Biochemical and molecular characterization of the chicken cysteine-rich protein, a developmentally regulated LIM-domain protein that is associated with the actin cytoskeleton

Integration of Non-targeted Proteomics Mass Spectrometry with Machine Learning for Screening Cooked Beef Adulterated Samples

The degradation of ingredients in heat-processed meat products makes their authentication challenging. In this study, protein profiles of raw beef, chicken, duck, pork, and binary simulated adulterated beef samples (chicken-beef, duck-beef, and pork-beef) and their heat-processed samples were obtained by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Heat-stable characteristic proteins were found by screening the overlapping characteristic protein ion peaks of the raw and corresponding heat-processed samples, which were discovered by partial least-squares discriminant analysis. Based on the 36 heat-stable characteristic proteins, qualitative classification for the raw and heat-processed meats was achieved by extreme gradient boosting. Moreover, quantitative analysis via partial least squares regression was applied to determine the adulteration ratio of the simulated adulterated beef samples. The validity of the approach was confirmed by a blind test with the mean accuracy of 97.4%. The limit of detection and limit of quantification of this method were determined to be 5 and 8%, respectively, showing its practical aspect for the beef authentication.

Perfil lipídico da carne de frangos de corte de diferentes cruzamentos criados em sistema alternativo

RESUMO Objetivou-se avaliar o perfil lipídico da carne de frangos de diferentes genótipos. O delineamento foi inteiramente ao acaso (DIC), disposto em esquema fatorial (5x2), sendo cinco genótipos (New Hampshire ˗ NHS; Gigante Negra de Jersey ˗ GNJ; Índio Gigante ˗ IG; cruzamento entre as raças IG e NHS ˗ IG x NHS; e entre as raças IG e GNJ ˗ IG x GNJ) e dois sexos, com cinco repetições, sendo cada uma representada por três aves, totalizando 150 aves, abatidas aos 105 dias. As análises de perfil lipídico foram realizadas no peito e na coxa. Foram calculadas as estimativas das atividades enzimáticas, os índices de aterogenicidade e de trombogenicidade. Os genótipos IG e IG x NHS apresentaram maiores teores de ácido araquidônico e DHA. Foram observados maiores teores de ácidos graxos saturados e monoinsaturados no peito para os genótipos IG x NHS e NHS, respectivamente. Maiores médias de ácidos graxos poli-insaturados e ômega 3 foram observadas para os genótipos IG e IG x NHS. O genótipo IG x NHS e as fêmeas apresentaram melhores características de qualidade de carne, por oferecerem uma maior fonte de ômega 3.

Building Blocks of Functioning Brain: Cytoskeletal Dynamics in Neuronal Development

Neural connectivity requires proper polarization of neurons, guidance to appropriate target locations, and establishment of synaptic connections. From when neurons are born to when they finally reach their synaptic partners, neurons undergo constant rearrangment of the cytoskeleton to achieve appropriate shape and polarity. Of particular importance to neuronal guidance to target locations is the growth cone at the tip of the axon. Growth-cone steering is also dictated by the underlying cytoskeleton. All these changes require spatiotemporal control of the cytoskeletal machinery. This review summarizes the proteins that are involved in modulating the actin and microtubule cytoskeleton during the various stages of neuronal development.

The LIM domain of zyxin is sufficient for force-induced accumulation of zyxin during cell migration

Cellular responses to mechanical perturbation are vital to cell physiology. In particular, migrating cells have been shown to sense substrate stiffness and alter cell morphology and speed. Zyxin is a focal adhesion protein that responds to external mechanical forces; however, the mechanisms of zyxin recruitment at force-bearing sites are unknown. Using force-sensing microfabricated substrates, we simultaneously measured traction force and zyxin recruitment at force-bearing sites. GFP-tagged zyxin accumulates at force-bearing sites at the leading edge, but not at the trailing edge, of migrating epithelial cells. Zyxin recruitment at force-bearing sites depends on Rho-kinase and myosin II activation, suggesting that zyxin responds not only to the externally applied force, as previously shown, but also to the internally generated actin-myosin force. Zyxin in turn recruits vasodilator-stimulated phosphoprotein, a regulator of actin assembly, to force-bearing sites. To dissect the domains of zyxin that are essential for this unique force-dependent accumulation, we generated two zyxin truncation mutants: one lacking the LIM domain (ΔLIM) and one containing only the LIM domain with all three LIM motifs (LIM). GFP-tagged ΔLIM does not localize to the force-bearing sites, but GFP-tagged zyxin LIM-domain is sufficient for the recruitment to and dynamics at force-bearing focal adhesions. Furthermore, one or two LIM motifs are not sufficient for force-dependent accumulation, suggesting that all three LIM motifs are required. Therefore, the LIM domain of zyxin recruits zyxin to force-bearing sites at the leading edge of migrating cells.

[The cytoskeletal protein zyxin--a universal regulator of cell adhesion and gene expression]

The attachment of a cell to an extracellular matrix or the surface of another cells affects not only the cell motility, but also gene expression. In view of this, an important problem is to establish the molecular mechanisms of signal transduction from the receptors of cell adhesion to the nucleus, in particular, to identify and investigate the protein transducers of these signals. One of these transducers, the LIM domain protein zyxin, is predominantly localized at the sites of cell adhesion, where it participates in the assembly of actin filaments. Owing to its location near the inner surface of the membrane, zyxin can interact with the transmembrane receptors of some signaling cascades and affect the signal transduction from the extracellular ligands of these receptors. Furthermore, under particular conditions, zyxin moves from the sites of cell contacts to the nucleus, where it directly participates in the regulation of gene expression. Of particular interest is the function of zyxin as a possible coordinator of gene expression and morphogenetic movements in embryogenesis. The published data discussed in the present review indicate the important role of zyxin in transmitting information from the regions of cell contacts to the genetic apparatus of the cell.

Loss of the serum response factor cofactor, cysteine-rich protein 1, attenuates neointima formation in the mouse

OBJECTIVE

Cysteine-rich protein (CRP) 1 and 2 are cytoskeletal lin-11 isl-1 mec-3 (LIM)-domain proteins thought to be critical for smooth muscle differentiation. Loss of murine CRP2 does not overtly affect smooth muscle differentiation or vascular function but does exacerbate neointima formation in response to vascular injury. Because CRPs 1 and 2 are coexpressed in the vasculature, we hypothesize that CRPs 1 and 2 act redundantly in smooth muscle differentiation.

METHODS AND RESULTS

We generated Csrp1 (gene name for CRP1) null mice by genetic ablation of the Csrp1 gene and found that mice lacking CRP1 are viable and fertile. Smooth muscle-containing tissues from Csrp1-null mice are morphologically indistinguishable from wild-type mice and have normal contractile properties. Mice lacking CRPs 1 and 2 are viable and fertile, ruling out functional redundancy between these 2 highly related proteins as a cause for the lack of an overt phenotype in the Csrp1-null mice. Csrp1-null mice challenged by wire-induced arterial injury display reduced neointima formation, opposite to that seen in Csrp2-null mice, whereas Csrp1/Csrp2 double-null mice produce a wild-type response.

CONCLUSIONS

Smooth muscle CRPs are not essential for normal smooth muscle differentiation during development, but may act antagonistically to modulate the smooth muscle response to pathophysiological stress.

