A Role of TGFß1 Dependent 14-3-3s Phosphorylation at Ser69 and Ser74 in the Regulation of Gene Transcription,

Transforming growth factor-b (TGFb) is a potent regulator of tumorigenesis, although mechanisms defining its tumor suppressing and tumor promoting activities are not understood. Here we describe phosphoproteome profiling of TGFb signaling in mammary epithelial cells, and show that 60 identified TGFb-regulated phosphoproteins form a network with scale-free characteristics. The network highlighted interactions, which may distribute signaling inputs to regulation of cell proliferation, metabolism, differentiation and cell organization. In this report, we identified two novel and TGFb-dependent phosphorylation sites of 14-3-3s, i.e. Ser69 and Ser74. We observed that 14-3-3s phosphorylation is a feed-forward mechanism in TGFb/Smad3-dependent transcription. TGFb-dependent 14-3-3s phosphorylation may provide a scaffold for the formation of the protein complexes which include Smad3 and p53 at the Smad3-specific CAGA element. Furthermore, breast tumor xenograft studies in mice and radiobiological assays showed that phosphorylation of 14-3-3s at Ser69 and Ser74 is involved in regulation of cancer progenitor population and radioresistance in breast cancer MCF7 cells. Our data suggest that TGFb-dependent phosphorylation of 14-3-3s orchestrates a functional interaction of TGFb/Smad3 with p53, plays a role in the maintenance of cancer stem cells and could provide a new potential target for intervention in breast cancer