Intracellular domain of the IFNaR2 interferon receptor subunit mediates transcription via Stat2

Abstract

We recently demonstrated that IFNaR2, a subunit of the interferon receptor, can be proteolytically cleaved in response to interferon‐alpha and other activators of protein kinase C. Cleavage occurs at multiple sites, via a mechanism similar to that employed by Notch and the Alzheimer's precursor protein, and releases the intracellular domain (ICD). In this study, we demonstrate that the IFNaR2 ICD, when fused to the yeast Gal4 DNA binding domain (Gal4DBD) selectively modulates transcription of four different promoters under the control of Gal4 upstream activating sequences. We previously showed that Stat2 binds constitutively to the ICD of IFNaR2, in a manner that is independent of tyrosine phosphorylation. Here, we show that ICD transcriptional modulation is dependent upon the carboxyl‐terminal transactivation domain of Stat2. Specifically, complementing Stat2 deficient cells with wild‐type Stat2 restored the ICD‐mediated transcriptional effects while complementation with a mutant form of Stat2 lacking the transcriptional activation domain (TAD) did not. In addition, mutation of the Stat2 binding site on the ICD reduced the transcriptional activity of the Gal4DBD–ICD. Finally, we demonstrate that the activity of Jak1, a tyrosine kinase also known to bind to IFNaR2, is required for ICD‐mediated transcriptional effects. © 2005 Wiley‐Liss, Inc.

Nuclear transit of the intracellular domain of the interferon receptor subunit IFNaR2 requires Stat2 and Irf9

“…Irf9 then provides a nuclear localization signal to move the ICD to the nucleus. We have previously shown that ICD-bound Stat2 can modulate transcription via its TAD [22]. While it remains to be determined if the ICD complex does indeed regulate physiological gene expression and whether regulated proteolysis mediates the IFN response, this report further supports the possibility of RIP signaling via an IFN receptor.…”

“…These findings suggested that IFNaR2 might signal by other, non-canonical mechanisms and, indeed, we subsequently found that this subunit of the IFN receptor is proteolytically cleaved in a regulated manner that resembles signaling by other RIP substrates [21]. We also showed that the receptor ICD can modulate transcription via the TAD of the bound Stat2 molecule [22]. Moreover, we have recently demonstrated that IFNaR2 is a substrate for TACE (unpublished data, A. Saleh, P.P.…”

“…Subsequently, we demonstrated that the intracellular domain of IFNaR2 (IFNaR2-ICD) can mediate gene transcription in a Stat2 dependent manner [22]. In this report, we investigate additional aspects of the regulated proteolysis of this receptor, demonstrating that Stat2 and Irf9 can facilitate the translocation of the IFNaR2-ICD to the nucleus.…”

Cytokine and growth factor receptors in the nucleus: What's up with that?

“…Stat2 binds the I2-ICD constitutively in a phosphotyrosineindependent manner Saleh et al, 2002]. Since we have also shown that the Stat2 TAD mediates the transcriptional effects of the I2-ICD [El Fiky et al, 2005], it is conceivable that RIP-ed IFNaR2 might control some of the same genes regulated by the canonical JAK-STAT signaling pathway. A comprehensive survey of the genes regulated by the I2-ICD is required to test this hypothesis.…”

“…The data from our lab on the transcriptional effects of the I2-ICD has mainly involved testing the effects of Gal4DBD-ICD fusions on Gal4UAS activity [El Fiky et al, 2005]. The I2-ICD, when fused to Gal4DBD, can either activate or repress various reporters linked to a Gal4UAS, possibly dependent on the presence of other transcriptional regulatory elements in the reporter constructs.…”