Chase A, Reiter A, Burci L, Cazzaniga G, Biondi A, Pickard J, Roberts I A, Goldman J M, Cross N C
Department of Haematology, Imperial College School of Medicine, Hammersmith Hospital, London, UK.
Blood. 1999 Feb 1;93(3):1025-31.
The t(12;13)(p13;q12) is a rare, recurrent translocation reported in a range of hematological malignancies. We have analyzed the molecular basis of this lesion in three patients with acute myeloid leukemia (AML), two of whom were known to have chromosome 12 breakpoints within the ETV6 gene. Fluorescence in situ hybridization (FISH) with ETV6 cosmids indicated that this gene was also disrupted in the third patient, while the normal ETV6 allele was retained. 3' rapid amplification of cDNA ends (RACE) polymerase chain reaction (PCR) from bone marrow mRNA of this individual identified a novel sequence fused to ETV6 that was homologous to a region just upstream of the mouse CDX2 homeobox gene, the human homologue of which has previously been mapped to chromosome 13q12. PCR primers designed to amplify an ETV6-CDX2 fusion identified two major transcripts from this patient. First, a direct in-frame fusion between exon 2 of ETV6 and exon 2 of CDX2, and second, a transcript that had an additional sequence of unknown origin spliced between these same exons. Surprisingly, apparently normal CDX2 transcripts, usually expressed only in intestinal epithelium, were also detectable in cDNA from this patient. Neither normal nor fusion CDX2 mRNA was detectable in the two other patients with a t(12;13), indicating that this translocation is heterogeneous at the molecular level. Reverse transcription-PCR analysis showed that CDX2 mRNA, but not ETV6-CDX2 mRNA, was strongly expressed in 1 of 10 patients with chronic myeloid leukemia in transformation, suggesting that deregulation of this gene may be more widespread in leukemia. CDX2 is known to regulate class I homeobox genes and its expression in hematopoietic cells may critically alter the balance between differentiation and proliferation.
t(12;13)(p13;q12)是一种罕见的、复发性易位，在一系列血液系统恶性肿瘤中均有报道。我们分析了3例急性髓系白血病（AML）患者中该病变的分子基础，其中2例已知在ETV6基因内有12号染色体断点。用ETV6黏粒进行荧光原位杂交（FISH）表明，该基因在第3例患者中也被破坏，而正常的ETV6等位基因得以保留。从该个体的骨髓mRNA进行3' cDNA末端快速扩增（RACE）聚合酶链反应（PCR），鉴定出一个与ETV6融合的新序列，该序列与小鼠CDX2同源框基因上游的一个区域同源，其人同源物先前已定位到13号染色体q12。设计用于扩增ETV6 - CDX2融合体的PCR引物，从该患者中鉴定出两种主要转录本。首先，是ETV6的外显子2与CDX2的外显子2之间的直接读码框融合，其次，是在这些相同外显子之间拼接了一个额外的未知来源序列的转录本。令人惊讶的是，通常仅在肠上皮中表达的明显正常的CDX2转录本，在该患者的cDNA中也可检测到。另外2例有t(12;13)的患者中，正常和融合的CDX2 mRNA均未检测到，表明这种易位在分子水平上是异质性的。逆转录 - PCR分析显示，在10例转化中的慢性髓系白血病患者中有1例强烈表达CDX2 mRNA，但不表达ETV6 - CDX2 mRNA，提示该基因的失调在白血病中可能更为普遍。已知CDX2调节I类同源框基因，其在造血细胞中的表达可能会严重改变分化与增殖之间的平衡。
