Identification of heterotrimeric GTP-binding proteins in human megakaryoblastic leukemia cell line, MEG-01, and their alteration during cellular differentiation.

Various heterotrimeric GTP-binding proteins (G proteins) are possible to have important functions in hematopoietic cells. However, there has been no information regarding their expression in magakaryoblasts and/or megakaryocytes. In the present study, protein contents of seven G protein alpha subunits (Gs alpha, Gi2 alpha, Gi3 alpha, Gz alpha, G11 alpha, Gq alpha and G12 alpha) and beta subunit in a human megakaryoblastic leukemia cell line, MEG-01, were analyzed by immunoblotting. Immature MEG-01 cells expressed the alpha subunits of Gs, Gi2, Gi3, Gz, G11 and G12 at protein molecule level. During the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced differentiation process, the contents of Gi2 alpha and Gi3 alpha increased, whereas the protein levels of Gz alpha, Gs alpha, G11 alpha and G12 alpha were observed to hardly change. beta subunit was also observed to be present in immature MEG-01 cells and to increase continuously throughout the differentiation process. For the expression of Gi2 alpha and beta subunits, chronic TPA-treatment was required although Rac2, a low M(r) GTP-binding protein, was expressed abundantly by only 30 min-TPA-treatment followed by 3 day-culture.