Reduction in membranous immunohistochemical staining for the intracellular domain of epithelial cell adhesion molecule correlates with poor patient outcome in primary colorectal adenocarcinoma

BACKGROUND

Epithelial cell adhesion molecule (epcam) is a multifunctional transmembrane glycoprotein expressed on both normal epithelium and epithelial neoplasms such as gastric, breast, and renal carcinomas. Recent studies have proposed that the proteolytic cleavage of the intracellular domain of epcam (epcam-icd) can trigger signalling cascades leading to aggressive tumour behavior. The expression profile of epcam-icd has not been elucidated for primary colorectal carcinoma. In the present study, we examined epcam-icd immunohistochemical staining in a large cohort of patients with primary colorectal adenocarcinoma and assessed its performance as a potential prognostic marker.

METHODS

Immunohistochemical staining for epcam-icd was assessed on tissue microarrays consisting of 137 primary colorectal adenocarcinoma samples. Intensity of staining for each core was scored by 3 independent pathologists. The membranous epcam-icd staining score was calculated as a weighted average from 3 core samples per tumour. Univariate analysis of the average scores and clinical outcome measures was performed.

RESULTS

The level of membranous epcam-icd staining was positively associated with well-differentiated tumours (p = 0.01); low preoperative carcinoembryonic antigen (p = 0.001); and several measures of survival, including 2-year (p = 0.02) and 5-year survival (p = 0.05), and length of time post-diagnosis (p = 0.03). A number of other variables-including stage, grade, and lymph node status-showed correlations with epcam staining and markers of poor outcome, but did not reach statistical significance.

CONCLUSIONS

Low membranous epcam-icd staining might be a useful marker to identify tumours with aggressive clinical behavior and potential poor prognosis and might help to select candidates who could potentially benefit from treatment targeting epcam.

RET ligand-induced internalization and its consequences for downstream signaling

RET is a receptor tyrosine kinase (RTK) with roles in cell growth, differentiation and survival. Ligand-induced activation of RET results in stimulation of multiple signal transduction pathways, including the MAP kinase/Erk and PI3 kinase/Akt pathways. However, the mechanisms governing receptor internalization and signal down- regulation have not been explored. As other RTKs are internalized through the clathrin-coated pit pathway in a ligand-dependant manner, we have investigated whether RET is internalized through a similar process. Using a highly sensitive fluorescence resonance energy transfer (FRET)-based assay, we have shown that RET is internalized from the plasma membrane in a ligand-dependant manner that requires RET kinase activity as well as the GTPase activity of the clathrin-coated vesicle scission protein dynamin 2. Further, we have demonstrated that RET colocalizes with Rab5a, a marker of clathrin-coated vesicles and early endosomes, after internalization. Finally, we demonstrated that RET internalization is required for complete activation of Erk1/2, but not for activation of Akt signaling. Our data suggest that ligand-induced internalization of RET not only plays an overall role in downregulation and termination of signaling, but also functions to traffic RET to subcellular locations where it can fully activate certain downstream signaling pathways.

Conservation of RET proto-oncogene splicing variants and implications for RET isoform function

The RET proto-oncogene encodes a receptor tyrosine kinase required for development of the kidney and neural crest-derived cell types. Alternative splicing of the 3' exons of human RET results in three protein isoforms with distinct C-termini: RET9, RET51, and RET43. These RET isoforms show differential binding to downstream adapter molecules, suggesting they may have distinct signaling functions. We have characterized Ret 3' sequences in mouse and investigated alternative splicing of this region. We found that the organization of Ret 3' sequences is very similar to human RET. The mouse locus also has alternatively spliced C-terminal coding regions, and the sequences corresponding to RET9 and RET51 are highly conserved in both position and sequence with the human locus. Further, we compared the predicted C-terminal amino acids of RET9 and RET51 in seven vertebrate species, and found that they are well conserved. We have identified sequence encoding a putative ret43 isoform in mouse, however the predicted amino acid sequence showed low homology to human RET43. Our data suggest that RET isoforms are evolutionarily highly conserved over a broad range of species, which may indicate that each isoform has a distinct role in normal RET function.

Reconsideration of biallelic inactivation of the VHL tumour suppressor gene in hemangioblastomas of the central nervous system

OBJECTIVES

Cerebellar haemangioblastoma occurs sporadically or as a component tumour of autosomal dominant von Hippel-Lindau disease. Biallelic inactivation of the VHL tumour suppressor gene, which is located on chromosome 3p, has been shown to be involved in the pathogenesis of both tumour entities. Mechanisms of VHL inactivation are intragenic mutations, mitotic recombination events, and hypermethylation of the promoter region. The systematic and complete examination of these genetic and epigenetic phenomena in large series of von Hippel-Lindau disease related and sporadic hemangioblastomas has, thus far, not been performed.

METHODS

In the largest series to date, 29 von Hippel-Lindau disease associated and 13 sporadic haemangioblastomas were investigated for all suggested inactivating mechanisms of the VHL gene using single strand conformational polymorphism (SSCP), loss of heterozygosity (LOH), and methylation analyses. Additionally, corresponding blood samples of all patients were screened for VHL germline mutations by SSCP and Southern blotting.

RESULTS

Germline mutations were identified in 94% of patients with von Hippel-Lindau disease and their tumours and 62% of these hemangioblastomas showed LOH of chromosome 3p. Of the 13 sporadic tumours, 23% showed a single somatic mutation of the VHL gene that was not present in the germline. 3p LOH was identified in 50% of informative sporadic tumours. No von Hippel-Lindau disease related or sporadic tumour demonstrated VHL promoter hypermethylation.

CONCLUSIONS

For most von Hippel-Lindau disease related haemangioblastomas, the inactivation or loss of both alleles of the VHL gene, as predicted by the Knudson two hit theory, is required. However, in a subset of tumours including most sporadic haemangioblastomas, the genetic pathways involved in tumorigenesis have yet to be defined and may represent alterations of a different pathway or pathways.

Cloning and characterization of the human GFRA2 locus and investigation of the gene in Hirschsprung disease

The glial-cell-line-derived neurotrophic factor (GDNF) family receptors alpha (GFRalpha) are cell surface bound glycoproteins that mediate interactions of the GDNF ligand family with the RET receptor. These interactions are crucial to the development of the kidney and some peripheral nerve lineages. In humans, mutations of RET or RET ligands are associated with the congenital abnormality Hirschsprung disease (HSCR) in which nerves and ganglia of the hind gut are absent. As the GFRalpha family are required for normal activation of the RET receptor, they are also candidates for a role in HSCR. The GFRA2 gene, which is required for the development of the myenteric nerve plexus, is an excellent candidate gene for HSCR. In this study, we cloned the human GFRA2 locus, characterized the gene structure, and compared it with other GFRA family members. We further investigated the GFRA2 gene for mutations in a panel of HSCR patients. GFRA2 has nine coding exons that are similar in size and organization to those of other GFRA family genes. We identified six sequence variants of GFRA2, four of which did not affect the amino acid sequence of the GFRalpha-2 protein. Two further changes that resulted in amino acid substitutions were found in exon 9 and were predicted to lie in the amino acid sequence encoding the glycosylphosphatidylinositol-linkage signal of GFRalpha-2. There was no difference in frequency of any of the sequence variants between control and HSCR populations. Our data indicate that members of the GFRA gene family are closely related in intron/exon structure and in sequence. We have not detected any correlation between sequence variants of GFRA2 and the HSCR phenotype.

