The Stat3 transcription factor is an important signal transducer for numerous cytokines and growth factor receptors, and is indispensable for fetal mouse development. Studies have shown that Stat3 is continuously activated in various human tumors and has potential carcinogenicity, with anti-apoptotic activity. The expression of Stat3 isoforms reflects biological functions. The relative expression levels of Stat3α (86 kDa) and Stat3β (79 kDa) depend on cell type, ligand exposure, or the stage of cell development and maturation. It is notable that the Stat3β protein lacks serine phosphorylation sites in its carboxyl-terminal transcriptional activation domain.
