Radiation-induced alterations in rat mesangial cell Tgfb1 and Tgfb3 gene expression are not associated with altered secretion of active Tgfb isoforms

Despite evidence of selective radiation-induced modulation of expression of rat mesangial cell Tgfb gene isoforms, it is unclear whether these changes in gene expression are accompanied by changes in protein secretion. To add ress this issue, primary cultures of rat mesangial cells (passage number 6- 11) were placed in serum-free medium 24 h prior to irradiation with single doses of 0.5-20 Gy of Cs-137 gamma rays. After irradiation, cells were main tained in serum-free medium for a further 24 h, Irradiation of quiescent me sangial cells resulted in a significant (P less than or equal to 0.05) dose -independent increase in steady-state levels of Tgfb1 mRNA 24 h postirradia tion. In contrast, steady-state levels of Tgfb3 mRNA exhibited a dose-depen dent reduction after irradiation; this reduction was statistically signific ant after doses of 5 and 10 Gy compared to control cells (P less than or eq ual to 0.05), These radiation-induced changes in Tgfb gene expression were associated with modest increases in Tgfb protein as determined using mink l ung epithelial cells transfected with the Pail promoter-luciferase construc t. Twenty-four hours after a single dose of 5 Gy, the total Tgfb protein se creted by the mesangial cells was 181 +/- 2.0% of that secreted by unirradi ated control cells (P less than or equal to 0.01), However, this increase w as seen in terms of latent Tgfb protein; radiation failed to increase signi ficantly the amount of active Tgfb protein secreted by mesangial cells. Bot h quiescent and irradiated rat mesangial cells secreted active Tgfb as prim arily the Tgfb3 isoform. These data reinforce the need to interpret changes in Tgfb gene expression with caution. (C) 1999 by Radiation Research Socie ty.