Over-representation of a germline variant in the gene encoding RET co-receptor GFRα-1 but not GFRα-2 or GFRα-3 in cases with sporadic medullary thyroid carcinoma

In contrast to the hereditary form of medullary thyroid carcinoma (MTC), little is known about the etiology of sporadic MTC. Somatic gain-of-function mutations in the RET proto-oncogene, encoding a receptor tyrosine kinase, are found in an average of 40% of sporadic MTC. We analysed 31 sporadic MTC for somatic and germline variants in GFRA1, GFRA2 and GFRA3 which encode the co-receptors of RET. Although there were no somatic mutations in any of the three genes, a sequence variant (-193C>G) in the 5'-UTR of GFRA1 was found in 15% of cases. Three patients were heterozygous (het); another three patients homozygous (hom) for the G variant. The G allele was not observed in 31 race-matched normal controls. Hence, the relative frequency of this variant in sporadic MTC cases and controls differed significantly (P<0.05). Since this variant lies in the 5' UTR, likely at the transcriptional start site, we analysed for differential expression of GFRalpha-1 at the transcript and protein levels. At the mRNA level, GFRA1 was over-expressed in tumors harboring the rare variant (P=0.06). The presence of the G polymorphic allele seemed to be associated with increased expression by immunostaining for GFRalpha-1. Interestingly, cytoplasmic staining was stronger in intensity for het patients and nuclear staining predominant in hom cases. In conclusion, mutation analysis of GFRA1, GFRA2 and GFRA3 revealed over-representation of a rare variant in GFRA1 (-193C>G) in the germline of sporadic MTC cases. Our data suggest that the mechanism is related to over-expression of GFRalpha-1 and differential subcellular compartmentalization but the precise mechanism as to how it acts as a low penetrance susceptibility allele for the development of sporadic MTC remains to be elucidated.

Multiple endocrine neoplasia type 2 and RET: from neoplasia to neurogenesis

Multiple endocrine neoplasia type 2 (MEN 2) is an inherited cancer syndrome characterised by medullary thyroid carcinoma (MTC), with or without phaeochromocytoma and hyperparathyroidism. MEN 2 is unusual among cancer syndromes as it is caused by activation of a cellular oncogene, RET. Germline mutations in the gene encoding the RET receptor tyrosine kinase are found in the vast majority of MEN 2 patients and somatic RET mutations are found in a subset of sporadic MTC. Further, there are strong associations of RET mutation genotype and disease phenotype in MEN 2 which have led to predictions of tissue specific requirements and sensitivities to RET activity. Our ability to identify genetically, with high accuracy, subjects with MEN 2 has revolutionised our ability to diagnose, predict, and manage this disease. In the past few years, studies of RET and its normal ligand and downstream interactions and the signalling pathways it activates have clarified our understanding of the roles played by RET in normal cell survival, proliferation, and differentiation, as well as in disease. Here, we review the current knowledge of the normal functions of RET and the effects of mutations of this gene in tumorigenesis and in normal development.

Sp1 and Sp3 transactivate the RET proto-oncogene promoter

The RET proto-oncogene plays an important role in the initiation and progression of tumors derived from the neural crest. The cis-regulatory elements responsible for RET basal promoter activity have not been identified. To characterize these elements, a RET promoter DNA fragment (-453 to +227bp) was fused to a luciferase reporter and introduced into TT, a neural crest-derived cell line. Sequential 5' deletions of the promoter revealed that optimal expression of the RET promoter in TT cells required only 70bp of sequence upstream of the transcription start site, and contains two Sp1 binding sites. DNase I footprinting, electrophoretic mobility shift analysis (EMSA), and supershift assays revealed that this region binds both Sp1 and its related protein, Sp3. Additionally, RET basal promoter activity was abrogated by removal of these Sp1/Sp3 binding sites. The proximal two GC boxes were sufficient to allow transactivation of the RET promoter in Drosophila SL2 cells. Sp3 expression in these cells caused an additional activation of the promoter. These results demonstrate that the transactivation of the RET promoter within a neural crest-derived cell line is dependent on Sp1 and Sp3.

Characterisation of the human GFRalpha-3 locus and investigation of the gene in Hirschsprung disease

BACKGROUND

The GDNF family receptor alpha (GFRalpha) proteins are extracellular cell surface bound molecules that act as adapters in binding of the GDNF family of soluble neurotrophic factors to the RET receptor. These molecules are essential for development of many neural crest derived cell types and the kidney. Mutations in RET and in two members of the GDNF ligand family are associated with Hirschsprung disease (HSCR), a congenital absence of the enteric ganglia. Members of the GFRalpha family are also candidates for HSCR mutations. One such gene is GFRalpha-3, which is expressed in the peripheral nervous system and developing nerves.

OBJECTIVE

We have characterised the structure of the human GFRalpha-3 locus and investigated the gene for sequence variants in a panel of HSCR patients.

METHODS

Long range PCR or subcloning of PAC clones was used to investigate GFRalpha-3 intron-exon boundaries. A combination of single strand conformation polymorphism (SSCP) analysis and direct sequencing was used to investigate GFRalpha-3 sequence variants.

RESULTS

GFRalpha-3 spans eight coding exons and has a gene structure and organisation similar to that of GFRalpha-1. We identified three polymorphic variants in GFRalpha-3 in a normal control population, a subset of which also occurred in HSCR patients. We did not detect any sequence variants within the coding sequence of GFRalpha-3. We found a base substitution in the 5' UTR of GFRalpha-3, 15 base pairs upstream of the translation start site. A second substitution was identified in intron 4 (IVS4-30G>A) between the splice branch site and the splice acceptor site. The final variant was a 2 base pair insertion within the splice donor consensus sequence of exon 7 (IVS7+4ins GG).

CONCLUSIONS

We did not detect any correlation between variants of GFRalpha-3 and the HSCR phenotype. Our data suggest that mutations of this gene are not a cause of HSCR.

Mutations of the RET proto-oncogene in the multiple endocrine neoplasia type 2 syndromes, related sporadic tumours, and hirschsprung disease

The RET proto-oncogene codes for a receptor tyrosine kinase thought to play a role in the development of neural crest and its derivatives. Mutations in the RET proto-oncogene have been found in patients with the multiple endocrine neoplasia type 2 syndromes (MEN 2), the related sporadic tumours medullary thyroid carcinoma and pheochromocytoma, and familial and sporadic Hirschsprung disease, a syndrome of congenital absence of enteric innervation. Germline mutations in one of eight codons within RET cause the three subtypes of MEN 2, namely, MEN 2A, MEN 2B, and familial medullary thyroid carcinoma. Somatic mutation in an overlapping group of nine codons have been found in a proportion of sporadic medullary thyroid carcinoma and pheochromocytoma. In contrast to MEN 2, approximately 25% of patients with Hirschsprung disease have germline mutations scattered throughout the length of RET.

