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PubMed1987

Deficiency in mRNA splicing in a cytochrome c mutant of neurospora crassa: importance of carboxy terminus for import of apocytochrome c into mitochondria.

Molecular cloning and characterization of cytochrome c cDNA clones of Neurospora crassa wild-type (74A) and a cytochrome c-deficient mutant (cyc1-1) are described. Southern blot analysis of genomic DNA indicates that only one cytochrome c gene exists in the N. crassa genome. The cDNA sequence of the wild-type cytochrome c confirmed the previously determined protein sequence. Sequence analysis of the cyc1-1 cDNA for cytochrome c revealed the presence of a larger open reading frame, owing to the presence of an unspliced intron in the 3' end of the coding region. Splicing of this intron is obviously prevented due to the presence of two base exchanges in the highly conserved intron consensus sequences. Consequently, cyc1-1 synthesizes apocytochrome c with an altered carboxy terminus, 19 amino acids longer than the wild-type cytochrome c, with the final 27 amino acids being of an unrelated sequence. This alteration in the carboxy terminus renders the apocytochrome c incompetent for binding to mitochondria and, consequently, import into mitochondria. Thus, unlike other mitochondrial precursor proteins, where it has been demonstrated that the amino terminus alone is sufficient to target the protein to the mitochondria, an intact carboxy terminus is required for efficient import of apocytochrome c into mitochondria. This is independent confirmation for the view that the import pathway of cytochrome c is unique with respect to all other mitochondrial proteins studied to date.

Amino Acid Sequence↗

PubMed1994

Tissue-specific differences of the mitochondrial protein import machinery: in vitro import, processing and degradation of the pre-F1 beta subunit of the ATP synthase in spinach leaf and root mitochondria.

In this study we report the first comparison of the mitochondrial protein import and processing events in two different tissues from the same organism. Both spinach leaf and root mitochondria were able to import and process the in vitro transcribed and translated Neurospora crassa F1 beta subunit of ATP synthase to the mature size product. Temperature optimum for protein import, 20 degrees C, was considerably lower than that found in other systems. In spinach leaf mitochondria, the processing peptidase has been shown to constitute an integral part of the bc1 complex of the respiratory chain. In accordance with these results, the majority of the processing activity in root mitochondria was also localized in the membrane. However, although the same amount of the processing peptidase was present per mg of membrane protein in both leaf and root mitochondria, as determined immunologically, the specific processing activity was several-fold higher in roots. Furthermore, in contrast to the processing enzyme in leaf, a portion of the processing activity could be disassociated from the root membrane with relatively weak salt treatment. The processing event in both the leaf and root membranes was always accompanied by a degradation of the F1 beta precursor. The degradation activity was found to be several-fold higher in roots than in leaves and was also partially dissociated from the membrane after salt treatment. Both the processing and degradation activities were inhibited by orthophenanthroline, a known metalloprotease inhibitor. These results show tissue-specific differences of the processing event catalyzed by the bc1 complex and indicate the presence of two populations of the processing peptidase in root mitochondria.

Blotting, Western↗

PubMed2002

The core protein of hepatitis C virus is imported into the nucleus by transport receptor Kap123p but inhibits Kap121p-dependent nuclear import of yeast AP1-like transcription factor in yeast cells.

The core protein of hepatitis C virus (HCV) is a major component of the viral nucleocapsid. The HCV core protein includes nuclear localization signal-like sequences and has various effects on cellular metabolism, playing roles, for example, in the regulation of transcription, apoptosis, and transformation. To examine the possibility of an effect of the core protein on nucleocytoplasmic transport, we used the yeast Saccharomyces cerevisiae as a model system. The core protein (p23) is processed to p21 and is localized in both the cytoplasm and nucleus in yeast cells, similar to that observed in mammalian cells in several cases. The nuclear import of the core protein requires the activity of small GTPase Ran/Gsp1p and is mediated by Kap123p in yeast cells. When the core protein was expressed in yeast cells, the import of the yeast AP1-like transcription factor Yap1p into the nucleus was inhibited. Experiments in vitro involving Kap121p, also known as Pse1p, a receptor for the nuclear import of Yap1p, indicated that the amount of Yap1p bound to Kap121p was reduced in the presence of core protein. These results suggest that the HCV core protein affects cellular metabolism by disturbing transport of proteins to the nucleus.

Active Transport, Cell Nucleus↗

PubMed2002

Nuclear import of PKCdelta is required for apoptosis: identification of a novel nuclear import sequence.

