Inactivation of CACNA1G, a T-type calcium channel gene, by aberrant methylation of its 5' CpG island in human tumors

Using a newly developed PCR-based technique called methylated CpG island amplification, we have identified several DNA fragments that are aberrantly methylated in a colon cancer cell line. One of the fragments, termed MINT31, mapped to human chromosome 17q21, where frequent loss of heterozygosity is detected in various human tumors. By characterizing the genomic sequence around this area, we identified a gene encoding a T-type calcium channel, CACNA1G, as a target for hypermethylation in human tumors. By reverse transcriptase-PCR we detected expression of CACNA1G in normal colon and bone marrow, but expression was absent in the five tumor cell lines in which methylation was found. After treatment with the methylation inhibitor 5-deoxyazacytidine, the expression of CACNA1G was restored in all five cell lines. Detailed methylation mapping of the 5' CpG island by bisulfite-PCR revealed that methylation of a region 300-800 bp upstream of the translation initiation site closely correlated with the inactivation of CACNA1G. This region contained the transcription start site, as determined by 5' rapid amplification of cDNA ends analysis. Aberrant methylation of CACNA1G was also examined in various human primary tumors and was detected in 17 of 49 (35%) colorectal cancers, 4 of 16 (25%) gastric cancers, and 3 of 23 (13%) acute myelogenous leukemia cases. Inactivation of CACNA1G may play a role in cancer development by modulating calcium signaling, which potentially affects cell proliferation and apoptosis.

CpG island methylator phenotype in colorectal cancer

Aberrant methylation of promoter region CpG islands is associated with transcriptional inactivation of tumor-suppressor genes in neoplasia. To understand global patterns of CpG island methylation in colorectal cancer, we have used a recently developed technique called methylated CpG island amplification to examine 30 newly cloned differentially methylated DNA sequences. Of these 30 clones, 19 (63%) were progressively methylated in an age-dependent manner in normal colon, 7 (23%) were methylated in a cancer-specific manner, and 4 (13%) were methylated only in cell lines. Thus, a majority of CpG islands methylated in colon cancer are also methylated in a subset of normal colonic cells during the process of aging. In contrast, methylation of the cancer-specific clones was found exclusively in a subset of colorectal cancers, which appear to display a CpG island methylator phenotype (CIMP). CIMP+ tumors also have a high incidence of p16 and THBS1 methylation, and they include the majority of sporadic colorectal cancers with microsatellite instability related to hMLH1 methylation. We thus define a pathway in colorectal cancer that appears to be responsible for the majority of sporadic tumors with mismatch repair deficiency.

Transcriptional silencing of the p73 gene in acute lymphoblastic leukemia and Burkitt's lymphoma is associated with 5' CpG island methylation

The p73 gene is located on 1p36.2-3, a region that is frequently deleted in human cancer. Because p73 encodes for a protein that is both structurally and functionally homologous to the p53 protein, p73 has been postulated to be a candidate tumor suppressor gene. To date, however, mutations of p73 have not been found. To study methylation of the p73 5'CpG island, a human bacterial artificial chromosome clone containing exon 1 and the 5' region of p73 was isolated. There was no evidence for p73 exon 1 methylation in normal tissues. In contrast, p73 was aberrantly methylated in approximately 30% of primary acute lymphoblastic leukemias (ALLs) and Burkitt's lymphomas. There was no evidence for methylation in any other types of hematological malignancies or solid tumors examined. In both leukemia cell lines and primary ALLs, methylation was associated with transcriptional loss of p73 by reverse transcription-PCR. We used single-strand conformational polymorphisms to screen for point mutations in a series of primary ALLs and found no mutations leading to a change in protein structure. Our results show that methylation of p73 is a frequent event in specific types of hematological malignancies and suggest that epigenetic silencing of p73 could have important consequences for cell-cycle regulation.

