The putative alpha helix 2 of human immunodeficiency virus type 1 Vpr contains a determinant which is responsible for the nuclear translocation of proviral DNA in growth-arrested cells

Several viral determinants were shown to play a role in the ability of human immunodeficiency virus type 1 (HIV-1) to infect nondividing cells. In particular, Vpr and Gag matrix (MA) were recognized to be involved in the nuclear transport of the viral preintegration complex. The goal of the present study was to evaluate the ability of isogenic HIV-1 viruses harboring different vpr and gag genes to infect nondividing cells. Surprisingly, our results reveal that the introduction of mutations in the MA nuclear localization signal marginally affected the ability of proviruses to establish infection in growth-arrested HeLa or MT4 cells. In contrast, we show that in our experimental system, the absence of Vpr expression leads to a reduction in viral infectivity and production which correlates with a decrease in the synthesis and nuclear transport of proviral DNA as determined by PCR analysis. Moreover, our data demonstrate that this reduction of viral replication is also observed with proviruses containing different mutated Vpr alleles. In particular, the Vpr Q65E mutant, which contains a substitution in the second predicted amphipathic alpha-helical structure located in the central region of the protein, is associated with an impairment of the protein nuclear localization and a concomitant reduction of the nuclear transport of proviral DNA. The results of this study provide evidence that a putative amphipathic alpha-helical structure in the central region of Vpr contains a determinant involved in the nuclear translocation of the preintegration complex in nondividing cells.

MuLV-based vectors pseudotyped with truncated HIV glycoproteins mediate specific gene transfer in CD4+ peripheral blood lymphocytes

Human immunodeficiency virus (HIV) infection ultimately leads to the destruction of the CD4+ lymphocyte subset and the onset of AIDS. In recent years, several gene therapy procedures making use of retroviral vectors that selectively target HIV susceptible cells have been proposed in order to interfere with HIV productive infection. However, the HIV glycoproteins' inability to be incorporated in other heterologous retroviruses considerably limits true HIV cell tropism of such vectors. We now report the use of murine leukemia virus (MuLV) viral particles harboring a truncated form of the HIV glycoprotein for specific gene delivery. Reporter lacZ gene transfer was determined to be appropriately specific to CD4+ cells when HeLaCD4 cells or peripheral blood lymphocytes (PBLs) were infected with these pseudotyped MuLV virus vectors. In contrast, MuLV viruses harboring amphotropic MuLV envelope glycoproteins displayed a broad and nonspecific infection of PBL subpopulations. This new approach, taking advantage of the ability of truncated HIV envelope glycoproteins to be incorporated into heterologous retroviral particles, may foreseeably be used in future interventions based on the coordinated delivery of therapeutic gene products specifically to cell types susceptible to HIV infection.

HIV transcriptional activation by the accessory protein, VPR, is mediated by the p300 co-activator

The accessory protein, Vpr, is a virion-associated protein that is required for HIV-1 replication in macrophages and regulates viral gene expression in T cells. Vpr causes arrest of cell cycle progression at G2/M, presumably through its effect on cyclin B1.Cdc2 activity. Here, we show that the ability of Vpr to activate HIV transcription correlates with its ability to induce G2/M growth arrest, and this effect is mediated by the p300 transcriptional co-activator, which promotes cooperative interactions between the Rel A subunit of NF-kappaB and cyclin B1.Cdc2. Vpr cooperates with p300, which regulates NF-kappaB and the basal transcriptional machinery, to increase HIV gene expression. Similar effects are seen in the absence of Vpr with a kinase-deficient Cdc2, and overexpression of p300 increases levels of HIV Vpr+ replication. Taken together, these data suggest that p300, through its interactions with NF-kappaB, basal transcriptional components, and Cdks, is modulated by Vpr and regulates HIV replication. The regulation of p300 by Vpr provides a mechanism to enhance viral replication in proliferating cells after growth arrest by increasing viral transcription.

