Activation of Signal Transducer and Activator of Transcription 1 (STAT1) Is Not Sufficient for the Induction of STAT1-dependent Genes in Endothelial Cells

Mahboubi, Keyvan; Pober, Jordan S.

doi:10.1074/jbc.m107542200

Cited by 30 publications

(28 citation statements)

References 56 publications

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“…Addition of PDGF to cells expressing this chimeric receptor produced phosphorylated STAT1α, but no genes responsive to IFNγ were activated (Mahboubi and Pober, 2002). The following arguments suggest the requirement of additional factor(s) for the migration of STATs into the nucleus.…”

Section: Discussionmentioning

confidence: 99%

The role of IFNγ nuclear localization sequence in intracellular function

Ahmed

Burkhart

Mujtaba

et al. 2003

Journal of Cell Science

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IntroductionThe current view is that interferon γ (IFNγ) activates cells via interaction with the extracellular domain of the receptor complex (reviewed in Stark et al., 1998). This in turn results in the activation of the receptor-associated tyrosine kinases JAK1 and JAK2, leading to phosphorylation and dimerization of the transcription factor STAT1α, which dissociates from the receptor cytoplasmic domain and undergoes nuclear translocation. This current view ascribes no further role to IFNγ or the receptor chains IFNGR1 and IFNGR2 in IFNγ signaling. The above scenario ignores several events associated with IFNγ signaling. First, both IFNγ and one of the receptor chains, IFNGR1, undergo internalization or endocytosis and nuclear translocation Subramaniam et al., 2000). Second, at least three separate studies showed that intracellular IFNγ possessed biological activity that was qualitatively not unlike that of extracellular IFNγ. In one, microinjection of human IFNγ into mouse macrophage cells induced Ia expression (Smith et al., 1990). Extracellularly added human IFNγ did not have an effect, since it does not recognize the extracellular domain of the mouse IFNγ receptor complex. Another study involved internalizing human IFNγ into mouse macrophages via a liposomal delivery system, resulting in induction of an antiproliferative effect (Killion et al., 1994).Finally, intracellular expression of the human IFNγ gene in mouse fibroblasts in a non-secretory form resulted in induction of antiviral activity (Sanceau et al., 1987).Recently, we have determined the structural basis for nuclear translocation of murine IFNγ by identification of a polycationic nuclear localization sequence in its C-terminus (Subramaniam et al., 1999). Further, internalized IFNγ binds to the cytoplasmic domain of the IFNGR1 receptor chain . Immunoprecipitation experiments showed that a cytoplasmic complex of IFNγ-IFNGR1-STAT1α complexed to the nuclear importin α protein, NPI-1, occurs in an NLSdependent fashion . Thus, the internalization of IFNγ and nuclear transport of IFNγ and IFNGR1 appear to be a mechanism for nuclear import of the IFNγ transcription factor STAT1α.In the present study, we have expressed a non-secretable form of human IFNγ and found it to be biologically active. In order to demonstrate that the NLS of IFNγ was key to the intracellular events described above, positively charged amino acids in the NLS were replaced with alanines, such that the NLS sequence 128 KTGKRKR 134 was mutated to 128 ATGAAAA 134 . Non-secreted forms of IFNγ or its NLSmutated version were tested in murine and human cells for their ability to induce IFNγ activity, to activate STAT1α and to carry out nuclear translocation of STAT1α. The data show that

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Section: Discussionmentioning

confidence: 99%

The role of IFNγ nuclear localization sequence in intracellular function

Ahmed

Burkhart

Mujtaba

et al. 2003

Journal of Cell Science

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“…Intriguingly, the STAT1 ''activated'' in response to IL-6 or OSM seems to be defective in mediating a transcriptional response (ref. 15, and H.I., B.S., A.P.C.-P., and I.M.K., unpublished work). The data are in accord with at least two mechanisms for the inhibition: the first governs the transcriptional activity of the ''activated'' STAT1, and the second governs the kinetics of the activation͞deactivation.…”

Section: Methodsmentioning

confidence: 99%

Mutational switch of an IL-6 response to an interferon-γ-like response

Costa-Pereira

Tininini

Strobl

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

244

217

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“…However, more recently it has been appreciated that the precise inducer and context of STAT1 activation are crucial determinants of the biological response. For example, gamma interferon and gp130-cytokine oncostatin M both activate STAT1, but only the former can induce STAT1-responsive target genes in human endothelial cells (15), and SOCS3 plays a pivotal role in preventing gamma interferon-like responses following IL-6 stimulation of murine macrophages and liver cells (5,12). Thus, the biological effects of efficient STAT1 activation by vIL-6, both on cells and on virus replication, will need to be determined empirically.…”

