Differential roles of STAT1alpha and STAT1beta in fludarabine-induced cell cycle arrest and apoptosis in human B cells.
Signal transducer and activator of transcription 1 (STAT1), a transcription factor known to participate in antiviral responses, acts as a tumor suppressor inhibiting cell growth and promoting apoptosis. To study the role of STAT1 in DNA damage-induced apoptosis in B lymphocytes, its active form, STAT1alpha, was specifically inhibited by the overexpression of STAT1beta, the STAT1alpha truncated inhibitory isoform. An episomal vector with a tetracycline-inducible bidirectional promoter was created to induce the expression of 2 proteins, STAT1beta and enhanced green fluorescence protein (EGFP). The same vector was used to overexpress STAT1alpha as a control. Expression of STAT1beta inhibited the phosphorylation, the DNA-binding activity, and the transcriptional activity of STAT1alpha, as well as the expression of STAT1alpha target genes such as p21WAF1/CIP1, TAP1, IRF1, and PKR. Inhibiting STAT1alpha by STAT1beta increased the growth rate of transfected cells and their resistance to fludarabine-induced apoptosis and cell cycle arrest. Overexpressing STAT1beta reversed the negative regulation of Mdm2 expression observed after treatment with interferon-gamma (IFN-gamma), which activates STAT1, or with fludarabine. Nuclear translocation of p53 after fludarabine treatment was decreased when STAT1beta was overexpressed, and it was increased when STAT1alpha was induced. Oligonucleotide pull-down experiments showed a physical STAT1/p53 interaction. Our results show that imbalance between the antiproliferative/proapoptotic isoform STAT1alpha and the proliferative isoform STAT1beta is likely to play a crucial role in the regulation of proliferation and apoptosis and that STAT1alpha may regulate p53 activity and sensitize B cells to fludarabine-induced apoptosis.
Baran-Marszak
Fanny
F
EA 3406 Université Paris 13, Service de Biochimie, Hôpital Avicenne, 125 route de Stalingrad, 93009 Bobigny Cedex, France.
Feuillard
Jean
J
Najjar
Imen
I
Le Clorennec
Christophe
C
Béchet
Jean-Marie
JM
Dusanter-Fourt
Isabelle
I
Bornkamm
Georg W
GW
Raphaël
Martine
M
Fagard
Remi
R
D017209:Apoptosis / Q000187:drug effects*; D001402:B-Lymphocytes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D015870:Gene Expression; D005822:Genetic Vectors / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D014740:Vidarabine; C024352:fludarabine