Enhancing untargeted metabolomics using metadata-based source annotation

Human untargeted metabolomics studies annotate only ~10% of molecular features. We introduce reference-data-driven analysis to match metabolomics tandem mass spectrometry (MS/MS) data against metadata-annotated source data as a pseudo-MS/MS reference library. Applying this approach to food source data, we show that it increases MS/MS spectral usage 5.1-fold over conventional structural MS/MS library matches and allows empirical assessment of dietary patterns from untargeted data.

Chk1 inhibits E2F6 repressor function in response to replication stress to maintain cell-cycle transcription

BACKGROUND

In eukaryotic cells, detection of replication stress results in the activation of the DNA replication checkpoint, a signaling cascade whose central players are the kinases ATR and Chk1. The checkpoint response prevents the accumulation of DNA damage and ensures cell viability by delaying progression into mitosis. However, the role and mechanism of the replication checkpoint transcriptional response in human cells, which is p53 independent, is largely unknown.

RESULTS

We show that, in response to DNA replication stress, the regular E2F-dependent cell-cycle transcriptional program is maintained at high levels, and we establish the mechanisms governing such transcriptional upregulation. E2F6, a repressor of E2F-dependent G1/S transcription, replaces the activating E2Fs at promoters to repress transcription in cells progressing into S phase in unperturbed conditions. After replication stress, the checkpoint kinase Chk1 phosphorylates E2F6, leading to its dissociation from promoters. This promotes E2F-dependent transcription, which mediates cell survival by preventing DNA damage and cell death.

CONCLUSIONS

This work reveals, for the first time, that the regular cell-cycle transcriptional program is part of the DNA replication checkpoint response in human cells and establishes the molecular mechanism involved. We show that maintaining high levels of G1/S cell-cycle transcription in response to replication stress contributes to two key functions of the DNA replication checkpoint response, namely, preventing genomic instability and cell death. Given the critical role of replication stress in oncogene transformation, a detailed understanding of the molecular mechanisms involved in the checkpoint response will contribute to a better insight into cancer development.

Turned on by genotoxic stress

Comment on: Travesa A, et al. EMBO J 2012; 31:1811-22.

DNA replication stress differentially regulates G1/S genes via Rad53-dependent inactivation of Nrm1

MBF and SBF transcription factors regulate a large family of coordinately expressed G1/S genes required for early cell-cycle functions including DNA replication and repair. SBF is inactivated upon S-phase entry by Clb/CDK whereas MBF targets are repressed by the co-repressor, Nrm1. Using genome-wide expression analysis of cells treated with methyl methane sulfonate (MMS), hydroxyurea (HU) or camptothecin (CPT), we show that genotoxic stress during S phase specifically induces MBF-regulated genes. This occurs via direct phosphorylation of Nrm1 by Rad53, the effector checkpoint kinase, which prevents its binding to MBF target promoters. We conclude that MBF-regulated genes are distinguished from SBF-regulated genes by their sensitivity to activation by the S-phase checkpoint, thereby, providing an effective mechanism for enhancing DNA replication and repair and promoting genome stability.

All eukaryotes: before turning off G1-S transcription, please check your DNA

The DNA replication and DNA damage checkpoints are required for the efficient response to genotoxic stress, which is critical for genome stability and cell survival. The DNA replication and damage checkpoints delay progression into mitosis, and at the same time induce the transcription of genes that promote repair of cellular lesions including stabilization of stalled replication forks and induction of DNA repair functions. The elucidation of the mechanism by which the DNA replication checkpoint activates transcription of G1/S genes is provided by our recent study reported in the August issue of Proceedings of the National Academy of Sciences. We show that, in response to stimulation of the DNA replication checkpoint, activation of G1-S transcription is established by inactivation, via phosphorylation by the checkpoint protein kinases, of the MBF-associated transcriptional corepressor Nrm1. This regulation is critical for the survival of cells responding to genotoxic stress. This provides a simple but elegant mechanism by which checkpoint activation can override the regular periodic transcriptional program by directly regulating a cell cycle dependent transcriptional repressor. We discuss the likely conservation of this regulatory pathway in yeast and man.

Ctp1 is a cell-cycle-regulated protein that functions with Mre11 complex to control double-strand break repair by homologous recombination

The Mre11-Rad50-Nbs1 (MRN) complex is a primary sensor of DNA double-strand breaks (DSBs). Upon recruitment to DSBs, it plays a critical role in catalyzing 5' --> 3' single-strand resection that is required for repair by homologous recombination (HR). Unknown mechanisms repress HR in G1 phase of the cell cycle during which nonhomologous end-joining (NHEJ) is the favored mode of DSB repair. Here we describe fission yeast Ctp1, so-named because it shares conserved domains with the mammalian tumor suppressor CtIP. Ctp1 is recruited to DSBs where it is essential for repair by HR. Ctp1 is required for efficient formation of RPA-coated single-strand DNA adjacent to DSBs, indicating that it functions with the MRN complex in 5' --> 3' resection. Transcription of ctp1(+) is periodic during the cell cycle, with the onset of its expression coinciding with the start of DNA replication. These data suggest that regulation of Ctp1 underlies cell-cycle control of HR.

G1 control in yeast and animal cells

In budding yeast, Saccharomyces cerevisiae, the cell cycle is controlled at the G1/S phase transition by regulating the activity of the CDC28 protein kinase. This is the budding yeast homologue of the cdc2 protein kinase associated in most organisms with control of mitosis. In budding yeast CDC28 controls both the G1/S phase transition and the G2/M phase transition by being differentially activated by two distinct classes of positive regulatory subunits known as G1 cyclins or CLNs and B-type cyclins or CLBs, respectively. To establish whether a similar dual role for Cdc2-related kinases exists in animal cells, we and others have sought human homologues of yeast G1 cyclins. Of several candidates, cyclin E is the most promising in that it accumulates prior to S phase and is associated with a pre-S phase protein kinase activity. The kinetics of accumulation of cyclin E-associated protein kinase activity is consistent with a role at the mammalian cell cycle restriction point.