Glycine-rich region regulates cysteine-rich protein 1 binding to actin cytoskeleton

Cysteine-rich protein 1 (CRP1) has a unique structure with two well separated LIM domains, each followed by a glycine-rich region. Although CRP1 has been shown to interact with actin-binding proteins and actin filaments, the mechanism regulating localization to the actin cytoskeleton in cells is not clear. Experiments using truncated forms showed that the first LIM domain and glycine-rich region are necessary for CRP1 bundling of actin filaments and localization to the actin cytoskeleton. Furthermore, domain swapping experiments replacing the first glycine-rich region with the second resulted in the loss of CRP1 bundling activity and localization to the actin cytoskeleton, identifying seven critical amino acid residues. These results highlight the importance of the first glycine-rich region for CRP1 bundling activity and localization to the actin cytoskeleton. In addition, this work identifies the first LIM domain and glycine-rich region as a distinct actin filament bundling module.

Transforming growth factor beta up-regulates cysteine-rich protein 2 in vascular smooth muscle cells via activating transcription factor 2

CRP2 (cysteine-rich protein) is a vascular smooth muscle cell (VSMC)-expressed LIM-only protein. CRP2 associates with the actin cytoskeleton and interacts with transcription factors in the nucleus to mediate smooth muscle cell gene expression. Using Csrp2 (gene symbol of the mouse CRP2 gene)-deficient mice, we previously demonstrated that an absence of CRP2 enhances VSMC migration and increases neointima formation following arterial injury. Despite its importance in vascular injury, the molecular mechanisms controlling CRP2 expression in VSMC are largely unknown. Transforming growth factor beta (TGFbeta), a key factor present in the vessel wall in the early phases of arterial response to injury, plays an important role in modulating lesion formation. Because both CRP2 and TGFbeta are mediators of VSMC responses, we examined the possibility that TGFbeta might regulate CRP2 expression. TGFbeta significantly induced CRP2 mRNA and protein expression in VSMCs. Promoter analysis identified a conserved cAMP-responsive element (CRE)-like site (TAACGTCA) in the Csrp2 promoter that was critical for basal promoter activity and response to TGFbeta. Gel mobility shift assays revealed that mainly ATF2 bound to this CRE-like element, and mutation of the CRE sequences abolished binding. TGFbeta enhanced the activation of ATF2, leading to increased phospho-ATF2 levels within the DNA-protein complexes. Furthermore, ATF2-transactivated Csrp2 promoter activity and TGFbeta enhanced this activation. In addition, a phosphorylation-negative ATF2 mutant construct decreased basal and TGFbeta-mediated Csrp2 promoter activity. Our results show for the first time in VSMC that TGFbeta activates ATF2 phosphorylation and Csrp2 gene expression via a CRE promoter element.

Cytoskeleton-interacting LIM-domain protein CRP1 suppresses cell proliferation and protects from stress-induced cell death

Members of the cysteine-rich protein (CRP) family are actin cytoskeleton-interacting LIM-domain proteins known to act in muscle cell differentiation. We have earlier found that CRP1, a founding member of this family, is transcriptionally induced by UV radiation in human diploid fibroblasts [M. Gentile, L. Latonen, M. Laiho, Cell cycle arrest and apoptosis provoked by UV radiation-induced DNA damage are transcriptionally highly divergent responses, Nucleic Acids Res. 31 (2003) 4779-4790]. Here we show that CRP1 is induced by growth-inhibitory signals, such as increased cellular density, and cytotoxic stress induced by UV radiation or staurosporine. We found that high levels of CRP1 correlate with differentiation-associated morphology towards the myofibroblast lineage and that expression of ectopic CRP1 suppresses cell proliferation. Following UV- and staurosporine-induced stresses, expression of CRP1 provides a survival advantage evidenced by decreased cellular death and increased cellular metabolic activity and attachment. Our studies identify that CRP1 is a novel stress response factor, and provide evidence for its growth-inhibitory and cytoprotective functions.

Csrp1 regulates dynamic cell movements of the mesendoderm and cardiac mesoderm through interactions with Dishevelled and Diversin

Zebrafish Csrp1 is a member of the cysteine- and glycine-rich protein (CSRP) family and is expressed in the mesendoderm and its derivatives. Csrp1 interacts with Dishevelled 2 (Dvl2) and Diversin (Div), which control cell morphology and other dynamic cell behaviors via the noncanonical Wnt and JNK pathways. When csrp1 message is knocked down, abnormal convergent extension cell movement is induced, resulting in severe deformities in midline structures. In addition, cardiac bifida is induced as a consequence of defects in cardiac mesoderm cell migration. Our data highlight Csrp1 as a key molecule of the noncanonical Wnt pathway, which orchestrates cell behaviors during dynamic morphogenetic movements of tissues and organs.

Cysteine-rich protein 1 (CRP1) regulates actin filament bundling

BACKGROUND

Cysteine-rich protein 1 (CRP1) is a LIM domain containing protein localized to the nucleus and the actin cytoskeleton. CRP1 has been demonstrated to bind the actin-bundling protein alpha-actinin and proposed to modulate the actin cytoskeleton; however, specific regulatory mechanisms have not been identified.

RESULTS

CRP1 expression increased actin bundling in rat embryonic fibroblasts. Although CRP1 did not affect the bundling activity of alpha-actinin, CRP1 was found to stabilize the interaction of alpha-actinin with actin bundles and to directly bundle actin microfilaments. Using confocal and photobleaching fluorescence resonance energy transfer (FRET) microscopy, we demonstrate that there are two populations of CRP1 localized along actin stress fibers, one associated through interaction with alpha-actinin and one that appears to bind the actin filaments directly. Consistent with a role in regulating actin filament cross-linking, CRP1 also localized to the membrane ruffles of spreading and PDGF treated fibroblasts.

CONCLUSION

CRP1 regulates actin filament bundling by directly cross-linking actin filaments and stabilizing the interaction of alpha-actinin with actin filament bundles.

Increased neointima formation in cysteine-rich protein 2-deficient mice in response to vascular injury

In response to arterial injury, medial vascular smooth muscle cells (VSMCs) proliferate and migrate into the intima, contributing to the development of occlusive vascular disease. The LIM protein cysteine-rich protein (CRP) 2 associates with the actin cytoskeleton and may maintain the cytoarchitecture. CRP2 also interacts with transcription factors in the nucleus to mediate SMC gene expression. To test the hypothesis that CRP2 may be an important regulator of vascular development or function we generated Csrp2 (gene symbol of the mouse CRP2 gene)-deficient (Csrp2(-/-)) mice by targeted mutation. Csrp2(-/-) mice did not have any gross vascular defects or altered expression levels of SM alpha-actin, SM22alpha, or calponin. Following femoral artery injury, CRP2 expression persisted in the vessel wall at 4 days and then decreased by 14 days. Intimal thickening was enhanced 3.4-fold in Csrp2(-/-) compared with wild-type (WT) mice 14 days following injury. Cellular proliferation was similar between WT and Csrp2(-/-) VSMC both in vivo and in vitro. Interestingly, Csrp2(-/-) VSMC migrated more rapidly in response to PDGF-BB and had increased Rac1 activation. Our data demonstrate that CRP2 is not required for vascular development. However, an absence of CRP2 enhanced VSMC migration and increased neointima formation following arterial injury.

