Augmentation of Human Monocyte Responses to Lipopolysaccharide by the Protein S and Mer/Tyro3 Receptor Tyrosine Kinase Axis.

Resolution of the inflammatory response requires coordinated regulation of pro- and anti-inflammatory mediator production, together with clearance of recruited inflammatory cells. Many different receptors have been implicated in phagocytosis of apoptotic cells (efferocytosis), including Mer, a receptor tyrosine kinase that can mediate recognition and subsequent internalization of apoptotic cells. In this manuscript, we examine the expression and function of the Tyro3/Axl/Mer (TAM) family of receptors by human monocytes. We demonstrate that the Mer ligand, protein S, binds to the surface of viable monocytes via phosphatidylserine-dependent and -independent mechanisms. Importantly, we have identified a novel role for receptor tyrosine kinase signaling in the augmentation of monocyte cytokine release in response to LPS. We propose that low-level phosphatidylserine exposure on the plasma membrane of viable monocytes allows protein S binding that leads to TAM-dependent augmentation of proinflammatory cytokine production. Our findings identify a potentially important role for TAM-mediated signaling during the initiation phase of inflammation.

Lack of protein S in mice causes embryonic lethal coagulopathy and vascular dysgenesis.

Protein S (ProS) is a blood anticoagulant encoded by the Pros1 gene, and ProS deficiencies are associated with venous thrombosis, stroke, and autoimmunity. These associations notwithstanding, the relative risk that reduced ProS expression confers in different disease settings has been difficult to assess without an animal model. We have now described a mouse model of ProS deficiency and shown that all Pros1-/- mice die in utero,from a fulminant coagulopathy and associated hemorrhages. Although ProS is known to act as a cofactor for activated Protein C (aPC), plasma from Pros1+/- heterozygous mice exhibited accelerated thrombin generation independent of aPC, and Pros1 mutants displayed defects in vessel development and function not seen in mice lacking protein C. Similar vascular defects appeared in mice in which Pros1 was conditionally deleted in vascular smooth muscle cells. Mutants in which Pros1 was deleted specifically in hepatocytes, which are thought to be the major source of ProS in the blood, were viable as adults and displayed less-severe coagulopathy without vascular dysgenesis. Finally, analysis of mutants in which Pros1 was deleted in endothelial cells indicated that these cells make a substantial contribution to circulating ProS. These results demonstrate that ProS is a pleiotropic anticoagulant with aPC-independent activities and highlight new roles for ProS in vascular development and homeostasis.

Role of protein C inhibitor and tissue factor in fertilization.

Semen coagulation is achieved by a series of biochemical processes designed to protect and guide the sperm during its migration through the female genital tract so that spermatozoa reach the ovum successfully. Thus, semen coagulation promotes fertilization. The mechanism of semen coagulation is similar in principle to blood coagulation and fibrinolysis because it requires the catalytic activity of proteases to convert a soluble substrate to an insoluble gel, and then dissolve the gel over a longer period of time. In fact, there are traces of most blood coagulation factors and fibrinolytic factors in semen; the roles of these factors in semen coagulation are still to be determined. This review focuses on two such proteins that have remarkably high levels in semen: protein C inhibitor and tissue factor. Protein C inhibitor is a serine protease inhibitor that modulates the activity of several blood-clotting factors and activated protein C. Tissue factor (thromboplastin) is a membrane protein crucial for the initiation of the extrinsic cascade of blood coagulation. The emerging roles of these two proteins in semen coagulation and in fertilization processes are summarized.

Antinuclear autoantibodies in prostate cancer: immunity to LEDGF/p75, a survival protein highly expressed in prostate tumors and cleaved during apoptosis.

