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J P Issa

Publications and source records attributed to J P Issa.

51 records · Page 3Linked to original sources
PubMed1997

DNA methylation changes in hematologic malignancies: biologic and clinical implications.

DNA methylation changes are among the most common detectable abnormalities in human neoplasia. Hypermethylation within the promoters of selected genes appears to be especially common in all types of human hematopoietic neoplasms, and is usually associated with inactivation of the involved gene(s). Such hypermethylation-associated silencing of gene expression has been shown for several genes regulating the growth and differentiation of hematopoietic cells, including the estrogen receptor (ER) gene, P15, P16 and others. Hypermethylation within the promoters of some genes appear to be an early event in the pathogenesis of neoplasia (ER, P15), while other genes seem to become methylated during the progression of leukemias (HIC1, c-abl). The high prevalence of promoter methylation suggests that this molecular abnormality can be used to monitor disease activity during therapy. In addition, new technology allows the sensitive identification of gene hypermethylation in a background of normal cells, suggesting possible new strategies for the detection of minimal residual disease. Finally, reactivation of tumor-suppressor gene expression through pharmacologic inhibition of DNA methyltransferase and resultant DNA demethylation appears to be a promising new avenue of therapy in acute leukemia.

Blood Cells↗
PubMed1996

Switch from monoallelic to biallelic human IGF2 promoter methylation during aging and carcinogenesis.

We have previously linked aging, carcinogenesis, and de novo methylation within the promoter of the estrogen receptor (ER) gene in human colon. We now examine the dynamics of this process for the imprinted gene for insulin-like growth factor II (IGF2). In young individuals, the P2-4 promoters of IGF2 are methylated exclusively on the silenced maternal allele. During aging, this promoter methylation becomes more extensive and involves the originally unmethylated allele. Most adult human tumors, including colon, breast, lung, and leukemias, exhibit increased methylation at the P2-4 IGF2 promoters, suggesting further spreading during the neoplastic process. In tumors, this methylation is associated with diminished or absent IGF2 expression from the methylated P3 promoter but maintained expression from P1, an upstream promoter that is not contained within the IGF2 CpG island. Our results demonstrate a remarkable evolution of methylation patterns in the imprinted promoter of the IGF2 gene during aging and carcinogenesis, and provide further evidence for a potential link between aberrant methylation and diseases of aging.

Adolescent↗
PubMed1996

Methylation of the estrogen receptor CpG island in lung tumors is related to the specific type of carcinogen exposure.

Promoter methylation has recently been shown to be an alternative to mutation in inactivating tumor suppressor genes in human neoplasia. Although specific carcinogen exposures have been associated with characteristic mutation patterns in genes, the factors that lead to promoter hypermethylation remain unknown. One gene target for inactivation through promoter methylation is the estrogen receptor (ER). The purpose of this investigation was to determine the methylation status of this gene in lung tumors from smokers and those who never smoked and in rodents exposed to specific environmental carcinogens. Promoter methylation at the ER locus was detected in 4 of 11 tumors from never-smokers (36.4%) and 7 of 35 tumors from smokers (20%, P < 0.001). Lung tumors induced by the tobacco-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone also had a low incidence (16.7%) of ER methylation. In marked contrast, spontaneous and plutonium-induced tumors had a very high (81.8%) incidence of ER methylation. X-ray-induced tumors had an intermediate frequency of ER methylation (38.1%). The presence of ER methylation was associated with absent ER expression in rodent lung cancer cell lines. These results show for the first time that gene-specific promoter methylation can be modulated differentially depending on carcinogen exposure.

Animals↗
PubMed1996

Increased cytosine DNA-methyltransferase activity is target-cell-specific and an early event in lung cancer.

