Platelet-derived growth factor B-chain gene expression in mesangial cells: effect of phorbol ester on gene transcription and mRNA stability.

We have investigated the effect of phorbol 12-myristate 13-acetate (PMA) on platelet-derived growth factor (PDGF) B-chain gene transcription as well as on mRNA stability in cultured human mesangial cells. Addition of actinomycin to cells stimulated with PMA decreases steady state levels of PDGF-B chain mRNA analysed by solution hybridization assay. PDGF-B chain gene transcription was also assayed directly by measuring elongation of transcripts in isolated nuclei followed by hybridization of labeled RNA transcripts to a cDNA encoding for PDGF-B chain. Our data show that PMA induces PDGF-B chain gene transcription by approximately 2-fold. alpha-Amanitin, an RNA polymerase II inhibitor, blocked transcription by more than 70%. In addition, we determined the effect of PMA on the halflife of PDGF-B chain mRNA directly by pulse chase method. In human mesangial cells, the PDGF-B chain mRNA exhibited halflife of approximately 105 min. In the presence of PMA, the halflife of PDGF-B chain mRNA was reduced to approximately 72 min. These studies indicate that regulation of PDGF-B chain gene by PMA in human mesangial cells involves a coordinate effort at the level of transcription and mRNA stability.