Alternate RNA splicing of murine nfkb1 generates a nuclear isoform of the p50 precursor NF-kappa B1 that can function as a transactivator of NF-kappa B-regulated transcription.
The NF-kappa B1 subunit of the transcription factor NF-kappa B is derived by proteolytic cleavage from the N terminus of a 105-kDa precursor protein. The C terminus of p105NF-kappa B1, like those of I kappa B proteins, contains ankyrin-related repeats that inhibit DNA binding and nuclear localization of the precursor and confer I kappa B-like properties upon p105NF-kappa B1. Here we report the characterization of two novel NF-kappa B1 precursor isoforms, p84NF-kappa B1 and p98NF-kappa B1, that arise by alternate splicing within the C-terminal coding region of murine nfkb1. p98NF-kappa B1, which lacks the 111 C-terminal amino acids (aa) of p105NF-kappa B1, has a novel 35-aa C terminus encoded by an alternate reading frame of the gene. p84NF-kappa B1 lacks the C-terminal 190 aa of p105NF-kappa B1, including part of ankyrin repeat 7. RNA and protein analyses indicated that the expression of p84NF-kappa B1 and p98NF-kappa B1 is restricted to certain tissues and that the phorbol myristate acetate-mediated induction of p84NF-kappa B1 and p105NF-kappa B1 differs in a cell-type-specific manner. Both p84NF-kappa B1 and p98NF-kappa B1 are found in the nuclei of transfected cells. Transient transfection analysis revealed that p98NF-kappa B1, but not p105NF-kappa B1 or p84NF-kappa B1, acts as a transactivator of NF-kappa B-regulated gene expression and that this is dependent on sequences in the Rel homology domain required for DNA binding and on the novel 35 C-terminal aa of this isoform. In contrast to previous findings, which indicated that p105NF-kappa B1 does not bind DNA, all of the NF-kappa B1 precursors were found to specifically bind with low affinity to a highly restricted set of NF-kappa B sites in vitro, thereby raising the possibility that certain of the NF-kappa B1 precursor isoforms may directly modulate gene expression.
Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Parkville, Australia.
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RJ
Grumont
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Fecondo
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Gerondakis
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D015870:Gene Expression; D066298:In Vitro Techniques; D008214:Lymphocytes; D051379:Mice; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016328:NF-kappa B / Q000737:chemistry / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D015534:Trans-Activators
D017931:DNA Primers; D004268:DNA-Binding Proteins; D016328:NF-kappa B; D009687:Nuclear Proteins; D011498:Protein Precursors; D012333:RNA, Messenger; D015534:Trans-Activators