Effects of Vpu expression on Xenopus oocyte membrane conductance

The HIV-1-specific vpu gene encodes an integral membrane phosphoprotein which affects three aspects of the HIV-1 infectious cycle: it enhances virion release from infected cells; it causes degradation of the CD4 protein in the endoplasmic reticulum; and it delays syncytia formation in HIV-1-infected CD4+ T-cells. Although little is known about how Vpu mediates these effects, it has been proposed to function as a nonspecific cation channel. In this report, voltage clamp measurements of Xenopus oocytes show that Vpu expression is not associated with increased transmembrane currents. Instead, Vpu expression diminishes membrane conductance. Injection of 4.6 ng of Vpu mRNA into these cells reduces endogenous potassium conductance by 50%. Only Vpu mutants which retain the ability to degrade CD4 can diminish K+ conductance. Inhibition by Vpu is not unique to K+ channels as it is also observed on several coexpressed membrane proteins but not on a coexpressed cytoplasmic protein. These results indicate that the CD4 degradative capability of Vpu and the Vpu-mediated modulation of membrane protein expression are mechanistically coupled and that Vpu may contribute to HIV pathogenesis by altering plasma membrane protein expression at the cell surface.

Human immunodeficiency virus type 1 Vpr localization: nuclear transport of a viral protein modulated by a putative amphipathic helical structure and its relevance to biological activity

Protein import into the nucleus is generally considered to involve specific nuclear localization signals (NLS) though it is becoming increasingly clear that efficient and well controlled import of proteins which lack a canonical NLS also occurs in cells. Human immunodeficiency virus type 1 (HIV-1) Vpr is one such protein which does not have an identifiable canonical NLS and yet efficiently localizes to the nuclear compartment. Here, we use confocal microscopy to demonstrate that mutations in the putative central hydrophobic helix of Vpr result in the retention of the protein in highly localized ring-like structures around the nuclear periphery with striking impairment in their ability to enter the nuclear interior. By characterizing other biological activities associated with this protein, such as its ability to incorporate into budding virions and its ability to arrest cells in G2, we show that this helical domain is specific for the nuclear translocation of the protein with very little effect on these other functions. Interestingly, however, perturbation of this helical motif also perturbs the protein's ability to augment viral replication in primary human macrophages indicating that the integrity of this secondary structure is essential for optimal infection in these non-dividing cells.

Human immunodeficiency virus type 1 Vpr is a positive regulator of viral transcription and infectivity in primary human macrophages

It is currently well established that HIV-1 Vpr augments viral replication in primary human macrophages. In its virion-associated form, Vpr has been suggested to aid efficient translocation of the proviral DNA into the cell nucleus. Although Vpr growth-arrests dividing T cells, the relevance of this biological activity in nondividing macrophages is unclear. Here we use Vpr-mutants to demonstrate that the molecular determinants involved in G2-arresting T cells are also involved in increasing viral transcription in macrophages, even though these cells are refractive to the diploid DNA status typical of G2 phase. Our results suggest that the two phenotypes, namely the nuclear localization and the G2-arrest activity of the protein, segregate functionally among the late and early functions of Vpr. The nuclear localization property of Vpr correlates with its ability to effectively target the proviral DNA to the cell nucleus early in the infection, whereas the G2-arrest phenotype correlates with its ability to activate viral transcription after establishment of an infection. These two functions may render Vpr's role essential and not accessory under infection conditions that closely mimic the in vivo situation, that is, primary cells being infected at low viral inputs.

Characterization of the cytotoxic factor(s) released from thymic dendritic cells upon human immunodeficiency virus type 1 infection

We previously demonstrated that infection of primary human thymic dendritic cells (DCs) with laboratory strains of HIV leads to the release of soluble factor(s) which induced thymocyte killing. In the present paper, we extend the characterization of this process. Our results reveal that primary HIV-1 isolates are similarly able to induce the production of cytotoxic factor(s) from thymic DCs and that the release of such factor(s) is dependent on viral infection. Interestingly, we observed that CD4+ and CD8+ purified thymocyte subsets, and activated PBMCs are susceptible to the cytotoxic activity, whereas freshly isolated resting PBMCs are resistant to this effect. Cycloheximide treatment prevents the killing of thymocytes exposed to HIV-infected DC supernatant, revealing that this form of cell death is an active biological process requiring protein synthesis. Finally, our data suggest that FasL and TNF alpha could both participate in the killing process. These in vitro observations provide a plausible model, whereby HIV-infected DCs can play a role in vivo in the induction of uninfected thymocyte killing.

