Carrier F, Bae I, Smith M L, Ayers D M, Fornace A J
Laboratory of Molecular Pharmacology, DTP, DCT, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Mutat Res. 1996 Jun 10;352(1-2):79-86. doi: 10.1016/0027-5107(95)00255-3.
We have previously reported that WI-L2-NS, a human lymphoblastoid cell line, has very high basal levels of GADD45 mRNA and protein in spite of a p53 mutation at amino acid 237. Regardless of the amount of Gadd45 in this cell line, no growth suppression activity was detected. We report here that in WI-L2-NS, the mutated p53 protein adopts predominantly a wild type (wt) conformation and binds to the p53 binding site in the GADD45 third intron. In this cell line, the already high levels of mutated p53 protein can be induced further by ionizing radiation (IR) but the response of the p53 downstream effector genes is altered. Induction of GADD45 and CIP1/WAF1 is reduced compared to p53 wt cell lines but is still substantially higher than the average fold induction obtained from 39 p53 mutant cell lines. Induction of the MDM2 gene was not detected in WI-L2-NS following IR. The induction pattern of the three p53 effector genes by the alkylating agent methylmethane sulfonate (MMS) was also attenuated in WI-L2-NS cells. In TK6 cells, a WI-L2-NS sister cell line having a p53 wt genotype, the induction of the p53 downstream effectors is normal, i.e. induced, both at the protein and the mRNA levels. These results indicate that the DNA binding activity of the mutated p53 protein in WI-L2-NS might be responsible, at least in part, for the high basal levels of GADD45 but can not mediate the full induction of the p53 downstream effector genes. The reason(s) for the inability of Gadd45 to suppress growth in this cell line remains however unknown.
我们之前报道过，人淋巴母细胞系WI-L2-NS尽管在第237位氨基酸处存在p53突变，但GADD45 mRNA和蛋白的基础水平非常高。尽管该细胞系中存在大量Gadd45，但未检测到生长抑制活性。我们在此报道，在WI-L2-NS中，突变的p53蛋白主要采用野生型（wt）构象，并与GADD45第三内含子中的p53结合位点结合。在该细胞系中，已经高水平的突变p53蛋白可被电离辐射（IR）进一步诱导，但p53下游效应基因的反应发生了改变。与p53野生型细胞系相比，GADD45和CIP1/WAF1的诱导降低，但仍显著高于从39个p53突变细胞系获得的平均诱导倍数。IR处理后，WI-L2-NS中未检测到MDM2基因的诱导。在WI-L2-NS细胞中，烷化剂甲磺酸甲酯（MMS）对三个p53效应基因的诱导模式也减弱。在TK6细胞中，即WI-L2-NS的具有p53野生型基因型的姐妹细胞系，p53下游效应物的诱导是正常的，即在蛋白质和mRNA水平上均被诱导。这些结果表明，WI-L2-NS中突变的p53蛋白的DNA结合活性可能至少部分地导致了GADD45的高基础水平，但不能介导p53下游效应基因的完全诱导。然而，Gadd45在该细胞系中无法抑制生长的原因仍然未知。
