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S B Baylin

Publications and source records attributed to S B Baylin.

At least 73 records · Page 4Linked to original sources
PubMed1998

Distinct patterns of E-cadherin CpG island methylation in papillary, follicular, Hurthle's cell, and poorly differentiated human thyroid carcinoma.

Expression of the invasion/metastasis suppressor, E-cadherin, is diminished or lost in thyroid carcinomas. Yet, mutational inactivation of E-cadherin is rare. Herein, we show that this loss is associated with hypermethylation of the E-cadherin 5' CpG island in a panel of human thyroid cancer cell lines. This aberrant methylation is evident in 83% of papillary thyroid carcinoma, 11% of follicular thyroid carcinoma, 40% of Hurthle's cell carcinoma, and 21% of poorly differentiated thyroid carcinomas. Contrary to previous reports, the majority of these poorly differentiated thyroid carcinomas express E-cadherin, but often within the cytoplasm rather than at the cell surface. Together, our data indicate that the invasion/metastasis suppressor function of E-cadherin is frequently compromised in human papillary, Hurthle's cell, and poorly differentiated thyroid carcinoma by epigenetic and biochemical events.

Cadherins↗
PubMed1998

Methylation of the HIC-1 candidate tumor suppressor gene in human breast cancer.

HIC-1 (hypermethylated in cancer) is a candidate tumor suppressor gene which is located at 17p13.3, a region which frequently undergoes allelic loss in breast and other human cancers. HIC-1 is proposed to be commonly inactivated in human cancers by hypermethylation of a normally unmethylated dense CpG island which encompasses the entire gene. To study whether HIC-1 inactivation may be important to the development of breast cancer, we first measured methylation of the HIC-1 gene in normal breast ductal tissues from microdissected frozen breast tissues and from epithelial cells purified from mammoplasty specimens. Surprisingly, in all normal breast ductal tissues we found approximately equal amounts of densely methylated HIC-1 and completely unmethylated HIC-1. This is in contrast to most normal tissues, in which all copies of HIC-1 are completely unmethylated. We then evaluated 39 primary breast cancer tissues and found virtually complete methylation of the HIC-1 gene in 26 (67%) of the cases. We also found loss of heterozygosity at the telomeric portion of chromosomal arm 17p in 22 of the 26 cases with strongly methylated HIC-1, suggesting that loss of an unmethylated HIC-1 allele may contribute to the inactivation of HIC-1 in cells with a pre-existing methylated allele. Finally, by RNase protection analysis, HIC-1 was found to be expressed in microdissected normal breast ductal tissues and unmethylated tumors but not in tumors with hypermethylation of the HIC-1 gene. These results indicate that hypermethylation of HIC-1 and associated loss of HIC-1 expression is common in primary breast cancer. Furthermore, the HIC-1 gene is densely methylated in approximately one-half of the alleles in normal breast epithelium, which may predispose this tissue to inactivation of this gene by loss of heterozygosity.

Breast Neoplasms↗
PubMed1998

Hypermethylation can selectively silence individual p16ink4A alleles in neoplasia.

Inactivation of p16ink4A and other tumor suppressor genes has been associated with promoter region hypermethylation in neoplasia. However, direct proof for aberrant DNA methylation as an independent event for loss of gene function has been difficult to obtain. We addressed this question in the colon carcinoma cell line HCT116, which contains one allele of p16ink4A with a coding region frameshift mutation and one wild-type allele. Neither allele contains a mutation in the proximal promoter region. The promoter of the wild-type allele, but not the mutant allele, is hypermethylated, and only the mutant allele is expressed. Transcription from the methylated/wild-type allele was restored after cell treatment with the demethylating agent 5-aza-2'-deoxycytidine. Thus, in neoplastic cells, stable allele-specific loss of transcription may arise from aberrant methylation of a nonmutated promoter region, identifying hypermethylation as a direct mechanism for tumor suppressor gene inactivation.

Alleles↗
PubMed1998

Effective long-term palliation of symptomatic, incurable metastatic medullary thyroid cancer by operative resection.