Myonecrosis after revascularization procedures

The detection of elevated cardiac enzyme levels and the occurrence of electrocardiographic (ECG) abnormalities after revascularization procedures have been the subject of recent controversy. This report represents an effort to achieve a consensus among a group of researchers with data on this subject. Creatine kinase (CK) or CK-MB isoenzyme (CK-MB) elevations occur in 5% to 30% of patients after a percutaneous intervention and commonly during coronary artery bypass graft surgery (CABG). Although Q wave formation is rare, other ECG changes are common. The rate of detection is highly dependent on the intensity of enzyme and ECG measurement. Because most events occur without the development of a Q wave, the ECG will not definitively diagnose them; even the ECG criteria for Q wave formation signifying an important clinical event have been variable. At least 10 studies evaluating > 10,000 patients undergoing percutaneous intervention have demonstrated that elevation of CK or CK-MB is associated not only with a higher mortality, but also with a higher risk of subsequent cardiac events and higher cost. Efforts to identify a specific cutoff value below which the prognosis is not impaired have not been successful. Rather, the risk of adverse outcomes increases with any elevation of CK or CK-MB and increases further in proportion to the level of intervention. This information complements similar previous data on CABG. Obtaining preprocedural and postprocedural ECGs and measurement of serial cardiac enzymes after revascularization are recommended. Patients with enzyme levels elevated more than threefold above the upper limit of normal or with ECG changes diagnostic for Q wave myocardial infarction (MI) should be treated as patients with an MI. Patients with more modest elevations should be observed carefully. Clinical trials should ensure systematic evaluation for myocardial necrosis, with attention paid to multivariable analysis of risk factors for poor long-term outcome, to determine the extent to which enzyme elevation is an independent risk factor after considering clinical history, coronary anatomy, left ventricular function and clinical evidence of ischemia. In addition, tracking of enzyme levels in clinical trials is needed to determine whether interventions that reduce periprocedural enzyme elevation also improve mortality.

Predictors of same-admission cardiac catheterization in patients with acute ischemic syndromes

BACKGROUND

Various strategies exist for the use of cardiac catheterization in unstable angina or non-Q wave myocardial infarction. At the authors' institution, the overall volume of cardiac catheterization has increased in recent years.

OBJECTIVE

To investigate whether this increased volume of cardiac catheterization was due to adoption of a more invasive approach to the management of patients with acute ischemic syndromes.

DESIGN

A retrospective cohort study was conducted using detailed chart review of coronary care unit admissions during 1990/91 and 1993/94.

SETTING

A university-affiliated tertiary care referral centre with facilities for cardiac catheterization.

PATIENTS

One hundred patients randomly selected from among those with unstable angina, non-Q wave myocardial infarction or chest pain not yet diagnosed in each of the study years. Detailed follow-up was complete for all patients.

OUTCOME MEASURE

The use of cardiac catheterization during the index admission was documented.

MAIN RESULTS

There was a trend towards more frequent use of same admission cardiac catheterization in the later period (21% [CI 14% to 31%] versus 12% [CI 7% to 20%], P = 0.09). However, after controlling for baseline characteristics and in-hospital events, the year of admission did not independently predict the use of catheterization (P = 0.60). By multivariate logistic regression, recurrence of chest pain and evidence of myocardial necrosis were most closely associated with same-admission cardiac catheterization.

CONCLUSIONS

Although clinical factors partially explain the increased use of catheterization over time, there may have also been shift towards a more aggressive practice style at the authors' institution. Further study is needed to address this possibility.

Clinical outcomes of patients more than one year following randomization in the Canadian Coronary Atherectomy Trial (CCAT)

BACKGROUND

The Canadian Coronary Atherectomy Trial (CCAT) assessed, in a randomized comparison, the clinical and angiographic outcomes following atherectomy with those following balloon angioplasty for the treatment of de novo lesions in the proximal one-third of the left anterior descending artery (LAD). Although the procedural success rate was somewhat higher and the postprocedure lumen larger in patients treated with atherectomy, lumen dimensions, restenosis rates and clinical outcomes were similar in the two groups at six months. To determine whether late differences emerged between the groups, clinical follow-up was obtained at a median of 18 (range 10 to 31) months after randomization.

