Difficult cases in heart failure: Reversible heart failure secondary to thyrotoxicosis.

Perhaps one of the most important steps in caring for a patient with heart failure is seeking a reversible form of heart failure. Often addressing a disease process, like myocardial ischemia or systemic hypertension, rapidly attenuates the progressive natural history of left ventricular dysfunction. Beyond the usual reversible causes, however, are some that may be overlooked.

Recognizing factitious hypoglycemia in the family practice setting.

Background: Factitious hypoglycemia is a deliberate attempt to induce a low serum glucose level using either insulin or oral hypoglycemic agents. Sulfonylurea-induced hypoglycemia is more common than incidents of insulin abuse, and hypoglycemia caused by these oral agents is biochemically indistinguishable from insulinoma.

Methods: We describe a case of factitious hypoglycemia resulting from insulin abuse in an adult diabetic patient, review the essentials of glucose homeostasis, and describe diagnostic tests that allow a differential diagnosis.

Expression of prokaryotic HhaI DNA methyltransferase is transforming and lethal to NIH 3T3 cells.

In neoplastic cells, levels of DNA methyltransferase activity are often increased, and evidence is accruing to suggest an important role for this event in tumorigenesis. To evaluate this possibility further, and to investigate the contribution of increasing de novo, as opposed to maintenance, DNA methylation in mammalian cells, we expressed the bacterial HhaI methyltransferase in cultured murine fibroblasts. This enzyme is a pure de novo DNA methyltransferase that methylates the internal C in the sequence GCGC.

Treatment of advanced medullary thyroid carcinoma with a combination of cyclophosphamide, vincristine, and dacarbazine.

Background: Medullary thyroid carcinoma (MTC) is a neoplasm of the parafollicular C cells of the thyroid gland, which belongs to the diffuse neuroendocrine system. This cancer usually behaves in a relatively indolent manner for most patients. However, approximately 20% of patients have a more aggressive course that requires effective management.

Pathobiology of the C-cells.

This brief review of the pathobiology of C-cells has stressed cellular and molecular aspects of MTC development. In the genetic forms of MTC, an alteration in one or more genes on chromosome 10, through an as yet unknown series of events, results in initial hyperproliferation of C-cells. Subsequent genetic steps, possibly at other chromosome loci, presumably result in selected clonal transformation of the hyperproliferative C-cells at risk for tumor development.

Regulation of human calcitonin gene transcription by cyclic AMP.

Transcription of the human calcitonin (CT) gene is markedly increased by cAMP in the TT line of medullary thyroid carcinoma. This response is conferred by 5' flanking DNA sequences located between -132 and -252 relative to the transcription initiation site. Within this region are an upstream cyclic AMP response element (CRE), a downstream CRE flanked by two octamer motifs, and two adjacent C-rich AP2-like sequences.

Human calcitonin gene regulation by helix-loop-helix recognition sequences.

Human calcitonin (CT) gene transcription is regulated by proximal 5' flanking sequences which mediate cAMP-induced expression, and by a distal basal enhancer region. Using transient expression of CT-CAT constructs, we showed that the basal enhancer is active in a CT-producing small cell lung cancer cell line (DMS53) and the thyroid C cell derived tumor line, TT, but is inactive in non-CT-producing cell lines. In deletional and direct mutational analyses of the distal enhancer region, disruption of two elements resembling recognition sequences for the helix-loop-helix (HLH) family of transcriptional regulatory proteins resulted in a significant loss of basal transcriptional enhancer action.

Abnormal patterns of DNA methylation in human neoplasia: potential consequences for tumor progression.

An imbalance of DNA methylation, involving widespread hypomethylation, regional hypermethylation and increased cellular capacity for methylation, is characteristic of human neoplasia. This imbalance begins in preneoplastic cells and becomes more extensive throughout subsequent stages of tumor progression. In normal cells, a primary function of DNA methylation may be to modulate compartmentalization of DNA to ensure that regional areas of transcriptionally active chromatin replicate earlier than the bulk transcriptionally inactive chromatin.