Immunohistochemical evidence of loss of PTEN expression in primary ductal adenocarcinomas of the breast

Germline mutations in PTEN, encoding a dual-specificity phosphatase on 10q23.3, cause Cowden syndrome (CS), which is characterized by a high risk of breast and thyroid cancers. Loss of heterozygosity of 10q22-24 markers and somatic PTEN mutations have been found to a greater or lesser extent in a variety of sporadic component and noncomponent cancers of CS. Among several series of sporadic breast carcinomas, the frequency of loss of flanking markers around PTEN is approximately 30 to 40%, and the somatic intragenic PTEN mutation frequency is <5%. In this study, we analyzed PTEN expression in 33 sporadic primary breast carcinoma samples using immunohistochemistry and correlated this to structural studies at the molecular level. Normal mammary tissue had a distinctive pattern of expression: myoepithelial cells uniformly showed strong PTEN expression. The PTEN protein level in mammary epithelial cells was variable. Ductal hyperplasia with and without atypia exhibited higher PTEN protein levels than normal mammary epithelial cells. Among the 33 carcinoma samples, 5 (15%) were immunohistochemically PTEN-negative; 6 (18%) had reduced staining, and the rest were PTEN-positive. In the PTEN-positive tumors as well as in normal epithelium, the protein was localized in the cytoplasm and in the nucleus (or nuclear membrane). Among the immunostain negative group, all had hemizygous PTEN deletion but no structural alteration of the remaining allele. Thus, in these cases, an epigenetic phenomenon such as hypermethylation, -ecreased protein synthesis or increased protein degradation may be involved. In the cases with reduced staining, 5 of 6 had hemizygous PTEN deletion and 1 did not have any structural abnormality. Finally, clinicopathological features were analyzed against PTEN protein expression. Three of the 5 PTEN immunostain-negative carcinomas were also both estrogen and progesterone receptor-negative, whereas only 5 of 22 of the PTEN-positive group were double receptor-negative. The significance of this last observation requires further study.

Mutation and deletion analysis of GFR alpha-1, encoding the co-receptor for the GDNF/RET complex, in human brain tumours

Glial cell line-derived neurotrophic factor (GDNF) plays a key role in the control of vertebrate neuron survival and differentiation in both the central and peripheral nervous systems. GDNF preferentially binds to GFRalpha-1 which then interacts with the receptor tyrosine kinase RET. We investigated a panel of 36 independent cases of mainly advanced sporadic brain tumours for the presence of mutations in GDNF and GFRalpha-1. No mutations were found in the coding region of GDNF. We identified six previously described GFRalpha-1 polymorphisms, two of which lead to an amino acid change. In 15 of 36 brain tumours, all polymorphic variants appeared to be homozygous. Of these 15 tumours, one also had a rare, apparently homozygous, sequence variant at codon 361. Because of the rarity of the combination of homozygous sequence variants, analysis for hemizygous deletion was pursued in the 15 samples and loss of heterozygosity was found in 11 tumours. Our data suggest that intragenic point mutations of GDNF or GFRalpha-1 are not a common aetiologic event in brain tumours. However, either deletion of GFRalpha-1 and/or nearby genes may contribute to the pathogenesis of these tumours.

Investigation of germline GFR alpha-1 mutations in Hirschsprung disease

Inactivating mutations of the RET proto-oncogene and of one of its soluble ligand molecules, glial cell line derived neurotrophic factor (GDNF), have been found in a subset of patients with Hirschsprung disease (HSCR). However, the majority of HSCR mutations remain unidentified. As normal RET function requires a multicomponent ligand complex for activation, other members of the RET ligand complex are primary candidates for these mutations. We investigated the presence of mutations in another member of the RET signalling complex, GDNF family receptor alpha-1 (GFR alpha-1), in a panel of 269 independent cases of HSCR. We identified 10 polymorphisms at the GFR alpha-1 locus. Surprisingly, however, we did not identify any sequence variants in our HSCR population that were not also present in a normal control population. Our data suggest that mutations of the GFR alpha-1 gene are not a common aetiological event in HSCR.

Analysis of the 10q23 chromosomal region and the PTEN gene in human sporadic breast carcinoma

We examined a panel of sporadic breast carcinomas for loss of heterozygosity (LOH) in a 10-cM interval on chromosome 10 known to encompass the PTEN gene. We detected allele loss in 27 of 70 breast tumour DNAs. Fifteen of these showed loss limited to a subregion of the area studied. The most commonly deleted region was flanked by D10S215 and D10S541 and encompasses the PTEN locus. We used a combination of denaturing gradient gel electrophoresis and single-strand conformation polymorphism analyses to investigate the presence of PTEN mutations in tumours with LOH in this region. We did not detect mutations of PTEN in any of these tumours. Our data show that, in sporadic breast carcinoma, loss of heterozygosity of the PTEN locus is frequent, but mutation of PTEN is not. These results are consistent with loss of another unidentified tumour suppressor in this region in sporadic breast carcinoma.

Mutation of the RET proto-oncogene is correlated with RET immunostaining in subpopulations of cells in sporadic medullary thyroid carcinoma

Mutations in the RET proto-oncogene, which encodes a receptor tyrosine kinase, are associated with the pathogenesis of medullary thyroid carcinoma (MTC). Somatic mutations in RET, predominantly at codon 918, and very rarely at codon 883, have been found in a proportion of sporadic MTC. We have previously shown that approximately 80% of sporadic MTCs had at least one subpopulation with a somatic RET mutation. Uneven distribution of somatic mutation within a single tumor or among metastases from a single individual was notable. In the present study, we sought to correlate RET expression, as demonstrated by RET immunohistochemistry, with mutation status in sporadic MTC for each tumor. Seventy evaluable subpopulations, belonging to 28 unrelated sporadic cases, comprising primary MTC and metastases, were immunostained with two different polyclonal antibodies raised against the C-terminus of RET. The regional presence of codon 918 or 883 seemed to coincide with increased RET immunopositivity in at least 62 of 70 (89%, P < 0.000001) tumor subpopulations. The reasons for this concordance are not entirely clear but could be related to either RNA or protein stability. Preliminary studies have suggested that the presence of somatic codon 918 mutation in MTC has a prognostic significance. If these preliminary results prove true, then given our data, we can further explore the feasibility of RET immunocytochemistry as a rapid assessment for the presence of somatic codon 918 for molecular diagnostic and prognostic purposes.

Analysis of PTEN and the 10q23 region in primary prostate carcinomas

Deletions involving chromosome 10q23 occur frequently in prostatic carcinomas. Recently, a novel tumour suppressor gene, PTEN, mapping to this interval, has been identified. Mutation or deletion of PTEN has been observed in a proportion of prostate cancer cell lines; however, primary prostate carcinomas have not been studied. We have investigated the involvement of PTEN in primary prostatic adenocarcinomas using a panel of 51 matched normal and prostate tumour DNAs. We first determined the proportion of tumours with allele loss at loci in 10q23 which span the region containing the PTEN gene. Our results show that LOH involving 10q23 is common in primary prostate carcinomas. Twenty-five of 51 (49%) tumours showed loss of heterozygosity (LOH) over the region spanning the PTEN locus. We next directly analysed the PTEN gene for mutations of the coding region using single strand conformation polymorphism (SSCP) and sequence analyses. Of those tumours with LOH, only a single tumour was found to carry a missense mutation in PTEN. No mutations in PTEN were identified in tumours without LOH. Our results suggest either that mutation of PTEN is a late event in prostate tumorigenesis, or that another tumour suppressor gene important in prostate cancer may lie close to PTEN in 10q23.

