Zabel U, Henkel T, Silva M S, Baeuerle P A
Laboratory for Molecular Biology, Ludwig-Maximilians-University, Munich, Martinsried, Germany.
EMBO J. 1993 Jan;12(1):201-11. doi: 10.1002/j.1460-2075.1993.tb05646.x.
I kappa B proteins specifically inhibit the DNA binding of NF-kappa B/Rel transcription factors. An additional role as inhibitors of nuclear uptake was supposed by subcellular fractionation and enucleation experiments. Using indirect immunofluorescence labeling of cells, we show here that the DNA-binding p50 and p65 subunits of NF-kappa B, as well as the I kappa B protein MAD-3, all occur in the nucleus when overexpressed on their own. Nuclear uptake of p65 and, to a lesser extent of p50, was, however, suppressed when MAD-3 was coexpressed. Likewise, nuclear uptake of MAD-3 was blocked by overexpressed p65 or p50. This directly demonstrates that I kappa B is a nuclear uptake regulatory protein and that the various subunits of NF-kappa B can mutually control their access to the nucleus. In the presence of MAD-3, antibodies specific for peptides overlapping the nuclear location signal (NLS) sequences of p65 and p50 could not recognize their epitopes on NF-kappa B, suggesting that the I kappa B protein rendered the signals inaccessible for NLS receptors.
IκB蛋白特异性抑制NF-κB/Rel转录因子与DNA的结合。亚细胞分级分离和去核实验推测其还具有抑制核摄取的作用。通过细胞间接免疫荧光标记，我们在此表明，NF-κB的DNA结合亚基p50和p65以及IκB蛋白MAD-3单独过度表达时均存在于细胞核中。然而，当共表达MAD-3时，p65以及程度较轻的p50的核摄取受到抑制。同样，过度表达的p65或p50会阻止MAD-3的核摄取。这直接证明IκB是一种核摄取调节蛋白，并且NF-κB的各个亚基可以相互控制其进入细胞核的过程。在存在MAD-3的情况下，与p65和p50的核定位信号（NLS）序列重叠的肽段特异性抗体无法识别NF-κB上的表位，这表明IκB蛋白使NLS受体无法识别这些信号。
