[Show abstract][Hide abstract] ABSTRACT: Invasive migration of carcinoma cells is a prerequisite for the metastatic dissemination of solid tumours. Numerous mechanisms control the ability of cancer cells to acquire a motile and invasive phenotype, and subsequently degrade and invade the basement membrane. Several genes that are up-regulated in breast carcinoma are responsible for mediating the metastatic cascade. Recent studies have revealed that the NFAT (nuclear factor of activated T-cells) is a transcription factor that is highly expressed in aggressive breast cancer cells and tissues, and mediates invasion through transcriptional induction of pro-invasion and migration genes. In the present paper we demonstrate that NFAT promotes breast carcinoma invasion through induction of GPC (glypican) 6, a cell-surface glycoprotein. NFAT transcriptionally regulates GPC6 induction in breast cancer cells and binds to three regulatory elements in the GPC6 proximal promoter. Expression of GPC6 in response to NFAT signalling promotes invasive migration, whereas GPC6 silencing with shRNA (small-hairpin RNA) potently blocks this phenotype. The mechanism by which GPC6 promotes invasive migration involves inhibition of canonical β-catenin and Wnt signalling, and up-regulation of non-canonical Wnt5A signalling leading to the activation of JNK (c-Jun N-terminal kinase) and p38 MAPK (mitogen-activated protein kinase). Thus GPC6 is a novel NFAT target gene in breast cancer cells that promotes invasive migration through Wnt5A signalling.
[Show abstract][Hide abstract] ABSTRACT: cis-urocanic acid (cis-UCA) is an endogenous amino acid metabolite capable of transporting protons from the mildly acidic extracellular medium into the cell cytosol. The resulting intracellular acidification suppresses many cellular activities. The current study was aimed at characterizing the molecular mechanisms underlying cis-UCA-mediated cytotoxicity in cultured cancer cells.
5367 bladder carcinoma cells were left untreated or treated with cis-UCA. Cell death was assessed by measuring caspase-3 activity, mitochondrial membrane polarization, formation and release of cytoplasmic histone-associated DNA fragments, and cellular permeabilization. Cell viability and metabolic activity were monitored by colorimetric assays. Nuclear labelling was used to quantify the effects of cis-UCA on cell cycle. The activity of the ERK and JNK signalling pathways was studied by immunoblotting with specific antibodies. Phosphatase activity in cis-UCA-treated cells was determined by assay kits measuring absorbance resulting from the dephosphorylation of an artificial substrate. All statistical analyses were performed using the two-way Student's t-test (p < 0.05).
Here we report that treatment of the 5637 human bladder carcinoma cells with 2% cis-UCA induces both apoptotic and necrotic cell death. In addition, metabolic activity of the 5637 cells is rapidly impaired, and the cells arrest in cell cycle in response to cis-UCA. Importantly, we show that cis-UCA promotes the ERK and JNK signalling pathways by efficiently inhibiting the activity of serine/threonine and tyrosine phosphatases.
Our studies elucidate how cis-UCA modulates several cellular processes, thereby inhibiting the proliferation and survival of bladder carcinoma cells. These anti-cancer effects make cis-UCA a potential candidate for the treatment of non-muscle invasive bladder carcinoma.