Investigation of the genes for RET and its ligand complex, GDNF/GFR alpha-I, in small cell lung carcinoma

RET is a receptor tyrosine kinase expressed in neuroendocrine cells and in tumors of these cell types. RET activation may be mediated by a ligand complex comprising glial cell line-derived neurotrophic factor (GDNF) and GDNF family receptor alpha-1 (GFR alpha-1). Activating RET mutations are found in the inherited cancer syndrome multiple endocrine neoplasia type 2 and in a subset of the related sporadic tumors, medullary thyroid carcinoma and pheochromocytoma, both being derived from neuroendocrine tissues. In one small study, mutations were identified in another tumor with neuroendocrine features, small cell lung carcinoma (SCLC). To determine whether RET mutations contribute to the pathogenesis of SCLC, we examined a panel of 54 SCLC cell lines. No mutations were identified in RET exons 10, 11, and 13-16, regions previously implicated in SCLC or other neuroendocrine tumors. We further examined the expression pattern of RET and the genes encoding the components of its ligand complex GDNF and GFR alpha-1, in 21 SCLC lines by using RT-PCR. Although we found no consistent pattern of expression for these three genes, RET was expressed in 57% of SCLC lines. Thus, although RET mutations appear unlikely to be an important step in the tumorigenesis of SCLC, the frequent expression of this gene suggests that RET may have a mitogenic role in a subset of SCLC cell lines.

Expression of RET 3' splicing variants during human kidney development

The mature mammalian kidney arises through a series of reciprocal inductive interactions between two different cell groups, the ureteric bud epithelium and the metanephric mesenchyme. The RET receptor tyrosine kinase is required for induction and development of the metanephric kidney. Differential splicing at the 3' end of RET results in transcripts encoding three isoforms that differ with respect to their C-terminal 9 (RET9), 51 (RET51) or 43 (RET43) amino acids. In vitro assays have identified differences in the abilities of the RET9 and RET51 isoforms to induce differentiation suggesting functional differences between these proteins. We examined the relative expression levels of the three RET 3' splicing variants in developing human kidney using semi-quantitative RT-PCR. We observed consistent expression of the RET9 and RET43 variants in kidney samples spanning 7.5 through 24 weeks gestation. At early gestational ages (7.5-8.5 weeks), RET51 expression was very low (+/-5%) compared to RET9; however, a rapid seven fold increase in expression was detected by 9 weeks. Our data suggest that RET51 may contribute to differentiation-related events occurring after 8.5 weeks gestation rather than to induction of the human kidney.

Genomic structure and chromosomal localization of the human GDNFR-alpha gene

GDNFR-alpha is a glycosyl-phosphotidylinositol-linked receptor for glial cell line-derived neurotrophic factor (GDNF). GDNF binds to GDNFR-alpha and this complex, in turn, is believed to interact with the RET receptor tyrosine kinase to effect downstream signalling. GDNFR-alpha belongs to a novel gene family without strong homology to known genes. Thus, little information has been available to help predict genomic structure or location of this gene. In this study, the genomic organization of human GDNFR-alpha was delineated through a combination of PAC clone characterization, long distance PCR and sequence analyses. Exon-intron boundaries were defined by comparing the size and sequence of the genomic PCR products to those predicted by the cDNA sequence. The human GDNFR-alpha gene comprises 9 exons. GDNFR-alpha PAC clones were used for FISH analysis to map this gene to 10q26.

Germline dinucleotide mutation in codon 883 of the RET proto-oncogene in multiple endocrine neoplasia type 2B without codon 918 mutation

The autosomal dominant multiple endocrine neoplasia type 2 syndromes (MEN 2) comprise three clinically distinct entities, MEN 2A, familial medullary thyroid carcinoma and MEN 2B, which share a common clinical feature: medullary thyroid carcinoma (MTC). MEN 2B is considered to have the most aggressive form of MTC. Therefore, early detection of MEN 2B in order to prevent potentially lethal MTC is important. More than 95% of all MEN 2B cases are caused by germline mutation at codon 918 (M918T) in exon 16 of the RET proto-oncogene. In this study, we demonstrate the presence of germline codon 883 mutation (A883F) in 2 of 3 unrelated MEN 2B cases without codon 918 mutation. Our data demonstrate a novel etiologic event which may have roles in predisposition to MEN 2B when present in the germline and in the pathogenesis of sporadic MTC when somatic.

Mutation analysis of glial cell line-derived neurotrophic factor, a ligand for an RET/coreceptor complex, in multiple endocrine neoplasia type 2 and sporadic neuroendocrine tumors

Causative germline missense mutations in the RET proto-oncogene have been associated with over 92% of families with the inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN 2). MEN 2A is characterized primarily by medullary thyroid carcinoma (MTC) and pheochromocytoma, both tumors of neural crest origin. Parathyroid hyperplasia or adenoma is also seen in MEN 2A, but rarely in MEN 2B, which has additional stigmata, including a marfanoid habitus, mucosal neuromas, and ganglioneuromatosis of the gastrointestinal tract. In familial MTC, MTC is the only lesion present. Somatic RET mutations have also been identified in a subset of sporadic MTCs, pheochromocytomas, and rarely, small cell lung cancer, but not in sporadic parathyroid hyperplasias/adenomas or other neuroendocrine tumors. Glial cell line-derived neurotrophic factor (GDNF) and its receptor molecule GDNFR-alpha, have recently been identified as members of the RET ligand binding complex. Therefore, the genes encoding both GDNF and GDNFR-alpha are excellent candidates for a role in the pathogenesis of those MEN 2 families and sporadic neuroendocrine tumors without RET mutations. No mutations were found in the coding region of GDNF in DNA samples from 9 RET mutation negative MEN 2 individuals (comprising 6 distinct families), 12 sporadic MTCs, 17 sporadic cases of parathyroid adenoma, and 10 small cell lung cancer cell lines. Therefore, we find no evidence that mutation within the coding regions of GDNF plays a role in the genesis of MEN 2 and sporadic neuroendocrine tumors.

The expression of RET and its multiple splice forms in developing human kidney

A series of inductive events between two different cell groups, the ureteric bud epithelium and metanephric mesenchyme, gives rise to the functional mammalian kidney. These reciprocal inductive interactions involve a number of molecules, one of which is the RET receptor tyrosine kinase. The phenotype of mice lacking functional RET includes kidney agenesis or severe dysgenesis, indicating a requirement for RET in kidney organogenesis. To investigate RET expression in human kidney development, we used a semi-quantitative RT-PCR-based strategy to examine a panel of kidney RNA samples ranging from 8-24 weeks gestational age. We found RET expression was highest earlier in development (14 weeks) with expression decreasing through to 24 weeks gestation. While three alternative RET transcripts generated by exon skipping at the 5' end of the gene were all detected throughout kidney development, expression of one transcript, RET2/6, where exon 2 was spliced to exon 6, varied relative to full length RET during this period. Levels of RET2/6 were highest at the earliest age of fetal kidney examined (8 weeks) and decreased relative to all other RET transcripts to low adult levels. The period of high expression coincides with a period of rapid bud bifurcation. Thus, it is possible that RET2/6 has a role in the early growth and differentiation of the human kidney.

Mutation of RET codon 768 is associated with the FMTC phenotype

Multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC) are inherited cancer syndromes resulting from mutations in the RET proto-oncogene. Missense mutations of five codons in exons 10 and 11 are found in both MEN 2A and FMTC families, while mutations at codon 768 in exon 13 have been identified in three FMTC families. We report here the results of mutation analysis on a large multi-generation family with multiple cases of medullary thyroid carcinoma (MTC) or C-cell hyperplasia and two individuals with isolated adrenal medullary hyperplasia. A mutation in exon 13, which alters codon 768 from a GAG (Glu) to a GAC (Asp), was found to segregate with the FMTC phenotype in this family but not with the adrenal medullary hyperplasia. These findings suggest that the codon 768 mutation does not predispose to adrenal medullary hyperplasia, but is an accurate predictor of the MTC phenotype in this family.

