IB kinase (IKK) catalytic subunits play a key role in cytokinemediated nuclear factor (NF)-B signaling, and a loss of NF-B function appears to inhibit inflammation and oncogenesis. Manumycin A is a potent and selective farnesyltransferase inhibitor with antitumor activity. We found that manumycin A caused a rapid and potent inhibition of IKK activity induced by tumor necrosis factor ␣ in a number of cell types. Most unexpectedly, other classes of farnesyltransferase inhibitors had no inhibitory effect. To identify the molecular mechanisms of manumycin A action, cultured human HepG2 hepatoma cells were transiently transfected with various IKK␣ and IKK␤ constructs, and a striking difference in manumycin A sensitivity was observed. Furthermore, cells expressing wild-type IKK␤ and IKK␤ mutated in the activation loop at Cys-179 exhibited covalent homotypic dimerization of IKK␤ in response to manumycin A, whereas substitution of Cys-662 and -716 conferred protection against dimer formation. Direct inhibition of IKK activity and formation of stable IKK␤ dimers were observed in the presence of manumycin A that could be blocked by dithiothreitol. IKK interaction with the adaptor protein IKK␥/NEMO was disrupted in manumycin A-treated cells. Most importantly, administration of manumycin A to mice xenografted with murine B16F10 tumors caused potent IKK-suppressive effects. Thus, manumycin A with its epoxyquinoid moieties plays an important regulatory function in IKK signaling through pathways distinct from its role as a protein farnesylation inhibitor.An increase in activity of the nuclear factor (NF) 3 -B family of eukaryotic transcription factors is a cardinal feature in the control of inflammation and oncogenesis. Cytokine-mediated activation of the multimeric IB kinase (IKK) complex is a key step involved in the activation of the NF-B pathway (1, 2). The IKK signalosome is a 600 -900-kDa complex that encompasses the IB kinases, IKK␣ and IKK␤, in addition to the tightly associated scaffold protein IKK␥ (also termed NEMO) (3, 4). Gene-disruption studies of the murine IKK genes have demonstrated that IKK␤ is the dominant kinase regulating NF-B activity via phosphorylation and subsequent proteasome-mediated degradation of inhibitors of NF-B (e.g. IB␣, -␤, and -⑀), a critical step that allows rapid translocation of p65/Rel NF-B heterodimers to the nucleus to activate gene expression (5, 6). Accordingly, fibroblasts isolated from IKK␤ knock-out mice are defective in IKK-dependent NF-B activation in response to either TNF␣ or interleukin (IL) 1 (7). IKK␥ mediates the recruitment of upstream activating kinases, including the NF-B-inducing kinase (NIK) (8,9), that modulate IKK␤ activity (7, 10). This scaffolding protein also binds a number of molecules other than IKKs that are involved in regulating IKK activity (11).It has been found that the Ras superfamily of small GTP-binding proteins plays an important role in the regulation of a variety of cellular functions (12, 13). The activity of these small GTPases is regulated by sig...

These data indicate that enhanced tumorigenesis occurs through increase in EGF-induced EGFR activation in FLNa-expressing melanoma cells and that high FLNa levels are predictors of negative outcome for patients with melanoma tumors.

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BackgroundAlthough downregulation of caveolin-1 (Cav-1), which is a key constituent of membrane caveolae and a regulator of cellular processes, is associated with colorectal cancer (CRC), its involvement in the disease progression is largely unknown. This study aimed to explore the role of Cav-1 in CRC and the associated mechanisms.Material/MethodsFresh tissues from patients with CRC and human CRC SW480 cells were used to evaluate Cav-1 and Ki-67 expression using immunohistochemistry and Western blotting. The MTS and Transwell assays were performed to determine the effects of Cav-1 overexpression via pcDNA3.1/Cav-1 plasmid on cell proliferation and metastasis. The effect of Cav-1 on the epidermal growth factor receptor (EGFR) activation was evaluated by Western blotting. The correlation of Cav-1 expression with clinicopathological factors was statistically analyzed.ResultsOverexpression of Cav-1 significantly reduced proliferation, migration, and invasion of SW480 cancer cells in vitro. The EGF-induced phosphorylation of EGFR and activations of the RAF-MEK-ERK and PI3K-AKT pathways were adversely regulated by Cav-1 overexpression in vitro. In 76 cases of CRC patients with EGFR expression, a negative correlation was observed between the level of Cav-1 and tumor-node-metastasis stage, lymph node metastasis, and distant metastasis (All p<0.05). Finally, the expression level of Cav-1 was negatively correlated with that of Ki-67.ConclusionsThis report is the first to show that overexpression of Cav-1significantly inhibits the proliferation, migration, and invasion potential of SW480 cells, possibly through reducing EGF-induced EGFR activation. High Cav-1 expression level may be a predictor of positive outcomes in patients with colorectal cancer.