Id helix-loop-helix proteins inhibit nucleoprotein complex formation by the TCF ETS-domain transcription factors.
(1/1311)
The Id subfamily of helix-loop-helix (HLH) proteins plays a fundamental role in the regulation of cellular proliferation and differentiation. Id proteins are thought to inhibit differentiation mainly through interaction with other HLH proteins and by blocking their DNA-binding activity. Members of the ternary complex factor (TCF) subfamily of ETS-domain proteins have key functions in regulating immediate-early gene expression in response to mitogenic stimulation. TCFs form DNA-bound complexes with the serum response factor (SRF) and are direct targets of MAP kinase (MAPK) signal transduction cascades. In this study we demonstrate functional interactions between Id proteins and TCFs. Ids bind to the ETS DNA-binding domain and disrupt the formation of DNA-bound complexes between TCFs and SRF on the c-fos serum response element (SRE). Inhibition occurs by disrupting protein-DNA interactions with the TCF component of this complex. In vivo, the Id proteins cause down-regulation of the transcriptional activity mediated by the TCFs and thereby block MAPK signalling to SREs. Therefore, our results demonstrate a novel facet of Id function in the coordination of mitogenic signalling and cell cycle entry. (+info)
Ral-specific guanine nucleotide exchange factor activity opposes other Ras effectors in PC12 cells by inhibiting neurite outgrowth.
(2/1311)
Ras proteins can activate at least three classes of downstream target proteins: Raf kinases, phosphatidylinositol-3 phosphate (PI3) kinase, and Ral-specific guanine nucleotide exchange factors (Ral-GEFs). In NIH 3T3 cells, activated Ral-GEFs contribute to Ras-induced cell proliferation and oncogenic transformation by complementing the activities of Raf and PI3 kinases. In PC12 cells, activated Raf and PI3 kinases mediate Ras-induced cell cycle arrest and differentiation into a neuronal phenotype. Here, we show that in PC12 cells, Ral-GEF activity acts opposite to other Ras effectors. Elevation of Ral-GEF activity induced by transfection of a mutant Ras protein that preferentially activates Ral-GEFs, or by transfection of the catalytic domain of the Ral-GEF Rgr, suppressed cell cycle arrest and neurite outgrowth induced by nerve growth factor (NGF) treatment. In addition, Rgr reduced neurite outgrowth induced by a mutant Ras protein that preferentially activates Raf kinases. Furthermore, inhibition of Ral-GEF activity by expression of a dominant negative Ral mutant accelerated cell cycle arrest and enhanced neurite outgrowth in response to NGF treatment. Ral-GEF activity may function, at least in part, through inhibition of the Rho family GTPases, CDC42 and Rac. In contrast to Ras, which was activated for hours by NGF treatment, Ral was activated for only approximately 20 min. These findings suggest that one function of Ral-GEF signaling induced by NGF is to delay the onset of cell cycle arrest and neurite outgrowth induced by other Ras effectors. They also demonstrate that Ras has the potential to promote both antidifferentiation and prodifferentiation signaling pathways through activation of distinct effector proteins. Thus, in some cell types the ratio of activities among Ras effectors and their temporal regulation may be important determinants for cell fate decisions between proliferation and differentiation. (+info)
Thyroid hormone promotes the phosphorylation of STAT3 and potentiates the action of epidermal growth factor in cultured cells.
(3/1311)
We have examined the effects of l-thyroxine (T4) on the activation of signal transducer and activator of transcription 3 (STAT3) and on the STAT3-dependent induction of c-Fos expression by epidermal growth factor (EGF). T4, at a physiological concentration of 100 nM, caused tyrosine phosphorylation and nuclear translocation (i.e. activation) of STAT3 in HeLa cells in as little as 10-20 min. Activation by T4 of STAT3 was maximal at 30 min (15+/-4-fold enhancement; mean+/-S.E.M.) in 18 experiments. This effect was reproduced by T4-agarose (100 nM) and blocked by CGP 41251, genistein, PD 98059 and geldanamycin, inhibitors of protein kinase C (PKC), protein tyrosine kinase (PTK), mitogen-activated protein kinase (MAPK) kinase and Raf-1 respectively. Tyrosine-phosphorylated MAPK also appeared in nuclear fractions within 10 min of treatment with T4. In the nuclear fraction of T4-treated cells, MAPK immunoprecipitate also contained STAT3. The actions of T4 were similar in HeLa and CV-1 cells, which lack thyroid hormone receptor (TR), and in TR-replete skin fibroblasts (BG-9). T4 also potentiated the EGF-induced nuclear translocation of activated STAT1alpha and STAT3 and enhanced the EGF-stimulated expression of c-Fos. Hormone potentiation of EGF-induced signal transduction and c-Fos expression was inhibited by CGP 41251, geldanamycin and PD 98059. Therefore the non-genomically induced activation by T4 of STAT3, and the potentiation of EGF by T4, require activities of PKC, PTK and an intact MAPK pathway. (+info)
Activation of c-fos promoter by Gbetagamma-mediated signaling: involvement of Rho and c-Jun N-terminal kinase.