The association between increased DNA-methyltransferase (DNA-MTase) activity and tumor development suggest a fundamental role for this enzyme in the initiation and progression of cancer. A true functional role for DNA-MTase in the neoplastic process would be further substantiated if the target cells affected by the initiating carcinogen exhibit changes in enzyme activity. This hypothesis was addressed by examining DNA-MTase activity in alveolar type II (target) and Clara (nontarget) cells from A/J and C3H mice that exhibit high and low susceptibility, respectively, for lung tumor formation. Increased DNA-MTase activity was found only in the target alveolar type II cells of the susceptible A/J mouse and caused a marked increase in overall DNA methylation in these cells. Both DNA-MTase and DNA methylation changes were detected 7 days after carcinogen exposure and, thus, were early events in neoplastic evolution. Increased gene expression was also detected by RNA in situ hybridization in hypertrophic alveolar type II cells of carcinogen-treated A/J mice, indicating that elevated levels of expression may be a biomarker for premalignancy. Enzyme activity increased incrementally during lung cancer progression and coincided with increased expression of the DNA-MTase activity are strongly associated with neoplastic development and constitute a key step in carcinogenesis. The detection of premalignant lung disease through increased DNA-MTase expression and the possibility of blocking the deleterious effects of this change with specific inhibitors will offer new intervention strategies for lung cancer.

Animals↗
PubMed1996

The estrogen receptor CpG island is methylated in most hematopoietic neoplasms.

Estrogen appears to be a negative regulator of normal hematopoiesis. Chromosome 6q, which contains the estrogen receptor (ER) gene, is frequently altered in human hematopoietic neoplasms. The ER gene, which has growth and metastasis suppressor activity in many different cell types, is inactivated by promoter methylation in some ER-negative breast tumors and 100% of colorectal tumors. We now report that the promoter region of the ER gene is aberrantly methylated in 86% of human hematopoietic tumors, including 8 of 9 pediatric acute lymphocytic leukemia, 17 of 18 adult acute lymphocytic leukemia, 21 of 23 adult acute myelogenous leukemia, 3 of 6 chronic phase chronic myelogenous leukemia, 9 of 9 blast crisis chronic myelogenous leukemia and 5 of 8 lymphomas. This methylation event was also present in all nine leukemia cell lines examined, where it was associated with very low or absent ER expression. In addition, rat and mouse leukemia cell line also exhibited this change, indicating that ER CpG island methylation in leukemias is conserved among species. Our results suggest that ER CpG island methylation could be an important step in the genesis of human hematopoietic neoplasms and might be a useful molecular marker for monitoring the clinical status of these diseases.

Adult↗
PubMed1996

Methylation of estrogen and progesterone receptor gene 5' CpG islands correlates with lack of estrogen and progesterone receptor gene expression in breast tumors.

Hormonal factors have a profound influence on the development, treatment, and outcome of breast cancer. The absence of steroid hormone receptors is highly correlated with resistance to antihormonal treatments. Work in cultured human breast cancer cell lines has shown that the absence of estrogen receptor (ER) gene expression in ER- cells is associated with extensive methylation of the ER gene 5' CpG island, and treatment with agents that demethylate the ER gene CpG island results in the production of functional ER protein. The current study shows that CpG islands in the 5' region of the ER and progesterone receptor (PR) genes are methylated in a significant fraction of primary human breast cancer tissues. The ER CpG island is methylated at the methylation-sensitive NotI restriction site in 9 of 39 (25%) of primary ER- breast cancers but remains unmethylated in 53 ER+ breast cancers and 9 normal breast specimens. Three methylation-sensitive restriction sites in the PR gene CpG island are not methylated in normal breast specimens and PR+ human breast cancers but are hypermethylated in 40% of PR- human breast tumors. These data demonstrate that methylation of the ER and PR gene CpG islands is associated with the lack of ER and PR gene expression in a significant fraction of human breast cancers.

Breast Neoplasms↗
PubMed1995

Inactivation of the CDKN2/p16/MTS1 gene is frequently associated with aberrant DNA methylation in all common human cancers.