Two major branches of anti-cadmium defense in the mouse: MTF-1/metallothioneins and glutathione

Metal-responsive transcription factor 1 (MTF-1) regulates expression of its target genes in response to various stress conditions, notably heavy metal load, via binding to metal response elements (MREs) in the respective enhancer/promoter regions. Furthermore, it serves a vital function in embryonic liver development. However, targeted deletion of Mtf1 in the liver after birth is no longer lethal. For this study, Mtf1 conditional knockout mice and control littermates were both mock- or cadmium-treated and liver-specific transcription was analyzed. Besides the well-characterized metallothionein genes, several new MTF-1 target genes with MRE motifs in the promoter region emerged. MTF-1 is required for the basal expression of selenoprotein W, muscle 1 gene (Sepw1) that encodes a glutathione-binding and putative antioxidant protein, supporting a role of MTF-1 in the oxidative stress response. Furthermore, MTF-1 mediates the cadmium-induced expression of N-myc downstream regulated gene 1 (Ndrg1), which is induced by several stress conditions and is overexpressed in many cancers. MTF-1 is also involved in the cadmium response of cysteine- and glycine-rich protein 1 gene (Csrp1), which is implicated in cytoskeletal organization. In contrast, MTF-1 represses the basal expression of Slc39a10, a putative zinc transporter. In a pathway independent of MTF-1, cadmium also induced the transcription of genes involved in the synthesis and regeneration of glutathione, a cadmium-binding antioxidant. These data provide strong evidence for two major branches of cellular anti-cadmium defense, one via MTF-1 and its target genes, notably metallothioneins, the other via glutathione, with an apparent overlap in selenoprotein W.

NRIP, a Novel Nuclear Receptor Interaction Protein, Enhances the Transcriptional Activity of Nuclear Receptors

Transcriptional regulation by members of the nuclear hormone receptor superfamily is a modular process requiring the mediation of distinct subclasses of coregulators. In this study, we isolated a novel WD40 repeat-containing gene, human nuclear receptor interaction protein (NRIP). We found NRIP interacts with either androgen or glucocorticoid receptors from in vitro and in vivo pulldown assays. Subsequently, transient transfection and luciferase activity assays suggested that NRIP was a ligand-dependent coactivator of steroid receptors (androgen and glucocorticoid) in distinct promoters. To further clarify the function of NRIP, we found an RNA interference-3-targeted NRIP gene sequence (5'-GATGATACAGCACGAGAAC-3') that could efficiently and specifically knock down endogenous and exogenous NRIP gene expression and that significantly diminished cell proliferation in prostate (LNCaP) and cervical (C33A) cells. Therefore, NRIP may play a role in enhancing the transcriptional activity of nuclear receptors and may be a critical target for developing therapeutic agents against nuclear receptor-mediated progression of prostate and cervical cancers.

A Lim protein involved in the progression of cytokinesis and regulation of the mitotic spindle

DdLimE regulates cell motility and cytokinesis in Dictyostelium. To specify its function, we generated knock-out mutants and analyzed mitosis by marking the mitotic apparatus with GFP-alpha-tubulin. Characteristic of DdLimE-null cells is a late reversal of cytokinesis caused by backward movement of the incipient daughter cells. This process of "retro-cytokinesis" is accompanied by a delay in disassembly of the mitotic spindle. The length of interphase microtubules is increased and their depolymerization at prophase is impaired. These data indicate that DdLimE links the cortical actin network, where it is located, to the microtubule system, whose dynamics it regulates.

Interstitial deletions including chromosome 3 common eliminated region 1 (C3CER1) prevail in human solid tumors from 10 different tissues

A human chromosomal segment regularly lost during tumor formation of microcell hybrids in SCID mice has been mapped to 3p21.3. This segment, called chromosome 3 common eliminated region 1 (C3CER1, also referred to as CER1), may harbor multiple tumor-suppressor genes. Because it was found that similar regions were eliminated in an inter- and intraspecies system and in two tumor types (mouse fibrosarcoma and human renal cell carcinoma), we hypothesized that the importance of C3CER1 would transgress tissue specificity, that is, it could occur in tumors derived from multiple tissues. To evaluate the loss of C3CER1 in various human tumor types, we conducted loss of heterozygosity (LOH) analysis of 576 human solid tumors from 10 different tissues and compared the frequency of deletion in the C3CER1 area to that in two other regions on 3p: the FHIT/FRA3B region, at 3p14.2, and the VHL region, at 3p25.3. Deletions were detected in the C3CER1 region in 83% of informative tumors. Half (47%) the LOH-positive tumors showed LOH at all informative markers, indicating a large deletion. The other half (53%) had a discontinuous LOH pattern, suggesting interstitial deletions or breakpoints. The proportion of tumors with C3CER1 deletions was high in all tumor types investigated, ranging from 70% to 94%, except for the soft-tissue sarcomas (40%). In the VHL and FHIT regions, deletions were observed in 73% and 43%, respectively, of the tumors. Of the three 3p regions analyzed, the highest deletion frequency was observed in the C3CER1 region. Furthermore, we demonstrated that the interstitial deletions including C3CER1 prevail over 3p14.2-pter losses in solid tumors.

Identification of a CArG-independent region of the cysteine-rich protein 2 promoter that directs expression in the developing vasculature

Cysteine-rich protein (CRP)2 is a member of the LIM-only CRP family that is expressed in vascular smooth muscle cells (VSMC). To gain insight into the transcription of CSRP2 (gene name for CRP2) in VSMC, we analyzed the 5'-flanking sequence of the CSRP2 gene. We showed previously that 4,855 bp of the 5'-flanking sequence of the CSRP2 gene directed lacZ reporter gene expression, primarily in the VSMC of transgenic mice. To further define the regulatory sequences important for CSRP2 expression in VSMC, a series of promoter constructs containing deletions of the 5'-flanking sequence upstream of a nuclear-localized lacZ reporter gene were generated and analyzed. Similar to that observed in the -4855CSRP2-lacZ mice, beta-galactosidase reporter activity was detected in the developing great vessels, aorta, intersegmental arteries, umbilical vessels, endocardial cushions, and neural tube in the -3513-, -2663-, -795-, and -664CSRP2-lacZ lines. However, an internal deletion of bp -573 to -550 abolished the vascular, but not the neural tube, staining. Interestingly, no CArG box [CC(A/T)6GG] was present in the -795-bp fragment. Cotransfection experiments showed that dominant-negative serum response factor (SRF) did not repress CSRP2 promoter activity, which was different from the repressive effect of dominant-negative SRF on the SM22 alpha promoter. Our data suggest the presence of a VSMC-specific element(s) within bp -573 to -550 of the CSRP2 5'-flanking sequence; however, in contrast to many other smooth muscle genes, transcriptional regulation of the CSRP2 gene is not dependent on SRF.

Combinatorial control of smooth muscle-specific gene expression

Alterations in the differentiated state of vascular smooth muscle cells (SMCs) are known to play a key role in vascular diseases, yet the mechanisms controlling SMC differentiation are still poorly understand. In this review, we discuss our present knowledge of control of SMC differentiation at the transcriptional level, pointing out some common themes, important paradigms, and unresolved issues in SMC-specific gene regulation. We focus primarily on the serum response factor-CArG box-dependent pathway, because it has been shown to play a critical role in regulation of multiple SMC marker genes. However, we also highlight several other important regulatory elements, such as a transforming growth factor beta control element, E-boxes, and MCAT motifs. We present evidence in support of the notion that SMC-specific gene regulation is not controlled by a few SMC-specific transcription factors but rather by complex combinatorial interactions between multiple general and tissue-specific proteins. Finally, we discuss the implications of chromatin remodeling on SMC differentiation.

