Chang K S, Stass S A, Chu D T, Deaven L L, Trujillo J M, Freireich E J
Division of Laboratory Medicine, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Mol Cell Biol. 1992 Feb;12(2):800-10. doi: 10.1128/mcb.12.2.800-810.1992.
A nonrandom chromosomal translocation breakpoint, t(15;17)(q22;q21), is found in almost all patients with acute promyelocytic leukemia (APL). Most of these breakpoints occur within the second intron of the retinoic acid receptor-alpha (RARA) gene. We screened a cDNA library of APL and have identified and sequenced a cDNA transcribed from the t(15;17) translocation breakpoint. The 5' end of cDNA p1715 consists of 503 bp of the RARA exon II sequence. A 1.76-kb cDNA without homology to any known gene available in GenBank was found truncated downstream. This cDNA sequence was assigned to chromosome 15 by dot blot hybridization of the flow cytometry-sorted chromosomes. We designate this fusion cDNA RARA/myl, which is different from myl/RARA reported by de The et al. (H. de The, C. Chomienne, M. Lanotte, L. Degos, and A. Dejean, Nature (London) 347:558-561, 1990). This result demonstrates that the two different types of hybrid mRNA can be transcribed from this breakpoint. We screened a non-APL cDNA library and identified a 2.8-kb myl cDNA. This cDNA is able to encode a polypeptide with a molecular weight of 78,450. Alternative splicing of the myl gene which resulted in myl proteins with different C terminals was found. Southern blot analysis of the genomic DNA isolated from 17 APL patients by using the myl DNA probe demonstrated that the myl gene in 12 samples was rearranged. Northern (RNA) blot analysis of RARA gene expression in two APL RNA samples showed abnormal mRNA species of 4.2 and 3.2 kb in one patient and of 4.8 and 3.8 kb in another patient; these were in addition to the normal mRNA species of 3.7 and 2.7-kb. The myl DNA probe detected a 2.6-kb abnormal mRNA in addition to the normal mRNA species of 3.2, 4.2, and 5.5 kb. Using the polymerase chain reaction, we demonstrated that both RARA/myl and myl/RARA were coexpressed in samples from three different APL patients. From this study, we conclude that the t(15;17) translocation breakpoint results in the transcription of two different fusion transcripts which are expected to be translated into fusion proteins.
在几乎所有急性早幼粒细胞白血病（APL）患者中都发现了一个非随机的染色体易位断点，即t(15;17)(q22;q21)。这些断点大多发生在维甲酸受体α（RARA）基因的第二个内含子内。我们筛选了APL的cDNA文库，鉴定并测序了一个从t(15;17)易位断点转录而来的cDNA。cDNA p1715的5'端由503 bp的RARA外显子II序列组成。发现一个与GenBank中任何已知基因均无同源性的1.76 kb cDNA在下游被截断。通过流式细胞术分选的染色体进行点杂交，将该cDNA序列定位到15号染色体上。我们将这个融合cDNA命名为RARA/myl，它与de The等人报道的myl/RARA不同（H. de The、C. Chomienne、M. Lanotte、L. Degos和A. Dejean，《自然》（伦敦）347:558 - 561，1990）。这一结果表明，从这个断点可以转录出两种不同类型的杂交mRNA。我们筛选了一个非APL的cDNA文库，鉴定出一个2.8 kb的myl cDNA。这个cDNA能够编码一种分子量为78,450的多肽。发现myl基因存在可变剪接，导致产生具有不同C末端的myl蛋白。用myl DNA探针对17例APL患者分离的基因组DNA进行Southern印迹分析表明，12个样本中的myl基因发生了重排。对两个APL RNA样本中RARA基因表达进行Northern（RNA）印迹分析，结果显示，一名患者中出现了4.2 kb和3.2 kb的异常mRNA种类，另一名患者中出现了4.8 kb和3.8 kb的异常mRNA种类；此外还有正常的3.7 kb和2.7 kb的mRNA种类。myl DNA探针除检测到正常的3.2 kb、4.2 kb和5.5 kb的mRNA种类外，还检测到一个2.6 kb的异常mRNA。利用聚合酶链反应，我们证明RARA/myl和myl/RARA在来自三名不同APL患者的样本中同时表达。从这项研究中，我们得出结论，t(15;17)易位断点导致两种不同融合转录本的转录，预计它们会被翻译成融合蛋白。