The tumor suppressor gene CDKN2/p16/MTS1, located on chromosome 9p21, is frequently inactivated in many human cancers through homozygous deletion. Recently, we have reported another pathway of inactivation that involves loss of transcription associated with de novo methylation of a 5' CpG island of CDKN2/p16 in lung cancers, gliomas, and head and neck squamous cell carcinomas. We now show that this aberrant CpG island methylation also occurs frequently in cell lines of breast cancer (33%), prostate cancer (60%), renal cancer (23%), and colon cancer (92%) and is associated with loss of transcription. Primary tumors of the breast (31%) and colon (40%) also displayed de novo methylation of this CpG island. This alteration of p16 in colon cancer was particularly striking, since inactivation does not occur through homozygous deletion in this tumor type. Our data show that in tumors, de novo methylation of the 5' CpG island is a frequent mode of inactivation of CDKN2/p16 and also firmly demonstrate that CDKN2/p16 is one of the most frequently altered genes in human neoplasia.

Carrier Proteins↗
PubMed1995

A microassay for measuring cytosine DNA methyltransferase activity during tumor progression.

The cytosine DNA methyltransferase (MT) enzyme, which catalyzes DNA methylation at CpG sites, is overexpressed at the mRNA level during the progressive stages of colon cancer. This paper describes the adaption of a sensitive microassay for determining MT enzyme activity during tumor progression in human colon and murine lung. MT activity was progressively elevated in mucosa from familial adenomatosis polyposis patients, mucosa adjacent to cancers, and in colonic adenocarcinomas when compared to colonic mucosa from control patients. In addition, the activity of this enzyme was increased in alveolar type II but not Clara cells isolated from A/J mice following carcinogen exposure and continued to increase during tumor progression. The use of a microassay for measuring MT activity indicates that changes in enzyme activity were in general agreement with previous findings of increased MT mRNA levels during colon cancer progression and also implicates the involvement of this pathway in lung cancer development.

Animals↗
PubMed1995

p53 activates expression of HIC-1, a new candidate tumour suppressor gene on 17p13.3.

For several human tumour types, allelic loss data suggest that one or more tumour suppressor genes reside telomeric to the p53 gene at chromosome 17p13.1. In the present study we have used a new strategy, involving molecular analysis of a DNA site hypermethylated in tumour DNA, to identify a candidate gene in this region (17p13.3). Our approach has led to identification of HIC-1 (hypermethylated in cancer), a new zinc-finger transcription factor gene which is ubiquitously expressed in normal tissues, but underexpressed in different tumour cells where it is hypermethylated. Multiple characteristics of this gene, including the presence of a p53 binding site in the 5' flanking region, activation of the gene by expression of a wild-type p53 gene and suppression of G418 selectability of cultured brain, breast and colon cancer cells following insertion of the gene, make HIC-1 gene a strong candidate for a tumour suppressor gene in region 17p13.3.

Amino Acid Sequence↗
PubMed1994

Methylation of the estrogen receptor gene CpG island marks loss of estrogen receptor expression in human breast cancer cells.

Breast cancer is the most common malignancy in women and hormone resistance is a challenging problem in its treatment. Loss of estrogen receptor expression is an important means of hormone resistance, but the mechanisms involved are poorly understood. We now demonstrate a potential role for abnormal DNA methylation in transcriptional inactivation of the estrogen receptor gene. Estrogen receptor-negative human breast cancer cells growing in culture lack estrogen receptor mRNA, have a higher capacity to methylate DNA, and display extensive methylation of the CpG island in the 5' promoter region of the estrogen receptor gene, which would correlate with silencing of expression. These results suggest that abnormal methylation could account for transcriptional inactivation of the estrogen receptor gene and subsequent hormone resistance in some human breast cancers.

Breast Neoplasms↗
PubMed1994

Methylation of the oestrogen receptor CpG island links ageing and neoplasia in human colon.

We report that CpG island methylation, an epigenetic modification of DNA known to correlate closely with silencing of gene transcription, appears in the oestrogen receptor (ER) gene in a subpopulation of cells which increases as a direct function of age in human colonic mucosa. This same methylation change characterizes virtually all cells in all 45 colorectal tumours examined, including the earliest stages of tumour formation. ER gene expression is diminished or absent in colorectal tumours, and introduction of an exogenous ER gene in cultured colon carcinoma cells resulted in marked growth suppression. Our data suggest that methylation associated inactivation of the ER gene in ageing colorectal mucosa could be one of the earliest events that predispose to sporadic colorectal tumorigenesis.

