Abstract
Signal transducer and activator of transcription 1 (STAT1) protein plays a pivotal role in various biological processes especially the regulation of innate and adaptive immune responses. Phosphorylation represents a key step in the activation of STAT1 and its transcriptional outcome. Binding of various extracellular ligands to their specific cell-surface receptors activates different phosphorylation of STAT1 followed by a distinct change of gene expression patterns. STAT1 is well-studied for its role in conducting the transcriptional response to interferons (IFNs), where it is activated by Janus kinase (JAK)–mediated phosphorylation of its Tyr701 residue. However, the STAT1 function expands beyond its Tyr701 phosphorylation. In this regard, we demonstrated that STAT1 serves as a proinflammatory effector downstream of toll-like receptor 4 (TLR4) endocytosis independently of IFN-ß signaling. In human macrophages, lipopolysaccharide (LPS)–bound TLR4 endocytosis activated noncanonical phosphorylation of STAT1 at Thr749, which altered its DNA target motif. Thr749–phosphorylated STAT1 promoted the expression of the gene encoding AT-rich interactive domain-containing protein 5A (ARID5A), which stabilizes interleukin 6 (IL6) mRNA. Moreover, Thr749– phosphorylated STAT1 directly enhanced the transcription of the gene encoding IL12B. By altering its DNA binding specificity, Thr749 phosphorylation confers STAT1 with proinflammatory properties in LPS-stimulated macrophages independent of its Tyr701 phosphorylation. Thus, our study highlights the importance of understanding STAT1 phosphorylation status on its DNA binding specificity and transcriptional outcome, which may help in developing better therapeutic or diagnostic strategies targeting STAT1.
Keywords
STAT1; Phosphorylation; Thr749, Tyr701
Commentary
Signal transducer and activator of transcription (STAT) proteins have been recognized about three decades ago for their dual function as signal transducers and transcriptional activators [1-3]. In mammals, there are seven STAT proteins; STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, and STAT6 that are involved in multiple signaling pathways regulating a wide-range of biological consequences such as host defense, development, cell growth and homeostasis [4]. For example, our group has identified STAT3 as the primary signaling transducer of interleukin 6 (IL-6) [5], a pleotropic cytokine regulating a wide range of biological processes such as hematopoiesis, apoptosis, inflammatory responses and metabolism [6,7]. Each of the STAT proteins remains latent in the cytoplasm until activated by specific extracellular proteins (primarily cytokines and growth factors) bound to their specific cell-surface receptors, culminating in differential signaling processing and transcriptional outcome [8].
All STAT proteins share conserved functional domains: N-terminal, DNA-binding, linker, Src-homology 2 (SH2), and C-terminal transactivation domain (TAD) [9,10]. The basic model for STAT proteins activation depends on binding of extracellular ligand resulting in active conformational change of the cytoplasmic domain of their specific receptors leading to the activation of various tyrosine kinases, which in turn phosphorylate a key tyrosine residue located at the region between the SH2 and the TAD (around residue 700) of STAT proteins resulting in STAT-STAT dimerization [10]. Among the well-studied STAT tyrosine kinases are the Janus kinases (JAKs), which comprise four members (JAK1, JAK2, JAK3 and TYK2) that are ubiquitously expressed and function in interferons (IFNs) and various cytokines signaling [11-15]. Given the large number of extracellular ligands compared to the small number of STAT proteins, it is evident that differential activation of multiple STATs by a single ligand or differential activation of a single STAT protein by two different ligands occur.