(4/1311)
Several extracellular stimuli mediated by G protein-coupled receptors activate c-fos promoter. Recently, we and other groups have demonstrated that signals from G protein-coupled receptors stimulate mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. The activation of these three MAPKs is mediated in part by the G protein betagamma subunit (Gbetagamma). In this study, we characterized the signals from Gbetagamma to c-fos promoter using transient transfection of c-fos luciferase into human embryonal kidney 293 cells. Activation of m2 muscarinic acetylcholine receptor and overexpression of Gbetagamma, but not constitutively active Galphai2, stimulated c-fos promoter activity. The c-fos promoter activation by m2 receptor and Gbetagamma was inhibited by beta-adrenergic receptor kinase C-terminal peptide (betaARKct), which functions as a Gbetagamma antagonist. MEK1 inhibitor PD98059 and kinase-deficient mutant of JNK kinase, but not p38 MAPK inhibitor SB203580, attenuated the m2 receptor- and Gbetagamma-induced c-fos promoter activation. Activated mutants of Ras and Rho stimulated the c-fos promoter activity, and the dominant negative mutants of Ras and Rho inhibited the c-fos promoter activation by m2 receptor and Gbetagamma. Moreover, c-fos promoter activation by m2 receptor, Gbetagamma, and active Rho, but not active Ras, was inhibited by botulinum C3 toxin. These data indicated that both Ras- and Rho-dependent signaling pathways are essential for c-fos promoter activation mediated by Gbetagamma. (+info)
Effect of tetrandrine on proto-oncogene c-fos expression in rat cerebrum.
(5/1311)
AIM: To detect the effect of tetrandrine (Tet) on c-fos gene expression in cerebrum induced by lindane, a neurotoxicant which activates Ca2+ channels. METHODS: Northern and dot blotting, dual wavelength thin layer chromatography scanner, were used in this study. RESULTS: Lindane 30 mg.kg-1 given by intragastric gavage (i.g.) increased the expression of c-fos gene to 146 mm2 in rat cerebrum 1 h after treatment. Tet 1, 2, and 4 mg.kg-1 given by i.g. 30 min prior to lindane reduced c-fos gene expression in a concentration-dependent manner. Expressed genes reached only 86, 40, and 39 mm2, respectively. CONCLUSION: Tet inhibited c-fos gene expression in rat cerebrum induced by Ca2+ agonist-lindane. (+info)
The effect of the orexins on food intake: comparison with neuropeptide Y, melanin-concentrating hormone and galanin.
(6/1311)
Orexin-A and orexin-B (the hypocretins) are recently described neuropeptides suggested to have a physiological role in the regulation of food intake in the rat. We compared the orexigenic effect of the orexins administered intracerebroventricular (ICV) with other known stimulants of food intake, one strong, neuropeptide Y (NPY), and two weaker, melanin-concentrating hormone (MCH) and galanin. Orexin-A consistently stimulated food intake, but orexin-B only on occasions. Both peptides stimulated food intake significantly less than NPY, but to a similar extent to MCH (2 h food intake: NPY 3 nmol, 7.2+/-0.9 g vs saline, 1.5+/-0.2 g, P<0.001, MCH 3 nmol, 3.2+/-0.8 g vs saline, P<0.01, orexin-B 30 nmol, 2. 6+/-0.5 g vs saline, P=0.11) and to galanin (1 h food intake: galanin 3 nmol, 2.0+/-0.4 g vs saline, 0.8+/-0.2 g, P<0.05, orexin-A 3 nmol 2.2+/-0.4 g vs saline, P<0.01; 2 hour food intake: orexin-B 3 nmol, 2.4+/-0.3 g vs saline, 1.3+/-0.2 g, P<0.05). Following ICV orexin-A, hypothalamic c-fos, a maker of neuronal activation, was highly expressed in the paraventricular nucleus (PVN), and the arcuate nucleus (P<0.005 for both). IntraPVN injection of orexin-A stimulated 2 h food intake by one gram (orexin-A 0.03 nmol, 1.6+/-0. 3 g vs saline, 0.5+/-0.3 g, P<0.005). These findings support the suggestion that the orexins stimulate food intake. However, this effect is weak and may cast doubt upon their physiological importance in appetite regulation in the rat. (+info)
Human SWI-SNF component BRG1 represses transcription of the c-fos gene.
(7/1311)
Yeast and mammalian SWI-SNF complexes regulate transcription through active modification of chromatin structure. Human SW-13 adenocarcinoma cells lack BRG1 protein, a component of SWI-SNF that has a DNA-dependent ATPase activity essential for SWI-SNF function. Expression of BRG1 in SW-13 cells potentiated transcriptional activation by the glucocorticoid receptor, which is known to require SWI-SNF function. BRG1 also specifically repressed transcription from a transfected c-fos promoter and correspondingly blocked transcriptional activation of the endogenous c-fos gene. Mutation of lysine residue 798 in the DNA-dependent ATPase domain of BRG1 significantly reduced its ability to repress c-fos transcription. Repression by BRG1 required the cyclic AMP response element of the c-fos promoter but not nearby binding sites for Sp1, YY1, or TFII-I. Using human C33A cervical carcinoma cells, which lack BRG1 and also express a nonfunctional Rb protein, transcriptional repression by BRG1 was weak unless wild-type Rb was also supplied. Interestingly, Rb-dependent repression by BRG1 was found to take place through a pathway that is independent of transcription factor E2F. (+info)
Quercetin inhibited DNA synthesis and induced apoptosis associated with increase in c-fos mRNA level and the upregulation of p21WAF1CIP1 mRNA and protein expression during liver regeneration after partial hepatectomy.
(8/1311)
Quercetin, a widely distributed bioflavonoid, inhibited DNA synthesis in regenerating liver after partial hepatectomy. This inhibition was accompanied by apoptosis, evidenced by in situ end-labeling and gel electrophoresis of DNA fragmentation. Characteristic DNA fragmentation was detected as early as 2 h after injection. Northern blot analysis revealed that quercetin induced the increases in c-fos and p21WAF1CIP1 mRNA levels within 2 h. The expression of p21 protein was also enhanced, while p53 mRNA and protein levels were not affected by quercetin. These results suggest that quercetin-induced apoptosis is associated with the increase in c-fos mRNA level and the upregulation of p21 mRNA and protein expression, probably in a p53-independent pathway. (+info)