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At least 325 records · Page 18Linked to original sources
PubMed1998

Reduced level of ATF is correlated with transcriptional repression of DNA topoisomerase II alpha gene during TPA-induced differentiation of HL-60 cells.

DNA topoisomerase II is a marker for the proliferation state of mammalian cells in culture, and the protein levels are markedly higher in exponentially growing cells than quiescent cells and can be downregulated by growth of the cells at high density and serum starvation. Correlation between ATF and TPA-repressed DNA topoisomerase II alpha (Topo II alpha) mRNA has been investigated during TPA-induced differentiation of HL-60 cells. Topo II alpha mRNA and unknotting activity were reduced at 24 hours in TPA-treated HL-60 cells. The level of Topo II alpha mRNA and the activity were gradually decreased in proportion to the concentration of TPA. Two DNA-protein complexes were formed by DNA mobility shift assay when ATF-binding site was incubated with nuclear extract prepared from TPA-free HL-60 cells, and the amount of ATF was vanished after TPA treatment. TPA-repressed Topo II alpha mRNA and ATF levels were partially restored after pretreatment of staurosporin. These results suggest that the reduced level of ATF may be important to the transcriptional repression of Topo II alpha gene during TPA-induced differentiation in HL-60 cells and related to protein kinase C signal pathway.

Activating Transcription Factors↗
PubMed1999

The PDZ domain of the LIM protein enigma binds to beta-tropomyosin.

PDZ and LIM domains are modular protein interaction motifs present in proteins with diverse functions. Enigma is representative of a family of proteins composed of a series of conserved PDZ and LIM domains. The LIM domains of Enigma and its most related family member, Enigma homology protein, bind to protein kinases, whereas the PDZ domains of Enigma and family member actin-associated LIM protein bind to actin filaments. Enigma localizes to actin filaments in fibroblasts via its PDZ domain, and actin-associated LIM protein binds to and colocalizes with the actin-binding protein alpha-actinin-2 at Z lines in skeletal muscle. We show that Enigma is present at the Z line in skeletal muscle and that the PDZ domain of Enigma binds to a skeletal muscle target, the actin-binding protein tropomyosin (skeletal beta-TM). The interaction between Enigma and skeletal beta-TM was specific for the PDZ domain of Enigma, was abolished by mutations in the PDZ domain, and required the PDZ-binding consensus sequence (Thr-Ser-Leu) at the extreme carboxyl terminus of skeletal beta-TM. Enigma interacted with isoforms of tropomyosin expressed in C2C12 myotubes and formed an immunoprecipitable complex with skeletal beta-TM in transfected cells. The association of Enigma with skeletal beta-TM suggests a role for Enigma as an adapter protein that directs LIM-binding proteins to actin filaments of muscle cells.

Actins↗
PubMed1999

Genetic analysis of rolled, which encodes a Drosophila mitogen-activated protein kinase.

Genetic and molecular characterization of the dominant suppressors of D-raf(C110) on the second chromosome identified two gain-of-function alleles of rolled (rl), which encodes a mitogen-activated protein (MAP) kinase in Drosophila. One of the alleles, rl(Su23), was found to bear the same molecular lesion as rl(Sem), which has been reported to be dominant female sterile. However, rl(Su23) and the current stock of rl(Sem) showed only a weak dominant female sterility. Detailed analyses of the rl mutations demonstrated moderate dominant activities of these alleles in the Torso (Tor) signaling pathway, which explains the weak dominant female sterility observed in this study. The dominant rl mutations failed to suppress the terminal class maternal-effect mutations, suggesting that activation of Rl is essential, but not sufficient, for Tor signaling. Involvement of rl in cell proliferation was also demonstrated by clonal analysis. Branching and integration of signals in the MAP kinase cascade is discussed.

Amino Acid Sequence↗
PubMed2003

Aurora-A and an interacting activator, the LIM protein Ajuba, are required for mitotic commitment in human cells.

