Identification of ezrin as an 81-kDa tyrosine-phosphorylated protein in T cells.
We have used APT affinity purification to isolate tyrosine-phosphorylated proteins from MRL lpr/lpr (lpr) mouse T cells. One such protein is pp81 ezrin, previously identified as a tyrosine-phosphorylated protein in epidermal growth factor-stimulated A431 carcinoma cells. Biochemical analyses in A431 and gastric parietal cells have revealed ezrin to be a cytoskeleton-associated cytosolic protein. In Jurkat T cells, however, using similar methods we have shown ezrin to be a cytosolic protein with no measurable cytoskeletal association. We also observed no increases in ezrin tyrosine phosphorylation in TCR-stimulated Jurkat T cells, unless the cells were pretreated with protein tyrosine phosphatase inhibitors, suggesting that T cell ezrin tyrosine phosphorylation is tightly controlled by protein tyrosine phosphatases. The fraction of tyrosine phosphorylated ezrin in lpr T cells was 5 to 10 times that observed in Jurkat T cells, which along with constitutive TCR-zeta phosphorylation and pp60fyn overexpression, is a feature of the lpr defect.
Egerton
M
M
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
Burgess
W H
WH
Chen
D
D
Druker
B J
BJ
Bretscher
A
A
Samelson
L E
LE
D000595:Amino Acid Sequence; D000818:Animals; D003598:Cytoskeletal Proteins; D006801:Humans; D008213:Lymphocyte Activation; D051379:Mice; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry*; D010766:Phosphorylation; D019000:Phosphotyrosine; D011233:Precipitin Tests; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000737:chemistry; D013601:T-Lymphocytes / Q000737:chemistry*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D000099149:Ezrin
D003598:Cytoskeletal Proteins; D010750:Phosphoproteins; D019000:Phosphotyrosine; D011948:Receptors, Antigen, T-Cell; D014443:Tyrosine; D000099149:Ezrin