STAT1

STAT1 Full Name

signal transducer and activator of transcription 1, 91kDa

STAT1 Introduction

STAT1 was the first member of the signal transducer and activator of transcription family to be purified, and its 91 kDa isoform gave the protein its alternative name. The gene lies at 2q32.2 and encodes a latent cytoplasmic factor that is activated within minutes of interferon engagement. Two splice variants are produced: the full-length STAT1alpha, which contains a C-terminal transactivation domain, and STAT1beta, which lacks it and can act as a dominant-negative modulator. STAT1 is expressed in essentially every nucleated cell and is additionally regulated by phosphorylation of serine 727, by arginine methylation and by sumoylation.

Figure 1. STAT1 gene: function,pathway,and clinical significance.

Interferon Signalling Through GAF and ISGF3
Binding of type II interferon to its receptor activates JAK1 and JAK2, which phosphorylate STAT1 at tyrosine 701; the phosphorylated protein dimerises through its SH2 domain and enters the nucleus as gamma-activated factor to bind GAS elements in promoters of genes controlling antimicrobial defence and antigen presentation. Type I interferons instead assemble ISGF3, a heterotrimer of STAT1, STAT2 and IRF9 that recognises interferon-stimulated response elements. The two routes overlap but are not identical, and the relative abundance of STAT1 versus STAT2, together with the duration of phosphorylation, determines whether cells mount an antiviral or an immunomodulatory programme.

Inborn Errors of Immunity and Tumour Immunity
Biallelic loss-of-function STAT1 variants cause Mendelian susceptibility to mycobacterial disease, with disseminated infection by weakly virulent mycobacteria and by Salmonella, reflecting the requirement for STAT1 in interferon-gamma-dependent macrophage activation. By contrast, heterozygous gain-of-function mutations produce chronic mucocutaneous candidiasis with impaired Th17 responses and are increasingly recognised in adults with autoimmune manifestations. In oncology, STAT1 is a double-edged mediator: it is required for cytotoxic T cell recruitment and for PD-L1 induction, yet sustained STAT1 activity can promote tumour cell death and growth arrest, so its net effect depends on the cellular context.

Alternate Names for STAT1

STAT1; signal transducer and activator of transcription 1, 91kDa; signal transducer and activator of transcription 1, 91kD; signal transducer and activator of transcription 1-alpha/beta; ISGF 3; STAT91; transcription factor ISGF 3 components p91/p84; transcription factor ISGF-3 components p91/p84; signal transducer and activator of transcription-1; CANDF7