[摘要]：Type 1 interferons (including IFN alpha/beta) activate their cell surface receptor to induce the intracellular signal transduction pathways that play an important role in host defenses against infectious agents and tumors. The extent of cellular responses to IFN alpha is limited by several important mechanisms including the ligand-stimulated and specific serine phosphorylation-dependent degradation of the IFNAR1 chain of Type 1 IFN receptor. Previous studies revealed that acceleration of IFNAR1 degradation upon IFN stimulation requires activities of tyrosine kinase TYK2 and serine/threonine protein kinase D2 (PKD2), whose recruitment to IFNAR1 is also induced by the ligand. Here we report that activation of PKD2 by IFN alpha (but not its recruitment to the receptor) depends on TYK2 catalytic activity. PKD2 undergoes IFN alpha-inducible tyrosine phosphorylation on specific phospho-acceptor site (Tyr-438) within the plekstrin homology domain. Activated TYK2 is capable of facilitating this phosphorylation in vitro. Tyrosine phosphorylation of PKD2 is required for IFN alpha-stimulated activation of this kinase as well as for efficient serine phosphorylation and degradation of IFNAR1 and ensuing restriction of the extent of cellular responses to IFN alpha.
