Sperm protein 17 is expressed on normal and malignant lymphocytes and promotes heparan sulfate-mediated cell-cell adhesion

Sperm protein 17 (Sp17) is a highly conserved mammalian protein present on acrosome-reacted sperm that is thought to promote fertilization by binding sulfated carbohydrates of the oocyte zona pellucida. Although Sp17 was orig inally described as a testis-specific antigen, emerging evidence indicates that it may be more ubiquitously expressed than was previously thought. Wit h the use of a specific antiserum, Sp17 was found to be present on the surf ace of malignant lymphoid cells, including B- and T-lymphold cell lines, an d on the surface of primary cells isolated from 2 patients having B-lymphoi d tumors. Surprisingly, circulating B lymphocytes isolated from healthy vol unteers also expressed Sp17, while circulating T lymphocytes exhibited only very weak expression. The role of Sp17 in promoting lymphoid cell adhesion was addressed with the use of recombinant Sp17 (rSp17). The rSp17 binds to the surface of myeloma cells but not to cells pretreated with heparitinase , an enzyme that removes heparan sulfate from the cell surface. Moreover, r Sp17 promotes extensive aggregation of cells that express the syndecan-1 he paran sulfate proteoglycan, but in contrast, cells lacking syndecan-1 expre ssion fall to aggregate in the presence of rSp17. These findings suggest th at Sp17 promotes heparan sulfate-mediated cell aggregation and thereby play s a role in regulating adhesion and migration of normal and malignant lymph ocytes. (C) 2001 by The American Society of Hematology.