Association of RACK1 and PKC beta with the common beta-chain of the IL-5/IL3/GM-CSF receptor

Granulocyte macrophage colony stimulating factor (GM-CSF), interleukin-3 (I L-3) and interleukin-5 (IL-5 belong to a family of cytokines that regulate proliferation, differentiation and function of haematopoietic cells. Their receptor consists of a ligand specific alpha-chain and a signal transducing beta-chain (beta c). While, the role of phosphotyrosine residues in the be ta c as mediators of downstream signalling cascades has been established, l ittle is known about non-phosphotyrosine mediated events. To identify prote ins interacting with beta c, me screened a yeast two-hybrid library with th e intracellular domain of beta c. We found that RACK1, a molecule associati ng with activated PKC, PLC gamma and Src kinases, associated with the membr ane proximal region of beta c in both yeast two-hybrid, immunoprecipitation and GST-pull-down assays. The association of RACK1 was constitutive, demon strating no alteration upon cellular stimulation. Furthermore, upon stimula tion of cells with IL-5 or PMA, a complex of beta c and PKC beta was found. Together, these findings suggest a novel role for RACK1 as a possible adap ter molecule associating with the intracellular domain of cytokine receptor s.