Constraining G1-specific transcription to late G1 phase: the MBF-associated corepressor Nrm1 acts via negative feedback

G1-specific transcription in yeast depends upon SBF and MBF. We have identified Nrm1 (negative regulator of MBF targets 1), as a stable component of MBF. NRM1 (YNR009w), an MBF-regulated gene expressed during late G1 phase, associates with G1-specific promoters via MBF. Transcriptional repression upon exit from G1 phase requires both Nrm1 and MBF. Inactivation of Nrm1 results in prolonged expression of MBF-regulated transcripts and leads to hydroxyurea (HU) resistance and enhanced bypass of rad53Delta- and mec1Delta-associated lethality. Constitutive expression of a stabilized form of Nrm1 represses MBF targets and leads to HU sensitivity. The fission yeast homolog SpNrm1, encoded by the MBF target gene nrm1(+) (SPBC16A3.07c), binds to MBF target genes and acts as a corepressor. In both yeasts, MBF represses G1-specific transcription outside of G1 phase. A negative feedback loop involving Nrm1 bound to MBF leads to transcriptional repression as cells exit G1 phase.

Multiple pathways for suppression of mutants affecting G1-specific transcription in Saccharomyces cerevisiae

In the budding yeast, Saccharomyces cerevisiae, control of cell proliferation is exerted primarily during G(1) phase. The G(1)-specific transcription of several hundred genes, many with roles in early cell cycle events, requires the transcription factors SBF and MBF, each composed of Swi6 and a DNA-binding protein, Swi4 or Mbp1, respectively. Binding of these factors to promoters is essential but insufficient for robust transcription. Timely transcriptional activation requires Cln3/CDK activity. To identify potential targets for Cln3/CDK, we identified multicopy suppressors of the temperature sensitivity of new conditional alleles of SWI6. A bck2Delta background was used to render SWI6 essential. Seven multicopy suppressors of bck2Delta swi6-ts mutants were identified. Three genes, SWI4, RME1, and CLN2, were identified previously in related screens and shown to activate G(1)-specific expression of genes independent of CLN3 and SWI6. The other four genes, FBA1, RPL40a/UBI1, GIN4, and PAB1, act via apparently unrelated pathways downstream of SBF and MBF. Each depends upon CLN2, but not CLN1, for its suppressing activity. Together with additional characterization these findings indicate that multiple independent pathways are sufficient for proliferation in the absence of G(1)-specific transcriptional activators.

Cell cycle-dependent transcription in yeast: promoters, transcription factors, and transcriptomes

In the budding yeast, Saccharomyces cerevisiae, a significant fraction of genes (>10%) are transcribed with cell cycle periodicity. These genes encode critical cell cycle regulators as well as proteins with no direct connection to cell cycle functions. Cell cycle-regulated genes can be organized into 'clusters' exhibiting similar patterns of regulation. In most cases periodic transcription is achieved via both repressive and activating mechanisms. Fine-tuning appears to have evolved by the juxtaposition of regulatory motifs characteristic of more than one cluster within the same promoter. Recent reports have provided significant new insight into the role of the cyclin-dependent kinase Cdk1 (Cdc28) in coordination of transcription with cell cycle events. In early G1, the transcription factor complex known as SBF is maintained in a repressed state by association of the Whi5 protein. Phosphorylation of Whi5 by Cdk1 in late G1 leads to dissociation from SBF and transcriptional derepression. G2/M-specific transcription is achieved by converting the repressor Fkh2 into an activator. Fkh2 serves as a repressor during most of the cell cycle. However, phosphorylation of a cofactor, Ndd1, by Cdk1 late in the cell cycle promotes binding to Fkh2 and conversion into a transcriptional activator. Such insights derived from analysis of specific genes when combined with genome-wide analysis provide a more detailed and integrated view of cell cycle-dependent transcription.

Regulation and recognition of SCFGrr1 targets in the glucose and amino acid signaling pathways

SCFGrr1, one of several members of the SCF family of E3 ubiquitin ligases in budding Saccharomyces cerevisiae, is required for both regulation of the cell cycle and nutritionally controlled transcription. In addition to its role in degradation of Gic2 and the CDK targets Cln1 and Cln2, Grr1 is also required for induction of glucose- and amino acid-regulated genes. Induction of HXT genes by glucose requires the Grr1-dependent degradation of Mth1. We show that Mth1 is ubiquitinated in vivo and degraded via the proteasome. Furthermore, phosphorylated Mth1, targeted by the casein kinases Yck1/2, binds to Grr1. That binding depends upon the Grr1 leucine-rich repeat (LRR) domain but not upon the F-box or basic residues within the LRR that are required for recognition of Cln2 and Gic2. Those observations extend to a large number of Grr1-dependent genes, some targets of the amino acid-regulated SPS signaling system, which are properly regulated in the absence of those basic LRR residues. Finally, we show that regulation of the SPS targets requires the Yck1/2 casein kinases. We propose that casein kinase I plays a similar role in both nutritional signaling pathways by phosphorylating pathway components and targeting them for ubiquitination by SCFGrr1.

Cln3 activates G1-specific transcription via phosphorylation of the SBF bound repressor Whi5

G1-specific transcriptional activation by Cln3/CDK initiates the budding yeast cell cycle. To identify targets of Cln3/CDK, we analyzed the SBF and MBF transcription factor complexes by multidimensional protein interaction technology (MudPIT). Whi5 was identified as a stably bound component of SBF but not MBF. Inactivation of Whi5 leads to premature expression of G1-specific genes and budding, whereas overexpression retards those processes. Whi5 inactivation bypasses the requirement for Cln3 both for transcriptional activation and cell cycle initiation. Whi5 associates with G1-specific promoters via SBF during early G1 phase, then dissociates coincident with transcriptional activation. Dissociation of Whi5 is promoted by Cln3 in vivo. Cln/CDK phosphorylation of Whi5 in vitro promotes its dissociation from SBF complexes. Mutation of putative CDK phosphorylation sites, at least five of which are phosphorylated in vivo, strongly reduces SBF-dependent transcription and delays cell cycle initiation. Like mammalian Rb, Whi5 is a G1-specific transcriptional repressor antagonized by CDK.