We have shown previously that protein kinase Cdelta (PKCdelta) is required for mitochondrial-dependent apoptosis. Here we show that PKCdelta is imported into the nucleus of etoposide-treated cells, that nuclear import is required for apoptosis and that it is mediated by a nuclear localization signal (NLS) in the C-terminus of PKCdelta. Mutation of the caspase cleavage site of PKCdelta inhibits nuclear accumulation in apoptotic cells, indicating that caspase cleavage facilitates this process. Expression of the PKCdelta catalytic fragment (CFdelta) in transfected cells results in nuclear localization and apoptosis. We show that the PKCdelta NLS is required for nuclear import of both full-length PKCdelta and CFdelta, and drives nuclear localization of a multimeric green fluorescent protein. Mutations within the NLS of CFdelta prevent nuclear accumulation and block apoptosis. Conversely, nuclear expression of a kinase-negative catalytic fragment (KN-CFdelta) protects cells from etoposide-induced apoptosis. Mutation of the NLS blocks the ability of KN-CFdelta to protect against etoposide-induced apoptosis. These results indicate that PKCdelta regulates an essential nuclear event(s) that is required for initiation of the apoptotic pathway.

Active Transport, Cell Nucleus↗

PubMed2000

Peroxisomal matrix protein import. Suppression of protein import defects in Hansenula polymorpha pex mutants by overproduction of the PTS1 receptor Pex5p.

In the past decade, much progress has been made in understanding the mechanisms that govern sorting of proteins to the peroxisomal lumen. This article summarizes the principal features of how peroxisomal matrix enzymes are thought to reach the peroxisome. In addition, it describes recent data that indicate that, in specific pex mutants of the methylotrophic yeast Hansenula polymorpha, defects in matrix protein import can be (partly) rescued by overproduction of the receptor essential for import of these proteins. The implication of these results on the mechanisms of matrix protein import is discussed.

Biological Transport↗

PubMed1998

Import for export; reporting and recordkeeping requirements for unapproved or violative products imported for further processing or incorporation and subsequent export--FDA. Proposed rule.

The Food and Drug Administration (FDA) is proposing reporting and recordkeeping regulations to implement certain sections of the Federal Food, Drug, and Cosmetic Act (the act) as amended by the FDA Export Reform and Enhancement Act of 1996. The proposed rule would require an importer to report to FDA each time it imports an unapproved or otherwise violative article that is to be exported after further processing or incorporation into another product in the United States and to keep records to ensure that the article is so processed or incorporated and then exported, and that any portion of the import that is not exported is destroyed.

Commerce↗

PubMed2005

Expanding the definition of clinical differences: from minimally clinically important differences to really important differences. Analyses in 8931 patients with rheumatoid arthritis.

OBJECTIVE: Minimally clinically important differences (MCID) have become an important way to interpret data of randomized clinical trials (RCT), but do not reflect the degree of improvement consistent with a "really important difference" (RID). To define RID, we compared mean and/or least desirable clinical states with best and/or most desirable states. METHODS: In total, 8931 patients with rheumatoid arthritis (RA) < 65 years of age completed the Health Assessment Questionnaire (HAQ) and Medical Outcomes Survey Short Form 36 Physical Component Score (PCS). Definitions of RID were based on values for HAQ and PCS corresponding with the best and worst category of the following conditions: disabled vs not disabled: joint replacement vs no joint replacement; < poverty level vs > poverty level; very satisfied with health vs not; and independent in participation activities vs not. RESULTS: In contrast to published MCID values for the HAQ of approximately 0.22, RID was as high as 0.76 using objective reference conditions and 0.87 using the subjective measure of dependence vs independence. The HAQ score of independent RA patients was 0.38 (SD 0.45), and was 0.42 (SD 0.53) for those very satisfied with their health. The difference in HAQ scores between disabled and working patients was approximately 0.75. PCS differences were similarly increased. CONCLUSION: RID values are 3 to 4 times greater than MCID values. Although MCID are meaningful statistics for RCT, the RID percentage achieved [(actual improvement/RID) 100%] is a simple way to put the results of RCT in a broader perspective that gives an idea of how much additional treatment effect is needed.

Arthritis, Rheumatoid↗

PubMed2001

Protein import channel of the outer mitochondrial membrane: a highly stable Tom40-Tom22 core structure differentially interacts with preproteins, small tom proteins, and import receptors.

