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Showing papers by "Bruce M. Spiegelman published in 1986"


Journal ArticleDOI
TL;DR: The results indicate that the aP2 gene contains sequence information necessary for differentiation-dependent expression in fat cells; common elements shared by adipocyte-specific genes may play a role in this process.
Abstract: We have isolated the mouse gene encoding adipocyte P2, aP2, the differentiation-dependent adipocyte protein homologous to myelin P2. The aP2 gene is present in a single copy in the mouse and is present in single or few copies in species from human to Drosophila. The entire gene spans 4 kilobases and consists of four exons encoding 25, 57, 34, and 16 amino acids; the overall exon structure is similar to the gene encoding liver fatty acid binding protein. A plasmid vector was constructed containing the entire aP2 gene with flanking sequences, modified by linker insertion. When this gene is stably introduced into 3T3-F442A cells, it is expressed only upon adipose differentiation, with a time course of induction very similar to that of the endogenous aP2 gene. We have compared the DNA sequence of the 5'-flanking region of the aP2 gene to the promoter regions of two other genes activated during adipocyte differentiation, glycerol-3-phosphate dehydrogenase and adipsin, and find a 13-base region of homology (Formula: see text) present in multiple copies in the 5'-flanking region of each gene. An adjacent 15-base sequence is present only in glycerol-3-phosphate dehydrogenase and aP2 genes. Both of these elements share homology with putative viral enhancer core sequences. These results indicate that the aP2 gene contains sequence information necessary for differentiation-dependent expression in fat cells; common elements shared by adipocyte-specific genes may play a role in this process.

324 citations


Journal ArticleDOI
TL;DR: The results show that adipsin is a novel serine protease gene whose expression is regulated by a macrophage-derived factor which modulates expression of other adipocyte-specific RNAs.
Abstract: We have isolated, mapped and sequenced adipsin, the adipocyte differentiation-dependent serine protease gene. This gene, which is present in a single form in the mouse, spans 1.7 kilobases and contains five exons. While the basic exon structure characteristic of serine protease genes is conserved in adipsin, there is also a fusion of two exons that are separate in other serine proteases. The sequence data also suggests a mechanism of alternative splicing which appears to account for the generation of two adipsin mRNA species differing by only three nucleotides and encoding two different signal peptides. To investigate the control of adipsin expression we have examined the effects of tumor necrosis factor (TNF) on adipocytes. The level of adipsin RNA is dramatically decreased by hormone treatment, but the change occurs more slowly than for other fat cell mRNAs, such as glycerophosphate dehydrogenase. These results show that adipsin is a novel serine protease gene whose expression is regulated by a macrophage-derived factor which modulates expression of other adipocyte-specific RNAs.

94 citations


Journal ArticleDOI
TL;DR: These vectors and these functional assays of T-antigen activity permit genetic analysis of the relationship between tumorigenesis by T antigens and the alteration of cellular growth and differentiation.
Abstract: We have constructed infectious retroviral vectors, derived from Moloney murine leukemia virus, that efficiently transduce the polyoma virus tumor (T) antigens individually. The parental vector we have chosen [pZIP-NeoSV(X)1] expresses a dominant selectable marker for neomycin resistance and is a shuttle vector capable of propagation in both eukaryotic and prokaryotic cells, thus facilitating its use in structure-function studies. To address the relationship between polyoma T-antigen tumorigenesis and the effects of individual T antigens on growth control and differentiation, we used these vectors to introduce and stably express large, middle-sized, or small T antigens into mouse fibroblasts and preadipocytes. All cDNAs introduced into the vector are expressed stably even in the absence of selective pressure. The stable expression of small T antigen is noted particularly because cell lines expressing small T antigen have not been readily available prior to the use of retroviral vectors. Small T antigen-induced increase in saturation density of NIH 3T3 cells can be scored on the basis of the morphology of drug-resistant colonies. Middle-sized T antigen eliminates the growth requirement of NIH 3T3 cells for epidermal growth factor in a defined medium and permits growth in platelet-poor plasma, indicating elimination of the platelet-derived growth factor requirement as well. Large T antigen suppresses mouse preadipocyte (3T3-F442A) differentiation. These vectors and these functional assays of T-antigen activity permit genetic analysis of the relationship between tumorigenesis by T antigens and the alteration of cellular growth and differentiation.

89 citations


Journal ArticleDOI
TL;DR: The data suggest that heparin potentiates angiogenesis in vivo by stimulating endothelial cell plasminogen activator, motility, or both, and that for adipocyte‐induced blood vessel formation, hepar in does not appear to affect the mitogenic activity.
Abstract: We have examined the cellular mechanisms by which heparin potentiates the ability of 3T3-adipocytes to stimulate the formation of new blood vessels. Both anticoagulant and non-anticoagulant heparin species enhanced the angiogenic activity of adipocyte-secreted products in the chick chorioallantoic membrane assay, indicating that the angiotropic effect of this glycosaminoglycan is independent of its effect on the coagulation cascade. Heparin alone was unable to produce a neovascular response. The ability of heparin to modulate three endothelial functions in vitro thought to be related to angiogenesis were examined: protease activity, motility, and mitogenesis. Heparin caused a 100% increase in the adipocyte-induced stimulation of endothelial cell plasminogen activator activity and motility, but had no effect on proliferation. The enhancement of plasminogen activator and chemoattractant activities had a similar ED50 (1-2 micrograms/ml) and optimum dose (10-30 micrograms/ml). When we examined the direct effect of heparin on the activity of two distinct plasminogen activator enzymes--urokinase and tissue-type--a dual action of heparin was observed: tissue-type enzyme activity was stimulated 100% by heparin at 10 micrograms/ml, whereas urokinase activity was inhibited by 77% at this dose. These data suggest that heparin potentiates angiogenesis in vivo by stimulating endothelial cell plasminogen activator, motility, or both. Our results further suggest that for adipocyte-induced blood vessel formation, in contrast to other angiogenesis systems, heparin does not appear to affect the mitogenic activity.

45 citations