Phospho- and Unphospho-STATs in Signal Transduction and Gene Regulation (STAT)
The STAT (Signal Transducers and Activators of Transcription) proteins were first identified as signaling proteins that function as second messengers and transcription factors in response to cytokines and growth factors (Santos and Costa-Pereira 2011; Li 2008). Mammals have seven STAT genes, namely, STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B, and STAT6 (Santos and Costa-Pereira 2011). All the STAT proteins are highly conserved and contain six domains including the SH2, linker, coiled-coil, and DNA binding domain (Bromberg and Darnell 2000). Traditionally, unphosphorylated STAT is believed to reside in the cytoplasm in an inactive form; upon phosphorylation by JAK or another tyrosine kinase, the phosphorylated (active) STAT translocates into the nucleus to induce transcription of target genes (Bromberg and Darnell 2000)....