Activation of multiple growth regulatory genes following inducible expression of IRF-1 or IRF/RelA fusion proteins.
Interferon Regulatory Factor (IRF)-1 has been characterized as an important growth regulatory and immunomodulatory transcription factor. To further characterize the potential targets of IRF-1 antiproliferative activity, IRF-1 was expressed under the control of the tetracycline-inducible system in murine NIH3T3 cells. Due to their ability to mimic IRF-1 transactivator function, the regulatory potential of IRF-1/RelA and IRF-2/RelA fusion proteins consisting of the DNA binding domains of IRF-1 or IRF-2 fused to the transactivation domain of NF-kappaB RelA(p65) was also examined. Cells inducibly expressing IRF-1 or IRF/RelA in response to doxycycline treatment displayed significantly reduced growth rates compared to control cells, and inhibition of cell growth correlated directly with the level of transgene expression. Interestingly, IRF-1 and IRF/RelA expression also induced a low level of apoptosis, as detected by microscopic analyses. Furthermore, expression of the interferon inducible, double stranded RNA dependent kinase PKR was increased following IRF-1 or IRF/RelA induction. Most strikingly, induction of IRF-1 and IRF/RelA expression resulted in a significant increase in STAT1 (p91) protein and increased ISGF3 DNA binding activity, suggesting that IRF-1 tumor suppressor activity may involve a novel mechanism which activates the JAK-STAT pathway through STAT1. WAF1 levels were also constitutively elevated in IRF-1 and IRF-1/RelA cells. These studies demonstrate that inducible expression of the transactivation function of IRF-1 or IRF/RelA mediates tumor suppressor activity by inducing cell growth arrest, apoptosis and the differential activation of growth regulatory genes such as PKR, STAT1 and WAF1.
Nguyen
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Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Department of Microbiology, McGill University, Montreal, Quebec, Canada.
Lin
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Hiscott
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D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D004318:Doxycycline / Q000494:pharmacology; D005786:Gene Expression Regulation; D005809:Genes, Regulator; D050856:Interferon Regulatory Factor-1; D007700:Kinetics; D051379:Mice; D016328:NF-kappa B / Q000096:biosynthesis / Q000378:metabolism; D010750:Phosphoproteins / Q000096:biosynthesis*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D050794:STAT1 Transcription Factor; D013752:Tetracycline / Q000494:pharmacology; D015534:Trans-Activators / Q000096:biosynthesis; D051996:Transcription Factor RelA; D014157:Transcription Factors / Q000096:biosynthesis; D015533:Transcriptional Activation; D014162:Transfection
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D050856:Interferon Regulatory Factor-1; C494258:Irf1 protein, mouse; D016328:NF-kappa B; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D050794:STAT1 Transcription Factor; C494080:Stat1 protein, mouse; D015534:Trans-Activators; D051996:Transcription Factor RelA; D014157:Transcription Factors; D013752:Tetracycline; D004318:Doxycycline