The preprotein translocase of the yeast mitochondrial outer membrane (TOM) consists of the initial import receptors Tom70 and Tom20 and a approximately 400-kDa (400 K) general import pore (GIP) complex that includes the central receptor Tom22, the channel Tom40, and the three small Tom proteins Tom7, Tom6, and Tom5. We report that the GIP complex is a highly stable complex with an unusual resistance to urea and alkaline pH. Under mild conditions for mitochondrial lysis, the receptor Tom20, but not Tom70, is quantitatively associated with the GIP complex, forming a 500K to 600K TOM complex. A preprotein, stably arrested in the GIP complex, is released by urea but not high salt, indicating that ionic interactions are not essential for keeping the preprotein in the GIP complex. Under more stringent detergent conditions, however, Tom20 and all three small Tom proteins are released, while the preprotein remains in the GIP complex. Moreover, purified outer membrane vesicles devoid of translocase components of the intermembrane space and inner membrane efficiently accumulate the preprotein in the GIP complex. Together, Tom40 and Tom22 thus represent the functional core unit that stably holds accumulated preproteins. The GIP complex isolated from outer membranes exhibits characteristic TOM channel activity with two coupled conductance states, each corresponding to the activity of purified Tom40, suggesting that the complex contains two simultaneously active and coupled channel pores.

Fungal Proteins↗

PubMed2001

New evidence that nuclear import of endogenous beta-catenin is LEF-1 dependent, while LEF-1 independent import of exogenous beta-catenin leads to nuclear abnormalities.

The once accepted idea that LEF-1 transports beta-catenin into nuclei has recently been challenged by experiments using exogenous beta-catenin. Here, we investigated the effects of beta-catenin and LEF-1 on nuclear import of beta-catenin using different combinations of exogenous and endogenous molecules over longer lengths of time than previously studied. Nuclear beta-catenin is not detectable in corneal fibroblasts and epithelia or NIH 3T3 and MDCK cells. In LEF-1 transfections, we show that the B-box of LEF-1 is required to move cytoplasmic endogenous beta-catenin into the nuclei of such cells, proving that LEF-1 does transport endogenous beta-catenin into nuclei. Moreover, transfection of uveal melanoma cells with B-box deficient LEF-1 inhibits nuclear import of beta-catenin by endogenous LEF-1. However, the movement of overexpressed exogenous beta-catenin into nuclei is unaffected by the presence or absence of LEF-1 and forms abnormal nuclear aggregates that are a prelude to subsequent apoptosis. We conclude that nuclear transport of exogenous beta-catenin independently of LEF-1 has questionable physiological significance.

Active Transport, Cell Nucleus↗

PubMed2000

Importance of sequences adjacent to the terminal tripeptide in the import of a peroxisomal Candida tropicalis protein in plant peroxisomes.

The peroxisome targeting signal (PTS) required for import of the rat acyl-CoA oxidase (AOX; EC 1.3.3.6) and the Candida tropicalis multifunctional protein (MFP) in plant peroxisomes was assessed in transgenic Arabidopsis thaliana (L.) Heynh. The native rat AOX accumulated in peroxisomes in A. thaliana cotyledons and targeting was dependent on the presence of the C-terminal tripeptide S-K-L. In contrast, the native C. tropicalis MFP, containing the consensus PTS sequence A-K-I was not targeted to plant peroxisomes. Modification of the carboxy terminus to the S-K-L tripeptide also failed to deliver the MFP to peroxisomes while addition of the last 34 amino acids of the Brassica napus isocitrate lyase, containing the terminal tripeptide S-R-M, enabled import of the fusion protein into peroxisomes. These results underline the influence of the amino acids adjacent to the terminal tripeptide of the C. tropicalis MFP on peroxisomal targeting, even in the context of a protein having a consensus PTS sequence S-K-L.

Acyl-CoA Oxidase↗

PubMed2005

The importance of valency in enhancing the import and cell routing potential of protein transduction domain-containing molecules.

