4.1R-deficient human red blood cells have altered phosphatidylserine exposure pathways and are deficient in CD44 and CD47 glycoproteins.
BACKGROUND
Protein 4.1R is an important component of the red cell membrane skeleton. It imparts structural integrity and has transmembrane signaling roles by direct interactions with transmembrane proteins and other membrane skeletal components, notably p55 and calmodulin.


METHODS
Spontaneous and ligation-induced phosphatidylserine exposure on erythrocytes from two patients with 4.1R deficiency were studied, using CD47 glycoprotein and glycophorin C as ligands. We also looked for protein abnormalities in the 4.1R-based multiprotein complex.


RESULTS
Phosphatidylserine exposure was significantly increased in 4.1R-deficient erythrocytes obtained from the two different individuals when ligands to CD47 glycoprotein were bound. Spontaneous phosphatidylserine exposure was normal. 4.1R, glycophorin C and p55 were missing or sharply reduced. Furthermore there was an alteration or deficiency of CD47 glycoprotein and a lack of CD44 glycoprotein. Based on a recent study in 4.1R-deficient mice, we found that there are clear functional differences between interactions of human red cell 4.1R and its murine counterpart.


CONCLUSIONS
Glycophorin C is known to bind 4.1R, and we have defined previously that it also binds CD47. From our evidence, we suggest that 4.1R plays a role in the phosphatidylserine exposure signaling pathway that is of fundamental importance in red cell turnover. The linkage of CD44 to 4.1R may be relevant to this process.
Jeremy
Kris P
KP
University of the West of England, Bristol, UK.
Plummer
Zoe E
ZE
Head
David J
DJ
Madgett
Tracey E
TE
Sanders
Kelly L
KL
Wallington
Amanda
A
Storry
Jill R
JR
Gilsanz
Florinda
F
Delaunay
Jean
J
Avent
Neil D
ND
D000328:Adult; D000595:Amino Acid Sequence; D051928:CD47 Antigen / Q000097:blood / Q000235:genetics; D002675:Child, Preschool; D003598:Cytoskeletal Proteins / Q000097:blood / Q000172:deficiency*; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors / Q000097:blood / Q000235:genetics; D008024:Ligands; D008297:Male; D008565:Membrane Proteins / Q000097:blood / Q000172:deficiency*; D008969:Molecular Sequence Data; D010718:Phosphatidylserines / Q000097:blood* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
C497483:CD44 protein, human; D051928:CD47 Antigen; C497894:CD47 protein, human; D003598:Cytoskeletal Proteins; D018960:Hyaluronan Receptors; D008024:Ligands; D008565:Membrane Proteins; D010718:Phosphatidylserines; C028841:erythrocyte membrane band 4.1 protein