Cell Cycle-dependent Phosphorylation of the DNA Polymerase Epsilon Subunit, Dpb2, by the Cdc28 Cyclin-dependent Protein Kinase

DNA polymerase epsilon (Polepsilon), one of the three major eukaryotic replicative polymerases, is comprised of the essential catalytic subunit, called Pol2 in budding yeast, and three accessory subunits, only one of which, Dpb2, is essential. Polepsilon is recruited to replication origins during late G(1) phase prior to activation of replication. In this work we show that the budding yeast Dpb2 is phosphorylated in a cell cycle-dependent manner during late G(1) phase. Phosphorylation results in the appearance of a lower mobility species. The appearance of that species in vivo is dependent upon the Cdc28 cyclin-dependent protein kinase (CDK), which can directly phosphorylate Dpb2 in vitro. Either G(1) cyclin (Cln) or B-type cyclin (Clb)-associated CDK is sufficient for phosphorylation. Mapping of phosphorylation sites by mass spectrometry using a novel gel-based proteolysis protocol shows that, of the three consensus CDK phosphorylation sites, at least two, Ser-144 and Ser-616, are phosphorylated in vivo. The Cdc28 CDK phosphorylates only Ser-144 in vitro. Using site-directed mutagenesis, we show that Ser-144 is sufficient for the formation of the lower mobility form of Dpb2 in vivo. In contrast, Ser-616 appears not to be phosphorylated by Cdc28. Finally, inactivation of all three CDK consensus sites in Dpb2 results in a synthetic phenotype with the pol2-11 mutation, leading to decreased spore viability, slow growth, and increased thermosensitivity. We suggest that phosphorylation of Dpb2 during late G(1) phase at CDK consensus sites facilitates the interaction with Pol2 or the activity of Polepsilon

Cell-cycle-regulatory elements and the control of cell differentiation in the budding yeast

The stable differentiation of cells into other cell types typically involves dramatic reorganization of cellular structures and functions. This often includes remodeling of the cell cycle and the apparatus that controls it. Here we review our understanding of the role and regulation of cell cycle control elements during cell differentiation in the yeast, Saccharomyces cerevisiae. Although the process of differentiation may be more overtly obvious in metazoan organisms, those systems are by nature more difficult to study at a mechanistic level. We consider the relatively well-understood mechanisms by which mating-type switching and the pheromone-induced differentiation of gametes are coupled to the cell cycle as well as the more obscure mechanisms that govern the remodeling of the cell cycle during meiosis and filamentous growth. In some cases, the cell cycle is a primary stimulus for differentiation whereas, in other cases, the signals that promote differentiation alter the cell cycle. Thus, despite relative simplicity of these processes in yeast, the nature of the interplay between the cell cycle and differentiation is diverse.

Grr1-dependent inactivation of Mth1 mediates glucose-induced dissociation of Rgt1 from HXT gene promoters

In budding yeast, HXT genes encoding hexose permeases are induced by glucose via a mechanism in which the F box protein Grr1 antagonizes activity of the transcriptional repressor Rgt1. Neither the mechanism of Rgt1 inactivation nor the role of Grr1 in that process has been understood. We show that glucose promotes phosphorylation of Rgt1 and its dissociation from HXT gene promoters. This cascade of events is dependent upon the F-box protein Grr1. Inactivation of Rgt1 is sufficient to explain the requirement for Grr1 but does not involve Rgt1 proteolysis or ubiquitination. We show that inactivation of Mth1 and Std1, known negative regulators of HXT gene expression, leads to the hyperphosphorylation of Rgt1 and its dissociation from HXT promoters even in the absence of glucose. Furthermore, inactivation of Mth1 and Std1 bypasses the requirement for Grr1 for induction of these events, suggesting they are targets for inactivation by Grr1. Consistent with that proposal, Mth1 is rapidly eliminated in response to glucose via a mechanism that requires Grr1. Based upon these data, we propose that glucose acts via Grr1 to promote the degradation of Mth1. Degradation of Mth1 leads to phosphorylation and dissociation of Rgt1 from HXT promoters, thereby activating HXT gene expression.

Transferable domain in the G(1) cyclin Cln2 sufficient to switch degradation of Sic1 from the E3 ubiquitin ligase SCF(Cdc4) to SCF(Grr1)

Degradation of Saccharomyces cerevisiae G(1) cyclins Cln1 and Cln2 is mediated by the ubiquitin-proteasome pathway and involves the SCF E3 ubiquitin-ligase complex containing the F-box protein Grr1 (SCF(Grr1)). Here we identify the domain of Cln2 that confers instability and describe the signals in Cln2 that result in binding to Grr1 and rapid degradation. We demonstrate that mutants of Cln2 that lack a cluster of four Cdc28 consensus phosphorylation sites are highly stabilized and fail to interact with Grr1 in vivo. Since one of the phosphorylation sites lies within the Cln2 PEST motif, a sequence rich in proline, aspartate or glutamate, serine, and threonine residues found in many unstable proteins, we fused various Cln2 C-terminal domains containing combinations of the PEST and the phosphoacceptor motifs to stable reporter proteins. We show that fusion of the Cln2 domain to a stabilized form of the cyclin-dependent kinase inhibitor Sic1 (Delta N-Sic1), a substrate of SCF(Cdc4), results in degradation in a phosphorylation-dependent manner. Fusion of Cln2 degradation domains to Delta N-Sic1 switches degradation of Sic1 from SCF(Cdc4) to SCF(Grr1). Delta N-Sic1 fused with a Cln2 domain containing the PEST motif and four phosphorylation sites binds to Grr1 and is unstable and ubiquitinated in vivo. Interestingly, the phosphoacceptor domain of Cln2 binds to Grr1 but is not ubiquitinated and is stable. In summary, we have identified a small transferable domain in Cln2 that can redirect a stabilized SCF(Cdc4) target for SCF(Grr1)-mediated degradation by the ubiquitin-proteasome pathway.