Hypermethylation of the DAP-kinase CpG island is a common alteration in B-cell malignancies

Death-associated protein kinase (DAP-Kinase) is a novel serine/threonine kinase whose expression is required for gamma interferon-induced apoptosis. A previous study suggested that DAP-Kinase expression may be lost epigenetically in cancer cell lines, because treatment of several nonexpressing cell lines with 5-aza-2'-deoxycytidine resulted in the expression of DAP-Kinase. Using methylation-specific polymerase chain reaction (MSP), we examined the DAP-Kinase CpG island for hypermethylation in cancer. Normal lymphocytes and lymphoblastoid cell lines are unmethylated in the 5' CpG island of DAP-Kinase. However, in primary tumor samples, all Burkitt's lymphomas and 84% of the B-cell non-Hodgkin's lymphomas were hypermethylated in the DAP-Kinase CpG island. In contrast, none of the T-cell non-Hodgkin's lymphoma samples and 15% or less of leukemia samples examined had hypermethylated DAP-Kinase alleles. U937, an unmethylated, DAP-Kinase-expressing leukemia cell line, was treated with gamma interferon and underwent apoptosis; however, Raji, a fully methylated, DAP-Kinase nonexpressing Burkitt's lymphoma cell line, only did so when treated with 5-aza-2'-deoxycytidine followed by gamma interferon. Our findings in cell lines and primary tumors suggest that hypermethylation of the DAP-Kinase gene and loss of gamma interferon-mediated apoptosis may be important in the development of B-cell malignancies and may provide a promising biomarker for B-cell-lineage lymphomas.

Identification of differentially methylated sequences in colorectal cancer by methylated CpG island amplification

CpG island methylation has been linked to tumor suppressor gene inactivation in neoplasia and may serve as a useful marker to clone novel cancer-related genes. We have developed a novel PCR-based method, methylated CpG island amplification (MCA), which is useful for both methylation analysis and cloning differentially methylated genes. Using restriction enzymes that have differential sensitivity to 5-methyl-cytosine, followed by adaptor ligation and PCR amplification, methylated CpG rich sequences can be preferentially amplified. In a model experiment using a probe from exon 1 of the p16 gene, signal was detected from MCA products of a colorectal cancer cell line but not in normal colon mucosa. To identify novel CpG islands differentially methylated in colorectal cancer, we have applied MCA coupled with representational difference analysis to the colon cancer cell line Caco2 as a tester and normal colon mucosa as a driver. Using this strategy, we isolated 33 differentially methylated DNA sequences, including fragments identical to several known genes (PAX6, Versican, alpha-tubulin, CSX, OPT, and rRNA gene). The association of hypermethylation of the clones obtained and transcriptional suppression in colorectal cancer was confirmed by examining the Versican gene, which we found to be silenced in methylated cell lines and reactivated by the methylation inhibitor 5-aza-2'-deoxycytidine. We therefore propose that MCA is a useful technique to study methylation and to isolate CpG islands differentially methylated in cancer.

Roles of trk family neurotrophin receptors in medullary thyroid carcinoma development and progression

Although initiating mutations in the ret protooncogene have been found in familial and sporadic medullary thyroid carcinoma (MTC), the molecular events underlying subsequent tumor progression stages are unknown. We now report that changes in trk family neurotrophin receptor expression appear to be involved in both preneoplastic thyroid C cell hyperplasia and later tumor progression. Only a subset of normal C cells expresses trk family receptors, but, in C cell hyperplasia, the affected cells consistently express trkB, with variable expression of trkA and trkC. In later stages of gross MTC tumors, trkB expression was substantially reduced, while trkC expression was increased and often intense. In a cell culture model of MTC, exogenous trkB expression resulted in severely impaired tumorigenicity and was associated with 11-fold lower levels of the angiogenesis factor vascular endothelial growth factor. These results suggest that trk family receptor genes participate in MTC development and progression, and, in particular, that trkB may limit MTC tumor growth by inhibition of angiogenesis.

Methylation-associated silencing of the tissue inhibitor of metalloproteinase-3 gene suggest a suppressor role in kidney, brain, and other human cancers

Tissue inhibitor of metalloproteinase-3 (TIMP-3) antagonizes matrix metalloproteinase activity and can suppress tumor growth, angiogenesis, invasion, and metastasis. Loss of TIMP-3 has been related to the acquisition of tumorigenesis. Herein, we show that TIMP-3 is silenced in association with aberrant promoter-region methylation in cell lines derived from human cancers. TIMP-3 expression was restored after 5-aza-2'deoxycytidine-mediated demethylation of the TIMP-3 proximal promoter region. Genomic bisulfite sequencing revealed that TIMP-3 silencing was related to the overall density of methylation and that discrete regions within the TIMP-3 CpG island may be important for the silencing of this gene. Aberrant methylation of TIMP-3 occurred in primary cancers of the kidney, brain, colon, breast, and lung, but not in any of 41 normal tissue samples. The most frequent TIMP-3 methylation was found in renal cancers, which originate in the tissue that normally expresses the highest TIMP-3 levels. This methylation correlated with a lack of detectable TIMP-3 protein in these tumors. Together, these data show that methylation-associated inactivation of TIMP-3 is frequent in many human tumors.