Molecular and phylogenetic characterization of Zyx102, a Drosophila orthologue of the zyxin family that interacts with Drosophila Enabled

Adherens junctions, which are cadherin-mediated junctions between cells, and focal adhesions, which are integrin-mediated junctions between cells and the extracellular matrix, are protein complexes that link the actin cytoskeleton to the plasma membrane and, in turn, to the extracellular environment. Zyxin is a LIM domain protein that is found in vertebrate adherens junctions and focal adhesions. Zyxin's molecular architecture and binding partner repertoire suggest roles in actin assembly and dynamics, cell motility, and nuclear-cytoplasmic communication. In order to study the function of zyxin in development, we have identified a zyxin orthologue in Drosophila melanogaster that we have termed Zyx102. Like its vertebrate counterparts, Zyx102 displays three carboxy-terminal LIM domains, a potential nuclear export signal, and three proline-rich motifs, one of which matches the consensus for mediating an interaction with Ena/VASP (Drosophila Enabled/Vasodilator-stimulated phosphoprotein) proteins. Here we show that Zyx102 and Enabled (Ena), the Drosophila member of the Ena/VASP family, can interact specifically in vitro and that this interaction does not occur when a particular mutant form of Ena, encoded by the lethal ena210 allele, is used. Lastly, we show that the zyx102 gene and Drosophila Ena are co-expressed during oogenesis and early embryogenesis, indicating that the two proteins may be able to interact during the development of the Drosophila egg chamber and early embryo.

Identification of genes that are downregulated in the absence of the POU domain transcription factor pou3f1 (Oct-6, Tst-1, SCIP) in sciatic nerve

Despite the importance of myelinating Schwann cells in health and disease, little is known about the genetic mechanisms underlying their development. The POU domain transcription factor pou3f1 (Tst-1, SCIP, Oct-6) is required for the normal differentiation of myelinating Schwann cells, but its precise role requires identification of the genes that it regulates. Here we report the isolation of six genes whose expression is reduced in the absence of pou3f1. Only one of these genes, the fatty acid transport protein P2, was known previously to be expressed in Schwann cells. The LIM domain proteins cysteine-rich protein-1 (CRP1) and CRP2 are expressed in sciatic nerve and induced by forskolin in cultured Schwann cells, but only CRP2 requires pou3f1 for normal expression. pou3f1 appears to require the claw paw gene product for activation of at least some of its downstream effector genes. Expression of the novel Schwann cell genes after nerve injury suggests that they are myelin related. One of the genes, tramdorin1, encodes a novel amino acid transport protein that is localized to paranodes and incisures. Our results suggest that pou3f1 functions to activate gene expression in the differentiation of myelinating Schwann cells.

Identification of genes that are downregulated in the absence of the POU domain transcription factor pou3f1 (Oct-6, Tst-1, SCIP) in sciatic nerve

Despite the importance of myelinating Schwann cells in health and disease, little is known about the genetic mechanisms underlying their development. The POU domain transcription factor pou3f1 (Tst-1, SCIP, Oct-6) is required for the normal differentiation of myelinating Schwann cells, but its precise role requires identification of the genes that it regulates. Here we report the isolation of six genes whose expression is reduced in the absence of pou3f1. Only one of these genes, the fatty acid transport protein P2, was known previously to be expressed in Schwann cells. The LIM domain proteins cysteine-rich protein-1 (CRP1) and CRP2 are expressed in sciatic nerve and induced by forskolin in cultured Schwann cells, but only CRP2 requires pou3f1 for normal expression. pou3f1 appears to require the claw paw gene product for activation of at least some of its downstream effector genes. Expression of the novel Schwann cell genes after nerve injury suggests that they are myelin related. One of the genes, tramdorin1, encodes a novel amino acid transport protein that is localized to paranodes and incisures. Our results suggest that pou3f1 functions to activate gene expression in the differentiation of myelinating Schwann cells.

The GLH proteins, Caenorhabditis elegans P granule components, associate with CSN-5 and KGB-1, proteins necessary for fertility, and with ZYX-1, a predicted cytoskeletal protein

The GLH proteins belong to a family of four germline RNA helicases in Caenorhabditis elegans. These putative ATP-dependent enzymes localize to the P granules, which are nonmembranous complexes of protein and RNA exclusively found in the cytoplasm of all C. elegans germ cells and germ cell precursors. To determine what proteins the GLHs bind, C. elegans cDNA libraries were screened by the yeast two-hybrid method, using GLHs as bait. Three interacting proteins, CSN-5, KGB-1, and ZYX-1, were identified and further characterized. GST pull-down assays independently established that these proteins bind GLHs. CSN-5 is closely related to the subunit 5 protein of COP9 signalosomes, conserved multiprotein complexes of plants and animals. RNA interference (RNAi) with csn-5 results in sterile worms with small gonads and no oocytes, a defect essentially identical to that produced by RNAi with a combination of glh-1 and glh-4. KGB-1 is a putative JNK MAP kinase that GLHs bind. A kgb-1 deletion strain has a temperature-sensitive, sterile phenotype characterized by the absence of mature oocytes and the presence of trapped, immature oocytes that have undergone endoreplication. ZYX-1 is a LIM domain protein most like vertebrate Zyxin, a cytoskeletal adaptor protein. In C. elegans, while zyx-1 appears to be a single copy gene, neither RNAi depletion nor a zyx-1 deletion strain results in an obvious phenotype. These three conserved proteins are the first members in each of their families reported to associate with germline helicases. Similar to the loss of GLH-1 and GLH-4, loss of either CSN-5 or KGB-1 causes oogenesis to cease, but does not affect the initial assembly of P granules.

Role of zyxin in differential cell spreading and proliferation of melanoma cells and melanocytes

Cell spreading, proliferation, and survival are modulated by focal adhesions linking extracellular matrix proteins, integrins, and the cytoskeleton. Zyxin is a focal-adhesion-associated phosphoprotein with one domain involved in the control of actin assembly and three protein-protein adapter domains implicated in the regulation of cell growth and differentiation. We characterized zyxin expression in normal human melanocytes and six melanoma cell lines in relation to cell spreading, growth, and differentiation using Western immunoblotting techniques, image analysis, flow cytometry, and confocal microscopy. We found that zyxin, focal adhesion kinase, and paxillin were significantly upregulated in melanoma cells compared to melanocytes. Zyxin expression directly related to cell spreading and proliferation and inversely related to differentiation, whereas focal adhesion kinase correlated only to cell spreading and paxillin did not significantly correlate with any of the parameters. Treatment of melanoma cells with 12-O-tetradecanoylphorbol-13-acetate downregulated zyxin expression, inhibited cell spreading and proliferation, and promoted differentiation. In contrast, 12-O-tetradecanoylphorbol-13-acetate, a mitogen for melanocytes, induced upregulation of zyxin expression in melanocytes. These findings are consistent with a role of zyxin in modulation of cell spreading, proliferation, and differentiation. Therapies directed at the downregulation of this focal adhesion phosphoprotein in melanoma cells implicate a new approach for controlling melanoma cell growth.

Expression of the gene encoding the LIM protein CRP2: a developmental profile

Members of the cysteine-rich protein (CRP) family are evolutionarily conserved Lin-11, Isl-1, Mac-3 (LIM) domain proteins that have been implicated in cell differentiation. Here we describe the expression pattern of the CRP family member CRP2 in mouse. Unlike other CRP family members, which are expressed primarily in muscle, CRP2 is more broadly expressed. In addition to expression in vascular smooth muscle cells, we also detect CRP2-specific transcripts in mesenchymal derivatives and several epithelia.

