title: Crosstalk between the Smad and the Mitogen-Activated Protein Kinase Pathways is Essential for Erythroid Differentiation of Erythroleukemia Cells Induced by TGF-β, Activin, Hydroxyurea and Butyrate.
abstract: The role of crosstalk between the Smad and the MAPK signaling pathways in activin-, transforming growth factor-β (TGF-β)-, hydroxyurea (HU) - and butyrate-dependent erythroid differentiation of K562 leukemic cells was studied. Treatment with all four inducers caused transient phosphorylation of Smad2/3 and MAPK proteins including ERK, p38 and JNK. Use of specific inhibitors of p38, ERK and JNK MAPK proteins, and TGF-β type I receptor indicated that differentiation induced by each of these agents involves activation of Smad2/3 and p38 MAPK, and inhibition of ERK MAPK. Also, treatment of cells with an inhibitor of protein serine/threonine phosphatase, okadaic acid (OA), induced phosphorylation of Smad2/3, and p38 MAPK, coincident with its induction of erythroid differentiation. Specific inhibition of TGF-β type I receptor kinase activity not only abolished TGF-β/activin effects but also prevented Smad2/3 activation and erythroid differentiation induced by OA, HU and butyrate. The TGF-β type I receptor kinase inhibitor blocked OA-induced differentiation but not p38 MAPK phosphorylation demonstrating that signals from both pathways are needed. As previously observed, addition of ERK1/2 MAPK inhibitors upregulated Smad2/3 phosphorylation and enhanced differentiation, but these effects were dependent on signals from the TGF-β type I receptor. These data indicate that activation of both Smad2/3 and p38 MAPK signaling pathways is a prerequisite to induce erythroid differentiation of erythroleukemia cells by activin, TGF-β, HU, OA and butyrate.
authors.affiliation: Leukocyte Biology Section, Laboratory of Experimental Immunology, Center for Cancer Research, NCI, Frederick, Maryland ; St. Louis Blood Bank and Cellular Therapy Laboratory, Cardinal Glennon Children's Medical Center, St. Louis, MO.
authors.forename: Salem
authors.initials: S
authors.lastname: Akel
authors.affiliation: Leukocyte Biology Section, Laboratory of Experimental Immunology, Center for Cancer Research, NCI, Frederick, Maryland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bertolette
authors.affiliation: Leukocyte Biology Section, Laboratory of Experimental Immunology, Center for Cancer Research, NCI, Frederick, Maryland.
authors.forename: Francis W
authors.initials: FW
authors.lastname: Ruscetti
keywords: Activin; Erythropoiesis; Hydroxyurea; Okadaic acid; Smads; Transforming Growth Factor-β; p38 MAP Kinase