信号转导及转录激活蛋白（英语：Signal Transducer and Activator of Transcription或英语：Signal Transduction And transcription，简称为STAT蛋白）在细胞的存活、生长和分化等许多方面起调节作用的转录因子家族，并由Janus激酶（曾名Just Another Kinase，JAK）激活。 dysregulation of this pathway is frequently observed in primary tumours and leads to increased angiogenesis, enhanced survival of tumours and 免疫抑制. 基因敲除 studies have provided evidence that STAT proteins are involved in the development and function of the immune system and play a role in maintaining 免疫耐受 and tumour surveillance.
STAT proteins were originally described as latent 胞质 transcription factors that require 磷酸化 for nuclear retention. The unphosphorylated STAT proteins shuttle between cytosol and the nucleus waiting for its activation signal. Once the activated transcription factor reaches the nucleus, it binds to consensus DNA-recognition motif called gamma-activated sites (GAS) in the 启动子 region of cytokine-inducible genes and activates transcription of these genes.
胞外的细胞因子与受体结合促使胞内的JAK激酶磷酸化STAT蛋白的一个酪氨酸残基，从而使STAT单体利用其SH2结构域二聚化。这磷酸化的二聚体随后通过输入蛋白a/b和RanGDP复合体主动转运到核内。一旦入核，活性STAT二聚体就会结合到细胞因子诱导型启动子区域含有GAS结构模体的基因上，并激活这些基因转录。 The STAT protein can be dephosphorylated by nuclear 磷酸酶, which leads to inactivation of STAT and the transcription factor becomes transported out of the nucleus by 输出蛋白（英语：exportin） crm1/RanGTP.