The antiapoptosis protein survivin is associated with cell cycle entry of normal cord blood CD34(+) cells and modulates cell cycle and proliferation of mouse hematopoietic progenitor cells.

The inhibitor of the apoptosis protein (IAP) survivin is expressed in proliferating cells such as fetal tissues and cancers. We previously reported that survivin is expressed and growth factor regulated in normal adult CD34(+) cells. Herein, we examined survivin expression in CD34(+) cells before and after cell cycle entry and demonstrate a role for survivin in cell cycle regulation and proliferation. Analysis of known human IAPs revealed that only survivin is cytokine regulated in CD34(+) cells. Survivin expression is coincident with cell cycle progression. Up-regulation of survivin by thrombopoietin (Tpo), Flt3 ligand (FL), and stem cell factor (SCF) occurred in underphosphorylated-retinoblastoma protein (Rb)(positive), Ki-67(negative), and cyclin D(negative) CD34(+) cells. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) and multivariate flow cytometry demonstrated that Tpo, SCF, and FL increase survivin mRNA and protein in quiescent G(0) CD34(+) cells without increasing Ki-67 expression, indicating that cytokine-stimulated up-regulation of survivin in CD34(+) cells occurs during G(0), before cells enter G(1). Selective inhibition of the PI3-kinase/AKT and mitogen-activated protein kinase (MAPK(p42/44)) pathways blocked survivin up-regulation by growth factors before arresting cell cycle. Retrovirus transduction of survivin-internal ribosome entry site-enhanced green fluorescent protein (survivin-IRES-EGFP) in primary mouse marrow cells increased granulocyte macrophage-colony-forming units (CFU-GM) by 1.7- to 6.2-fold and the proportion of CFU-GM in S phase, compared to vector control. An antisense survivin construct decreased total and S-phase CFU-GM. These studies provide further evidence that survivin up-regulation by growth factors is not a consequence of cell cycle progression and strongly suggest that survivin is an important early event for cell cycle entry by CD34(+) cells.