Heterogeneity of cell death.

Cell death constitutes a number of heterogeneous processes. Despite the dynamic nature of cell death, studies of cell death have primarily focused on apoptosis, and cell death has often been viewed as static events occurring in linear pathways. In this article we review cell death heterogeneity with specific focus on 4 aspects of cell death: the type of cell death; how it is induced; its mechanism(s); the results of cell death, and the implications of cell death heterogeneity for both basic and clinical research. This specifically reveals that cell death occurs in multiple overlapping forms that simultaneously occur within a population. Network and pathway heterogeneity in cell death is also discussed. Failure to integrate cell death heterogeneity within analyses can lead to inaccurate predictions of the amount of cell death that takes place in a tumor. Similarly, many molecular methods employed in cell death studies homogenize a population removing heterogeneity between individual cells and can be deceiving. Finally, and most importantly, cell death heterogeneity is linked to the formation of new genome systems through induction of aneuploidy and genome chaos (rapid genome reorganization).

Synthesis and localization of two sulphated glycoproteins associated with basement membranes and the extracellular matrix.

Two sulphated glycoproteins (sgps) of apparent molecular weight (Mr) 180,000 and 150,000, are synthesized by murine PYS and PF HR9 parietal endoderm and Swiss 3T3 cells. The Mr 150,000 sgp has a similar chemical structure to the sulphated glycoprotein, C, synthesized and laid down in Reichert's membrane by mouse embryo parietal endoderm cells (Hogan, B. L.M., A. Taylor, and A.R. Cooper, 1982, Dev. Biol., 90:210-214). Both the Mr 180,000 and 150,000 sgps are deposited in the detergent-insoluble matrix of cultured cells, but they do not apparently undergo any disulphide-dependent intermolecular interactions and are not precursors or products of each other. They contain asparagine-linked oligosaccharides, but these are not the exclusive sites of sulphate labeling. Antiserum raised against the Mr 150,000 sgp C of Reichert's membranes has been used in an immunohistochemical analysis of rat skin. In early foetal and adult skin the antigen is present only in basement membranes, but transiently before and after birth it is also found throughout the upper part of the dermis. This suggests that 150,000 sgp C is at times synthesized by nonepithelial cells and contributes to the extracellular matrix of mesenchymal tissues.

Biosynthesis and supramolecular assembly of procollagen IV in neonatal lung.

The rate of biosynthesis of procollagen IV, the principal collagen of basement membranes, and the concentration of specific RNAs coding for procollagen IV were measured in neonatal rat lungs. Both decreased sharply at birth and then recovered again a few days later. The supramolecular assembly of procollagen IV was followed in neonatal rat, mouse, and chick lungs, which actively elaborate endothelial and alveolar basement membranes, and in chick embryo gizzard which is rich in smooth muscle. The tetramer of four procollagen IV molecules linked covalently through their amino ends was isolated as an assembly intermediate from all these tissues. While noncovalent association of the carboxyl ends of two procollagen IV molecules occurred readily, the subsequent establishment of covalent cross-links was substantially slower in the junctional complexes of the carboxyl ends than of the amino ends. Both disulfide bonds and other, unidentified covalent links formed. The six component carboxyl peptides of a junctional complex became progressively covalently linked into two kinds of carboxyl peptide pairs. We conclude that both amino-linked tetramers and carboxyl-linked dimers of procollagen IV molecules are intermediates in the biological assembly of the collagen networks of these basement membranes.

Isolation of the pericellular matrix of human fibroblast cultures.

The pericellular matrix of human fibroblast cultures was isolated, using sequential extraction with sodium deoxycholate and hypotonic buffer in the presence of protease inhibitor. The matrix attached to the growth substratum had a "sackcloth-like" structure as seen by phase contrast, immunofluorescence, and scanning electron microscopy, and it had a vaguely filamentous ultrastructure similar to that seen in intact cell layers. The matrix consisted of hyaluronic acid and heparan sulfate as the major glycosaminoglycan components and fibronectin and procollagen as major polypeptides as shown by metabolic labeling, gel electrophoresis, immunofluorescence, and collagenase digestion. This pericellular matrix can be regarded as an in vitro equivalent of the loose connective tissue matrix.

A genomic clone encoding a novel proliferation-dependent histone H2A.1 mRNA enriched in the poly(A)+ fraction.

