FOXO transcription factors cooperate with delta EF1 to activate growth suppressive genes in B lymphocytes.
Forkhead transcription factors regulate many aspects of lymphocyte development and function. The FOXO subgroup of Forkhead factors opposes proliferation and survival, and FOXO inactivation is an important outcome of Ag receptor signaling. FOXO activity at target promoters is modulated by other transcription factors in a manner dependent on cell type and external stimulus. We have investigated the mechanisms by which FOXO proteins activate the promoters of two target genes in murine B lymphocytes, Ccng2 (encoding cyclin G2) and Rbl2 (p130), each of which has been implicated in cell cycle arrest. FOXO proteins bound directly to both promoters in vitro and in vivo, augmented transcriptional activity in reporter assays, and increased expression of the endogenous genes. Each of the promoter sequences has consensus binding sites for the deltaEF1 transcription factor, previously shown to either repress or activate different promoters. deltaEF1 bound to the Ccng2 and Rbl2 promoters in vitro and in vivo and increased reporter activity as well as endogenous mRNA levels for these genes. Strikingly, deltaEF1 synergized with FOXO proteins to strongly activate transcription from both promoters. Coexpression of deltaEF1 enhanced FOXO-induced cell cycle arrest in B lymphoma cells. These findings establish a novel mechanism of FOXO function at target promoters: cooperation with deltaEF1.
Chen
Jing
J
Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA.
Yusuf
Isharat
I
Andersen
Hilde-Marie
HM
Fruman
David A
DA
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D001483:Base Sequence; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D056766:Cyclin G1; D056767:Cyclin G2; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D051858:Forkhead Transcription Factors / Q000502:physiology*; D005786:Gene Expression Regulation / Q000276:immunology*; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000378:metabolism; D050717:Retinoblastoma-Like Protein p130 / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation; D000071799:Zinc Finger E-box-Binding Homeobox 1
D056766:Cyclin G1; D056767:Cyclin G2; D016213:Cyclins; D051858:Forkhead Transcription Factors; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D050717:Retinoblastoma-Like Protein p130; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C534703:Ccng1 protein, mouse; C493838:Rbl2 protein, mouse; C519422:ZEB1 protein, mouse; D000071799:Zinc Finger E-box-Binding Homeobox 1