Allele loss on chromosome 11q and microsatellite instability in malignant melanoma

A new ferroptosis-related genetic mutation risk model predicts the prognosis of skin cutaneous melanoma

Background: Ferroptosis is an iron-dependent cell death mode and closely linked to various cancers, including skin cutaneous melanoma (SKCM). Although attempts have been made to construct ferroptosis-related gene (FRG) signatures for predicting the prognosis of SKCM, the prognostic impact of ferroptosis-related genetic mutations in SKCM remains lacking. This study aims to develop a prediction model to explain the relationship between ferroptosis-related genetic mutations and clinical outcomes of SKCM patients and to explore the potential value of ferroptosis in SKCM treatment. Methods: FRGs which significantly correlated with the prognosis of SKCM were firstly screened based on their single-nucleotide variant (SNV) status by univariate Cox regression analysis. Subsequently, the least absolute shrinkage and selection operator (LASSO) and Cox regressions were performed to construct a new ferroptosis-related genetic mutation risk (FerrGR) model for predicting the prognosis of SKCM. We then illustrate the survival and receiver operating characteristic (ROC) curves to evaluate the predictive power of the FerrGR model. Moreover, independent prognostic factors, genomic and clinical characteristics, immunotherapy, immune infiltration, and sensitive drugs were compared between high-and low-FerrGR groups. Results: The FerrGR model was developed with a good performance on survival and ROC analysis. It was a robust independent prognostic indicator and followed a nomogram constructed to predict prognostic outcomes for SKCM patients. Besides, FerrGR combined with tumor mutational burden (TMB) or MSI (microsatellite instability) was considered as a combined biomarker for immunotherapy response. The high FerrGR group patients were associated with an inhibitory immune microenvironment. Furthermore, potential drugs target to high FerrGR samples were predicted. Conclusion: The FerrGR model is valuable to predict prognosis and immunotherapy in SKCM patients. It offers a novel therapeutic option for SKCM.

Melanoma: Prognostic Factors and Factors Predictive of Response to Therapy

BACKGROUND

A better understanding of prognostic factors and biomarkers that predict response to treatment is required in order to further improve survival rates in patients with melanoma. Prognostic Factors: The most important histopathological factors prognostic of worse outcomes in melanoma are sentinel lymph node involvement, increased tumor thickness, ulceration and higher mitotic rate. Poorer survival may also be related to several clinical factors, including male gender, older age, axial location of the melanoma, elevated serum levels of lactate dehydrogenase and S100B. Predictive Biomarkers: Several biomarkers have been investigated as being predictive of response to melanoma therapies. For anti-Programmed Death-1(PD-1)/Programmed Death-Ligand 1 (PD-L1) checkpoint inhibitors, PD-L1 tumor expression was initially proposed to have a predictive role in response to anti-PD-1/PD-L1 treatment. However, patients without PD-L1 expression also have a survival benefit with anti-PD-1/PD-L1 therapy, meaning it cannot be used alone to select patients for treatment, in order to affirm that it could be considered a correlative, but not a predictive marker. A range of other factors have shown an association with treatment outcomes and offer potential as predictive biomarkers for immunotherapy, including immune infiltration, chemokine signatures, and tumor mutational load. However, none of these have been clinically validated as a factor for patient selection. For combined targeted therapy (BRAF and MEK inhibition), lactate dehydrogenase level and tumor burden seem to have a role in patient outcomes.

CONCLUSION

With increasing knowledge, the understanding of melanoma stage-specific prognostic features should further improve. Moreover, ongoing trials should provide increasing evidence on the best use of biomarkers to help select the most appropriate patients for tailored treatment with immunotherapies and targeted therapies.