This paradigm is clear in case of STAT1, which is involved in conducting the signaling of IFNs culminating in the transcription of interferon stimulated genes (ISGs) and shaping an antiviral response. There are three different classes of IFN and they signal through distinct cell-surface receptor complexes: type I IFN binds to IFN-α receptor 1 (IFNAR1) and IFNAR2 heterodimer; type III IFN binds to IL-10 receptor 2 (IL- 10R2) and IFN-λ receptor 1 (IFNLR1) heterodimers; and type II IFN binds to IFN-γ receptor 1 (IFNGR1) and IFNGR2 heterodimer [16]. Type II IFN activates JAK1/ JAK2 kinase complex, which in turn promotes tyrosine phosphorylation at residue 701 (Tyr701) of STAT1, followed by its homodimerization, nuclear translocation and transcriptional activation of IFN-γ–induced genes through binding at gamma-activated sequence (GAS) of their DNA promoter regions [17-20]. On the other hand, type I and III IFNs activates JAK1/TYK2 kinase complex, which promotes tyrosine phosphorylation of both STAT1 (Tyr701) and STAT2 (Tyr690) leading to their heterodimerization and association with IFN regulatory factor 9 (IRF9) forming the ISG factor 3 (ISGF3) complex that activates the transcription of multiple ISGs through binding to IFN-stimulated regulatory elements (ISREs) in their DNA promoter regions [21-26]. Intriguingly, the GAS sequence is not only activated by STAT1, but it is also shared among all other STATs except for STAT2 with variable gene expression pattern mediated by each STAT protein [27], denoting that the relative abundance STAT proteins and their DNA binding partners play important role in shaping their transcriptional outcome. For example, IL-21 activates opposing functions of STAT1 and STAT3 in CD4+ T cells. Although IL-21 activates mainly STAT3, it also mediates STAT1 activation to a lesser extent that is augmented in the absence of STAT3 protein. IL-21–activated STAT1 augments Tbx21 and Ifng expression, which promotes T helper type 1 (Th1) differentiation that is negatively regulated by STAT3 under the physiological condition [28]. Correspondingly, IL-21– mediated STAT1 activation and IFNG and TBX21 expression was augmented in CD4+ T cells from patients with autosomal dominant hyper-IgE syndrome [28], a disease caused by STAT3 deficiency [29,30]. A potential explanation of these findings is that specific transcription factors interacts with different members of STAT proteins providing an additional layer for fine-tuning STATs transcriptional outcome.
Although Tyr701 phosphorylation is a key step in STAT1 activation and function, many reports have shown that STAT1 function extends beyond this phosphorylation. The first report in this perspective came from the analysis of tumor necrosis factor (TNF)-induced apoptosis [31]. By using STAT1-null human fibrosarcoma cells (U3A), Stark and colleagues have shown that U3A cells were resistant to TNF-induced apoptosis, while parental 2fTGH cells and reconstituted U3A with wild-type STAT1 (U3A-R) are sensitive. Furthermore, U3A cells showed defective expression of caspases 1,2, and 3 compared to 2fTGH and U3A-R cells. TNF-mediated apoptosis doesn’t require Tyr701 STAT1 phosphorylation as shown by the sensitivity to apoptosis of U3A cells reconstituted with the Tyr701 non-phosphomimic (Y701F) STAT1 mutant (U3A-701) [31]. Also, Tyr701–unphosphorylated STAT1 has been shown to regulate the expression of the gene encoding the low molecular mass polypeptide (LMP2), a component of 20S proteasome [32]. Comparison of the transcription profiles using DNA microarrays from U3A, U3A-701, U3A-R and 2fTGH showed that Tyr701 phosphorylation is dispensable for the consecutive expression of multiple genes such as major histocompatibility complex (MHC) class I and β2-microglobulin [33-35]. For example, in cardiac myocytes, STAT1–mediated cell death following ischemia-reperfusion injury depends on Ser727 but not Tyr701 phosphorylation [36]. STAT1 Ser727 phosphorylation is mediated by various kinases [37-40]. In response to IFNs, STAT1 Ser727 phosphorylation occurs to the Tyr701-phosphorylated DNA-bound STAT1 dimers and modulates its transcriptional activity [41,42]. On the other hand, Ser727 phosphorylation occurs independent of Tyr701 phosphorylation in response to various stimuli [43,44]. In addition, upon IFN-β stimulation, IκB kinase (IKK)-related kinase ε (IKKε) mediates the phosphorylation of STAT1 at Ser708, which alters the DNA binding specificity of the ISGF3 and promotes the transcription of distinct set of the ISGs [45]. Furthermore, unphosphorylated STAT1 (U-STAT1) provides additional layer of complexity to the STAT1 functions in interferon and cytokines signaling. Following IFN stimulation, Tyr701 phosphorylated STAT1 trans-locates to the nucleus, which is then dephosphorylated and nuclear unphosphorylated STAT1 associates with unphosphorylated STAT2 and IRF9 sustaining the expression of multiple ISGs [46,47]. Moreover, STAT1 dimerization and nuclear translocation have been reported to occur in the absence of Tyr701 phosphorylation and is important for regulation of distinct sets of targeted gene [48-53]. These studies show that STAT1 transcriptional outcome depends strongly on its phosphorylation status and its associating proteins.
