Buitenhuis Miranda, Verhagen Liesbeth P, van Deutekom Hanneke W M, Castor Anders, Verploegen Sandra, Koenderman Leo, Jacobsen Sten-Eirik W, Coffer Paul J
Molecular Immunology Lab, Department of Immunology, University Medical Center, Utrecht, the Netherlands.
Blood. 2008 Jan 1;111(1):112-21. doi: 10.1182/blood-2006-07-037572. Epub 2007 Sep 21.
Hematopoiesis is a highly regulated process resulting in the formation of all blood lineages. Aberrant regulation of phosphatidylinositol-3-kinase (PI3K) signaling has been observed in hematopoietic malignancies, suggesting that regulated PI3K signaling is critical for regulation of blood cell production. An ex vivo differentiation system was used to investigate the role of PI3K and its downstream effector, protein kinase B (PKB/c-akt) in myelopoiesis. PI3K activity was essential for hematopoietic progenitor survival. High PKB activity was found to promote neutrophil and monocyte development, while, conversely, reduction of PKB activity was required to induce optimal eosinophil differentiation. In addition, transplantation of beta2-microglobulin (-/-) NOD/SCID mice with CD34(+) cells ectopically expressing constitutively active PKB resulted in enhanced neutrophil and monocyte development, whereas ectopic expression of dominant-negative PKB induced eosinophil development in vivo. Inhibitory phosphorylation of C/EBPalpha on Thr222/226 was abrogated upon PKB activation in hematopoietic progenitors. Ectopic expression of a nonphosphorylatable C/EBPalpha mutant inhibited eosinophil differentiation ex vivo, whereas neutrophil development was induced, demonstrating the importance of PKB-mediated C/EBPalpha phosphorylation in regulation of granulopoiesis. These results identify an important novel role for PKB in regulation of cell fate choices during hematopoietic lineage commitment.
造血是一个受到高度调控的过程，最终形成所有的血细胞谱系。在造血系统恶性肿瘤中已观察到磷脂酰肌醇-3-激酶（PI3K）信号传导的异常调控，这表明受调控的PI3K信号传导对于血细胞生成的调节至关重要。利用体外分化系统来研究PI3K及其下游效应物蛋白激酶B（PKB/c-akt）在髓系造血中的作用。PI3K活性对于造血祖细胞的存活至关重要。发现高PKB活性可促进中性粒细胞和单核细胞的发育，相反，诱导最佳嗜酸性粒细胞分化则需要降低PKB活性。此外，将组成型活性PKB异位表达的CD34(+)细胞移植到β2-微球蛋白（-/-）NOD/SCID小鼠体内，可增强中性粒细胞和单核细胞的发育，而显性负性PKB的异位表达则在体内诱导嗜酸性粒细胞发育。造血祖细胞中PKB激活后，C/EBPα在Thr222/226位点的抑制性磷酸化被消除。非磷酸化C/EBPα突变体的异位表达在体外抑制嗜酸性粒细胞分化，而诱导中性粒细胞发育，这表明PKB介导的C/EBPα磷酸化在粒细胞生成调节中具有重要作用。这些结果确定了PKB在造血谱系定向过程中细胞命运选择调节中的一个重要新作用。
