Okuda T, Shurtleff S A, Valentine M B, Raimondi S C, Head D R, Behm F, Curcio-Brint A M, Liu Q, Pui C H, Sherr C J
Department of Pathology, St Jude Children's Research Hospital, Memphis, TN, USA.
Blood. 1995 May 1;85(9):2321-30.
The tandemly linked p16INK4aMTS1 and p15INK4b/MTS2 genes on chromosome 9, band p21 encode proteins that function as specific inhibitors of the cyclin D-dependent kinases CDK4 and CDK6. This locus undergoes frequent bi-allelic deletion in human cancer cell lines, suggesting that the encoded proteins may function as tumor suppressors. However, more recent analysis of primary tumor samples has shown a much lower frequency of abnormalities affecting this region, raising doubt over the importance of these proteins in human malignancies. Hemizygous deletions and rearrangements of chromosome 9, band p21, are among the most frequent cytogenetic abnormalities detected in pediatric acute lymphoblastic leukemia (ALL), occurring in approximately 10% of cases. To determine if the p16INK4a/p15INK4b locus might be the target of these chromosomal lesions, we analyzed both genes in primary clinical samples from 43 pediatric ALL patients using interphase fluorescence in situ hybridization, Southern blot analysis, and the polymerase chain reaction. Deletions of p16INK4a/p15INK4b were identified in 18 of 20 cases with cytogenetically observed abnormalities of 9p and 5 of 23 with apparently normal chromosomes 9p, with the majority containing bi-allelic deletions (16 homozygous/7 hemizygous). Although most homozygous deletions involved both genes, Southern blot analysis showed an interstitial deletion in a single case that was confined to p16INK4a, suggesting that p15INK4b was not the critical target gene in this case. Sequence analysis of both p16INK4a and p15INK4b in all seven cases with hemizygous deletions failed to show mutations within the coding regions of the retained alleles. In this select group of patients, deletion of p16INK4a/p15INK4b was associated with T-cell phenotype, nonhyperdiploid karyotype (< 50 chromosomes), and poor event-free survival. These findings indicate that deletion of the p16INK4a/p15INK4b locus is one of the most common genetic abnormalities so far detected in pediatric ALL, and that loss of one or more of these cell cycle kinase inhibitors is important in leukemogenesis.
位于9号染色体p21带的串联连接的p16INK4a/MTS1和p15INK4b/MTS2基因编码的蛋白质可作为细胞周期蛋白D依赖性激酶CDK4和CDK6的特异性抑制剂。该基因座在人类癌细胞系中经常发生双等位基因缺失，这表明所编码的蛋白质可能起到肿瘤抑制因子的作用。然而，最近对原发性肿瘤样本的分析显示，影响该区域的异常频率要低得多，这让人对这些蛋白质在人类恶性肿瘤中的重要性产生怀疑。9号染色体p21带的半合子缺失和重排是小儿急性淋巴细胞白血病（ALL）中最常见的细胞遗传学异常之一，约10%的病例会出现这种情况。为了确定p16INK4a/p15INK4b基因座是否可能是这些染色体病变的靶点，我们使用间期荧光原位杂交、Southern印迹分析和聚合酶链反应，对43例小儿ALL患者的原发性临床样本中的这两个基因进行了分析。在20例细胞遗传学观察到9p异常的病例中有18例以及23例9p染色体明显正常的病例中有5例发现了p16INK4a/p15INK4b的缺失，其中大多数为双等位基因缺失（16例纯合子/7例半合子）。虽然大多数纯合子缺失涉及两个基因，但Southern印迹分析显示在一个病例中存在仅限于p16INK4a的间质缺失，这表明在该病例中p15INK4b不是关键的靶基因。对所有7例半合子缺失病例中的p16INK4a和p15INK4b进行序列分析，均未在保留等位基因的编码区内发现突变。在这一特定患者群体中，p16INK4a/p15INK4b的缺失与T细胞表型、非超二倍体核型（染色体数<50条）以及无事件生存期差有关。这些发现表明，p16INK4a/p15INK4b基因座的缺失是小儿ALL中迄今为止检测到的最常见的遗传异常之一，并且这些细胞周期激酶抑制剂中一种或多种的缺失在白血病发生过程中很重要。
