The 29-kDa proteins phosphorylated in thrombin-activated human platelets are forms of the estrogen receptor-related 27-kDa heat shock protein.
Thrombin plays a critical role in platelet activation, hemostasis, and thrombosis. Cellular activation by thrombin leads to the phosphorylation of multiple proteins, most of which are unidentified. We have characterized several 29-kDa proteins that are rapidly phosphorylated following exposure of intact human platelets to thrombin. A murine monoclonal antibody raised to an unidentified estrogen receptor-related 29-kDa protein selectively recognized these proteins as well as a more basic, unphosphorylated 27-kDa protein. Cellular activation by thrombin led to a marked shift in the proportion of protein from the 27-kDa unphosphorylated form to the 29-kDa phosphoprotein species. Using this antibody, we isolated and sequenced a human cDNA clone encoding a protein that was identical to the mammalian 27-kDa heat shock protein (HSP27), a protein of uncertain function that is known to be phosphorylated to several forms and to be transcriptionally induced by estrogen. The 29-kDa proteins were confirmed to be phosphorylated forms of HSP27 by immunoprecipitation studies. Thus, the "estrogen receptor-related protein" is HSP27, and the three major 29-kDa proteins phosphorylated in thrombin-activated platelets are forms of HSP27. These data suggest a role for HSP27 in the signal transduction events of platelet activation.
Mendelsohn
M E
ME
Department of Medicine, Brigham and Women's Hospital, Boston, MA.
Zhu
Y
Y
O'Neill
S
S
D000595:Amino Acid Sequence; D001345:Autoradiography; D001483:Base Sequence; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004274:DNA, Recombinant / Q000302:isolation & purification; D015180:Electrophoresis, Gel, Two-Dimensional; D015723:Gene Library; D006360:Heat-Shock Proteins / Q000097:blood* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011960:Receptors, Estrogen / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology*
D004274:DNA, Recombinant; D006360:Heat-Shock Proteins; D010761:Phosphorus Radioisotopes; D011960:Receptors, Estrogen; D004247:DNA; D013917:Thrombin