The molecular biology of medullary thyroid carcinoma. A model for cancer development and progression

Medullary thyroid carcinoma (MTC) is an important human cancer for the study of molecular abnormalities that underlie initiation of neoplasia and subsequent cellular changes during tumor progression. This tumor can occur in different inherited forms, each mediated by autosomal dominant genetic events. Germline abnormalities on chromosome 10 are linked to at least one type of genetic MTC, multiple endocrine neoplasia type II. Our studies of chromosome 10 in DNA from MTC tumors failed to detect frequent loss of polymorphic DNA markers, suggesting that the genetic mechanisms involved in MTC development may be different from those for other inherited cancers such as retinoblastoma. During tumor progression of MTC, abnormalities develop in expression of the mature phenotype of the endocrine cell from which the tumor arises. In cell culture, chemical modulation or gene insertion can lead to partial correction of these defects in differentiation capacity by activating cellular signaling processes. These studies offer opportunities to dissect the molecular events that regulate endocrine cell differentiation, to determine the precise abnormalities that may underlie the initiation and tumor progression events in MTC and related cancers, and, thereby, to identify new targets for therapeutic intervention.     

Choosing art as a complement to healing.

Art à la Carte is a volunteer program that enables long-term care patients to decorate their hospital room with an art print of their choice. Thirty-seven participants were interviewed to evaluate the program. The data suggest that art adds a personal touch to the sterile hospital environment, facilitates interaction between staff and patients, and provides positive distractions. Choosing a work of art also helps patients to regain a sense of control. These themes coincide with the key components of supportive health care environment. The data suggest that Art à la Carte can provide a meaningful complement to the healing process.     

Expression of an exogenous eukaryotic DNA methyltransferase gene induces transformation of NIH 3T3 cells.

Abnormal regional increases in DNA methylation, which have potential for causing gene inactivation and chromosomal instability, are consistently found in immortalized and tumorigenic cells. Increased DNA methyltransferase activity, which is also a characteristic of such cells, is a candidate to mediate these abnormal DNA methylation patterns. We now show that, in NIH 3T3 mouse fibroblasts, constitutive overexpression of an exogenous mouse DNA methyltransferase gene results in a marked increase in overall DNA methylation which is accompanied by tumorigenic transformation. These transformation changes can also be elicited by dexamethasone-inducible expression of an exogenous DNA methyltransferase gene. Our findings provide strong evidence that the increase in DNA methyltransferase activity associated with tumor progression could be a key step in carcinogenesis and provide a model system that can be used to further study this possibility.     

A histological survey of green fluorescent protein expression in 'green' mice: implications for stem cell research

AIMS: The transgenic enhanced green fluorescent protein (EGFP) expressing 'green' mouse (C57BL/6-TgN(ACTbEGFP)1Osb) is a widely used tool in stem cell research, where the ubiquitous nature of EGFP expression is critical to track the fate of single or small groups of transplanted haematopoietic stem cells (HSC). Our aim was to investigate this assumed ubiquitous expression by performing a detailed histological survey of EGFP expression in these mice. METHODS: Fluorescent microscopy of frozen tissue sections was used to perform a detailed histological survey of the pattern of EGFP expression in these mice. Flow cytometry was also used to determine the expression pattern in blood and bone marrow. RESULTS: Three patterns of EGFP expression were noted. In most tissues there was an apparently stochastic variegation of the transgene, with individual cell types demonstrating highly variable rates of EGFP expression. Certain specific cell types such as pancreatic ductal epithelium, cerebral cortical neurones and glial cells and glomerular mesangial cells consistently lacked EGFP expression, while others, including pancreatic islet cells, expressed EGFP only at extremely low levels, barely distinguishable from background. Lastly, in the colon and stomach the pattern of EGFP expression was suggestive of clonal inactivation. Only cardiac and skeletal muscle showed near ubiquitous expression. CONCLUSIONS: These findings raise questions regarding the 'ubiquitous' expression of EGFP in these transgenic mice and suggest caution in relying overly on EGFP alone as an infallible marker of donor cell origin.     

The importance of early diagnosis in patients with hereditary medullary thyroid carcinoma.

