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 cGMP-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 alpha-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 alpha-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.
Ikuta
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Center for Human Genetics, Boston University School of Medicine, Boston, MA 02118, USA. tikuta@bu.edu
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D002087:Butyrates / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000502:physiology*; D015870:Gene Expression / Q000187:drug effects; D005914:Globins / Q000235:genetics*; D006162:Guanylate Cyclase / Q000502:physiology*; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D020014:K562 Cells; D004915:Leukemia, Erythroblastic, Acute; D015398:Signal Transduction / Q000502:physiology*; D012995:Solubility; D014407:Tumor Cells, Cultured
D002087:Butyrates; D006427:Hemin; D005914:Globins; D017869:Cyclic GMP-Dependent Protein Kinases; D006162:Guanylate Cyclase; D006152:Cyclic GMP