Distinct roles of the NH2- and COOH-terminal domains of the protein inhibitor of activated signal transducer and activator of transcription (STAT) 1 (PlAS1) in cytokine-induced PlAS1--Stat1 interaction

摘要

STATs are activated by tyrosine phosphorylation on cytokine stimulation. A tyrosine-phosphorylated STAT forms a functional dimer through reciprocal Src homology 2 domain (SH2)-phospho- tyrosyl peptide interactions. lFN treatment induces the association of PIAS1 and Stat1, which results in the inhibition of Stat1- mediated gene activation. The molecular basis of the cytokine- dependent PlAS1-Stat1 interaction has not been understood. We report here that a region near the COOH terminus of PIAS1 (amino acids 392--541) directly interacts with the NH2-terminal domain of Stat1 (amino acids 1--191). A mutant PlAS1 lacking the Stat1- interacting domain failed to inhibit Stat1-mediated gene activa- tion. By using a modified yeast two-hybrid assay. we demon- strated that PlAS1 specifically interacts with the Stat1 dimer. but not tyrosine-phosphorylated or -unphosphorylated Stat1 mono- mer. In addition. whereas the NH2-terminal region of PlAS1 does not interact with Stat1, it serves as a modulatory domain by preventing the interaction of the COOH-terminal domain of PIAS1 with the Stat1 monomer. Thus, the cytokine-induced PIAS1--Stat1 interaction is mediated through the specific recognition of the dimeric form of Stat1 by PlAS1.