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Biomedical subjects

L Holmgren

Publications and source records attributed to L Holmgren.

At least 19 recordsLinked to original sources
PubMed2001

Horizontal transfer of oncogenes by uptake of apoptotic bodies.

Tumor formation involves the accumulation of a series of genetic alterations that are required for malignant growth. In most malignancies, genetic changes can be observed at the chromosomal level as losses or gains of whole or large portions of chromosomes. Here we provide evidence that tumor DNA may be horizontally transferred by the uptake of apoptotic bodies. Phagocytosis of apoptotic bodies derived from H-ras(V12)- and human c-myc-transfected rat fibroblasts resulted in loss of contact inhibition in vitro and a tumorigenic phenotype in vivo. Fluorescence in situ hybridization analysis revealed the presence of rat chromosomes or of rat and mouse fusion chromosomes in the nuclei of the recipient murine cells. The transferred DNA was propagated, provided that the transferred DNA conferred a selective advantage to the cell and that the phagocytotic host cell was p53-negative. These results suggest that lateral transfer of DNA between eukaryotic cells may result in aneuploidy and the accumulation of genetic changes that are necessary for tumor formation.

Animals↗
PubMed2001

Angiomotin: an angiostatin binding protein that regulates endothelial cell migration and tube formation.

Angiostatin, a circulating inhibitor of angiogenesis, was identified by its ability to maintain dormancy of established metastases in vivo. In vitro, angiostatin inhibits endothelial cell migration, proliferation, and tube formation, and induces apoptosis in a cell type-specific manner. We have used a construct encoding the kringle domains 1--4 of angiostatin to screen a placenta yeast two-hybrid cDNA library for angiostatin-binding peptides. Here we report the identification of angiomotin, a novel protein that mediates angiostatin inhibition of migration and tube formation of endothelial cells. In vivo, angiomotin is expressed in the endothelial cells of capillaries as well as larger vessels of the human placenta. Upon expression of angiomotin in HeLa cells, angiomotin bound and internalized fluorescein-labeled angiostatin. Transfected angiomotin as well as endogenous angiomotin protein were localized to the leading edge of migrating endothelial cells. Expression of angiomotin in endothelial cells resulted in increased cell migration, suggesting a stimulatory role of angiomotin in cell motility. However, treatment with angiostatin inhibited migration and tube formation in angiomotin-expressing cells but not in control cells. These findings indicate that angiostatin inhibits cell migration by interfering with angiomotin activity in endothelial cells.

Amino Acid Sequence↗
PubMed2000

Sense of coherence in different stages of health and disease in northern Sweden--gender and psychosocial differences.

OBJECTIVE: To investigate "Sense of Coherence" (SOC) and its relation to perceived health, different stages of disease, and different psychosocial factors in a population-based study. DESIGN: Postal survey of a population-based sample, the MONICA study (1994). SETTING: Norrbotten and Västerbotten, the two northernmost counties in Sweden, with a total population of 510000 inhabitants. SUBJECTS: 837 men and 882 women in three mutually-exclusive groups: stomach trouble of many years' standing, identified disease (stroke, cardiac infarction, diabetes, anti-hypertension treatment) and no reported disease. MAIN OUTCOME MEASURES: SOC scores in relation to sociodemographic variables and perceived health. RESULTS: We found a relationship between low SOC scores and poor perceived health, low social support and low emotional support on a population level. When comparing persons with stomach trouble with those without disease, or with established diseases, we found similar relationships between low mean SOC scores in all strata for both women and men. "Perceived health", however, was only significantly correlated for women, and women had an overall stronger relationship. CONCLUSIONS: In a study in northern Sweden, female patients with stomach trouble comprise a vulnerable group. The concept of SOC introduces a new dimension for perceiving health and disease. In clinical practice, care providers can identify and elaborate on the relationship between SOC scores and sociodemographic data.

Adult↗
PubMed1999

Functional gene transfer of HIV DNA by an HIV receptor-independent mechanism.