Identification of a CArG box-dependent enhancer within the cysteine-rich protein 1 gene that directs expression in arterial but not venous or visceral smooth muscle cells

Smooth muscle cells (SMCs) are heterogeneous with respect to their contractile, synthetic, and proliferative properties, though the regulatory factors responsible for their phenotypic diversity remain largely unknown. To further our understanding of smooth muscle gene regulation, we characterized the cis-regulatory elements of the murine cysteine-rich protein 1 gene (CRP1/Csrp1). CRP1 is expressed in all muscle cell types during embryogenesis and predominates in vascular and visceral SMCs in the adult. We identified a 5-kb enhancer within the CRP1 gene that is sufficient to drive expression in arterial but not venous or visceral SMCs in transgenic mice. This enhancer also exhibits region-specific activity in the outflow tract of the heart and the somites. Within the 5-kb CRP1 enhancer, we found a single CArG box that binds serum response factor (SRF), and by mutational analysis, demonstrate that the activity of the enhancer is dependent on this CArG element. Our findings provide further evidence for the existence of distinct regulatory programs within SMCs and suggest a role for SRF in the activation of the CRP1 gene.

Identification and characterization of thymus LIM protein: targeted disruption reduces thymus cellularity

We have identified a novel LIM gene encoding the thymus LIM protein (TLP), expressed specifically in the thymus in a subset of cortical epithelial cells. TLP was identified as a gene product which is upregulated in a thymus in which selection of T cells is occurring (Rag(-/-) OT-1) compared to its expression in a thymus in which selection is blocked at the CD4+ CD8+ stage of T-cell development (Rag(-/-) Tap(-/-) OT-1). TLP has an apparent molecular mass of 23 kDa and exists as two isomers (TLP-A and TLP-B), which are generated by alternative splicing of the message. The sequences of TLP-A and TLP-B are identical except for the C-terminal 19 or 20 amino acids. Based on protein sequence alignment, TLP is most closely related to the cysteine-rich proteins, a subclass of the family of LIM-only proteins. In both medullary and cortical thymic epithelial cell lines transduced with TLP, the protein localizes to the cytoplasm but does not appear to be strongly associated with actin. In immunohistochemical studies, TLP seems to be localized in a subset of epithelial cells in the cortex and is most abundant near the corticomedullary junction. We generated mice with a targeted disruption of the Tlp locus. In the absence of TLP, thymocyte development and thymus architecture appear to be normal but thymocyte cellularity is reduced by approximately 30%, with a proportional reduction in each subpopulation.

Interaction of zyxin, a focal adhesion protein, with the e6 protein from human papillomavirus type 6 results in its nuclear translocation

Zyxin, a focal adhesion molecule, interacts specifically with the E6 protein from human papillomavirus (HPV) type 6 in a yeast two-hybrid screen of a cDNA library prepared from human keratinocytes. Zyxin does not interact significantly with E6 proteins from HPV types 11, 16, or 18. The interaction was confirmed by in vitro and in vivo analyses and it requires the LIM domains (Lin-11, Isl-1, and Mec-3 [G. Freyd, S. K. Kim, and H. R. Horvitz, Nature 344:876-879, 1990]) found at the carboxyl terminus of zyxin. Cotransfection of E6 from HPV ((6)E6) and zyxin results in the accumulation of zyxin in the nucleus where it can function as a transcriptional activator. (6)E6 can also mobilize endogenous zyxin to the nucleus.

A novel muscle LIM-only protein is generated from the paxillin gene locus in Drosophila

Paxillin is a protein containing four LIM domains, and functions in integrin signaling. We report here that two transcripts are generated from the paxillin gene locus in Drosophila; one encodes a protein homolog of the vertebrate Paxillin (DPxn37), and the other a protein with only three LIM domains, partly encoded by its own specific exon (PDLP). At the myotendinous junctions of Drosophila embryos where integrins play important roles, both DPxn37 and PDLP are highly expressed with different patterns; DPxn37 is predominantly concentrated at the center of the junctions, whereas PDLP is highly enriched at neighboring sides of the junction centers, primarily expressed in the mesodermal myotubes. Northern blot analysis revealed that DPxn37 is ubiquitously expressed throughout the life cycle, whereas PDLP expression exhibits a biphasic pattern during development, largely concomitant with muscle generation and remodeling. Our results collectively reveal that a unique system exists in Drosophila for the generation of a novel type of LIM-only protein, highly expressed in the embryonic musculature, largely utilizing the Paxillin LIM domains.

Transcriptional regulation of vascular development

Vascular development is a highly organized sequence of events that requires the correct spatial and temporal expression of specific sets of genes leading to the development of a primary vascular network. The first step in this process is the differentiation of pluripotent stem cells into endothelial cells. This is followed by endothelial proliferation, migration, and eventual formation of endothelial tubes. Maturation of these primitive tubes into fully developed blood vessels requires the recruitment of surrounding pericytes and their differentiation into vascular smooth muscle cells. Many of the events that occur during vasculogenesis are recapitulated during angiogenesis. Transcription factors have been shown to serve as master switches for regulating a number of developmental processes. Using a candidate gene approach, the genomic regulatory regions required to direct vascular-specific gene expression of several receptor tyrosine kinases that are critical for vasculogenesis have been characterized and some of the transcription factors that are involved in the regulation of these genes have recently been identified. Many of these factors are also involved in the regulation of hematopoiesis and may have overlapping functions in determining hematopoietic and endothelial differentiation. Targeted disruption of other transcription factors that were not previously thought to be involved in vascular development have also been recently shown to play a role in blood vessel development. The purpose of this review is to provide an update on the progress that has been made in our understanding of the transcriptional regulation of vascular development over the past few years.

EsMlp, a muscle-LIM protein gene, is up-regulated during cold exposure in the freeze-avoiding larvae of Epiblema scudderiana

Screening of a cDNA library identified transcripts that were up-regulated by cold (4 or -20 degrees C) exposure in larvae of the freeze-avoiding goldenrod gall moth, Epiblema scudderiana. One clone contained a full-length open reading frame encoding a protein of 94 amino acids. The gene product, with 79.1% of residues identical with the Drosophila LIM protein Mlp60A, was named EsMlp and contained a single LIM domain and consensus sequences characteristic of a LIM protein. Transcript levels rose approx twofold when larvae were shifted from 4 to -20 degrees C and approx threefold over the midwinter months compared with larvae sampled in October or April. EsMlp expression was high in larval head (possibly due to expression in pharyngeal muscles) and body wall but was not detected in fat body. Immunoblotting revealed a three- to fourfold increase in EsMlp protein in midwinter larvae (January-February) compared with November-collected animals and a further rise to eightfold higher than November values in larvae collected in April. Cold up-regulation of EsMlp and the pattern of EsMlp levels in the larvae suggest possible roles for the protein, such as in muscle maintenance over the winter or as a preparative function that could facilitate the rapid resumption of development and metamorphosis when environmental temperatures rise in the spring.

