title: PDK1 selectively phosphorylates Thr(308) on Akt and contributes to human platelet functional responses.
abstract: 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.
authors.forename: C
authors.initials: C
authors.lastname: Dangelmaier
authors.forename: B K
authors.initials: BK
authors.lastname: Manne
authors.forename: E
authors.initials: E
authors.lastname: Liverani
authors.forename: J
authors.initials: J
authors.lastname: Jin
authors.forename: P
authors.initials: P
authors.lastname: Bray
authors.affiliation: Satya P. Kunapuli, PhD, Department of Physiology, Temple University, Rm. 217 MRB, 3420 N. Broad Street, Philadelphia, Pennsylvania 19140, USA, Tel.: +1 215 707 4615, Fax: +1 215 707 4003, E-mail: spk@temple.edu.
authors.forename: S P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D003018:Clot Retraction / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000187:drug effects; D011743:Pyrimidines / Q000494:pharmacology; D018179:Receptors, Thrombin / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013876:Thiophenes / Q000494:pharmacology; D013912:Threonine / Q000378:metabolism*; D013931:Thromboxanes / Q000378:metabolism
chemical_list: C484523:AKT1S1 protein, human; D048868:Adaptor Proteins, Signal Transducing; C579675:BX795; D011743:Pyrimidines; D018179:Receptors, Thrombin; D013876:Thiophenes; D013931:Thromboxanes; D013912:Threonine; D012694:Serine; D000255:Adenosine Triphosphate; D064413:3-Phosphoinositide-Dependent Protein Kinases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051058:Oncogene Protein v-akt; C578562:PDPK1 protein, human; D038362:Glycogen Synthase Kinase 3; C112908:protease-activated receptor 4
keywords: Kinases; platelet pharmacology; signal transduction