Novel chimaeric protein expressed in Philadelphia positive acute lymphoblastic leukaemia

Cytogenic changes are becoming increasingly important in understanding the pathogenesis of human malignancies. The t(9;22) (q34;q11) translocation is one of the most consistent and generates the Philadelphia chromosome (Ph1) (ref. 1) in chronic myeloid leukaemia (CML); it has also been observed in some acute lymphoblastic leukaemias (ALL) (ref. 2). In CML the breakpoints occur on chromosome 22 in the region designated bcr (ref. 3) and result in the expression of a bcr-abl fusion product of relative molecular mass (MT) 210,000 (210K) with associated in vitro tyrosine kinase activity (P210bcr-abl). In some cases of Ph1-positive ALL, a novel abl-related protein (P190all-abl) of 190K has been shown to have tyrosine kinase activity. In this report we demonstrate that the P190all-abl protein has a bcr determinant from the amino-terminal region, but is lacking a bcr determinant normally found in the P210bcr-abl near the bcr-abl junction. The chimaeric nature of the P190all-abl was confirmed by sequential immunoprecipitation with antisera against abl and bcr peptides.     

A novel abl protein expressed in Philadelphia chromosome positive acute lymphoblastic leukaemia

The Philadelphia (Ph) chromosome breakpoints in chronic myelocytic leukaemia are clustered on chromosome 22 band q11 in a 5.8-kilobase (kb) region designated bcr. The c-abl protooncogene is translocated from chromosome 9 band q34 into bcr and the biochemical consequence of this molecular rearrangement is the production of an abnormal fusion protein bcr-abl p210 with enhanced protein-tyrosine kinase activity compared to the normal p145 c-abl protein. The Ph chromosome translocation is also seen in some acute lymphoblastic leukaemias with B-cell precursor phenotypes some of which have bcr rearrangement (bcr+) and some do not (bcr-). We present evidence that the Ph+, bcr- leukaemias are associated with a novel p190 abl kinase. We propose that acute lymphoblastic leukaemias that are bcr+, p210+ are probably lymphoid blast crises following a clinically silent chronic phase of chronic myelocytic leukaemia arising in multipotential stem cells whereas bcr-, p190+ cases are de novo acute lymphoblastic leukaemias arising in more restricted precursors.     

Localization of the c-ab1 oncogene adjacent to a translocation break point in chronic myelocytic leukaemia

The human c-ab1 oncogene maps within the region (q34-qter) of chromosome 9 which is translocated to chromosome 22, the Philadelphia (Ph') chromosome, in chronic myelocytic leukaemia (CML). The position of the Ph' chromosomal break point is shown to be variable and, in one CML patient, has been localized immediately 5' of, or within, the c-ab1 oncogene. A DNA restriction fragment corresponding to this site has been molecularly cloned and shown to represent a chimaeric fragment of DNA from chromosomes 9 and 22.     

辛伐他汀联合5-FU对K562细胞增殖及凋亡的影响

目的:探讨辛伐他汀(Sim)联合5-FU对白血病K562细胞增殖及凋亡的影响,探讨其作用机制。方法:体外培养人白血病K562细胞,用MTT法观察Sim联合5-FU对细胞的增殖抑制作用,实时荧光定量RT-PCR观察对bcr/abl融合基因mRNA表达水平的影响。流式细胞术、Hoechst33258染色观察Sim与5-FU联合应用诱导细胞凋亡的作用。结果:低浓度的Sim与5-FU联合应用在抑制细胞的增殖,诱导细胞凋亡,均较各单一高浓度用药组的作用明显增强,并且下调bcr/abl融合基因mRNA表达。结论:Sim与5-FU联用具有明显的协同抑制细胞增殖的作用,其作用机制可能与诱导细胞凋亡,下调bcr/abl融合基因的表达有关。     

Translocation of the p53 gene in t(15;17) in acute promyelocytic leukaemia

Recent studies have demonstrated that the cellular tumour antigen p53 (ref. 1) can complement activated ras genes in the transformation of rat fibroblasts, suggesting that the gene encoding p53 may act as an oncogene. Here, by using in situ chromosomal hybridization, we have mapped the p53 gene to human chromosome 17, at bands 17q21-q22, the region containing one of the breakpoints in the translocation t(15;17) (q22;q21) associated with acute promyelocytic leukaemia (APL). Hybridization of p53 and erb-A (17q11-q12) probes to malignant cells from three APL patients indicated that the p53 gene is translocated to chromosome 15 (15q+), whereas erb-A remains on chromosome 17. Analysis of variant translocations demonstrates that the 15q+ chromosome contains the conserved junction, suggesting a role for p53 in the pathogenesis of APL. However, rearrangements of the p53 gene were not detected on Southern blotting of DNA from leukaemic cells of four APL patients with t(15;17).     

Metallothionein gene cluster is split by chromosome 16 rearrangements in myelomonocytic leukaemia

The metallothioneins (MTs) are a family of proteins of low relative molecular mass which bind heavy-metal ions. MTs exist in several molecular forms (MT-I, MT-II) and are encoded by a multi-gene family containing at least 14 closely related genes and pseudogenes. These proteins function in the regulation of trace-metal metabolism, the storage of these ions in the liver, and as a protective mechanism against heavy-metal toxicity. Somatic cell hybridization has shown that most MT genes, including the functional MT genes (MT1A, MT1B, MT2A), lie on human chromosome 16. Using in situ hybridization, we have now localized the MT genes to band q22 of chromosome 16. This chromosomal band is also a breakpoint in two specific rearrangements, the inv(16)(p13q22) and t(16; 16)(p13;q22) rearrangements, found in a subgroup of patients with acute myelomonocytic leukaemia (AMML). Hybridization of a MT probe to malignant cells from two patients with an inv(16) showed labelled sites on both arms of the inverted chromosome, indicating that the breakpoint at 16q22 splits the MT gene cluster. Similar results were obtained when this probe was hybridized to metaphase cells from two patients with a t(16; 16). These results suggest that the MT genes or their regulatory regions may function as an 'activating' sequence for an as yet unidentified cellular gene located at 16p13.     