Inactivation of the DNA repair gene O6-methylguanine-DNA methyltransferase by promoter hypermethylation is a common event in primary human neoplasia

The DNA repair protein O6-methylguanine DNA methyltransferase (MGMT) removes alkyl adducts from the O6 position of guanine. MGMT expression is decreased in some tumor tissues, and lack of activity has been observed in some cell lines. Loss of expression is rarely due to deletion, mutation, or rearrangement of the MGMT gene, but methylation of discrete regions of the CpG island of MGMT has been associated with the silencing of the gene in cell lines. We used methylation-specific PCR to study the promoter methylation of the MGMT gene. All normal tissues and expressing cancer cell lines were unmethylated, whereas nonexpressing cancer cell lines were methylated. Among the more than 500 primary human tumors examined, MGMT hypermethylation was present in a subset of specific types of cancer. In gliomas and colorectal carcinomas, aberrant methylation was detected in 40% of the tumors, whereas in non-small cell lung carcinomas, lymphomas, and head and neck carcinomas, this alteration was found in 25% of the tumors. MGMT methylation was found rarely or not at all in other tumor types. We also analyzed MGMT expression by immunohistochemistry in relation to the methylation status in 31 primary tumors. The presence of aberrant hypermethylation was associated with loss of MGMT protein, in contrast to retention of protein in the majority of tumors without aberrant hypermethylation. Our results suggest that epigenetic inactivation of MGMT plays an important role in primary human neoplasia.

Detection of aberrant promoter hypermethylation of tumor suppressor genes in serum DNA from non-small cell lung cancer patients

Recent evidence suggests that tumor cells may release DNA into the circulation, which is enriched in the serum and plasma, allowing detection of ras and p53 mutations and microsatellite alterations in the serum DNA of cancer patients. We examined whether aberrant DNA methylation might also be found in the serum of patients with non-small cell lung cancer. We tested 22 patients with non-small cell lung cancer using methylation-specific PCR, searching for promoter hypermethylation of the tumor suppressor gene p16, the putative metastasis suppressor gene death-associated protein kinase, the detoxification gene glutathione S-transferase P1, and the DNA repair gene O6-methylguanine-DNA-methyltransferase. Aberrant methylation of at least one of these genes was detected in 15 of 22 (68%) NSCLC tumors but not in any paired normal lung tissue. In these primary tumors with methylation, 11 of 15 (73%) samples also had abnormal methylated DNA in the matched serum samples. Moreover, none of the sera from patients with tumors not demonstrating methylation was positive. Abnormal promoter methylation in serum DNA was found in all tumor stages. Although these results need to be confirmed in larger studies and in other tumor types, detection of aberrant promoter hypermethylation of cancer-related genes in serum may be useful for cancer diagnosis or the detection of recurrence.

Synergy of demethylation and histone deacetylase inhibition in the re-expression of genes silenced in cancer

Densely methylated DNA associates with transcriptionally repressive chromatin characterized by the presence of underacetylated histones. Recently, these two epigenetic processes have been dynamically linked. The methyl-CpG-binding protein MeCP2 appears to reside in a complex with histone deacetylase activity. MeCP2 can mediate formation of transcriptionally repressive chromatin on methylated promoter templates in vitro, and this process can be reversed by trichostatin A (TSA), a specific inhibitor of histone deacetylase. Little is known, however, about the relative roles of methylation and histone deacetylase activity in the stable inhibition of transcription on densely methylated endogenous promoters, such as those for silenced alleles of imprinted genes, genes on the female inactive X chromosome and tumour-suppressor genes inactivated in cancer cells. We show here that the hypermethylated genes MLH1, TIMP3 (TIMP3), CDKN2B (INK4B, p15) and CDKN2A (INK4, p16) cannot be transcriptionally reactivated with TSA alone in tumour cells in which we have shown that TSA alone can upregulate the expression of non-methylated genes. Following minimal demethylation and slight gene reactivation in the presence of low dose 5-aza-2'deoxycytidine (5Aza-dC), however, TSA treatment results in robust re-expression of each gene. TSA does not contribute to demethylation of the genes, and none of the treatments alter the chromatin structure associated with the hypermethylated promoters. Thus, although DNA methylation and histone deacetylation appear to act as synergistic layers for the silencing of genes in cancer, dense CpG island methylation is dominant for the stable maintenance of a silent state at these loci.

