Nuclear β-Arrestin1 Functions as a Scaffold for the Dephosphorylation of STAT1 and Moderates the Antiviral Activity of IFN-γ

Abstract

Signal transducers and activators of transcription 1 (STAT1) is activated by tyrosine phosphorylation upon interferon-gamma (IFN-gamma) stimulation. Phosphorylated STAT1 translocates into nucleus to initiate the transcription of IFN-gamma target genes that are important in mediating antiviral, antiproliferative, and immune response. The inactivation of STAT1 is mainly accomplished via tyrosine dephosphorylation by the nuclear isoform of T cell protein tyrosine phosphatase (TC45) in nucleus. Here we show that beta-arrestin1 directly interacts with STAT1 in nucleus after IFN-gamma treatment and accelerates STAT1 tyrosine dephosphorylation by recruiting TC45. Consequently, beta-arrestin1 negatively regulates STAT1 transcription activity as well as the IFN-gamma-induced gene transcription. Application of beta-arrestin1 siRNA significantly enhances IFN-gamma-induced antiviral response in vesicular stomatitis virus (VSV)-infected cells. Our results reveal that nuclear beta-arrestin1, acting as a scaffold for the dephosphorylation of STAT1, is an essential negative regulator of IFN-gamma signaling and participates in the IFN-gamma-induced cellular antiviral response.

Identification of a Nuclear Localization Sequence in β-Arrestin-1 and Its Functional Implications

“…Indeed, our results from electrophoretic mobility shift assays show not only an overall decrease in NF-B-DNA interaction but also a more pronounced loss of p65/RelA-specific binding to the DNA probe. Transcriptional regulation by ␤-arrestin-1 was also reported in other studies and contributes to the regulation of expression of p27 and c-fos (18) and IFN-␥ (19). Taken together, these findings support an important function of ␤-arrestin-1 in transcriptional regulation in the nucleus.…”

“…In addition to its role in scaffolding signaling pathways within the cytosol, emerging evidence suggests that ␤-arrestin-1 mediates signaling within the nucleus. In studies conducted by different groups, ␤-arrestin-1 was found to serve as an activator of CREB-mediated transcription following ␦ opioid receptor activation (18), but act as an inhibitor of STAT1-mediated transcription following IFN-␥ stimulation (19). These data indicate that ␤-arrestin-1 can facilitate both activation and repression depending on cell type and the nature of stimulation.…”

“…In all reported cases, ␤-arrestin-1 acts essentially by a scaffolding mechanism in the nucleus and the cytosol, recruiting specific proteins for complex formation. In these examples it is by the recruitment of the histone acetyltransferase p300 (18) or the tyrosine phosphatase TC45 (19) that ␤-arrestin-1 serves as an activator or inhibitor, respectively. Work on the nuclear function of the ␤-arrestins has been primarily limited to ␤-arrestin-1, because ␤-arrestin-2 has a strong nuclear export signal (NES) in its C terminus, which excludes it from the sustained presence in the nucleus (20).…”

βArrestin1 Regulates the Guanine Nucleotide Exchange Factor RasGRF2 Expression and the Small GTPase Rac-mediated Formation of Membrane Protrusion and Cell Motility

“…Indeed, ␤Arr1 was shown to increase the transcription of IL-1␤ (27), p27, and c-fos (28) genes. ␤Arr1 was also shown to negatively regulate transcription of ␥-interferon-responsive genes (29). Here, we observed inhibition of rasgrf2 gene expression by ␤Arr1; depletion of ␤Arr1 resulted in the up-regulation of rasgrf2 mRNA and protein levels.…”

Wedelolactone, a Naturally Occurring Coumestan, Enhances Interferon-γ Signaling through Inhibiting STAT1 Protein Dephosphorylation

“…STAT phosphorylation is a nodal point for regulating STAT-mediated signaling. The collective work of multiple research groups has uncovered complex molecules and mechanisms regulating STATs phosphorylation, including kinases (32), phosphatases (9, 33, 34), conformational reorientation (35,36), and scaffold proteins (37). We know a great deal about the function and regulation of the kinases and phosphorylation of STATs and have developed various compounds to target the kinases that inhibit STAT signaling for treating STAT signaling-related diseases (38 -40).…”