RHD基因转录子的选择性剪切

通过RT-PCR技术分析红系细胞和非红系细胞RHD的转录情况，同时进一步比较不同D表达个体的RHD的转录关系.采用逆转录PCR（RT-PCR）技术检测HL-60,K562,Jurkat,THP-1,胚肺成纤维细胞系（HECF）,10名不同Rh表型个体的网织红细胞（CcDEe 3名,CCDEe 2名,CCDee 2名,CcDee 2名和CCDuee 1名）以及10名不同Rh表型（2 CCDEe,2 CCDee,2 ccDee,2 CcDee,ccDEe和CcDEe）个体的白细胞的RhD mRNA，然后进行cDNA测序分析.结果表明,HL-60,Jurkat,THP-1,胚肺成纤维细胞系（HECF）以及不同Rh表型个体的外周血有核细胞中除网状红细胞外皆不存在RhD mRNA，K562具有一个正常的RHD基因转录本，而不同表型个体的网织红细胞具有复杂的RhD cDNA形式，有的缺少RHD基因的外显子7,有的缺少外显子7～9或外显子4～9,但这些个体都有一个正常形式的RhD mRNA.由此得出结论,选择性剪切使RHD基因的产生多种形式的转录子，但这些不同形式的转录子仅来自红系的血细胞如网织红细胞和K562细胞系，白细胞、单核细胞、T淋巴细胞以及胚肺成纤维细胞都不具有RHD的mRNA.     

Genome-wide analysis of genetic alterations in acute lymphoblastic leukaemia

Chromosomal aberrations are a hallmark of acute lymphoblastic leukaemia (ALL) but alone fail to induce leukaemia. To identify cooperating oncogenic lesions, we performed a genome-wide analysis of leukaemic cells from 242 paediatric ALL patients using high-resolution, single-nucleotide polymorphism arrays and genomic DNA sequencing. Our analyses revealed deletion, amplification, point mutation and structural rearrangement in genes encoding principal regulators of B lymphocyte development and differentiation in 40% of B-progenitor ALL cases. The PAX5 gene was the most frequent target of somatic mutation, being altered in 31.7% of cases. The identified PAX5 mutations resulted in reduced levels of PAX5 protein or the generation of hypomorphic alleles. Deletions were also detected in TCF3 (also known as E2A), EBF1, LEF1, IKZF1 (IKAROS) and IKZF3 (AIOLOS). These findings suggest that direct disruption of pathways controlling B-cell development and differentiation contributes to B-progenitor ALL pathogenesis. Moreover, these data demonstrate the power of high-resolution, genome-wide approaches to identify new molecular lesions in cancer.     

Localization of gene for human p53 tumour antigen to band 17p13

Recently the gene for the cellular tumour antigen p53, a phosphoprotein found in increased concentration in a variety of human cells, had been mapped to region 17q22 by in situ hybridization techniques and has been shown to translocate to the chromosome carrying the translocation [t(15; 17)] associated with acute promyelocytic leukaemia (APL). Based on this finding it has been postulated that this gene has a role in the pathogenesis of APL. Here we present evidence that the gene for p53 is not located on the long arm of chromosome 17, but maps to band 17p13. We therefore suggest that this gene is not directly involved in the chromosome translocation observed in APL.     

T—ALL／淋巴瘤中BCL11B基因转录本的分析

目的:分析T-ALL/淋巴瘤中BCL11B基因转录本的特点。方法:利用逆转录聚合酶链式反应(RT-PCR)和实时定量聚合酶链式反应(RQ-PCR)方法分析12例T-ALL/淋巴瘤外周血单个核细胞(PBMC)中BCL11B基因的表达情况;限制性内切酶消化确定PCR产物的特异性。结果:3例T-ALL/淋巴瘤患者中出现2种BCL11B转录本:野生型和第3外显子缺失型,其余9例均表达第3外显子缺失型的转录本。两组病人PBMC中BCL11B表达水平无显著差别(P=0.301)。结论:3例T-ALL/淋巴瘤病人中存在2种BCL11B基因转录本,但在表达水平上无明显差别。     

A novel c-abl protein product in Philadelphia-positive acute lymphoblastic leukaemia

Activation of cellular proto-oncogenes as a result of chromosomal abnormalities has been implicated in the development of some human malignancies. Perhaps one of the most striking examples of this association occurs in chronic myelogenous leukaemia, where the Philadelphia (Ph) translocation results in substitution of the 5' end of the c-abl proto-oncogene with bcr gene sequences. A unique hybrid bcr-abl message is produced. As the Ph translocation is also present in some patients with acute lymphoblastic leukaemia, we initiated studies to determine if similar genomic events occur in these two different forms of Ph-positive leukaemia. Here we report that the Ph translocation in acute lymphoblastic leukaemia can result in production of a novel aberrant c-abl protein that is distinct from the bcr-abl protein found in Ph-positive chronic myelogenous leukaemia. Our observations suggest that alternative mechanisms of activation of c-abl exist, and may be important in the development of human acute lymphoid rather than chronic myeloid malignancies.