METHODS AND RESULTS

Patients were contacted monthly by telephone for the first six months. Subsequent follow-up information was obtained in 272 (99%) of the 274 randomized patients via a clinic visit or telephone interview with the patient and/or a relative. Additional information was obtained from the referring physician as required. There were no differences in adverse events between the two groups during follow-up. In patients randomized to atherectomy compared with balloon angioplasty, death occurred in 1.5% versus 2.2% (cardiac death 0.7% versus 0.7%); myocardial infarction in 5.1% versus 5.9% (Q wave 1.5% versus 1.5%); coronary bypass surgery in 13.1% versus 12.6%; and repeat target lesion intervention in 22.6% versus 21.5%. Persistent or recurrent Canadian Cardiovascular Society class III/IV angina not treated by a further intervention was present in 1.5% versus 2.2%. The combined end-point of death or nonfatal myocardial infarction occurred in nine (6.6%) versus 11 (8.1%) patients and any adverse cardiac event in 50 (36.5%) versus 53 (39.3%). Multivariate logistic regression indicated that unstable angina, reference vessel size and preprocedure minimum lumen diameter were the only variables independently associated with adverse events.

CONCLUSIONS

The initial choice of directional atherectomy or balloon angioplasty had no impact on clinical outcome over a period of 18 months in this patient population. With either technique, just over 60% of patients with proximal LAD disease experienced sustained symptomatic improvement without an adverse event following a single procedure, and 80% achieved this status following a repeat percutaneous intervention.

Enhancement of retroviral production from packaging cell lines expressing the human immunodeficiency type 1 VPU gene

The HIV-1 Vpu protein stimulates virus production by enhancing the release of viral particles from infected cells. Interestingly, Vpu was also shown to enhance the release of capsids produced by gag gene contructs of other retroviruses that lack a Vpu-like activity. To investigate the effect of Vpu expression on viral particle production in retroviral packaging cell line, we developed the Damp-VpuP cell line in which vpu expression is under the control of the tetracycline-responsive promoter. Retroviral production was measured by dosage of virion-associated reverse transcriptase activity, by capsid protein immuno-detection in cell-free supernatants and by evaluating the transfer of antibiotic resistance to target cells. Induction of the Damp-VpuP cell line caused a 40-fold increase in the titer of infectious virus-like particles when compared with control cell lines. This increase in viral titer was not the result of a clonal effect nor was it a consequence of high selective pressure but rather the effect of a Vpu-mediated enhancement of viral particle production. Similar results using the third generation psi CRIP packaging cell line confirmed these findings. Constitutive expression of vpu caused a 13-fold increase in viral titer in this packaging cell line. These results indicate that the expression of HIV-1 vpu in retroviral packaging cell lines can significantly improve the titers of infectious retroviral particles.

Two distinct oncornaviruses harbor an intracytoplasmic tyrosine-based basolateral targeting signal in their viral envelope glycoprotein

It has been clearly established that the budding of the human immunodeficiency virus (HIV-1), a lentivirus, occurs specifically through the basolateral membrane in polarized epithelial cells. More recently, the signal was assigned to a tyrosine-based motif located in the intracytoplasmic domain of the envelope glycoprotein, as previously observed on various other viral and cellular basolateral proteins. In the present study, expression of human T-cell leukemia virus type 1 (HTLV-1) or Moloney murine leukemia virus envelope glycoproteins was used for trans-complementation of an envelope-negative HIV-1. This demonstrated the potential of oncornaviral retrovirus envelope glycoproteins to confer polarized basolateral budding in epithelial Madin-Darby canine kidney cells (MDCK cells). Site-directed mutagenesis confirmed the importance of a common motif encompassing at least one crucial membrane-proximal intracytoplasmic tyrosine residue. The conservation of a similar basolateral maturation signal in different retroviruses further supports its importance in the biology of this group of viruses.

Putative alpha-helical structures in the human immunodeficiency virus type 1 Vpu protein and CD4 are involved in binding and degradation of the CD4 molecule

