Flotillin-1 (Flot-1) has been shown to regulate cancer progression, but the regulatory role of post-translational modifications of Flot-1 on cancers remains elusive. Herein, we show that up-regulated E2 conjugating enzyme UBC9 sumoylates Flot-1 at Lys-51 and Lys-195 with small ubiquitin-like modifier (SUMO)-2/3 modification in metastatic prostate cancer. Mitogen induced the sumoylation and nuclear translocation of Flot-1. The nuclear-targeted Flot-1 physically interacted with Snail, and inhibited Snail degradation through the proteasome in a sumoylation-dependent manner, thereby promoting epithelial-to-mesenchymal transition (EMT). Sumoylation of Flot-1 by up-regulated UBC9 in human metastatic prostate cancer tissues and prostate cancer cells with high metastatic potential positively correlated with the stabilization of Snail and the induction of Snail-mediated EMT genes in the metastatic prostate cancer. Our study reveals a new mechanism of sumoylated Flot-1-mediating Snail stabilization, and identifies a novel sumoylated Flot-1-Snail signaling axis in EMT of metastatic prostate cancer.

Here, we explored flotillin-1-mediated regulation of insulin-like growth factor-1 (IGF-1) signaling. Flotillin-1-deficient cells exhibited a reduction in the activation of IGF-1 receptor (IGF-1R), ERK1/2 and Akt pathways, and the transcriptional activation of Elk-1 and the proliferation in response to IGF-1 were reduced in these cells. We found that IGF-1-independent flotillin-1 palmitoylation at Cys34 in the endoplasmic reticulum (ER) was required for the ER exit and the plasma membrane localization of flotillin-1 and IGF-1R. IGF-1-dependent depalmitoylation and repalmitoylation of flotillin-1 sustained tyrosine kinase activation of the plasma-membrane-targeted IGF-1R. Dysfunction and blocking the turnover of flotillin-1 palmitoylation abrogated cancer cell proliferation after IGF-1R signaling activation. Our data show that flotillin-1 palmitoylation is a new mechanism by which the intracellular localization and activation of IGF-1R are controlled.

We investigated whether altering caveolin-2 (cav-2) expression affects the proliferation of cancer cells. Cav-2 was not detected in HepG2, SH-SY5Y and LN-CaP cells, and the loss of cav-2 expression was not restored by 5-aza-2'-deoxycytidine treatment. In contrast, C6, HeLa, A549, MCF7 and PC3M cells expressed cav-2. Effects of re-expression of exogenous cav-2 in HepG2, SH-SY5Y and LN-CaP cells, and siRNA-mediated down-regulation of endogenous cav-2 in C6, HeLa, A549, MCF7 and PC3M cells on cancer proliferation were examined by MTT assay, colony formation assay and flow cytometric analysis. Cav-2 transfection in HepG2 hepatocellular carcinoma cells and knockdown in C6 glioma cells caused reduction in cell proliferation and growth with retarded entry into the S phase. Cav-2 re-expression in SH-SY5Y neuroblastoma cells and depletion in HeLa epithelial cervical cancer and A549 lung adenocarcinoma cells promoted cancer cell proliferation. Luciferase reporter assay showed that transcriptional activation of Elk-1 and STAT3 was significantly decreased in cav-2-transfected HepG2 hepatocellular carcinoma and down-regulated C6 glioma cells. Our data suggest that cav-2 acts as a modulator of cancer progression.