RESUMEN
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.
Asunto(s)
Células Precursoras Eritroides/fisiología , Eritropoyesis/genética , Factores de Transcripción SOXD/fisiología , Animales , Antígenos CD34/metabolismo , Diferenciación Celular/genética , Procesos de Crecimiento Celular/genética , Células Cultivadas , Ensayo de Unidades Formadoras de Colonias , Células Precursoras Eritroides/metabolismo , Eritropoyesis/fisiología , Regulación de la Expresión Génica/fisiología , Humanos , Células K562 , Ratones , Modelos Biológicos , Factores de Transcripción SOXD/genética , Factores de Transcripción SOXD/metabolismo , Proteína 3 Supresora de la Señalización de Citocinas , Proteínas Supresoras de la Señalización de Citocinas/genética , Proteínas Supresoras de la Señalización de Citocinas/metabolismo , Proteínas Supresoras de la Señalización de Citocinas/fisiología , TransfecciónRESUMEN
The Sox6 transcription factor plays critical roles in various cell types, including erythroid cells. Sox6-deficient mice are anemic due to impaired red cell maturation and show inappropriate globin gene expression in definitive erythrocytes. To identify new Sox6 target genes in erythroid cells, we used the known repressive double Sox6 consensus within the εy-globin promoter to perform a bioinformatic genome-wide search for similar, evolutionarily conserved motifs located within genes whose expression changes during erythropoiesis. We found a highly conserved Sox6 consensus within the Sox6 human gene promoter itself. This sequence is bound by Sox6 in vitro and in vivo, and mediates transcriptional repression in transient transfections in human erythroleukemic K562 cells and in primary erythroblasts. The binding of a lentiviral transduced Sox6FLAG protein to the endogenous Sox6 promoter is accompanied, in erythroid cells, by strong downregulation of the endogenous Sox6 transcript and by decreased in vivo chromatin accessibility of this region to the PstI restriction enzyme. These observations suggest that the negative Sox6 autoregulation, mediated by the double Sox6 binding site within its own promoter, may be relevant to control the Sox6 transcriptional downregulation that we observe in human erythroid cultures and in mouse bone marrow cells in late erythroid maturation.