Somatic VHL gene alterations in MEN2-associated medullary thyroid carcinoma.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Koch
Christian A
CA
Division of Endocrinology and Nephrology, University of Leipzig, Philipp-Rosenthalstr, 27, 04103 Leipzig, Germany. ckoch@medicine.umsmed.edu
Brouwers
Frederieke M
FM
Vortmeyer
Alexander O
AO
Tannapfel
Andrea
A
Libutti
Steven K
SK
Zhuang
Zhengping
Z
Pacak
Karel
K
Neumann
Hartmut P H
HP
Paschke
Ralf
R
D018276:Carcinoma, Medullary / Q000235:genetics* / Q000503:physiopathology*; D004252:DNA Mutational Analysis; D018450:Disease Progression; D018095:Germ-Line Mutation; D006801:Humans; D019656:Loss of Heterozygosity; D018813:Multiple Endocrine Neoplasia Type 2a / Q000150:complications / Q000235:genetics; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000503:physiopathology*; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics*
D051794:Von Hippel-Lindau Tumor Suppressor Protein; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; C497446:VHL protein, human