Replication-dependent histone mRNAs are prime examples of nonpolyadenylated mRNAs. We isolated and characterized cDNAs and a genomic clone for a replication-dependent histone H2A.1 mRNA which segregated into the poly(A)+ fraction during mRNA isolation through an oligo(dT)-cellulose column. However, the results of sequencing of the genomic clone suggested that the mRNA did not contain a poly(A) tail. Instead, the genomic sequence revealed a nonterminal oligo(A) tract directly upstream from the typical 3'-terminal hairpin loop of replication-dependent histone mRNAs. The nonterminal oligo(A) tract consisted of 14 adenylate residues interrupted by one guanylate residue (A4GA10). We concluded that this short oligo(A) stretch mediated binding of the mRNA to oligo(dT) even after stringent washes with 0.1 M NaCl, indicating that rather short oligo(A) sequences can ensure binding to oligo(dT)-cellulose. The cDNA and genomic clones contained an AAATAAG sequence at the end of the coding region. It has been suggested that this sequence contains a polyadenylation signal in some yeast and mouse transcripts, but it does not function as a polyadenylation signal in the histone transcript described in this paper.

Erg, an Ets-family member, differentially regulates human collagenase1 (MMP1) and stromelysin1 (MMP3) gene expression by physically interacting with the Fos/Jun complex.

Collagenase1 (MMP1) and stromelysin1 (MMP3) are extracellular proteolytic enzymes that degrade connective tissue macromolecules and basement membranes. Both genes are regulated by the Ets and Fos/Jun families of transcription factors/oncoproteins. Here, we show that two members of the Ets-family, Ets2 and Erg and their combinations differentially regulate collagenase1 and stromelysin1 promoter activity. In transiently transfected cells, Ets2 activates both promoters whereas Erg induces collagenase1 but not stromelysin1 promoter activity. Moreover, Erg completely inhibits stromelysin1 promoter activation by Ets2. In gel shift assays however, the Erg protein bound little or not to the collagenase1 promoter, whereas it bound to the stromelysin1 promoter. By site-specific mutagenesis, we identified one major site at -88 that abolished collagenase1 promoter activation by Erg. Surprisingly, mutation of the collagenase1 AP1 site at -73 also abolished the activation by Erg suggesting that Erg cooperates with Fos/Jun in collagenase1 promoter regulation. Indeed, gel shift and in vitro protein interaction studies showed that Erg binds to the Fos/Jun complex. Thus, Erg represents the first example of a transcription factor that can distinguish between the collagenase1 and stromelysin1 promoters in that when Erg is recruited by Fos/Jun at the promoter, it transcriptionally activates collagenase1 gene but not stromelysin1 expression.

Polypeptides of human plasma fibronectin are similar but not identical.

Human plasma fibronectin migrated in electrophoresis after reduction of the disulfide bonds in SDS-polyacrylamide gels as two closely spaced polypeptide bands. These polypeptides, the A chain (Mr 220 000) and the B chain (215 000), were isolated from slices of slab gels. The two isolated chains were immumologically indistinguishable when tested by double immunodiffusion against antiserum to plasma fibronectin. Identical peptides were obtained from both chains after Staphylococcus aureus proteinase digesting or after cyanogen bromide cleavage, respectively. Kinetic analysis of plasmin digestion of isolated dimeric fibronectin, however, suggested that the A chain was cleaved more rapidly than the B chain and that the primary plasmin cleavage products of fibronectin, the 200 000 and 190 000 polypeptides, were derived from the A and B chain, respectively. The basis for the difference between the A and B chains of human plasma fibronectin identified here, is, at present, unknown. Proteolytic or some other posttranslational processing of a common fibronectin polypeptide seems unlikely since also the newly synthesized fibronectin, isolated from human fibroblast cultures pulse-labeled for 5 min, appeared as two closely spaced polypeptide bands in SDS-gel electrophoresis.

Cloning and developmental regulation of tissue inhibitor of metalloproteinases-3 (TIMP3) in Xenopus laevis early embryos.

