The Jak-Stat Signaling Pathway of Interferons System: Snapshots

Interferons (IFNs) are a family of small regulatory glycoproteins that play a central role in the defense against viral infections. Although IFNs have been initially discovered as antiviral fac-tors, today they are known as an integral part of the cytokine network that affect a wide range of biological processes. IFNs exert their pleiotropic effects through their multisubunit cell surface receptors in a species specific manner that is believed to be controlled at the receptor and the post-receptor levels. Although IFN-mediated signaling and transcription activation of cellular gene expression is currently best understood in the context of the JAK-STAT signal transduc-tion, additional IFNs signaling pathways may also act in certain conditions. The Janus family of tyrosine kinase (JAK) enzymes and two families of transcriptional regulators, signal transducer and activator of transcription (STATS) and IFN regulatory factors (IRFs), are the principal components of the JAK-STAT pathway. Overlapping subsets of JAKS are involved in signaling by type I (IFN-α/ß) and type II (IFN-γ IFNs, indicating that the receptor subunits confer speci-ficity for activating particular JAK family members. A considerable cross talk can exist between separate signaling pathways. The emergence of new tools and approaches for study of IFNs sig