Dipartimento di Medicina Sperimentale e Clinica G Salvatore, Università Magna Graecia, Campus Universitario Germaneto, 88100 Catanzaro, Italy.
Eur J Endocrinol. 2012 Mar;166(3):551-60. doi: 10.1530/EJE-11-0929. Epub 2011 Nov 30.
The aim of this study was to investigate the presence of germline mutations in the CDKN1B gene that encodes the cyclin-dependent kinase (Cdk) inhibitor p27 in multiple endocrine neoplasia 1 (MEN1)-like Spanish index patients. The CDKN1B gene has recently been identified as a tumor susceptibility gene for MEN4, with six germline mutations reported so far in patients with a MEN-like phenotype but negative for MEN1 mutations.
Fifteen Spanish index cases with MEN-like symptoms were screened for mutations in the CDKN1B gene and the mutant variant was studied functionally by transcription/translation assays in vitro and in transiently transfected HeLa cells.
We report the identification of a heterozygous GAGA deletion in the 5'-UTR of CDKN1B, NM_004064.3:c.-32_-29del, in a patient affected by gastric carcinoid tumor and hyperparathyroidism. This deletion falls inside the region that is responsible for CDKN1B transcription and is predicted to destroy a secondary stem and loop structure that includes the GAGAGA element responsible for ribosome recruitment. Accordingly, in vitro studies of coupled transcription/translation assays and transient transfection in HeLa cells showed that the GAGA deletion in the CDKN1B 5'-UTR significantly impairs the transcription of downstream reporter luciferase (of ∼40-60%) and, possibly, the translation of the corresponding mRNA. This mutation was associated with a significant reduction in the amount of CDKN1B mRNA in peripheral blood leukocytes from the patient, as demonstrated by quantitative real-time PCR.
Our results confirm that germline CDKN1B mutations may predispose to a human MEN4 condition and add novel evidence that alteration in the transcription/translation rate of CDKN1B mRNA might be the mechanism implicated in tumor susceptibility.
本研究旨在探讨编码细胞周期蛋白依赖性激酶（Cdk）抑制剂 p27 的 CDKN1B 基因是否存在种系突变，这些突变与 1 型多发性内分泌肿瘤（MEN1）样西班牙索引患者有关。最近，CDKN1B 基因被鉴定为 MEN4 的肿瘤易感性基因，迄今为止，已有 6 种种系突变报告发生在 MEN 样表型但 MEN1 突变阴性的患者中。
对 15 例具有 MEN 样症状的西班牙索引病例进行 CDKN1B 基因突变筛查，并通过体外转录/翻译试验和瞬时转染 HeLa 细胞研究突变的功能。
我们报告了在患有胃类癌和甲状旁腺功能亢进的患者中，CDKN1B 基因 5'-UTR 中的 GAGA 缺失，NM_004064.3:c.-32_-29del，杂合子。该缺失位于负责 CDKN1B 转录的区域内，预计会破坏包括负责核糖体募集的 GAGAGA 元件的二级茎环结构。因此，体外 coupled transcription/translation 试验和 HeLa 细胞瞬时转染研究表明，CDKN1B 5'-UTR 中的 GAGA 缺失显著降低下游报告荧光素酶的转录（约 40-60%），并可能降低相应 mRNA 的翻译。该突变与患者外周血白细胞中 CDKN1B mRNA 量的显著减少有关，这一点通过定量实时 PCR 得到证实。
我们的结果证实，种系 CDKN1B 突变可能导致人类 MEN4 状态，并提供新的证据表明，CDKN1B mRNA 的转录/翻译率的改变可能是肿瘤易感性的机制。