Protein transduction domains (PTDs) are peptides that afford the internalization of cargo macromolecules (including plasmid DNA, proteins, liposomes, and nanoparticles). In the case of polycationic peptides, the efficiency of PTDs to promote cellular uptake is directly related to their molecular mass or their polyvalent presentation. Similarly, the efficiency of routing to the nucleus increases with the number of nuclear localization signals (NLS) associated with a cargo. The quantitative enhancement, however, depends on the identity of the PTD sequence as well as the targeted cell type. Thus the choice and multivalent presentation of PTD and NLS sequences are important criteria guiding the design of macromolecules intended for specific intracellular localization. This review outlines synthetic and recombinant strategies whereby PTDs and signal sequences can be assembled into multivalent peptide dendrimers and promote the uptake and routing of their cargoes. In particular, the tetramerization domain of the tumour suppressor p53 (p53tet) is emerging as a useful scaffold to present multiple routing and targeting moieties. Short cationic peptides fused to the 31-residue long p53tet sequence resulted in tetramers displaying a significant enhancement (up to 1000 fold) in terms of their ability to be imported into cells and delivered to the cell nucleus in relation to their monomeric analogues. The design of future polycationic peptide dendrimers as effective delivering vehicles will need to incorporate selective cell targeting functions and provide solutions to the issue of endosomal entrapment.

Active Transport, Cell Nucleus↗

PubMed1995

Identification of a protein complex that is required for nuclear protein import and mediates docking of import substrate to distinct nucleoporins.

We have identified and characterized a 9S protein complex from a Xenopus ovary cytosolic subfraction (fraction A) that constitutes this fraction's activity in recognizing a model nuclear import substrate and docking it at the nuclear pore complex. Because of its function, the complex is termed karyopherin. The 54- and 56-kDa subunits of the complex are termed alpha 1 and alpha 2, respectively, and the 97-kDa subunit is termed beta. In an alternative approach we have identified karyopherin beta from a rat liver cytosolic subfraction A by using immobilized rat nucleoporin Nup98 in a single, affinity-based enrichment step. We have molecularly cloned and sequenced rat karyopherin beta. Comparison with protein sequence data banks showed no significant similarity to other known proteins. Using nitrocellulose-immobilized rat liver nuclear envelope proteins and nuclear import substrate as a ligand, we found Xenopus fraction A-dependent binding to at least three bona fide nucleoporins (Nup214, Nup153, and Nup98) and to a candidate nucleoporin with an estimated molecular mass of 270 kDa. We propose that these nucleoporins function as docking proteins for karyopherin-mediated binding of substrate in a nuclear import/export pathway across the nuclear pore complex.

Amino Acid Sequence↗

PubMed2000

Mutations of the second extracellular loop of the human lutropin receptor emphasize the importance of receptor activation and de-emphasize the importance of receptor phosphorylation in agonist-induced internalization.

Alanine scanning mutagenesis of the second extracellular loop of the human lutropin receptor (hLHR) showed that mutation of most of the residues present in this region either enhance or impair the internalization of agonist. A more complete analysis of four mutants, two that enhanced internalization (F515A and T521A) and two that impaired internalization (S512A and V519A), showed that the two mutants that impaired internalization also show a decrease in the sensitivity for agonist-induced cAMP accumulation, whereas the two mutants that enhanced internalization show an increase in the sensitivity for agonist-induced cAMP accumulation. None of these mutants had an effect on the agonist-induced phosphorylation of the hLHR, however. We conclude that, in contrast to the prevailing view of the relative importance of receptor phosphorylation in the internalization of G protein-coupled receptors, the phosphorylation of the hLHR is less important than the agonist-induced activation of the hLHR in the process of internalization.

Cell Line↗

PubMed1979

The importance of significance and the significance of importance.

This article has attempted to illustrate the following principles of statistical significance. 1. An investigator must state the hypothesis to be tested beforehand, so that a null hypothesis can be constructed and validly tested using standard statistical techniques. 2. A statistically significant difference does not prove that a difference exists. It merely establishes that if no difference exists, there is only a small chance that the results obtained would have occurred. A small chance is traditionally and arbitrarily defined as 5% or less. However, even 5% may be too large when important decisions depend on the results. 3. Failure to establish a statistically significant difference does not prove that no difference exists. Chance alone or the small numbers used may have prevented the investigators from rejecting the null hypothesis. 4. A statistically significant difference may be too small to be clinically useful. Statistical significance can be demonstrated for even the most inconsequential of differences if the number of individuals used in the study is large enough. 5. The clinical usefulness of a statistically significant difference may be limited by the degree of overlap. This is reflected in the standard deviation around the averages. In answer to the questions posed at the beginning of this article: If it is statistically significant, it might be true. If it is statistically significant, it might be important. If it is statistically significant, it might be clinically useful.

Humans↗

PubMed1997

HIV-1 infection of non-dividing cells: evidence that the amino-terminal basic region of the viral matrix protein is important for Gag processing but not for post-entry nuclear import.

