Megakaryocytic differentiation of HIMeg-1 cells induced by interferon gamma and tumour necrosis factor alpha but not by thrombopoietin

Activated macrophage-conditioned medium (M-CM) induces megakaryocytic diffe rentiation of HIMeg-1 cells. The megakaryocytic differentiation activity (M DA) is proteinaceous since it is susceptible to treatments by proteinases, heat, and reducing agents. MDA is not thrombopoietin (TPO) since (1) TPO al one or in conjunction with several other recombinant cytokines fails to ind uce any degree of HIMeg-1 cell differentiation; and (2) a neutralizing anti body against TPO or an antibody against the extracellular domain of c-mpl i s unable to abolish M-CM-induced CD41 expression on HIMeg-1 cells. Reverse transcriptase-mediated polymerase chain reaction shows that HIMeg-1 cells e xpress c-mpl but not TPO, Additional neutralizing antibody studies suggest that MDA is not one of the cytokines known to induce some degree of megakar yopoiesis in vitro or in vivo including interleukin 3 (IL-3), IL-6, IL-11, granulocyte-macrophage colony-stimulating factor, erythropoietin, or stem c ell factor. On the other hand, MDA appears to be a combination of interfero n gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha), since neu tralizing antibodies against these two cytokines completely abolish MDA-ind uced CD41 expression. In addition, either recombinant human IFN-gamma or TN F-alpha alone is capable of inducing CD41 and CD42 expression on HIMeg-1 ce lls. In combination, IFN-gamma and TNF-alpha induce a maximal level of CD41 and CD42 expression, which is also accompanied by an increase in cell size and DIVA ploidy level. Thus, our studies indicate that IFN-gamma/TNF-alpha is capable of inducing megakaryocytic differentiation of the HIMeg-1 cell line and that HIMeg-1 is a good system for studying the molecular mechanism mediating megakaryocytic differentiation. (C) 1998 Academic Press.