title: Thrombin-sensitive expression of the store operated Ca(2+) channel Orai1 in platelets.
abstract: Thrombin activates pore forming channel protein Orai1 resulting in store operated Ca(2+) entry (SOCE) with subsequent Ca(2+)-dependent release of platelet granules, activation of integrin αIIbβ3, adhesion, aggregation and thrombus formation. Platelets lack nuclei and are thus unable to modify protein abundance by transcriptional regulation. Nevertheless, they still contain pre-mRNA and mRNA and are thus able to express protein by stimulation of rapid translation. Platelet translation is sensitive to phosphoinositide-3-kinase (PI3K) and actin polymerization. The present study explored whether platelet activation via thrombin modifies Orai1 protein abundance. According to RT-PCR platelets contain pre-mRNA and mRNA encoding Orai1. Activation with thrombin (0.1 U/ml) results in a significant decline of pre-mRNA, which is, according to Western blotting and confocal microscopy, paralleled by a marked and statistically significant increase of Orai1 protein abundance. The increase of Orai1 protein abundance is insensitive to inhibition of transcription with actinomycin (4 μg/ml), but is significantly blunted by inhibition of translation with puromycin (100 nM) and by inhibition of PI3K with wortmannin (100 nM) or LY294002 (25 μM). In conclusion, activation of platelets stimulates the translational expression of Orai1, thus augmenting platelet Ca(2+) signaling.
authors.affiliation: Department of Physiology, University of Tübingen, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Münzer
authors.forename: Alexander
authors.initials: A
authors.lastname: Tolios
authors.forename: Lisann
authors.initials: L
authors.lastname: Pelzl
authors.forename: Evi
authors.initials: E
authors.lastname: Schmid
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Schmidt
authors.forename: Britta
authors.initials: B
authors.lastname: Walker
authors.forename: Henning
authors.initials: H
authors.lastname: Fröhlich
authors.forename: Oliver
authors.initials: O
authors.lastname: Borst
authors.forename: Meinrad
authors.initials: M
authors.lastname: Gawaz
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D000071740:ORAI1 Protein; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015539:Platelet Activation; D011691:Puromycin / Q000494:pharmacology; D012322:RNA Precursors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism*; D013927:Thrombosis / Q000378:metabolism; D013997:Time Factors; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D015220:Calcium Channels; D002867:Chromones; D009025:Morpholines; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D012322:RNA Precursors; D012333:RNA, Messenger; D003609:Dactinomycin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D011691:Puromycin; D019869:Phosphatidylinositol 3-Kinases; D013917:Thrombin; D002118:Calcium; D000077191:Wortmannin