[Show abstract][Hide abstract] ABSTRACT: Cellular FLICE-inhibitory protein (c-FLIP) proteins are crucial regulators of the death-inducing signaling complex (DISC) and caspase-8 activation. To date, three c-FLIP isoforms with distinct functions and regulation have been identified. Our previous studies have shown that the stability of c-FLIP proteins is subject to isoform-specific regulation, but the underlying molecular mechanisms have not been known. Here, we identify serine 193 as a novel in vivo phosphorylation site of all c-FLIP proteins and demonstrate that S193 phosphorylation selectively influences the stability of the short c-FLIP isoforms, as S193D mutation inhibits the ubiquitylation and selectively prolongs the half-lives of c-FLIP short (c-FLIP(S)) and c-FLIP Raji (c-FLIP(R)). S193 phosphorylation also decreases the ubiquitylation of c-FLIP long (c-FLIP(L)) but, surprisingly, does not affect its stability, indicating that S193 phosphorylation has a different function in c-FLIP(L). The phosphorylation of this residue is operated by the protein kinase C (PKC), as S193 phosphorylation is markedly increased by treatment with 12-O-tetradecanoylphorbol-13-acetate and decreased by inhibition of PKCalpha and PKCbeta. S193 mutations do not affect the ability of c-FLIP to bind to the DISC, although S193 phosphorylation is increased by death receptor stimulation. Instead, S193 phosphorylation affects the intracellular level of c-FLIP(S), which then determines the sensitivity to death-receptor-mediated apoptosis. These results reveal that the differential stability of c-FLIP proteins is regulated in an isoform-specific manner by PKC-mediated phosphorylation.
Cell death and differentiation 05/2009; 16(9):1215-26. · 8.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fever has a major impact on immune responses by modulating survival, proliferation, and endurance of lymphocytes. Lymphocyte persistence in turn is determined by the equilibrium between death and survival-promoting factors that regulate death receptor signaling in these cells. A potential integrator of death receptor signaling is the caspase-8 inhibitor c-FLIP, the expression of which is dynamically regulated, either rapidly induced or down-regulated. In this study, we show in activated primary human T lymphocytes that hyperthermia corresponding to fever triggered down-regulation of both c-FLIP-splicing variants, c-FLIPshort (c-FLIP(S)) and c-FLIPlong, with consequent sensitization to apoptosis mediated by CD95 (Fas/APO-1). The c-FLIP down-regulation and subsequent sensitization was specific for hyperthermic stress. Additionally, we show that the hyperthermia-mediated down-regulation was due to increased ubiquitination and proteasomal degradation of c-FLIP(S), the stability of which we have shown to be regulated by its C-terminal splicing tail. Furthermore, the induced sensitivity to CD95 ligation was independent of heat shock protein 70, as thermotolerant cells, expressing substantially elevated levels of heat shock protein 70, were not rescued from the effect of hyperthermia-mediated c-FLIP down-regulation. Our findings indicate that fever significantly influences the rate of lymphocyte elimination through depletion of c-FLIP(S). Such a general regulatory mechanism for lymphocyte removal has broad ramifications for fever-mediated regulation of immune responses.
The Journal of Immunology 04/2007; 178(6):3944-53. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The caspase-8 inhibitor c-FLIP exists as two splice variants, c-FLIP(L) and c-FLIP(S), with distinct roles in death receptor signaling. The mechanisms determining their turnover have not been established. We found that in differentiating K562 erythroleukemia cells both c-FLIP isoforms were inducibly degraded by the proteasome, but c-FLIP(S) was more prone to ubiquitylation and had a considerably shorter half-life. Analysis of the c-FLIP(S)-specific ubiquitylation revealed two lysines, 192 and 195, C-terminal to the death effector domains, as principal ubiquitin acceptors in c-FLIP(S) but not in c-FLIP(L). Furthermore the c-FLIP(S)-specific tail of 19 amino acids, adjacent to the two target lysines, was demonstrated to be the key element determining the isoform-specific instability of c-FLIP(S). Molecular modeling in combination with site-directed mutagenesis demonstrated that the C-terminal tail is required for correct positioning and subsequent ubiquitylation of the target lysines. Because the antiapoptotic operation of c-FLIP(S) was not affected by the tail deletion, the antiapoptotic activity and ubiquitin-mediated degradation of c-FLIP(S) are functionally and structurally independent processes. The presence of a small destabilizing sequence in c-FLIP(S) constitutes an important determinant of c-FLIP(S)/c-FLIP(L) ratios by allowing differential degradation of c-FLIP isoforms. The conformation-based predisposition of c-FLIP(S) to ubiquitin-mediated degradation introduces a novel concept to the regulation of the death-inducing signaling complex.
Journal of Biological Chemistry 08/2005; 280(29):27345-55. · 4.65 Impact Factor