HIV-1 enters target cells mainly via binding to CD4 and its coreceptors. The presence of HIV-1 in CD4- cells suggests, however, that there exist other mechanisms for viral entry. Here it is reported that HIV-1 DNA may be transferred from one cell to another by uptake of apoptotic bodies in a CD4-independent way. This was investigated by coculturing CD4-, chemokine receptor CCR5- and CXCR4- human fetal fibroblasts with apoptotic HIV-1-infected HuT78 cells or apoptotic PBMC isolated from HIV-1-infected patients. After 2 wk of coculture, fibroblasts contained HIV-1 DNA and expressed HIV-1 proteins p24 and gp120. Transfer of HIV-1 DNA was verified by coculturing fibroblasts with apoptotic bodies derived from cells infected with a defective HIV-1 virus. These cells contain one integrated copy of a reverse transcriptase (RT)-negative HIV-1 strain (8E5/LAV RT- cells) and consequently cannot produce free virus. Intracellular HIV-1 gag DNA was detected in both fibroblasts and dendritic cells after coculture with apoptotic 8E5/LAV RT- cells. Transfer of viral DNA after uptake of apoptotic bodies may explain HIV-1 infection of CD4- cells in vivo and furthermore may be relevant for Ag presentation.

Apoptosis↗
PubMed1999

Horizontal transfer of DNA by the uptake of apoptotic bodies.

In this study we have raised the question of whether DNA can be transferred from one cell to another by phagocytosis of apoptotic bodies. We have used integrated copies of the Epstein-Barr virus (EBV) as a marker to follow the fate and expression pattern of apoptotic DNA in the phagocytotic host. Apoptosis was induced in EBV-carrying cell lines by irradiation before cultivation with either human fibroblasts, macrophages, or bovine aortic endothelial cells. Analysis of the expression pattern of EBV-encoded genes was performed by immunofluorescent staining as well as in situ hybridization. Cocultivation of apoptotic bodies from lymphoid cell lines containing integrated but not episomal copies of EBV resulted in expression of the EBV-encoded genes EBER and EBNA1 in the recipient cells at a high frequency. Fluorescence in situ hybridization analysis showed uptake of human chromatin as well as integrated EBV-DNA into the nuclei of bovine aortic endothelial cells. These data show that DNA may be rescued and reused from apoptotic bodies by somatic cells. In addition, our findings suggest that apoptotic bodies derived from EBV-carrying B lymphocytes may serve as the source of viral transfer to cells that lack receptors for the EBV virus in vivo.

Animals↗
PubMed1999

The mahogany protein is a receptor involved in suppression of obesity.

Genetic studies have shown that mutations within the mahogany locus suppress the pleiotropic phenotypes, including obesity, of the agouti-lethal-yellow mutant. Here we identify the mahogany gene and its product; this study, to our knowledge, represents the first positional cloning of a suppressor gene in the mouse. Expression of the mahogany gene is broad; however, in situ hybridization analysis emphasizes the importance of its expression in the ventromedial hypothalamic nucleus, a region that is intimately involved in the regulation of body weight and feeding. We present new genetic studies that indicate that the mahogany locus does not suppress the obese phenotype of the melanocortin-4-receptor null allele or those of the monogenic obese models (Lep(db), tub and Cpe(fat)). However, mahogany can suppress diet-induced obesity, the mechanism of which is likely to have implications for therapeutic intervention in common human obesity. The amino-acid sequence of the mahogany protein suggests that it is a large, single-transmembrane-domain receptor-like molecule, with a short cytoplasmic tail containing a site that is conserved between Caenorhabditis elegans and mammals. We propose two potential, alternative modes of action for mahogany: one draws parallels with the mechanism of action of low-affinity proteoglycan receptors such as fibroblast growth factor and transforming growth factor-beta, and the other suggests that mahogany itself is a signalling receptor.

Amino Acid Sequence↗
PubMed1998

Multiple forms of angiostatin induce apoptosis in endothelial cells.

