Transient suppression of core-binding factor alpha 1 expression by basic fibroblast growth factor in rat...

Core-binding factor alpha 1 (Cbfa1) is considered a prerequisite transcription factor for osteoblastic differentiation, based on experiments performed in knock-out mice. Cbfa1 binding sequences have been located in the promoter regions of various osteoblast phenotype-related genes, which are also known to be regulated by fibroblast growth factor (FGF). To elucidate the molecular mechanisms of FGF regulation of osteoblasts, we investigated the effects of FGF on Cbfa1 expression in osteoblast-like cells. We found that basic FGF, at 10 ng/ml, suppressed Cbfa1 mRNA expression in ROS17/2.8 cells. To detect the two distinct mRNA species that give rise to Pebp2alphaA/Cbfa1 and Osf2/Til-1/Cbfa1, we used semi-quantitative reverse transcription-polymerase chain reaction analysis using specific sets of primers. This analysis indicated that treatment with FGF transiently decreased the abundance of only the Osf2/Til-1/Cbfa1 isoform and not the Pebp2alphaA/Cbfa1 isoform in ROS17/2.8 cells. The suppression of Osf2/Til-1/Cbfa1 was time dependent and was observed up until 48h, and Cbfa1 mRNA levels then returned closer to control levels. Dose-dependent suppression by FGF was observed only with regard to mRNA levels of Osf2/Til-1/Cbfa1 and not for Pebp2alphaA/Cbfa1 mRNA. These data indicate that FGF suppresses Cbfa1 mRNA expression and that the Osf2/Til-1/Cbfa1 isoform is the specific target of FGF regulation in osteoblastic osteosarcoma ROS17/2.8 cells.