Identification of amino acid residues critical for the Src-homology 2 domain-dependent docking of Stat2 to the interferon alpha receptor

Abstract

The interaction between Src-homology 2 domains (SH2) domains and phosphorylated tyrosine residues serves a critical role in intracellular signaling. In addition to the phosphotyrosine, adjacent residues are critical mediators of the specificity of this interaction. Upon treatment of cells with interferon alpha (IFNalpha), the IFNaR1 subunit of the IFNalpha receptor becomes tyrosine phosphorylated at position 466. The region surrounding phosphorylated tyrosine 466 subsequently acts as a docking site for the SH2 domain of Stat2, facilitating phosphorylation of the latter and, thus, the transduction of the IFNalpha signal. In this report site-specific mutagenesis was employed to analyze the nature of the interaction between the SH2 domain of Stat2 and the region surrounding tyrosine 466 on IFNaR1. Mutation of the valine at the +1 position carboxyl-terminal to tyrosine 466 or of the serine at the +5 position inhibits the association of Stat2 with phosphorylated IFNaR1. Moreover, receptors mutated at either of these two positions act in a dominant manner to decrease IFNalpha signaling, as assayed by both Stat2 phosphorylation and expression of an IFNalpha-responsive reporter. The demonstration that these two residues are critical in mediating the interaction between Stat2 and IFNaR1 suggests that STAT proteins might utilize a structurally distinct subset of SH2 domains to mediate signal transduction from the cell surface to the nucleus.