PMID- 10455022
OWN - NLM
STAT- MEDLINE
DCOM- 19991101
LR  - 20181113
IS  - 0264-6021 (Print)
IS  - 0264-6021 (Linking)
VI  - 342 ( Pt 2)
DP  - 1999 Sep 1
TI  - Rab6 is phosphorylated in thrombin-activated platelets by a protein kinase
      C-dependent mechanism: effects on GTP/GDP binding and cellular distribution.
PG  - 353-60
AB  - In platelets and other secretory cells, protein kinase C (PKC) plays a role in
      exocytosis stimulated by physiological extracellular signals, although its
      linkage to the secretory machinery is poorly understood. We investigated whether 
      Rab6, a GTP-binding protein that fractionates with platelet alpha-granules, may
      be involved in linking these processes. We found that Rab6 contains two PKC
      consensus phosphorylation sites that are evolutionarily conserved. In platelets
      metabolically labelled with [(32)P]P(i), Rab6 phosphorylation was induced by
      phorbol esters or by thrombin. This phosphorylation was blocked by a specific PKC
      inhibitor (Ro-31-8220), but not by a p38 mitogen-activated protein kinase
      inhibitor (PD-169316). Physiological stimulation of platelets caused a
      PKC-dependent translocation of Rab6 from platelet particulate fractions, nearly
      doubling the fraction of Rab6 in the cytosol. A human Rab6 isoform (Rab6C) that
      is preferentially expressed in human platelet RNA was cloned and its
      phosphorylation by PKC was characterized. Rab6C incorporated up to 2 mol of
      [(32)P]P(i) per mol of active protein. Rab6C bound GDP and GTP with K(d) values
      of 113+/-12 and 119+/-27 nM respectively, and hydrolysed GTP at a rate of
      100+/-15 micromol of GTP/mol of Rab6C per min. PKC phosphorylation of Rab6C
      increased the affinity for GTP by 3-fold, although it had lesser effects on GDP
      (1.6-fold). Phosphorylation did not alter the GTPase activity. In summary,
      thrombin activation of platelets leads to PKC-dependent phosphorylation of Rab6
      and a translocation of Rab6 to the cytosol. We suggest that PKC phosphorylation
      may be an important mechanism through which Rab functional interactions in
      vesicle trafficking and secretion can be altered in response to an external
      stimulus.
FAU - Fitzgerald, M L
AU  - Fitzgerald ML
AD  - Cardiovascular Biology Laboratory, Harvard School of Public Health, 677
      Huntington Avenue, Boston, MA 02115, USA.
FAU - Reed, G L
AU  - Reed GL
LA  - eng
GR  - HL57301/HL/NHLBI NIH HHS/United States
GR  - R01 HL57314/HL/NHLBI NIH HHS/United States
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PT  - Research Support, U.S. Gov't, P.H.S.
PL  - England
TA  - Biochem J
JT  - The Biochemical journal
JID - 2984726R
RN  - 0 (DNA Primers)
RN  - 0 (Guanine Nucleotide Dissociation Inhibitors)
RN  - 0 (Protein Isoforms)
RN  - 0 (Rab6 protein)
RN  - 146-91-8 (Guanosine Diphosphate)
RN  - 86-01-1 (Guanosine Triphosphate)
RN  - EC 2.7.11.13 (Protein Kinase C)
RN  - EC 3.4.21.5 (Thrombin)
RN  - EC 3.6.5.2 (rab GTP-Binding Proteins)
SB  - IM
MH  - Amino Acid Sequence
MH  - Animals
MH  - Base Sequence
MH  - Binding Sites
MH  - Blood Platelets/drug effects/*metabolism
MH  - Cattle
MH  - Consensus Sequence
MH  - Cytosol/metabolism
MH  - DNA Primers/genetics
MH  - Guanine Nucleotide Dissociation Inhibitors/blood
MH  - Guanosine Diphosphate/*blood
MH  - Guanosine Triphosphate/*blood
MH  - Humans
MH  - In Vitro Techniques
MH  - Molecular Sequence Data
MH  - Phosphorylation
MH  - Platelet Activation/drug effects/physiology
MH  - Protein Isoforms/blood/chemistry/genetics
MH  - Protein Kinase C/*blood
MH  - Sequence Homology, Amino Acid
MH  - Thrombin/pharmacology
MH  - rab GTP-Binding Proteins/*blood/chemistry/genetics
PMC - PMC1220472
EDAT- 1999/08/24 00:00
MHDA- 1999/08/24 00:01
CRDT- 1999/08/24 00:00
PHST- 1999/08/24 00:00 [pubmed]
PHST- 1999/08/24 00:01 [medline]
PHST- 1999/08/24 00:00 [entrez]
PST - ppublish
SO  - Biochem J. 1999 Sep 1;342 ( Pt 2):353-60.