Differential distribution of both IL-12Rbeta chains in the plasma membrane of human T cells.

IL-12 is a cytokine that stimulates the expression of CD26, a T cell- and raft-associated ectopeptidase. IL-12 also enhances the interaction between CD26 and CD45RO, which removes the phosphatase CD45RO from raft microdomains. Since Janus kinases are known CD45 substrates, our hypothesis was that this relocation of CD45RO in nonraft areas of the membrane could be important to switch off the signaling via cytokine receptors, e.g., the IL-12 receptor (IL-12R). Accordingly, both IL-12R and CD45RO should be equally positioned in the cell membrane upon IL-12R ligation. However, there were no data available on the membrane distribution of IL-12R on human T cells. Working with phytohemagglutinin (PHA) lymphoblasts, we tried to fill that gap. The high-affinity IL-12R is made of two chains: IL-12Rbeta1 and IL-12Rbeta2. Using flow cytometry, Western blot and confocal microscopy, we obtained data suggesting that IL-12Rbeta1 is mainly associated to phospholipid-rich membrane areas, a location even enhanced upon IL-12 incubation of PHA blasts. Instead, IL-12Rbeta2 is found more segregated into membrane rafts, which could explain why two IL-12-triggered events, T-cell proliferation and ERK1/2 activation, are both methyl-beta-cyclodextrin-sensitive events. Ligation of IL-12R with IL-12 seems to induce a partial enrichment of IL-12Rbeta2 in phospholipid-rich areas, where according to our data IL-12Rbeta1 is already present. Therefore, although new data will be required, the present results support the initial hypothesis.