While type I IFN-JAK–mediated Tyr701 STAT1 phosphorylation plays a central role in the antiviral immune response and host defense against intra-cellular bacteria like Listeria monocytogenes, its contribution to host defense against extracellular bacterial pathogens is elusive, with mounting evidence indicating a detrimental effect [54]. Toll-like receptor 4 (TLR4) is the mammalian receptor for bacterial lipopolysaccharide (LPS), which is major component of the outer membrane of Gramnegative bacteria [55]. While endocytosis of LPS-bound TLR4 is essential for IFN-β production [56], the IFN-β– JAK–STAT1-Tyr701 phosphorylation signaling pathway is unlikely to contribute to proinflammatory cytokine production as shown by deficiencies of IFN-β, IFNAR, or TYK2 did not affect the production of proinflammatory cytokines, such as IL-6, in response to bacterial infections [57-59]. In contrast, STAT1 deficiency results in diminished production of IL-6 and enhanced survival in response to bacterial infections [60,61], indicating that the role of STAT1 extends beyond that of its Tyr701 phosphorylation in the context of host defense against bacterial pathogens. Supporting this premise, our work revealed that in LPS-stimulated human macrophages, STAT1 independent of its Tyr701 phosphorylation promoted the expression of AT-rich interactive domain-containing protein 5a (ARID5A), a post-transcriptional stabilizer of IL6 mRNA. We found that deficiency of IFNAR2 in LPSstimulated human macrophages did not affect ARID5A transcripts and protein. By contrast, knocking down STAT1 in IFNAR2 deficient human macrophages that do not express Tyr701 phosphorylation reduced the amounts of ARID5A transcripts and protein [62]. Our work unraveled a noncanonical IKKβ-mediated STAT1 phosphorylation at Thr749 downstream of TLR4 endocytosis, which promotes ARID5A and IL12B transcription. Additionally, we found that the canonical phosphorylation of STAT1 at Tyr701 and Ser727 were dispensable for the IKKβ-mediated phosphorylation of STAT1 at Thr749, indicating possible distinct gene-regulatory functions of this noncanonical phosphorylation. Of note, phosphorylation of Thr749 did not affect STAT1 nuclear translocation. Instead, it facilitated STAT1 binding to and activation of the ARID5A and IL12B promoters. While Thr749 non-phosphomimic (T749A) STAT1 mutant retained its transcriptional activity on IRF1 (containing GAS) and MX2 (containing ISRE) promoters, it failed to induce ARID5A and IL12B promoter activity. By using site-directed mutagenesis, we found that the phosphorylation of Thr749 facilitates STAT1 binding to a noncanonical DNA motif (5’-TTTGANNC-3’) at the promoter regions of ARID5A and IL12B conferring STAT1 with a proinflammatory function, which expands its role into regulating IL12B and IL6 transcription and mRNA stabilization, respectively [62]. Collectively, our study highlights the importance of differential phosphorylation of STAT1 on its DNA binding specificity and transcriptional outcome. Thus, a better understanding of STAT1 phosphorylation status and its interaction with other transcriptional proteins may help to fine-tune therapeutic and diagnostic modalities targeting STAT1.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Funding
This work was supported by the Kishimoto Foundation. H.M. is supported by KAKENHI Research Activity Startup grant (No. 19K23864).
