摘要:

AbstractGlucokinase contributes to the maintenance of blood glucose homeostasis by catalyzing the high Kmphosphorylation of glucose in the liver and the pancreatic β cell, the only two tissues known to express this enzyme. Molecular biological studies of the glucokinase gene and its products have advanced our understanding of how this gene is differentially regulated in the liver and β cell. The production of an active glucokinase isoform is determined by both transcriptional and post‐transcriptional events. Two different promoter regions that are widely separated in a single glucokinase gene are used to produce glucokinase mRNAs in the liver, pancreatic β cell, and pituitary. The different transcription control regions are tissue‐specific in their expression and are differentially regulated. In liver, glucokinase gene expression is regulated by insulin and cAMP, whereas in the β cell it is regulated by glucose. The upstream glucokinase promoter region, which gives rise to the glucokinase mRNA in pituitary and pancreas, is structurally and functionally different from the downstream promoter region, which gives rise to the glucokinase mRNA in liver. The use of distinct promoter regions in a single glucokinase gene enables a different set of transcription factors to be utilized in the liver and islet, thus allowing a functionally similar gene product to be regulated in a manner consistent with the different functions of these two tissues. In addition, the splicing of the glucokinase pre‐mRNA is regulated in a tissue‐specific manner and can affect the activity of the gene product. This is most apparent in the pituitary where an alternately spliced glucokinase mRNA is produced that does not encode a functional enzyme due to an introduced

ISSN:0730-2312    

DOI:10.1002/jcb.240480202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractInsulin resistance is a major pathologic feature of human obesity and diabetes. Understanding the fundamental mechanisms underlying this insulin resistance has been advanced by the recent cloning of the genes encoding a family of facilitated diffusion glucose transporters which are expressed in characteristic patterns in mammalian tissues. Two of these transporters, GLUT1 and GLUT4, are present in muscle and adipose cells, tissues in which glucose transport is markedly stimulated by insulin. To understand the mechanisms underlying in vivo insulin resistance, regulation of these transporters is being investigated. Studies reveals divergent changes in the expression of GLUT1 and GLUT4 in a single cell type as well as tissue specific regulation. Importantly, alterations in glucose transport in rodent models of diabetes and in human obesity and diabetes cannot be entirely explained by changes in glucose transporter expression. This suggests that defects in glucose transporter function such as impaired translocation, fusion with the plasma membrane, or activation probably contribute importantly to in vivo insulin resistance.

ISSN:0730-2312    

DOI:10.1002/jcb.240480203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractInsulin induces glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) gene transcription in part by regulating one or more proteins that bind a cis‐acting element, IRE‐A. We have recently cloned a protein, IRE‐ABP, that binds the IRE‐A element. IRE‐ABP is a member of the HMG class of transcriptional regulators and is 67% identical within its HMG box domain to the candidate gene for the testis‐determining factor, SRY. IRE‐ABP and SRY share binding specificity for the IRE‐A motif. This sequence is also highly conserved with a core motif, 5′‐Py‐ctttg(a/t)‐3′, contained in T‐cell specific genes that have high affinity for TCF‐1α, another member of the HMG class of transcriptional regulators. Thus, diverse members of the HMG family interact with similar nucleotide sequences to regulate expression of genes that initiate and maintain the differentiated phenotype. We have found this core motif in the upstream region of many genes that are positively and negatively regulated by insulin. These observations suggest that IRE‐ABP or a related family member may coordinate the expression of these genes. The HMG family of proteins has diverse functions ranging from the regulation of differentiation and mating type in yeast to the regulation of tissue‐and species‐specific gene expression in mammals. Insulin regulates GAPDH gene transcription in a tissue‐specfic manner. We propose that members of the IRE‐ABP family play an important role in controllin

ISSN:0730-2312    

DOI:10.1002/jcb.240480204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractInsulin and IGF‐l receptors are homologous disulfide linked α2β2tetramers. These tetramers are formed biosynthetically when proreceptors containing α and β subunits in a single uninterrupted linear peptide from disulfide linked homodimers and are subsequently proteolytically cleaved at the α‐β junctions. Cells expressing both receptors also express hybrid receptors that contain one insulin receptor α and β subunit, and one IGF‐l receptor α and β subunit. These presumably from by the association of mixed proreceptors. Hybrid receptors greatly expand the possible repertoire of cellular responses to hormonal stimulation. Although not yet examined in detail, both the hormone binding and the signaling properties of the hybrid receptor appear to be different from that of either insulin or IGF‐l receptor. Regulatory mechanisms that involve either insulin or IGF‐l receptor, at the level of expression or subsequently, could alter the expression or function of the hybrid receptor or the other receptor. Similarly, pathology in one receptor could affect both the hybrid and other receptor, or perhaps be partially compensated for by a hybrid receptor. The magnitude of these effects could vary greatly in different tissues depending upon the relative level of expression of the different receptor forms. These postulated responses might explain some of the complex heterogeneity and linkage of these receptors that have been

