Eukaryotic initiation factor 2 alpha subunit associates with TGF beta receptors and 14-3-3 epsilon and acts as a modulator of the TGF beta response.

Abstract

Schistosoma mansoni receptor kinase 1 (SmRK1) is a divergent member of the TGF beta receptor family. Intracellular proteins that associate with these receptors are likely to play an important role in signaling. 14-3-3 epsilon is a previously described cytoplasmic protein, which associates with both SmRK1 and the human type I TGF beta receptor (T beta RI); overexpression of 14-3-3 epsilon leads to enhanced TGF beta-mediated signaling by T beta RI. We now describe the identification of S. mansoni eukaryotic translation initiation factor 2 alpha subunit (eIF2 alpha), through its interaction with SmRK1 in a yeast two-hybrid assay. S. mansoni eIF2 alpha also interacts with human TGF beta receptors. Strongest association was demonstrated with kinase inactive receptors, particularly the type II TGF beta receptor (T beta RII). Both T beta RI and T beta RII phosphorylate eIF2 alpha in vitro, at sites other than the previously described eIF2 alpha phosphorylation sites. EIF2 alpha also modulates signaling by TGF beta receptors; however, in contrast to 14-3-3 epsilon, eIF2 alpha overexpression inhibits the TGF beta-driven response. These data suggest a novel function for eIF2 alpha in the TGF beta signaling pathway. In addition, we have demonstrated an independent interaction between eIF2 alpha and 14-3-3 epsilon. Coexpression of 14-3-3 epsilon with eIF2 alpha leads to the abrogation of the inhibitory effect of eIF2 alpha on TGF beta-mediated signaling. The interaction of these two regulatory proteins with each other and with the TGF beta receptors and their relative expression levels are likely to be important in fine-tuning the regulation of TGF beta signal transduction.