Emerging biomarkers for cancer immunotherapy in melanoma

The treatment and prognosis of metastatic melanoma has changed substantially since the advent of novel immune checkpoint inhibitors (ICI), agents that enhance the anti-tumor immune response. Despite the success of these agents, clinically actionable biomarkers to aid patient and regimen selection are lacking. Herein, we summarize and review the evidence for candidate biomarkers of response to ICIs in melanoma. Many of these candidates can be examined as parts of a known molecular pathway of immune response, while others are clinical in nature. Due to the ability of ICIs to illicit dramatic and durable responses, well-validated biomarkers that can be effectively implemented in the clinic will require strong negative predictive values that do not limit patients with who may benefit from ICI therapy.

Deficient mismatch repair: Read all about it (Review)

Defects in the DNA mismatch repair (MMR) proteins, result in a phenotype called microsatellite instability (MSI), occurring in up to 15% of sporadic colorectal cancers. Approximately one quarter of colon cancers with deficient MMR (dMMR) develop as a result of an inherited predisposition syndrome, Lynch syndrome (formerly known as HNPCC). It is essential to identify patients who potentially have Lynch syndrome, as not only they, but also family members, may require screening and monitoring. Diagnostic criteria have been developed, based primarily on Western populations, and several methodologies are available to identify dMMR tumours, including immunohistochemistry and microsatellite testing. These criteria have provided evidence supporting the introduction of reflex testing. Yet, it is becoming increasingly clear that tests have a limited sensitivity and specificity and may yet be superseded by next generation sequencing. In this review, the limitations of diagnostic criteria are discussed, and current and emerging screening technologies explained. There is now useful evidence supporting the prognostic and predictive value of dMMR status in colorectal tumours, but much less is known about their value in extracolonic tumours, that may also feature in Lynch syndrome. This review assesses current literature relating to dMMR in endometrial, ovarian, gastric and melanoma cancers, which it would seem, may benefit from large-scale clinical trials in order to further close the gap in knowledge between colorectal and extracolonic tumours.

Implication of the β2-microglobulin gene in the generation of tumor escape phenotypes

Classical MHC molecules present processed peptides from endogenous protein antigens on the cell surface, which allows CD8(+) cytotoxic T lymphocytes (CTLs) to recognize and respond to the abnormal antigen repertoire of hazardous cells, including tumor cells. The light chain, β2-microglobulin (β2m), is an essential constant component of all trimeric MHC class I molecules. There is convincing evidence that β2m deficiency generates immune escape phenotypes in different tumor entities, with an exceptionally high frequency in colorectal carcinoma (CRC) and melanoma. Damage of a single β2m gene by LOH on chromosome 15 may be sufficient to generate a tumor cell precommitted to escape. In addition, this genetic lesion is followed in some tumors by a mutation of the second gene (point mutation or insertion/deletion), which produces a tumor cell unable to express any HLA class I molecule. The pattern of mutations found in microsatellite unstable colorectal carcinoma (MSI-H CRC) and melanoma showed a striking similarity, namely the predominance of frameshift mutations in repetitive CT elements. This review emphasizes common but also distinct molecular mechanisms of β2m loss in both tumor types. It also summarizes recent studies that point to an acquired β2m deficiency in response to cancer immunotherapy, a barrier to successful vaccination or adoptive cellular therapy.

Myelodysplastic syndromes with deletions of chromosome 11q lack cryptic MLL rearrangement and exhibit characteristic clinicopathologic features

Deletions of chromosome 11q[del(11q)] as part of a non-complex karyotype are infrequent in myelodysplastic syndromes (MDS), leaving the clinicopathologic and genetic features largely undefined. From three large medical centers over a 10-year period, we identified 32 MDS cases where del(11q) was present either as a sole (n=23) or associated with another abnormality (n=9), showing an overall 0.6% frequency in MDS. These patients included 15 men and 17 women, with a median age of 68 years. Three were therapy-related, and 29 were primary MDS. These cases were characterized by transfusion-dependent anemia (65%); frequent ring sideroblasts (RS) (59%); bone marrow hypocellularity (22%), and less severe thrombocytopenia. With a median follow-up of 32 months, 9/24 (38%) cases progressed to acute myeloid leukemia (AML), and the overall survival (OS) was 35 months (3-105). Fluorescence in situ hybridization (FISH) showed MLL deletion in 6/10 cases, but no cryptic MLL translocations in all 15 MDS cases tested. In contrast, FISH performed in AML with del(11q) showed MLL rearrangement in 3/17 (18%) cases. In summary, del(11)q occurring in a non-complex karyotype is predominantly associated with primary MDS, lack of cryptic MLL rearrangements, and shows characteristic clinicopathological features. These clinicopathological features are likely attributed to commonly deleted regions of 11q and their involved genes.

