Thromb Haemost 2014; 111(03): 508-517
DOI: 10.1160/TH13-06-0484
Platelets and Blood Cells
Schattauer GmbH

PDK1 selectively phosphorylates Thr(308) on Akt and contributes to human platelet functional responses

Carol Dangelmaier
1   Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Temple University Hospital, Philadelphia, Pennsylvania, USA
,
Bhanu Kanth Manne
1   Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Temple University Hospital, Philadelphia, Pennsylvania, USA
,
Elizabetta Liverani
1   Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Temple University Hospital, Philadelphia, Pennsylvania, USA
,
Jianguo Jin
1   Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Temple University Hospital, Philadelphia, Pennsylvania, USA
,
Paul Bray
2   Cardeza Foundation for Hematologic Research, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
,
Satya P. Kunapuli
1   Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Temple University Hospital, Philadelphia, Pennsylvania, USA
› Author Affiliations
Further Information

Publication History

Received: 14 June 2013

Accepted after major revision: 14 November 2013

Publication Date:
22 November 2017 (online)

Summary

3-phosphoinositide-dependent protein kinase 1 (PDK1), a member of the protein A,G and C (AGC) family of proteins, is a Ser/Thr protein kinase that can phosphorylate and activate other protein kinases from the AGC family, including Akt at Thr308, all of which play important roles in mediating cellular responses. The functional role of PDK1 or the importance of phosphorylation of Akt on Thr308 for its activity has not been investigated in human platelets. In this study, we tested two pharmacological inhibitors of PDK1, BX795 and BX912, to assess the role of Thr308 phosphorylation on Akt. PAR4-induced phosphorylation of Akt on Thr308 was inhibited by BX795 without affecting phosphorylation of Akt on Ser473. The lack of Thr308 phosphorylation on Akt also led to the inhibition of PAR4-induced phosphorylation of two downstream substrates of Akt, viz. GSK3β and PRAS40. In vitro kinase activity of Akt was completely abolished if Thr308 on Akt was not phosphorylated. BX795 caused inhibition of 2-MeSADP-induced or collagen-induced aggregation, ATP secretion and thromboxane generation. Primary aggregation induced by 2-MeSADP was also inhibited in the presence of BX795. PDK1 inhibition also resulted in reduced clot retraction indicating its role in outside-in signalling. These results demonstrate that PDK1 selectively phosphorylates Thr308 on Akt thereby regulating its activity and plays a positive regulatory role in platelet physiological responses.

 
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