We cloned a cDNA encoding tissue inhibitor of metalloproteinases-3 (TIMP3) from the frog Xenopus laevis. Similar to TIMP3 from other species, Xenopus TIMP3 has 188 residues including 12 conserved cysteines and Asn184, a putative site for N-linked sugars. Xenopus TIMP3 is 84% identical with human TIMP3. As shown by Northern blotting and RT-PCR, Xenopus TIMP3 mRNA is maternally inherited in eggs and midblastula (stage 8) embryos, downregulated in gastrula and then upregulated in neurula and pretailbud embryos. In select adult tissues, TIMP3 mRNA is present in heart, muscle, liver, skin, intestine and ovaries. These results suggest that TIMP3 is involved in the regulation of expression of matrix metalloproteinases in Xenopus early development and adult tissue remodeling.

Nucleotide sequence coding for the human type IV collagen alpha 2 chain cDNA reveals extensive homology with the NC-1 domain of alpha 1 (IV) but not with the collagenous domain or 3'-untranslated region.

We have isolated two overlapping cDNA clones that provide the complete nucleotide sequence coding for the NC-1 domain and 3'-untranslated region of the alpha 2 chain of human type IV collagen as well as a sequence encoding 232 residues of the collagenous domain. An extensive homology was observed between the sequences of the NC-1 domain of the alpha 1(IV) and alpha 2(IV) chains, but considerably less between the sequences encoding collagenous and 3'-untranslated regions. There were four interruptions in the collagenous sequence studied whereas the comparable region of the alpha 1(IV) chain had only two. A potential oligosaccharide attachment site was found in a 6-residue long interruption of the collagenous domain but none in the NC-1 domain.

Fibronectin and the pericellular matrix of normal and transformed adherent cells.

Fibronectin is a major glycoprotein component of normal fibroblasts in culture. External fibronectin is predominantly present in a pericellular fibrillar matrix that mediates distant cell-cell and cell-substratum contacts. A small proportion of external fibronectin is closely associated with the plasma membrane. In the matrix, fibronectin is partially disulfide bonded into complexes. Plasma transglutaminase, activated by thrombin, also cross-links external fibronectin into high-molecular-weight covalent complexes. In cultures of normal fibroblasts, pericellular matrix fibronectin displays extensive codistribution with (pro)collagens types I and III. Transformed adherent cells show decreased formation of the fibronectin-collagen matrix. The deficient synthesis of fibronectin and other matrix components and abnormal interactions with the matrix may account for several phenotypic characteristics of transformed cells. The pericellular matrix structure has been prepared by use of deoxycholate and hypotonic medium to solubilize the cells. The matrix contains glycosaminoglycans, procollagens, and fibronectin. The fibronectin codistributes with the procollagens. The matrix may be considered to be an in vitro equivalent of the connective tissue matrix and basal laminae found in vivo. Human sarcoma cells spread rapidly on the prepared matrix and assume an elongated morphology characteristic of normal fibroblasts. The prepared matrix may provide a general tool to study the effects of matrix on cellular behavior and differentiation.

Silent brain infarcts, leukoaraiosis, and long-term prognosis in young ischemic stroke patients.

OBJECTIVE: To investigate prognostic relevance of silent brain infarcts (SBIs) and leukoaraiosis (LA) in young patients with ischemic stroke. METHODS: This observational cohort study included consecutive MRI-scanned patients aged 15 to 49 with first-ever ischemic stroke treated at Helsinki University Central Hospital (1994-2007) with long-term follow-up data available. Outcome measures were 1) nonfatal or fatal ischemic stroke, 2) composite vascular endpoint, and 3) death from any cause. Trial of ORG 10172 in Acute Stroke Treatment (TOAST) and Bamford criteria allowed for stroke subtyping. Number of SBIs was categorized into none, single, or multiple. LA fell into groups of none, mild, or moderate to severe (validated visual rating scale). RESULTS: The 655 patients (mean age 40.0 ± 8.0 years) included were followed for a mean 8.7 ± 3.8 years (survivors). Of the 86 (13.1%) patients with SBIs, 46 had single and 40 had multiple SBIs. In the 50 (7.6%) patients with LA, these changes were mild in 21 and moderate to severe in 29. In Cox regression analysis, multiple SBIs independently raised the risk for recurrent ischemic stroke (odds ratio 2.48; 95% confidence interval 1.24-4.94) adjusted for age, gender, risk factors, stroke etiology, and LA. After further adjustment for initial stroke severity, TOAST and Bamford subgroups, and presence of SBIs, moderate to severe LA increased the risk for death (3.43; 1.58-7.42). Neither SBIs nor LA associated with the composite vascular endpoint. CONCLUSIONS: MRI-defined SBIs and LA are prognostically valuable in young adults after their first-ever ischemic stroke.

Silent brain infarcts and leukoaraiosis in young adults with first-ever ischemic stroke.

BACKGROUND: We recently observed that 13% of 1,008 consecutive adults aged 15-49 years with first-ever ischemic stroke had one or more silent brain infarcts (SBIs), and more than 5% presented with leukoaraiosis on CT or MRI. We sought to investigate the features of and risk factors for magnetic resonance (MR)-defined SBIs and leukoaraiosis in these patients. METHODS: We analyzed the radiologic features of SBIs and leukoaraiosis in MR-scanned patients (n = 669) blinded to clinical data and examined their relation with subtype of the overt stroke. We used logistic regression to identify factors predisposing to SBIs and leukoaraiosis. RESULTS: Of the 669 patients included, 86 (13%) had SBIs, 50 (7%) had leukoaraiosis, 17 (3%) had both, and 550 had no SBIs or leukoaraiosis and served as controls. The majority (54%) had a single SBI, 20% had two SBIs, and 27% had three or more SBIs. Most SBIs were located in basal ganglia (39%) or subcortical regions (21%), but cerebellar SBIs also were rather frequent (15%). Leukoaraiosis was mainly mild to moderate. Independent risk factors for SBIs were type 1 diabetes (odds ratio [OR] 5.78, 95% confidence interval 2.37-14.10), obesity (OR 2.12, 1.07-4.19), smoking (OR 1.69, 1.05-2.72), and increasing age (OR 1.08, 1.04-1.13). Risk factors for leukoaraiosis were type 1 diabetes (OR 9.75, 3.39-28.04), obesity (OR 2.42, 1.04-5.68), female sex (OR 2.25, 1.16-4.34), and increasing age (OR 1.19, 1.10-1.29). Small-vessel disease was the predominant cause of stroke in both those with SBIs (31%) and leukoaraiosis (44%). CONCLUSIONS: Silent brain infarcts and leukoaraiosis are not uncommon among young stroke patients--type 1 diabetes being the strongest risk factor.

Fibronectin matrix: antibody-induced reorganization in human fibroblast cultures.

Fibronectin, a major pericellular glycoprotein of adherent cells, was predominantly present in fibrillar structures in human fibroblast cultures as shown by indirect immunofluorescence. In conventional "patching experiments" where one day old cells were exposed to anti-fibronectin IgG in the cold, washed, and reincubated at 37 degrees no redistribution was seen. However, continuous exposure of the cultures to IgG at 37 degrees resulted in redistribution. The fibrillar structures were lost and fibronectin aggregates (patches) were found. Fab-fragments had no such effect. These results support the findings that fibronectin is predominantly a matrix protein and show that matrix components may be redistributed in cell culture conditions.

Cloning and characterization of a novel matrix metalloproteinase (MMP), CMMP, from chicken embryo fibroblasts. CMMP, Xenopus XMMP, and human MMP19 have a conserved unique cysteine in the catalytic domain.

We cloned a novel matrix metalloproteinase (MMP) called CMMP from cultured primary chicken embryo fibroblasts. The cDNA-derived CMMP sequence contains 472 amino acids including a putative 19-residue signal peptide and a unique cysteine in the catalytic domain, an insertion in a sequence motif that binds the structural (noncatalytic) zinc of MMPs. Strikingly, a homologously inserted cysteine is also found in Xenopus XMMP and human MMP19, two recently cloned novel members of the MMP family. Phylogenetic analysis suggest that XMMP and MMP19 represent founding members of the MMP family, whereas CMMP is related to collagenase MMPs. Bacterially produced recombinant CMMP (without the amino-terminal inhibition domain), which was autoproteolyzed at the carboxyl-terminal domain, digested casein and gelatin. As shown by Northern blotting, CMMP mRNA of 1.8 kilobase pairs was constitutively expressed in cultured primary chicken embryo fibroblasts and up-regulated by tumor necrosis factor-alpha and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate, but it was not regulated by interleukin-1, basic fibroblast growth factor, or retinoic acid. CMMP mRNA of 1.8 kb was also detected in the head and body of 8-day-old chicken embryos and dramatically up-regulated in 9-day-old embryos.