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 t he malignant lymphocytes of cutaneous T-cell lymphoma and adult T-cell leukemia, on some lymphocytes from patients with acquired immunodefic iency syndrome and on Epstein-Barr virus-transformed B cells. BE2-78 p ositivity of cutaneous T-cell lymphoma tumor cells is a useful diagnos tic and prognostic determinant in evaluating patients with that disord er. The BE2-78 protein was isolated from Epstein Barr virus-transforme d B cells, purified by 1- and 2-dimensional electrophoresis and then s equenced. The sequence of 4 isolated peptide fragments was highly homo logous with the 78-kDa heat shock protein, BiP, an endoplasmic reticul um chaperone. The similarity between BiP and BE2-78 was supported by t he 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 cel l surface of cutaneous T-cell lymphoma or Epstein Barr virus-transform ed 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 sh ock protein. The possibility that malignant or transformed lymphocytes may express cell surface molecules with the capacity to bind a spectr um of exogenous or endogenous peptides has potential implications for tumor immunology. (C) 1997 Wiley-Liss, Inc.