Translocation of a human focal adhesion LIM-only protein, FHL2, during myofibrillogenesis and identification of LIM2 as the principal determinants of FHL2 focal adhesion localization

LIM domain proteins are found to be important regulators in cell growth, cell fate determination, cell differentiation, and remodeling of the cell cytoskeleton. Human Four-and-a-half LIM-only protein 2 (FHL2) is expressed predominantly in human heart and is only slightly expressed in skeletal muscle. Since FHL2 is an abundant protein in human heart, it may play an important role in the regulation of cell differentiation and myofibrillogenesis of heart at defined subcellular compartment. Therefore, we hypothesized that FHL2 act as a multi-functional protein by the specific arrangement of the LIM domains of FHL2 and that one of the LIM domains of FHL2 can function as an anchor and localizes it into a specific subcellular compartment in a cell type specific manner to regulate myofibrillogenesis. From our results, we observed that FHL2 is localized at the focal adhesions of the C2C12, H9C2 myoblast as well as a nonmyogenic cell line, HepG2 cells. Colocalization of vinculin-CFP and FHL2-GFP at focal adhesions was also observed in cell lines. Site-directed mutagenesis, in turn, suggested that the second LIM domain-LIM2 is essential for its specific localization to focal adhesions. Moreover, FHL2 was observed along with F-actin and focal adhesion of C2C12 and H9C2 myotubes. Finally, we believe that FHL2 moves from focal adhesions and then stays at the Z-discs of terminally differentiated heart muscle.

Fine mapping of the alpha-actinin binding site within cysteine-rich protein

The cysteine-rich proteins (CRPs) are a family of highly conserved LIM (an acronym derived from the three gene products lin-11, isl-1 and mec-3) domain proteins that have been implicated in muscle differentiation. All CRP family members characterized so far have been shown to interact with the filamentous actin cross-linker alpha-actinin. The region of CRP required for this interaction has previously been broadly mapped to the molecule's N-terminal half. Here we report that the alpha-actinin-binding region of CRP, which we have mapped by using a combination of blot overlay and Western immunoblot techniques, is confined to an 18-residue sequence occurring within the protein's N-terminal glycine-rich repeat. A site-directed mutagenesis analysis of the binding region has revealed the critical importance of a single lysine residue (lysine 65 in human CRP1). Alterations at this site lead to a 10-fold decrease in alpha-actinin binding in comparison with wild-type CRP. The critical lysine residue localizes within a short alpha-helix, raising the possibility that mutagenesis-induced alterations in alpha-actinin-binding capacity might be attributed to the disruption of a key structural element.

The cysteine- and glycine-rich LIM domain protein CRP2 specifically interacts with a novel human protein (CRP2BP)

We used the interaction trap to isolate a novel human protein that specifically interacts with the double LIM domain protein CRP2. This protein, designated CRP2BP (for CRP2 binding partner), was previously postulated by sequencing contigs of human chromosome 20. The observed interaction is mediated via the LIM1 domain of CRP2 and is of functional relevance in cellular environment. This novel single copy gene spans approximately 45-bp and is organized into at least ten exons. CRP2BP is expressed in all human tissues tested, with a major mRNA of 4-kb in size and an additional 3.2-kb transcript in placenta.

Identification of differentially expressed genes in dorsal root ganglia following partial sciatic nerve injury

Partial sciatic nerve injury, a model of neuropathic pain, elicits a variety of neurochemical, electrophysiological and neuroanatomical changes in primary sensory neurons. We have used the technique of messenger RNA differential display to identify genes with altered expression in these neurons which may contribute to the development of aberrant sensation following such peripheral nerve damage. This approach identified 14 distinct complementary DNA clones, representing transcripts with increased ipsilateral expression in L4/5 dorsal root ganglia, two weeks after unilateral partial ligation of the rat sciatic nerve. Both Zucker diabetic fatty rats and their lean counterparts were used in this study but none of the transcripts identified showed an induction that was confined to one of the two groups. The majority of the clones did not show significant sequence similarity to previously reported genes and therefore may represent novel messenger RNA sequences or, alternatively, unknown regions of partially characterised messenger RNAs. Two of the clones represented transcripts for the known proteins muscle LIM protein and acidic epididymal glycoprotein, neither of which had previously been associated with expression in the nervous system. Reverse transcriptase-polymerase chain reaction analysis and in situ hybridization confirmed that the messenger RNA expression of both muscle LIM protein and acidic epididymal glycoprotein was induced in an ipsilateral-specific manner. Their localisations, examined with in situ hybridization in L5 dorsal root ganglia, were limited in each case to a sub-population of neuronal profiles. Those neuronal profiles that demonstrated muscle LIM protein hybridization were distributed across the profile size range, whereas the distribution of acidic epididymal glycoprotein-positive profiles appeared to be skewed towards smaller profiles. The induction of muscle LIM protein and acidic epididymal glycoprotein in dorsal root ganglia may play an important functional role in the adaptive response of primary sensory neurons following partial sciatic nerve injury.

Cysteine-rich protein 2, a novel substrate for cGMP kinase I in enteric neurons and intestinal smooth muscle

Nitric oxide/cGMP/cGMP kinase I (cGKI) signaling causes relaxation of intestinal smooth muscle. In the gastrointestinal tract substrates of cGKI have not been identified yet. In the present study a protein interacting with cGKIbeta has been isolated from a rat intestinal cDNA library using the yeast two-hybrid system. The protein was identified as cysteine-rich protein 2 (CRP2), recently cloned from rat brain (Okano, I., Yamamoto, T., Kaji, A., Kimura, T., Mizuno, K., and Nakamura, T. (1993) FEBS Lett. 333, 51-55). Recombinant CRP2 is specifically phosphorylated by cGKs but not by cAMP kinase in vitro. Co-transfection of CRP2 and cGKIbeta into COS cells confirmed the phosphorylation of CRP2 in vivo. Cyclic GMP kinase I phosphorylated CRP2 at Ser-104, because the mutation to Ala completely prevented the in vivo phosphorylation. Immunohistochemical analysis using confocal laser scan microscopy showed a co-localization of CRP2 and cGKI in the inner part of the circular muscle layer, in the muscularis mucosae, and in specific neurons of the myenteric and submucosal plexus. The co-localization together with the specific phosphorylation of CRP2 by cGKI in vitro and in vivo suggests that CRP2 is a novel substrate of cGKI in neurons and smooth muscle of the small intestine.

Identification of a novel LIM domain gene, LMCD1, and chromosomal localization in human and mouse

A new human LIM domain gene LMCD1 was identified from RT-PCR products, and partial sequencing of two expressed sequence tag clones flanking the assembled cDNA contig revealed a 1743-bp full-length cDNA with 1098-bp open reading frame. The coding sequence of the putative protein is 57.6% identical to murine testin 1 gene (Tes1), whereas the predicted 365-amino-acid protein is 49.5% identical to the mouse Tes1 protein. The predicted LMCD1 protein contains a novel cysteine-rich domain residing in the amino-terminal region and two LIM domains with regular spacing in the carboxy-terminal region. Northern blot analysis indicated expression of the 1.7-kb transcript in many tissues, with highest abundance in skeletal muscle. Radiation hybrid mapping localized human LMCD1 to the telomeric region of chromosome 3p, and genetic mapping assigned the mouse Lmcd1 locus to the central region of chromosome 6.

