Regulation of ascidian Rel by its alternative splice variant.
The Rel/NF-kappaB family of transcription factors play key roles in morphogenesis and immune responses. We reported previously that As-rel1 and As-rel2 of the ascidian Halocynthia roretzi are involved in notochord formation. The As-rel1 protein is a typical Rel/NF-kappaB family member, whereas the As-rel2 protein is a novel truncated product of As-rel1 that lacks a nuclear localization signal and the unique C-terminal region. Here, we present conclusive evidence that As-rel1 and As-rel2 are generated from a single gene by alternative splicing. We analyzed the roles of As-rel2 using cells transfected with As-rel1 or As-rel2 or both. As-rel1 was localized in the nucleus and As-rel2 in the cytoplasm when they were transfected individually. In contrast, when they were transfected simultaneously, both were localized in the nucleus because of the association of As-rel2 with As-rel1. In this case, the transcriptional activity of As-rel1 was suppressed by As-rel2. Ascidian IkappaB was found to sequester As-rel1 in the cytoplasm and suppress its transcriptional activity when As-rel1 and IkappaB were transfected simultaneously. In contrast, when As-rel1 and IkappaB were transfected together with As-rel2, As-rel1 was transported into the nucleus and its transcriptional activity was rescued from inhibition by IkappaB, whereas As-rel2 remained localized in the cytoplasm, suggesting IkappaB sequestration in the cytoplasm by As-rel2. From these findings, we conclude that the alternative splice variant, As-rel2, regulates the nuclear localization and transcriptional activity of As-rel1.
Kawai
Narudo
N
Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
Shimada
Masumi
M
Kawahara
Hiroyuki
H
Satoh
Noriyuki
N
Yokosawa
Hideyoshi
H
D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D017089:Ankyrin Repeat / Q000235:genetics; D001483:Base Sequence; D002460:Cell Line; D002938:Ciona intestinalis; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D009672:Notochord / Q000196:embryology; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014561:Urochordata / Q000235:genetics*
D020672:I-kappa B Proteins; D016328:NF-kappa B; D020033:Protein Isoforms; D012333:RNA, Messenger