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D Loskutoff

Publications and source records attributed to D Loskutoff.

8 recordsLinked to original sources
PubMed2001

The plasminogen activator inhibitor PAI-1 controls in vivo tumor vascularization by interaction with proteases, not vitronectin. Implications for antiangiogenic strategies.

The plasminogen (Plg)/plasminogen activator (PA) system plays a key role in cancer progression, presumably via mediating extracellular matrix degradation and tumor cell migration. Consequently, urokinase-type PA (uPA)/plasmin antagonists are currently being developed for suppression of tumor growth and angiogenesis. Paradoxically, however, high levels of PA inhibitor 1 (PAI-1) are predictive of a poor prognosis for survival of patients with cancer. We demonstrated previously that PAI-1 promoted tumor angiogenesis, but by an unresolved mechanism. We anticipated that PAI-1 facilitated endothelial cell migration via its known interaction with vitronectin (VN) and integrins. However, using adenoviral gene transfer of PAI-1 mutants, we observed that PAI-1 promoted tumor angiogenesis, not by interacting with VN, but rather by inhibiting proteolytic activity, suggesting that excessive plasmin proteolysis prevents assembly of tumor vessels. Single deficiency of uPA, tissue-type PA (tPA), uPA receptor, or VN, as well as combined deficiencies of uPA and tPA did not impair tumor angiogenesis, whereas lack of Plg reduced it. Overall, these data indicate that plasmin proteolysis, even though essential, must be tightly controlled during tumor angiogenesis, probably to allow vessel stabilization and maturation. These data provide insights into the clinical paradox whereby PAI-1 promotes tumor progression and warrant against the uncontrolled use of uPA/plasmin antagonists as tumor angiogenesis inhibitors.

Angiogenesis Inhibitors↗
PubMed1997

Expression of fibrinolytic genes in tissues from human atherosclerotic aneurysms and from obese mice.

The disturbances in the balance of pro- and antifibrinolytic activity, as observed in AAA and obesity, respectively, have considerable potential for influencing both intra- and extravascular fibrinolytic events and may be causally related to the development of vascular disease. For example, the wall of the aortic atherosclerotic aneurysm seems to host an uneven distribution and imbalanced expression of the various components of the fibrinolytic system. The sites of increased proteolytic activity may contribute to localized neovascularization and promote the rapid breakdown of ECM components, which result in mural weakening and eventual rupture of untreated aortic aneurysms. On the other hand, the disturbance of the normal hemostatic balance observed in obesity appears to result from the elevated expression of PAI-1 by the adipose tissue. Our data strongly suggest that the adipocyte is one of the primary cells in the adipose tissue capable of expressing PAI-1 both in obesity, and in response to cytokines and hormones like TNF-alpha and insulin. Since both TNF-alpha and insulin are known to increase in obesity, the elevated levels of PAI-1 observed in the plasma of obese individuals may result from TNF-alpha and/or insulin induction of PAI-1 in the adipose tissue itself.

Aneurysm↗
PubMed1995

Glomerular tissue factor expression in crescentic glomerulonephritis. Correlations between antigen, activity, and mRNA.

Correlations between glomerular expression of tissue factor (TF) activity and antigen and cellular localization of TF mRNA was studied in crescentic glomerulonephritis (GN) in rabbits. Glomerular TF activity increased 8.7-fold 24 hours after initiation of GN (234 +/- 49 mU/10(3) glomeruli; normal, 27 +/- 10 mU/10(3) glomeruli; P = 0.003) in association with a 2.1-fold increase in TF antigen (154 +/- 34 ng/10(3) glomeruli; normal, 72 +/- 10 ng/10(3) glomeruli; P = 0.055), early macrophage infiltration, and no significant increase in TF mRNA. At the peak glomerular macrophage infiltration (day 4), TF activity remained augmented (230 +/- 63 mU/10(3) glomeruli) and TF mRNA, colocalized within macrophages, was significantly increased compared with normal (267 +/- 42%; P = 0.001). TF antigen was not increased in glomeruli (114 +/- 17 ng/10(3) glomeruli), although significant urinary excretion of TF antigen was detectable (478 +/- 121 ng/24 hours; normal, < 1 ng/24 hours; P = 0.032). At this time, the M(r) of glomerular TF (49 to 61 kd) was increased compared with TF in normal glomeruli (49 to 58 kd) as a result of increased glycosylation. At day 7, TF activity and antigen within glomeruli had decreased, although urinary excretion of TF antigen and glomerular TF mRNA remained elevated. These studies suggest that early up-regulation of TF activity is largely a result of functional up-regulation of constitutive TF in intrinsic glomerular cells. In more advanced disease, infiltrating macrophages are the major site of TF synthesis. The increased M(r) of glomerular TF, as a result of synthesis of more highly glycosylated protein by macrophages and the shedding of TF into the urine, suggests that substantial turnover of glomerular TF occurs at this stage.