Mutation analysis of glial cell line-derived neurotrophic factor (GDNF), a ligand for the RET/GDNF receptor alpha complex, in sporadic phaeochromocytomas

Phaeochromocytomas usually occur sporadically but may also be a feature of three autosomal dominantly inherited cancer syndromes, multiple endocrine neoplasia type 2, von Hippel-Lindau disease (VHL), and, very rarely, type 1 neurofibromatosis. Germ-line missense mutations in the RET proto-oncogene, which encodes a receptor tyrosine kinase, cause multiple endocrine neoplasia type 2. In VHL, germ-line mutations in one of the three exons of the VHL tumor suppressor gene have been found in the majority of families. Whereas somatic mutations in the VHL gene have been common in sporadic renal cell carcinoma, a component cancer of VHL, somatic mutations in the RET and VHL genes together have been found in approximately 10% of sporadic phaeochromocytomas. Hence, other genes must also contribute to the pathogenesis of sporadic phaeochromocytomas. Recent data have suggested that glial cell line-derived neurotrophic factor (GDNF) is a ligand for RET and acts via a heterotetrameric receptor complex that includes GDNF receptor alpha, which provides ligand binding capabilities, and RET, which provides the signaling component. Thus, both GDNF and GDNFR-alpha are plausible candidate genes for involvement in the pathogenesis of phaeochromocytomas. To investigate the role of GDNF in sporadic phaeochromocytomas, we scanned a panel of 22 tumors. Among these samples, only a conservative sequence variant was detected in exon 2 of GDNF. No disease-associated somatic GDNF mutations or gross gene amplification were detected in these tumors, suggesting only a minor role for GDNF in the genesis of phaeochromocytomas.

RET proto-oncogene mutations in multiple endocrine neoplasia type 2 and medullary thyroid carcinoma

Multiple endocrine neoplasia type 2 (MEN-2) is a familial cancer syndrome inherited in an autosomal dominant fashion with age-related penetrance. The main tumour type present in all manifestations of this syndrome. MEN-2A, MEN-2B and familial medullary thyroid carcinoma (FMTC), is medullary thyroid carcinoma (MTC). MTC arises from the parafollicular or C cells of the thyroid. MEN-2A is characterised by the triad of MTC, phaeochromocytoma, and parathyroid hyperplasia. MEN-2B is characterised by features similar to those of MEN-2A, except for the absence of clinically apparent parathyroid hyperplasia, and additional stigmata including a marfanoid habitus, mucosal neuromas and ganglioneuromatosis of the gastrointestinal tract. FMTC families have MTC as their only phenotype. Missense mutations affecting conserved cysteine codons adjacent to the transmembrane domain of the RET proto-oncogene have been identified in the germline DNA of patients with MEN-2A and FMTC. A single mutation at codon 918 in the tyrosine kinase domain of the RET receptor has been associated with the MEN-2B phenotype. In a small number of FMTC families, missense point mutations have also been identified in the intracellular domain of the RET protein. RET mutation analysis of MEN-2 families has allowed the identification of genotype-phenotype correlations. While 25% of all MTCs are hereditary, the great majority of MTCs, 75%, are sporadic. Various somatic RET mutations have been identified in sporadic MTCs. In a small number of hereditary MTCs with germline mutations in RET, an additional somatic missense RET mutation has been identified. The discovery of RET mutations in MEN-2 has made possible accurate DNA-based diagnosis and predictive testing. The clinical significance of somatic RET mutations has yet to be determined.

De novo mutation of GDNF, ligand for the RET/GDNFR-alpha receptor complex, in Hirschsprung disease

Hirschsprung disease (HSCR) is a common congenital abnormality characterized by absence of the enteric ganglia in the hind gut. In 10-40% of HSCR cases, mutations of the RET receptor tyrosine kinase have been found. The recent identification of a multimeric RET ligand/receptor complex suggested that mutations of genes encoding other components of this complex might also occur in HSCR. To investigate this role, we examined the gene for glial cell line-derived neurotrophic factor (GDNF), the circulating ligand of the RET receptor complex, for mutations in a panel of sporadic and familial HSCR. We identified GDNF sequence variants in 2/36 HSCR patients. The first of these was a conservative change which did not affect the GDNF protein sequence. The second variant was a de novo missense mutation in a family with no history of HSCR and without mutation of the RET gene. Thus, our data are consistent with a causative role for GDNF mutations in some HSCR cases.

The relationship between specific RET proto-oncogene mutations and disease phenotype in multiple endocrine neoplasia type 2. International RET mutation consortium analysis

OBJECTIVE

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant disorder. The 3 recognized subtypes include MEN 2A, characterized by medullary thyroid carcinoma (MTC), pheochromocytoma (pheo), and hyperparathyroidism (HPT); MEN 2B, by MTC, pheo, and characteristic stigmata; and familial MTC (FMTC), by the presence of MTC only. The purpose of this study was to establish the relationship between specific mutations and the presence of certain disease features in MEN 2 which could help in clinical decision making.

DESIGN

Correlative survey study of 477 MEN 2 families.

SETTING

Eighteen tertiary referral centers worldwide.

PATIENTS

A total of 477 independent MEN 2 families.

MAIN OUTCOME MEASURES

Association between the position and type of germline mutation in the RET proto-oncogene and the presence or absence of MTC, pheo, HPT, and/or other features in a family.

RESULTS

There is a statistically significant association between the presence of any mutation at a specific position (codon 634) and the presence of pheo and HPT. The presence of a specific mutation, CGC at codon 634, has yet to be associated with FMTC. Conversely, mutations at codons 768 and 804 are thus far seen only with FMTC, while codon 918 mutation is MEN 2B--specific. Rare families with both MEN 2 and Hirschsprung disease were found to have MEN 2-specific codon mutations. Patients with Hirschsprung disease presenting with such mutations should be monitored for the possible development of MEN 2 tumors.

CONCLUSIONS

This consortium analysis suggests that genotype-phenotype correlations do exist and, if made reliably absolute, could prove useful in the future in clinical management with respect to screening, surveillance, and prophylaxis, as well as provide insight into the genetic effects of particular mutations.

Mutation analysis of the c-mos proto-oncogene and the endothelin-B receptor gene in medullary thyroid carcinoma and phaeochromocytoma

The characteristic tumours of MEN 2 are medullary thyroid carcinoma (MTC) and phaeochromocytoma. Somatic RET mutations have been found in only 23-40% of sporadic MTC and 10% of sporadic phaeochromocytomas. Thus, we sought other genes which may play a role in the pathogenesis of these tumours. We carried out direct sequence analysis of human c-mos and human ENRB in a series of sporadic MTC and phaeochromocytomas to determine if somatic mutations in these two genes could account for some of the sporadic MEN 2-related tumours in which no RET mutations are detected. No somatic mutations were found.