Aurora family kinases contribute to regulation of mitosis. Using RNA interference in synchronized HeLa cells, we now show that Aurora-A is required for mitotic entry. We found that initial activation of Aurora-A in late G2 phase of the cell cycle is essential for recruitment of the cyclin B1-Cdk1 complex to centrosomes, where it becomes activated and commits cells to mitosis. A two-hybrid screen identified the LIM protein Ajuba as an Aurora-A binding protein. Ajuba and Aurora-A interact in mitotic cells and become phosphorylated as they do so. In vitro analyses revealed that Ajuba induces the autophosphorylation and consequent activation of Aurora-A. Depletion of Ajuba prevented activation of Aurora-A at centrosomes in late G2 phase and inhibited mitotic entry. Overall, our data suggest that Ajuba is an essential activator of Aurora-A in mitotic commitment.

Animals↗
PubMed2000

Solution structure of the focal adhesion adaptor PINCH LIM1 domain and characterization of its interaction with the integrin-linked kinase ankyrin repeat domain.

PINCH is a recently identified adaptor protein that comprises an array of five LIM domains. PINCH functions through LIM-mediated protein-protein interactions that are involved in cell adhesion, growth, and differentiation. The LIM1 domain of PINCH interacts with integrin-linked kinase (ILK), thereby mediating focal adhesions via a specific integrin/ILK signaling pathway. We have solved the NMR structure of the PINCH LIM1 domain and characterized its binding to ILK. LIM1 contains two contiguous zinc fingers of the CCHC and CCCH types and adopts a global fold similar to that of functionally distinct LIM domains from cysteine-rich protein and cysteine-rich intestinal protein families with CCHC and CCCC zinc finger types. Gel-filtration and NMR experiments demonstrated a 1:1 complex between PINCH LIM1 and the ankyrin repeat domain of ILK. A chemical shift mapping experiment identified regions in PINCH LIM1 that are important for interaction with ILK. Comparison of surface features between PINCH LIM1 and other functionally different LIM domains indicated that the LIM motif might have a highly variable mode in recognizing various target proteins.

Amino Acid Sequence↗
PubMed2006

The parvins.

The parvins are a family of proteins involved in linking integrins and associated proteins with intracellular pathways that regulate actin cytoskeletal dynamics and cell survival. Both alpha-parvin (PARVA) and beta-parvin (PARVB) localize to focal adhesions and function in cell adhesion, spreading, motility and survival through interactions with partners, such as integrin-linked kinase (ILK), paxillin, alpha-actinin and testicular kinase 1. A complex of PARVA with ILK and the LIM protein PINCH-1 is critical for cell survival in a variety of cells, including certain cancer cells, kidney podocytes and cardiac myocytes. While PARVA inhibits the activities of Rac1 and testicular kinase 1 and cell spreading, PARVB binds alphaPIX and alpha-actinin, and can promote cell spreading. In contrast to PARVA, PARVB inhibits ILK activity and reverses some of its oncogenic effects in cancer cells. This review focuses on the structure and function of the parvins and some possible roles in human diseases.

Actinin↗
PubMed2005

c-Src-mediated phosphorylation of TRIP6 regulates its function in lysophosphatidic acid-induced cell migration.

TRIP6 (thyroid receptor-interacting protein 6), also known as ZRP-1 (zyxin-related protein 1), is a member of the zyxin family that has been implicated in cell motility. Previously we have shown that TRIP6 binds to the LPA2 receptor and associates with several components of focal complexes in an agonist-dependent manner and, thus, enhances lysophosphatidic acid (LPA)-induced cell migration. Here we further report that the function of TRIP6 in LPA signaling is regulated by c-Src-mediated phosphorylation of TRIP6 at the Tyr-55 residue. LPA stimulation induces tyrosine phosphorylation of endogenous TRIP6 in NIH 3T3 cells and c-Src-expressing fibroblasts, which is virtually eliminated in Src-null fibroblasts. Strikingly, both phosphotyrosine-55 and proline-58 residues of TRIP6 are required for Crk binding in vitro and in cells. Mutation of Tyr-55 to Phe does not alter the ability of TRIP6 to localize at focal adhesions or associate with actin. However, it abolishes the association of TRIP6 with Crk and p130cas in cells and significantly reduces the function of TRIP6 to promote LPA-induced ERK activation. Ultimately, these signaling events control TRIP6 function in promoting LPA-induced morphological changes and cell migration.

