The JAK-STAT signaling pathway transmits information from chemical signals outside the cell, through the cell membrane, and into gene promoters on the DNA in the cell nucleus, which causes DNA transcription and activity in the cell. The JAK-STAT system is a major signaling alternative to the second messenger system

Second messenger system

Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm or nucleus. They relay the signals of hormones like epinephrine , growth factors, and others, and cause some kind of change in the activity of the cell...

. The JAK-STAT system consists of three main components: a receptor, JAK

Janus kinase

Janus kinase is a family of intracellular, non-receptor tyrosine kinases that transduce cytokine-mediated signals via the JAK-STAT pathway. They were initially named "just another kinase" 1 & 2 , but were ultimately published as "Janus kinase"...

 and STAT

STAT protein

The STAT protein regulates many aspects of growth, survival and differentiation in cells...

.

JAK is short for Janus Kinase, and STAT is short for Signal Transducer and Activator of Transcription.

The receptor is activated by a signal from interferon, interleukin, growth factors, or other chemical messengers.