Mechanism for fetal globin gene expression: Role of the soluble guanylate cyclase-cGMP-dependent protein kinase pathway

Despite considerable concerns with pharmacological stimulation of fetal hemoglobin (Hb F) as a therapeutic option for the beta -globin disorders, the molecular basis of action of Hb F-inducing agents remains unclear, Here we show that an intracellular pathway including soluble guanylate cyclase (sGC) and cCMP-dependent protein kinase (PKG) plays a role in induced expression of the gamma -globin gene. sGC, an obligate heterodimer of alpha- and beta -subunits, participates in a variety of physiological processes by converting GTP to cGMP, Northern blot analyses with erythroid cell lines expressing different beta -like globin genes showed that, whereas the beta -subunit is expressed at similar levels, high-level expression of the or-subunit is preferentially observed in erythroid cells expressing gamma -globin but not those expressing beta -globin, Also, the levels of expression of the gamma -globin gene correlate to those of the or-subunit, sGC activators or cGMP analogs increased expression of the gamma -globin gene in erythroleukemic cells as well as in primary erythroblasts from normal subjects and patients with beta -thalassemia, Nuclear run-off assays showed that the sGC activator protoporphyrin IX stimulates transcription of the gamma -globin gene. Furthermore, increased expression of the gamma -globin gene by well known Hb F-inducers such as hemin and butyrate was abolished by inhibiting sGC or PKG activity. Taken together, these results strongly suggest that the sGC-PKG pathway constitutes a mechanism that regulates expression of the gamma -globin gene. further characterization of this pathway should permit us to develop new therapeutics for the beta -globin disorders.