OBJECTIVE: To evaluate the short- and long-term consequences of palliative reresection of specific symptomatic lesions in patients with widely disseminated (incurable) medullary thyroid cancer (MTC). SUMMARY BACKGROUND DATA: Although reoperative neck microdissections can normalize calcitonin levels in patients with metastatic MTC confined to regional lymph nodes, there is no curative therapy for widely metastatic disease. However, these patients frequently have prolonged survival, but often with debilitating symptoms. METHODS: Between October 1981 and January 1997, 16 patients (mean age, 46 +/- 3 years; 10/16 female) underwent 21 palliative reoperations for unresectable MTC at the Johns Hopkins Hospital. All patients had significant symptom(s) or impending compromise of vital structures by a discrete lesion and had unequivocal preoperative evidence of a total disease burden that was unresectable. RESULTS: The mean interval from initial thyroidectomy to palliative surgery was 5.8 +/- 1.5 years. All patients had significant tumor burdens as evidenced by preoperative calcitonin values ranging from 900 to 222,500 pg/mL (nL < or = 17 pg/mL). The palliative operations consisted of reoperative neck dissection/mass excision (11), mediastinal mass resection (4), esophagectomy (1), liver trisegmentectomy (1), sigmoidectomy (1), bilateral simple mastectomies (1), pituitary resection (1), and subcutaneous mass excisions (1). All but two of the operative specimens contained MTC. There was no perioperative mortality. The long-term morbidity rate was limited to one recurrent laryngeal nerve injury. All patients had initial relief of the index symptom(s) after the palliative surgery, followed by a median actuarial symptom-free survival rate of 8.2 years. CONCLUSIONS: Patients with widely metastatic MTC often live for years, but many develop symptoms secondary to tumor persistence or progression. Judicious palliative, reoperative resection of discrete, symptomatic lesions can provide significant long-term relief of symptoms with minimal operative mortality and morbidity. In selected patients with metastatic MTC lesions causing significant symptoms or physical compromise, palliative reoperative resection should be considered despite the presence of widespread incurable metastatic disease.

Adult↗
PubMed1998

Infection with human immunodeficiency virus type 1 upregulates DNA methyltransferase, resulting in de novo methylation of the gamma interferon (IFN-gamma) promoter and subsequent downregulation of IFN-gamma production.

The immune response to pathogens is regulated by a delicate balance of cytokines. The dysregulation of cytokine gene expression, including interleukin-12, tumor necrosis factor alpha, and gamma interferon (IFN-gamma), following human retrovirus infection is well documented. One process by which such gene expression may be modulated is altered DNA methylation. In subsets of T-helper cells, the expression of IFN-gamma, a cytokine important to the immune response to viral infection, is regulated in part by DNA methylation such that mRNA expression inversely correlates with the methylation status of the promoter. Of the many possible genes whose methylation status could be affected by viral infection, we examined the IFN-gamma gene as a candidate. We show here that acute infection of cells with human immunodeficiency virus type 1 (HIV-1) results in (i) increased DNA methyltransferase expression and activity, (ii) an overall increase in methylation of DNA in infected cells, and (iii) the de novo methylation of a CpG dinucleotide in the IFN-gamma gene promoter, resulting in the subsequent downregulation of expression of this cytokine. The introduction of an antisense methyltransferase construct into lymphoid cells resulted in markedly decreased methyltransferase expression, hypomethylation throughout the IFN-gamma gene, and increased IFN-gamma production, demonstrating a direct link between methyltransferase and IFN-gamma gene expression. The ability of increased DNA methyltransferase activity to downregulate the expression of genes like the IFN-gamma gene may be one of the mechanisms for dysfunction of T cells in HIV-1-infected individuals.

CD4-Positive T-Lymphocytes↗
PubMed1998

Alterations in DNA methylation: a fundamental aspect of neoplasia.