Differential utilization of calcitonin gene regulatory DNA sequences in cultured lines of medullary thyroid carcinoma and small-cell lung carcinoma.

Regulation of expression of the human calcitonin gene was found to differ between two tumor lines of different tissue origin, medullary thyroid carcinoma (TT line) and small-cell lung carcinoma (DMS53 line). Distal 5' DNA elements between -750 and -2000 exhibited a stronger basal activity in DMS53 than in TT cells, whereas proximal DNA sequences between -132 and -252 mediated a dramatic cyclic AMP response in TT but not DMS53 cells.

Changes in calcitonin gene RNA processing during growth of a human medullary thyroid carcinoma cell line.

The ratios of calcitonin (CT) to calcitonin gene-related peptide (CGRP) mRNA, both generated by alternative RNA processing from the same primary RNA transcript, are shown by Northern blotting of cytoplasmic RNA to vary as a function of growth in a human medullary thyroid carcinoma cell line (TT). Upon initial seeding, CT mRNA levels are relatively high, and CGRP mRNA levels are relatively low. During the early logarithmic growth phase, CGRP mRNA levels rise severalfold, while CT mRNA levels change only slightly.

Low incidence of loss of chromosome 10 in sporadic and hereditary human medullary thyroid carcinoma.

Genetic linkage has been recently documented between a centromeric region of chromosome 10 and familial multiple endocrine neoplasia type II (MEN II). This syndrome consists of initial thyroid C-cell and adrenal chromaffin cell hyperplasia which result in multifocal medullary thyroid carcinomas and bilateral adrenal pheochromocytomas. Other hereditary cancers, such as retinoblastoma, appear to result from a series of genetic events involving, first the inheritance of a germ line abnormality, and subsequent loss of chromosome loci opposite this initial defect.

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.

The short arm of chromosome 11 is a "hot spot" for hypermethylation in human neoplasia.

Inactivation of normally expressed genes may play a role in the formation and/or progression of human cancers. Methylation of cytosine in DNA could potentially participate in such alterations of gene expression. Abnormalities in DNA methylation are a consistent feature of human neoplasms, and we now show that these include not only previously recognized widespread genomic hypomethylation, but also regional increases in gene methylation.

Transcriptional and posttranscriptional modulation of calcitonin gene expression by sodium n-butyrate in cultured human medullary thyroid carcinoma.

The TT cell line of human medullary thyroid carcinoma produces large quantities of calcitonin (CT) and calcitonin gene-related peptide (CGRP) mRNAs by alternative splicing of a primary CT gene transcript. We have previously shown that the relative levels of these mRNAs depend on the growth stages of the TT cells in culture and that these mRNAs can be increased acutely at the transcriptional level by phorbol esters (12-O-tetradecanoylphorbol-13-acetate) and the cyclic nucleotide, cyclic AMP. We show here that the naturally occurring fatty acid butyrate, unlike 12-O-tetradecanoylphorbol-13-acetate or cyclic AMP, has a delayed stimulatory effect on CT gene transcription, and also can modulate the posttranscriptional processing of RNA from this gene.

Hypermethylation of the 5' region of the calcitonin gene is a property of human lymphoid and acute myeloid malignancies.

An abnormal increase in numbers of CCGG sites methylated in the 5' region of the human calcitonin (CT) gene occurred in tumor cell DNA samples from 90% (17 of 19) of patients with non-Hodgkin's T and B cell lymphoid neoplasms and in 95% (21 of 22) of tumor cell DNA samples from patients with acute nonlymphocytic leukemia (ANLL). The changes were not seen in patients with chronic myelogenous leukemia (0 of 9). The abnormal methylation patterns appear to be a property only of transformed or malignant cells since they were not found in DNA from nonneoplastic adult tissues including sperm, early myeloid progenitor cells, benign lymphoid hyperplasia, peripheral lymphocytes stimulated to divide, or early myeloid progenitor cells (obtained by immunoaffinity using anti-My-10 antibody), but they did appear after Epstein-Barr virus transformation of lymphocytes.