Allelotyping, microsatellite instability, and BRAF mutation analyses in common and atypical melanocytic nevi and primary cutaneous melanomas

Loss of heterozygosity (LOH) in several chromosomal regions is found in melanoma, and it has been partially studied in nevi. BRAF mutations are found in melanoma and nevi and in colorectal cancer are linked to mismatch repair deficiency. We studied early genetic events involved in melanomagenesis through analysis of allelic loss, microsatellite instability (MSI), and BRAF mutations. DNA extracted from microdissected cells of 22 common nevi, 23 atypical nevi, and 25 primary cutaneous melanomas were examined for LOH and MSI by polymerase chain reaction-based analysis of 24 microsatellite markers and BRAF mutation. Allelic loss index was higher in atypical nevi (0.20) and melanomas (0.27) than common nevi (0.07). LOH was frequent at 9p21, 17q21, 6q23, and 5q35 in melanoma. LOH at any of this loci occurred in 27% of common nevi, 57% of atypical nevi, and 68% of melanomas. BRAF mutations were not related to MSI presence and MSI index was not related with BRAF mutational status. Similar genetic alterations in atypical nevi and melanomas support the concept of atypical nevus as melanoma precursor. Novel deletion loci at 5q35 and 17q21 (BRCA1) in atypical nevi and melanomas were identified. Mismatch repair deficiency is not a crucial event for BRAF mutation in melanocytic tumors.

Loss of the eukaryotic initiation factor 3f in melanoma

Aberrant regulation of the translation initiation is known to contribute to tumorigenesis. eIF3 plays an important role in translation initiation. eIF3f is the p47 subunit of the eIF3 complex whose function in cancer is not clear. Initial studies from our group indicated that eIF3f expression is decreased in melanoma. Overexpression of eIF3f inhibits translation and induces apoptosis in melanoma cells. The eIF3f gene is located at chromosome region 11p15.4. Loss of 11p15.4 is a common event in many tumors including melanoma. In order to investigate the molecular mechanism of the decreased expression of eIF3f in melanoma, we performed loss of heterozygosity (LOH) analysis in 24 melanoma specimens using three microsatellite markers encompassing the eIF3f gene. We showed that the prevalence of LOH ranged from 75% to 92% in melanoma. We also performed eIF3f gene copy number analysis using quantitative real-time PCR to further confirm the specific allelic loss of the eIF3f gene in melanoma. We demonstrated a statistically significant decrease of the eIF3f gene copy number in melanoma compared with normal tissues with a tumor/normal ratio of 0.52. To further elucidate the somatic genetic alterations, we carried out mutation analysis covering the entire coding region and 5'UTR of the eIF3f gene in melanoma tissues and cell lines. Despite some polymorphisms, we did not find any mutations. Furthermore, immunohistochemistry analysis demonstrated that eIF3f protein expression is decreased in melanoma compared to benign nevi. These data provide new insight into the understanding of the molecular pathogenesis of eIF3f during melanoma tumorigenesis.

Concordant loss of heterozygosity of DNA repair gene, hOGG1, in melanoma in situ and atypical melanocytic hyperplasia

BACKGROUND

One major risk factor for cutaneous melanoma is chronic sun-exposure and oxidative stress. Among various oxidative DNA damages, 8-oxoquanine is the most abundant and is potentially mutagenic if not sufficiently repaired. The human 8-oxoquanine DNA glycosylase 1 (hOGG1) gene specifically repairs 8-oxoguanine, and this gene shows frequent loss of heterozygosity (LOH) in human tumors. In this study, we investigate whether hOGG1 LOH occurs in melanoma in situ (MIS) and adjacent atypical melanocytic hyperplasia (AMH).

