PubMed · 4774585
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
E Grasso. 1973-11-24. [Proceedings: Notes on hemostasis].. https://pubmed.ncbi.nlm.nih.gov/4774585/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Previous studies have demonstrated that overexpression of GRP78/BiP, an endoplasmic reticulum (ER)-resident molecular chaperone, in mammalian cells inhibits the secretion of specific coagulation factors. However, the effects of GRP78/BiP on activation of the coagulation cascade leading to thrombin generation are not known. In this study, we examined whether GRP78/BiP overexpression mediates cell surface thrombin generation in a human bladder cancer cell line T24/83 having prothrombotic characteristics. We report here that cells overexpressing GRP78/BiP exhibited significant decreases in cell surface-mediated thrombin generation, prothrombin consumption and the formation of thrombin-inhibitor complexes, compared with wild-type or vector-transfected cells. This effect was attributed to the ability of GRP78/BiP to inhibit cell surface tissue factor (TF) procoagulant activity (PCA) because conversion of factor X to Xa and factor VII to VIIa were significantly lower on the surface of GRP78/BiP-overexpressing cells. The additional findings that (i) cell surface factor Xa generation was inhibited in the absence of factor VIIa and (ii) TF PCA was inhibited by a neutralizing antibody to human TF suggests that thrombin generation is mediated exclusively by TF. GRP78/BiP overexpression did not decrease cell surface levels of TF, suggesting that the inhibition in TF PCA does not result from retention of TF in the ER by GRP78/BiP. The additional observations that both adenovirus-mediated and stable GRP78/BiP overexpression attenuated TF PCA stimulated by ionomycin or hydrogen peroxide suggest that GRP78/BiP indirectly alters TF PCA through a mechanism involving cellular Ca(2+) and/or oxidative stress. Similar results were also observed in human aortic smooth muscle cells transfected with the GRP78/BiP adenovirus. Taken together, these findings demonstrate that overexpression of GRP78/BiP decreases thrombin generation by inhibiting cell surface TF PCA, thereby suppressing the prothrombotic potential of cells.
Activation of factor VIII by factor Xa is followed by proteolytic inactivation resulting from cleavage within the A1 subunit (residues 1-372) of factor VIIIa. Factor Xa attacks two sites in A1, Arg(336), which precedes the highly acidic C-terminal region, and a recently identified site at Lys(36). By using isolated A1 subunit as substrate for proteolysis, production of the terminal fragment, A1(37-336), was shown to proceed via two pathways identified by the intermediates A1(1-336) and A1(37-372) and generated by initial cleavage at Arg(336) and Lys(36), respectively. Appearance of the terminal product by the former pathway was 7-8-fold slower than the product obtained by the latter pathway. The isolated A1 subunit was cleaved slowly, independent of the presence of phospholipid. The A1/A3-C1-C2 dimer demonstrated an approximately 3-fold increased cleavage rate constant, and inclusion of phospholipid further enhanced this value by approximately 2-fold. Although association of A1 or A1(37-372) with A3-C1-C2 enhanced the rate of cleavage at Arg(336), inclusion of A3-C1-C2 did not affect the cleavage at Lys(36) in A1(1-336). A synthetic peptide 337-372 blocked the cleavage at Lys(36) (IC(50) = 230 microm) while showing little if any effect on cleavage at Arg(336). Proteolysis at Lys(36), and to a lesser extent Arg(336), was inhibited in a dose-dependent manner by heparin. These results suggest that inactivating cleavages catalyzed by factor Xa at Lys(36) and Arg(336) are regulated in part by the A3-C1-C2 subunit. Furthermore, cleavage at Lys(36) appears to be selectively modulated by the C-terminal acidic region of A1, a region that may interact with factor Xa via its heparin-binding exosite.
BACKGROUND: Hyperestrogenic conditions have been related to alterations in the coagulation parameters. The objective of this study was to identify changes in coagulation parameters in women undergoing in vitro fertilization and embryo transfer (IVF-ET). METHODS: A group of 15 patients was studied prospectively, immediately before and during the course of an IVF-ET cycle. Blood was drawn in the preovulatory period of the cycle preceeding IVF-ET for complete blood count, fibrinogen, prothrombin time (TP), thromboplastin partial actived time (ATTP), coagulation time and estradiol. A another blood sample for the same tests was collected during controlled ovarian hyperstimulation, on the hCG day. Both samples were compared by a paired t-test. RESULTS: There was an increase in fibrinogen (340.9 pg/mL to 383.1 pg/mL, p = 0.01). On the other hand, hematocrit levels decreased (40.5% to 38.4 %, p = 0.0001). The other coagulation tests showed no difference. Estradiol levels increased (167 pg/mL to 1435 pg/ml, p=0.0001), as expected during such treatment. CONCLUSIONS: The data suggest a tendency towards an increase in coagulability, as expected in hyperestrogenic situations. However, even considering the statistical significance of the results, they might have limited clinical impact, since they were within the normal range. This study suggests that, despite the marked increase in estradiol and changes in coagulation parameters, IVF-ET is a safe procedure in terms of thromboembolic risks.