ATPases Associated with Diverse Cellular Activitie↗
PubMed2005

The LIM/homeodomain protein Islet1 recruits Janus tyrosine kinases and signal transducer and activator of transcription 3 and stimulates their activities.

Islet1 (Isl1) belongs to the LIM homeodomain transcription factor family. Its roles in differentiation of motor neurons and organogenesis of pancreas and heart have been revealed. However, less is known about its regulatory mechanism and the target genes. In this study, we identified interactions between Isl1 and Janus tyrosine kinase (JAK), as well as signal transducer and activator of transcription (Stat)3, but not Stat1 and Stat5, in mammalian cells. We found that Isl1 not only forms a complex with Jak1 and Stat3 but also triggers the tyrosine phosphorylation of Jak1 and its kinase activity, thereby elevating the tyrosine phosphorylation, DNA binding activity, and target gene expression of Stat3. In vivo, the tyrosine-phosphorylated Stat3 was colocalized with Isl1 in the nucleus of the mouse motor neurons in spinal cord after nerve injury. Correspondingly, electroporation of Isl1 and Stat3 into the neural tube of chick embryos resulted in the activation of a reporter gene expression controlled by a Stat3 regulatory sequence, and cotransfection of Isl1 and Stat3 promoted the proliferation of the mouse motor neuron cells. Our data suggest a novel role of Isl1 as an adaptor for Jak1 and Stat3 and reveal a possible functional link between LIM homeodomain transcription factors and the Jak-Stat pathway.

Animals↗
PubMed2002

Discrimination of polycythemias and thrombocytoses by novel, simple, accurate clonality assays and comparison with PRV-1 expression and BFU-E response to erythropoietin.

Essential thrombocythemia (ET) and polycythemia vera (PV) are clonal myeloproliferative disorders that are often difficult to distinguish from other causes of elevated blood cell counts. Assays that could reliably detect clonal hematopoiesis would therefore be extremely valuable for diagnosis. We previously reported 3 X-chromosome transcription-based clonality assays (TCAs) involving the G6PD, IDS, and MPP1 genes, which together were informative in about 65% of female subjects. To increase our ability to detect clonality, we developed simple TCA for detecting the transcripts of 2 additional X-chromosome genes: Bruton tyrosine kinase (BTK) and 4-and-a-half LIM domain 1 (FHL1). The combination of TCA established the presence or absence of clonal hematopoiesis in about 90% of female subjects. We show that both genes are subject to X-chromosome inactivation and are polymorphic in all major US ethnic groups. The 5 TCAs were used to examine clonality in 46 female patients along with assays for erythropoietin-independent erythroid colonies (EECs) and granulocyte PRV-1 mRNA levels to discriminate polycythemias and thrombocytoses. Of these, all 19 patients with familial polycythemia or thrombocytosis had polyclonal hematopoiesis, whereas 22 of 26 patients with clinical evidence of myeloproliferative disorder and 1 patient with clinically obscure polycythemia were clonal. Interestingly, interferon alpha therapy in 2 patients with PV was associated with reversion of clonal to polyclonal hematopoiesis. EECs were observed in 14 of 14 patients with PV and 4 of 12 with ET, and increased granulocyte PRV-1 mRNA levels were found in 9 of 13 patients with PV and 2 of 12 with ET. Thus, these novel clonality assays are useful in the diagnosis and follow-up of polycythemic conditions and disorders with increased platelet levels.

Adolescent↗
PubMed2002

The oncogenic protein kinase Tpl-2/Cot contributes to Epstein-Barr virus-encoded latent infection membrane protein 1-induced NF-kappaB signaling downstream of TRAF2.