The human immunodeficiency virus type 1 (HIV-1) vpu gene encodes a 16-kDa class I integral membrane phosphoprotein with an N-terminal membrane-spanning region and a C-terminal cytoplasmic domain. In the cytoplasmic domain, two amphipathic alpha-helices joined by a flexible turn containing two phosphoacceptor sites have been predicted. Previous studies have shown that Vpu downregulates CD4 molecules by inducing their specific degradation in the endoplasmic reticulum. Phosphorylation of serine residues 52 and 56, present within the cytoplasmic domain of the Vpu protein, has been shown to be essential to this Vpu function. However, the contribution of these two phosphoacceptor sites in the mechanism of CD4 degradation remains undefined. Interestingly, a specific interaction between Vpu and CD4 was recently demonstrated in coimmunoprecipitation experiments. Binding of Vpu was shown to be necessary but not sufficient to mediate CD4 degradation, indicating that interaction between Vpu and CD4 represents an early step critical in triggering a process leading to CD4 degradation. To delineate the sequence(s) and/or structural determinant(s) involved in this Vpu-CD4 interaction and in the Vpu-mediated CD4 degradation, we performed a mutational analysis of the cytoplasmic domain of CD4 and Vpu. Coimmunoprecipitation experiments reveal that disruption of the putative alpha-helical structure in the membrane-proximal cytoplasmic domain of CD4 affects the binding to Vpu, suggesting that this structure may act as an interface for the CD4-Vpu interaction that mediates CD4 degradation. Vpu proteins containing mutations in either or both of the phosphoacceptor sites (Ser52 or/and Ser56) were inactive in regard to CD4 degradation yet retained the capacity to interact with the cytoplasmic domain of CD4. In an attempt to define the minimal region responsible for this interaction, we tested a panel of mutations which were designed to affect the integrity of the putative alpha-helices present in the cytoplasmic domain of Vpu. Our results indicate that although both C-terminal alpha-helices are required for degradation of CD4, only alpha-helix I, located in the membrane-proximal cytoplasmic region of Vpu, is involved in the interaction between Vpu and CD4. Taken together, these results demonstrate that alpha-helical structures in the HIV-1 Vpu and CD4 proteins are involved in binding and degradation of CD4 molecules.

Use of evidence-based medical therapy in patients undergoing percutaneous coronary revascularization in the United States, Europe, and Canada. Coronary Angioplasty Versus Excisional Atherectomy Trial (CAVEAT-I) and Canadian Coronary Atherectomy Trial (CCAT) investigators

The objective of this study was to examine whether there are international variations in the use of evidence-based medical therapy in patients undergoing percutaneous coronary revascularization. We analyzed the medical therapy of patients in the United States (US) (n = 878), Europe (n = 134), and Canada (n = 274) who underwent percutaneous coronary revascularization in either the Coronary Angioplasty Versus Excisional Atherectomy Trial (CAVEAT-I) (enrollment from August 1991 to April 1992) or the Canadian Coronary Atherectomy Trial (CCAT) (enrollment from July 1991 to August 1992). We found that at the time of hospital admission, Canadian patients had the highest rates of treatment with aspirin (95% vs 57% US and 78% Europe; p = 0.002), calcium antagonists (75% vs 48% US and 43% Europe; p 0.0001), beta blockers (60% vs 32% US and 46% Europe; p = 0.02), and combination anti-ischemic therapy (67% vs 43% US and 56% Europe; p = 0.0001). By discharge, however, Canadian patients had the lowest rates of treatment with nitrates (12% vs 40% US and 44% Europe; p = 0.0001) and combination anti-ischemic therapy (29% vs 53% US and 47% Europe; p < 0.01). At both admission and discharge, rates of treatment with angiotensin-converting enzyme inhibitors and lipid-lowering agents were < 15% in all 3 regions. We conclude that significant international variations exist in the use of evidence-based medical therapy in patients undergoing percutaneous coronary revascularization.

The membrane-proximal intracytoplasmic tyrosine residue of HIV-1 envelope glycoprotein is critical for basolateral targeting of viral budding in MDCK cells

Budding of retroviruses from polarized epithelial Madin-Darby canine kidney cells (MDCK) takes place specifically at the basolateral membrane surface. This sorting event is suspected to require a specific signal harbored by the viral envelope glycoprotein and it was previously shown that, as for most basolateral proteins, the intracytoplasmic domain plays a crucial role in this targeting phenomenon. It is well known that tyrosine-based motifs are a central element in basolateral targeting signals. In the present study, site-directed mutagenesis was used to generate conservative or non-conservative substitutions of each four intracytoplasmic tyrosines of the human immunodeficiency virus (HIV-1) envelope glycoprotein. This approach revealed that the membrane-proximal tyrosine is essential to ensure both the basolateral localization of envelope glycoprotein and the basolateral targeting of HIV-1 virions. Substitutions of the membrane-proximal tyrosine did not appear to affect incorporation of envelope glycoprotein into the virions, as assayed by virion infectivity and protein content, nor its capability to ensure its role in viral infection, as determined by viral multiplication kinetics. Altogether, these results indicate that the intracytoplasmic domain of the HIV-1 envelope glycoprotein harbors a unique, tyrosine-based, basolateral targeting signal. Such a tyrosine-based targeting signal may play a fundamental role in HIV transmission and pathogenesis.

