Biomedical subjects

L H Johnston

Publications and source records attributed to L H Johnston.

At least 19 recordsLinked to original sources

PubMed2002

CD40 regulates the processing of NF-kappaB2 p100 to p52.

The nf-kb2 gene encodes the cytoplasmic NF-kappaB inhibitory protein p100 from which the active p52 NF-kappaB subunit is derived by proteasome-mediated proteolysis. Ligands which stimulate p100 processing to p52 have not been defined. Here, ligation of CD40 on transfected 293 cells is shown to trigger p52 production by stimulating p100 ubiquitylation and subsequent proteasome-mediated proteolysis. CD40-mediated p52 accumulation is dependent on de novo protein synthesis and triggers p52 translocation into the nucleus to generate active NF-kappaB dimers. Endogenous CD40 ligation on primary murine splenic B cells also stimulates p100 processing, which results in the delayed nuclear translocation of p52-RelB dimers. In both 293 cells and primary splenic B cells, the ability of CD40 to trigger p100 processing requires functional NF-kappaB-inducing kinase (NIK). In contrast, NIK activity is not required for CD40 to stimulate the degradation of IkappaBalpha in either cell type. The regulation of p100 processing by CD40 is likely to be important for the transcriptional regulation of CD40 target genes in adaptive immune responses.

Active Transport, Cell Nucleus↗

PubMed2001

Order of function of the budding-yeast mitotic exit-network proteins Tem1, Cdc15, Mob1, Dbf2, and Cdc5.

The Dbf2 protein kinase functions as part of the mitotic-exit network (MEN), which controls the inactivation of the Cdc28-Clb2 kinase in late mitosis [1]. The MEN includes the Tem1 GTP binding protein; the kinases Cdc15 and Cdc5; Mob1, a protein of unknown function; and the phosphatase Cdc14 [2]. Here we have used Dbf2 kinase activity to investigate the regulation and order of function of the MEN. We find that Tem1 acts at the top of the pathway, upstream of Cdc15, which in turn functions upstream of Mob1 and Dbf2. The Cdc5 Polo-like kinase impinges at least twice on the MEN since it negatively regulates the network, probably upstream of Tem1, and is also required again for Dbf2 kinase activation. Furthermore, we find that regulation of Dbf2 kinase activity and actin ring formation at the bud neck are causally linked. In metaphase-arrested cells, the MEN inhibitor Bub2 restrains both Dbf2 kinase activity [3] and actin ring formation [4]. We find that the MEN proteins that are required for Dbf2 kinase activity are also required for actin ring formation. Thus, the MEN is crucial for the regulation of cytokinesis, as well as mitotic exit.

Fungal Proteins↗

PubMed2001

Rme1, which controls CLN2 expression in Saccharomyces cerevisiae, is a nuclear protein that is cell cycle regulated.

In Saccharomyces cerevisiae commitment to cell division occurs at a point in G1 termed Start. This important transition is regulated by the cyclin-dependent kinase Cdc28, in association with the G1 cyclins Cln1, 2 and 3. Transcription of the G1 cyclins is induced by the transcription factor complexes SBF (Swi4-Swi6) and MBF (Mbp1-Swi6); however, data suggest that other proteins are also able to regulate their expression. We previously identified Rme1, a transcription factor with a well documented role in negatively regulating IME1 expression and meiosis, as an activator of CLN2 transcription. We now show that Rme1 acts through two specific Rme1 response elements in the CLN2 promoter to induce expression of the gene. We have analysed in detail the timing of RME1 transcription at the end of mitosis and in G1, and the roles of the transcription factors Ace2 and Swi5 in mediating this expression. We also demonstrate that the Rme1 protein is cell cycle regulated, peaking in G1 and appearing in the nucleus at this time. Finally, the role of RME1 in cell cycle regulation is confirmed by the observation of periodic RME1 expression in diploid cells, where it has no IME1 repressor function; this finding emphasises its role in the regulation of CLN2 expression in G1.

Blotting, Northern↗

PubMed2001

Overlapping and distinct roles of the duplicated yeast transcription factors Ace2p and Swi5p.

