Identification of a novel tumor suppressor gene in lymphoid neoplasms

我们在B细胞非霍奇金淋巴瘤等位基因型研究中发现了1 q、3 p、6p和6 q的杂合性丢失（洛）。我们对6p进行了精细的缺失定位，发现了两个常见的缺失区域，一个是D 6S 1721和D 6S 260之间（6p 23 -24），另一个是D 6S 265和D 6S 291之间（6p 21）。接下来，我们开始在1 q上寻找新的肿瘤抑制基因。PROX 1是果蝇同源异型盒基因的同源物，位于染色体1 q32，是我们发现的恶性淋巴瘤中常见的染色体缺失病变。虽然PROX 1 mRNA在正常血淋巴系统中广泛表达，但在几种血淋巴细胞系中不表达。RT-PCR检测不到Raji细胞中PROX 1的表达，但5-AzaC处理后PROX 1的表达恢复。亚硫酸氢盐修饰后的核苷酸序列分析显示，PROX 1在血淋巴细胞系和正常外周血单个核细胞中的表达与PROX 1基因内含子1的高甲基化密切相关。PROX 1基因的突变分析在5个细胞系（BALL 1、HEL、THP 6、RPMI 8402和Jurkat）中发现了6个缺失和/或无义突变。这些结果表明，PROX 1在几种血淋巴样肿瘤中失活，主要是通过DNA甲基化。这些结果有力地表明PROX 1是一个新的候选抑癌基因，与血淋巴肿瘤。由于PROX 1作为肿瘤抑制因子的功能仍然不确定，我们现在正在评估PROX 1对细胞生长或转化的功能。

We have identified frequent loss of heterozygosity (LOH) at 1q, 3p, 6p, and 6q in B-cell non-Hodgkin lymphomaby allelotype studies. We have conducted fine deletion mapping on 6p and identified two common deleted regions, one is between D6S1721 and D6S260 (at 6p23-24), and the other between D6S265 and D6S291 (at 6p21). Next we started a search for a novel tumor suppressor gene on 1q. PROX1, a homologue of Drosophilla homeobox gene, is located on chromosome 1q32, which is a common chromosomal deleted lesion in malignant lymphoma that we have identified. Although PROX1 mRNA is ubiquitously expressed in normal hematolymphoid systems, it was not expressed in several hematolymphoid cell lines. PROX1 expression in Raji cell was not detected by RT-PCR method, but it was restored after 5-AzaC treatment. Nucleotide sequence analysis after bisulfite modification revealed that PROX1 expression in hematolymphoid cell lines and normal peripheral blood mononuclear cells was correlated very well with hypermethylation in intron 1 of PROX1 gene. Mutational analyses of PROX1 gene have revealed 6 missence and/or nonsense mutations in 5 cell lines (BALL1, HEL, THP6, RPMI8402 and Jurkat). These results indicated that PROX1 is inactivated in several hematolymphoid neoplasms, mainly by DNA methylation. These results strongly suggested that PROX1 is a novel candidate for tumor suppressor gene that is related to hematolymhoid neoplasms. Since PROX1 function as a tumor suppressor is still uncertain, we are now evaluating PROX1 functions on cellular growth or transformation.