Identification of a novel tumor suppressor gene in lymphoid neoplasms

在B细胞非霍奇金淋巴瘤的等位基因研究中，我们发现了1q、3p、6p和6q的频繁杂合性丢失(LOH)。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，一个位于D6S1721和D6S260之间(位于6p23-24)，另一个位于D6S265和D6S291之间(位于6p21)。接下来，我们开始在1Q上寻找一个新的肿瘤抑制基因。PROX1是果蝇同源盒基因的同源物，位于染色体1q32上，是我们已发现的一种常见的恶性淋巴瘤的染色体缺失性病变。虽然PROX1mRNA在正常血淋巴系统中普遍表达，但在几种血淋巴细胞系中不表达。RT-PCR法未检测到Raji细胞中PROX1的表达，但经5-azaC处理后可恢复表达。亚硫酸氢盐修饰后的核苷酸序列分析表明，PROX1在血淋巴细胞系和正常外周血单核细胞中的表达与PROX1基因内含子1的高甲基化有很好的相关性。PROX1基因突变分析显示，在5个细胞系(BALL1、HEL、THP6、RPMI8402和Jurkat)中有6个错义和/或无义突变。这些结果表明，PROX1在几种血淋巴肿瘤中失活，主要是通过DNA甲基化。这些结果有力地表明PROX1是一个新的与血淋巴肿瘤相关的抑癌基因的候选基因。由于PROX1作为肿瘤抑制因子的功能仍不确定，我们现在正在评估PROX1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.