Mechanical agitation induces gene expression of NOR-1 and its closely related orphan nuclear receptors in leukemic cell lines

NOR-1, NGFI-B and Nurr1 are closely related transcription factors that constitute a distinct subfamily within the nuclear receptor superfamily. Genes for these proteins are immediate–early genes, and are inducible in diverse cell types by various stimuli. In the present study, we investigated the effect of mechanical agitation on the gene expression of these transcription factors in cultured suspension cells by the quantitative reverse transcription-polymerase chain reaction. We found that mechanical agitation transiently induced NOR-1, NGFI-B and Nurr1 mRNAs in several leukemic cell lines in a dose-dependent manner. This induction was most pronounced in the HL-60 promyelocytic leukemia cell line, but also occurred to a lesser extent in other cell lines including KG-1, THP-1 and U937 cells. The induction was attenuated by serum or albumin, which are shear stress protectants for suspension culture cells. These reagents did not suppress forskolin-induced NOR-1 gene expression. These findings suggest the involvement of fluid shear stress in agitation-induced immediate–early gene expression. Since even moderate agitation could cause the induction, investigators should be cautious when evaluating the expression of immediate–early genes in some leukemic cell lines.