富亮氨酸重复超家族新成员LRRC4的克隆与在脑瘤中的表达分析

在染色体7q31-32多种肿瘤杂合性丢失（loss of heterozygosity,LOH）高频区，采用表达序列标签（expressed sequence tag,EST）介导的定位候选克隆策略获得了一个定位于人染色体7q31-32的新基因（GenBank 登录号: AF196976）.该基因编码653个氨基酸，蛋白质理论pI/m:6.58/72.7 ku.它包含七个典型的LRR、一个IgC2样结构域.此外，它还包含一个N端信号肽、一个C端跨膜区.其结构特征表明它是富亮氨酸重复（leucine-rich repeat，LRR）超家族的新成员.经过人类基因组命名委员会的同意，将该基因命名为LRRC4.此外，通过序列相似性匹配还获得了定位于小鼠6号染色体的LRRC4的同源基因（GenBank 登录号: AF290542）.RNA印迹和RT-PCR检测发现LRRC4在正常人脑组织相对特异表达，而在多种原发性脑瘤表达明显下调或缺失.综合考虑LRRC4基因的序列特征及表达谱，提示LRRC4基因可能在神经系统中发挥重要作用.

Identification of LRRC4, a Novel Member of Leucine-rich Repeat (LRR) Superfamily, and Its Expression Analysis in Brain Tumor

In order to clone novel gene associated with tumor in human chromosome 7q31 32 harboring one or more tumor suppressor gene, expressed sequence tag(EST) mediated positional cloning strategy was used and a novel human brain cDNA was identified. The isolated cDNA encodes a polypeptide of 653 amino acids with a theoretical molecular mass of 72 7 ku and a calculated isoelectric point of 6 58. The deduced amino acids contains seven typical leucine rich repeats(LRRs) flanked by N and C terminal cysteine rich LRR region, one immunoglobulin C2 like domain, one signal peptide at N terminal and one transmembrane region at C terminal. Amino acid sequence of this novel gene exhibits high similarity and similar domain organization as many other LRR proteins. Analysis of this novel gene shows no significant homology to any reported genes in database of GenBank. So it is a novel member of leucine rich repeat superfamily and designated as LRRC4 according to the guide of HUGO Gene Nomenclature Committee(GenBank Accession No.AF196976). Northern Blot and RT PCR analysis revealed that normal expression of LRRC4 was highly specific for brain,whereas absent or significantly down regulated in primary brain tumors including glioma, meningioma and pituitary adenoma. In addition, mouse homology of LRRC4 has been mapped to mouse chromosome 6 by similarity analysis(GenBank Accession No.AF290542). Taking the structural properties and expression patterns into consideration, LRRC4 may play an important role in nervous system.