Neoplastic cells simultaneously harbor widespread genomic hypomethylation, more regional areas of hypermethylation, and increased DNA-methyltransferase (DNA-MTase) activity. Each component of this "methylation imbalance" may fundamentally contribute to tumor progression. The precise role of the hypomethylation is unclear, but this change may well be involved in the widespread chromosomal alterations in tumor cells. A main target of the regional hypermethylation are normally unmethylated CpG islands located in gene promoter regions. This hypermethylation correlates with transcriptional repression that can serve as an alternative to coding region mutations for inactivation of tumor suppressor genes, including p16, p15, VHL, and E-cad. Each gene can be partially reactivated by demethylation, and the selective advantage for loss of gene function is identical to that seen for loss by classic mutations. How abnormal methylation, in general, and hypermethylation, in particular, evolve during tumorigenesis are just beginning to be defined. Normally, unmethylated CpG islands appear protected from dense methylation affecting immediate flanking regions. In neoplastic cells, this protection is lost, possibly by chronic exposure to increased DNA-MTase activity and/or disruption of local protective mechanisms. Hypermethylation of some genes appears to occur only after onset of neoplastic evolution, whereas others, including the estrogen receptor, become hypermethylated in normal cells during aging. This latter change may predispose to neoplasia because tumors frequently are hypermethylated for these same genes. A model is proposed wherein tumor progression results from episodic clonal expansion of heterogeneous cell populations driven by continuous interaction between these methylation abnormalities and classic genetic changes.

Aging↗
PubMed1997

Role of estrogen receptor gene demethylation and DNA methyltransferase.DNA adduct formation in 5-aza-2'deoxycytidine-induced cytotoxicity in human breast cancer cells.

The cytosine analog 5-aza-2'-deoxycytidine is a potent inhibitor of DNA methyltransferase. Its cytotoxicity has been attributed to several possible mechanisms including reexpression of growth suppressor genes and formation of covalent adducts between DNA methyltransferase and 5-aza-2'-deoxycytidine-substituted DNA which may lead to steric inhibition of DNA function. In this study, we use a panel of human breast cancer cell lines as a model system to examine the relative contribution of two mechanisms, gene reactivation and adduct formation. Estrogen receptor-negative cells, which have a hypermethylated estrogen receptor gene promoter, are more sensitive than estrogen receptor-positive cells and underwent apoptosis in response to 5-aza-2'-deoxycytidine. For the first time, we show that reactivation of a gene silenced by methylation, estrogen receptor, plays a major role in this toxicity in one estrogen receptor-negative cell line as treatment of the cells with anti-estrogen-blocked cell death. However, drug sensitivity of other tumor cell lines correlated best with increased levels of DNA methyltransferase activity and formation DNA.DNA methyltransferase adducts as analyzed in situ. Therefore, both reexpression of genes like estrogen receptor and formation of covalent enzyme. DNA adducts can play a role in 5-aza-2'-deoxycytidine toxicity in cancer cells.

Antimetabolites, Antineoplastic↗
PubMed1997

Mapping patterns of CpG island methylation in normal and neoplastic cells implicates both upstream and downstream regions in de novo methylation.

Promoter region CpG island methylation is associated with tumor suppressor gene silencing in neoplasia. GenBank sequence analyses revealed that a number of CpG islands are juxtaposed to multiple Alu repeats, which have been proposed as "de novo methylation centers." These islands also contain multiple Sp1 elements located upstream and downstream of transcription start, which have been shown to protect CpG islands from methylation. We mapped the methylation patterns of the E-cadherin (E-cad) and von Hippel-Lindau (VHL) tumor suppressor gene CpG island regions in normal and neoplastic cells. Although unmethylated in normal tissue, these islands were embedded between densely methylated flanking regions containing multiple Alu repeats. These methylated flanks were segregated from the unmethylated, island CpG sites by Sp1-rich boundary regions. Finally, in human fibroblasts overexpressing DNA methyltransferase, de novo methylation of the E-cad CpG island initially involved sequences at both ends of the island and the adjacent, flanking regions and progressed with time to encompass the entire CpG island region. Together, these data suggest that boundaries exist at both ends of a CpG island to maintain the unmethylated state in normal tissue and that these boundaries may be progressively overridden, eliciting the de novo methylation associated with tumor suppressor gene silencing in neoplasia.

Base Sequence↗
PubMed1997

Association between CpG island methylation and microsatellite instability in colorectal cancer.