Heterogeneous mutation of the RET proto-oncogene in subpopulations of medullary thyroid carcinoma

Mutations in the RET proto-oncogene are associated with the pathogenesis of medullary thyroid carcinoma (MTC). In an attempt to understand this process, we examined microdissected subpopulations from MTC and multiple metastases from these tumors. Approximately 80% of sporadic MTC's had at least one subpopulation with the RET codon 918 mutation, which is a mutation previously detected in sporadic MTC as a somatic mutation and in multiple endocrine neoplasia type 2B as a germline mutation. However, the distribution of this mutation was nonhomogeneous, occurring only in subpopulations in most tumors and among subsets of multiple metastases, thus implying that although the codon 918 mutation could be an early event, it is not necessarily an early or essential event in tumorigenesis. This heterogeneity suggests either that the codon 918 mutation can arise as an event in progression within a metastatic clone or within a single tumor, or that MTC can be of polyclonal origin. Of significance, one of two multiple endocrine neoplasia type 2A MTCs carried a somatic mutation at codon 918, in addition to the RET mutation present in the germline. We found no correlation between the presence of other somatic genetic events, such as loss of heterozygosity on chromosome arms 1p and 22q, and RET mutation status in the various subpopulations of MTC.

A 9.75-Mb map across the centromere of human chromosome 10

We present a yeast artificial chromosome (YAC) and pulsed-field gel electrophoresis (PFGE) map across the centromere of human chromosome 10 that links expressed sequences in 10p11 to expressed sequences in 10q11.2. This map is the first of its kind to link genes across a human centromere. It consists of a 2.5-Mb YAC contig extending from 10p11 to our previously published 5.35-Mb PFGE map of the centromeric satellite arrays, and a 2.65-Mb YAC contig extending from these satellite arrays to 10q11.2. This map covers approximately 6.5-7% of the total DNA of chromosome 10. Two Généthon genetic markers, D10S578 and D10S604, are included. These markers are only 1 cM apart but are separated by a physical distance of more than 9.2 Mb, including the centromere. This gives a ratio of genetic to physical distance of 0.11 cM/Mb, 9-11 times lower than average estimates for the human genome and chromosome 10. Markers linked to the centromere include the duplicated zinc finger genes ZNF11A, ZNF33A, and ZNF37A (which map to 10p11) and ZNF11B, ZNF33B, and ZNF37B (which map to 10q11.2). Restriction mapping confirms that the genes on each arm lie in opposite orientation with respect to the centromere, consistent with the hypothesis that a pericentric inversion has occurred in this region during primate evolution.

Germline and somatic mutations in an oncogene: RET mutations in inherited medullary thyroid carcinoma

Inherited cancer syndromes predispose an individual to development of specific tumors. Somatic and germline mutations in the same tumor suppressor gene, as described in Knudson's two-mutation model, are well recognized. Inherited mutations in the RET proto-oncogene, which encodes a receptor tyrosine kinase, predispose individuals to the multiple endocrine neoplasia type 2 (MEN 2) cancer syndromes. The major component tumor of these syndromes is medullary thyroid carcinoma (MTC). To date, somatic mutations in RET have not been identified in tumors from individuals with MEN 2, although they have been well documented in sporadic MEN 2-related tumors. We have identified, among 16 MEN 2 cases with well-defined RET germline mutations, a somatic missense mutation at codon 918 of RET in 3 of 15 MTCs and in a sample with hyperplastic C-cells (presumed precursor to hereditary MTC). We suggest that the presence of a somatic mutation, in addition to the preexisting germline mutation in hereditary MTCs, may contribute to tumorigenesis in vivo.

Mutations in the RET proto-oncogene and the von Hippel-Lindau disease tumour suppressor gene in sporadic and syndromic phaeochromocytomas

Phaeochromocytomas may occur sporadically, or as part of the inherited cancer syndromes multiple endocrine neoplasia (MEN) type 2, von Hippel-Lindau disease (VHL), and, rarely, in type 1 neurofibromatosis. In MEN 2, germline missense mutations have been found in one of eight codons within exons 10, 11, 13, 14, and 16 of the RET proto-oncogene. In VHL, germline mutations within one of the three exons are responsible for the majority of cases. To determine if somatic mutations similar to those seen in the germline in MEN 2 or VHL disease play a role in the pathogenesis of sporadic or familial phaeochromocytomas, we analysed 48 sporadic tumours and tumours from 17 MEN 2 and five VHL patients for mutations in RET exons 9, 10, 11, 13, 14, 15, and 16, and the entire coding sequence of VHL. Five of 48 sporadic phaeochromocytomas had RET mutations within exons 10, 11, and 16. Of these, one was proven to be germline and two were proven to be somatic mutations. Four of 48 had VHL mutations; these included both the bilateral cases in the series (one was proven to be a germline mutation) and two others, of which one was proven somatic.

Characterization of RET proto-oncogene 3' splicing variants and polyadenylation sites: a novel C-terminus for RET

The RET proto-oncogene, which encodes a receptor tyrosine kinase, displays multiple alternative splicing variants. Splicing of sequences 3' of exon 19 to generate several coding and untranslated region (UTR) sequences has been previously reported. We have sequenced the full length RET coding region and characterized the transcripts and 3' UTRs generated by alternative splicing of the RET 3' terminus. These analyses were performed using both RET cDNA cloned from a pheochromocytoma library and reverse transcriptase PCR products generated using RNA from a neuroblastoma cell line (LA-N-2). Three different carboxyl termini were identified. In addition to the nine and 51 terminal amino acid forms already known, we identified a third with 43 terminal amino acids predicted to encode a novel RET protein isoform. A total of 3621 base pairs of DNA 3' of exon 19, which spans the alternatively spliced exons and RET UTRs, was sequenced. Four polyadenylation sites were identified. The observed combinations of polyadenylation sites and 3' coding sequence suggest that RET transcripts with up to 10 different 3' sequences and up to 40 different full length RET transcripts may exist.

Five distinct deleted regions on chromosome 17 defining different subsets of human primary breast tumors

In this study, we analyzed 105 paired sporadic primary breast tumor and normal tissue samples for loss of heterozygosity (LOH) on chromosome 17, using 12 polymorphic markers. We have identified partial or interstitial LOH in five separate regions of chromosome 17. Two of the deleted regions lie on the short arm of the chromosome, the first (region I, D17S5) in the telomeric part, distal to TP53 and the second spanning the TP53 gene (region II). Three of the five deleted regions lie on the long arm of chromosome 17: region III, on the proximal long arm between D17S250 and THRA1; region IV, between D17S776 and D17S579, including the BRCA1 gene, and region V, located distal to D17S733. No statistically significant correlations were observed between clinicopathological characteristics or steroid hormone receptor status and deletion of either region I or II. However, patients whose tumors had LOH for region I showed relapse or death more frequently than patients with tumors informative for this region but without LOH (p = 0.002). Statistically significant correlations between LOH at each of the three deleted regions of 17q and a high mitotic index were observed (region III, p = 0.005; region IV, p = 0.02, and region V, p = 0.004). In addition, LOH at region IV showed a significant association with paucity of estrogen receptors (p = 0.01). Our results show a complex pattern of LOH on chromosome 17 in breast cancer and a correlation of these events with different clinical parameters. This pattern suggests that particular subsets of allele loss may contribute specifically to different clinically defined subsets of sporadic breast tumors.

Consequences of direct genetic testing for germline mutations in the clinical management of families with multiple endocrine neoplasia, type II

OBJECTIVE

Multiple endocrine neoplasia, type II (MEN-II) is an autosomal dominant disorder characterized by tumors of thyroid C cells and pheochromocytoma. Recently, germline mutations in the RET proto-oncogene have been identified in patients with MEN-II. The aims of this study were (1) to define the mutations in clinically diagnosed MEN-II families, (2) to compare the results of genetic and biochemical testing, and (3) to evaluate the impact of mutation analyses for the members of these families.

