PHORBOL-MYRISTATE ACETATE INDUCES BOTH HIGH-AFFINITY AND LOW AFFINITY INTERLEUKIN-2-RECEPTORS ON A PRE-B LEUKEMIC-CELL LINE

The human pre-B leukemic cell line Reh6 does not constitutively express the Tac molecule (p55), which is one of the two polypeptide chains of the interleukin 2-receptor (IL2-R). Cell incubation with Phorbol Myristate Acetate (PMA) induces expression of the Tac molecule in a dose and time-dependent manner. Binding experiments with radiolabelled recombinant IL2 (rIL2) revealed both high and low affinity IL2-R (225 ± 105 sites/cell with a Kd of 130 ± 51 pM and 24060 sites/cell with a Kd of 17.3 nM respectively), whereas unstimulated Reh6 cells only expressed intermediate affinity IL2-R (58 sites per cell with a Kd of 460 pM). Cross-linking of radiolabelled rIL2 to PMA-incubated Reh6 cells revealed the presence of two polypeptide chains of mol. wts 55,000 (Tac molecule) and 70,000, as in normal activated T cells, while the 70,000 mol. wt chain alone was observed in unstimulated Reh6 cells. IL2-R-bearing Reh6 cells could absorb rIL2 in a dose-dependent manner and this absorption was inhibited by a monoclonal antibody against the Tac molecule (anti-Tac). Moreover, partial internalization of IL2 bound under high affinity conditions occurred at 37°C. IL2-R expressed on PMA-induced cells were functional since rIL2 specifically enhanced the proliferation in vitro of PMA-treated cells in semi-solid but not liquid cultures. These findings thus demonstrate an IL2-dependent mechanism of proliferation in vitro of pre-B leukemic cells induced by PMA, which can express high affinity, functional IL2-R. © 1990.