A role for the Swe1 checkpoint kinase during filamentous growth of Saccharomyces cerevisiae

In this study we show that inactivation of Hsl1 or Hsl7, negative regulators of the Swe1 kinase, enhances the invasive behavior of haploid and diploid cells. The enhancement of filamentous growth caused by inactivation of both genes is mediated via the Swe1 protein kinase. Whereas Swe1 contributes noticeably to the effectiveness of haploid invasive growth under all conditions tested, its contribution to pseudohyphal growth is limited to the morphological response under standard assay conditions. However, Swe1 is essential for pseudohyphal differentiation under a number of nonstandard assay conditions including altered temperature and increased nitrogen. Swe1 is also required for pseudohyphal growth in the absence of Tec1 and for the induction of filamentation by butanol, a related phenomenon. Although inactivation of Hsl1 is sufficient to suppress the defect in filamentous growth caused by inactivation of Tec1 or Flo8, it is insufficient to promote filamentous growth in the absence of both factors. Moreover, inactivation of Hsl1 will not bypass the requirement for nitrogen starvation or growth on solid medium for pseudohyphal differentiation. We conclude that the Swe1 kinase modulates filamentous development under a broad spectrum of conditions and that its role is partially redundant with the Tec1 and Flo8 transcription factors.

F-box protein Grr1 interacts with phosphorylated targets via the cationic surface of its leucine-rich repeat

The flexibility and specificity of ubiquitin-dependent proteolysis are mediated, in part, by the E3 ubiquitin ligases. One class of E3 enzymes, SKp1/cullin/F-box protein (SCF), derives its specificity from F-box proteins, a heterogeneous family of adapters for target protein recognition. Grr1, the F-box component of SCF(Grr1), mediates the interaction with phosphorylated forms of the G(1) cyclins Cln1 and Cln2. We show that binding of Cln2 by SCF(Grr1) was dependent upon its leucine-rich repeat (LRR) domain and its carboxy terminus. Our structural model for the Grr1 LRR predicted a high density of positive charge on the concave surface of the characteristic horseshoe structure. We hypothesized that specific basic residues on the predicted concave surface are important for recognition of phosphorylated Cln2. We show that point mutations that converted the basic residues on the concave surface but not those on the convex surface to neutral or acidic residues interfered with the capacity of Grr1 to bind to Cln2. The same mutations resulted in the stabilization of Cln2 and Gic2 and also in a spectrum of phenotypes characteristic of inactivation of GRR1, including hyperpolarization and enhancement of pseudohyphal growth. It was surprising that the same residues were not important for the role of Grr1 in nutrient-regulated transcription of HXT1 or AGP1. We concluded that the cationic nature of the concave surface of the Grr1 LRR is critical for the recognition of phosphorylated targets of SCF(Grr1) but that other properties of Grr1 are required for its other functions.

Regulation of transcription by ubiquitination without proteolysis: Cdc34/SCF(Met30)-mediated inactivation of the transcription factor Met4

Polyubiquitination of proteins by Cdc34/SCF complexes targets them for degradation by the 26S proteasome. The essential F-box protein Met30 is the substrate recognition subunit of the ubiquitin ligase SCF(Met30). The critical target of SCF(Met30) is the transcription factor Met4, as deletion of MET4 suppresses the lethality of met30 mutants. Surprisingly, Met4 is a relatively stable protein and its abundance is not influenced by Met30. However, transcriptional repression of Met4 target genes correlates with Cdc34/SCF(Met30)-dependent ubiquitination of Met4. Functionally, ubiquitinated Met4 associates with target promoters but fails to form functional transcription complexes. Our data reveal a novel proteolysis-independent function for Cdc34/SCF and indicate that ubiquitination of transcription factors can be utilized to directly regulate their activities.

White coat hypertension and pregnancy outcome

The presence and outcome effect of white coat hypertension in pregnancy was determined with 24-h ambulatory blood pressure (BP) monitoring. Sixty women presenting with high clinic BP (>/=140/90 mm Hg) in the second trimester were included. Patients were divided into two groups based on daytime ambulatory BP findings: <135/85 mm Hg, white coat hypertension (n = 37); >/=135/85 mm Hg, 'true' hypertension (n = 23). Complicated pregnancy outcome was defined as the presence of pre-eclampsia and/or intrauterine growth restriction. Groups were compared for pregnancy outcome and for background and delivery factors. The predictive value of ambulatory BP measurements for pregnancy outcome was determined. Pregnancy outcome was better in the white coat hypertension group than in the true hypertension group: pre-eclampsia-3 (8.1%) vs 13 (56.5%) (P = 0.0046); intrauterine growth restriction-5 (13.5%) vs 10 (43.4%) (P = 0. 0139); and preterm delivery-11 (29.7%) vs 15 (65.2%) (P = 0.015). Night-time ambulatory BP measurements were the best predictor of complicated pregnancy, followed by daytime and 24-h measurements. We conclude that second trimester ambulatory BP monitoring can be used to differentiate patients who have white coat hypertension, which is associated with a better pregnancy outcome than true hypertension.

DNA polymerase epsilon catalytic domains are dispensable for DNA replication, DNA repair, and cell viability

DNA polymerase epsilon (Pol epsilon) is believed to play an essential catalytic role during eukaryotic DNA replication and is thought to participate in recombination and DNA repair. That Pol epsilon is essential for progression through S phase and for viability in budding and fission yeasts is a central element of support for that view. We show that the amino-terminal portion of budding yeast Pol epsilon (Pol2) containing all known DNA polymerase and exonuclease motifs is dispensable for DNA replication, DNA repair, and viability. However, the carboxy-terminal portion of Pol2 is both necessary and sufficient for viability. Finally, the viability of cells lacking Pol2 catalytic function does not require intact DNA replication or damage checkpoints.

