GM-CSF induces cyclin D1 expression and proliferation of endothelial progenitor cells via PI3K and MAPK signaling.

BACKGROUND/AIMS Endothelial progenitor cells (EPCs), which can be isolated from the bone marrow or the peripheral blood, have generated interest because of their capacity to migrate to sites of vascularization and endothelialization and differentiate into endothelial cells in a process termed neovasculogenesis. EPCs are therefore possible regenerative tools for the treatment of vascular diseases and potential targets for the inhibition of angiogenesis during tumor development. Here, we investigated the mechanisms underlying the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the acceleration of EPC proliferation and colony formation. METHODS EPCs were isolated, identified and cultured in the presence of GM-CSF. The effect of GM-CSF on endothelial cell colony formation and proliferation was examine by colony formation assay and MTT assay, separately. Cell cycle was analyzed by flow cytometry. The expression of cyclin D1 and cyclin E were detected by western bloting. JAK/Stat, PI3K/Akt and MAPK signaling were analyzed. RESULTS GM-CSF accelerated the G1/S phase transition in EPCs by upregulating the expression of cyclins D1 and E. The GM-CSF induced increase in the levels of cyclin D1 and the subsequent phosphorylation of the retinoblastoma (Rb) protein activated E2F-1, resulting in the upregulation of the transcription of cyclin E. Furthermore, the induction of cyclin D1 expression and cell cycle progression by GM-CSF was mediated by the PI3K/Akt, JNK and ERK signaling pathways through the phosphorylation of GSK3β or the activation of AP-1 transcription factors. CONCLUSION Our findings shed light on the mechanisms underlying the effect of GM-CSF on the modulation of cell cycle progression in EPCs, which is important considering their role in vascular repair and their therapeutic potential in several diseases.