The yeast transcription factors Ace2p and Swi5p regulate the expression of several target genes involved in mating type switching, exit from mitosis and cell wall function. We describe the analysis of 12 novel targets, some regulated by Ace2p or Swi5p alone and some by both. We show that Ace2p is the major regulator of four genes (CTS1, YHR143W, SCW11 and YER124C). Expression of all four is inhibited by Swi5p. Like Cts1p and Scw11p, the two new Ace2p targets are associated with cell wall metabolism. Yhr143p is localized to the cell wall, and deletion affects cell separation and enhances pseudohyphal growth. Deleting YER124C also affects cell separation and sensitivity to drugs targeted against the cell wall. Expression of PIR1, YPL158C and YNL046W is dependent on Swi5p alone. In contrast, expression of YBR158W, YNL078W and YOR264W is minimized when both ace2 and swi5 are disrupted. We propose that, although Ace2p and Swi5p co-operate to induce the expression of a subset of genes, some functional divergence has occurred. This results in a delay in the expression of those genes predominantly regulated by Ace2p, compared with those predominantly regulated by Swi5p.

Cell Cycle Proteins↗

PubMed2001

The Spo12 protein of Saccharomyces cerevisiae: a regulator of mitotic exit whose cell cycle-dependent degradation is mediated by the anaphase-promoting complex.

The Spo12 protein plays a regulatory role in two of the most fundamental processes of biology, mitosis and meiosis, and yet its biochemical function remains elusive. In this study we concentrate on the genetic and biochemical analysis of its mitotic function. Since high-copy SPO12 is able to suppress a wide variety of mitotic exit mutants, all of which arrest with high Clb-Cdc28 activity, we speculated whether SPO12 is able to facilitate exit from mitosis when overexpressed by antagonizing mitotic kinase activity. We show, however, that Spo12 is not a potent regulator of Clb-Cdc28 activity and can function independently of either the cyclin-dependent kinase inhibitor (CDKi), Sic1, or the anaphase-promoting complex (APC) regulator, Hct1. Spo12 protein level is regulated by the APC and the protein is degraded in G1 by an Hct1-dependent mechanism. We also demonstrate that in addition to localizing to the nucleus Spo12 is a nucleolar protein. We propose a model where overexpression of Spo12 may lead to the delocalization of a small amount of Cdc14 from the nucleolus, resulting in a sufficient lowering of mitotic kinase levels to facilitate mitotic exit. Finally, site-directed mutagenesis of highly conserved residues in the Spo12 protein sequence abolishes both its mitotic suppressor activity as well as its meiotic function. This result is the first indication that Spo12 may carry out the same biochemical function in mitosis as it does in meiosis.

Amino Acid Sequence↗

PubMed2001

The Bub2-dependent mitotic pathway in yeast acts every cell cycle and regulates cytokinesis.

In eukaryotes an abnormal spindle activates a conserved checkpoint consisting of the MAD and BUB genes that results in mitotic arrest at metaphase. Recently, we and others identified a novel Bub2-dependent branch to this checkpoint that blocks mitotic exit. This cell-cycle arrest depends upon inhibition of the G-protein Tem1 that appears to be regulated by Bfa1/Bub2, a two-component GTPase-activating protein, and the exchange factor Lte1. Here, we find that Bub2 and Bfa1 physically associate across the entire cell cycle and bind to Tem1 during mitosis and early G1. Bfa1 is multiply phosphorylated in a cell-cycle-dependent manner with the major phosphorylation occurring in mitosis. This Bfa1 phosphorylation is Bub2-dependent. Cdc5, but not Cdc15 or Dbf2, partly controls the phosphorylation of Bfa1 and also Lte1. Following spindle checkpoint activation, the cell cycle phosphorylation of Bfa1 and Lte1 is protracted and some species are accentuated. Thus, the Bub2-dependent pathway is active every cell cycle and the effect of spindle damage is simply to protract its normal function. Indeed, function of the Bub2 pathway is also prolonged during metaphase arrests imposed by means other than checkpoint activation. In metaphase cells Bub2 is crucial to restrain downstream events such as actin ring formation, emphasising the importance of the Bub2 pathway in the regulation of cytokinesis. Our data is consistent with Bub2/Bfa1 being a rate-limiting negative regulator of downstream events during metaphase.

Anaphase-Promoting Complex-Cyclosome↗

PubMed2001

The name of the game: a review of sexual exploitation of females in sport.