Animals↗
PubMed1994

Expression of plasminogen activator inhibitor type 2 in normal and psoriatic epidermis.

The plasminogen activator (PA) proteolytic cascade has been implicated in the regulation of cell activities, including proliferation and differentiation, both of which occur continuously in normal human epidermis and are aberrant in psoriatic epidermis. To elucidate further the mechanisms by which PA is regulated in epidermis, we evaluated the levels of PA inhibitors type 1 (PAI-1) and type 2 (PAI-2) in normal and psoriatic epidermis. PAI-2, but not PAI-1, was detectable by mRNA, antigen, and activity assays, indicating that PAI-2 is the predominant epidermal PA inhibitor. In situ hybridization revealed that PAI-2 mRNA occurred throughout normal epidermis, although the signal was most intense in the granular layers. Similarly, PAI-2 antigen was most prominent in the granular layers; its distribution in these differential layers was along the cell periphery. Diffuse, fainter staining for PAI-2 was also detected in the basal cells and in some spinous layers of normal epidermis. Extracts of normal epidermis contained PA inhibitory activity identified as PAI-2 by immunoprecipitation with specific antibody. In psoriatic epidermis, PAI-2 mRNA and antigen were most prominent in the more superficial layers beneath the cornified cells. As with normal epidermis, PAI-2 assumed a pericellular distribution in the psoriatic cells. These data demonstrate that PAI-2 is constitutively expressed in vivo by keratinocytes in human epidermis and indicate that this protein is the predominant inhibitor of PA activity in normal and psoriatic human epidermis.

Antigens↗
PubMed1986

Identification and regulation of tissue plasminogen activator activity in rat cumulus-oocyte complexes.

Plasminogen activators convert plasminogen into plasmin, a serine protease that initiates extracellular proteolysis. Two types of plasminogen activator activities have recently been demonstrated in granulosa cells, and the proteolysis-inducing enzymes are believed to be involved in ovulation. However, little attention has been paid to the presence of these enzymes in oocytes. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by a fibrin overlay technique, we studied plasminogen activator activity in oocytes. Denuded oocytes collected from ovaries of hypophysectomized, estrogen-treated immature rats contained a tissue-type plasminogen activator (tPA), but not urokinase (uPA). In contrast, oocyte-free granulosa cells in these preantral follicles contained uPA, but not tPA. The tPA activity found in oocytes was plasminogen-dependent; incubation with increasing numbers (25-200) of denuded oocytes resulted in a dose-dependent increase in fibrinolysis only in the presence of plasminogen. Cellular localization of tPA was studied in the preantral follicles using an immuno-cytochemical method. Positive tPA staining was detected in the cytoplasm, but not in the germinal vesicle or zona pellucida of the oocytes. Furthermore, analysis using a reverse fibrin-overlay method did not reveal the presence of a plasminogen activator inhibitor. Culturing of denuded oocytes for 24 h increased the cellular content of tPA, but the enzyme activity was not further enhanced by treatment with FSH or forskolin. Also, no tPA activity was detected in the medium. We further studied plasminogen activator activities in the cumulus-oocyte complexes. Although only tPA activity was detected in freshly obtained cumulus-oocyte complexes, incubation for 24 h increased both tPA and uPA activity. Furthermore, tPA, but not uPA, activity was stimulated by treatment with FSH or forskolin. This was accompanied by the secretion of tPA into the medium. The identity of tPA and uPA in the cumulus-oocyte complexes was further confirmed by immunoprecipitation with specific antibodies. Isolation of denuded oocytes and cumulus cells after hormonal stimulation of the cumulus-oocyte complexes suggested that tPA activity was stimulated in both cell types and that the cumulus cells may mediate the action of FSH and forskolin on oocytes. In conclusion, the detection and regulation of tPA activity in cumulus-oocyte complexes suggest possible involvement of this enzyme in ovulation or the process of cumulus cell expansion and dispersion. Changes in oocyte tPA content may also serve as an indicator of oocyte development.

Animals↗
PubMed1978

Membrane characteristics of cultured endothelial cells: identification of gap junction.

Membrane characteristics of cultured endothelial cells derived from the superior vena cava of the rabbit were studied in freeze-fracture replicas. Gap junctions were identified, but tight junctions were not seen. In addition to pinocytic vesicles, fenestrations of plasma membrane which are not normally seen in the endothelium of vena cava in situ were found. This finding may be explained by the absence of platelets in the culture medium and is consistent with the current concept of endothelial-platelet interaction.

Animals↗