Enhanced phosphorylation of transcription factor sp1 in response to herpes simplex virus type 1 infection is dependent on the ataxia telangiectasia-mutated protein

The ataxia telangiectasia-mutated (ATM) protein, a member of the related phosphatidylinositol 3-like kinase family encoded by a gene responsible for the human genetic disorder ataxia telangiectasia, regulates cellular responses to DNA damage and viral infection. It has been previously reported that herpes simplex virus type I (HSV-1) infection induces activation of protein kinase activity of ATM and hyperphosphorylation of transcription factor, Spl. We show that ATM is intimately involved in Spl hyperphosphoryllation during HSV-1 infection rather than individual HSV-1-encoded protein kinases. In ATM-deficient cells or cells silenced for ATM expression by short hairpin RNA targeting, hyperphosphorylation of SpI was prevented even as HSV-1 infection progressed. Mutational analysis of putative ATM phosphorylation sites on Spl and immunoblot analysis with phosphopeptide- specific Spl antibodies clarified that at least Ser-56 and Ser-101 residues on SpI became phosphorylated upon HSV-1 infection. Serine-to-alanine mutations at both sites on SpI considerably abolished hyperphosphoryllation of Spl upon infection. Although ATM phosphorylated Ser-101 but not Ser-56 on Spl in vitro, phosphorylation of Spl at both sites was not detected at all upon infection in ATM-deficient cells, suggesting that cellular kinase(s) activated by ATM could be involved in phosphorylation at Ser-56. Upon viral infection, Spl-dependent transcription in ATM expression- silenced cells was almost the same as that in ATM-intact cells, suggesting that ATM-dependent phosphorylation of Spl might hardly affect its transcriptional activity during the HSV-1 infection. ATM-dependent SpI phosphorylation appears to be a global response to various DNA damage stress including viral DNA replication.