Microalbuminuria after pregnancy complicated by pre-eclampsia

BACKGROUND

Microalbuminuria is an important risk factor for underlying vascular disease. Its detection after pregnancy complicated by pre-eclampsia may have predictive value for the later development of chronic hypertension or renal disease.

METHOD

The study group consisted of 48 women in whom pregnancy had been complicated by pre-eclampsia. Urinary albumin excretion rate, blood pressure, and renal function parameters were assessed 2-4 months and 3-5 years after the pregnancy. Results were compared with those in 44 women after normal pregnancy.

RESULTS

Mean urinary albumin excretion rate was significantly higher in the study group than in the controls both at 2-4 months after delivery (27.0 +/- 33 vs 6.1 +/- 3.3 mg/24 h) and at 3-5 years after delivery (23.5 +/- 26.8 vs 6.7 +/- 2.8 mg/24 h) (P = 0.001). The rate of occurrence of microalbuminuria was not significantly different between the early (58%) and late (42%) time-points within the study group or between the nulliparous and the multiparous women.

CONCLUSIONS

A history of pregnancy complicated by pre-eclampsia is associated with a high occurrence of microalbuminuria. Whether the presence of microalbuminuria reflects a possible underlying vascular disease in affected patients needs to be further investigated in large-scale studies.

Acute and chronic effects of spirapril, alone or in combination with isradipine on kidney function and blood pressure in patients with reduced kidney function and hypertension

In the present study we investigated the effect of a single dose, and 3 months of treatment with spirapril on kidney function, renin-angiotensin system, renal handling of sodium and blood pressure, in patients with reduced kidney function (serum creatinine 1.5-3 mg%) and hypertension. A single dose of 6 mg spirapril given at the beginning of the study did not affect glomerular filtration rate (GFR), renal plasma flow (RPF), angiotensin converting enzyme (ACE) activity, plasma renin activity (PRA) or renal handling of sodium. When the single dose of spirapril was given after 3 months of treatment with this agent, renal hemodynamics and PRA did not change. ACE activity, which was depressed by the previous spirapril treatment, decreased further (from 9.5 +/- 3.1 to 1.4 +/- 1.0 nmol/ml/min), (p < 0.05). Administration of 6 mg spirapril o.d. for 3 months did not have any effect on GFR or RPF. Serum ACE activity decreased from 92.1 +/- 8.0 to 5.1 +/- 2.6 nmol/ml/min (p < 0.05) and PRA increased from 1.4 +/- 1.2 to 4.1 +/- 3.6 ng/ml/min (p < 0.05). Plasma aldosterone did not change. Similar results were obtained when spirapril was combined with 5 mg isradipine in the initial and final single dose, or in the 3 months' treatment (5 mg o.d.). Blood pressure was normalized in 38% of the patients who received spirapril and in 71% of the patients who received spirapril and isradipine. Thus, (a) treatment with spirapril in patients with mild to moderate chronic renal insufficiency was not associated with deleterious effects on kidney function; (b) spirapril in a dose of 6 mg alone or in combination with 5 mg isradipine is effective in reducing blood pressure in hypertensive patients with reduced kidney function.

Yeast G1 cyclins are unstable in G1 phase

In most eukaryotes, commitment to cell division occurs in late G1 phase at an event called Start in the yeast Saccharomyces cerevisiae, and called the restriction point in mammalian cells. Start is triggered by the cyclin-dependent kinase Cdc28 and three rate-limiting activators, the G1 cyclins Cln1, Cln2 and Cln3. Cyclin accumulation in G1 is driven in part by the cell-cycle-regulated transcription of CLN1 and CLN2, which peaks at Start. CLN transcription is modulated by physiological signals that regulate G1 progression, but it is unclear whether Cln protein stability is cell-cycle-regulated. It has been suggested that once cells pass Start, Cln proteolysis is triggered by the mitotic cyclins Clb1, 2, 3 and 4. But here we show that G1 cyclins are unstable in G1 phase, and that Clb-Cdc28 activity is not needed fgr G1 cyclin turnover. Cln instability thus provides a means to couple Cln-Cdc28 activity to transcriptional regulation and protein synthetic rate in pre-Start G1 cells.

CLB5 and CLB6 are required for premeiotic DNA replication and activation of the meiotic S/M checkpoint

Initiation of DNA replication during the mitotic cell cycle requires the activation of a cyclin-dependent protein kinase (CDK). The B-type cyclins Clb5 and Clb6 are the primary activators of the S phase function of the budding yeast CDK Cdc28. However, in mitotically growing cells this role can be fulfilled by the other B-type cyclins Clb1-Clb4. We report here that cells undergoing meiotic development also require Clb dependent CDK activity for DNA replication. Diploid clb5/clb5 clb6/clb6 mutants are unable to perform premeiotic DNA replication. Despite this defect, the mutant cells progress into the meiotic program and undergo lethal segregation of unreplicated DNA suggesting that they fail to activate a checkpoint that restrains meiotic M phase until DNA replication is complete. We have found that a DNA replication checkpoint dependent on the ATM homolog MEC1 operates in wild-type cells during meiosis and can be invoked in response to inhibition of DNA synthesis. Although cells that lack clb5 and clb6 are unable to activate the meiotic DNA replication checkpoint, they do possess an intact DNA damage checkpoint which can restrain chromosome segregation in the face of DNA damage. We conclude that CLB5 and CLB6 are essential for premeiotic DNA replication and, consequently, for activation of a meiotic DNA replication checkpoint.