DESIGN

Register-based survey study of clinically affected and unaffected members of MEN-II families.

SETTING

Register of families from Germany and Spain with pheochromocytomas. Two research laboratories at Cambridge University in the United Kingdom.

PATIENTS

We investigated consenting affected and unaffected members belonging to a series of 10 families who met the clinical criteria for MEN-II.

MAIN OUTCOME MEASURES

(1) Presence or absence of germline mutation in the RET proto-oncogene in affected and unaffected members of the 10 families, and (2) in the absence of RET mutation in a given family, presence or absence of germline mutation in the von Hippel-Lindau (VHL) gene, which is the susceptibility gene involved in a closely related syndrome, von Hippel-Lindau disease.

RESULTS

In eight of these families, RET mutations were identified. The specific mutations were detected in all affected members. The remaining two families without RET mutations were subsequently shown to have a mutation within the VHL gene. The VHL mutations were identified in both families and represent a previously undescribed base change. After identification of the mutation, premorbid genetic testing was performed in all MEN-II and VHL families, resulting in detection of asymptomatic carriers in the MEN-II families. Clinically, the two VHL families differed from the eight MEN-II families by the presence of a C-cell tumor in only one individual from each family and extra-adrenal pheochromocytoma in three of nine affected individuals in the two families combined.

CONCLUSIONS

The diagnosis of MEN-II should be confirmed by molecular genetic analysis and the diagnosis of VHL syndrome should be considered for families with an absence of RET mutations and a preponderance of pheochromocytomas.

Genotype-phenotype correlation in multiple endocrine neoplasia type 2: report of the International RET Mutation Consortium

The International RET Mutation Consortium was first convened as part of the Fifth International Workshop on Multiple Endocrine Neoplasia, Stockholm, Sweden, in an attempt to analyse the relationship of RET mutation and disease phenotype in the autosomal dominantly inherited multiple endocrine neoplasia type 2 (MEN 2) syndromes. Out of 361 families studied, 41% had MEN 2A, 17.7% MEN 2B, 6.4% FMTC and the remaining subjects were unclassified. RET mutations were detected in 87.3% of families overall. Over 93% of MEN 2B families had the RET 918 ATG-->ACG mutation, while the most frequent mutation detected in MEN 2A families was cysteine codon 634 (87% of all mutations).

Diversity of RET proto-oncogene mutations in familial and sporadic Hirschsprung disease

Hirschsprung disease (HSCR) is a common congenital malformation (1 in 5,000 live births) due to the absence of autonomic ganglia in the terminal hindgut, and resulting in intestinal obstruction in neonates. Recently, a dominant gene for familial HSCR has been mapped to chromosome sub-band 10q11.2 and the disease has been ascribed to mutations in a tyrosine kinase receptor gene mapping to this region, the RET proto-oncogene. Studying the 20 exons of the RET gene by a combination of denaturating gradient gel electrophoresis and single strand conformation polymorphism in a large series of HSCR patients (45 sporadic cases and 35 familial forms), we found mutations of the RET gene in 50% of familial HSCR, regardless of the length of the aganglionic segment. The mean penetrance of the mutant allele in familial HSCR was significantly higher in males (72%) than in females (51%). Most interestingly, mutations at the RET locus accounted for at least 1/3 of sporadic HSCR in our series. These mutations were scattered along the length of the gene. Finally, among the mutations identified in sporadic cases (16/45), seven proved to be de novo mutations suggesting that new mutations at the RET locus significantly contribute to sporadic HSCR. Taken together, the low penetrance of the mutant gene, the lack of genotype-phenotype correlation, the sex-dependent effect of RET mutations and the variable clinical expression of the disease support the existence of one or more modifier genes in familial HSCR.

Low frequency of germline mutations in the RET proto-oncogene in patients with apparently sporadic medullary thyroid carcinoma

BACKGROUND AND OBJECTIVES

Medullary thyroid carcinoma (MTC) occurs both sporadically and in the autosomal dominantly inherited multiple endocrine neoplasia (MEN) type 2 syndromes. The distinction between true sporadic MTC and a new mutation familial case is important for future clinical management of both the patient and family. The susceptibility gene for MEN 2 is the RET proto-oncogene. Systematic analysis for germline mutations of the RET proto-oncogene was performed in a series of 67 patients with apparently sporadic MTC to determine whether they were true sporadic cases or unsuspected de novo MEN 2 cases.

DESIGN AND PATIENTS

Sixty-seven unselected patients with sporadic MTC were randomly ascertained from clinic patients from four centres. The diagnosis of MTC was confirmed by histopathology. Germline DNA was extracted from peripheral blood leucocytes or from paraffin-embedded tissue and subsequently used for polymerase chain reaction amplification.

MEASUREMENTS

Polymerase chain reaction based RET mutation analysis was performed by direct double-stranded cycle sequencing of exons 10, 11, 13 and 16, within which the majority of MEN2 mutations have been shown to occur.

RESULTS

In this series, there was one proven case of germline mutation in RET codon 620, which previously has been shown to be responsible for MEN 2, thus indicating heritable disease. No germline mutation in codon 918, typical of MEN 2B, was found.

CONCLUSIONS

A figure of 1.5% germline mutations in 67 apparently sporadic MTC is lower than the incidence of familial disease reported in previous series involving clinical and biochemical screening. The presence of a germline mutation in the RET proto-oncogene in a patient with MTC indicates heritable disease. The absence of germline RET exon 10, 11, 13 or 16 mutation appears to rule out MEN 2A to a high probability, although the presence of a familial form of MTC other than classical MEN 2A cannot be excluded conclusively.

Multiple mRNA isoforms of the human RET proto-oncogene generated by alternate splicing

The RET proto-oncogene encodes a receptor tyrosine kinase. We and others have recently shown that distinct germline mutations of the RET proto-oncogene account for the majority of cases of the dominantly inherited multiple endocrine neoplasia (MEN) type 2 syndromes, and can cause a dominantly inherited form of Hirschsprung disease, a disorder of development of the autonomic innervation of the gut. RET is also oncogenically activated in some sporadic thyroid and adrenal tumours. Here we report the characterisation of multiple mRNA isoforms of RET generated by alternate splicing. Two isoforms are predicted to encode membrane-spanning receptors with a truncated extracellular ligand-binding domain. A third isoform is predicted to encode a soluble, secreted form of the receptor. These mRNA isoforms are expressed in both normal and tumour tissues.

Mutation of the RET protooncogene in sporadic medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) occurs sporadically or as part of the inherited cancer syndrome multiple endocrine neoplasia (MEN) type 2. In MEN 2A, germline missense mutations are found in one of five cysteine codons within exons 10 and 11 in the extracellular domain of the RET protooncogene. In MEN 2B, germline mutations occur in codon 918 (exon 16) within the catalytic core of the tyrosine kinase domain. To determine if RET mutations similar to those in MEN 2A and 2B play a role in the pathogenesis of sporadic MTC, we analysed 71 sporadic tumours comprising 68 primary tumours and three cell lines, for mutations in RET exons 10, 11, and 16. We found that 23% of sporadic MTC had RET codon 918 mutations, while only 3% had exon 10 mutations, and none had mutations in exon 11. We found no exon 16 mutations in MTC from 14 MEN 2A cases. Thus, exon 10 and 11 mutations, commonly found in familial MTC and MEN 2A, rarely occur in sporadic MTC; somatic mutation of RET codon 918 appears to play a role in the tumourigenesis of a significant minority of sporadic MTC but not MEN 2A tumours. In addition to their biological interest, these findings may have some clinical application in determining whether a patient presenting with isolated MTC is truly sporadic or is part of an inherited cancer syndrome.

