Koch Christian A, Brouwers Frederieke M, Vortmeyer Alexander O, Tannapfel Andrea, Libutti Steven K, Zhuang Zhengping, Pacak Karel, Neumann Hartmut P H, Paschke Ralf
Division of Endocrinology and Nephrology, University of Leipzig, Philipp-Rosenthalstr, 27, 04103 Leipzig, Germany.
BMC Cancer. 2006 May 17;6:131. doi: 10.1186/1471-2407-6-131.
Germline mutations in RET are responsible for multiple endocrine neoplasia type 2 (MEN2), an autosomal dominantly inherited cancer syndrome that is characterized by medullary thyroid carcinoma (MTC), pheochromocytoma, and parathyroid hyperplasia/adenoma. Recent studies suggest a "second hit" mechanism resulting in amplification of mutant RET. Somatic VHL gene alterations are implicated in the pathogenesis of MEN2 pheochromocytomas. We hypothesized that somatic VHL gene alterations are also important in the pathogenesis of MEN2-associated MTC.
We analyzed 6 MTCs and 1 C-cell hyperplasia (CCH) specimen from 7 patients with MEN2A and RET germline mutations in codons 609, 618, 620, or 634, using microdissection, microsatellite analysis, phosphorimage densitometry, and VHL mutation analysis.
First, we searched for allelic imbalance between mutant and wild-type RET by using the polymorphic markers D10S677, D10S1239, and RET on thyroid tissue from these patients. Evidence for RET amplification by this technique could be demonstrated in 3 of 6 MTCs. We then performed LOH analysis using D3S1038 and D3S1110 which map to the VHL gene locus at 3p25/26. VHL gene deletion was present in 3 MTCs. These 3 MTCs also had an allelic imbalance between mutant and wild-type RET. Mutation analysis of the VHL gene showed a somatic frameshift mutation in 1 MTC that also demonstrated LOH at 3p25/26. In the 2 other MTCs with allelic imbalance of RET and somatic VHL gene deletion, no somatic VHL mutation could be detected. The CCH specimen did neither reveal RET imbalance nor somatic VHL gene alterations.
These data suggest that a RET germline mutation is necessary for development of CCH, that allelic imbalance between mutant and wild-type RET may set off tumorigenesis, and that somatic VHL gene alterations may not play a major role in tumorigenesis of MEN2A-associated MTC.
RET基因的种系突变导致2型多发性内分泌肿瘤（MEN2），这是一种常染色体显性遗传癌症综合征，其特征为甲状腺髓样癌（MTC）、嗜铬细胞瘤和甲状旁腺增生/腺瘤。最近的研究提示一种导致突变RET扩增的“二次打击”机制。体细胞VHL基因改变与MEN2嗜铬细胞瘤的发病机制有关。我们推测体细胞VHL基因改变在MEN2相关MTC的发病机制中也很重要。
我们使用显微切割、微卫星分析、荧光图像密度测定法和VHL突变分析，对7例患有MEN2A且RET种系突变发生在密码子609、618、620或634的患者的6个MTC和1个C细胞增生（CCH）标本进行了分析。
首先，我们使用多态性标记D10S677、D10S1239和RET，在这些患者的甲状腺组织中寻找突变型和野生型RET之间的等位基因失衡。通过该技术可在6个MTC中的3个中证实RET扩增的证据。然后我们使用定位于3p25/26的VHL基因座的D3S1038和D3S1110进行杂合性缺失（LOH）分析。3个MTC中存在VHL基因缺失。这3个MTC在突变型和野生型RET之间也存在等位基因失衡。VHL基因的突变分析显示1个MTC中存在体细胞移码突变，该MTC在3p25/26处也显示出LOH。在另外2个具有RET等位基因失衡和体细胞VHL基因缺失的MTC中，未检测到体细胞VHL突变。CCH标本既未显示RET失衡，也未显示体细胞VHL基因改变。
这些数据提示，CCH的发生需要RET种系突变，突变型和野生型RET之间的等位基因失衡可能引发肿瘤发生，而体细胞VHL基因改变可能在MEN2A相关MTC的肿瘤发生中不发挥主要作用。
