Controlling nuclear JAKs and STATs for specific gene activation by IFNγ

Abstract

We previously showed that gamma interferon (IFNγ) and its receptor subunit, IFNGR1, interacted with the promoter region of IFNγ-activated genes along with transcription factor STAT1α. Recent studies have suggested that activated Janus kinases pJAK2 and pJAK1 also played a role in gene activation by phosphorylation of histone H3 on tyrosine 41. This study addresses the question of the role of activated JAKs in specific gene activation by IFNγ. We carried out chromatin immunoprecipitation (ChIP) followed by PCR in IFNγ treated WISH cells and showed association of pJAK1, pJAK2, IFNGR1, and STAT1 on the same DNA sequence of the IRF-1 gene promoter. The β-actin gene, which is not activated by IFNγ, did not show this association. The movement of activated JAK to the nucleus and the IRF-1 promoter was confirmed by the combination of nuclear fractionation, confocal microscopy and DNA precipitation analysis using the biotinylated GAS promoter. Activated JAKs in the nucleus was associated with phosphorylated tyrosine 41 on histone H3 in the region of the GAS promoter. Unphosphorylated JAK2 was found to be constitutively present in the nucleus and was capable of undergoing activation in IFNγ treated cells, most likely via nuclear IFNGR1. Association of pJAK2 and IFNGR1 with histone H3 in IFNγ treated cells was demonstrated by histone H3 immunoprecipitation. Unphosphorylated STAT1 protein was associated with histone H3 of untreated cells. IFNγ treatment resulted in its disassociation and then re-association as pSTAT1. The results suggest a novel role for activated JAKs in epigenetic events for specific gene activation.

Nuclear JAK2

“…The fractionation methodology used by the Girodon et al was not detailed in their manuscript, and so we are unable to comment on this. However, it is worth noting that several groups have used biochemical fractionation to demonstrate JAK2 in the nucleus of mammary cells, 7 kidney and neuroepithelial cells, 4 amniotic epithelium, 8 and adrenocortical cells. 9 In hematopoietic cells, the Nimer laboratory has used cell fractionation techniques to demonstrate that JAK2V617F is found in both the cytoplasm and the nucleus, and that nuclear JAK2V617F interacts with the chromatin modifier PRMT5 to regulate its histone methyltransferase activity.…”

Upregulation of Peptide Transporters PEPT1 and PEPT2 by Janus Kinase JAK2

“…The janus-activated kinase-2 JAK2 is involved in the signaling of a variety of hormones and cytokines [1,2,3], such as leptin [4], growth hormone [5,6], erythropoietin [2], thrombopoietin [2] and granulocyte colony-stimulating factor [2]. Moreover, JAK2 is activated by oxidative stress [7], ischemia [7] and hypertonicity [8,9].…”

Type I Interferon Mimetics Bypass Vaccinia Virus Decoy Receptor Virulence Factor for Protection of Mice against Lethal Infection

“…We showed that activated JAK2 for IFN-␥ and activated tyrosine kinase 2 (TYK2) for type I IFNs phosphorylated histone H3 at tyrosine 41 in genes that are specifically activated by the IFNs (14,15). This caused the release of the histone inhibitory protein 1␣ (HPI␣).…”

“…We have recently shown that type I IFN has a noncanonical signaling mechanism that is similar to that of IFN-␥ (9,14,15). We preliminarily showed that long N-terminal-truncated type I IFNs failed to recognize the extracellular domain of their receptor, but if the truncated proteins were internalized, they induced an antiviral state similar to that of intact IFN (15).…”