Lübbert M, Miller C W, Crawford L, Koeffler H P
Department of Medicine, UCLA Medical Center 90024.
J Exp Med. 1988 Mar 1;167(3):873-86. doi: 10.1084/jem.167.3.873.
The p53 is a nuclear protein that is associated with normal cellular proliferation and can cooperate with Ha-ras in causing cellular transformation in vitro. Lineage association is known to exist between p53 expression and normal lymphopoiesis, but not myelopoiesis. We studied the expression of p53 using chronic myelogenous leukemia (CML) cell lines, somatic hybrids of these cells, and leukemic cells from CML patients. Lymphoid CML lines expressed both p53 mRNA and protein. We also analyzed p53 synthesis by two B-lymphoid lines from the same CML patient; cells of one line were derived from the neoplastic clone, cells of the other were derived from the normal clone. Both synthesized equal amounts of a phosphorylated p53 protein. None of the myeloid CML lines expressed detectable p53 protein and two of four expressed negligible p53 mRNA. Two other myeloid CML lines and myeloid cells from three of four patients expressed p53 mRNA. These findings suggest that expression of the gene is not regulated normally in CML. Several approaches were pursued to explore the differential expression of p53. Southern blot analyses showed no gross alterations in the p53 gene from cells of either the expressing or the nonexpressing lines. No difference in the pattern of demethylated CpG sites was noted in the region of the p53 gene in cells from K562 (myeloid p53 nonexpressor) and in BV173 (lymphoid p53 expressor). The sites of demethylation clustered in and around the p53 promoter in both cell lines. Somatic hybrids formed between a p53 mRNA nonexpressor myeloid line (K562) and the parental p53 expressor lymphoid lines (Daudi, PUT) produced p53 mRNA and protein, suggesting that p53 is a dominantly expressed protein and that lack of expression in myeloid cells is not mediated by a trans-acting negative regulatory protein. DNA transfection experiments performed using the indicator gene chloramphenicol acetyltransferase attached to promoter sequences of p53 showed that these constructs were equally activated in BV173 (p53 expressor) and K562 (p53 mRNA nonexpressor). The mechanism of p53 regulation in CML remains unclear.
p53是一种核蛋白，与正常细胞增殖相关，在体外可与Ha-ras协同导致细胞转化。已知p53表达与正常淋巴细胞生成之间存在谱系关联，但与髓细胞生成无关。我们使用慢性粒细胞白血病（CML）细胞系、这些细胞的体细胞杂种以及CML患者的白血病细胞研究了p53的表达。淋巴样CML细胞系表达p53 mRNA和蛋白。我们还分析了来自同一CML患者的两个B淋巴细胞系的p53合成；一个细胞系的细胞来源于肿瘤克隆，另一个细胞系的细胞来源于正常克隆。两者合成等量的磷酸化p53蛋白。没有一个髓样CML细胞系表达可检测到的p53蛋白，四个中有两个表达可忽略不计的p53 mRNA。另外两个髓样CML细胞系以及四个患者中三个患者的髓样细胞表达p53 mRNA。这些发现表明，该基因在CML中表达异常。我们采用了几种方法来探究p53的差异表达。Southern印迹分析显示，表达或不表达细胞系的细胞中p53基因没有明显改变。在K562（髓样p53不表达细胞）和BV173（淋巴样p53表达细胞）的细胞中，p53基因区域内甲基化的CpG位点模式没有差异。两个细胞系中去甲基化位点聚集在p53启动子及其周围。一个p53 mRNA不表达的髓样细胞系（K562）与亲代p53表达的淋巴样细胞系（Daudi、PUT）形成的体细胞杂种产生了p53 mRNA和蛋白，这表明p53是一种显性表达的蛋白，髓样细胞中缺乏表达不是由反式作用的负调节蛋白介导的。使用与p53启动子序列相连的指示基因氯霉素乙酰转移酶进行的DNA转染实验表明，这些构建体在BV173（p53表达细胞）和K562（p53 mRNA不表达细胞）中被同等激活。CML中p53调节的机制仍不清楚。