A novel point mutation in the tyrosine kinase domain of the RET proto-oncogene in sporadic medullary thyroid carcinoma and in a family with FMTC

Germline mutations within one of six codons of the RET proto-oncogene account for the majority of cases of multiple endocrine neoplasia (MEN) type 2A and type 2B and familial medullary thyroid carcinoma (FMTC). MEN 2A and FMTC mutations characterised thus far occur exclusively in the cysteine-rich domain of the extracellular region of RET. We now report a missense mutation in the intracellular tyrosine kinase domain of RET in the germline of a family with FMTC that does not have a cysteine codon mutation. In this family, the mutation, which alters GAG (Glu) to GAC (Asp) at codon 768, segregates with the FMTC phenotype. The same mutation was also detected in sporadic MTC but not in corresponding constitutional DNA, confirming that it is likely to be of pathological significance rather than a rare polymorphism.

Clinical value of direct DNA analysis of the RET proto-oncogene in families with multiple endocrine neoplasia type 2A

BACKGROUND

The multiple endocrine neoplasia type 2A gene is the RET proto-oncogene located on the long arm of chromosome 10, and many mutations within this gene have been reported.

METHODS

Peripheral blood DNA was analyzed from 95 members of twelve families with multiple endocrine neoplasia type 2A and known mutations in codon 634 (of exon 11) of the RET proto-oncogene. This region was amplified by the polymerase chain reaction, followed by digestion with Cfo I, which detects restriction sites created by the most common TGC- > CGC mutation and by a TGC- > TGG mutation or with Rsa I, which detects a restriction site created by a TGC- > TAC mutation.

RESULTS

Diagnoses were confirmed in 39 patients; 15 of 56 at-risk persons were gene carriers and 41 were noncarriers. The noncarriers included seven persons who had previously undergone thyroidectomies for suspected C-cell hyperplasia but were negative for the RET mutation present in affected members of their families.

CONCLUSIONS

Identification of the specific gene alterations within families permits direct DNA diagnosis of at-risk family members. The 41 noncarriers will not require further testing nor need to be concerned about transmitting multiple endocrine neoplasia type 2A to their descendants. The normal DNA findings in seven of these persons emphasize the importance of DNA studies in patients with C-cell hyperplasia but no medullary thyroid cancer at operation.

Diverse phenotypes associated with exon 10 mutations of the RET proto-oncogene

Mutations of the RET proto-oncogene are the underlying cause of some cases of Hirschsprung disease (HSCR) and the inherited cancer syndromes multiple endocrine neoplasia types 2A (MEN 2A) and 2B (MEN 2B) and familial medullary thyroid carcinoma (FMTC). In HSCR these mutations are dispersed throughout the gene, while in MEN 2A and FMTC, they are tightly clustered in five cysteine codons of the RET extracellular domain. HSCR and MEN 2 are usually distinct but occasional families have been reported with both diseases. In each of five families with HSCR with or without MEN 2A or FMTC, we have identified a nucleotide substitution in one of the five cysteine codons previously associated with MEN 2A or FMTC. In one family, which had HSCR as its only phenotype, we detected a Cys-->Trp mutation at codon 609 which had not been previously observed. In three families, both HSCR and MEN 2A were associated with a single Cys-->Arg mutation at either codon 618 or 620 of RET. In the fifth family, FMTC and HSCR were present but we could not determine whether HSCR arose from mutation of the RET locus. We suggest that specific mutations in cysteine codons 618 and 620 result in MEN 2A or FMTC, but can also predispose to HSCR with low penetrance.

A novel polymorphism in the coding sequence of the human RET proto-oncogene

A novel polymorphism in the coding sequence of the human RET proto-oncogene is described. The RET proto-oncogene maps to chromosome 10q11.2, and is involved in multiple endocrine neoplasia (MEN 2A, MEN 2B), familial medullary thyroid carcinoma and Hirschsprung's disease.

Second locus for Hirschsprung disease/Waardenburg syndrome in a large Mennonite kindred

We have studied a large Mennonite kindred in which 20 members were affected with Hirschsprung disease (HSCR), 5 of whom had one or more manifestations of Waardenburg syndrome (WS) type II (WS2). Eleven additional relatives had signs of WS2 without HSCR. Since HSCR and WS2 each represent perturbations of neural crest migration/differentiation, this large pedigree with apparent cosegregation of HSCR and WS2 offered an opportunity to search for linkage between these loci, candidate genes, and random DNA markers, particularly in view of recent discoveries of genes for Waardenburg syndrome type I (WS1) and Hirschsprung disease (c-ret). We have examined the following possible linked markers in 69 relatives in this family: the c-ret gene (HSCR); the human PAX3 gene (HuP2) on chromosome 2q (WS1) and placental alkaline phosphatase (ALPP) on chromosome 2q (linked to WS1); argininosuccinate synthetase (ASS) on chromosome 9q, close to ABO blood groups which have shown weak linkage to WS; and the beta 1 GABA receptor gene (GABARB1) on chromosome 4q13-11, close to c-kit, deletions of which cause piebaldism. Linkage between any of these loci and HSCR/WS in this kindred was excluded, demonstrating that there is at least one further locus for HSCR other than c-ret.

Haplotype analysis of MEN 2 mutations

Multiple endocrine neoplasia type 2 (MEN 2) is a dominantly inherited cancer syndrome which affects thyroid C cells, and with variable frequency, the adrenal medulla, parathyroid and enteric autonomic ganglia. The syndrome is due to germline mutation in the receptor tyrosine kinase gene, RET. We have recently shown an unexpected correlation between one particular RET mutation, cys634-->arg, and the probability of parathyroid involvement in families with MEN 2A. Here we use haplotype analysis in the families to show that this correlation is not explained by a single founder chromosome which carries both the cys634-->arg mutation and a separate allele conferring susceptibility to parathyroid abnormality, but is probably due to the cys634-->arg mutation itself. The results also indicate that new mutations to MEN 2 are not infrequent.

A rapid screening method for the detection of mutations in the RET proto-oncogene in multiple endocrine neoplasia type 2A and familial medullary thyroid carcinoma families

Multiple endocrine neoplasia type 2A (MEN2A) and familial medullary thyroid carcinoma (FMTC) are autosomal dominant inherited cancer syndromes with incomplete penetrance. Following the identification of mutations in the RET proto-oncogene that segregate with the disease phenotype in MEN2A, MEN2B, and FMTC, genetic screening of individuals with mutations in RET may be performed. We have employed restriction endonuclease digestion of polymerase chain reaction products as an alternative to sequence analysis for rapid identification of mutant gene carriers in families in which MEN2A and FMTC are segregating. Twenty-one Australasian MEN2A and FMTC families have been screened for mutations in a cysteine-rich region of the RET proto-oncogene. Seven independent mutations were identified in key individuals in 16 of these families. We have identified a mutation in codon 620, 2053 T-->C (Cys620Arg), and two mutations in codon 634 of exon 11 of RET, 2095 T-->C (Cys634Arg) and 2096 G-->A (Cys634Tyr), all three of which were present in both MEN2A and FMTC families.