Deletion of p16INK4A/CDKN2 and p15INK4B in human somatic cell hybrids and hybrid-derived tumors

Deletion or epigenetic inactivation of the tumor suppressor gene p16INK4/CDKN2 (p16) has been observed in multiple human tumors. We assayed hybrid cell lines between human diploid fibroblasts and fibrosarcoma cells for p16 allelic status and expression and found that p16 was expressed in the parental diploid fibroblast cell lines used, whereas the parental fibrosarcoma cell line HT1080.6TG exhibited homozygous deletion of p16. Most immortalized hybrid cell lines derived from these parent cell lines, whether tumorigenic or nontumorigenic, exhibited loss of fibroblast-derived p16 alleles. All p16-negative hybrid cell lines also exhibited deletion of p15INK4B (p15). Hybrid cell lines yielded tumors upon s.c. injection into athymic nude mice regardless of p16/p15 status. Tumors derived from six p16/p15-positive hybrid cells, however, revealed deletions of both p16 and p15. When human diploid fibroblasts were fused with A388.6TG squamous cell carcinoma cells, which exhibit aberrant methylation of p16, the resulting hybrids again exhibited deletion of the unmethylated fibroblast-derived p16 alleles. Transfection of both HT1080.6TG and A388.6TG cells with wild-type p16 expression vector resulted in decreased clonogenicity in culture. Although the determinants directing genetic versus epigenetic inactivation of p16 and p15 remain unclear, these results demonstrate that p16-mediated growth suppression could be abrogated by either mechanism in somatic cell hybrids.

Aging and DNA methylation in colorectal mucosa and cancer

DNA methylation of promoter-associated CpG islands may function as an alternate mechanism of silencing tumor suppressor genes in multiple neoplasias including colorectal cancer. De novo methylation of genes appears to be an early and frequent event in most neoplasias. For the ER and IGF2 genes, we have previously shown that methylation actually begins in the normal colon mucosa as an age-related event and progresses to hypermethylation in cancer. In this study, we have determined the frequency of age-related methylation in normal colonic mucosa among the genes hypermethylated in colorectal cancer. We studied six genes, including N33, MYOD, p16, HIC-1, THBS1, and CALCA. The N33 gene showed partial methylation in normal colon mucosa, which was age-related (r = 0.7; P = 0.003 using regression analysis). Adenomas and cancers showed further hypermethylation at this locus. Similarly, the MYOD gene showed age-related methylation in normal colon mucosa (r = 0.7; P < 0.00001 using regression analysis) and hypermethylation in cancers. Age-related methylation seems to be gene specific, because p16, THBS1, HIC-1, and CALCA were not affected. Furthermore, this process may also be modulated by tissue-specific factors. Our study suggests that aging is a major contributing factor to hypermethylation in cancer.

MLH1 promoter hypermethylation is associated with the microsatellite instability phenotype in sporadic endometrial carcinomas

Microsatellite instability (MSI) has been detected in endometrial carcinomas occurring in women affected by hereditary nonpolyposis colorectal carcinoma (HNPCC) as well as in 20% of presumably sporadic endometrial tumors. While the MSI+ phenotype observed in endometrial tumors from HNPCC patients is attributed to germ line mutations in mismatch repair (MMR) genes, somatic mutations of known MMR genes are infrequent in MSI+ sporadic endometrial carcinomas. Recently, cytosine methylation of the MLH1 promoter region has been identified in a subset of MSI+ colon primary carcinomas and cell lines. We studied the MLH1 and MSH2 promoter methylation status in 29 presumably sporadic uterine endometrioid carcinomas (UECs), which had previously been characterized for the MSI phenotype and a subset for DNA MMR gene mutational status. We found that 13 (45%) of 29 cases of EC were hypermethylated in the 5' CpG island of MLH1. Hypermethylation of MSH2 was not observed. MLH1 was hypermethylated in 12 (92%) of 13 MSI+ tumors, while only 1 (6%) of 16 MSI- tumors (Fischer's exact test P<O.0001). Other tumor types we tested did not demonstrate MLH1 promoter hypermethylation. Our data suggest that hypermethylation of MLH1, but not of MSH2, is associated with the MSI phenotype in sporadic endometrial carcinomas.

