To elucidate the physiological significance of MEK5 in vivo, we have examined the effect of mek5 gene elimination in mice. Heterozygous mice appear to be healthy and were fertile. However, mek5 ؊/؊ embryos die at approximately embryonic day 10.5 (E10.5). The phenotype of the mek5 ؊/؊ embryos includes abnormal cardiac development as well as a marked decrease in proliferation and an increase in apoptosis in the heart, head, and dorsal regions of the mutant embryos. The absence of MEK5 does not affect cell cycle progression but sensitizes mouse embryonic fibroblasts (MEFs) to the ability of sorbitol to enhance caspase 3 activity. Further studies with mek5 ؊/؊ MEFs indicate that MEK5 is required for mediating extracellular signalregulated kinase 5 (ERK5) activation and for the regulation of the transcriptional activity of myocyte enhancer factor 2. Overall, this is the first study to rigorously establish the role of MEK5 in vivo as an activator of ERK5 and as an essential regulator of cell survival that is required for normal embryonic development.The mitogen-activated protein kinase (MAPK) cascades constitute a complex network of signaling pathways that are involved in the regulation of numerous cell functions (9). They consist of the sequential activation of protein kinases that include MAPKs, MAPK/extracellular signal-regulated kinase (ERK) kinases (MEKs or MKKs), and MEK kinases (MEKKs) (9). MAPKs are activated by dual phosphorylation on threonine (T) and tyrosine (Y) residues within a T-X-Y motif by MEKs. MEKs are activated by MEKKs. Two main mechanisms have been proposed to ensure specific transmission of the signals from upstream kinases to MAPKs (38, 40): (i) scaffold proteins that assemble the different components of a cascade; (ii) physical interactions between the components of a cascade. Both mechanisms may operate in parallel and allow different responses of the same MAPK signaling pathways to different stimuli.At least four MAPK subfamilies have been identified: ERK1/2, ERK5, c-Jun NH 2 -terminal protein kinases (JNKs), and p38 MAPKs. MAPK activators include MEK1 and MEK2 for ERK1/2, MEK5 for ERK5, MKK4 and MKK7 for JNKs, and MKK3 and MKK6 for p38 MAPKs (9). Targeted deletion of the mapk and mek/mkk genes has contributed substantially to our increased understanding of the physiological role of these pathways in development and pathogenesis. In particular, the recent elimination of the erk5 gene in mice has provided genetic evidence that ERK5 is required for normal cardiac development (31,34,42). ERK5, also known as big MAPK, is almost twice the size (815 amino acids) of the other MAPKs (45). Its unique COOH-terminal tail contains a myocyte enhancer factor 2 (MEF2)-interacting domain and a potent transcriptional activation domain (12). The ERK5 catalytic NH 2 -terminal domain is 50% identical to ERK2. The activity of a number of transcription factors has been shown to be regulated by ERK5, including MEF2, c-Fos and Fra-1, Sap1, c-Myc, and NF-B (6,11,13,15,28,37). In vitro, the ERK5 signaling pathway has...

Matrix metalloproteinase-3 (MMP-3) plays an important role in intervertebral disc degeneration, a ubiquitous condition closely linked to low back pain and disability. Elevated expression of syndecan 4, a cell surface heparan sulfate proteoglycan, actively controls disc matrix catabolism. However, the relationship between MMP-3 expression and syndecan 4 in the context of inflammatory disc disease has not been clearly defined. We investigated the mechanisms by which cytokines control MMP-3 expression in rat and human nucleus pulposus cells. Cytokine treatment increased MMP-3 expression and promoter activity. Stable silencing of syndecan 4 blocked cytokine-mediated MMP-3 expression; more important, syndecan 4 did not mediate its effects through NF-κB or mitogen-activated protein kinase (MAPK) pathways. However, treatment with MAPK and NF-κB inhibitors resulted in partial blocking of the inductive effect of cytokines on MMP-3 expression. Loss-of-function studies confirmed that NF-κB, p38α/β2/γ/δ, and extracellular signal-regulated kinase (ERK) 2, but not ERK1, contributed to cytokine-dependent induction of MMP3 promoter activity. Similarly, inhibitor treatments, lentiviral short hairpin-p65, and short hairpin-IκB kinase β significantly decreased cytokine-dependent up-regulation in MMP-3 expression. Finally, we show that transforming growth factor-β can block the up-regulation of MMP-3 induced by tumor necrosis factor (TNF)-α by counteracting the NF-κB pathway and syndecan 4 expression. Taken together, our results suggest that cooperative signaling through syndecan 4 and the TNF receptor 1-MAPK-NF-κB axis is required for TNF-α-dependent expression of MMP-3 in nucleus pulposus cells. Controlling these pathways may slow the progression of intervertebral disc degeneration and matrix catabolism.

