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Abnormal cAMP‐induced phosphorylation of rap 1 , protein in grey platelet syndrome platelets
Author(s) -
Enouf Jocelyne,
Corvazier Elisabeth,
Papp Béla,
Quarck Rozenn,
Magnier Clarice,
Kovàcs Tünde,
Bredoux Raymonde,
LévyTolédano Sylviane,
Gunzburg Jean,
Wuytack Frank,
Caen Jacques
Publication year - 1994
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1111/j.1365-2141.1994.tb04736.x
Subject(s) - platelet , serca , phosphorylation , endoplasmic reticulum , gene isoform , atpase , immunoprecipitation , platelet activation , protein kinase a , microbiology and biotechnology , biology , chemistry , biochemistry , enzyme , immunology , gene
Summary We previously demonstrated abnormal Ca 2+ transport by microsomes in platelets from a grey platelet syndrome patient. Here, we investigated the platelet Ca 2+ ATPases that mediate this transport, as well as its possible regulation by rap 1 protein. We showed that grey platelet syndrome platelets expressed the same two distinct Ca 2+ ATPases as those recently described in normal platelets; the 100 kD SERCA 2‐b isoform (Sarco/Endoplasmic Reticulum Ca 2+ ATPase) and a new 97 kD SERCA isoform. The two Ca 2+ ATPases formed similar amounts of transient phosphorylated intermediates. The expression of these two Ca 2+ ATPases was compared by Western blotting using specific antibodies, which again emerged in similar amounts in normal and grey platelet syndrome platelets. As regards the protein phosphorylated by cAMP, it was found to be identical to rap 1 protein when it was immunoprecipitated with an antibody raised against a synthetic peptide specific for rap 1 protein. Although the expression of rap 1 protein was similar in membranes isolated from grey platelet syndrome and normal platelets, its exogenous phosphorylation by cAMP was abnormal, with a concentration (10 μg/ml) of the catalytic subunits of the cAMP‐dependent protein kinase (C.Sub.), as it decreased to half the control level. It is concluded that the abnormal Ca 2+ transport found in grey platelet syndrome platelets is not due to the abnormal expression of the Ca 2+ ATPases, but is associated with an abnormality of rap 1 protein phosphorylation by cAMP.