Angiostatin is a circulating inhibitor of angiogenesis generated by proteolytic cleavage of plasminogen. In this study we have used recombinant human and murine angiostatins (kringles 1-4) as well as native human angiostatin (prepared by elastase digestion of plasminogen [kringles 1-3] or by plasmin autocatalysis in the presence of a free sulfhydryl donor [kringles 1-4]). We report that angiostatin reduces endothelial cell number in a 4-day proliferation assay without affecting cell cycle progression into S-phase (as determined by bromodeoxyuridine labeling). This suggested that the reduction in cell number in the proliferation assay might in part be due to cytotoxicity. This was confirmed by the observation that ethidium homodimer incorporation (a measure of plasma membrane integrity) into endothelial cells was increased by angiostatin in a manner similar to that seen with tumor necrosis factor- (TNF-) and transforming growth factor-beta1 (TGF-beta1), both of which induce apoptosis in endothelial cells. In contrast to TNF- and TGF-beta1, angiostatin did not induce cytotoxicity in human MRC-5 fibroblast, rat smooth muscle, canine MDCK epithelial, or murine B16-F10 melanoma cell lines. Angiostatin-induced apoptosis was confirmed by endothelial cell nuclear acridine orange incorporation as well as by annexin V and TUNEL staining. These in vitro findings point to endothelial cell apoptosis as a mechanism for the antiangiogenic effect of angiostatin in vivo.

Angiostatins↗
PubMed1998

p53 induces angiogenesis-restricted dormancy in a mouse fibrosarcoma.

The p53 tumor-suppressor gene is inactivated in over 50% of all human cancers. In normal cells, p53 induces growth arrest and apoptosis in response to DNA damage. We show that p53 acts as potent tumor-suppressor gene independent of its well-documented effects on tumor-cell proliferation and apoptosis. p53 activates target genes in a murine fibrosarcoma cell-line but does not affect tumor cell-cycle progression or survival. Exogenous expression of wt-p53 does, however, block the angiogenic potential of the tumor cells resulting in formation of dormant tumors in vivo. These data provide evidence that: (1) p53 acts as a tumor suppressor gene independent of its anti-proliferative effects; (2) By inhibiting angiogenesis p53 can indirectly induce apoptosis in vivo but not in vitro; (3) p53-gene therapy which alters a tumors angiogenic potential, can revert tumors to a dormant phenotype.

Animals↗
PubMed1996

Identification and characterization of the mouse obesity gene tubby: a member of a novel gene family.

The mutated gene responsible for the tubby obesity phenotype has been identified by positional cloning. A single base change within a splice donor site results in the incorrect retention of a single intron in the mature tub mRNA transcript. The consequence of this mutation is the substitution of the carboxy-terminal 44 amino acids with 24 intron-encoded amino acids. The normal transcript appears to be abundantly expressed in the hypothalamus, a region of the brain involved in body weight regulation. Variation in the relative abundance of alternative splice products is observed between inbred mouse strains and appears to correlate with an intron length polymorphism. This allele of tub is a candidate for a previously reported diet-induced obesity quantitative trait locus on mouse chromosome 7.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Antiangiogenic therapy of transgenic mice impairs de novo tumor growth.

Angiogenesis is activated during multistage tumorigenesis prior to the emergence of solid tumors. Using a transgenic mouse model, we have tested the proposition that treatment with angiogenesis inhibitors can inhibit the progression of tumorigenesis after the switch to the angiogenic phenotype. In this model, islet cell carcinomas develop from multifocal, hyperproliferative nodules that show the histological hallmarks of human carcinoma in situ. Mice were treated with a combination of the angiogenesis inhibitor AGM-1470 (TNP-470), the antibiotic minocycline, and interferon alpha/beta. The treatment regimen markedly attenuated tumor growth but did not prevent tumor formation; tumor volume was reduced to 11% and capillary density to 40% of controls. The proliferation index of tumor cells in treated and control mice was similar, whereas the apoptotic index was doubled in treated tumors. This study shows that de novo tumor progression can be restricted solely by antiangiogenic therapy. The results suggest that angiogenesis inhibitors represent a valid component of anticancer strategies aimed at progression from discrete stages of tumorigenesis and demonstrate that transgenic mouse models can be used to evaluate efficacy of candidate antiangiogenic agents.

Adenoma, Islet Cell↗
PubMed1996

Identification of the murine beige gene by YAC complementation and positional cloning.

