Inhibition of NF-kappaB signaling via tyrosine phosphorylation of Ymer.

Cytoplasmic zinc finger protein A20 functionally dampens inflammatory signals and apoptosis via inhibition of NF-kappaB activation. We have reported that Ymer interacts with A20 and lysine (K)-63-linked polyubiquitin chain and that Ymer inhibits NF-kappaB signaling in collaboration with A20. It has also been reported that Ymer is phosphorylated by EGF stimulation. We found that Ymer was considerably phosphorylated on tyrosine residues also via Src family kinases such as Lck. A luciferase reporter assay showed that mutation of tyrosines on Ymer (YmerY217/279/304F) results in loss of the inhibitory activity for NF-kappaB signaling. Furthermore, a soft agar colony formation assay showed that the combination of SrcY527F and YmerY217/279/304F has no ability for anchorage-independent growth, suggesting that tyrosine phosphorylation of Ymer is important for inhibition of the NF-kappaB-mediated apoptotic pathway. These findings demonstrate that Ymer is likely to be a negative regulator for the NF-kappaB signaling pathway.