Acknowledgments
We thank Mari Okawa for her assistance.
References
2. Schindler C, Fu XY, Improta T, Aebersold R, Darnell JE. Proteins of transcription factor ISGF-3: one gene encodes the 91-and 84-kDa ISGF-3 proteins that are activated by interferon alpha. Proceedings of the National Academy of Sciences. 1992 Aug 15;89(16):7836-9.
3. Schindler C, Shuai K, Prezioso VR, Darnell JE. Interferon-dependent tyrosine phosphorylation of a latent cytoplasmic transcription factor. Science. 1992 Aug 7;257(5071):809-13.
4. Levy DE, Darnell JE. Stats: transcriptional control and biological impact. Nature Reviews Molecular Cell Biology. 2002 Sep;3(9):651-62.
5. Akira S, Nishio Y, Inoue M, Wang XJ, We S, Matsusaka T, Yoshida K, Sudo T, Naruto M, Kishimoto T. Molecular cloning of APRF, a novel IFN-stimulated gene factor 3 p91-related transcription factor involved in the gp130- mediated signaling pathway. Cell. 1994 Apr 8;77(1):63- 71.
6. Kang S, Narazaki M, Metwally H, Kishimoto T. Historical overview of the interleukin-6 family cytokine. Journal of Experimental Medicine. 2020 May 4;217(5).
7. Kang S, Tanaka T, Narazaki M, Kishimoto T. Targeting interleukin-6 signaling in clinic. Immunity. 2019 Apr 16;50(4):1007-23.
8. Horvath CM. STAT proteins and transcriptional responses to extracellular signals. Trends in Biochemical Sciences. 2000 Oct 1;25(10):496-502.
9. Leonard WJ, O’Shea JJ. Jaks and STATs: biological implications. Annual Review of Immunology. 1998 Apr;16(1):293-322.
10. Stark GR, Kerr IM, Williams BR, Silverman RH, Schreiber RD. How cells respond to interferons. Annual Reviews. 1998; 67(1):227-264.
11. Wang X, Lupardus P, LaPorte SL, Garcia KC. Structural biology of shared cytokine receptors. Annual Review of Immunology. 2009 Apr 23;27:29-60.
12. Broughton SE, Hercus TR, Lopez AF, Parker MW. Cytokine receptor activation at the cell surface. Current Opinion in Structural Biology. 2012 Jun 1;22(3):350-9.
13. Negishi H, Taniguchi T, Yanai H. The interferon (IFN) class of cytokines and the IFN regulatory factor (IRF) transcription factor family. Cold Spring Harbor Perspectives in Biology. 2018 Nov 1;10(11):a028423.
14. Malmgaard L. Induction and regulation of IFNs during viral infections. Journal of Interferon & Cytokine Research. 2004 Aug 1;24(8):439-54.
15. Kishimoto T, Taga T, Akira S. Cytokine signal transduction. Cell. 1994 Jan 28;76(2):253-62.
16. Schneider WM, Chevillotte MD, Rice CM. Interferonstimulated genes: a complex web of host defenses. Annual Review of Immunology. 2014 Mar 21;32:513-45.
17. Shuai K, Stark GR, Kerr IM, Darnell JE. A single phosphotyrosine residue of Stat91 required for gene activation by interferon-gamma. Science. 1993 Sep 24;261(5129):1744-6.
18. Shuai K, Schindler C, Prezioso VR, Darnell JE. Activation of transcription by IFN-gamma: tyrosine phosphorylation of a 91-kD DNA binding protein. Science. 1992 Dec 11;258(5089):1808-12.
