摘要:

AbstractThe fibrinolytic system comprises a proenzyme, plasminogen, which can be converted to the active enzyme, plasmin, which degrades fibrin. Plasminogen activation is mediated by plasminogen activators, which are classified as either tissue‐type plasminogen activators (t‐PA) or urokinase‐type plasminogen activators (u‐PA). Inhibition of the fibrinolytic system may occur at the level of the activators or at the level of generated plasmin.Plasmin has a low substrate specificity, and when circulating freely in the blood it degrades several proteins including fibrinogen, factor V, and factor VIII. Plasma does, however, contain a fast‐acting plasmin inhibitor, α2‐antiplasmin, which inhibits free plasmin extremely rapidly but which reacts much slower with plasmin bound to fibrin. A “systemic fibrinolytic state” may, however, occur by extensive activation of plasminogen and depletion of α2‐antiplasmin. Clot‐specific thrombolysis therefore requires plasminogen activation restricted to the vicinity of the fibrin.Two physiological plasminogen activators, t‐PA and single‐chain u‐PA (scu‐PA) induce clot‐specific thrombolysis, via entirely different mechanisms, however. t‐PA is relatively inactive in the absence of fibrin, but fibrin strikingly enhances the activation rate of plasminogen by t‐PA. This is explained by an increased affinity of fibrin‐bound t‐PA for plasminogen and not by alteration of the catalytic rate constant of the enzyme. The high affinity of t‐PA for plasminogen in the presence of fibrin thus allows efficient activation on the fibrin clot, while no significant plasminogen activation by t‐PA occurs in plasma. scu‐PA has a high affinity for plasminogen (Km= 0.3 μM) but a low catalytic rate constant (kcat= 0.02 sec−1). However, scu‐PA does not activate plasminogen in plasma in the absence of a fibrin clot, owing to the presence of (a) competitive inhibitor(s). Fibrin‐specific thrombolysis appears to be due to the fact that fibrin reverses the competitive inhibition.The thrombolytic efficacy and fibrin specificity of natural and recombinant t‐PA has been demonstrated in animal models of pulmonary embolism, venous thrombosis, and coronary artery thrombosis. In all these studies intravenous infusion of t‐PA at sufficiently high rates caused efficient thromblysis in the absence of systemic fibrinolytic activation.The efficacy and relative fibrinogen‐sparing effect of t‐PA was recently confirmed in three multicenter clinical trials in patients with acute myocardial infarction. Intravenous infusion of 0.5–1 mg of t‐PA per kg body weight over 1–3 hr resulted in coronary reperfusion in approximately 70% of patients. It raised the plasma level about 1,000‐fold but was associated with an average decrease of the plasma fibrinogen level by 30%.Specific thrombolysis by scu‐PA has also been demonstrated in animal models of pulmonary embolism, venous thrombosis, and coronary thrombosis, Again, intravenous infusion of scu‐PA at sufficiently high rates caused thrombolysis in the absence of systemic fibrinolytic activation. We have treated six patients with acute myocardial infarction with scu‐PA and have obtained coronary reperfusion during intravenous infusion of 40 mg scu‐PA over 60 min in four of the patients and during subsequent intracoronary infusion in one additional patient. A decrea

ISSN:0730-2312    

DOI:10.1002/jcb.240330202

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

年代:1987

数据来源: WILEY

摘要:

AbstractRat kidney (NRK) cells infected with a temperature‐sensitive mutant of the Kirsten sarcoma virus were arrested in the G0/G1phase of their cell cycle by incubation in serum‐deficient medium at ap21‐inactivating temperature of 41°C. These quiescenttsK‐NRK cells were then stimulated to transit g1and initiate DNA replication by lowering the temperature to 36°C, which rapidly reactivatedp21Reactivating the viral Ki‐RAS protein by temperature shift led to an increase in adenylate cyclase activity in early G1phase. The Ki‐RAS protein increased the sensitivity of adenylate cyclase to guany1 nucleotides by a mechanism that seemed to involve inactivation of the enzyme's inhibitory G1regul