The beige mutation is a murine autosomal recessive disorder, resulting in hypopigmentation, bleeding and immune cell dysfunction. The gene defective in beige is thought to be a homologue of the gene for the human disorder Chediak-Higashi syndrome. We have identified the murine beige gene by in vitro complementation and positional cloning, and confirmed its identification by defining mutations in two independent mutant alleles. The sequence of the beige gene message shows strong nucleotide homology to multiple human ESTs, one or more of which may be associated with the Chediak-Higashi syndrome gene. The amino acid sequence of the Beige protein revealed a novel protein with significant amino acid homology to orphan proteins identified in Saccharomyces cerevisiae, Caenorhabditis elegans and humans.

Amino Acid Sequence↗
PubMed1996

Identification and mutation analysis of the complete gene for Chediak-Higashi syndrome.

Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive disorder characterized by hypopigmentation, severe immunologic deficiency with neutropenia and lack of natural killer (NK) cells, a bleeding tendency and neurologic abnormalities. Most patients die in childhood. The CHS hallmark is the occurrence of giant inclusion bodies and organelles in a variety of cell types, and protein sorting defects into these organelles. Similar abnormalities occur in the beige mouse, the proposed model for human CHS. Two groups have recently reported the identification of the beige gene, however the two cDNAs were not at all similar. Here we describe the sequence of a human cDNA homologous to mouse beige, identify pathologic mutations and clarify the discrepancies of the previous reports. Analysis of the CHS polypeptide demonstrates that its modular architecture is similar to the yeast vacuolar sorting protein, VPS15.

Adult↗
PubMed1996

Angiostatin induces and sustains dormancy of human primary tumors in mice.

There is now considerable direct evidence that tumor growth is angiogenesis-dependent. The most compelling evidence is based on the discovery of angiostatin, an angiogenesis inhibitor that selectively instructs endothelium to become refractory to angiogenic stimuli. Angiostatin, which specifically inhibits endothelial proliferation, induced dormancy of metastases defined by a balance of apoptosis and proliferation. We now show that systemic administration of human angiostatin potently inhibits the growth of three human and three murine primary carcinomas in mice. An almost complete inhibition of tumor growth was observed without detectable toxicity or resistance. The human carcinomas regressed to microscopic dormant foci in which tumor cell proliferation was balanced by apoptosis in the presence of blocked angiogenesis. This regression of primary tumors without toxicity has not been previously described. This is also the first demonstration of dormancy therapy, a novel anticancer strategy in which malignant tumors are regressed by prolonged blockade of angiogenesis.

Angiostatins↗
PubMed1995

Dormancy of micrometastases: balanced proliferation and apoptosis in the presence of angiogenesis suppression.

In cancer patients, dormant micrometastases are often asymptomatic and clinically undetectable, for months or years, until relapse. We have studied dormant lung metastases under angiogenesis suppression in mice. The metastases exhibited rapid growth when the inhibition of angiogenesis was removed. Tumour cell proliferation, as measured by bromodeoxyuridine incorporation and immunohistochemical staining proliferating cell nuclear antigen, was not significantly different in dormant and growing metastases. However, tumour cells of dormant metastases exhibited a more than threefold higher incidence of apoptosis. These data show that metastases remain dormant when tumour cell proliferation is balanced by an equivalent rate of cell death and suggest that angiogenesis inhibitors control metastatic growth by indirectly increasing apoptosis in tumour cells.

Animals↗
PubMed1994

Angiostatin: a novel angiogenesis inhibitor that mediates the suppression of metastases by a Lewis lung carcinoma.

The phenomenon of inhibition of tumor growth by tumor mass has been repeatedly studied, but without elucidation of a satisfactory mechanism. In our animal model, a primary tumor inhibits its remote metastases. After tumor removal, metastases neovascularize and grow. When the primary tumor is present, metastatic growth is suppressed by a circulating angiogenesis inhibitor. Serum and urine from tumor-bearing mice, but not from controls, specifically inhibit endothelial cell proliferation. The activity copurifies with a 38 kDa plasminogen fragment that we have sequenced and named angiostatin. A corresponding fragment of human plasminogen has similar activity. Systemic administration of angiostatin, but not intact plasminogen, potently blocks neovascularization and growth of metastases. We here show that the inhibition of metastases by a primary mouse tumor is mediated, at least in part, by angiostatin.

Amino Acid Sequence↗