Sexual harassment and abuse has been a recognized problem in the workplace, schools, and residential homes for more than three decades. Many professional policies highlight the potential for abusing positions of trust, and therefore forbid intimate relationships between, for example, doctors and patients, and psychologists and clients. Yet, abuse of power in the coach-athlete relationship has only recently been acknowledged. This paper discusses definitions of sexual exploitation, prevalence figures, methods used for entrapping athletes, potential risk factors, signs of abuse and harassment, and the consequences for survivors.

Adolescent↗

PubMed2000

Characterization of the yeast Cdc7p/Dbf4p complex purified from insect cells. Its protein kinase activity is regulated by Rad53p.

The yeast Saccharomyces cerevisiae Cdc7p/Dbf4p protein kinase complex was purified to near homogeneity from insect cells. The complex efficiently phosphorylated yeast Mcm2p and less efficiently the remaining Mcm proteins or other replication proteins. Significantly, when pretreated with alkaline phosphatase, Mcm2p became completely inactive as a substrate, suggesting that it must be phosphorylated by other protein kinase(s) to be a substrate for the Cdc7p/Dbf4p complex. Mutant Cdc7p/Dbf4p complexes containing either Cdc7-1p or Dbf4-1 approximately 5p were also partially purified from insect cells and characterized in vitro. Furthermore, the autonomously replicating sequence binding activity of various dbf4 mutants was also analyzed. These studies suggest that the autonomously replicating sequence-binding and Cdc7p protein kinase activation domains of Dbf4p collaborate to form an active Cdc7p/Dbf4p complex and function during S phase in S. cerevisiae. It is shown that Rad53p phosphorylates the Cdc7p/Dbf4p complex in vitro and that this phosphorylation greatly inhibits the kinase activity of Cdc7p/Dbf4p. This result suggests that Rad53p controls the initiation of chromosomal DNA replication by regulating the protein kinase activity associated with the Cdc7p/Dbf4p complex.

Alkaline Phosphatase↗

PubMed2000

The forkhead protein Fkh2 is a component of the yeast cell cycle transcription factor SFF.

In the yeast Saccharomyces cerevisiae, the MADS-box protein Mcm1, which is highly related to mammalian SRF (serum response factor), forms a ternary complex with SFF (Swi five factor) to regulate the cell cycle expression of genes such as SWI5, CLB2 and ACE2. Here we show that the forkhead protein Fkh2 is a component of SFF and is essential for ternary complex formation on the SWI5 and ACE2 promoters. Fkh2 is essential for the correct cell cycle periodicity of SWI5 and CLB2 gene expression and is phosphorylated with a timing that is consistent with a role in this expression. Furthermore, investigation of the relationship between Fkh2 and a related forkhead protein Fkh1 demonstrates that these proteins act in overlapping pathways to regulate cell morphology and cell separation. This is the first example of a eukaryotic transcription factor complex containing both a MADS-box and a forkhead protein, and it has important implications for the regulation of mammalian gene expression.

Cell Cycle↗

PubMed2000

A Cdc7p-Dbf4p protein kinase activity is conserved from yeast to humans.

DBF4 and CDC7 were identified as budding yeast cell cycle mutants that arrest immediately before S phase. The Dbf4p and Cdc7p proteins interact to form a protein kinase, Cdc7p being the catalytic subunit and Dbf4p is a cyclin-like molecule that activates the kinase in late G1. Dbf4p also targets Cdc7p to origins of replication where likely substrates include the Mcm proteins. Dbf4p and Cdc7p related proteins occur in the fission yeast and in metazoans. These also phosphorylate Mcm proteins and preliminary evidence indicates a similar function to Dbf4p/Cdc7p in budding yeast. The Dbf4p/Cdc7p activity will therefore very likely be conserved in all eukaryotes.

Cell Cycle↗

PubMed2000

Regulation of the Pcl7-Pho85 cyclin-cdk complex by Pho81.