METHODS

Twelve skin biopsies with MIS and adjacent AMH were included. DNA samples derived from manual microdissection of tissues were subjected to polymerase chain reaction amplification using three fluorescent-labeled microsatellite makers, followed by fragment analysis.

RESULTS

Five of 12 cases were informative for both telomeric (3S1297) and centromeric (3S1289 or 3S1300) markers, bordering the hOGG1 locus. Among them, four (80%) MIS and three (60%) AMH showed hOGG1 LOH at both markers.

CONCLUSIONS

These results shows that LOH at hOGG1 gene is associated with MIS and AMH and suggest that the hOGG1 gene may play a role in melanocytic tumor progression.

DNA mismatch repair protein expression and microsatellite instability in primary mucosal melanomas of the head and neck

AIMS

To examine the expression of DNA mismatch repair (MMR) proteins and the presence of microsatellite instability (MSI) in seven primary mucosal melanomas of the head and neck (MMHN).

METHODS AND RESULTS

Haematoxylin and eosin staining and immunohistochemical analysis for routine diagnostic markers and for MMR proteins were performed. Six cases were examined for MSI. Four cases were monomorphous and three cases were pleomorphic type MMHN. Melanocytic markers were positive in all cases. Immunoreactivity for MMR proteins was weak in normal epithelium. The neoplastic tissue in six cases showed positivity for all MMR proteins with different percentages. One case showed weak positivity for hMSH2 and hMSH6 and no immunoreactivity for hMLH1 or hPMS2. Staining intensity was higher in tumour cells than in matched normal mucosa in three cases for hMSH2 and hMLH1 and in two cases for hPMS2. None of the examined cases showed MSI.

CONCLUSIONS

Expression of hMSH2 and hMLH1 proteins was up-regulated in three cases, whereas in two cases that of hPMS2 was increased. hMSH6 expression was comparable to that of normal cells in all cases. The percentage of positive neoplastic cells and the intensity of staining seemed to be greater in pleomorphic melanomas. Six cases were MMR-proficient and microsatellite stable.

Promoter Hypermethylation of the O6-Methylguanine DNA Methyltransferase Gene and Microsatellite Instability in Metastatic Melanoma

Tumor spread to distant organs is the most serious consequence of melanoma, as only 10-20% of stage IV patients respond to current chemotherapies. Tumor sensitivity to alkylating agents is affected by the activity of cellular DNA repair proteins, such as O(6)-methylguanine DNA methyltransferase (MGMT) and the DNA mismatch repair proteins. Chemosensitivity may be enhanced by reduced MGMT activity, but the frequency of MGMT promoter silencing through hypermethylation is unknown in distant melanoma metastases. The frequency and significance of microsatellite instability (MSI) in metastatic melanoma is also unclear, and it has been suggested that MSI frequency increases during the metastatic process. We undertook an analysis of 84 melanoma metastases from 47 patients. MGMT methylation was detected using methylation-specific PCR in 26 of the 84 metastases (31%), but there was discordance between individual metastases from the same patient. Therefore, as a result of this variation, MGMT methylation may have only limited value as a predictor of chemosensitivity. High MSI involving mononucleotide repeat markers was not found. Low MSI was detected in five of 50 metastases (10%) and only one of the five metastases also had MGMT methylation. These results demonstrate that in contrast to some previous reports, these tumors have a low frequency of MSI.