19. Decker T, Kovarik P, Meinke A. GAS elements: a few nucleotides with a major impact on cytokine-induced gene expression. Journal of Interferon & Cytokine Research. 1997 Mar;17(3):121-34.
20. Decker T, Lew DJ, Mirkovitch J, Darnell Jr JE. Cytoplasmic activation of GAF, an IFN-gammaregulated DNA-binding factor. The EMBO Journal. 1991 Apr;10(4):927-32.
21. Reich N, Evans B, Levy D, Fahey D, Knight E, Darnell JE. Interferon-induced transcription of a gene encoding a 15-kDa protein depends on an upstream enhancer element. Proceedings of the National Academy of Sciences. 1987 Sep 1;84(18):6394-8.
22. Levy D, Larner A, Chaudhuri A, Babiss LE, Darnell JE. Interferon-stimulated transcription: isolation of an inducible gene and identification of its regulatory region. Proceedings of the National Academy of Sciences. 1986 Dec 1;83(23):8929-33.
23. Levy DE, Kessler DS, Pine R, Reich N, Darnell JE. Interferon-induced nuclear factors that bind a shared promoter element correlate with positive and negative transcriptional control. Genes & Development. 1988 Apr 1;2(4):383-93.
24. Levy DE, Kessler DS, Pine R, Darnell JE. Cytoplasmic activation of ISGF3, the positive regulator of interferonalpha- stimulated transcription, reconstituted in vitro. Genes & Development. 1989 Sep 1;3(9):1362-71.
25. Schindler C, Fu XY, Improta T, Aebersold R, Darnell JE. Proteins of transcription factor ISGF-3: one gene encodes the 91-and 84-kDa ISGF-3 proteins that are activated by interferon alpha. Proceedings of the National Academy of Sciences. 1992 Aug 15;89(16):7836-9.
26. Fu XY, Kessler DS, Veals SA, Levy DE, Darnell JE. ISGF3, the transcriptional activator induced by interferon alpha, consists of multiple interacting polypeptide chains. Proceedings of the National Academy of Sciences. 1990 Nov 1;87(21):8555-9.
27. Lin JX, Leonard WJ. Fine-tuning cytokine signals. Annual Review of Immunology. 2019 Apr 26;37:295-324.
28. Wan CK, Andraski AB, Spolski R, Li P, Kazemian M, Oh J, et al. Opposing roles of STAT1 and STAT3 in IL- 21 function in CD4+ T cells. Proceedings of the National Academy of Sciences. 2015 Jul 28;112(30):9394-9.
29. Holland SM, DeLeo FR, Elloumi HZ, Hsu AP, Uzel G, Brodsky N, Freeman AF, Demidowich A, Davis J, Turner ML, Anderson VL. STAT3 mutations in the hyper-IgE syndrome. New England Journal of Medicine. 2007 Oct 18;357(16):1608-19.
30. Minegishi Y, Saito M, Tsuchiya S, Tsuge I, Takada H, Hara T, et al. Dominant-negative mutations in the DNAbinding domain of STAT3 cause hyper-IgE syndrome. Nature. 2007 Aug;448(7157):1058-62.
31. Kumar A, Commane M, Flickinger TW, Horvath CM, Stark GR. Defective TNF-a-induced apoptosis in STAT1- null cells due to low constitutive levels of caspases. Science. 1997 Nov 28;278(5343):1630-2.
32. Chatterjee-Kishore M, Kishore R, Hicklin DJ, Marincola FM, Ferrone S. Different requirements for signal transducer and activator of transcription 1a and interferon regulatory factor 1 in the regulation of low molecular mass polypeptide 2 and transporter associated with antigen processing 1 gene expression. Journal of Biological Chemistry. 1998 Jun 26;273(26):16177-83.
33. Chatterjee-Kishore M, van den Akker F, Stark GR. Adenovirus E1A down-regulates LMP2 transcription by interfering with the binding of stat1 to IRF1. Journal of Biological Chemistry. 2000 Jul 7;275(27):20406-11.