Saccharomyces cerevisiae strains lacking a functional Pho85 cyclin-dependent kinase (cdk) exhibit a complex phenotype, including deregulation of phosphatase genes controlled by the transcription factor Pho4, slow growth on rich media, failure to grow using galactose, lactate or glycerol as a carbon source and hyperaccumulation of glycogen. The ability of Pho85 to regulate the transcription factor Pho4 is mediated by its association the Pho80 cyclin. Some other regulatory functions of the Pho85 cdk have been shown to be mediated via its interaction with a recently identified family of Pho80-related cyclins (Pcls). Here, we show that the poorly characterized Pho80-like protein Pcl7 forms a functional kinase complex with the Pho85 cdk, and that the activity of this complex is inhibited in response to phosphate starvation. Additionally, we show that Pcl7 interacts with the phosphate-regulated cyclin-cdk inhibitor Pho81, and that the regulation of the Pcl7-Pho85 complex in response to changes in phosphate levels is dependent on Pho81. Thus, we demonstrate for the first time that the Pho81 regulator is not dedicated to regulating Pho80, but may act to co-ordinate the activity of both the Pho80-Pho85 and Pcl7-Pho85 cyclin-cdk complexes in response to phosphate levels. We also demonstrate that expression of Pcl7 is cell cycle regulated, with maximal activity occurring in mid to late S-phase, perhaps suggesting a role for Pcl7 in cell cycle progression. Finally, we describe the phenotype of pcl7Delta and pcl6Delta yeast strains that have defects in carbon source utilization.

Amino Acid Sequence↗

PubMed2000

The Skn7 response regulator of Saccharomyces cerevisiae interacts with Hsf1 in vivo and is required for the induction of heat shock genes by oxidative stress.

The Skn7 response regulator has previously been shown to play a role in the induction of stress-responsive genes in yeast, e.g., in the induction of the thioredoxin gene in response to hydrogen peroxide. The yeast Heat Shock Factor, Hsf1, is central to the induction of another set of stress-inducible genes, namely the heat shock genes. These two regulatory trans-activators, Hsf1 and Skn7, share certain structural homologies, particularly in their DNA-binding domains and the presence of adjacent regions of coiled-coil structure, which are known to mediate protein-protein interactions. Here, we provide evidence that Hsf1 and Skn7 interact in vitro and in vivo and we show that Skn7 can bind to the same regulatory sequences as Hsf1, namely heat shock elements. Furthermore, we demonstrate that a strain deleted for the SKN7 gene and containing a temperature-sensitive mutation in Hsf1 is hypersensitive to oxidative stress. Our data suggest that Skn7 and Hsf1 cooperate to achieve maximal induction of heat shock genes in response specifically to oxidative stress. We further show that, like Hsf1, Skn7 can interact with itself and is localized to the nucleus under normal growth conditions as well as during oxidative stress.

Adenosine Triphosphatases↗

PubMed2000

The psychological impact of injury: effects of prior sport and exercise involvement.

OBJECTIVES: To test the assumption that the psychological impact of injury varies with involvement in sport and exercise, and that those who are more involved in sport and exercise before injury would experience greater negative affect and retarded recovery. METHOD: Patients attending for physiotherapy completed a battery of questionnaires including measures of mood and perceived recovery, at the beginning, middle, and end of formal rehabilitation. Complete data were available for 93 patients. RESULTS: Those who were more involved in sport and exercise before injury registered higher levels of confusion and perceived their recovery to be less, possibly reflecting greater information needs and a greater mismatch between current status and that before injury in the athletic sample. Reported negative affect did not vary with sport and exercise involvement. CONCLUSIONS: Incapacitation for those not involved in sport and exercise before injury may have much the same affective impact as it does for those with considerable involvement. However, those with considerable involvement did report higher levels of confusion and perceived their recovery to be less towards the end of rehabilitation. This suggests that it may be important to assess affective reactions and perceived recovery during the re-entry phase.

Adult↗

PubMed2000

The budding yeast Dbf2 protein kinase localises to the centrosome and moves to the bud neck in late mitosis.

Dbf2 is a multifunctional protein kinase in Saccharomyces cerevisiae that functions in transcription, the stress response and as part of a network of genes in exit from mitosis. By analogy with fission yeast it seemed likely that these mitotic exit genes would be involved in cytokinesis. As a preliminary investigation of this we have used Dbf2 tagged with GFP to examine intracellular localisation of the protein in living cells. Dbf2 is found on the centrosomes/spindle pole bodies (SPBs) and also at the bud neck where it forms a double ring. The localisation of Dbf2 is cell cycle regulated. It is on the SPBs for much of the cell cycle and migrates from there to the bud neck in late mitosis, consistent with a role in cytokinesis. Dbf2 partly co-localises with septins at the bud neck. A temperature-sensitive mutant of dbf2 also blocks progression of cytokinesis at 37 degrees C. Following cytokinesis some Dbf2 moves into the nascent bud. Localisation to the bud neck depends upon the septins and also the mitotic exit network proteins Mob1, Cdc5, Cdc14 and Cdc15. The above data are consistent with Dbf2 acting downstream in a pathway controlling cytokinesis.