Inactivation of glutathione S-transferase P1 gene by promoter hypermethylation in human neoplasia

Glutathione S-transferases (GSTs) are a family of isoenzymes that play an important role in protecting cells from cytotoxic and carcinogenic agents. The pi-class GST has been associated with preneoplastic and neoplastic changes. Recently, it has been reported that regulatory sequences near the GSTP1 gene, which encodes the human pi-class GST, are commonly hypermethylated in prostatic carcinomas. In the present study, we studied more than 300 primary human tumors originating in other organs for aberrant methylation of GSTP1 using methylation-specific PCR. GSTP1 hypermethylation was most frequent in breast and renal carcinoma, showing aberrant methylation in 30 and 20% of the cases, respectively. Other tumor types showed promoter methylation only rarely or not at all. Hypermethylation of GSTP1 was associated with loss of expression demonstrated by immunohistochemistry. Our results suggest that aberrant methylation of GSTP1 may contribute to the carcinogenetic process in breast and renal carcinomas.

Aberrant methylation of p16(INK4a) is an early event in lung cancer and a potential biomarker for early diagnosis

The p16(INK4a) (p16) tumor suppressor gene can be inactivated by promoter region hypermethylation in many tumor types including lung cancer, the leading cause of cancer-related deaths in the U.S. We have determined the timing of this event in an animal model of lung carcinogenesis and in human squamous cell carcinomas (SCCs). In the rat, 94% of adenocarcinomas induced by the tobacco specific carcinogen 4-methylnitrosamino-1-(3-pyridyl)-1-butanone were hypermethylated at the p16 gene promoter; most important, this methylation change was frequently detected in precursor lesions to the tumors: adenomas, and hyperplastic lesions. The timing for p16 methylation was recapitulated in human SCCs where the p16 gene was coordinately methylated in 75% of carcinoma in situ lesions adjacent to SCCs harboring this change. Moreover, the frequency of this event increased during disease progression from basal cell hyperplasia (17%) to squamous metaplasia (24%) to carcinoma in situ (50%) lesions. Methylation of p16 was associated with loss of expression in both tumors and precursor lesions indicating that both alleles were functionally inactivated. The potential of using assays for aberrant p16 methylation to identify disease and/or risk was validated by detection of this change in sputum from three of seven patients with cancer and 5 of 26 cancer-free individuals at high risk. These studies show for the first time that an epigenetic alteration, aberrant methylation of the p16 gene, can be an early event in lung cancer and may constitute a new biomarker for early detection and monitoring of prevention trials.

Hypomethylation of pericentromeric DNA in breast adenocarcinomas

Drug-induced DNA demethylation in normal human cells and inherited localized hypomethylation in mitogen-stimulated lymphocytes from patients with a rare recessive disease (ICF: immunodeficiency, centromeric region instability, facial anomalies) are associated with karyotypic instability. This chromosomal recombination is targeted to heterochromatin in the vicinity of the centromere (pericentromeric region) of human chromosome 1. Pericentromeric rearrangements in this chromosome as well as overall genomic hypomethylation are frequently observed in many kinds of cancer, including breast adenocarcinoma. We found that almost half of 25 examined breast adenocarcinomas exhibited hypomethylation in satellite 2 DNA, which is located in the long region of heterochromatin adjacent to the centromere of chromosome 1 and is normally highly methylated. One of the 19 examined non-malignant breast tissues displaying fibrocystic changes was similarly hypomethylated in this satellite DNA. We also looked at an opposing type of methylation alteration in these cancers, namely, hypermethylation in a tumor-suppressor gene region that is frequently hypermethylated in breast cancers. We found that increased methylation in the E-cadherin promoter region and decreased methylation in satellite 2 DNA were often present in the same breast cancers. While hypermethylation in certain tumor-suppressor gene regions may favor tumorigenesis by repressing transcription, demethylation of other DNA sequences may predispose to cancer-promoting chromosomal re-arrangements.

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.