ISSN:0730-2312    

DOI:10.1002/jcb.240480205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMouse PFHR9 laminin, B1B2‐heterodimers, and free B1‐chains were separated from one another by gel filtration on superose 6. The cell attachment promoting activity of these species was measured after immunoprecipitation with monoclonal anti‐laminin antibodies coupled to Sepharose 6MB beads. These antibodies, Which did not react with the laminin E8 fragment, were directed against epitopes in the NH2‐terminus of the laminin B1‐chain and in the central region of laminin. After incubation with purified EHS laminin, the immunosorbents revealed efficient adhesion substrates for a rat rhabdomyosarcoma cell line which attached preferentially to the laminin E8 fragment. Although both were immunoprecipitated efficiently, B1B2‐heterodimers and B1‐chains, unlike PFHR9 laminin, did not support the attachment of RMS cells. On a molar basis B1B2‐heterodimers were 24 times less efficient than PFHR9 laminin or EHS laminin in supporting cell attachment. These data suggest that heterotrimeric configuration is essential to the adhesive function of the lami

ISSN:0730-2312    

DOI:10.1002/jcb.240480206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe influence of various normal and malignant human cells on the level of collagen synthesis by human fibroblasts was tested in coculture. As revealed by immunoperoxidase staining, in cocultures with breast adenocarcinoma cells (MCF7, SA52, T47D) fibroblasts synthesized collagen while tumor cells did not. Fibroblasts displayed increased collagen production without change in the overall protein synthesis. Several other types of cells derived from normal human tissues (keratinocytes, normal mammary cells) or from fibrosarcoma, melanoma, cervical carcinoma, choriocarcinoma, or other breast adenocarcinoma (SW613, MDA, BT20) did not affect collagen synthesis of fibroblasts. Although to a lesser extent, this stimulating effect was reproduced by using the conditioned medium (CM) of the active cells but not with CM of the other cell types. A slight stimulation was also obtained when tumoral MCF7 cells and fibroblasts shared the same medium but were physically separated, suggesting that close contact was required for optimal stimulation of collagen synthesis. The collagen synthesis stimulating activity was not related to a modification of fibroblast proliferation rate. The production of collagen types I, III, and VI and fibronectin were increased in cocultures of fibroblasts with MCF7 cells. The increased synthesis of collagen types I and III and fibronectin was paralleled by similar changes in the steady‐state level of their mRNAs. On the contrary, the increased production of collagen type VI appeared regulated at a post‐transcriptional le

ISSN:0730-2312    

DOI:10.1002/jcb.240480207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMetastatic variant cell lines of the murine RAW117 large cell lymphoma were used to study the cell surface components involved in syngeneic tumor cell/microvessel endothelial cell interactions. Poorly liver‐metastatic parental RAW 117‐P cell line adhered to murine hepatic sinusoidal endothelial cell monolayers at significantly lower rates than the liver‐selected, highly liver‐metastatic RAW117‐H10 line and both cell lines were poorly adherent to lung microvessel and bovine aorta endothelial cells. Viable, 2% 1‐butanol‐treated RAW117‐H10 tumor cells formed fewer liver tumor nodules in experimental metastasis assays than untreated H10 cells and were significantly less adherent to murine hepatic sinusoidal endothelial cell monolayers. When 2% 1‐butanol extracts of metabolically labeled or CHAPS detergent Iysates of cell surface‐labeled tumor cells were analyzed for their ability to bind to fixed microvessel endothelial cell monolayers, quantitative differences were found in the extractable tumor cell surface components that bound to the different organ‐derived microvessel endothelial cells. Cell surface components (1‐butanol extractable), of Mr∼ 85,000–90,000 and ∼ 37,000–40,000 bound to hepatic sinusoidal endothelial cell monolayers to a greater extent than to murine lung microvessel endothelial or bovine aortic endothelial cell monolayers, Whereas tumor cell surface components of Mr∼ 45,000, ∼ 33,000, and ∼ 25,000 bound similarly to endothelial cells regardless of origin. The results suggest but do not prove that tumor cell/endothelial cell adhesion involves multiple tumor cell surface components, some of which commonly bind to various endothelial cells and others for which binding may be dictated by the tissue origin and type of endothelial cell. Particular RAW117 butanol‐extractable cell membrane components were associated with tumor cell‐endothelial cell adhesion, and these components could be responsible, in part, for the preferential adhesion of RAW117 cells to liver sinusoidal