34. Remoli AL, Marsili G, Perrotti E, Gallerani E, Ilari R, Nappi F, et al. Intracellular HIV-1 Tat protein represses constitutive LMP2 transcription increasing proteasome activity by interfering with the binding of IRF-1 to STAT1. Biochemical Journal. 2006 Jun 1;396(2):371-80.
35. Lee CK, Gimeno R, Levy DE. Differential regulation of constitutive major histocompatibility complex class I expression in T and B lymphocytes. The Journal of Experimental Medicine. 1999 Nov 15;190(10):1451-64.
36. Stephanou A, Scarabelli TM, Brar BK, Nakanishi Y, Matsumura M, Knight RA, et al. Induction of apoptosis and Fas receptor/Fas ligand expression by ischemia/ reperfusion in cardiac myocytes requires serine 727 of the STAT-1 transcription factor but not tyrosine 701. Journal of Biological Chemistry. 2001 Jul 27;276(30):28340-7.
37. Bancerek J, Poss ZC, Steinparzer I, Sedlyarov V, Pfaffenwimmer T, Mikulic I, Dölken L, et al. CDK8 kinase phosphorylates transcription factor STAT1 to selectively regulate the interferon response. Immunity. 2013 Feb 21;38(2):250-62.
38. Deb DK, Sassano A, Lekmine F, Majchrzak B, Verma A, Kambhampati S, et al. Activation of protein kinase Cδ by IFN-γ. The Journal of Immunology. 2003 Jul 1;171(1):267-73.
39. Nair JS, DaFonseca CJ, Tjernberg A, Sun W, Darnell JE, Chait BT, Zhang JJ. Requirement of Ca2+ and CaMKII for Stat1 Ser-727 phosphorylation in response to IFN-γ. Proceedings of the National Academy of Sciences. 2002 Apr 30;99(9):5971-6.
40. Kovarik P, Stoiber D, Eyers PA, Menghini R, Neininger A, Gaestel M, et al. Stress-induced phosphorylation of STAT1 at Ser727 requires p38 mitogen-activated protein kinase whereas IFN-γ uses a different signaling pathway. Proceedings of the National Academy of Sciences. 1999 Nov 23;96(24):13956-61.
41. Wen Z, Zhong Z, Darnell Jr JE. Maximal activation of transcription by Statl and Stat3 requires both tyrosine and serine phosphorylation. Cell. 1995 Jul 28;82(2):241- 50.
42. Sadzak I, Schiff M, Gattermeier I, Glinitzer R, Sauer I, Saalmüller A, et al. Recruitment of Stat1 to chromatin is required for interferon-induced serine phosphorylation of Stat1 transactivation domain. Proceedings of the National Academy of Sciences. 2008 Jul 1;105(26):8944-9.
43. Nguyen H, Chatterjee-Kishore M, Jiang Z, Qing Y, Ramana CV, Bayes J, et al. IRAK-dependent phosphorylation of Stat1 on serine 727 in response to interleukin-1 and effects on gene expression. Journal of Interferon & Cytokine Research. 2003 Apr 1;23(4):183- 92.
44. Zhu X, Wen Z, Xu LZ, Darnell JE. Stat1 serine phosphorylation occurs independently of tyrosine phosphorylation and requires an activated Jak2 kinase. Molecular and cellular biology. 1997 Nov 1;17(11):6618- 23.
45. Ng SL, Chua MA, McWhirter SM, García-Sastre A, Maniatis T. Multiple functions of the IKK-related kinase IKKe in interferon-mediated antiviral immunity. Science. 2007 Mar 2;315(5816):1274-8.
46. Cheon H, Stark GR. Unphosphorylated STAT1 prolongs the expression of interferon-induced immune regulatory genes. Proceedings of the National Academy of Sciences. 2009 Jun 9;106(23):9373-8.
