STAT-3 and p42/44 MAPK Are Dynamically Phosphorylated during Bone Marrow Stem Cell Differentiation into Endothelial Cells.

The transcription factor signal transducer and activator of transcription 3 (STAT-3) is an important mediator for cell differentiation. Extracellular signal regulated kinas (ERK)I (p44 MAPK) and ERK2 (p42 MAPK) also play an important role in the process of cell differentiation. In the present study, experiments were designed to investigate the expression of STAT-3 and MAPK during stem cell differentiation into endothelial cells and their relationship to the development of endothelial cells. Adult mouse bone marrow multipotent progenitor cells were used as the source of stem cells. The stem cells were induced to differentiate into endothelial cells in serum-free medium in the presence of vascular endothelial growth factor (VEGF). The course of differentiation was closely monitored with endothelial cell markers Von Willebrand factor (vWF) and CD31. The differentiating cells were collected at rain 0, 5, 10, 15, 30, 60, hr 2, 3, 4, 6, 8, 24, day 3, 5, 7, 10, 14, and 21 after the initiation of differentiation to evaluate the expression of STAT-3, MAPK, vWF, CD31, and endothelial nitric oxide synthase (eNOS) with Western blot analysis, quantitative real-time PCR, and immunofluorescence staining. As expected, the differentiating cells started to express, vWF, CD31 and eNOS from day 5 and reached the maximal levels at day 14 during differentiation. VEGF-induced phosphorylation of STAT-3 began 2 hours after initiation of differentiation. STAT-3 phosphorylation increased over time thereafter, and reached a plateau at day 7 during the course of differentiation. No STAT-3 phosphorylation was identified in the undifferentiated bone marrow stem cells. On the other hand, VEGF-induced phosphorylation of MAPK occurred from day 3, reached a plateau at day 7, and remained stable thereafter during the course of differentiation. The fact that phosphorylation of STAT-3 occurred very early, followed by MAPK phosphorylation in the process of endothelial cell development indicates that STAT-3 and MAPK may play a critical role in bone marrow stem cell differentiation into endothelial cells. [ABSTRACT FROM AUTHOR]