cultures o f logarithmically growing megakaryoblast cell lines DAMI, CHRF-288 or MEG01 , which contain primarily 2N cells, only 15% of the cells expressed CTAP II I, The addition of PMA stimulated high levels of CTAP III after 24 h in mor e than 75% of the cells, being expressed in both the 2N and large polyploid MKs. Reverse transcription polymerase chain reaction (RT-PCR) revealed upr egulation of CTAP III mRNA after only Ih of exposure to PMA that was sustai ned for 24 h. In the bone marrow of idiopathic thrombocytopenic pupura (ITP ) patients undergoing accelerated ME; maturation and thrombopoiesis. 99% of large MKs and 95% of small MKs expressed high levels of CTAP III. While th e biological function of this chemokine in MKs is not known, these studies demonstrate that molecular upregulation of CTAP III in MKs is associated wi th maturation and, as with other chemokines, may be involved in proliferati on arrest and cellular interactions with extracellular matrix and platelet production.