Induction of erythroid differentiation by altered G(alpha 16) activity as detected by a reporter gene assay in MB-02 cells

Heterotrimeric G proteins may assume modulatory roles in cellular prolifera tion and differentiation. The G protein alpha-subunit G(alpha 16) which is specifically expressed in hematopoietic cells, is highly regulated during d ifferentiation of normal and leukemic cells. In human erythroleukemia cells , suppression of G(alpha 16) inhibited cellular growth rates. A reporter ge ne system was established to assess the role of G(alpha 16) on erythroid di fferentiation of MB-02 erythroleukemia cells. It is based on transient tran sfection with a plasmid that expresses green fluorescent protein under the control of the beta-globin promoter. Expression of G(alpha 16) led to a sig nificant increase in green fluorescent protein-positive cells, as did trans fection with a G(alpha 16) antisense plasmid (154 and 156% of controls, res pectively). The GTPase-deficient, constitutively active mutant of G(alpha 1 6), G(alpha 16)R186C, further stimulated differentiation to 195% of control values. Because the effect of G(alpha 16) is triggered most efficiently by the GTP-bound protein, an indirect action through interference of overexpr essed G(alpha 16) with G protein beta gamma-subunits can be excluded, The c orresponding mutant of G(alpha q) (G(alpha q)R182C), the phylogenetically c losest family member of G(alpha 16), had no effect. The data define a speci fic role for G(alpha 16)-dependent signal transduction in cellular differen tiation: deviations from optimal levels of G(alpha 16) functional activity lead to reduced growth rates and promote differentiation in hematopoietic c ells.