Protein phosphatase inhibitor calyculin A modulates activation markers in TRAP-stimulated human platelets

Zsuzsa Simon, Andrea Kiss, Ferenc Erdödi, Hendra Setiadi, Ildik Beke Debreceni, Béla Nagy, Jnos Kappelmayer

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2 Citations (Scopus)


Platelet activation is accompanied with the phosphorylation of a number of proteins on serine (Ser) and threonine (Thr) residues. The phosphorylation level of these proteins is dependent upon the protein kinase/phosphatase activity ratio. The aim of this study was to investigate the consequences of inhibiting protein phosphatase 1 (PP1) and 2A (PP2A) on platelet functions. Protein phosphatases were inhibited by preincubation of platelet rich plasma (PRP) samples with calyculin-A (CLA). Subsequently, platelets were activated by thrombin-receptor activating peptide (TRAP) and platelet aggregation, platelet-derived microparticle (PMP) formation, surface expressions of P-selectin (CD62), lysosome-associated membrane protein (CD63), glycoprotein Ib and IIb were examined. Phosphatase activity was determined by using phosphorylated 20 kDa myosin light chain (P-MLC20) as substrate. In CLA-treated platelets substantial decrease of P-MLC20 phosphatase activity was observed. CLA significantly suppressed TRAP-induced surface expression of P-selectin and CD63 in a concentration-dependent manner as compared to non-treated samples and moderately decreased platelet aggregation. In TRAP-activated samples, 50 nM of CLA pretreatment completely abolished the level of PMPs and the prevention of GPIb downregulation was also observed; however, no difference was found in GPIIb expression. In conclusion, PP1 and PP2A-catalyzed dephosphorylation processes have crucial roles in PMP formation and in the regulation of alpha-granule and lysosome secretion in human platelets.

Original languageEnglish
Pages (from-to)555-562
Number of pages8
Issue number7
Publication statusPublished - Nov 1 2010



  • Calyculin-A
  • P-selectin
  • Ser/Thr specific protein phosphatase
  • microparticles

ASJC Scopus subject areas

  • Hematology

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