Leukemia inhibitory factor and steel factor regulate tie message stability in CD34+ cells from human umbilical cord...

The cell-surface receptor tyrosine kinase, Tie, is expressed in hematopoietic stem/progenitor cells. Leukemia Inhibitory Factor (LIF) and Steel Factor (SLF) have both been shown to up-regulate Tie gene expression in a population of CD34+ cells derived from human umbilical cord blood (UCB) which is enriched for hematopoietic stem/progenitor cells. In the present study, we examined the possible mechanism of Tie gene up-regulation by LIF and SLF in CD34+ cells using semi-quantitative RT-PCR analysis. In the presence of Actinomycin D (Act D) alone for 24 hrs, Tie transcripts in CD34+ cells decreased. Tie mRNA was increased by an average of 2-4 fold and remained elevated level for 24 hours in CD34+ cells prestimulated with LIF or SLF followed by Act D, compared to that in CD34+ cells treated with Act D without prestimulation. After treatment of CD34+ cells with cycloheximide, Tie mRNA levels were decreased in the presence or absence of LIF or SLF at 24 hours. These findings suggest that LIF and SLF regulate Tie gene expression in UCB CD34+ cells at least in part through an increase in Tie message stability.