1994 Fiscal Year Final Research Report Summary
Molecular Biological Studies on The Activation of Platelet Functions and Its Disorders
| Project/Area Number |
04454570
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
General fisheries
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
OKUMA Minoru KYOTO UNIVERSITY MEDICINE PROFESSOR, 医学部, 教授 (50026986)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAYAMA Hiroshi KYOTO UNIVERSITY MEDICINE INSTRUCTOR, 医学部, 助手 (10197220)
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| Project Period (FY) |
1992 – 1994
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| Keywords | Platelet / Thromboxane A_2 receptor / Missense mutation / 12-Lipoxygenase / Messenger RNA / Collagen receptor / Protein tyrosine phosphorylation / p62 (GPVI) |
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| Research Abstract |
Morecular mechanisms of platelet activation and of specific defects in some functional disorders of platelets were studied, and following results were abtained.
1. MOLECULAR ABNORMALITIES IN THE THROMBOXANE A_2 (TXA_2) RECEPTOR OF PLATELETS WITH DEFECTIVE RESPONSE TO TXA_2, AND STRUCTURE-FUNCTION RELATIONSHIP OF THE RECEPTOR.We identified Arg^<60> to Leu mutation in the TXA_2 receptor in a dominant lyinherited bleeding disorder with defective platelet response to TXA_2. This mutation was found exclusively in affected members of two unrelated families with the disorder. These results suggested that the Arg^<60> to Leu mutation is responsible for the disorder and it was confirmed by the expression experiments with the mutant receptor. Functional significnace of the Arg^<60> in the receptor was also demonstrated.
2. PLATELET 12-LIPOXYGENASE (12-LOX) DEFICIENCY.Decreased mRNA of 12-LOX was found in platelets with deficient 12-LOX activity of 3 patinets with myeloproliferative disorders (MPD)
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. Therefore, the 12-LOX deficiency in these patients was attributable to the decreased 12-LOX mRNA level and thus impaired synthesis of the enzyme protein in their platelets. In another MPD patient with a deficiency of this enzyme activity, we found normal amount of the enzyme protein, suggesting its molecular abnormality which is now being investigated.
3. P62 (GPVI) AS A PUTATIVE PLATELET COLLAGEN RECEPTOR AND P62-MEDIATED SIGNALING.We previously reported platelet 62 kD protein (p62, GPVI) might be a putative collagen receptor. To further study functional significance of this protein, a crude p62 fraction was prepared from outdated human platelets by serial chromatographies followed by preparative SDS-PAGE.This crude p62 diminished platelet-aggregating activity of collagen suggesting p62/collagen interations. Stimulation of p62 with anti-p62 antibody induced tyrosine phosphorylation of numerous platelet proteins. The protein-tyrosine kinase inhibitor completely abolished platelet aggregation induced by anti-p62 antibody, suggesting a role of tyrosine kinase activity in generating p62-mediated signaling. Furthermore, it was suggested that stimulation of p62 induces cAMP-insensitive activation of the tyrosine kinase Syk in a manner similar to collagen stimulation. Less
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