ISSN:0730-2312    

DOI:10.1002/jcb.240480208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractProlyl 4‐hydroxylase, a key enzyme in collagen biosynthesis, catalyzes the conversion of selected prolyl residues totrans‐hydroxyproline in nascent or completed pro‐α chains of procollagen. The enzyme is a tetramer composed of two nonidentical subunits, designated α and β. To compare the enzyme and its subunits from different sources, the chick embryo and human placental prolyl 4‐hydroxylases were purified to homogeneity and their physicochemical and immunological properties were determined. Both enzymes were glycoproteins with estimated apparent molecular weights ranging between 400 and 600 kDa. Amino acid and carbohydrate analyses showed slight differences between the two holomeric enzymes, consistent with their deduced amino acid sequences from their respective cDNAs. Human placental prolyl 4‐hydroxylase contained more tightly bound iron than the chick embryo enzyme. Immunodiffusion of the human placental enzyme with antibodies raised against the purified chick embryo prolyl 4‐hydroxylase demonstrated partial identity, indicating different antigenic determinants in their tertiary structures. The enzymes could be separated by high‐resolution capillary electrophoresis, indicating differential charge densities for the native chick embryo and human placental proteins.Electrophoretic studies revealed that the human prolyl 4‐hydroxylase is a tetrameric enzyme containing two nonidentical subunits of about 64 and 62 kDa, in a ratio of approximately 1 to 2, designated α and β, respectively. In contrast, the chick embryo α and β subunit ratio was 1 to 1. Notably, the human α subunit was partially degraded when subjected to electrophoresis under denaturing conditions. Analogously, when the chick embryo enzyme was subjected to limited proteolysis, selective degradation of the α subunit was observed. Finally, only the α subunit was bound to Concanavalin A demonstrating that the α subunits of prolyl 4‐hydroxylase in both species were glycosylated. Using biochemical techniques, these results demonstrated that the 4‐trans‐hydroxy‐L‐proline residues in human placental collagens are synthesized by an enzyme whose primary structure and immunological properties differ from those of the previously well‐characterized chick embryo enzyme, consistent with their recently deduced

ISSN:0730-2312    

DOI:10.1002/jcb.240480209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe human myeloid cell nuclear differentiation antigen (MNDA) is expressed specifically in cells of the granulocyte/monocyte lineage. The MNDA has been isolated by using a monoclonal antibody affinity matrix and reversed‐phase high performance liquid chromatography. Its NH2‐terminal sequence has been obtained, as well as additional sequence information derived from peptides produced by cyanogen bromide and SV8protease cleavages. Meaningful similarities were observed in extended regions between the MNDA and the reported β interferon‐inducible proteins, 202 and 204, from Ehrlich ascites mouse tumor cells. An amphipathic, basic α‐helical region, showing no similarity to the 202 and 204 proteins, exhibited close similarity to a region in the interferon response factor‐2, a protein which binds the interferon stimulated response element. The relatively high number of S(T)PXX motifs present in the partial amino acid sequence of the MNDA, described herein, suggests that the MNDA binds DNA and is a transcrip

ISSN:0730-2312    

DOI:10.1002/jcb.240480210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe time‐dependent concentrations of interferon‐α and tumor necrosis factor‐α associated with the membrane and internalized by cells contain information on the kinetics of endocytosis and their cellular processing. This information can be reduced quantitatively by application of the respective compartmental models. In our studies of human epithelial tumor cells interacting with human interferon‐α and human tumor necrosis factor ‐α, we accounted only for actual endocytosis and elimination of the tracer from cells by a novel method sensitive to changes in the rate of endocytosis, to the delay in tracer elimination, and to the nonlinear regulatory coupling between endocytosis and the internalized ligand. Data reduced by this method resulted in best‐fit parameter values statistically superior to values obtained by previous methods (Bajzer et al., 1989). The results indicate a change with time in the rate of endocytosis of tumor necrosis factor‐α and the inhibition of endocytosis by the endocytosed ligand‐receptor complex. We conclude that sorting and processing of interferon‐α and tumor necrosis factor ‐α are restricted by the type of both

ISSN:0730-2312    

DOI:10.1002/jcb.240480211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY