Characterization of CD200 Ectodomain Shedding.
We have previously reported the existence of a soluble form of CD200 (sCD200) in human plasma, and found sCD200 to be elevated in the plasma of Chronic Lymphocytic Leukemia (CLL) patients. CLL cells release CD200 at a constitutive level, which could be attenuated partially by ADAM28 silencing. In this study, we further explored mechanisms of CD200 shedding beyond that of ADAM28, and performed biochemical analysis of sCD200 using materials derived from purified CLL cells and Hek293 cells stably transfected with CD200, and antibodies generated specifically against either the extracellular or cytoplasmic regions of CD200. CD200 shedding was enhanced by PMA stimulation, and the loss of cell surface CD200 could be monitored as a reduction in CD200 cell surface expression by flow cytometry, in parallel with an increase in the detection of sCD200 in the supernatant. Western blot analyses and functional studies using CD200R1 expressing Hek293 cells showed that the shed CD200 detected in CLL and Hek293-hCD200 supernatants lacked the cytoplasmic domain of CD200 but retained the functional extracellular domain required for binding to, and phosphorylation of, CD200R. These data confirms that a functionally active CD200 extracellular moiety can be cleaved from the surface of CD200 expressing cells following ectodomain shedding.
Institute of Medical Science, University of Toronto, Toronto, ON, Canada.
Karrie K
0000-0001-8998-6416
KK
Wong
Institute of Medical Science, University of Toronto, Toronto, ON, Canada.|Transplant Research Division, University Health Network & University of Toronto, Toronto, ON, Canada.
Fang
F
Zhu
Transplant Research Division, University Health Network & University of Toronto, Toronto, ON, Canada.
Ismat
I
Khatri
Transplant Research Division, University Health Network & University of Toronto, Toronto, ON, Canada.
Qiang
Q
Huo
Division of Molecular and Cellular Biology, Sunnybrook Research Institute, University of Toronto, Toronto, ON, Canada.
David E
DE
Spaner
Institute of Medical Science, University of Toronto, Toronto, ON, Canada.|Transplant Research Division, University Health Network & University of Toronto, Toronto, ON, Canada.
Reginald M
RM
Gorczynski
D051722:ADAM Proteins / Q000235:genetics; D015703:Antigens, CD / Q000378:metabolism*; D045744:Cell Line, Tumor; D004797:Enzyme-Linked Immunosorbent Assay; D020868:Gene Silencing; D057809:HEK293 Cells; D006801:Humans
D015703:Antigens, CD; D051722:ADAM Proteins; C410224:ADAM28 protein, human; C042739:antigens, CD200