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-membranetargeted 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.
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.
The role of caveolin-2 (cav-2), independently of caveolin-1 (cav-1) and caveolae, has remained elusive. Our data show that cav-2 exists in the plasma membrane (PM) in cells lacking cav-1 and forms homo-oligomeric complexes. Cav-2 did not interact with cavin-1 and cavin-2 in the PM. Rab6-GTP was required for the microtubule-dependent exocytic transport of cav-2 from the Golgi to the PM independently of cav-1. The cav-2-oligomerized noncaveolar microdomain was unaffected by cholesterol depletion and protected from shearing of silica-coated PM. Activation of insulin receptor (IR) was processed in the microdomain. Actin depolymerization affected the formation and sustenance of cav-2-oligomerized noncaveolar microdomain and attenuated IR recruitment to the microdomain thereby inhibiting IR signaling activation. Cav-2 shRNA stable cells and the cells ectopically expressing an oligomerization domain truncation mutant, cav-2∆47-86 exhibited retardation of IR signaling activation via the noncaveolar microdomain. Elevation in status of cav-2 expression rendered the noncaveolar activation of IR signaling in cav-1 down-regulated or/and cholesterol-depleted cells. Our findings reveal a novel homo-oligomeric cav-2 microdomain responsible for regulating activation of IR signaling in the PM.
Here, we demonstrate that insulin receptor (IR) tyrosine kinase catalyzes Tyr-19 and Tyr-27 phosphorylation of caveolin-2 (cav-2), leading to stimulation of signaling proteins downstream of IR, and that the catalysis is dependent on fatty acylation status of cav-2, promoting its interaction with IR. Cav-2 is myristoylated at Gly-2 and palmitoylated at Cys-109, Cys-122, and Cys-145. The fatty acylation deficient mutants are unable to localize in the plasma membrane and not phosphorylated by IR tyrosine kinase. IR interacts with the C-terminal domain of cav-2 containing the cysteines for palmitoylation. IR mutants, Y999F and K1057A, but not W1220S, fail interaction with cav-2. Insulin receptor substrate-1 (IRS-1) is recruited to interact with the IR-catalyzed phospho-tyrosine cav-2, which facilitates IRS-1 association with and activation by IR to initiate IRS-1-mediated downstream signaling. Cav-2 fatty acylation and tyrosine phosphorylation are necessary for the IRS-1-dependent PI3K-Akt and ERK activations responsible for glucose uptake and cell survival and proliferation. In conclusion, fatty acylated cav-2 is a new substrate of IR tyrosine kinase, and the fatty acylation and phosphorylation of cav-2 present novel mechanisms by which insulin signaling is activated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.