Tài liệu Báo cáo khoa học: Identification of GAS-dependent interferon-sensitive target genes whose

Identification of GAS-dependent interferon-sensitive target

genes whose transcription is STAT2-dependent but

ISGF3-independent

Melissa M. Brierley1

, Katie L. Marchington1

, Igor Jurisica2 and Eleanor N. Fish1

1 Department of Cell and Molecular Biology, Toronto General Research Institute, University Health Network, and Department of

Immunology, University of Toronto, ON, Canada

2 Division of Signaling Biology, Ontario Cancer Institute, University Health Network, and Department of Medical Biophysics,

University of Toronto, ON, Canada

The type I interferons (IFN)-a ⁄ b are multifunctional

cytokines that mediate host defense against microbial

challenges, influence both normal and neoplastic pro￾liferation, and modulate innate and adaptive immune

responses [1,2]. The binding of type I IFNs to their

shared cognate receptor, type I interferon receptor

(IFNAR), activates multiple intracellular signaling

cascades that coordinate to trigger both the tran￾scriptional activation and translational modifications

necessary to invoke various biological responses [3,4].

Arguably the most notable of these cascades is the

Janus kinase (Jak)-signal transducer and activator of

transcription (STAT) pathway that regulates the

transcription of numerous IFN-sensitive genes (ISGs).

Upon IFN binding to IFNAR, the receptor-associated

kinases tyrosine kinase 2 (Tyk2) and Jak1 phos￾phorylate key tyrosine residues within the intra￾cellular domains of the receptor subunits [5]. These

Keywords

gene regulation; interferon; signal

transduction; transcription factors

Correspondence

E. N. Fish, Toronto General Research

Institute, 67 College Street, Rm 424,

Toronto, ON M5G 2M1, Canada

Fax: +1 416 340 3453

Tel: +1 416 340 5380

E-mail: [email protected]

(Received 19 January 2006, revised 6 Febru￾ary 2006, accepted 13 February 2006)

doi:10.1111/j.1742-4658.2006.05176.x

Signal transducer and activator of transcription 2 (STAT2) is best known

as a critical transactivator component of the interferon-stimulated gene

factor 3 (ISGF3) complex that drives the expression of many interferon

(IFN)-inducible genes. However, STAT2 is also involved in DNA binding

in non-ISGF3 transcriptional complexes. We used a DNA microarray to

survey the expression of genes regulated by IFN-inducible, STAT2-depend￾ent DNA binding, and compared the cDNAs of IFN-treated cells over￾expressing intact STAT2 to those of IFN-treated cells overexpressing

mutated STAT2 lacking the DNA binding domain. The IFN-inducible

expression of genes known to be regulated by ISGF3 was similar in both

cases. However, a subset of IFN-inducible genes was identified whose

expression was decreased in cells expressing the mutated STAT2. Impor￾tantly, these genes all contained gamma-activated sequence (GAS)-like ele￾ments in their 5¢ flanking sequences. Our data reveal the existence of a

collection of GAS-regulated target genes whose expression is IFN-inducible

and independent of ISGF3 but highly dependent on the STAT2 DNA

binding domain. This report is the first analysis of the contribution of the

STAT2 DNA binding domain to IFN responses on a global basis, and

shows that STAT2 is required for the IFN-inducible activation of the full

spectrum of GAS target genes.

Abbreviations

IFN, interferon; ISG, IFN-sensitive gene; ISGF3, IFN-stimulated gene factor 3; ISRE, IFN-stimulated response element; IFNAR, type I

interferon receptor; GAS, gamma-activated sequence; IRF, IFN regulatory factor; BSTVQ, binary tree-structured vector quantization; OPHID,

online predicted human protein interaction database; SOM, self-organizing map; STAT2, signal transducer and activator of transcription 2;

TSS, transcriptional start site.

FEBS Journal 273 (2006) 1569–1581 ª 2006 The Authors Journal compilation ª 2006 FEBS 1569