RESUMO
Yin Yang 1 (YY1) is a DNA-binding transcription factor that either activates or represses gene expression. YY1 has previously been implicated in the transcriptional silencing of many retroviruses by binding to DNA sequences in the U3 region of the viral long terminal repeat (LTR). We here show that YY1 overexpression leads to profound activation, rather than repression, of human T lymphotropic virus type 1 (HTLV-1) expression, while YY1 down-regulation reduces HTLV-1 expression. The YY1 responsive element mapped not to YY1 DNA-binding sites in the HTLV-1 LTR but to the R region. The HTLV-1 R sequence alone is sufficient to provide YY1 responsiveness to a nonresponsive promoter, but only in the sense orientation and only when included as part of the mRNA. YY1 binds to the R region of HTLV-1 RNA in vitro and in vivo, leading to increased transcription initiation and elongation. The findings indicate that YY1 is a potent transactivator of HTLV-1 gene expression acting via binding viral RNA, rather than DNA.
Assuntos
Regulação Viral da Expressão Gênica/genética , Vírus Linfotrópico T Tipo 1 Humano , RNA/metabolismo , Sequências Repetidas Terminais/genética , Fator de Transcrição YY1 , Células HEK293 , Vírus Linfotrópico T Tipo 1 Humano/genética , Vírus Linfotrópico T Tipo 1 Humano/metabolismo , Humanos , Células Jurkat , Ligação Proteica/genética , RNA/genética , Ativação Transcricional/genética , Fator de Transcrição YY1/genética , Fator de Transcrição YY1/metabolismoRESUMO
Yin Yang 1 (YY1) is a member of the GLI-Krüppel class of DNA and RNA binding transcription factors that can either activate or repress gene expression during cell growth, differentiation, and embryogenesis. Although much is known about YY1 interacting proteins and the target promoters regulated by YY1, much less is known about YY1 regulation through post-translational modifications. In this study we show that YY1 is tyrosine-phosphorylated in multiple cell types. Using a combination of pharmacological inhibition, kinase overexpression, and kinase knock-out studies, we demonstrate that YY1 is a target of multiple Src family kinases in vitro and in vivo. Moreover, we have identified multiple sites of YY1 phosphorylation and analyzed the effect of phosphorylation on the activity of YY1-responsive retroviral and cellular promoters. Phosphorylation of tyrosine 383 interferes with DNA and RNA binding, leading to the down-regulation of YY1 activity. Finally, we provide the first evidence that YY1 is a downstream target of epidermal growth factor receptor signaling in vivo. Taken together, the identification of YY1 as a target of Src family kinases provide key insights into the inhibitory role of tyrosine kinases in modulating YY1 activity.
Assuntos
Tirosina/metabolismo , Fator de Transcrição YY1/metabolismo , Quinases da Família src/metabolismo , Animais , Sítios de Ligação/genética , Western Blotting , Linhagem Celular , Linhagem Celular Tumoral , Fator de Crescimento Epidérmico/farmacologia , Expressão Gênica/efeitos dos fármacos , Células HEK293 , Células HeLa , Humanos , Mesilato de Imatinib/farmacologia , Indóis/farmacologia , Células Jurkat , Mutação , Fosforilação/efeitos dos fármacos , Regiões Promotoras Genéticas/genética , Ligação Proteica/genética , Inibidores de Proteínas Quinases/farmacologia , Proteínas Proto-Oncogênicas c-fos/genética , Interferência de RNA , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sulfonamidas/farmacologia , Tirosina/genética , Fator de Transcrição YY1/genética , Quinases da Família src/antagonistas & inibidores , Quinases da Família src/genéticaRESUMO
Embryonic cells transcriptionally repress the expression of endogenous and exogenous retroelements. Trim28, a key player in this silencing, is known to act in a large DNA-bound complex, but the other components of the complex are not fully characterized. Here, we show that the zinc finger protein Yin Yang 1 (YY1) is one such component. YY1 binds to the long terminal repeat (LTR) region of both exogenous and endogenous retroviruses (ERVs). Deletion of the YY1-binding site from the retroviral genome leads to a major loss of silencing in embryonic cells and a coordinated loss of repressive histone marks from the proviral chromatin. Depletion of YY1 protein results in marked upregulation of expression of exogenous viruses and of selected ERVs. Finally, we report an embryonic cell-specific interaction between YY1 and Trim28. Our results suggest a major role for YY1 in the silencing of both exogenous retroviruses and ERVs in embryonic cells.