Suppressor of cytokine signaling-3 is overexpressed in erythroid precursors of myelodysplastic syndrome

Sox6 enhances erythroid differentiation in human erythroid progenitors

Sox6 belongs to the Sry (sex-determining region Y)-related high-mobility-group-box family of transcription factors, which control cell-fate specification of many cell types. Here, we explored the role of Sox6 in human erythropoiesis by its overexpression both in the erythroleukemic K562 cell line and in primary erythroid cultures from human cord blood CD34+ cells. Sox6 induced significant erythroid differentiation in both models. K562 cells underwent hemoglobinization and, despite their leukemic origin, died within 9 days after transduction; primary erythroid cultures accelerated their kinetics of erythroid maturation and increased the number of cells that reached the final enucleation step. Searching for direct Sox6 targets, we found SOCS3 (suppressor of cytokine signaling-3), a known mediator of cytokine response. Sox6 was bound in vitro and in vivo to an evolutionarily conserved regulatory SOCS3 element, which induced transcriptional activation. SOCS3 overexpression in K562 cells and in primary erythroid cells recapitulated the growth inhibition induced by Sox6, which demonstrates that SOCS3 is a relevant Sox6 effector.

Advances in the molecular characterization of Philadelphia-negative chronic myeloproliferative disorders

PURPOSE OF REVIEW

The identification and characterization of somatic disease alleles have greatly improved our understanding of the molecular pathogenesis of myeloproliferative disorders. This review focuses on recent studies investigating the role of activated tyrosine kinase signaling in the Philadelphia chromosome negative myeloproliferative disorders.

RECENT FINDINGS

Previously identified tyrosine kinase mutations in chronic myeloid leukemia and other myeloproliferative disorders suggested the possibility that polycythemia vera, essential thrombocythemia and primary myelofibrosis are also caused by activated tyrosine kinases. Recent studies identified an activating mutation in the JAK2 tyrosine kinase (JAK2V617F) in most patients with polycythemia vera and in approximately half of those with essential thrombocythemia and primary myelofibrosis. More recently, activating mutations in the thrombopoietin receptor and in JAK2 exon 12 have been identified in JAK2V617F negative myeloproliferative disorders.

SUMMARY

The discovery of activated tyrosine kinases in the majority of patients with polycythemia vera, essential thrombocythemia and primary myelofibrosis has diagnostic and pathogenetic implications. Subsequent studies are needed to elucidate the cause of myeloproliferative disorders without known disease alleles and to determine if inhibition of JAK2 signaling has therapeutic efficacy in the treatment of polycythemia vera, essential thrombocythemia and primary myelofibrosis.