Deciphering the human platelet sheddome.
Activated platelets shed surface proteins, potentially modifying platelet function as well as providing a source of bioactive fragments. Previous studies have identified several constituents of the platelet sheddome, but the full extent of shedding is unknown. Here we have taken a global approach, analyzing protein fragments in the supernate of activated platelets using mass spectroscopy and looking for proteins originating from platelet membranes. After removing plasma proteins and microparticles, 1048 proteins were identified, including 69 membrane proteins. Nearly all of the membrane proteins had been detected previously, but only 10 had been shown to be shed in platelets. The remaining 59 are candidates subject to confirmation. Based on spectral counts, protein representation in the sheddome varies considerably. As proof of principle, we validated one of the less frequently detected proteins, semaphorin 7A, which had not previously been identified in platelets. Surface expression, cleavage, and shedding of semaphorin 7A were demonstrated, as was its association with α-granules. Finally, cleavage of semaphorin 7A and 12 other proteins was substantially reduced by an inhibitor of ADAM17, a known sheddase. These results define a subset of membrane proteins as sheddome candidates, forming the basis for further studies examining the impact of ectodomain shedding on platelet function.
Fong
Karen P
KP
Department of Medicine, Division of Hematology, University of Pennsylvania, Philadelphia, PA 19104, USA.
Barry
Colin
C
Tran
Anh N
AN
Traxler
Elizabeth A
EA
Wannemacher
Kenneth M
KM
Tang
Hsin-Yao
HY
Speicher
Kaye D
KD
Blair
Ian A
IA
Speicher
David W
DW
Grosser
Tilo
T
Brass
Lawrence F
LF
D051722:ADAM Proteins / Q000378:metabolism*; D000072198:ADAM17 Protein; D000328:Adult; D001792:Blood Platelets / Q000502:physiology*; D015153:Blotting, Western; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D015539:Platelet Activation / Q000502:physiology*; D011804:Quinolines / Q000494:pharmacology; D039961:Semaphorins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D053719:Tandem Mass Spectrometry
C476910:BMS561392; D008565:Membrane Proteins; D011804:Quinolines; D039961:Semaphorins; D051722:ADAM Proteins; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human