Aging↗
PubMed1994

Stabilization of DNA methyltransferase levels and CpG island hypermethylation precede SV40-induced immortalization of human fibroblasts.

De novo methylation of normally unmethylated CpG islands and increased expression of DNA (cytosine-5)-methyltransferase (DNA MTase) are common characteristics of immortalized cell lines and human tumors. To examine the acquisition of these properties with respect to cellular immortalization, we studied CpG island methylation and DNA MTase expression in aging normal human fibroblasts and their SV40-infected preimmortal (precrisis) and immortal (postcrisis) derivatives. The levels of DNA MTase enzyme activity decreased by 50% as normal fibroblasts were cultured to senescence. By contrast, DNA MTase activity did not decrease in SV40-infected pre- or postcrisis cells but remained similar to that of young fibroblasts and 2-4-fold higher than that of senescent fibroblasts. DNA MTase mRNA levels paralleled those of enzyme activity. Several loci were examined to determine the relationship between the dynamics of DNA MTase expression and the appearance of de novo CpG island methylation. Ten CpG island loci examined were unmethylated in normal young fibroblasts. By contrast, four of these loci (the CALC1, MyoD, and IGF-2 genes on chromosome 11p and the estrogen receptor gene on chromosome 6q) were de novo methylated in fully immortalized, postcrisis cells. Two of these four were actually methylated in extended life span precrisis cells, and one, the estrogen receptor locus, exhibited de novo methylation with aging in normal fibroblasts. The data indicate that an ability to maintain DNA MTase levels is acquired with SV40-induced escape from senescence. Furthermore, aberrant CpG island methylation can be established prior to immortalization, either as a function of normal aging or in response to SV40-induced escape from senescence.

Blotting, Northern↗
PubMed1993

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.

3T3 Cells↗
PubMed1993

Increased cytosine DNA-methyltransferase activity during colon cancer progression.

BACKGROUND: Molecular changes during progressive stages of colon cancer and other human tumors commonly involve altered regulation of DNA methylation. These changes include overall genomic hypomethylation, regional hypermethylation, and increased levels of messenger RNA (mRNA) for cytosine DNA-methyltransferase (DNA-MTase), the enzyme that catalyzes DNA methylation at CpG (cytosine-phospho-guanine) sites. This increase in DNA-MTase transcripts (mRNA), if accompanied by increased DNA-MTase activity, could play a role in the abnormal DNA methylation patterns that appear early in colon tumor progression. PURPOSE: We sought to determine whether increased DNA-MTase mRNA levels during colon cancer progression are associated with increased cellular DNA-MTase enzymatic activity. METHODS: We adapted a microassay for DNA-MTase and used it to measure activity in human colon carcinoma and in colon mucosa of normal control subjects and of patients with colon cancer or with familial adenomatous polyposis (FAP), which is a risk factor for colon cancer. Steady-state DNA-MTase gene transcripts were measured by a reverse transcriptase polymerase chain reaction assay. To compare DNA-MTase activity with mRNA levels, we determined both variables simultaneously for one colon cancer specimen, its adjacent mucosa, and the colon mucosa of a control patient and compared the values. RESULTS: Compared with DNA-MTase activity in mucosa from normal control subjects, activity was elevated 1.4-fold in FAP mucosa, 1.6-fold in the uninvolved mucosa of patients with cancer, and 5.4-fold in the cancer specimens. All these differences were statistically significant. Fourteen of 15 cancer samples and 47% of the uninvolved adjacent mucosa samples had values that were higher than the highest value in normal mucosa. In one patient who had both a benign adenomatous polyp and a malignant adenocarcinoma, increasing DNA-MTase activity was observed at each stage of tumor progression. CONCLUSION: These results demonstrate that an increased DNA methylation capacity accompanies the increase in DNA-MTase transcripts observed during progressive stages of colon cancer. IMPLICATION: Further studies are needed to determine whether this abnormal methylation capacity plays a role in establishing the abnormal DNA methylation patterns seen in human malignancies.

Adenocarcinoma↗