Mechanism of induction of mouse erythrocyte receptor switch in human B cells.
An early event in phorbol ester-induced maturation of chronic lymphocytic leukemic (CLL) B cells is a membrane change characterized by the inactivation of a mouse erythrocyte receptor (MER). This event, the MER-switch, is quantified by inhibition of rosette formation. By using [3H]phorbol dibutyrate ([3H]PDBu), both to stimulate MER-switch and assay binding of PDBu to CLL cells, it was shown that MER-switch was an irreversible, time-dependent event which occurred some time after maximal binding of [3H]PDBu to cells. Two classes of binding sites, one of high affinity (Kd 1 to 2 nM) at low frequency (1.5 to 5 X 10(4) sites per cell), and a lower affinity site (Kd 33 to 50 nM) of higher frequency (2 to 3.5 X 10(5) sites per cell), were detected. Binding of [3H]PDBu was inhibited by phorbol ester analogs that stimulated MER-switch, but not by inactive analogs. This, and the similarity in shapes of the binding and rosette inhibition curves over a range of concentrations, suggests that stimulation of MER-switch by phorbol esters is due to this specific binding. The phorbol ester receptor and MER are distinct because MER-ve T cells and MER-ve atypical B cells from a patient with CLL had both classes of PDBu receptor. Solubilized MER did not bind [3H]PDBu. Time-course studies, and the irreversibility of the switch, despite removal of most of the bound [3H]PDBu, indicate that inhibition of rosetting is not due to competitive or steric hindrance by phorbol esters. Equivalent activities of soluble MER were released from fresh and phorbol ester-treated CLL cells, indicating a rearrangement of MER, rather than a loss. A supernatant of phytohemagglutinin-stimulated human spleen cells also induced MER-switch in CLL lymphocytes, suggesting that a lymphokine may be a natural inducer of this event.
D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D001667:Binding, Competitive; D002273:Carcinogens; D004224:Diterpenes; D004306:Dose-Response Relationship, Immunologic; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D007945:Leukemia, Lymphoid / Q000378:metabolism; D008222:Lymphokines / Q000494:pharmacology; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate; D010703:Phorbol Esters / Q000494:pharmacology; D011947:Receptors, Antigen, B-Cell / Q000032:analysis* / Q000187:drug effects; D012397:Rosette Formation; D013729:Terpenes / Q000494:pharmacology
D002273:Carcinogens; D004224:Diterpenes; D008222:Lymphokines; D010703:Phorbol Esters; D011947:Receptors, Antigen, B-Cell; D013729:Terpenes; C011309:mezerein; D015240:Phorbol 12,13-Dibutyrate