Interaction of CD163 with the regulatory subunit of casein kinase II (CKII) and dependence of CD163 signaling on CKII and protein kinase C

CD163 is a recently identified member of the scavenger receptor cysteine-ri ch superfamily, which is expressed on peripheral blood monocytes and most t issue macrophages and is thought to play an important role in the regulatio n of the inflammatory response of these cells. Cross-linking of CD163 on gl ucocorticoid-stimulated macrophages results in the secretion of several pro inflammatory cytokines, but the precise mechanism of CD163 mediated signal transduction is not understood. The existence of several CD163 isoforms, wh ich differ in the structure of their cytoplasmic domains and putative phosp horylation sites, suggests that these isoforms also differ in their signali ng mechanism. Using the Yeast Two-Hybrid system and further in vitro and in vivo studies, we identified the regulatory beta -subunit of casein kinase II (CKII), which specifically binds to the cytoplasmic domain of CD163 and its isoforms. We also found, that in vitro the CD163 isoforms differ in the ir association with the CKII holoenzyme and in the phosphorylation by CKII. Furthermore, we demonstrated that the cytoplasmic domains of CD163 variant s are phosphorylated by PKC-alpha in vitro. Inhibition studies using specif ic kinase inhibitors reveal that both CKII and PKC are involved in the CD16 3 signaling mechanism resulting in the secretion of proinflammatory cytokin es.