Phase 1 human trial of adenosine-potassium cardioplegia

BACKGROUND

The cardioprotective role of adenosine in various models of ischemia-reperfusion, including adenosine supplementation to cardioplegic formulations, has been studied extensively. The appropriate dose of adenosine in humans is uncertain and could be limited by systemic hypotension or AV block.

METHODS AND RESULTS

An open-label, nonrandomized phase 1 adenosine dose-ranging study was performed. Patients scheduled for primary isolated coronary bypass surgery were eligible for the study. Antegrade warm blood potassium cardioplegia (ratio, 4:1, blood to crystalloid) was administered in the routine fashion, with adenosine added to the initial 1000-mL dose and final 500-mL dose. Patients were studied in blocks of 4 per concentration. An escalating adenosine dosage schedule was planned to produce blood cardioplegia concentrations from 0 to 250 mumol/L, and the blocks were tested sequentially. Stopping rules were defined for systemic hypotension (phenylephrine dose during cardiopulmonary bypass > or = 5.0 mg; phenylephrine dose during cardioplegic induction > or = 800 micrograms) and AV block (permanent pacemaker insertion; temporary pacing dependency for > 90 minutes after cardiopulmonary bypass). Doses of 1, 2.5, 5, 10, and 25 mumol/L were well tolerated. With 50 mumol/L, systemic hypotension occurred during cardioplegic induction in 3 of 4 patients versus 1 of 24 (P < .005) at all lower concentrations (880 +/- 217 versus 297 +/- 286 micrograms phenylephrine per patient). The studies were repeated with an 8:1 blood-to-crystalloid cardioplegia delivery system. Adenosine concentrations of 0 (n = 4), 15 (n = 12), 20 (n = 8), and 25 mumol/L (n = 4) were tested. Hypotension during cardioplegic induction was more prevalent (P = .05) with the higher doses (15 mumol/L, 394 +/- 189 micrograms, 1 of 12 patients; 20 mumol/L, 360 +/- 355 micrograms, 2 of 8 patients; 25 mumol/L, 600 +/- 478 micrograms, 2 of 4 patients). There were no differences with respect to systemic hypotension during cardiopulmonary bypass or for pacing > 90 minutes after discontinuation of cardiopulmonary bypass, and no patient required permanent pacing. There have been no deaths, Q-wave myocardial infarctions, intra-aortic balloon pump insertions, or cerebral infarctions in the total sample of 56 patients.

CONCLUSIONS

Our initial investigations have shown that adenosine can be safely administered during cardiopulmonary bypass. The authors recommend that further studies are warranted using adenosine 15 to 25 mumol/L, depending on the delivery system.

Molecular analysis of the cytoplasmic domain of CD4: overlapping but noncompetitive requirement for lck association and down-regulation by Nef

Expression of the HIV Nef protein results in the down-regulation of cell surface expression of CD4, with a di-leucine motif in the cytoplasmic domain of CD4 being required for this effect. However, our results indicate that this motif is not sufficient to confer sensitivity to down-regulation by Nef. Using site-directed mutagenesis and a transient expression system, we demonstrate that an alpha-helical stretch of amino acids of the cytoplasmic tail of CD4 is also required for the down-regulation of CD4 induced by Nef. Some CD4 mutations allowed the discrimination between PMA- and Nef-induced down-regulation, suggesting the existence of multiple pathways. In addition, our results demonstrate that this motif is involved in the association of CD4 with the tyrosine kinase p56lck, thus defining a multifunctional domain of CD4. Although there is overlap between the sequence requirement for lck association and susceptibility to Nef, we fail to detect any preferential decrease in lck association with CD4 when Nef is expressed during acute HIV infection. Altogether, these results demonstrate that there is an overlapping, but noncompetitive, sequence requirement in the cytoplasmic domain of CD4 for lck association and down-regulation by Nef.

Molecular analysis of the cytoplasmic domain of CD4: overlapping but noncompetitive requirement for lck association and down-regulation by Nef

Expression of the HIV Nef protein results in the down-regulation of cell surface expression of CD4, with a di-leucine motif in the cytoplasmic domain of CD4 being required for this effect. However, our results indicate that this motif is not sufficient to confer sensitivity to down-regulation by Nef. Using site-directed mutagenesis and a transient expression system, we demonstrate that an alpha-helical stretch of amino acids of the cytoplasmic tail of CD4 is also required for the down-regulation of CD4 induced by Nef. Some CD4 mutations allowed the discrimination between PMA- and Nef-induced down-regulation, suggesting the existence of multiple pathways. In addition, our results demonstrate that this motif is involved in the association of CD4 with the tyrosine kinase p56lck, thus defining a multifunctional domain of CD4. Although there is overlap between the sequence requirement for lck association and susceptibility to Nef, we fail to detect any preferential decrease in lck association with CD4 when Nef is expressed during acute HIV infection. Altogether, these results demonstrate that there is an overlapping, but noncompetitive, sequence requirement in the cytoplasmic domain of CD4 for lck association and down-regulation by Nef.

Analysis of atherosclerotic plaques obtained by coronary atherectomy: Foam cells correlated positively with subsequent restenosis

Restenosis following coronary intervention is a complex process the mechanisms of which remains mostly unknown. Tissue obtained by atherectomy is an important means to study restenosis. Previous studies on atherectomy-retrieved tissue have not identified histologic features that correlate with restenosis. We performed an histopathologic evaluation on atherosclerotic plaque tissue obtained by atherectomy from 58 patients, all of whom had a 6-month angiographic follow-up. We identified macrophages and lymphocytes and localized tumor necrosis factor-α expression in the tissue by immunohistochemistry. Histopathology was correlated with late angiographic outcomes. Of 10 histologic features evaluated in the plaque tissue, only the presence of foam cells, identified in paraffin sections, correlated positively with restenosis (p = 0.04). Immunohistochemistry showed that macrophages (p = .07), tumor necrosis factor-α (p = .07), and lymphocytes (p = .14) were more prominent, but not significantly so, in lesions from patients with foam cells and restenosis than in lesions from patients without foam cells or restenosis. Thus the presence of foam cells in primary lesions obtained by atherectomy as identified in paraffin-embedded tissue appears to be a marker for restenosis.

Coronary artery stenting: indications and cost implications

The practice of coronary stenting is evolving rapidly, with new stent designs, deployment techniques, and adjunctive therapy. In many respects, clinical practice is changing in advance of the availability of supporting data. The consistent excellent angiographic result with stent deployment exceeds that achieved by any other previous interventional device, and the extent to which this accounts for the exponential increase in stent utilization cannot be accurately determined but is undoubtedly considerable. Controlled randomized trials have confirmed that stent deployment is superior to balloon angioplasty in certain lesion subsets or clinical scenarios. These include focal de novo native vessel lesions, lesions with late recoil after balloon angioplasty, acute closure after balloon angioplasty, and proximal left anterior descending coronary artery lesions. In addition, observational data is persuasive in focal coronary saphenous vein graft lesions and aorto-ostial lesions. On the other hand, the evidence supporting the use of stents strictly to improve on a suboptimal result, possibly the most frequent indication, is indirect and circumstantial. Stents are expensive, but it was anticipated that with the reduction in restenosis not only would they be cost-effective but also ultimately would reduce costs. This hope has not as yet been realized. However, there is little question that the introduction of intracoronary stents has been the most significant and exciting development since the introduction of percutaneous revascularization almost 20 years ago. It has revitalized the field.

In vitro characterization of purified human thymic dendritic cells infected with human immunodeficiency virus type 1

In the thymus, dendritic cells (DC) are functionally associated with thymocytes and are recognized to play a major role in the intrathymic differentiation of T cells. Several studies have previously investigated the role of DC during HIV-infection, but the status of thymic DC in HIV-1 pathogenesis remains unclear. In this study, we investigated the susceptibility of purified human thymic DC to HIV-1 infection in vitro. HIV-1 was not detected in cell-free supernatants collected from HIV-infected DC. However, these cultures were shown to transmit HIV-1 infection since coculture with permissive MT4 cells resulted in virus production. The exposure of DC in culture to HIV-1 was shown to promote severe DC morphological changes and killing. We also found that one or several heat labile soluble cytotoxic agents present in the HIV-1-infected DC supernatant mediated the killing of thymocytes. Our observations raise the possibility that (1) the HIV-1-induced DC killing, (2) the capacity of DC to transmit viral infection, and/or (3) the release of HIV-1-mediated cytotoxic agent(s) from DC may contribute to AIDS pathogenesis in vivo.