title: Identification of a Novel C-Terminal Truncated WT1 Isoform with Antagonistic Effects against Major WT1 Isoforms.
abstract: The Wilms' tumor gene WT1 consists of 10 exons and encodes a zinc finger transcription factor. There are four major WT1 isoforms resulting from alternative splicing at two sites, exon 5 (17AA) and exon 9 (KTS). All major WT1 isoforms are overexpressed in leukemia and solid tumors and play oncogenic roles such as inhibition of apoptosis, and promotion of cell proliferation, migration and invasion. In the present study, a novel alternatively spliced WT1 isoform that had an extended exon 4 (designated as exon 4a) with an additional 153 bp (designated as 4a sequence) at the 3' end was identified and designated as an Ex4a(+)WT1 isoform. The insertion of exon 4a resulted in the introduction of premature translational stop codons in the reading frame in exon 4a and production of C-terminal truncated WT1 proteins lacking zinc finger DNA-binding domain. Overexpression of the truncated Ex4a(+)WT1 isoform inhibited the major WT1-mediated transcriptional activation of anti-apoptotic Bcl-xL gene promoter and induced mitochondrial damage and apoptosis. Conversely, suppression of the Ex4a(+)WT1 isoform by Ex4a-specific siRNA attenuated apoptosis. These results indicated that the Ex4a(+)WT1 isoform exerted dominant negative effects on anti-apoptotic function of major WT1 isoforms. Ex4a(+)WT1 isoform was endogenously expressed as a minor isoform in myeloid leukemia and solid tumor cells and increased regardless of decrease in major WT1 isoforms during apoptosis, suggesting the dominant negative effects on anti-apoptotic function of major WT1 isoforms. These results indicated that Ex4a(+)WT1 isoform had an important physiological function that regulated oncogenic function of major WT1 isoforms.
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Tatsumi
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Nozomi
authors.initials: N
authors.lastname: Hojo
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sakamoto
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Rena
authors.initials: R
authors.lastname: Inaba
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Nahoko
authors.initials: N
authors.lastname: Moriguchi
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Matsuno
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: Department of Surgery, National Hospital Organization, Kinki-Chuo Chest Medical Center, Osaka, Japan.
authors.forename: Akihide
authors.initials: A
authors.lastname: Matsumura
authors.affiliation: National Hospital Organization, Kinki-Chuo Chest Medical Center, Osaka, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Hayashi
authors.affiliation: Department of Cancer Immunology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Soyoko
authors.initials: S
authors.lastname: Morimoto
authors.affiliation: Department of Cancer Immunotherapy, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Nakata
authors.affiliation: Department of Cancer Immunology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Fujiki
authors.affiliation: Department of Respiratory Medicine, Allergy and Rheumatic Disease, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Sumiyuki
authors.initials: S
authors.lastname: Nishida
authors.affiliation: Department of Cancer Immunology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Nakajima
authors.affiliation: Department of Cancer Immunotherapy, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Tsuboi
authors.affiliation: Department of Cancer Immunology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Oka
authors.affiliation: Department of Cancer Stem Cell Biology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Hosen
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Haruo
authors.initials: H
authors.lastname: Sugiyama
authors.affiliation: Department of Cancer Stem Cell Biology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Oji
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001483:Base Sequence; D003001:Cloning, Molecular; D004317:Doxorubicin / Q000633:toxicity; D005091:Exons; D018922:HL-60 Cells; D000882:Haplorhini; D006801:Humans; D020014:K562 Cells; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D017422:Sequence Analysis, DNA; D025721:WT1 Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D000903:Antibiotics, Antineoplastic; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D025721:WT1 Proteins; D004317:Doxorubicin