Section: Fig 2 Comparisons Of Stat1 and Stat3 Activation By Vil-6 mentioning

confidence: 99%

Signal Transduction by Human Herpesvirus 8 Viral Interleukin-6 (vIL-6) IsModulated by the Nonsignaling gp80 Subunit of the IL-6 Receptor Complex and Is Distinct from Signaling Induced by Human IL-6

Nicholas

2006

J Virol

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Human herpesvirus 8 (HHV-8) viral interleukin-6 (vIL-6) mediates signaling through the gp130 signal transducer but unlike human IL-6 (hIL-6) does not require the nonsignaling gp80 ␣ subunit of the IL-6 receptor complex. By utilizing a gp80-refractory vIL-6 variant, vIL-6(R189L), we found that signal transduction, as measured by STAT1 and STAT3 activation and gp130 tyrosine phosphorylation in gp80 ؉ /gp130 ؉ HEK293T cells, was modulated by gp80. Furthermore, the signaling and BAF-130 cell growth-promoting activities of vIL-6 and hIL-6 could be distinguished, and exogenous addition of soluble gp80 enhanced cell growth supported by vIL-6. Our findings demonstrate that gp80 can modulate vIL-6 activity and that vIL-6 and hIL-6 signaling are not directly equivalent.Several cytokines transduce signals via gp130, in association with other signaling or nonsignaling receptor subunits that allow functional complex formation (reviewed in reference 8). Cellular interleukin-6 (IL-6) proteins associate with the nonsignaling gp80 ␣ receptor subunit and gp130 to form hexameric signaling complexes (IL-6 2 :gp80 2 :gp130 2 ), dimerization of gp130 leading to phosphorylation of gp130 cytoplasmic tyrosine residues by gp130-associated Janus kinases (Jaks) (8). This triggers recruitment and activation of signal transducer and activator of transcription 1 (STAT1) and/or STAT3 transcription factors or Src homology protein 2 (SHP2) that initiates mitogen-activated protein kinase signaling. Negative feedback regulation is mediated in part by SHP2 and STAT-activated suppressor of cytokine signaling 3 (SOCS3) recruitment to gp130 phosphotyrosine-759, leading to tyrosine dephosphorylation and Jak inactivation. It remains unclear what the conformational requirements are for inducing Jak phosphorylation of gp130 tyrosines and whether signaling can be modulated as a function of conformational restraints imposed by specific ligands or non-gp130 receptor subunits. Recent electron microscopy studies with extracellular portions of gp80 and gp130 suggested that the gp80 subunits of the IL-6 receptor complex allow the close juxtapositioning of gp130 subunits at the membrane surface (19). However, human herpesvirus 8 (HHV-8) viral IL-6 (vIL-6) can signal in the absence of gp80, via formation of stable tetrameric complexes with gp130 (vIL-6 2 : gp130 2 ), although vIL-6 also can signal via hexameric complexes that incorporate gp80 (2,14,16,22). It is possible, therefore, that conformational differences with respect to gp130 dimers in the presence and absence of gp80 might influence signal transduction.To address this issue, we first sought to dissociate tetrameric signaling by vIL-6 from hexameric signal transduction through the use of an engineered vIL-6 protein. Using coprecipitationbased procedures, we screened several previously reported vIL-6 variants (14) for their abilities to interact with gp130 and gp80 and to induce dimerization of gp130 and heterodimerization of gp130 and gp80; results for one of the vIL-6 proteins, vIL-6(R189L), are shown i...

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Activation of Signal Transducer and Activator of Transcription 1 (STAT1) Is Not Sufficient for the Induction of STAT1-dependent Genes in Endothelial Cells

Cited by 30 publications

References 56 publications

The role of IFNγ nuclear localization sequence in intracellular function

The role of IFNγ nuclear localization sequence in intracellular function

Mutational switch of an IL-6 response to an interferon-γ-like response

Signal Transduction by Human Herpesvirus 8 Viral Interleukin-6 (vIL-6) IsModulated by the Nonsignaling gp80 Subunit of the IL-6 Receptor Complex and Is Distinct from Signaling Induced by Human IL-6

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