Purification and characterization of an alpha-actinin-binding PDZ-LIM protein that is up-regulated during muscle differentiation

alpha-Actinin is required for the organization and function of the contractile machinery of muscle. In order to understand more precisely the molecular mechanisms by which alpha-actinin might contribute to the formation and maintenance of the contractile apparatus within muscle cells, we performed a screen to identify novel alpha-actinin binding partners present in chicken smooth muscle cells. In this paper, we report the identification, purification, and characterization of a 36-kDa smooth muscle protein (p36) that interacts with alpha-actinin. Using a variety of in vitro binding assays, we demonstrate that the association between alpha-actinin and p36 is direct, specific, and saturable and exhibits a moderate affinity. Furthermore, native co-immunoprecipitation reveals that the two proteins are complexed in vivo. p36 is expressed in cardiac muscle and tissues enriched in smooth muscle. Interestingly, in skeletal muscle, a closely related protein of 40 kDa (p40) is detected. The expression of p36 and p40 is dramatically up-regulated during smooth and skeletal muscle differentiation, respectively, and p40 colocalizes with alpha-actinin at the Z-lines of differentiated myotubes. We have established the relationship between p36 and p40 by molecular cloning of cDNAs that encode both proteins and have determined that they are the products of a single gene. Both proteins display an identical N-terminal PDZ domain and an identical C-terminal LIM domain; an internal 63-amino acid sequence present in p36 is replaced by a unique 111-amino acid sequence in p40. Analysis of the sequences of p36 and p40 suggest that they are the avian forms of the actinin-associated LIM proteins (ALPs) recently described in rat (Xia, H., Winokur, S. T., Kuo, W.-L., Altherr, M. R., and Bredt, D. S. (1997) J. Cell Biol. 139, 507-515). The expression of the human ALP gene has been postulated to be affected by mutations that cause facioscapulohumeral muscular dystrophy; thus, the characterization of ALP function may ultimately provide insight into the mechanism of this disease.

Muscle LIM proteins are associated with muscle sarcomeres and require dMEF2 for their expression during Drosophila myogenesis

A genetic hierarchy of interactions, involving myogenic regulatory factors of the MyoD and myocyte enhancer-binding 2 (MEF2) families, serves to elaborate and maintain the differentiated muscle phenotype through transcriptional regulation of muscle-specific target genes. Much work suggests that members of the cysteine-rich protein (CRP) family of LIM domain proteins also play a role in muscle differentiation; however, the specific functions of CRPs in this process remain undefined. Previously, we characterized two members of the Drosophila CRP family, the muscle LIM proteins Mlp60A and Mlp84B, which show restricted expression in differentiating muscle lineages. To extend our analysis of Drosophila Mlps, we characterized the expression of Mlps in mutant backgrounds that disrupt specific aspects of muscle development. We show a genetic requirement for the transcription factor dMEF2 in regulating Mlp expression and an ability of dMEF2 to bind, in vitro, to consensus MEF2 sites derived from those present in Mlp genomic sequences. These data suggest that the Mlp genes may be direct targets of dMEF2 within the genetic hierarchy controlling muscle differentiation. Mutations that disrupt myoblast fusion fail to affect Mlp expression. In later stages of myogenic differentiation, which are dedicated primarily to assembly of the contractile apparatus, we analyzed the subcellular distribution of Mlp84B in detail. Immunofluorescent studies revealed the localization of Mlp84B to muscle attachment sites and the periphery of Z-bands of striated muscle. Analysis of mutations that affect expression of integrins and alpha-actinin, key components of these structures, also failed to perturb Mlp84B distribution. In conclusion, we have used molecular epistasis analysis to position Mlp function downstream of events involving mesoderm specification and patterning and concomitant with terminal muscle differentiation. Furthermore, our results are consistent with a structural role for Mlps as components of muscle cytoarchitecture.

Ajuba, a novel LIM protein, interacts with Grb2, augments mitogen-activated protein kinase activity in fibroblasts, and promotes meiotic maturation of Xenopus oocytes in a Grb2- and Ras-dependent manner

LIM domain-containing proteins contribute to cell fate determination, the regulation of cell proliferation and differentiation, and remodeling of the cell cytoskeleton. These proteins can be found in the cell nucleus, cytoplasm, or both. Whether and how cytoplasmic LIM proteins contribute to the cellular response to extracellular stimuli is an area of active investigation. We have identified and characterized a new LIM protein, Ajuba. Although predominantly a cytosolic protein, in contrast to other like proteins, it did not localize to sites of cellular adhesion to extracellular matrix or interact with the actin cytoskeleton. Removal of the pre-LIM domain of Ajuba, including a putative nuclear export signal, led to an accumulation of the LIM domains in the cell nucleus. The pre-LIM domain contains two putative proline-rich SH3 recognition motifs. Ajuba specifically associated with Grb2 in vitro and in vivo. The interaction between these proteins was mediated by either SH3 domain of Grb2 and the N-terminal proline-rich pre-LIM domain of Ajuba. In fibroblasts expressing Ajuba mitogen-activated protein kinase activity persisted despite serum starvation and upon serum stimulation generated levels fivefold higher than that seen in control cells. Finally, when Ajuba was expressed in fully developed Xenopus oocytes, it promoted meiotic maturation in a Grb2- and Ras-dependent manner.

Genomic structure, tissue expression and chromosomal location of the LIM-only gene, SLIM1

Human SLIM1 is a recently described gene of the LIM-only class encoding four and a half tandemly repeated LIM domains. LIM domains are double zinc finger structures which provide an interface for protein/protein interactions and are conserved in a variety of nuclear and cytoplasmic factors important in cell fate determination and cellular regulation. Here we report the structural organization, expression pattern and chromosomal localization of the human SLIM1 gene. SLIM1 was found to contain at least five exons with all four introns disrupting the coding region at a similar position relative to the respective complete LIM domains. Northern blot analysis confirmed strikingly high expression of SLIM1 in skeletal muscle and heart, with much lower expression observed in several other tissues including colon, small intestine and prostate. The SLIM1 gene was assigned to human chromosome Xq26 using fluorescence in situ hybridization.

Solution structure of the chicken cysteine-rich protein, CRP1, a double-LIM protein implicated in muscle differentiation

The mechanism by which the contractile machinery of muscle is assembled and maintained is not well-understood. Members of the cysteine-rich protein (CRP) family have been implicated in these processes. Three vertebrate CRPs (CRP1-3) that exhibit developmentally regulated muscle-specific expression have been identified. All three proteins are associated with the actin cytoskeleton, and one has been shown to be required for striated muscle structure and function. The vertebrate CRPs identified to date display a similar molecular architecture; each protein is comprised of two tandemly arrayed LIM domains, protein-binding motifs found in a number of proteins with roles in cell differentiation. Each LIM domain coordinates two Zn(II) ions that are bound independently in CCHC (C=Cys, H=His) and CCCC modules. Here we describe the solution structure of chicken CRP1 determined by homonuclear and 1H-15N heteronuclear magnetic resonance spectroscopy. Comparison of the structures of the two LIM domains of CRP1 reveals a high degree of similarity in their tertiary folds. In addition, the two component LIM domains represent two completely independent folding units and exhibit no apparent interactions with each other. The structural independence and spatial separation of the two LIM domains of CRP1 are compatible with an adapter or linker role for the protein.

