Patients with
bladder cancer often have a poor prognosis due to the highly invasive and metastatic characteristics of
bladder cancer cells. Epithelial-to-mesenchymal transition (EMT) has been causally linked to
bladder cancer invasion. The
E3 ubiquitin ligase,
tumor necrosis factor receptor-associated factor 4 (
TRAF4) has been implicated as a
tumor promoter in a wide range of
cancers. In contrast, here we show that low
TRAF4 expression is associated with poor overall survival in patients with
bladder cancer. We show that the
TRAF4 gene is epigenetically silenced and that ERK mediates
TRAF4 phosphorylation, resulting in lower
TRAF4 protein levels in
bladder cancer cells. In addition, we demonstrate that
TRAF4 is inversely correlated with an EMT gene signature/
protein marker expression. Functionally, by manipulating
TRAF4 expression, we show that
TRAF4 regulates EMT genes and epithelial and invasive properties in
bladder cancer cells. Transcriptomic analysis of dysregulated
TRAF4 expression in
bladder cancer cell lines revealed that high
TRAF4 expression enhances the
bone morphogenetic protein (BMP)/SMAD and inhibits the NF-κB signaling pathway. Mechanistically, we show that
TRAF4 targets the
E3 ubiquitin ligase SMURF1, a negative regulator of BMP/SMAD signaling, for proteasomal degradation in
bladder cancer cells. This was corroborated in patient samples where
TRAF4 positively correlates with phospho-SMAD1/5, and negatively correlates with phospho-NFκb-p65. Lastly, we show that genetic and pharmacologic inhibition of SMURF1 inhibits the migration of aggressive mesenchymal
bladder cancer cells.
IMPLICATIONS: