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

Granulocyte macrophage colony stimulating factor (GM-CSF), interleukin-3 (IL-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 beta c as mediators of downstream signalling cascades has been established, little is known about non-phosphotyrosine mediated events. To identify proteins interacting with beta c, me screened a yeast two-hybrid library with the intracellular domain of beta c. We found that RACK1, a molecule associating with activated PKC, PLC gamma and Src kinases, associated with the membrane proximal region of beta c in both yeast two-hybrid, immunoprecipitation and GST-pull-down assays. The association of RACK1 was constitutive, demonstrating no alteration upon cellular stimulation. Furthermore, upon stimulation 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 adapter molecule associating with the intracellular domain of cytokine receptors.