A lymphocyte cell surface heat shock protein homologous to the endoplasmic reticulum chaperone, immunoglobulin heavy chain binding protein BIP

BE2 is a cell surface monomeric 78‐kDa protein (BE2‐78) expressed on the malignant lymphocytes of cutaneous T‐cell lymphoma and adult T‐cell leukemia, on some lymphocytes from patients with acquired immunodeficiency syndrome and on Epstein‐Barr virus‐transformed B cells. BE2‐78 positivity of cutaneous T‐cell lymphoma tumor cells is a useful diagnostic and prognostic determinant in evaluating patients with that disorder. The BE2‐78 protein was isolated from Epstein Barr virus‐transformed B cells, purified by 1‐ and 2‐dimensional electrophoresis and then sequenced. The sequence of 4 isolated peptide fragments was highly homologous with the 78‐kDa heat shock protein, BiP, an endoplasmic reticulum chaperone. The similarity between BiP and BE2‐78 was supported by the demonstration that BE2‐78, like BiP, avidly binds to ATP. However, polyclonal and monoclonal reagents that recognize cytoplasmic 70‐ and 78‐kDa heat shock proteins do not detect the BE2‐78 antigen on the cell surface of cutaneous T‐cell lymphoma or Epstein Barr virus‐transformed lymphocytes, and peptide mapping demonstrates sequence divergence, suggesting that either they are distinct or conformationally different molecules. Our results indicate that BE2‐78 is a cell surface heat shock protein. The possibility that malignant or transformed lymphocytes may express cell surface molecules with the capacity to bind a spectrum of exogenous or endogenous peptides has potential implications for tumor immunology. Int. J. Cancer 71: 1077‐1085, 1997. © 1997 Wiley‐Liss Inc.