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      Thrombin Promotes Fibroblast Proliferation during the Early Stages of Experimental Radiation Pneumonitis

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          Abstract

          Huang, L., Ogushi, F., Tani, K., Ogawa, H., Kawano, T., Endo, T., Izumi, K., Ueno, J., Nishitani, H. and Sone, S. Thrombin Promotes Fibroblast Proliferation during the Early Stages of Experimental Radiation Pneumonitis. Radiat. Res. 156, 45-52 (2001). To clarify the role of thrombin in the pathogenesis of radiation-induced pneumonitis, we measured the thrombin activity and fibroblast growth-inducing activity in bronchoalveolar lavage fluid obtained from the irradiated lungs of rats at 1, 2, 4, 8 and 18 weeks after irradiation. Thrombin activity was not detected in the bronchoalveolar lavage fluid from unirradiated rats, but the bronchoalveolar lavage fluid from irradiated rats showed significantly increased thrombin activity which reached a maximum at 4 weeks after treatment. Higher fibroblast growth-inducing activity was detected in the bronchoalveolar lavage fluid from irradiated rats at 4 and 18 weeks than in fluid from unirradiated rats. Bronchoalveolar lavage fluid from irradiated rats that were pretreated with the thrombin inhibitors antithrombin III and argatroban showed significantly inhibited fibroblast growth-inducing activity and thrombin activity at 4 weeks. However, these thrombin inhibitors did not inhibit fibroblast growth-inducing activity in bronchoalveolar lavage fluid from irradiated rats at 18 weeks. Purified rat thrombin similarly induced proliferation of fibroblasts derived from irradiated and unirradiated rats. These findings suggest that thrombin may play an important role as a fibroblast growth-inducing factor during the early stages of radiation pneumonitis.

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          Simple method of estimating severity of pulmonary fibrosis on a numerical scale.

          A continuous numerical scale for determining the degree of fibrosis in lung specimens was devised for correlation with other pulmonary variables such as lung function tests or mineral burden. Grading was scored on a scale from 0 to 8, using the average of microscope field scores. The system allows fibrosis to be measured in small samples of tissue (1 cm) which can provide a detailed description of the changes in a lung, currently not possible with most existing methods.
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            Molecular cloning of a functional thrombin receptor reveals a novel proteolytic mechanism of receptor activation.

            We isolated a cDNA encoding a functional human thrombin receptor by direct expression cloning in Xenopus oocytes. mRNA encoding this receptor was detected in human platelets and vascular endothelial cells. The deduced amino acid sequence revealed a new member of the seven transmembrane domain receptor family with a large amino-terminal extracellular extension containing a remarkable feature. A putative thrombin cleavage site (LDPR/S) resembling the activation cleavage site in the zymogen protein C (LDPR/I) was noted 41 amino acids carboxyl to the receptor's start methionine. A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. "Uncleavable" mutant thrombin receptors failed to respond to thrombin but were responsive to the new amino-terminal peptide. These data reveal a novel signaling mechanism in which thrombin cleaves its receptor's amino-terminal extension to create a new receptor amino terminus that functions as a tethered ligand and activates the receptor.
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              Rapid colorimetric assay for cell growth and survival

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                Author and article information

                Journal
                Radiation Research
                Radiation Research
                Radiation Research Society
                0033-7587
                1938-5404
                July 2001
                July 2001
                : 156
                : 1
                : 45-52
                Article
                10.1667/0033-7587(2001)156[0045:TPFPDT]2.0.CO;2
                11418072
                a468c9e2-7490-424e-a7f7-888eb3fc0888
                © 2001
                History

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