Ninety-two patients from 12 kindreds with hereditary medullary thyroid carcinoma (MTC) were evaluated. We sought to determine if the stimulated plasma calcitonin (CT) level at the time of diagnosis was of prognostic significance. The patients were divided into four groups according to their preoperative stimulated plasma CT levels (1) 250-1,000 pg/ml (n=25); (2) 1,000-5,000 pg/ml (n=36); (3) 5,000-10,000 pg/ml (n=8); (4) greater than 10,000 pg/ml (n=23). Compared between the four groups were several parameters, including incidence of regional lymph node metastases, incidence of residual MTC post-thyroidectomy (as indicated by increased (greater than 300 pg/ml) plasma CT levels after operation), incidence of distant metastases, and incidence of death. Also compared were the incidences of microscopic or gross MTC in thyroidectomy specimens. The incidence of regional lymph node involvement ranged from a minimum of one (4%) of 25 patients in Group 1 to 13 (57%) of 23 patients in Group 4. Similarly, plasma CT levels were elevated in only one (4%) of 25 patients in Group 1 compared to 14 (61%) of 23 patients in Group 4. There was no evidence of distant metastases or death in the patients in Groups 1, 2, or 3. In the 23 patients in group 4, however, four (17.4%) had distant metastases and two (8.7%) died of disease during the period of observation. Of th 25 patients in Group 1, MTC was evident only by microscopic examination in 14 (56%). Eleven (44%) of the patients in Group 1 had macroscopically evident medullary thyroid carcinoma. This is in contrast with patients in Group 4 where all 23 had grossly evident MTC. These data indicate that the stimulated plasma CT level at the time of diagnosis is an excellent prognostic indicator of the extent of a disease in patients with hereditary MTC. Aggressive screening of kindred members at risk is of critical importance for establishing the diagnosis and instituting therapy at a time when the neoplasm is confined to the thyroid gland.     

Estimating the burden of disease in one Swiss canton: what do disability adjusted life years (DALY) tell us?

BACKGROUND: Examining life expectancy and general mortality rates, the health of the population of Geneva can be described as one of the best in the world. However, in some areas Geneva fares worse than the rest of Switzerland or Europe. To re-appraise the current health priorities of the Genevan population, we analysed the relative importance of specific diseases and injuries calculating DALYs. METHODS: We followed the procedures developed for the Global Burden of Disease (GBD) study to ensure comparability. Some adaptations were made for mortality coding. Disability was estimated based on data for countries classified as Established Market Economies (EME) in the GBD study. RESULTS: Non-communicable diseases accounted for 79% of the disability adjusted life years (DALY), injuries represented 12%, and communicable diseases and other disorders 9%. Ischaemic heart disease was the largest single contributor to DALY, followed by unipolar major depression. Neuropsychiatric disorders and mental health accounted for more than 23% of DALY. CONCLUSIONS: Some of the most important problems identified-depression, osteoarthritis and alcohol abuse-would have been overlooked in an analysis based solely on mortality data. The most striking finding is the importance of mental health problems. The main limitation is the lack of morbidity data for Geneva.     

Tumor-specific down-regulation of the tumor necrosis factor-related apoptosis-inducing ligand decoy receptors DcR1 and DcR2 is associated with dense promoter hypermethylation

TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) induces apoptosis in a large variety of cancer cells but not in most normal human cells. This feature makes TRAIL, a potential antitumor agent. TRAIL can bind to four different receptors, two pro-apoptotic death receptors (DRs), DR4 and DR5, and two antiapoptotic decoy receptors (DcRs), DcR1 and DcR2. Normal cells express all four of the receptors. The increased TRAIL sensitivity of tumor cells has been postulated to result from the lack of DcR expression. We studied the tumor-specific down-regulation of the TRAIL receptors DcR1 and DcR2, as well as DR4 and DR5, in a group of pediatric tumor cell lines [nine neuroblastoma and three peripheral primitive neuro-ectodermal tumors (PNETs)] and three cell lines from adult tumors. Lack of expression of DcR1 and DcR2 was widespread (13 of the 15 cell lines and 10 of 15, respectively), both in the adult tumor cell lines and in the pediatric tumor lines. DR4 and DR5 were expressed in 8 of 15 and 12 of 15 cell lines, respectively. To understand the tumor-specific down-regulation of the TRAIL receptors, the promoter regions were studied for possible methylation changes of their CpG islands. All normal tissues were completely unmethylated, whereas in the tumor cell lines, we found frequent hypermethylation of the promoter. For DcR1 and DcR2, we found dense hypermethylation in 9 (69%) of 13 and 9 (90%) of 10 of nonexpressing cell lines, respectively. DR4 and DR5 were methylated in 5 (71%) of 7 and 2 (67%) of 3 nonexpressing cell lines, respectively. Treatment with the demethylating agent 5-aza-2'deoxycytidine resulted in partial demethylation and restored mRNA expression. In addition, we performed mutation analysis of the death domains of DR4 and DR5 by sequencing exon 9. Mutations were not present in any of the neuroblastoma or PNET cell lines. A panel of 28 fresh neuroblastoma tumor samples also lacked expression of DcR1 and DcR2 in 85 and 74% of cases, respectively. Hypermethylation was observed in 6 (21%) of 28 for DcR1 and 7 (25%) of 28 for DcR2. DR4 and DR5 were both expressed in 22 of 28 tumors, and no promoter methylation was observed. These data suggest that hypermethylation of the promoters of DcR1 and DcR2 is important in the down-regulation of expression in neuroblastoma and other tumor types.