IRF1 supports DNA binding of STAT1 by promoting its phosphorylation

Abstract

The signal transducer and activator of transcription 1 (STAT1), a pivotal transcription factor in Janus kinase (JAK)-STAT signaling, regulates the expression of a wide range of immune-related genes, including interferon (IFN) regulatory factor 1 (IRF1). In this study, we found that IRF1 could induce STAT1 phosphorylation and in turn STAT1 activation. When IRF1 was transiently expressed in HEK293 cells, STAT1 phosphorylated at Y701, dimerized and bound to an oligonucleotide containing a gamma-activated sequence (GAS) derived from the IRF1 promoter. IRF1 expression also induced GAS-dependent promoter reporter activity, and phosphorylation of JAK1, a kinase upstream of STAT1. Although no direct interaction between IRF1 and STAT1 was observed, the transactivation domain of IRF1 was required for IRF1-mediated STAT1 activation, indicating the involvement of gene product(s) regulated by IRF1. Moreover, supernatants from cells expressing IRF1 induced phosphorylation of STAT1 and JAK1, and subsequent GAS binding by STAT1 that could not be blocked by treatment with antibodies against IFN-β or IFN-γ. IFN-γ-induced STAT1 phosphorylation persisted for up to 30 h following stimulation of HEK293, but declined in IRF1-deficient HEK293 cells. IRF1-promoter activity induced by IFN-γ was also reduced in IRF1-deficient HEK293 cells, which could be rescued by complementation with IRF1. Together these results indicate that IRF1 promotes DNA binding of STAT1, which can in turn participate in a positive feedback loop of JAK-STAT signaling.

Parâmetros Clínicos, Biológicos E Moleculares Na Resposta Ao Tratamento Com Interferon-Beta Em Pacientes Com Esclerose Múltipla

“…Essa ligação ocasiona o rearranjo e dimerização das subunidades do receptor seguida de ativação das proteínas acopladas a essas subunidades, levando a mecanismos em cascata de auto-fosforilação e fosforilação de proteínas. É importante saber que as subunidades do receptor de IFN I estão acopladas a proteínas das famílias: tirosina quinase (TYK) e Janus activated kinase (JAK), enquanto que no receptor do IFN II estão acopladas proteínas pertencentes apenas à família JAK (ZENKE et al, 2018).…”

“…A fosforilação das proteínas STAT é uma etapa de extrema importância na resposta ao tratamento com IFN, pois é essencial para a ativação da transcrição do gene. As proteínas quinase também são responsáveis pela fosforilação do STAT 1, tendo grande importância no mecanismo de sinalização mediado por IFN-β, o qual faz parte da família de proteínas quinase C, juntamente com os outros integrantes dos IFNs do tipo I (ZENKE et al, 2018).…”

“…A cascata de sinalização da proteína p38 pode ter um papel mais importante na geração de sinais mediados por IFN, sendo que esta é fosforilada e ativada, e é necessária para a transcrição de alguns genes induzidos por IFN I. Os diferentes mecanismos de sinalização iniciados logo após a ligação do IFN tipo I ao seu receptor são proporcionais ao efeito pleiotrópico exercido pelo IFN (SCHREIBER, 2017;ZENKE et al, 2018).…”

Do the two transcription factors form a positive feedback amplifier circuit in their common fight against pathogens?

“…Zenke and co‐authors reported that the transcriptional activity of IRF1 is required for enhanced STAT1 activation, as a truncated mutant lacking the carboxy‐terminal IAD domain, which is required for transactivation and dimerization, failed to increase STAT1 tyrosine phosphorylation . Based on these observations, they concluded that IRF1 is engaged in a positive feedback loop of the IFNγ‐induced JAK‐STAT signaling pathway, which may have functional consequences in the regulation of immune reactions.…”

“…In an interesting article published in this issue of Immunology & Cell Biology , Zenke and co‐authors reported that IRF1 promotes activation of STAT1 (i.e. tyrosine phosphorylation at residue Y701 and subsequent DNA binding) …”