Interferon regulatory factors IRF5 and IRF7 inhibit growth and induce senescence in immortal Li-Fraumeni fibroblasts.
Cellular immortalization is one of the prerequisite steps in carcinogenesis. By gene expression profiling, we have found that genes in the interferon (IFN) pathway were dysregulated during the spontaneous cellular immortalization of fibroblasts from Li-Fraumeni syndrome (LFS) patients with germ-line mutations in p53. IFN signaling pathway genes were down-regulated by epigenetic silencing during immortalization, and some of these same IFN-regulated genes were activated during replicative senescence. Bisulfite sequencing of the promoter regions of two IFN regulatory transcription factors (IRF5 and IRF7) revealed that IRF7, but not IRF5, was epigenetically silenced by methylation of CpG islands in immortal LFS cells. The induction of IRF7 gene by IFNalpha in immortal LFS cells was potentiated by pretreatment with the demethylation agent 5-aza-2'-deoxycytidine. Overexpression of IRF5 and IRF7 revealed that they can act either alone or in tandem to activate other IFN-regulated genes. In addition, they serve to inhibit the proliferation rate and induce a senescence-related phenotype in immortal LFS cells. Furthermore, polyinosinic:polycytidylic acid treatment of the IRF-overexpressing cells showed a more rapid induction of several IFN-regulated genes. We conclude that the epigenetic inactivation of the IFN pathway plays a critical role in cellular immortalization, and the reactivation of IFN-regulated genes by transcription factors IRF5 and/or IRF7 is sufficient to induce cellular senescence. The IFN pathway may provide valuable molecular targets for therapeutic interventions at early stages of cancer development.
Li
Qunfang
Q
Program in Molecular Biology and Genetics, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, 110 East Warren, Detroit, MI 48201, USA.
Tang
Lin
L
Roberts
Paul Christopher
PC
Kraniak
Janice M
JM
Fridman
Aviva Levine
AL
Kulaeva
Olga I
OI
Tehrani
Omid S
OS
Tainsky
Michael A
MA
D002460:Cell Line; D049109:Cell Proliferation; D016922:Cellular Senescence; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D050839:Interferon Regulatory Factor-7 / Q000378:metabolism*; D050835:Interferon Regulatory Factors / Q000378:metabolism*; D016898:Interferon-alpha / Q000378:metabolism; D007372:Interferons / Q000378:metabolism; D016864:Li-Fraumeni Syndrome / Q000378:metabolism*; D008954:Models, Biological; D020133:Reverse Transcriptase Polymerase Chain Reaction
C431713:IRF5 protein, human; C494234:IRF7 protein, human; D050839:Interferon Regulatory Factor-7; D050835:Interferon Regulatory Factors; D016898:Interferon-alpha; D007372:Interferons