47. Cheon H, Holvey-Bates EG, Schoggins JW, Forster S, Hertzog P, Imanaka N, et al. IFNß-dependent increases in STAT1, STAT2, and IRF9 mediate resistance to viruses and DNA damage. The EMBO Journal. 2013 Oct 16;32(20):2751-63.
48. Wenta N, Strauss H, Meyer S, Vinkemeier U. Tyrosine phosphorylation regulates the partitioning of STAT1 between different dimer conformations. Proceedings of the National Academy of Sciences. 2008 Jul 8;105(27):9238-43.
49. Braunstein J, Brutsaert S, Olson R, Schindler C. STATs dimerize in the absence of phosphorylation. Journal of Biological Chemistry. 2003 Sep 5;278(36):34133-40.
50. Meyer T, Gavenis K, Vinkemeier U. Cell typespecific and tyrosine phosphorylation-independent nuclear presence of STAT1 and STAT3. Experimental Cell Research. 2002 Jan 1;272(1):45-55.
51. Zhong M, Henriksen MA, Takeuchi K, Schaefer O, Liu B, ten Hoeve J, et al. Implications of an antiparallel dimeric structure of nonphosphorylated STAT1 for the activation–inactivation cycle. Proceedings of the National Academy of Sciences. 2005 Mar 15;102(11):3966-71.
52. Mao X, Ren Z, Parker GN, Sondermann H, Pastorello MA, Wang W, et al. Structural bases of unphosphorylated STAT1 association and receptor binding. Molecular Cell. 2005 Mar 18;17(6):761-71.
53. Begitt A, Droescher M, Meyer T, Schmid CD, Baker M, Antunes F, Knobeloch KP, Owen MR, Naumann R, Decker T, Vinkemeier U. STAT1-cooperative DNA binding distinguishes type 1 from type 2 interferon signaling. Nature Immunology. 2014 Feb;15(2):168-76.
54. McNab F, Mayer-Barber K, Sher A, Wack A, O’garra A. Type I interferons in infectious disease. Nature Reviews Immunology. 2015 Feb;15(2):87-103.
55. Akira S, Takeda K. Toll-like receptor signalling. Nature Reviews Immunology. 2004 Jul;4(7):499-511.
56. Kagan JC, Su T, Horng T, Chow A, Akira S, Medzhitov R. TRAM couples endocytosis of Toll-like receptor 4 to the induction of interferon-ß. Nature Immunology. 2008 Apr;9(4):361-8.
57. Robinson N, McComb S, Mulligan R, Dudani R, Krishnan L, Sad S. Type I interferon induces necroptosis in macrophages during infection with Salmonella enterica serovar Typhimurium. Nature Immunology. 2012 Oct;13(10):954.
58. Perkins DJ, Rajaiah R, Tennant SM, Ramachandran G, Higginson EE, Dyson TN, et al. Salmonella typhimurium co-opts the host type I IFN system to restrict macrophage innate immune transcriptional responses selectively. The Journal of Immunology. 2015 Sep 1;195(5):2461-71.
59. Karaghiosoff M, Steinborn R, Kovarik P, Kriegshäuser G, Baccarini M, Donabauer B, et al. Central role for type I interferons and Tyk2 in lipopolysaccharideinduced endotoxin shock. Nature Immunology. 2003 May;4(5):471-7.
60. Herzig DS, Luan L, Bohannon JK, Toliver-Kinsky TE, Guo Y, Sherwood ER. The role of CXCL10 in the pathogenesis of experimental septic shock. Critical Care. 2014 Jun;18(3):1-8.
61. Ohmori Y, Hamilton TA. Requirement for STAT1 in LPS-induced gene expression in macrophages. Journal of Leukocyte Biology. 2001 Apr;69(4):598-604.
62. Metwally H, Tanaka T, Li S, Parajuli G, Kang S, Hanieh H, et al. Noncanonical STAT1 phosphorylation expands its transcriptional activity into promoting LPS-induced IL-6 and IL-12p40 production. Science Signaling. 2020 Mar 24;13(624).