Actins↗

PubMed1999

Juvenile Parkinson's disease with REM sleep behavior disorder, sleepiness, and daytime REM onset.

We describe an unmedicated patient with juvenile PD with difficulties maintaining wakefulness and the atonia of REM sleep. Laboratory testing showed enhanced muscle activity in REM sleep consistent with a history of dream enactment behavior (i.e., REM sleep behavior disorder) and daytime sleepiness, and REM-sleep onsets on multiple sleep latency testing. The results emphasize the potential role of dopamine and basal ganglia circuits in the modulation of activated behavioral states (e.g., wakefulness and REM sleep).

Adolescent↗

PubMed1999

A Bub2p-dependent spindle checkpoint pathway regulates the Dbf2p kinase in budding yeast.

Exit from mitosis in all eukaroytes requires inactivation of the mitotic kinase. This occurs principally by ubiquitin-mediated proteolysis of the cyclin subunit controlled by the anaphase-promoting complex (APC). However, an abnormal spindle and/or unattached kinetochores activates a conserved spindle checkpoint that blocks APC function. This leads to high mitotic kinase activity and prevents mitotic exit. DBF2 belongs to a group of budding yeast cell cycle genes that when mutated prevent cyclin degradation and block exit from mitosis. DBF2 encodes a protein kinase which is cell cycle regulated, peaking in metaphase-anaphase B/telophase, but its function remains unknown. Here, we show the Dbf2p kinase activity to be a target of the spindle checkpoint. It is controlled specifically by Bub2p, one of the checkpoint components that is conserved in fission yeast and higher eukaroytic cells. Significantly, in budding yeast, Bub2p shows few genetic or biochemical interactions with other members of the spindle checkpoint. Our data now point to the protein kinase Mps1p triggering a new parallel branch of the spindle checkpoint in which Bub2p blocks Dbf2p function.

Anaphase↗

PubMed1999

TPL-2 kinase regulates the proteolysis of the NF-kappaB-inhibitory protein NF-kappaB1 p105.

The transcription factor NF-kappaB is composed of homodimeric and heterodimeric complexes of Rel/NF-kappaB-family polypeptides, which include Rel-A, c-Rel, Rel-B, NF-kappaB/p50 and NF-kappaB2/p52 . The NF-kappaB1 gene encodes a larger precursor protein, p105, from which p50 is produced constitutively by proteasome-mediated removal of the p105 carboxy terminus. The p105 precursor also acts as an NFkappaB-inhibitory protein, retaining associated p50, c-Rel and Rel-A proteins in the cytoplasm through its carboxy terminus. Following cell stimulation by agonists, p105 is proteolysed more rapidly and released Rel subunits translocate into the nucleus. Here we show that TPL-2 , which is homologous to MAP-kinase-kinase kinases in its catalytic domain, forms a complex with the carboxy terminus of p105. TPL-2 was originally identified, in a carboxy-terminal-deleted form, as an oncoprotein in rats and is more than 90% identical to the human oncoprotein COT. Expression of TPL-2 results in phosphorylation and increased degradation of p105 while maintaining p50 production. This releases associated Rel subunits or p50-Rel heterodimers to generate active nuclear NF-kappaB. Furthermore, kinase-inactive TPL-2 blocks the degradation of p105 induced by tumour-necrosis factor-alpha. TPL-2 is therefore a component of a new signalling pathway that controls proteolysis of NF-kappaB1 p105.

3T3 Cells↗

PubMed1999

First the CDKs, now the DDKs.

In budding yeast, Dbf4p and Cdc7p control initiation of DNA synthesis. They form a protein kinase - Cdc7p being the catalytic subunit and Dbf4p a cyclin-like molecule that activates the kinase in late G1 phase. Dbf4p also targets Cdc7p to origins of replication, where probable substrates include certain Mcm proteins. Recent studies have identified Dbf4p- and Cdc7p-related proteins in fission yeast and metazoans. These homologues also phosphorylate Mcm proteins and could have a similar function to that of Dbf4p-Cdc7p in budding yeast. Thus, it seems likely that, like the cyclin-dependent kinases (CDKs), the Dbf4p-Cdc7p activity is conserved in all eukaryotes.

Animals↗