Regulation of cell size by glucose is exerted via repression of the CLN1 promoter

Yeast cells are keenly sensitive to the availability and quality of nutrients. Addition of glucose to cells growing on a poorer carbon source elicits a cell cycle delay during G1 phase and a concomitant increase in the cell size. The signal is transduced through the RAS-cyclic AMP pathway. Using synchronized populations of G1 cells, we show that the increase in cell size required for budding depends upon CLN1 but not other G1 cyclins. This delay in cell cycle initiation is associated specifically with transcriptional repression of CLN1. CLN2 is not repressed. Repression of CLN1 is not limited to the first cycle following glucose addition but occurs in each cell cycle during growth on glucose. A 106-bp fragment of the CLN1 promoter containing the three MluI cell cycle box (MCB) core elements responsible for the majority of CLN1-associated upstream activation sequence activity is sufficient to confer glucose-induced repression on a heterologous reporter. A mutant CLN2 promoter that is rendered dependent upon its three MCB core elements due to inactivation of its Swi4-dependent cell cycle box (SCB) elements is also repressed by glucose. The response to glucose is partially suppressed by inactivation of SWI4, but not MBP1, which is consistent with the dependence of MCB core elements upon the SCB-binding transcription factor (SBF). We suggest that differential regulation of CLN1 and CLN2 by glucose results from differences in the capacity of SBF to activate transcription driven by SCB and MCB core elements. Finally, we show that transcriptional repression is sufficient to explain the cell cycle delay that occurs in response to glucose.

Prednisone dosage and pregnancy outcome in renal allograft recipients

BACKGROUND

The literature contains reports of 2309 pregnancies in some 1600 women who have undergone renal transplantation. Certain pre-pregnancy factors, especially hypertension, renal graft dysfunction, short interval between transplant and pregnancy, and high immunosuppressive drug dosage, appear to increase the neonatal risks.

METHOD

We describe the outcome of 42 pregnancies in 27 allograft recipients at Rabin Medical Center (Beilinson Campus) in Israel during the last 8 years. All were treated with combination immunosuppression regimens.

RESULTS

The average interval from transplantation to conception was 3.7 +/- 0.4 years (2 months to 9 years). Rejection episodes occurred in 37% prior to pregnancy but in none during or immediately after pregnancy. Twenty-eight percent of the pregnancies ended in therapeutic or spontaneous abortions, and 29 of the 30 deliveries ended in a live birth. The prematurity rate (63%) was similar to that described in the literature for this patient group. Renal deterioration was evident in seven women (26%) within 2 years after delivery. Use of 7.5 mg/d prednisone (vs. 10 mg/d) before pregnancy was observed as the most significant preconception parameter related to better pregnancy outcome. A long interval from transplantation to conception and lack of pre-existing hypertension were also significant.

CONCLUSION

The better pregnancy outcome associated with lower prednisone dosage is probably related to the fact that the patients selected to receive the low-dose regimen have had a longer and less complicated post-transplantation course.

Course and prognosis in patients > or = 70 years of age with congestive heart failure and normal versus abnormal left ventricular ejection fraction

In this study of 501 patients aged > or =70 years hospitalized with congestive heart failure, 34.1% had normal left ventricular systolic function. Reduced left ventricular ejection fraction was an independent predictor of an adverse prognosis at 3 months but not at 1 year.

Pregnancy outcome in renal allograft recipients in Israel

The literature contains reports of 2,309 pregnancies in some 1,600 women who have undergone renal transplantation. Certain pre-pregnancy factors, especially hypertension, renal graft dysfunction and short interval between transplant and pregnancy, appear to increase the neonatal risks. We describe the outcome of 42 pregnancies in 27 allograft recipients at Beilinson Medical Center in Israel during the last 8 years. All were treated with combination immunosuppression regimens. The average interval from time of transplantation to conception was 3.7 +/- 0.4 years (2 months to 9 years). Rejection episodes occurred in 37% prior to pregnancy but in none during or immediately after pregnancy. Of the 42 pregnancies 28% ended in therapeutic or spontaneous abortions, and 29 of the 30 deliveries ended in a life birth. The prematurity rate (65%) was similar to that described in the literature. Renal deterioration was evident in seven women (26%) within 2 years after delivery. Despite this significant success rate, pregnancy in organ transplant patients should still be considered high risk.

Effect of a multidisciplinary intervention on medication compliance in elderly patients with congestive heart failure

PURPOSE

The objectives of this investigation were to prospectively assess medication compliance rates in elderly patients with congestive heart failure, to identify factors associated with reduced compliance, and to evaluate the effect of a multidisciplinary treatment approach on medication adherence.

PATIENTS AND METHODS

A total of 156 patients > or = 70 years of age (mean, 79.4 +/- 6.0; 67% female, 65% nonwhite) hospitalized with congestive heart failure were evaluated prospectively. Prior to discharge, patients were randomized to the study intervention (n = 80) or conventional care (n = 76). The intervention consisted of comprehensive patient education, dietary and social service consultations, medication review, and intensive postdischarge follow-up. Detailed data were collected on all prescribed medications at the time of discharge, and compliance was assessed by pill counts 30 +/- 2 days later.

RESULTS

The overall compliance rate during the first 30 days after discharge was 84.6 +/- 15.1% (range, 23.1-100%). Compliance was 87.9 +/- 12.0% in patients randomized to the study intervention, compared with 81.1 +/- 17.2% in the control group (P = 0.003). A compliance rate of > or = 80% was achieved by 85.0% of the treatment group versus 69.7% of the control group (P = 0.036). By multivariate analysis, assignment to the treatment group was the strongest independent predictor of compliance (P = 0.008). Other variables included in the model were Caucasian race (P = 0.044) and not living alone (P = 0.09).

CONCLUSIONS

A multidisciplinary treatment strategy is associated with improved medication compliance during the first 30 days following hospital discharge in elderly patients with congestive heart failure. Improved compliance may contribute to improved outcomes in these patients.