The Epstein-Barr virus-encoded latent infection membrane protein 1 (LMP1) is a pleiotropic protein, the activities of which include effects on cell transformation and phenotype, growth, and survival. The ability of LMP1 to mediate at least some of these phenomena could be attributed to the activation of the transcription factor NF-kappaB. LMP1 promotes NF-kappaB activation through the recruitment of the adapter protein TRAF2 and the formation of a dynamic multiprotein complex that includes the NF-kappaB kinase, the IkappaB kinases, and their downstream targets, IkappaBs and p105. In this study, we have identified the oncogenic kinase Tpl-2/Cot as a novel component of LMP1-induced NF-kappaB signaling. We show that Tpl-2 is expressed in primary biopsies from patients with nasopharyngeal carcinoma and Hodgkin's disease, where LMP1 is also found. Inducible expression of LMP1 promotes the activation of Tpl-2, and a catalytically inactive Tpl-2 mutant suppresses LMP1-induced NF-kappaB signaling. In colocalization and coimmunoprecipitation experiments, Tpl-2 and TRAF2 were found to interact with Tpl-2 functioning downstream of TRAF2. Consistent with this observation, catalytically inactive Tpl-2 also blocked CD40-mediated NF-kappaB activation, which largely depends on TRAF2. The ability of Tpl-2 to influence LMP1-induced NF-kappaB occurs through modulation of both IkappaBalpha and p105 functions. Furthermore, Tpl-2 was found to influence the expression of angiogenic mediators, such as COX-2 in LMP1-transfected cells. These data identify Tpl-2 as a component of LMP1 signaling downstream of TRAF2 and as a modulator of LMP1-mediated effects.

3T3 Cells↗
PubMed2001

A critical role of the PINCH-integrin-linked kinase interaction in the regulation of cell shape change and migration.

The interaction of cells with extracellular matrix recruits multiple proteins to cell-matrix contact sites (e.g. focal and fibrillar adhesions), which connect the extracellular matrix to the actin cytoskeleton and regulate cell shape change, migration, and other cellular processes. We previously identified PINCH, an adaptor protein comprising primarily five LIM domains, as a binding protein for integrin-linked kinase (ILK). In this study, we show that PINCH co-localizes with ILK in both focal adhesions and fibrillar adhesions. Furthermore, we have investigated the molecular basis underlying the targeting of PINCH to the cell-matrix contact sites and the functional significance of the PINCH-ILK interaction. We have found that the N-terminal LIM1 domain, which mediates the ILK binding, is required for the targeting of PINCH to the cell-matrix contact sites. The C-terminal LIM domains, although not absolutely required, play an important regulatory role in the localization of PINCH to cell-matrix contact sites. Inhibition of the PINCH-ILK interaction, either by overexpression of a PINCH N-terminal fragment containing the ILK-binding LIM1 domain or by overexpression of an ILK N-terminal fragment containing the PINCH-binding ankyrin domain, retarded cell spreading, and reduced cell motility. These results suggest that PINCH, through its interaction with ILK, is crucially involved in the regulation of cell shape change and motility.

Binding Sites↗
PubMed2006

Thymosin beta4 triggers an epithelial-mesenchymal transition in colorectal carcinoma by upregulating integrin-linked kinase.

The epithelial-mesenchymal transition (EMT) is crucial for the invasion and metastasis of many epithelial tumors including colorectal carcinoma (CRC). In the present study, a scattering and fibroblastic morphology with reduced intercellular contacts was found in the SW480 colon cancer cells overexpressing the gene encoding thymosin beta4 (Tbeta4), which was accompanied by a loss of E-cadherin as well as a cytosolic accumulation of beta-catenin, two most prominent markers of EMT. Whereas E-cadherin downregulation was likely to be accounted by a ZEB1-mediated transcriptional repression, the accumulation of beta-catenin was a result of glycogen synthase kinase-3beta inactivation mediated by integrin-linked kinase (ILK) and/or its downstream effector, Akt. Intriguingly, ILK upregulation in Tbeta4-overexpressing SW480 cells seemed to be attributed mainly to a stabilization of this kinase by complexing with particularly interesting new Cys-His protein (PINCH) more efficiently. In the meantime, a strong correlation between the expression levels of Tbeta4, ILK and E-cadherin in CRC patients was also revealed by immunohistochemical analysis. Taken together, these data suggest a novel role of Tbeta4 in promoting CRC progression by inducing an EMT in tumor cells via upregulating ILK and consequentially its signal transduction.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Phenytoin treatment reduces atherosclerosis in mice through mechanisms independent of plasma HDL-cholesterol concentration.

