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A de Bustros

Publications and source records attributed to A de Bustros.

14 recordsLinked to original sources
PubMed1992

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. In transfection experiments in TT cells, the downstream CRE, combined with CT promoter sequences, generated 70% of the maximal cAMP response. The upstream CRE and the C-rich elements conferred 10 and 30% of this response, respectively. In gel mobility shift assays, specific TT cell proteins bound to each of these sequences. Therefore, the cAMP response of the CT gene is complex, requiring multiple elements acting in concert.

Base Sequence↗
PubMed1992

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. These results suggest that HLH recognition motifs may mediate a significant portion of constitutive CT gene transcriptional activity in these cells. Nuclear protein extracts from DMS53 cells formed specific binding complexes with oligonucleotides containing two of these candidate enhancer sequences. However, proteins capable of binding to these CT gene HLH consensus recognition sites were not restricted to CT-producing cells. We conclude that members of the HLH protein family, some expressed ubiquitously and some expressed or activated in a tissue-restricted fashion, may combine to enhance CT gene transcription in tumor cells of neuroendocrine derivation.

Base Sequence↗
PubMed1991

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. We argue here that the altered methylation patterns observed during tumor progression, especially regional hypermethylation, may mark--or even help to establish--abnormalities of chromatin organization. In turn, these changes in chromatin structure may, through direct transcriptional inactivation of genes, predisposition to mutations, and allelic deletions, mediate the progressive losses of gene expression associated with tumor development.

Chromatin↗
PubMed1990

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.

Calcitonin↗
PubMed1989

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. As the cells approach confluence, both CT and CGRP mRNA levels rise. Subsequently, CGRP mRNA levels fall substantially in postconfluent cells, while CT mRNA levels remain high. By actinomycin D blocking of nascent transcription, we have shown that these growth-related, reversible changes in the ratio of CT to CGRP mRNA are not due to changes in mRNA stability. Our data rather suggest that TT cells reversibly alter alternative RNA-processing patterns dependent upon growth conditions in vitro, such that CT mRNA is lowest and CGRP mRNA is highest during rapid growth. The mechanisms underlying this RNA-processing alteration may play a role in certain patients with aggressive forms of medullary thyroid carcinoma, in whom a decrease or loss of CT levels heralds a poor prognosis.

Blotting, Northern↗
PubMed1988

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. Treatment of the TT cells with butyrate leads to a 5-fold increase in CT gene transcription after a lag period of 48 h and to a sustained decrease in the calcitonin gene-related peptide to CT mRNA ratio throughout the growth curve of these cells. In addition to its effects on CT gene expression, butyrate also decreases cellular proliferation and c-myc expression in the TT cells. These changes suggest that butyrate induces cultured human medullary thyroid carcinoma cells to acquire in vitro properties more consistent with the differentiated phenotype of the mature thyroid C-cell which is characterized by a low calcitonin gene-related peptide to CT ratio.

Butyrates↗
PubMed1988

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. A hot spot for abnormal methylation of C + G-rich areas has been detected on the short arm of chromosome 11 in an area known to harbor tumor suppressor genes. This change occurs consistently in common forms of human cancer and appears early during the transformation of cells with viruses including members of the human T-cell leukemia (HTLV) family. Furthermore, in one chromosome 11 gene examined, calcitonin, the increased methylation in somatic tumor cells coincides with the presence of an "inactive" chromatin pattern in the transcriptional regulatory area. The increased regional DNA methylation demonstrated may then participate in or mark chromosomal changes associated with gene inactivation events that are central to the genesis and/or progression of human cancers.

Calcitonin↗
PubMed1987

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. The expression of v-Ha-ras is associated with decreased cellular proliferation and DNA synthesis. There is a marked increase in the number of cytoplasmic secretory granules that are a classic feature of differentiated thyroid C cells. v-Ha-ras expression induces increased expression of the calcitonin gene and the processing of the primary gene transcript is shifted to favor calcitonin mRNA rather than calcitonin-gene-related peptide (CGRP) mRNA production. These studies with cultured human MTC cells provide a model system to study the role of Ha-ras and related genes in neuroendocrine differentiation. The findings suggest an important approach for identifying genes in solid tumors whose altered expression may play a role in the impaired maturational capacity characteristic of cancer cells during tumor progression.

Calcitonin↗
PubMed1987

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. Moreover, during the course of therapy in patients with ANLL, the hypermethylation pattern reflects the presence of the leukemic clone even in normal-appearing granulocytes derived from this clone. The increased methylation of the CT gene may then provide an important molecular marker for biologic events in human cell transformation or tumor progression and may prove clinically useful in monitoring patients with lymphoid and acute myelogenous neoplasms.

Acute Disease↗
PubMed1986

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. In the spectrum of the four major types of lung cancer (small cell, adeno-, squamous, and large cell carcinomas), the frequency of occurrence of hypermethylation in the 5'-region of the CT gene parallels that for presence of the neuroendocrine related biochemistry which characterizes small cell lung carcinoma. In medullary thyroid carcinoma, a tumor which expresses high levels of CT gene mRNA, the 5'-region of the CT gene is hypomethylated. Our findings provide a potential new molecular marker for two important human cancers (lung cancer and lymphomas) and suggest that there is a close relationship between abnormal CT gene methylation and developmental events for these tumors.

Calcitonin↗
PubMed1985

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. We found that the phorbol esters, 12-O-tetradecanoyl phorbol 13-acetate and phorbol 12,13-dibutyrate 1) altered the morphology of the TT cells towards that of high-calcitonin-containing cells; 2) enhanced calcitonin secretion 7-fold; 3) increased calcitonin production at the transcriptional level by 2-fold; 4) inhibited cellular proliferation; and 5) decreased, by 80%, the levels of the c-myc gene mRNA. These data suggest that phorbol esters induce, in human medullary thyroid carcinoma cells in culture, a programmed pattern of events resulting in differentiation of these cells.

Calcitonin↗
PubMed1984

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.

Base Sequence↗
PubMed1984

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.

Animals↗