Cell type-specific signaling in response to interferon-gamma.

Type II interferon-gamma (IFN-gamma) is a pleiotropic cytokine that regulates many different cellular functions. The major signaling pathway activated by IFN-gamma involves sequential phosphorylation of the tyrosine residues of the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) proteins, providing the primary mechanism through which gene expression is induced. However, recent work has revealed that the responses are complex, as shown by the activation of kinases in addition to JAKs, differential patterns of activation of STAT1, STAT3, and STAT5 in different cells, and activation of transcription factors other than STATs. This complexity is used to regulate biological functions differentially in a cell type-specific manner, by activating different specific signals and patterns of gene expression.