Phenytoin (PHT) increases high density lipoprotein cholesterol (HDL-C) and reduces coronary artery disease mortality in humans. We report the results of PHT treatment on atherosclerosis susceptibility and lipid profile in four different types of mouse: control C57BL/6 mice and cholesteryl ester transfer protein transgenic mice as models of fatty streak, and LDL receptor-deficient mice and apolipoprotein E-deficient mice as models of mature atherosclerosis. Each mouse type was fed an appropriate diet to induce atherosclerosis and prevent liver toxicity. PHT treatment demonstrated a protective effect in all models. Reduction in aortic atherosclerotic area by PHT treatment was more evident in early atherosclerosis (2.3-fold) than in mature atherosclerosis (decreases of 40 and 23%, respectively, but only in mice in the upper 50% percentile of plasma PHT concentration). Atherosclerosis prevention was not concomitant with a consistent increase in HDL-C or any other protective change in the lipid profile. Different analyses of potential antiatherogenic HDL functions did not provide additional information. Microarray liver gene expression analyses identified a potential atheroprotective mechanism characterized by decreased expression of syndecan-4, RhoA2, double LIM protein-1, zeta-chain-associated protein kinase-70 and interleukin 6 receptor-alpha. However, to demonstrate that these changes are part of a PHT-antiatherogenic effect, they will need to be found also in arteries, maintained at protein level and proved to be causal rather than reactive.

Analysis of Variance↗
PubMed2006

Cyclic strain promotes shuttling of PYK2/Hic-5 complex from focal contacts in osteoblast-like cells.

We showed that cyclic strain (CS) of osteoblastic cells induced tyrosine phosphorylation of two homologous tyrosine kinases FAK and PYK2, and of two homologous adaptor proteins paxillin and Hic5, with similar kinetics. Immunostaining showed that all four proteins were localized to focal contacts in controls. In contrast, the dynamics of their subcellular localization observed after CS differed. While FAK and paxillin remained at the focal contact, Hic-5 and PYK2 translocated outside ventral focal contacts as early as 30 min after CS and were sequestered by the cytoskeleton. Co-immunoprecipitation showed that the association of PYK2/Hic-5 and PYK2/FAK increased with time after strain while that of paxillin and Hic-5 decreased. Altogether these results suggested that CS regulates focal contact activity in osteoblasts by modulating PYK2-containing complexes in particular by shuttling out of the focal contact the adaptor Hic-5 and favoring the anchorage of FAK within contacts.

Animals↗
PubMed2003

Microarray analysis of murine palatogenesis: temporal expression of genes during normal palate development.

The mammalian face is assembled in utero in a series of complex and interdependent molecular, cell and tissue processes. The orofacial complex appears to be exquisitely sensitive to genetic and environmental influence and this explains why clefts of the lip and palate are the most common congenital anomaly in humans (one in 700 live births). In this study, microarray technology was used to identify genes that may play pivotal roles in normal murine palatogenesis. mRNA was isolated from murine embryonic palatal shelves oriented vertically (before elevation), horizontally (following elevation, before contact), and following fusion. Changes in gene expression between the three different stages were analyzed with GeneChip microarrays. A number of genes were upregulated or downregulated, and large changes were seen in the expression of loricrin, glutamate decarboxylase, gamma-amino butyric acid type A receptor beta3 subunit, frizzled, Wnt-5a, metallothionein, annexin VIII, LIM proteins, Sox1, plakophilin1, cathepsin K and creatine kinase. In this paper, the changes in genetic profile of the developing murine palate are presented, and the possible role individual genes/proteins may play during normal palate development are discussed. Candidate genes with a putative role in cleft palate are also highlighted.

Animals↗
PubMed2003

Chondrogenesis induced by actin cytoskeleton disruption is regulated via protein kinase C-dependent p38 mitogen-activated protein kinase signaling.