Human immunodeficiency virus type-1 (HIV-1) is able to infect non-dividing cells such as tissue macrophages productively because post-entry viral nucleoprotein complexes are specifically imported into the nucleus in the absence of mitosis. Although it has been proposed that an amino-terminal region of the viral matrix (MA, p17Gag) protein harbors a basic-type nuclear localization sequence (NLS) that contributes to this process, utilization of three distinct nuclear import assays failed to provide any direct supporting evidence. Instead, we found that disruption of this region (26KK-->TT) reduces the rate at which the viral Gag polyprotein (p55Gag) is post-translationally processed by the viral protease. Consistent with the fact that appropriate proteolytic processing is essential for efficient viral growth in all cell types, we also show that the 26KK-->TT MA mutation is equivalently deleterious to the replication of a primary macrophage-tropic viral isolate in cultures of non-dividing and dividing cells. Taken together, these observations suggest that proteins other than MA supply the NLS(s) that enable HIV-1 to infect non-dividing cells.

Amino Acid Sequence↗

PubMed1997

Importin alpha from Arabidopsis thaliana is a nuclear import receptor that recognizes three classes of import signals.

Protein import into the nucleus is a two-step process. In vitro import systems from vertebrate cell extracts have shown several soluble factors are required. One of these factors is the receptor importin alpha, which binds to nuclear localization signals (NLS) in vitro. We previously cloned an importin alpha homolog from Arabidopsis thaliana (At-IMP alpha) and demonstrated that this protein was not depleted from tobacco (Nicotiana tabacum) protoplasts after permeabilization of the plasma membrane, (Hicks et al., 1996). To determine if At-IMP alpha is functional, we used an in vitro NLS-binding assay. We found that At-IMP alpha is specific, and the receptor is able to recognize three classes of NLS identified in plants. Purified antibodies to At-IMP alpha were used to determine the in vivo location of importin alpha in tobacco protoplasts. Importin alpha is found in the cytoplasm and nucleus, and it is most highly concentrated at the nuclear envelope. The biochemical properties of nuclear importin alpha and localization studies using purified nuclei demonstrate that importin alpha is tightly associated with the plant nucleus. Moreover, these results suggest that a fraction of nuclear importin alpha interacts with the nuclear pore complex.

Amino Acid Sequence↗

PubMed1993

Increasing importance of Trichophyton tonsurans in childhood tinea in New South Wales. The pattern of childhood tinea in New South Wales, Australia 1979-1988: the emergence of Trichophyton tonsurans as an important pathogen in tinea capitis in white children.

A retrospective study was undertaken of 192 cases of culture proven tinea capitis occurring between 1979 and 1988 in a predominantly white population of children in New South Wales (NSW). The aim of the study was to identify whether Trichophyton tonsurans was increasing in importance in the causation of this condition in Australia as it was in many other parts of the world. The results of our study were compared with those of earlier Australian studies. Our study demonstrated that Trichophyton tonsurans is now equal in importance to Microsporum canis which was previously the strongly predominant organism.

Adolescent↗

PubMed2005

The importance of agricultural tire habitats for mosquitoes of public health importance in New York State.

The presence of mosquito species breeding in agricultural "bunker tires" on dairy farms in New York state was evaluated. Twelve species of mosquitoes (Aedes vexans, Anopheles barberi, An. punctipenriis, An. perplexens, Culex pipiens pipiens, Cx. restuans, Cx. salinarius, Cx. territans, Toxorhynchites rutilus septentrionalis, Ochlerotatus atropalpus, Oc. japonicus japonicus, and Oc. triseriatus) were collected from 8 New York state dairy farms in 2001 and from 17 dairy farms in 2002. All but 2 of these species have been found naturally infected with arboviruses and could be important vectors affecting human and animal health. Because of the potential public and animal health importance of the invasive species Oc. j. japonicus, active surveillance to identify breeding sites and distribution of this mosquito is essential. In 2001, Oc. j. japonicus was recovered from 5 of 8 central New York dairy farms surveyed. In 2002, Oc. j. japonicus was recovered from 4 of the same dairy farms plus an additional dairy out of 5 surveyed. This species appears to be established on dairy farms in the south, central, and eastern regions of New York state, with greatest abundance in the southeastern region. A single Oc. j. japonicus larva was collected from the northern region on the final sampling date in September 2002. Our data demonstrate that agricultural tire habitats can be productive breeding sites for arbovirus vectors. As a consequence, these habitats should not be ignored in vector control and surveillance programs.

Aedes↗