Abstract
Transforming growth factor b (TGF-b) is a pluripotent cytokine that regulates cell growth and differentiation in a cell type-dependent fashion. TGF-b exerts its effects through the activation of several signaling pathways. One involves membrane proximal events that lead to nuclear translocation of members of the Smad family of transcriptional regulators. TGF-b can also activate MAPK cascades. Here, we show that TGF-b induces nuclear translocation of the NF-YA subunit of the transcription factor NF-Y by a process that requires activation of the ERK cascade. This results in increased binding of endogenous NF-Y to chromatin and TGF-b-dependent transcriptional regulation of the NF-Y target gene cyclin A2. Interestingly, the kinetics of NF-YA relocalization differs between epithelial cells and fibro-blasts. NIH3T3 fibroblasts show an elevated basal level of phosphorylated p38 and delayed nuclear accumulation of NF-YA after TGF-b treatment. In contrast, MDCK cells show low basal p38 activation, higher basal ERK phosphorylation and more rapid localization of NF-YA after induction. Thus, NF-Y activation by TGF-b1 involves ERK1/2 and potentially an interplay between MAPK pathways, thereby opening the possibility for finely tuned transcriptional regulation.