Cloning and characterization of androgen receptor coactivator, ARA55, in human prostate

Androgen receptor (AR) is a hormone-activated transcriptional factor that can bind to androgen response elements and that regulates the transcription of target genes via a mechanism that presumably involves cofactors. We report here the cloning of a novel AR coactivator ARA55 using a yeast two-hybrid system. ARA55 consists of 444 amino acids with the predicted molecular mass of 55 kDa and its sequence shows very high homology to mouse hic5, a TGF-beta1-inducible gene. Yeast and mammalian two-hybrid systems and co-immunoprecipitation assays all prove ARA55 can bind to AR in a ligand-dependent manner. Transient transfection assay in prostate cancer DU145 cells further demonstrates that ARA55 can enhance AR transcriptional activity in the presence of 1 nM dihydrotestosterone or its antagonists such as 100 nM 17beta-estradiol or 1 microM hydroxyflutamide. Our data also suggest the C-terminal half of ARA55, which includes three LIM motifs, is sufficient to interact with AR. Northern blot and polymerase chain reaction quantitation showed ARA55 can be expressed differently in normal prostate and prostate tumor cells. Together, our data suggests that ARA55 may play very important roles in the progression of prostate cancer by the modulation of AR transactivation.

The LIM protein, CRP1, is a smooth muscle marker

LIM domains are double zinc-finger motifs found in many proteins that play central roles in cell differentiation. Members of the cysteine-rich protein (CRP) family display two LIM domains and are implicated in muscle development. Here we describe the characterization of one member of this family, CRP1, in the mouse. We have isolated and sequenced murine cDNAs that encode CRP1. We have determined by Northern analysis and in situ hybridization that CRP1 expression is developmentally regulated in the embryonic mouse and displays organ specific regulation in adults. The gene encoding CRP1 is expressed in the smooth muscle cells (SMCs) of the dorsal aorta at E9.5, thus illustrating that CRP1 is an early marker for SMC differentiation at that site. As development proceeds, CRP1 transcripts are observed throughout the SMC lineage, with minimal, transient expression detected in skeletal and cardiac muscle. Interestingly, although several markers of mature smooth muscle are already expressed, CRP1 expression in the bladder is not upregulated until the onset of bladder expansion at embryonic day 16.5, at which time its expression becomes very prominent. CRP1 expression persists into adulthood with prominent expression observed in both vascular and visceral smooth muscle. The results reported here define CRP1 as a general marker of smooth muscle lineages.

The LIM-only protein PINCH directly interacts with integrin-linked kinase and is recruited to integrin-rich sites in spreading cells

PINCH is a widely expressed and evolutionarily conserved protein comprising primarily five LIM domains, which are cysteine-rich consensus sequences implicated in mediating protein-protein interactions. We report here that PINCH is a binding protein for integrin-linked kinase (ILK), an intracellular serine/threonine protein kinase that plays important roles in the cell adhesion, growth factor, and Wnt signaling pathways. The interaction between ILK and PINCH has been consistently observed under a variety of experimental conditions. They have interacted in yeast two-hybrid assays, in solution, and in solid-phase-based binding assays. Furthermore, ILK, but not vinculin or focal adhesion kinase, has been coisolated with PINCH from mammalian cells by immunoaffinity chromatography, indicating that PINCH and ILK associate with each other in vivo. The PINCH-ILK interaction is mediated by the N-terminal-most LIM domain (LIM1, residues 1 to 70) of PINCH and multiple ankyrin (ANK) repeats located within the N-terminal domain (residues 1 to 163) of ILK. Additionally, biochemical studies indicate that ILK, through the interaction with PINCH, is capable of forming a ternary complex with Nck-2, an SH2/SH3-containing adapter protein implicated in growth factor receptor kinase and small GTPase signaling pathways. Finally, we have found that PINCH is concentrated in peripheral ruffles of cells spreading on fibronectin and have detected clusters of PINCH that are colocalized with the alpha5beta1 integrins. These results demonstrate a specific protein recognition mechanism utilizing a specific LIM domain and multiple ANK repeats and suggest that PINCH functions as an adapter protein connecting ILK and the integrins with components of growth factor receptor kinase and small GTPase signaling pathways.

A conserved LIM protein that affects muscular adherens junction integrity and mechanosensory function in Caenorhabditis elegans

We describe here the molecular and functional characterization of the Caenorhabditis elegans unc-97 gene, whose gene product constitutes a novel component of muscular adherens junctions. UNC-97 and homologues from several other species define the PINCH family, a family of LIM proteins whose modular composition of five LIM domains implicates them as potential adapter molecules. unc-97 expression is restricted to tissue types that attach to the hypodermis, specifically body wall muscles, vulval muscles, and mechanosensory neurons. In body wall muscles, the UNC-97 protein colocalizes with the beta-integrin PAT-3 to the focal adhesion-like attachment sites of muscles. Partial and complete loss-of-function studies demonstrate that UNC-97 affects the structural integrity of the integrin containing muscle adherens junctions and contributes to the mechanosensory functions of touch neurons. The expression of a Drosophila homologue of unc-97 in two integrin containing cell types, muscles, and muscle-attached epidermal cells, suggests that unc-97 function in adherens junction assembly and stability has been conserved across phylogeny. In addition to its localization to adherens junctions UNC-97 can also be detected in the nucleus, suggesting multiple functions for this LIM domain protein.

cDNA cloning and characterization of sciellin, a LIM domain protein of the keratinocyte cornified envelope

Sciellin is a precursor of the cornified envelopes of mammalian keratinizing tissues. We have cloned the cDNA encoding sciellin by screening a human keratinocyte expression library with a sciellin-specific monoclonal antibody. The composite cDNA of 2.35 kilobase pairs encodes a protein of 75.3 kDa with a pI of 10.09. The translated sequence has a central domain containing 16 repeats of 20 amino acids each that is rich in Gln and Lys residues, which are potential transglutaminase substrates, and a carboxyl domain, which contains a single LIM motif. Sciellin cDNA probes hybridize to bands of 3.4 and 4.4 kilobase pairs on Northern blots of cultured human keratinocyte RNA. The gene was mapped to human chromosome band 13q22 by fluorescence in situ hybridization. Radiation hybrid mapping demonstrated that sciellin is linked to the sequence tagged site marker WI-457 with a logarithm of the odds score of 7.77. In situ hybridization of human foreskin tissue sections demonstrated that sciellin is expressed in the stratum granulosum. Immunofluorescent staining with a polyclonal rabbit antibody made to a recombinant sciellin protein showed peripheral cytoplasmic localization in the upper cell layers of epidermis and in stratified squamous epithelia such as the oral cavity, esophagus, and vagina. Simple and columnar epithelia, with the exception of the amnion, showed no reaction.

Embryonic expression suggests an important role for CRP2/SmLIM in the developing cardiovascular system

Proteins of the LIM family are critical regulators of development and differentiation in various cell types. We have described the cloning of cysteine-rich protein 2/smooth muscle LIM protein (CRP2/SmLIM), a LIM-only protein expressed in differentiated vascular smooth muscle cells. As a first step toward understanding the potential functions of CRP2/SmLIM, we analyzed its expression after gastrulation in developing mice and compared the expression of CRP2/SmLIM with that of the other 2 members of the CRP subclass, CRP1 and CRP3/MLP. In situ hybridization in whole-mount and sectioned embryos showed that CRP2/SmLIM was expressed in the sinus venosus and the 2 cardiac chambers at embryonic day 9. Vascular expression of CRP2/SmLIM was first seen at embryonic day 10. At subsequent time points, CRP2/SmLIM expression decreased in the heart but remained high in the vasculature. CRP1 was expressed both in vascular and nonvascular tissues containing smooth muscle cells, whereas CRP3/MLP was expressed only in tissues containing striated muscle. These patterns of expression were maintained in the adult animal and suggest an important role for this gene family in the development of smooth and striated muscle.