Are STATS Arginine-methylated?

Abstract

Transcription factors of the STAT (signal transducer and activator of transcription) family are important in signal transduction of cytokines. They are subject to post-translational modification by phosphorylation on tyrosine and serine residues. Recent evidence suggested that STATs are methylated on a conserved arginine residue within the N-terminal region. STAT arginine methylation has been described to be important for STAT function and loss of arginine methylation was discussed to be involved in interferon resistance of cancer cells. Here we provide several independent lines of evidence indicating that the issue of arginine methylation of STATs has to be reassessed. First, we show that treatment of melanoma and fibrosarcoma cells with inhibitors used to suppress methylation (N-methyl-2-deoxyadenosine, adenosine, DL-homocysteine) had profound and rapid effects on phosphorylation of STAT1 and STAT3 but also on p38 and Erk signaling cascades which are known to cross-talk with the Jak/STAT pathway. Second, we show that anti-methylarginine antibodies did not precipitate specifically STAT1 or STAT3. Third, we show that mutation of Arg 31 to Lys led to destabilization of STAT1 and STAT3, implicating an important structural role of Arg 31 . Finally, purified catalytically active protein arginine methyltransferases (PRMT1, -2, -3, -4, and -6) did not methylate STAT proteins, and cotransfection with PRMT1 did not affect STAT1-controlled reporter gene activity. Taken together, our data suggest the absence of arginine methylation of STAT1 and STAT3.Signal transducers and activators of transcription (STAT) 1 proteins comprise a family of transcription factors (molecular mass: ϳ90 kDa), which are specifically activated to regulate gene transcription when cells encounter cytokines and growth factors. Subsequent to receptor binding, the STAT proteins are phosphorylated on a single tyrosine residue (Tyr 701 in STAT1 and Tyr 705 in STAT3). The phosphorylated STATs dissociate from the receptors, form active dimers through interactions of their SH2 domains, and translocate to the nucleus to induce gene transcription. In addition to tyrosine phosphorylation, STATs 1, 3, and 5 also require phosphorylation on a serine residue in the C-terminal region to achieve maximal transactivation potential (1-3).Previously, a model has been proposed suggesting that STAT1 methylation on arginine at position 31 is functionally necessary since it suppresses the interaction with the negative regulatory protein PIAS (4). Later, it was published by the same group that methylation of Arg 31 of STAT1 is necessary for its dephosphorylation by the phosphatase TcPTP (5). Similarly, for STAT6, arginine methylation has been described to be important for STAT6 function (6). Mostly, these studies have made use of antibodies directed against methylarginine, STAT mutants, and inhibitors of methylation, methylthioadenosine (MTA) (4) or N-methyl-2-deoxyadenosine (MDA), in the presence of adenosine and DL-homocysteine (5-7). In addition, STAT3 has been shown to ...

Molecular characterisation and inductive expression of a fish protein arginine methyltransferase 1 gene in response to virus infection

“…To our knowledge, this is the first report on the induction of fish PRMT1 by virus infection. Recently, the significance about arginine methylation of STAT1 in IFN signalling pathway has been reassessed [50,51]. In this study, we only showed that PoPRMT was up-regulated in virus-infected FEC cells and flounder, but the link with the IFN signalling pathway was not at all addressed.…”

S-adenosylmethionine and betaine correct hepatitis C virus induced inhibition of interferon signalingin vitro

“…14 Recently, the role of STAT1 methylation has been disputed in two reports. 43,44 In both reports, no conclusive evidence for STAT1 methylation could be found. In contrast to these reports and in accordance with the report by Mowen et al, 14 we consistently found in our experimental systems that the manipulation of STAT1 methylation had consequences on DNA binding of STAT1 and the induction of IFN␣ target genes (ISGs).…”

Upregulated Protein Arginine Methyltransferase 1 by IL-4 Increases Eotaxin-1 Expression in Airway Epithelial Cells and Participates in Antigen-Induced Pulmonary Inflammation in Rats

“…Recent evidence suggested that STATs are methylated on a conserved arginine residue within the N-terminal region. STAT arginine methylation has been described to be important for STAT function, and loss of arginine methylation was discussed to be involved in IFN resistance of cancer cells (34,35). IL-4 and IL-13 share receptor FIGURE 5.…”