Cdc53 targets phosphorylated G1 cyclins for degradation by the ubiquitin proteolytic pathway

In budding yeast, cell division is initiated in late G1 phase once the Cdc28 cyclin-dependent kinase is activated by the G1 cyclins Cln1, Cln2, and Cln3. The extreme instability of the Cln proteins couples environmental signals, which regulate Cln synthesis, to cell division. We isolated Cdc53 as a Cln2-associated protein and show that Cdc53 is required for Cln2 instability and ubiquitination in vivo. The Cln2-Cdc53 interaction, Cln2 ubiquitination, and Cln2 instability all depend on phosphorylation of Cln2. Cdc53 also binds the E2 ubiquitin-conjugating enzyme, Cdc34. These findings suggest that Cdc53 is a component of a ubiquitin-protein ligase complex that targets phosphorylated G1 cyclins for degradation by the ubiquitin-proteasome pathway.

Plugging it in: signaling circuits and the yeast cell cycle

Signal transduction pathways provide the means to transmit information and elicit specific responses. Modulation of the cell cycle machinery is one such response. Molecular genetic approaches with budding yeast have been instrumental in elucidating the components of these complex signaling pathways and the inter-relationships among these components. Recent progress has revealed pathways that link extracellular signals with the machinery governing both cell cycle progression and morphogenesis. The nature of the interface between nutritional and checkpoint signals with the cell cycle apparatus is just now emerging.

Rapid degradation of the G1 cyclin Cln2 induced by CDK-dependent phosphorylation

Cyclins regulate the major cell cycle transitions in eukaryotes through association with cyclin-dependent protein kinases (CDKs). In yeast, G1 cyclins are essential, rate-limiting activators of cell cycle initiation. G1-specific accumulation of one G1 cyclin, Cln2, results from periodic gene expression coupled with rapid protein turnover. Site-directed mutagenesis of CLN2 revealed that its phosphorylation provides a signal that promotes rapid degradation. Cln2 phosphorylation is dependent on the Cdc28 protein kinase, the CDK that it activates. These findings suggest that Cln2 is rendered self-limiting by virtue of its ability to activate its cognate CDK subunit.

Rme1, a negative regulator of meiosis, is also a positive activator of G1 cyclin gene expression

Control of G1 cyclin expression in Saccharomyces cerevisiae is mediated primarily by the transcription factor SBF (Swi4/Swi6). In the absence of Swi4 and Swi6 cell viability is lost, but can be regained by ectopic expression of the G1 cyclin encoding genes, CLN1 or CLN2. Here we demonstrate that the RME1 (regulator of meiosis) gene can also bypass the normally essential requirement for SBF. RME1 encodes a zinc finger protein which is able to repress transcription of IME1 (inducer of meiosis) and thereby inhibit cells from entering meiosis. We have found that expression of RME1 from a high copy number plasmid can specifically induce CLN2 expression. Deletion of RME1 alone shows no discernible effect on vegetative growth, however, deletion of RME1 in a swi6 delta swi4ts strain results in a lowering of the non-permissive temperature for viability. This suggests that Rme1 plays a significant but ancillary role in SBF in inducing CLN2 expression. We show that Rme1 interacts directly with the CLN2 promoter and have mapped the region of the CLN2 promoter required for Rme1-dependent activation. Consistent with Rme1 having a cell cycle role in G1, we have found that RME1 mRNA is synthesized periodically in the cell cycle, with maximum accumulation occurring at the M/G1 boundary. Thus Rme1 may act both to promote mitosis, by activating CLN2 expression, and prevent meiosis, by repressing IME1 expression.

CLN3, not positive feedback, determines the timing of CLN2 transcription in cycling cells

Transcriptional activation of the budding yeast CLN1 and CLN2 genes during the late G1 phase of the cell cycle has been attributed to a positive feedback loop, wherein the transcription of both genes is stimulated by the accumulation of their protein products. We demonstrate that in cycling cells CLN2 does not play a role in determining the timing of its own transcriptional activation. First, we show that CLN3 alone is sufficient to maximally activate CLN2 transcription. Cells that lack functional CLN1 and CLN2 genes activate the CLN2 promoter with the same kinetics and at the same size as cells in which all three CLN genes are functional. In addition, CLN2 transcription is activated with similar kinetics in cells that have CLN2 as their only functional CLN gene and in CLN-deficient cells. Promoter analysis shows that CLN3-dependent activation of CLN2 transcription is directed primarily through the previously identified UAS1 region although another cis-acting region, UAS2, also can contribute to CLN2 activation under some conditions. The ability to activate transcription of CLN2 is not a unique property of CLN3 because ectopically expressed CLN2 can both activate the endogenous CLN2 promoter and induce Start. We propose that failure of the endogenous CLN2 gene to contribute significantly to activation of its own transcription results from its relative effectiveness at inducing Start, cell cycle progression and, subsequently, inactivation of CLN2 expression.

A multidisciplinary intervention to prevent the readmission of elderly patients with congestive heart failure

BACKGROUND

Congestive heart failure is the most common indication for admission to the hospital among older adults. Behavioral factors, such as poor compliance with treatment, frequently contribute to exacerbations of heart failure, a fact suggesting that many admissions could be prevented.

METHODS

We conducted a prospective, randomized trial of the effect of a nurse-directed, multidisciplinary intervention on rates of readmission within 90 days of hospital discharge, quality of life, and costs of care for high-risk patients 70 years of age or older who were hospitalized with congestive heart failure. The intervention consisted of comprehensive education of the patient and family, a prescribed diet, social-service consultation and planning for an early discharge, a review of medications, and intensive follow-up.

RESULTS

Survival for 90 days without readmission, the primary outcome measure, was achieved in 91 of the 142 patients in the treatment group, as compared with 75 of the 140 patients in the control group, who received conventional care (P = 0.09). There were 94 readmissions in the control group and 53 in the treatment group (risk ratio, 0.56; P = 0.02). The number of readmissions for heart failure was reduced by 56.2 percent in the treatment group (54 vs. 24, P = 0.04), whereas the number of readmissions for other causes was reduced by 28.5 percent (40 vs. 29, P not significant). In the control group, 23 patients (16.4 percent) had more than one readmission, as compared with 9 patients (6.3 percent) in the treatment group (risk ratio, 0.39; P = 0.01). In a subgroup of 126 patients, quality-of-life scores at 90 days improved more from base line for patients in the treatment group (P = 0.001). Because of the reduction in hospital admissions, the overall cost of care was $460 less per patient in the treatment group.