Disruption of the actin cytoskeleton in subconfluent mesenchymal cells induces chondrogenic differentiation via protein kinase C (PKC) alpha signaling. In this study, we investigated the role of p38 mitogen-activated protein (MAP) kinase in the chondrogenic differentiation of mesenchymal cells that is induced by depolymerization of the actin cytoskeleton. Treatment of mesenchymal cells derived from chick embryonic limb buds with cytochalasin D (CD) disrupted the actin cytoskeleton with concomitant chondrogenic differentiation. The chondrogenesis was accompanied by an increase in p38 MAP kinase activity and inhibition of p38 MAP kinase with SB203580 blocked chondrogenesis. Together these results suggest an essential role for p38 MAP kinase in chondrogenesis. In addition, inhibition of p38 MAP kinase did not alter CD-induced increased expression and activity of PKC alpha, whereas down-regulation of PKC by prolonged exposure of cells to phorbol ester inhibited CD-induced p38 MAP kinase activation. Our results therefore suggest that PKC is involved in the regulation of chondrogenesis induced by disruption of the actin cytoskeleton via a p38 MAP kinase signaling pathway.

Actins↗
PubMed1998

A conserved negative regulatory region in alphaPAK: inhibition of PAK kinases reveals their morphological roles downstream of Cdc42 and Rac1.

AlphaPAK in a constitutively active form can exert morphological effects (E. Manser, H.-Y. Huang, T.-H. Loo, X.-Q. Chen, J.-M. Dong, T. Leung, and L. Lim, Mol. Cell. Biol. 17:1129-1143, 1997) resembling those of Cdc42G12V. PAK family kinases, conserved from yeasts to humans, are directly activated by Cdc42 or Rac1 through interaction with a conserved N-terminal motif (corresponding to residues 71 to 137 in alphaPAK). alphaPAK mutants with substitutions in this motif that resulted in severely reduced Cdc42 binding can be recruited normally to Cdc42G12V-driven focal complexes. Mutation of residues in the C-terminal portion of the motif (residues 101 to 137), though not affecting Cdc42 binding, produced a constitutively active kinase, suggesting this to be a negative regulatory region. Indeed, a 67-residue polypeptide encoding alphaPAK83-149 potently inhibited GTPgammaS-bound Cdc42-mediated kinase activation of both alphaPAK and betaPAK. Coexpression of this PAK inhibitor with Cdc42G12V prevented the formation of peripheral actin microspikes and associated loss of stress fibers normally induced by the p21. Coexpression of PAK inhibitor with Rac1G12V also prevented loss of stress fibers but not ruffling induced by the p21. Coexpression of alphaPAK83-149 completely blocked the phenotypic effects of hyperactive alphaPAKL107F in promoting dissolution of focal adhesions and actin stress fibers. These results, coupled with previous observations with constitutively active PAK, demonstrate that these kinases play an important role downstream of Cdc42 and Rac1 in cytoskeletal reorganization.

Actins↗
PubMed1998

Leupaxin is a novel LIM domain protein that forms a complex with PYK2.

We have identified a novel cytoplasmic protein, leupaxin, that is preferentially expressed in hematopoietic cells and is most homologous to the focal adhesion protein, paxillin. Leupaxin possesses two types of protein interaction domains. There are four carboxyl-terminal LIM domains in leupaxin that share 70% amino acid identity and 80% similarity with those in paxillin. Paxillin LIM domains mediate localization to focal contacts. In the amino-terminal region of leupaxin there are three short stretches of approximately 13 amino acids that share 70-90% similarity with paxillin LD motifs. Paxillin LD motifs have been implicated in focal adhesion kinase (FAK) and vinculin binding resulting in the localization of FAK to focal adhesions. Leupaxin is expressed in cell types, such as macrophage, that lack FAK. We demonstrate here that leupaxin associates with a second FAK family member, PYK2. As leupaxin and PYK2 are both preferentially expressed in leukocytes they may therefore form a cell type-specific signaling complex. We also demonstrate that leupaxin is a substrate for a tyrosine kinase in lymphoid cells and thus may function in and be regulated by tyrosine kinase activity. Leupaxin is thus a phosphotyrosine protein with LD and LIM binding motifs most homologous to paxillin that may assemble and regulate PYK2 signaling complexes in leukocytes.

Amino Acid Sequence↗