text: STAT3 is a member of the STAT protein family. In response to cytokines and growth factors, STAT3 is phosphorylated by receptor-associated Janus kinases (JAK), forms homo- or heterodimers, and translocates to the cell nucleus where it acts as a transcription activator. Specifically, STAT3 becomes activated after phosphorylation of tyrosine 705 in response to such ligands as interferons, epidermal growth factor (EGF), interleukin (IL-)5 and IL-6. Additionally, activation of STAT3 may occur via phosphorylation of serine 727 by mitogen-activated protein kinases (MAPK) and through c-src non-receptor tyrosine kinase. STAT3 mediates the expression of a variety of genes in response to cell stimuli, and thus plays a key role in many cellular processes such as cell growth and apoptosis.
  STAT3-deficient mouse embryos cannot develop beyond embryonic day 7, when gastrulation begins. It appears that at these early stages of development, STAT3 activation is required for self-renewal of embryonic stem cells (ESCs). Indeed, LIF, which is supplied to murine ESC cultures to maintain their undifferentiated state, can be omitted if STAT3 is activated through some other means.
  STAT3 is essential for the differentiation of the TH17 helper T cells, which have been implicated in a variety of autoimmune diseases. During viral infection, mice lacking STAT3 in T-cells display impairment in the ability to generate T-follicular helper (Tfh) cells and fail to maintain antibody based immunity.
  STAT3 caused upregulation in E-selectin, a factor in metastasis of cancers.
  Hyperactivation of STAT3 occurs in COVID-19 infection and other viral infections.