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

Abstract

Transforming growth factor-β (TGFβ) 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 TGFβ signaling in mammary epithelial cells, and show that 60 identified TGFβ-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 TGFβ-dependent phosphorylation sites of 14-3-3σ, i.e. Ser69 and Ser74. We observed that 14-3-3σ phosphorylation is a feed-forward mechanism in TGFβ/Smad3-dependent transcription. TGFβ-dependent 14-3-3σ 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 14-3-3σ at Ser69 and Ser74 is involved in regulation of cancer progenitor population and radioresistance in breast cancer MCF7 cells. Our data suggest that TGFβ-dependent phosphorylation of 14-3-3σ orchestrates a functional interaction of TGFβ/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.

Role of TGF-<i>β</i> in breast cancer bone metastases

“…Also, breast tumor mouse xenograft and radiobiological assays suggested the involvement of phosphorylation of 14-3-3 σ at Ser69 and Ser74 in the cancer progenitor population regulation and the radioresistance in breast cancer MCF7 cells. This study suggests that TGF β -dependent phosphorylation of 14-3-3 σ may play a role in the maintenance of cancer stem cells [ 53 ]. Recently, it was demonstrated that TGF- β 1 down-regulated the junction adhesion molecule A (JAM-A) expression via its effects on both the transcriptional and post-translational regulations of JAM-A thus attenuating cell adhesion and promoting cell invasion and that the effect of TGF- β was achieved via the activation of Smads [ 54 ].…”

Signaling pathways governing the maintenance of breast cancer stem cells and their therapeutic implications

“…It is well known that TGF-β signaling is an important regulator of tumorigeneses by inducing epithelial-mesenchymal transition and regulating BCSCs maintenance. TGF-β ser 69 and 74 phosphorylation recruit SMAD3/p53 complex and regulate the transcription of BCSCs resistance genes ( Zakharchenko et al, 2013 ). Zheng et al, (2014) showed that TGF-β2 expression correlates with the BCSCs marker ALDH1 and represents a bad prognosis.…”

Comprehensive molecular tumor profiling in radiation oncology: How it could be used for precision medicine

“…Several studies highlight the importance of the analysis of protein phosphorylation in elucidating the radio- and chemoresistance mechanisms and identifying promising drug combinations [6,30,31,96–103]. For example, a phosphoproteome array in HNSCC cells treated with cetuximab showed activation of the c-Jun N-terminal kinase (JNK) pathway which attenuated the efficacy of cetuximab itself [30].…”