ALTERNATE RNA SPLICING OF MURINE NFKB1 GENERATES A NUCLEAR ISOFORM OFTHE P50 PRECURSOR NF-KAPPA-B1 THAT CAN FUNCTION AS A TRANSACTIVATOR OF NF-KAPPA-B-REGULATED TRANSCRIPTION
Rj. Grumont et al., ALTERNATE RNA SPLICING OF MURINE NFKB1 GENERATES A NUCLEAR ISOFORM OFTHE P50 PRECURSOR NF-KAPPA-B1 THAT CAN FUNCTION AS A TRANSACTIVATOR OF NF-KAPPA-B-REGULATED TRANSCRIPTION, Molecular and cellular biology, 14(12), 1994, pp. 8460-8470
The NF-kappa B1 subunit of the transcription factor NF-kappa B is deri
ved 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 p
roteins, contains ankyrin-related repeats that inhibit DNA binding and
nuclear localization of the precursor and confer I kappa B-like prope
rties 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 regi
on of murine nfkb1. p98NF-kappa B1, which lacks the 111 C-terminal ami
no acids (aa) of p(105)NF-kappa B1, has a novel 35-aa C terminus encod
ed 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 repea
t 7. RNA and protein analyses indicated that the expression of p84NF-k
appa B1 and p98NF-kappa B1 is restricted to certain tissues and that t
he phorbol myristate acetate-mediated induction of p84NF-kappa B1 and
p105NF-kappa B1 differs in a cell-type-specific manner. Both p84NF-kap
pa 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 p83NF-kappa B1, acts as a transactivator of NF-kap
pa 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, wh
ich indicated that p105NF-kappa B1 does not bind DNA, all of the NF-ka
ppa 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 ma
y directly modulate gene expression.