Changes in TPO mRNA expression not due to cell proliferation.

In experiments to investigate the up-regulation of TPO mRNA expression, BM stromal cells were allowed to become quiescent by placing them in 1% serum for 24 hours. The increase in TPO mRNA expression with the addition of PDGF or FGF was not due to an increase in cell proliferation, as shown by thymidine incorporation. In experiments to investigate the inhibition of TPO gene expression, the confluent cells were left in complete medium containing 25% serum for 24 hours. Suppression of TPO mRNA expression by PF4, TSP, or TGF-β was not a result of cell toxicity. The results shown are the mean ± SD values from 3 separate experiments carried out in triplicate.