The Journal of Immunology, Vol 149, Issue 6 1847-1852, Copyright © 1992 by American Association of Immunologists

ARTICLES

Identification of ezrin as an 81-kDa tyrosine-phosphorylated protein in T cells

M Egerton, WH Burgess, D Chen, BJ Druker, A Bretscher and LE Samelson
Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.

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.

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