De novo methylation of promoter region CpG islands has been increasingly associated with transcriptional inactivation of important genes in neoplasia. To study the potential mechanisms underlying aberrant methylation in cancer, we have determined the methylation patterns of selected genes in colorectal cancers with and without microsatellite instability (MI), which results from defects in one of several base mismatch repair genes. A total of 47 colorectal cancers were analyzed, of which 15 were MI+ (32%). We now report that both the frequency and the extent of de novo methylation are strikingly increased in MI+ cancers. Hypermethylation of the p16 gene was found in 60% of MI+ cancers, compared to only 22% in MI- cancers (P = 0.02). Similarly, hypermethylation of the thrombospondin-1 (TSP-1) gene, an angiogenesis inhibitor, was increased in MI+ cancers (27% versus 0%; P = 0.008). Extensive methylation of insulin-like growth factor II (IGF2) and hypermethylated in cancer-1 (HIC-1) genes was observed in 60 and 80% of MI+ cancers, respectively, as contrasted with 6 and 38% of MI- cancers (P = 0.0002 and 0.01, respectively). Furthermore, 60% of the MI+ cancers displayed the hypermethylation events at two or more loci in a concordant manner compared to only 9% of the MI- cancers (P < 0.001). These results demonstrate a strong link between promoter hypermethylation and genetic instability due to deficient DNA repair.

Carrier Proteins↗
PubMed1997

Abrogation of the Rb/p16 tumor-suppressive pathway in virtually all pancreatic carcinomas.

The Rb/p16 tumor-suppressive pathway is abrogated frequently in human tumors, either through inactivation of the Rb or p16INK4a/CDKN2/MTS1 tumor-suppressor proteins, or through alteration or overexpression of the cyclin D1 or cyclin-dependent kinase 4 oncoproteins. We reported previously that the p16 gene was genetically inactivated in 82% of pancreatic carcinomas. Nearly half of these inactivations were by intragenic mutation of p16, and the remainder were by homozygous deletion of the gene. Here, we analyzed pancreatic carcinomas for additional mechanisms by which the Rb/p16 pathway might be inactivated. Transcriptional silencing of the p16 gene in association with methylation of its 5'-CpG island was examined by methylation-specific PCR in 18 pancreatic carcinomas. Nine of these were known to harbor an intragenic mutation in p16, and nine had a wild-type p16 coding sequence. Seven of the 18 tumors were hypermethylated, and all 7 were p16 wild-type (P = 0.001). Complete silencing of transcription from methylated wild-type gene sequences was demonstrated. Immunohistochemical analysis revealed normal expression levels of the Rb protein in all carcinomas studied. None of the carcinomas had genomic amplification of the cyclin D1 or CDK4 genes, and none had mutation of the p16-binding domain of CDK4. An additional p16 mutation was identified. In total, the Rb/p16 pathway was abrogated in 49 of the 50 carcinomas (98%) studied, all through inactivation of the p16 gene. Similar results were obtained in an independently analyzed series of 19 pancreatic carcinomas. These data demonstrate the central role of the Rb/p16 pathway in the development of pancreatic carcinoma.

Carrier Proteins↗
PubMed1997

Conservation of the Drosophila lateral inhibition pathway in human lung cancer: a hairy-related protein (HES-1) directly represses achaete-scute homolog-1 expression.

The achaete-scute genes encode essential transcription factors in normal Drosophila and vertebrate nervous system development. Human achaete-scute homolog-1 (hASH1) is constitutively expressed in a human lung cancer with neuroendocrine (NE) features, small cell lung cancer (SCLC), and is essential for development of the normal pulmonary NE cells that most resemble this neoplasm. Mechanisms regulating achaete-scute homolog expression outside of Drosophila are presently unclear, either in the context of the developing nervous system or in normal or neoplastic cells with NE features. We now provide evidence that the protein hairy-enhancer-of-split-1 (HES-1) acts in a similar manner as its Drosophila homolog, hairy, to transcriptionally repress achaete-scute expression. HES-1 protein is detected at abundant levels in most non-NE human lung cancer cell lines which lack hASH1 but is virtually absent in hASH1-expressing lung cancer cells. Moreover, induction of HES-1 in a SCLC cell line down-regulates endogenous hASH1 gene expression. The repressive effect of HES-1 is directly mediated by binding of the protein to a class C site in the hASH1 promoter. Thus, a key part of the process that determines neural fate in Drosophila is conserved in human lung cancer cells. Furthermore, modulation of this pathway may underlie the constitutive hASH1 expression seen in NE tumors such as SCLC, the most virulent human lung cancer.

Animals↗
PubMed1997

HIC1 hypermethylation is a late event in hematopoietic neoplasms.

