STAT3 interrupts ATR-Chk1 signaling to allow oncovirus-mediated cell proliferation

Abstract

DNA damage response (DDR) is a signaling network that senses DNA damage and activates response pathways to coordinate cellcycle progression and DNA repair. Thus, DDR is critical for maintenance of genome stability, and presents a powerful defense against tumorigenesis. Therefore, to drive cell-proliferation and transformation, viral and cellular oncogenes need to circumvent DDRinduced cell-cycle checkpoints. Unlike in hereditary cancers, mechanisms that attenuate DDR and disrupt cell-cycle checkpoints in sporadic cancers are not well understood. Using Epstein-Barr virus (EBV) as a source of oncogenes, we have previously shown that EBV-driven cell proliferation requires the cellular transcription factor STAT3. EBV infection is rapidly followed by activation and increased expression of STAT3, which mediates relaxation of the intra-S phase cell-cycle checkpoint; this facilitates viral oncogene-driven cell proliferation. We now show that replication stress-associated DNA damage, which results from EBV infection, is detected by DDR. However, signaling downstream of ATR is impaired by STAT3, leading to relaxation of the intra-S phase checkpoint. We find that STAT3 interrupts ATR-to-Chk1 signaling by promoting loss of Claspin, a protein that assists ATR to phosphorylate Chk1. This loss of Claspin which ultimately facilitates cell proliferation is mediated by caspase 7, a protein that typically promotes cell death. Our findings demonstrate how STAT3, which is constitutively active in many human cancers, suppresses DDR, fundamental to tumorigenesis. This newly recognized role for STAT3 in attenuation of DDR, discovered in the context of EBV infection, is of broad interest as the biology of cell proliferation is central to both health and disease.autosomal dominant hyper-IgE syndrome | infectious mononucleosis | latent membrane protein 1 | Epstein-Barr nuclear antigen

Cellular STAT3 Functions via PCBP2 To Restrain Epstein-Barr Virus Lytic Activation in B Lymphocytes

“…For the flow cytometry experiment depicted in Fig. 5B, combinations of siRNA (targeted or scrambled) and FITC-scrambled siRNA were transfected at a 3:1 ratio to identify transfected cells (12).…”

“…Staining and microscopy were performed as described previously (9,12). Briefly, cells were stained as described above for flow cytometry by using rabbit anti-human STAT3 (Santa Cruz Biotechnology) followed by FITC-anti-rabbit IgG (Life Technologies), washed, cytospun onto glass slides, air dried, and mounted with 4=,6-diamidino-2-phenylindole (DAPI) Prolong Gold Antifade (Life Technologies).…”

STAT3 Regulates Lytic Activation of Kaposi's Sarcoma-Associated Herpesvirus

“…Since chemical inhibitors are often associated with off-target effects, we used previously validated siRNAs (22,30) to specifically inhibit STAT3. Figure 3A shows that, compared to scrambled-siRNA-treated cells, introduction of 2 different siRNAs targeting STAT3 into latently infected cells resulted in significant increases in mRNA levels from ORF50, ORF59, ORF9, and ORFK8.1.…”

Involvement of fish signal transducer and activator of transcription 3 (STAT3) in nodavirus infection induced cell death

“…Activation of STAT3 plays important roles not only in cell proliferation, apoptosis, as well as tumor angiogenesis, invasion, and migration, but also in virus infection [3,4,7,8]. Mammalian viruses, including DNA and RNA virus, could activate STAT3 for efficient infection [3,49].…”

“…Mammalian viruses, including DNA and RNA virus, could activate STAT3 for efficient infection [3,49]. Our previous studies demonstrated that fish STAT3 was involved in Singapore grouper iridovirus (SGIV) infection, and inhibition of STAT3 activation decreased virus replication and inhibited virus induced paraptosis [10].…”