Introduction of v-Ha-ras oncogene induces differentiation of cultured human medullary thyroid carcinoma cells.

Medullary thyroid carcinoma (MTC) is an endocrine tumor of the thyroid C cells that expresses high levels of the neuroendocrine peptide hormone calcitonin. During tumor progression in the host, there is an apparent loss of differentiation in MTC cells that involves a consistent decrease in calcitonin content of the tumor cells associated with decreased expression of the calcitonin gene and/or changes in a mRNA alternative-processing pattern away from that characteristic of the parent thyroid C cell. We now report that introduction of the viral Harvey ras (v-Ha-ras) oncogene into cultured human MTC cells can reverse such changes in gene expression and can induce endocrine differentiation of the tumor cells.

DNA methylation patterns of the calcitonin gene in human lung cancers and lymphomas.

Generalized hypomethylation of the genome and of specific genes has been described in human tumors. We now report that in human lung cancers, especially in the most aggressive form, small cell lung carcinoma, and in lymphomas, the 5'-region of the calcitonin (CT) gene exhibits methylation of increased numbers of CCGG sites in comparison with normal adult tissues. These unusual methylation patterns are found much less frequently in other tumor types examined.

Phorbol esters increase calcitonin gene transcription and decrease c-myc mRNA levels in cultured human medullary thyroid carcinoma.

Medullary thyroid carcinoma is a tumor of the calcitonin-secreting thyroid C-cell, with a variable malignant potential. Virulent tumors are characterized by decreased calcitonin production, suggesting the emergence of a less differentiated medullary thyroid carcinoma cell. In order to further delineate relationships between tumor progression and status of differentiation of medullary thyroid carcinoma cells, we have sought to chemically manipulate the TT cell line, an established culture of human medullary thyroid carcinoma, derived from a patient with aggressive disease.

Structure and expression of a gene encoding human calcitonin and calcitonin gene related peptide.

Messenger RNAs for calcitonin (CT) and calcitonin gene related peptide (CGRP) have been detected in a human medullary thyroid carcinoma cell line. DNA sequences of their cloned cDNAs, and genomic restriction mapping, indicate that both mRNAs probably originate from a single gene; the separate mRNAs are derived by alternative processing. The calcitonin gene is expressed in 10 of 10 examined culture lines of human lung cancer; most of these lines express a higher ratio of CGRP to CT specific mRNA than does the medullary thyroid carcinoma cell line.

Human medullary thyroid carcinoma in culture provides a model relating growth dynamics, endocrine cell differentiation, and tumor progression.

We used an unique model, human medullary thyroid carcinoma (MTC) in culture (the TT line), to study features of neuroendocrine-related biochemistry in relationship to growth, differentiation, and tumor progression. Tumor tissues from patients with virulent MTC contain a very heterogeneous distribution of cells staining for calcitonin (CT) and have a high ratio of intracellular L-dopa decarboxylase activity (DDC) to CT. We found, in a culture line of MTC derived from a patient with virulent disease, that the degree of the inverse relationship between DDC and CT and the heterogeneous cellular distribution of CT probably relate to the rate of cellular growth and the biochemical set of individual cell clones.

The human calcitonin gene is located on the short arm of chromosome 11.

By molecular hybridization of human calcitonin cDNA probes to DNA from human-rodent hybrid cells containing identified human chromosomes, we have mapped the human calcitonin gene to the short arm of chromosome 11. This location has been confirmed by in situ hybridization, which further localized the calcitonin gene to region 11p13-15. The significance of this region regarding gene linkage and possible markers for inherited cancers is discussed.