HIC1, a candidate tumor suppressor gene on 17p13.3, is hypermethylated and silenced in a large number of solid tumors. To determine its potential role in leukemias, we studied its methylation status in normal and neoplastic hematopoietic cells. We found HIC1 to be unmethylated in peripheral blood cells, bone marrow cells, and CD34+ cells. HIC1 was rarely methylated in newly diagnosed acute myelogenous leukemias (10%) but was relatively frequently methylated in newly diagnosed non-Hodgkin's lymphoma (25%), acute lymphocytic leukemia (ALL; 53%), and chronic-phase chronic myelogenous leukemia (50%). By contrast, HIC1 was hypermethylated in 100% of recurrent ALL and 100% of blast crisis chronic myelogenous leukemia. In two patients with ALL for whom paired diagnosis/relapse samples were available, HIC1 was unmethylated at diagnosis but was highly methylated at relapse after a chemotherapy-induced complete remission. HIC1 methylation, therefore, seems to be a progression event in hematopoietic neoplasms.

Bone Marrow↗
PubMed1997

An achaete-scute homologue essential for neuroendocrine differentiation in the lung.

In Drosophila and in vertebrates, the achaete-scute family of basic helix-loop-helix transcription factors plays a critical developmental role in neuronal commitment and differentiation. Relatively little is known, however, about the transcriptional control of neural features in cells outside a neuronal context. A minority of normal bronchial epithelial cells and many lung cancers, especially small-cell lung cancer, exhibit a neuroendocrine phenotype that may reflect a common precursor cell population. We show here that human achaete-scute homologue-1 (hASH1) is selectively expressed in normal fetal pulmonary neuroendocrine cells, as well as in the diverse range of lung cancers with neuroendocrine features. Strikingly, newborn mice bearing a disruption of the ASH1 gene have no detectable pulmonary neuroendocrine cells. Depletion of this transcription factor from lung cancer cells by antisense oligonucleotides results in a significant decrease in the expression of neuroendrocrine markers. Thus, a homologue of Drosophila neural fate determination genes seems to be necessary for progression of lung epithelial cells through a neuroendocrine differentiation pathway that is a feature of small-cell lung cancer, the most lethal form of human lung cancer.

Animals↗
PubMed1997

Distinct patterns of inactivation of p15INK4B and p16INK4A characterize the major types of hematological malignancies.

Inactivation of the cyclin-dependent kinase inhibitors p16INK4A and p15INK4B are frequent alterations in neoplasia, often resulting from homozygous deletion or promoter region hypermethylation. We have analyzed both modes of inactivation of p15INK4B and p16INK4A in the major types of adult and pediatric hematological malignancies. Hypermethylation of p15INK4B, without alteration of p16INK4A, was an almost universal finding in adult acute myelogenous leukemia, and occurred very frequently in adult acute lymphocytic leukemia and pediatric acute myelogenous leukemia and acute lymphocytic leukemia. In contrast, neither p15INK4B nor p16INK4A were inactivated in any stage of chronic myelogenous leukemia. Hypermethylation of p16INK4A, often without alterations of p15INK4B, was found in non-Hodgkin's lymphoma and was much more frequent in cases with high-grade than low-grade histology. Enriched normal bone marrow stem cells had no detectable promoter region methylation of these genes, as analyzed by a newly developed PCR method. Remarkably distinct patterns of inactivation of p15INK4B and p16INK4A characterize different types of hematological malignancy, and alterations in these tumor suppressor genes are one of the most common alterations in hematological malignancies.

Adult↗
PubMed1997

Expression and function of Trk-C in favourable human neuroblastomas.

Human neuroblastomas express the neurotrophin receptors trk-A and trk-B. Favourable outcome is associated with expression of trk-A, while unfavourable, MYCN amplified tumours express trk-B. In this study we examined the expression of trk-C in primary neuroblastoma tumour-derived cell lines. We found by Northern blot analysis that trk-C mRNA is expressed in 14 of 55 (25%) primary tumours. Trk-C was expressed in significantly more lower stage tumours (stage 1, 2, 4S) than higher stage tumours (stage 3, 4, P < 0.04). The expression of trk-C was correlated positively with survival and negatively correlated with MYCN amplification. We also studied the function of trk-C in transfected cell lines and found that NT-3 promotes both cell survival and differentiation. Our results suggest that trk-C is involved in the biology of favourable neuroblastomas.

Blotting, Northern↗