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Coordinated partitioning of intracellular cargoes between nuclear and cytoplasmic compartments is critical for cell survival and differentiation. The karyopherin α/β heterodimer functions to import cytoplasmic proteins that possess classical nuclear localisation signals into the nucleus. Seven karyopherinαsubtypes have been identified in mammals. The aim of this study was to determine the relative abundance of transcripts encoding seven karyopherinαsubtypes in porcine oocytes and embryos at discrete stages of cleavage development, and to determine the developmental requirements of karypopherinα7 (KPNA7), an oocyte and cleavage stage embryo-specific karyopherinαsubtype. We hypothesised that knockdown of KPNA7 would negatively affect porcine cleavage development. To test this hypothesis, in vitro matured and fertilised porcine oocytes were injected with a double-stranded interfering RNA molecule that targeted KPNA7; nuclei were counted in all embryos 6 days after fertilisation. Embryos injected with KPNA7-interfering RNAs possessed significantly lower cell numbers than their respective control groups (P<0.05). In vitro binding assays also suggest that KPNA7 may transport intracellular proteins that possess unique nuclear localisation signals. Our data suggest that embryos have differential requirements for individual karyopherinαsubtypes and that these karyopherinαsubtypes differentially transport intracellular cargo during cleavage development.

Purpose: To investigate the in vivo antitumor efficacy of quercetin in U937 xenografts and the functional roles of Mcl-1 and Bax in quercetin-induced apoptosis in human leukemia.Experimental Design: Leukemia cells were treated with quercetin, after which apoptosis, Mcl-1 expression, and Bax activation and translocation were evaluated. The efficacy of quercetin as well as Mcl-1 expression and Bax activation were investigated in xenografts of U937 cells.Results: Administration of quercetin caused pronounced apoptosis in both transformed and primary leukemia cells but not in normal blood peripheral mononuclear cells. Quercetin-induced apoptosis was accompanied by Mcl-1 downregulation and Bax conformational change and mitochondrial translocation that triggered cytochrome c release. Knockdown of Bax by siRNA reversed quercetin-induced apoptosis and abrogated the activation of caspase and apoptosis. Ectopic expression of Mcl-1 attenuated quercetinmediated Bax activation, translocation, and cell death. Conversely, interruption of Mcl-1 by siRNA enhanced Bax activation and translocation, as well as lethality induced by quercetin. However, the absence of Bax had no effect on quercetin-mediated Mcl-1 downregulation. Furthermore, in vivo administration of quercetin attenuated tumor growth in U937 xenografts. The TUNEL-positive apoptotic cells in tumor sections increased in quercetin-treated mice as compared with controls. Mcl-1 downregulation and Bax activation were also observed in xenografts.Conclusions: These data suggest that quercetin may be useful for the treatment of leukemia by preferentially inducing apoptosis in leukemia versus normal hematopoietic cells through a process involving Mcl-1 downregulation, which, in turn, potentiates Bax activation and mitochondrial translocation, culminating in apoptosis. Clin Cancer Res; 16(23); 5679-91. Ó2010 AACR.

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FYN, one of the members of the Src family of kinases (SFKs), has been reported to be overexpressed in various types of cancers and correlated with cell motility and proliferation. However, the mechanism is still unclear. In the present study, we found that FYN was overexpressed in breast cancer and overexpression of FYN promoted cell proliferation, migration and invasion in the MCF10A cells, whereas depletion of FYN suppressed cell proliferation, migration and invasion in the MDA-MB-231 cells. Moreover, FYN upregulated the expression of mesenchymal markers and epithelial-mesenchymal transition (EMT)-related transcription factors, and downregulated the expression of epithelial markers, suggesting that FYN induces EMT in breast cancer cells. Furthermore, FYN was transcriptionally regulated by FOXO1 and mediated FGF2-induced EMT through both the PI3K/AKT and ERK/MAPK pathways.

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