Age-Related Disease Penetrance in a Large Medullary Thyroid Cancer Family With a Codon 609 RET Gene Mutation.

Background: Familial medullary thyroid cancer (MTC) is a form of type 2 multiple endocrine neoplasia in which individuals develop MTC as the sole phenotypic manifestation of their disease. A previous study has suggested that patients with familial MTC may have a later age of onset (and more indolent course) of MTC than is observed in individuals with multiple endocrine neoplasia type 2A. Methods and Results: The age-related penetrance of MRC, C-cell hyperlasia, and a positive pentagastrin test for carriers of a codon 609 mutation of the RET gene in a large MTC family was determined. Pentagastrin testing and surgical pathology findings for patients who had thyroidectomies were correlated with RET sequence analysis findings. The penetrance of this mutation for the development of MTC was 0% at age 20, 10% at age 20, 10% at age 30, 50% at age 45, and approximately 100% at age 60. The ages of onset of C-cell hyperplasia and a positive pentagastrin stimulation test were similar, and both preceded the age of onset of MTC. Carriers of the mutated gene in this family had a later age of onset of disease that has been reported for families with multiple endocrine neoplasia type 2A and 2B syndromes. Conclusions: These results may have implications for the clinical management of MTC families with a 609 mutation.

RET mutation screening in MEN2 patients and discovery of a novel mutation in a sporadic medullary thyroid carcinoma.

RET germline mutations were found to predispose to the development of three variants of multiple endocrine neoplasia type 2, MEN2A, MEN2B, and familial medullary thyroid carcinoma (FMTC). We have screened for RET mutations at exons 10, 11, 13, and 16 in leukocyte DNA extracted from 37 individuals, and have identified RET germline mutations in 12 affected individuals from 9 unrelated families. No RET germline mutation was found in 19 individuals with apparent sporadic diseases. We have also screened for RET mutations at exons 10, 11, and 16 in tumor DNA extracted from 13 freshly frozen medullary thyroid carcinomas (MTC). RET mutation was detected in every tumor, either inherited or sporadic, indicating that RET plays an important role in the development of both inherited and sporadic MTC. We initially screened for RET mutations by direct DNA sequencing of the genomic PCR products amplified from patients' leukocyte or tumor DNA. Recently, we utilized the "Cold SSCP" method, nonradioactive single-stranded conformation polymorphism analysis, to screen for RET mutations and have identified a novel mutation, a 6-bp deletion preceding the cysteine-634, in a sporadic MTC.

Characterization of the promoter region and oligomerization domain of H4 (D10S170), a gene frequently rearranged with the ret proto-oncogene.

PTC-1, the predominant form of PTC oncogene in human papillary thyroid carcinoma, encodes a fusion protein containing the N-terminus of H4 (D10S170) fused 5' to the ret tyrosine kinase domain. Accordingly, the PTC-1 expression is driven by the H4 gene promoter. Our study showed that H4 is expressed in various human tissues, including thyroid. Furthermore, we have localized the transcriptional start sites of H4 to a region 100 to 190 bp upstream of the translation initiation site (ATG) by primer extension assay, and the H4 promoter to a region within 259 bp upstream of the ATG site by luciferase assay. Interestingly, protein sequence analysis indicated a potential coiled-coil domain in the N-terminal region of H4. Indeed, oligomerization was demonstrated by an in vitro assay with recombinant proteins containing this region. As dimerization is considered to be a crucial step for receptor tyrosine kinase activation, we hypothesize that both unscheduled expression of ret tyrosine kinase and constitutive oligomerization of PTC-1 proteins are responsible for PTC-1 transforming activity in thyroid.

Thyroid peroxidase expression and DNA polymorphisms in thyroid cancer.

Using non-quantitative reverse-transcription polymerase chain reaction (RT-PCR), we found that thyroid peroxidase (TPO) is expressed in all differentiated thyroid carcinomas examined, although the ratio of the shorter to longer transcript is decreased in tumors that had lost the iodide concentrating capacity. TPO expression is lost in several thyroid carcinoma cell lines (TPC-1, 8305C, 8505C) and altered in another (TC-80). Nucleotide sequencing of the PCR products revealed missense polymorphisms in the TPO gene. Four out of five samples tested are heterozygous for TPO alleles in exon 15, showing both C and T at nucleotide 2612 (GTG coding for Val, GCG for Ala). One tumor is homozygous for T at this position. In exon 8, three samples show T at nucleotide 1189 (TCG, Ser) and C at 1265 (ACC, Thr), while most published sequences report G at both positions (GCG coding for Ala at 1189 and AGC coding for Ser at 1265).

Cloning of the human taurine transporter and characterization of taurine uptake in thyroid cells.

A cDNA clone encoding a taurine transporter, designated HTAU, has been isolated from human thyroid. It contains an open reading frame encoding a protein of 619 amino acids with a calculated molecular weight of 69,675 Da. The predicted amino acid sequence of HTAU is highly homologous to those of dog kidney and rat brain. The HTAU mRNA was detectable in various human tissues examined. Transient expression of HTAU in COS-7 cells conferred a higher taurine uptake. The taurine uptake in FRTL-5 cells appears to be regulated by thyrotropin through cAMP. Finally, a higher taurine uptake may be associated with a higher proliferation rate in some cultured cell lines.