Molecular and ligand-binding characterization of the σ-receptor in the Jurkat human T lymphocyte cell line

The σ binding site present in the Jurkat human T lymphocyte cell line was investigated. Jurkat cell membranes were found to have a single saturable binding site for [³H]haloperidol, a ligand (dissociation constant, 3.9 ± 0.3 nM). The binding of [³H]haloperidol was inhibited by several σ ligands. Northern analysis and reverse transcription-polymerase chain reaction provided evidence for the expression of the recently cloned type 1 σ- receptor (σ-R1) in Jurkat cells. The σ-R1 cDNA cloned from these cells was functional in heterologous expression systems. When expressed in mammalian celts, the cDNA-induced binding was saturable with dissociation constants of 1.9 ± 0.3 nM for [³H]haloperidol and 12 ± 2 nM for (+)- pentazocine. The binding of [³H]progesterone, a putative endogenous ligand to σ-R1, to the Jurkat cell σ-receptor could be directly demonstrated by using heterologously expressed σ-R1 cDNA. The binding of [³H]progesterone was saturable, with a dissociation constant of 88 ± 7 nM. Progesterone and haloperidol interacted with the receptor competitively. Reverse transcription-polymerase chain reaction also produced evidence for the existence of an alternatively spliced σ-R1 variant in Jurkat cells. This splice variant was found to be nonfunctional in ligand binding assays. This constitutes the first report on the molecular characterization of the σ- receptor in immune cells.