BACKGROUND: Cancer patients produce autoantibodies to self-proteins called tumor-associated antigens (TAA). These autoantibodies represent potentially valuable tools for identifying novel biomarkers and therapeutic targets. This study was designed to identify TAA in prostate cancer (PCa). METHODS: Serum autoantibodies to the survival protein lens epithelium-derived growth factor p75 (LEDGF/p75) were detected by immunofluorescence microscopy, ELISA, and immunoblotting. Expression of LEDGF/p75 in prostate cells and tumors was evaluated by immunoblotting or immunohistochemistry. Apoptotic cleavage of LEDGF/p75 was detected by immunoblotting. RESULTS: Anti-LEDGF/p75 autoantibodies were detected by ELISA in 18.4% of PCa patients and 5.5% of matched controls (P < 0.001) but not in patients with benign prostatic hyperplasia (BPH). LEDGF/p75 expression was detected in 93% of prostate tumors but not in normal prostate. Strong expression of the protein was observed in 61% of prostate tumors. Moderate to high expression was also detected in BPH tissue. Cleavage of LEDGF/p75 was detected in apoptotic prostate cells. CONCLUSIONS: The high expression of LEDGF/p75 in prostate tumors and BPH could be induced by inflammation and oxidative stress. LEDGF/p75 cleavage fragments generated during prostate tumor cell death might trigger autoantibodies under inflammatory conditions in certain patients.

Preferential humoral immune response in prostate cancer to cellular proteins p90 and p62 in a panel of tumor-associated antigens.

BACKGROUND: Cytoplasmic p90 autoantigen was recently cloned from a cDNA expression library using serum antibody from a cancer patient. The humoral immune response to p90 in prostate cancer and benign prostatic hyperplasia (BPH) was examined. METHODS: An antigenic fragment of recombinant p90 protein and several other tumor-associated antigens (TAAs) were used in ELISA and Western blotting to detect antibodies in sera from patients with prostate cancer, BPH, and other controls. RESULTS: Autoantibodies to p90 were detected in 30.8% of 133 prostate cancer patients versus 1.5% in 68 BPH patients. When a selected panel of six TAAs including p90 were used for immunoscreening, the cumulative positive reactions in prostate cancer sera reached 92.5%, significantly higher than in BPH and other control sera. Antibodies to p90 showed the highest frequency in prostate cancer (30.8%), followed by antibodies to p62 (22.6%). CONCLUSIONS: A panel of six selected TAAs was shown to have high sensitivity and specificity as immunodiagnostic markers in prostate cancer.

Protein C pathway impairment in nonsymptomatic cigarette smokers.

Increased risk of thrombosis in cigarette smokers implies the existence of an underlying prethrombotic state. It is known that oxidative damage to the endothelium surface occurs in chronic smokers. Protein C activation takes place mostly on the endothelium of small vessels and the anticoagulant activity of protein C requires the presence of lipid membranes that are vulnerable to oxidation. Our objective was to analyze the relationship between smoking and plasma levels of activated protein C, protein C zymogen, activated protein C complexed with serpins, total and free protein S, C4b-binding protein, and thrombomodulin, as well as fibrinogen, fibrinopeptide A, and protease-cleaved antithrombin III. Of the 189 plasma donors used in this study 83 were nonsymptomatic smokers (age range 20-44 years, women/men ratio = 1.13) and 106 were healthy nonsmokers (age range 22-59 years, women/men ratio = 1.36). Smokers had 23.3% lower circulating activated protein C than nonsmokers (p = 0.003) and the differences were more pronounced in males than in females. Protein C levels were also significantly lower in smokers than in nonsmokers (p = 0.034). Correlations were negative between the intensity of smoking and circulating activated protein C levels (r = -0.31, p = 0.004) and between smoking and the ratio of activated protein C to protein C zymogen (r = -0.37, p = 0.001). Positive correlations were found between smoking intensity and fibrinogen (r = 0.21, p = 0.042), or fibrinopeptide A (r = 0.219, p = 0.034). Other parameters tested did not show a statistically significant dose-response for the number of cigarettes smoked. Cigarette smoke dose-dependent hypercoagulability due to acquired activated protein C deficiency could contribute to the increased risk of thrombosis in smokers.