ISSN:0730-2312    

DOI:10.1002/jcb.240330203

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

年代:1987

数据来源: WILEY

摘要:

AbstractTransforming growth factors (TGFs) are peptides that affect the growth and phenotypic of cultured cells and bring about in nonmalignant fibroblastic cells phenotypic properties that resemble those of malignant cells. Two types of TGFs have been well characterized. One of these, TGFβ, is related to epidermal growth factor (EGF) and binds to the EGF receptor, whereas the other. TGFβ, is not structurally or functionally related to TGFβ or EGF and mediates its effects via distinct receptors.TGFβ is produced by a variety of normal and malignant cells. Depending upon the assay system employed, TGFβ has both growth‐inhibitory and growth‐stimulating properties. Many of the mitogenic effects of TGFβ are probably an indirect result of the activation of certain growth factor genes in the target cell. The ubiquitous nature of the TGFβ receptor and the production of TGFβ in a latent form by most cultured cells suggests that the differing cellular responses to TGFβ are regulated either by events involved in the activation of the factor or by postreceptor mechanisms. The combined effects of TGFβ with other growth factors or inhibitors evidently play a central role in the control of normal and malignant cellular growth as well as in cell differentiation and morphogenesis. Since transforming growth factor as a concept has partially proven misleading and insufficient, there is a need to find a new nomenclature for these regulators of cellular growth and di

ISSN:0730-2312    

DOI:10.1002/jcb.240330204

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe product of the c‐fmsproto‐oncogene is related to, and possibly identical with, the receptor for the macrophage colony‐stimulating factor, M‐CSF (CSF‐1). Unlike the product of the v‐erbB oncogene, which is a truncated version of the EGF receptor, the glycoprotein encoded by the v‐fmsoncogene retains an intact extracellular ligand‐binding domain so that cells transformed by v‐fmsexpress CSF‐1 receptors at their surface. Although fibroblasts susceptible to transformation by v‐fmsgenerally produce CSF‐1, v‐fms‐mediated transformation does not depend on an exogenous source of the growth factor, and neutralizing antibodies to CSF‐1 do not affect the transformed phenotype. An alteration of the v‐fmsgene product at its extreme carboxyl‐terminus represents the major structural difference between it and the c‐fms‐coded glycoprotein and may affect the tyrosine kinase activity of the v‐fms‐coded receptor. Consistent with this interpretation, tyrosine phosphorylation of the v‐fmsproducts in membranes was observed in the absence of CSF‐1 and was not enhanced by addition of the murine growth factor. Cells transformed by v‐fmshave a constitutively elevated specific activity of a guanir.c nucleotide‐dependent, phosphatidylinositol‐4,5‐diphosphate‐specific phospholipase C. We speculate that the tyrosine kinase activity of the v‐fms/c‐fmsgene products may be coupled to this phospholipase C, possibly through a G regulatory protein, thereby increasing phosphatidylinositol turnover and generating the intracellular

ISSN:0730-2312    

DOI:10.1002/jcb.240330205

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

年代:1987

数据来源: WILEY

摘要:

AbstractTransformation of a specific clone of Fischer rat embryo (CREF) cells with wild‐type 5 adenovirus (Ad5) or the Ela plus Elb transforming gene regions of Ad5 results in epithelioid transformants that grow efficiently in agar but that do not induce tumors when inoculated into nude mice or syngeneic Fischer rats. In contrast, CREF cells transformed by a host‐range Ad5 mutant. H5hrl, which contains a single base‐pair deletion of nucleotide 1055 in Ela resulting in a 28‐kd protein (calculated) in place of the wild‐type 51‐kd acidic protein, display a cold‐sensitive transformation phenotype and an incomplete fibroblastic morphology but surprisingly do induce tumors in nude mice and syngeneic rats. Tumors develop in both types of animals following injection of CREF cells transformed by other cold‐sensitive Ad5 Ela mutants (H5dl 101 and H5in l06), which contain alterations in their 13S mRNA and consequently truncated 289AA proteins. CREF cells transformed with only the Ela gene (0–4.5 m.u.) from H5hrl or H5dll01 also produce tumors in these animals. To directly determine the role of the 13S Ela encoded 289AA protein and the 12S Ela encoded 243AA protein in initiating an oncogenic phenotype in adenovirus‐transformed CREF cells, we generated transformed cell lines following infection with the Ad2 mutant pm975. which synthesizes the 289AA Ela protein but not the 243AA protein, and the Ad5 mutant H5dl 520 and the Ad2 mutant H2dl 1500, which do not produce the 289AA Ela protein but synthesize the normal 243AA Ela protein. All three types of mutant adenovirus‐transformed CREF cells induced tumors in nude mice and syngeneic rats. Tumor formation by these mutant adenovirus‐transformed CPEF cells was not associated with changes in the arrangement of integrated adenovirus DNA or in the expression of adenovirus early genes. These results indicate, therefore, that oncogenic transformation of CREF cells can occur in the presence of a wild‐type 13S Ela protein or a wild‐type 12S Ela protein when either protein is present alone, but does not occur when both wild‐

ISSN:0730-2312    

DOI:10.1002/jcb.240330206

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

年代:1987

数据来源: WILEY

摘要:

AbstractWe have previously described the preparation of hepatocytes from which the plasm membrane was removed by digitonin treatment. Such “nude” cells were found to be very stable in sucrose media containing above 50 mM NaCl or KC1, but they disintegrate near instantly in salt‐free media, liberating nuclei, mitochondria, and other organelles. We show here that disintegration occurs at a physiologic pH and in the presence of oxygen. Disintegration was blocked by rotenone, oligomycin, KCN, and carboxyatractyloside, establishing that oxidative phosphorylation and ATP generation is essential for disintegration to occur. The addition of ATP, GTP, ITP, or ADP (but not AMP) in the presence of the inhibitors, induced breakdown.Taxol, an inhibitor of tubulin depolymerization and phalloidin, a drug that stabilizes actin fibers, prevented disintegration in salt‐free media. The effect of these drugs was counteracted by the addition of ATP.Our results show that two conditions are essential to induce the disintegration of the nude cell: media of low ionic strength, and ATP generation. The ATP effect is likely to be of physiological significance, suggesting role for ATP generation in affecting polymerization of cytoskeletal e

ISSN:0730-2312    

DOI:10.1002/jcb.240330207

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe differentiation of murine mesenchymal stem cells occurs in nonterminal and terminal phases. In previous reports we established the characteristics of nonterminally differentiated cells and showed that transition from the nonterminal to the terminal state of differentiation can be induced by human plasma. We also showed that this transition is blocked by protein synthesis inhibitors and other pharmacological agents. In this paper, we have employed two‐dimensional gel electrophoresis to evaluate changes in specific polypeptides that arc induced when cells lose proliferative capacity associated with the terminal event in differentiation. Using silver staining procedures for analysis of electrophoretograms, we detected only seven major polypeptide differences between nonterminally differentiated and terminally differentiated cells. Six polypeptides were expressed only in preparations of terminally differentiated cells; these included two polypeptides identified in cytosolic fractions and four polypeptides identified in nuclear fractions. One polypeptide was also found to be selectively expressed only in nuclear fractions of nonterminally differentiated cells. Based on these observations we conclude that the loss of proliferative potential that occurs during the terminal event in mesenchymal stem cell differentiation is associated with changes in the composition of a limited number of specific polypeptides. We suggest that one or more of these polypeptides may be important in the regulation of cellular proliferatio

ISSN:0730-2312    

DOI:10.1002/jcb.240330208

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

年代:1987

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240330201

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

年代:1987

数据来源: WILEY