Lisa F. Lincz

DECIPHERING THE APOPTOTIC PATHWAY : ALL ROADS LEAD TO DEATH

Research into apoptosis is proceeding at such a fast and ferocious pace that anyone who is not completely engrossed in the field has difficulty keeping track of the constant stream of newly identified proteins involved in the process. Apart from being an enticing concept, the process of cell suicide is an important function with wide‐reaching implications. Virologists, biologists, immunologists, physiologists and oncologists alike have had to incorporate this phenomenon into their disciplines. The purpose of this article is to provide a solid background on which to further review recent advances in this exciting field. The Bcl‐2 and caspase family homologues are discussed in detail and various models are proposed to explain how they function to regulate and execute the death programme. Finally, the importance of programmed cell death with respect to immune function is explored, emphasizing the targets of viral inhibitors of apoptosis.

Common variants at 6p21.1 are associated with large artery atherosclerotic stroke

Genome-wide association studies (GWAS) have not consistently detected replicable genetic risk factors for ischemic stroke, potentially due to etiological heterogeneity of this trait. We performed GWAS of ischemic stroke and a major ischemic stroke subtype (large artery atherosclerosis, LAA) using 1,162 ischemic stroke cases (including 421 LAA cases) and 1,244 population controls from Australia. Evidence for a genetic influence on ischemic stroke risk was detected, but this influence was higher and more significant for the LAA subtype. We identified a new LAA susceptibility locus on chromosome 6p21.1 (rs556621: odds ratio (OR) = 1.62, P = 3.9 × 10−8) and replicated this association in 1,715 LAA cases and 52,695 population controls from 10 independent population cohorts (meta-analysis replication OR = 1.15, P = 3.9 × 10−4; discovery and replication combined OR = 1.21, P = 4.7 × 10−8). This study identifies a genetic risk locus for LAA and shows how analyzing etiological subtypes may better identify genetic risk alleles for ischemic stroke.

Detection and Measurement of Microparticles: An Evolving Research Tool for Vascular Biology

Microparticles are small, membrane-bound vesicles that are generated from cells of different origin. It now appears that all circulating blood cells as well as endothelial cells release membranous fragments ~1 mum in size or smaller bearing at least some characteristics of the parent cell. Elevated levels of microparticles have been described in cardiovascular states, thrombotic conditions, and cancer. Various methods of detection for microparticles include flow cytometry, enzyme-linked immunoassays, and functional assays. Flow cytometry has several advantages including its ability to quantitate and identify microparticles of different cellular origin. However, the standardization of preanalytical and analytical variables for enumeration of microparticles remains a significant challenge. Newer approaches are being investigated, and an international collaboration is working on standardization of detection as well as quantitation of microparticles by flow cytometry. Although it has evolved as an important vascular biology research tool, microparticle detection needs further evaluation and refinement before it becomes truly useful as a clinical tool.

Involvement of integrins in cell survival

SummaryApoptosis is a regulated process of cell death by which cells actively participate in their own destruction. In multicellular organisms, the balance between cell proliferation and apoptosis provides homeostatic control, and a regulatory failure of either event can contribute to oncogenesis. The extracellular matrix (ECM) is known to play a regulatory role in cellular growth and differentiation, but only more recently has it been recognized as a regulator of apoptosis. In these processes the major transmitters of ECM-derived signals to the cell are members of the integrin family, although the mechanical process of cell spreading also plays a role. Bothin vivo andin vitro the loss of adhesion to specific components of the ECM can lead to cell death, and such apoptosis can be induced experimentally by blocking integrin binding. Heterotypic and homotypic cell-cell adhesion can also protect from adhesion-dependent apoptosis and there is evidence to suggest that this too is integrin mediated. In addition, some integrin mediated signaling appears to promote apoptosis. The downstream mechanisms of integrin signaling causing cell death have not been greatly explored, but there is evidence from two different systems that the induction of ICE transcription and nuclear translocation of p53 are candidate processes. Alterations in integrin expression or signaling therefore are likely to contribute to tumor development by enabling escape from apoptosis. Also, the recognition of the importance of cell-cell adhesion in tumor cell survival offers the potential of developing improved drug regimes for the treatment of malignancy.

Association between xenobiotic gene polymorphisms and non‐Hodgkin's lymphoma risk

Summary. The last four decades have seen a significant increase in the incidence of non‐Hodgkins lymphoma (NHL) as a possible result of increasing environmental carcinogen exposure, particularly pesticides and solvents. Based on the increasing evidence for an association between carcinogen exposure‐related cancer risk and xenobiotic gene polymorphisms, we have undertaken a case–control study of xenobiotic gene polymorphisms in individuals with a diagnosis of NHL. Polymorphisms of six xenobiotic genes (CYP1A1, GSTT1, GSTM1, PON1, NAT1, NAT2) were characterized in 169 individuals with NHL and 205 normal controls using polymerase chain reaction‐based methods. Polymorphic frequencies were compared using Fishers exact tests, and odds ratios for NHL risk were calculated. Among the NHL group, the incidence of GSTT1 null and PON1 BB genotypes were significantly increased compared with controls, 34%vs 14%, and 24%vs 11% respectively. Adjusted odds ratios calculated from multivariate analyses demonstrated that GSTT1 null conferred a fourfold increase in NHL risk (OR = 4·27; 95% CI, 2·40–7·61, P < 0·001) and PON1 BB a 2·9‐fold increase (OR = 2·92; 95% CI, 1·49–5·72, P = 0·002). Furthermore, GSTT1 null combined with PON1 BB or GSTM1 null conferred an additional risk of NHL. This is the first time that a PON1 gene polymorphism has been shown to be associated with cancer risk. We conclude that the two polymorphisms, GSTT1 null and PON1 BB, are common genetic traits that pose low individual risk but may be important determinants of overall population NHL risk, particularly among groups exposed to NHL‐related carcinogens.

TRAIL-induced eradication of primary tumour cells from multiple myeloma patient bone marrows is not related to TRAIL receptor expression or prior chemotherapy

TNF-related apoptosis-inducing ligand (TRAIL) shares significant homology with CD95 (Fas) ligand and has the ability to induce apoptosis in sensitive cells through a caspase-mediated pathway. We have evaluated the activity of purified human recombinant soluble TRAIL (S-TRAIL, comprising residues 114–281; Biomol, Plymouth Meeting, PA, USA) and a leucine zipper construct of TRAIL (LZ-TRAIL; Immunex, Seattle WA, USA) against myeloma cell lines NCI H929, U266, RPMI 8226, the FasL-sensitive Jurkat T cell ALL line, the lymphoblastoid cell line MC/CAR and primary tumour cells from 16 myeloma patients. Furthermore, we examined the relationship between TRAIL-induced apoptosis and TRAIL receptor expression utilising RT-PCR and flow cytometry. Two of three myeloma cell lines and Jurkat were TRAIL sensitive whereas MC/CAR was relatively resistant. Five of 16 (31%) primary tumours demonstrated ⩾20% reduction in myeloma cells following TRAIL incubation (20–59%). This did not correlate with prior therapy. Four cell lines (two sensitive) and five primary tumours (two sensitive) demonstrated mRNA expression of the intra-cellular death domain containing TRAIL-R1. Variable expression of the two decoy (TRAIL-R3 and R4) and soluble (osteoprotegerin) receptors was seen and this did not correlate with TRAIL resistance. We conclude that myeloma cell expression of death effector receptors for TRAIL is insufficient to confer sensitivity to TRAIL-induced apoptosis but that in a significant minority of patients, irrespective of prior therapy, tumour cells are sensitive to TRAIL. The further investigation of TRAIL as an adjunct to presently available therapies for myeloma is justified.

Microparticles in health and disease.

Microparticles (MPs) are small fragments of membrane-bound cytoplasm that are shed from the surface of an activated or apoptotic cell. Recently, their function as vectors of transcellular exchange of biologic information, in addition to better described forms of intercellular communication such as growth factors, cytokines, and chemokines, has become well recognized. Circulating levels of MPs are thought to reflect a balance between cell stimulation, proliferation, and death. The production of MPs is thought to predominately occur by vesiculation or blebbing of the cell membrane. The mechanisms governing the remodeling of the plasma membrane are complex, involving cytoskeletal changes and a shift from normal phospholipid asymmetry. Increased intracellular calcium subsequent to cell activation leads to intracellular increases in several proteins including gelsolin and calpain, as well as the activity of enzymes such as translocase, floppase, and scramblase, which play important roles in the homeostasis of the cell membrane. The membrane vesiculation and phospholipids asymmetry leading to the production of MPs occurs by the complex interplay of the proteins involved. There are several clinical conditions associated with elevated MPs, and most are also associated with an increased risk of thrombosis. Apart from cardiovascular disease and venous thromboembolism, MPs are also elevated in solid tumors with metastatic disease. The measurement of MPs is being regarded as a potential biomarker, given the range of conditions in which they are elevated and the association with prothrombotic states. The utility of measuring MPs as a diagnostic and prognostic marker is currently a subject of intense investigation. The further development of the various methods for the detection and measurement of MPs and prospective clinical trials establishing the utility of such tests will be critical prior to the routine measurement of MPs in the diagnostic laboratory.

Methionine synthase genetic polymorphism MS A2756G alters susceptibility to follicular but not diffuse large B‐cell non‐Hodgkin's lymphoma or multiple myeloma

Summary. Lymphoproliferative diseases are characterized by chromosomal aberrations, and susceptibility may depend on inherited activity of enzymes required for DNA synthesis and methylation. We analysed genetic polymorphisms for methionine synthase (MS) A2756G, methylenetetrahydrofolate reductase (MTHFR) C677T and MTHFR A1298C in Caucasians with non‐Hodgkins lymphoma (NHL; n = 151), multiple myeloma (MM; n = 90) and 299 control subjects. The MS 2756 AG/GG genotypes were significantly under‐represented in NHL (26·2%) vs control subjects (37·2%; P = 0·02), and conferred a 2·4‐fold lower risk of follicular (odds ratio = 0·41, 95% confidence interval: 0·19–0·88, p = 0·02) but not diffuse large B‐cell lymphoma. MM patients showed no significant difference in the polymorphisms compared with control subjects.

The role of tenascin C in cardiovascular disease

The extracellular matrix protein tenascin C (TnC) is expressed in a variety of embryonic tissues, but its expression in adult arteries is co-incident with sites of vascular disease. TnC expression has been linked to the development and complications of intimal hyperplasia, pulmonary artery hypertension, atherosclerosis, myocardial infarction, and heart failure. This review identifies the growing collection of evidence linking TnC with cardiovascular disease development. The transient upregulation of this extracellular matrix protein at sites of vascular disease could provide a means to target TnC in the development of diagnostics and new therapies. Studies in TnC-deficient mice have implicated this protein in the development of intimal hyperplasia. Further animal and human studies are required to thoroughly assess the role of TnC in some of the other pathologies it has been linked with, such as atherosclerosis and pulmonary hypertension. Large population studies are also warranted to clarify the diagnostic value of this extracellular matrix protein in cardiovascular disease, for example by targeting its expression using radiolabelled antibodies or measuring circulating concentrations of TnC.

Polymorphisms in Platelet Glycoprotein 1bα and Factor VII and Risk of Ischemic Stroke: A Meta-Analysis

Background and Purpose— Platelets and components of the coagulation cascade are known to be instrumental in the pathogenesis of arterial occlusive disorders. The aim of this meta-analysis is to test the hypothesis that genetic variation in the platelet glycoprotein 1bα and Factor VII genes influence the occurrence of ischemic stroke. All genetic association studies that examined the R353Q (rs6046) polymorphism of the Factor VII gene and 2 polymorphisms of the platelet glycoprotein (1bα) gene (Thr/Met rs6065 and Kozak sequence −5 C/T rs2243093) in relation to ischemic stroke were examined. Methods— Electronic databases Embase, Medline, and HuGEnet were searched for all years up until June 2006 for all studies that evaluated any of these candidate genes and stroke. Results— Pooled ORs were calculated with 95% CIs using both fixed and random effects models. Meta-analysis for Factor VII (R353Q) did not detect any effect on ischemic stroke risk. Further estimation resulted in pooled OR1 QQ versus RR=0.9 (95% CI: 0.4 to 1.9) and pooled OR2 for RQ versus RR=0.9 (95% CI: 0.6 to 1.4). These results were robust and homogeneous. Pooling ORs for the platelet glycoprotein 1bα Kozak variant −5 T/C polymorphism showed extreme heterogeneity with differing effect directions across studies. Fishers method of pooling was therefore used to calculate a combined probability value, which was highly significant (P<0.001). The pooled OR for platelet glycoprotein 1bα Met/Met v Thr/Thr was 1.0 to 2.0, depending on the sensitivity analyses, and for Thr/Met versus Thr/Thr, the pooled OR was between 1.3 and 1.4. These results were consistent, reasonably robust, and implied a dominant genetic effect. Conclusion— This analysis provides strong evidence that the Factor VII R353Q gene polymorphism is not associated with ischemic stroke, that the Thr/Met polymorphism of GP1bα is associated with ischemic stroke in a dominant genetic model, and that the Kozak sequence polymorphism of GP1bα may be close to another causative locus that is associated with ischemic stroke.