Sakuma S, Saya H, Ijichi A, Tofilon P J
Department of Experimental Radiotherapy, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Radiat Res. 1995 Jul;143(1):1-7.
Radiation-induced gene expression was examined in rat astrocyte cultures using differential display of mRNA via reverse transcriptase-polymerase chain reaction. A 0.3-kb cDNA that was consistently observed in irradiated cultures but not in unirradiated cultures was cloned and sequenced. It was found to be identical to Ptk-3, a receptor tyrosine kinase gene identified recently. The protein encoded by Ptk-3 is a member of a novel class of receptor tyrosine kinases whose extracellular domain contains regions of homology with coagulation factors V and VIII and complement component C1. Northern blot analysis revealed that the expression of Ptk-3 was increased in rat astrocytes by 0.5 h after exposure to 10 Gy and remained at the same elevated level for at least 24 h. The maximum increase occurred after 5 Gy. Cloning studies indicated the presence of at least two Ptk-3 mRNA transcripts, which are probably the result of an alternative splicing mechanism. The short isoform lacks a 37-amino acid sequence in the glycine/proline-rich juxtamembrane region. The splicing pattern of the Ptk-3 gene was not altered by radiation. However, the ratios of the longer to the shorter mRNA transcripts differed between adult cortex, neonatal cortex and in vitro astrocyte cultures.
利用逆转录-聚合酶链反应对mRNA进行差异显示，在大鼠星形胶质细胞培养物中检测辐射诱导的基因表达。克隆并测序了一个在辐照培养物中始终可见但在未辐照培养物中未见的0.3kb cDNA。发现它与最近鉴定的受体酪氨酸激酶基因Ptk-3相同。Ptk-3编码的蛋白质是一类新型受体酪氨酸激酶的成员，其细胞外结构域包含与凝血因子V和VIII以及补体成分C1具有同源性的区域。Northern印迹分析显示，暴露于10 Gy后0.5小时，大鼠星形胶质细胞中Ptk-3的表达增加，并在至少24小时内保持在相同的升高水平。最大增加发生在5 Gy之后。克隆研究表明存在至少两种Ptk-3 mRNA转录本，这可能是选择性剪接机制的结果。短异构体在富含甘氨酸/脯氨酸的近膜区域缺少一个37个氨基酸的序列。Ptk-3基因的剪接模式不受辐射影响。然而，较长和较短mRNA转录本的比例在成年皮质、新生皮质和体外星形胶质细胞培养物之间有所不同。