CONCLUSIONS

A nurse-directed, multidisciplinary intervention can improve quality of life and reduce hospital use and medical costs for elderly patients with congestive heart failure.

Dosage suppressors of the dominant G1 cyclin mutant CLN3-2: identification of a yeast gene encoding a putative RNA/ssDNA binding protein

Three G1 cyclins, CLN1, CLN2, and CLN3, have been identified in the budding yeast Saccharomyces cerevisiae. G1 cyclins are essential, albeit functionally redundant, rate-limiting activators of cell cycle initiation. We have isolated dosage-dependent suppressor genes (designated HMD genes) of the mating defect caused by CLN3-2, a dominant mutation in CLN3, HMD2 and HMD3 are identical to STE4 and STE5, respectively, HMD1 is an essential gene that encodes a protein containing a putative RNA binding domain. Overproduction of HMD1 results in a relatively specific reduction in the level of the CLN3 or CLN3-2 transcript. This reduction occurs subsequent to transcription initiation of CLN3 since overexpression of HMD1 did not affect expression of a heterologous transcript from the CLN3 promoter but did result in a reduction of CLN3 transcript expressed from a heterologous promoter. HMD1 has at least one essential role independent of its effect on CLN3 since HMD1 remains essential for viability in the absence of a functional CLN3 gene.

Which cuff size is preferable for blood pressure monitoring in most hypertensive patients?

The accuracy of blood pressure (BP) measurements in obese hypertensives is still controversial. We investigated whether a large sized cuff could be appropriate for BP measurements in patients with different arm circumferences. Fifty hypertensive patients (23 males and 27 females, mean age 54 +/- 12 years, mean weight 75 +/- 12 kg) underwent BP measurements under standardised conditions using both a standard cuff (23 x 12 cm) and a large cuff (34 x 15 cm). Ambulatory blood pressure monitoring (ABPM) was subsequently performed in each subject using a large cuff. The average of two measurements performed in the clinic was compared with the mean daytime measurements. Thirty-one subjects had an arm circumference of < 30 cm (group 1) and weighted 68 +/- 10 kg, while 19 (group 2) had a larger arm circumference (> or = 30 cm) and were overweight (86 +/- 8 kg). BP in group 1 was 149 +/- 23/91 +/- 12 mmHg with the standard cuff and 143 +/- 24/88 +/- 13 mmHg with the large cuff (P < 0.003). In group 2, the respective readings were 153 +/- 22/100 +/- 16 mmHg (standard cuff) and 144 +/- 19/93 +/- 16 mmHg (large cuff; P < 0.0004). These findings suggest that in overweight hypertensives, the use of the standard cuff results in overestimation of BP and that large cuffs should be used exclusively in this population. The use of a large cuff in lean patients has yet to be clarified.

Cell cycle-dependent transcription of CLN2 is conferred by multiple distinct cis-acting regulatory elements

The budding yeast Saccharomyces cerevisiae CLN1, CLN2, and CLN3 genes encode functionally redundant G1 cyclins required for cell cycle initiation. CLN1 and CLN2 mRNAs accumulate periodically throughout the cell cycle, peaking in late G1. We show that cell cycle-dependent fluctuation in CLN2 mRNA is regulated at the level of transcriptional initiation. Mutational analysis of the CLN2 promoter revealed that the major cell cycle-dependent upstream activating sequence (UAS) resides within a 100-bp fragment. This UAS contains three putative SWI4-dependent cell cycle boxes (SCBs) and two putative MluI cell cycle boxes (MCBs). Mutational inactivation of these elements substantially decreased CLN2 promoter activity but failed to eliminate periodic transcription. Similarly, inactivation of SWI4 decreased CLN2 transcription without affecting its periodicity. We have identified a second UAS in the CLN2 upstream region that can promote cell cycle-dependent transcription with kinetics similar to that of the intact CLN2 promoter. Unlike the major CLN2 UAS, this newly identified UAS promotes transcription in cells arrested in G1 by inactivation of cdc28. This novel UAS is both necessary and sufficient for regulated transcription driven by a CLN2 promoter lacking functional SCBs and MCBs. Although this UAS itself contains no SCBs or MCBs, its activity is dependent upon SWI4 function. The characteristics of this novel UAS suggest that it might have a role in initiating CLN2 expression early in G1 to activate the positive feedback loop that drives maximal Cln accumulation.

FAR1 is required for posttranscriptional regulation of CLN2 gene expression in response to mating pheromone

Yeast cells arrest during the G1 interval of the cell cycle in response to peptide mating pheromones. The FAR1 gene is required for cell cycle arrest but not for a number of other aspects of the pheromone response. Genetic evidence suggests that FAR1 is required specifically for inactivation of the G1 cyclin CLN2. From these observations, the FAR1 gene has been proposed to encode an element of the interface between the mating pheromone signal transduction pathway and the cell cycle regulatory apparatus. We show here that FAR1 is necessary for the decrease in CLN1 and CLN2 transcript accumulation observed in response to mating pheromone but is unnecessary for regulation of the same transcripts during vegetative growth. However, the defect in regulation of CLN1 expression is dependent upon CLN2. We show that pheromone regulates the abundance of Cln2 at a posttranscriptional level and that FAR1 is required for that regulation. From these observations, we suggest that FAR1 function is limited to posttranscriptional regulation of CLN2 expression by mating pheromone. The failure of mating pheromone to repress CLN2 transcript levels in far1 mutants can be explained by the stimulatory effect of the persistent Cln2 protein on CLN2 transcription via the CLN/CDC28-dependent feedback pathway.