Post-transcriptional silencing of RET occurs, but is not required, during raf-1 mediated differentiation of medullary thyroid carcinoma cells

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor of the calcitonin secreting thyroid C-cells. Somatic and germline mutations in the RET proto-oncogene are associated with sporadic and inherited cases of MTC, respectively. The human MTC cell line, TT, can be differentiated by activated raf-1. This differentiation is characterized, in part, by down-regulation of the RET proto-oncogene. We now show that raf-1 induction is followed by activation of the downstream kinases MEK1/2 and ERK1/2 and that differentiation is dependent on activation of MEK1/2. The concurrent down-regulation of RET appears to involve altered nuclear compartmentalization and transport of RET mRNA. Although RET is down-regulated during raf-1 mediated differentiation, overexpression of activated RET alleles which resist down-regulation does not alter the raf-1 mediated differentiation response. These data suggest that RET down-regulation is associated with, but not required, for raf-1 mediated MTC cell differentiation and that the raf-1 signal transduction pathway plays a dominant role in promoting MTC cell differentiation.

Concordant methylation of the ER and N33 genes in glioblastoma multiforme

Methylation of promoter-associated CpG islands appears to be a potential way by which tumor suppressor genes are inactivated in cancer. Using Southern blot analysis, we have studied the methylation of several genes in glioblastoma multiforme (GBM), trying to determine their contribution to tumorigenesis. Genes studied included the estrogen receptor (ER), N33, the candidate tumor-suppressors P15, P16 and HIC1 and a control gene, c-abl. Hypermethylation of N33, ER, HIC1, P16, P15 and c-abl were found in 61%, 59%, 60%, 5%, 2% and 0% of GBM respectively. HIC1 methylation was detected in normal brain as well, but appeared to be more extensive in tumors. ER and N33 methylation were significantly more frequent in tumors from individuals over the age of 40 (70% and 88% vs 36% and 14%). In addition, there was a strong association between ER and N33 methylation, which were concordant in 81% of the cases (P<0.01). ER and N33 methylation in GBM may therefore appear as a result of shared etiologic factors, which may relate in part to aging cell populations in the brain.

Incidence and functional consequences of hMLH1 promoter hypermethylation in colorectal carcinoma

Inactivation of the genes involved in DNA mismatch repair is associated with microsatellite instability (MSI) in colorectal cancer. We report that hypermethylation of the 5' CpG island of hMLH1 is found in the majority of sporadic primary colorectal cancers with MSI, and that this methylation was often, but not invariably, associated with loss of hMLH1 protein expression. Such methylation also occurred, but was less common, in MSI- tumors, as well as in MSI+ tumors with known mutations of a mismatch repair gene (MMR). No hypermethylation of hMSH2 was found. Hypermethylation of colorectal cancer cell lines with MSI also was frequently observed, and in such cases, reversal of the methylation with 5-aza-2'-deoxycytidine not only resulted in reexpression of hMLH1 protein, but also in restoration of the MMR capacity in MMR-deficient cell lines. Our results suggest that microsatellite instability in sporadic colorectal cancer often results from epigenetic inactivation of hMLH1 in association with DNA methylation.

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.

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.

Mechanisms of inactivation of E-cadherin in breast cancer cell lines

Loss of E-cadherin (CDH1) function is thought to contribute to progression in breast cancer and other solid tumors by increasing proliferation, invasion, and/or metastasis. In some cases, the restoration of CDH1 function may be an important therapeutic option. This possibility will depend on the mechanism by which CDH1 is inactivated. Here we present analyses of CDH1 expression, genetic mutation, and promoter methylation in CDH1 in 10 commonly used breast cancer cell lines. Five cell lines (BT-474, MCF-7, MDA-MB-361, MDA-MB-468, and T-47D) expressed CDH1 and were genetically normal. Five others (SK-BR-3, 600 MPE, MDA-MB-134 IV, CAMA1, and MDA-MB-435) did not express CDH1. Fluorescence in situ hybridization analyses of each of these cell lines showed evidence for the physical deletion of one allele of CDH1, and three cell lines were found to carry homozygous deletions. SK-BR-3 was deleted from exon 12 through the promoter; exon 6 was deleted in MDA-MB-134 IV cells, and 600 MPE cells carried a 21-bp deletion in the splicing acceptor site for exon 9. CAMA1 seemed to have been inactivated through promoter methylation. No explanation was found for the inactivation of CDH1 in MDA-MB-435.