Comparative Analysis of Loss of Heterozygosity and Microsatellite Instability in Adult and Pediatric Melanoma

Although 0.3% of melanomas occur in children, the incidence has risen in past decades. In adult melanoma, some chromosomal regions in 1p, 6q, 9p, 10q, and 11q are frequently deleted. Microsatellite instability (MSI), which reflects impaired DNA repair, has been found at low levels in adult melanoma and melanocytic nevi. To investigate the molecular changes in pediatric melanoma, a screening for loss of heterozygosity and microsatellite instability was performed and compared with changes found in adult melanoma. Formalin-fixed, paraffin-embedded tissues from 10 adult melanomas, 9 melanocytic nevi, and 8 pediatric melanomas were microdissected and the DNA was extracted. Loss of heterozygosity and microsatellite instability were evaluated using 13 microsatellite repeat polymorphisms located in 1p36, 1q32, 2p12, 2p22-25, 2q33-37, 9p21, 10q23.3, 11q23, 13q14, 17p13, and 17q21. The overall frequency of loss of heterozygosity was 0.09 for nevi, 0.30 for adult melanoma, and 0.43 for pediatric melanoma (nevi vs. adult melanoma, P = 0.0082; nevi vs. pediatric melanoma, P = 0.0092). Pediatric melanoma has more loss of heterozygosity (44%) in 11q23 than adult melanoma (7%, P = 0.046). The microsatellite instability overall frequency was greater in pediatric melanoma (0.24) than nevi (0.05, P = 0.0031) and adult melanoma (0.09, P = 0.0195). Our findings suggest that pediatric melanoma has a different abnormal pattern than adult melanoma. Pediatric melanoma has more microsatellite instability than adult melanoma. 11q23 could contain genes related to the early age onset of melanoma. The high frequency of microsatellite instability is coincidental with the finding of higher levels of microsatellite instability in pediatric brain tumors and could play a role in the pathogenesis of pediatric melanoma.

Definition of a region of loss of heterozygosity at chromosome 11q23.3-25 in head and neck squamous cell carcinoma using laser capture microdissection technique

To date, loss of heterozygosity (LOH) studies on HNSCC have had limited success in identifying a confined region of loss on chromosome 11q partially due to the heterogeneous nature of tumor tissue examined. Additionally, little is known about the role of the 11q allelic deletion in HNSCC tumorigenesis and current reports are conflicting. The aim of this study was to better define LOH at distal 11q by using combination of a pure cell population procured by laser capture microdissection (LCM) and subsequent sensitive PCR amplification of polymorphic microsatellites. This study analyzed HNSCC for LOH using a panel of 5 microsatellite markers spanning 11q23-25. Thirty-four paired DNA samples from tumor and autologous normal tissue were harvested by LCM technique to ensure a pure cell population for PCR amplification. Approximately 2000 to 3000 cells were procured from each sample. Twenty-one of 34 cases (62%, P < 0.001) showed LOH on at least one of the loci examined. The highest frequency of LOH was found at the 11q23.3-25 segment, with 44% at marker D11S968 and 35% at marker D11S1316. A distinct novel region of frequent LOH at 11q23.3-25, defined by D11S1316 and D11S968, was identified. No allelic loss was found in any normal squamous tissue samples. To study LOH in HNSCC, combination of pure cell population procurement by LCM and sensitive PCR provides a more accurate approach than the conventional method using a bulk of heterogeneous tissue. A novel region of LOH at 11q23.3-25 was defined. LOH in this region may harbor putative tumor suppressor gene(s) critical for HNSCC. Furthermore, these allelic losses were not found in any non-neoplastic squamous tissue samples, clarifying prior discrepant data.

Genetic pathways to melanoma tumorigenesis

The incidence of cutaneous malignant melanomas is growing faster than that of any other cancer and therefore posing a major heath threat worldwide. In melanocytic skin tumours, the feasibility of correlating a specific pathological stage with a corresponding genetic alteration provides a remarkable opportunity to study the multistep tumorigenesis model. This multistep melanoma tumorigenesis is best described as a continuum of transformation of the melanocytes, melanocytic dysplasia, and melanoma formation. These steps involve genotypic alterations including loss of tumour suppressor genes, microsatellite instability, and alterations of the mismatch repair system. This review seeks to examine melanoma tumorigenesis based on these genetic changes.

Instability of microsatellites is an infrequent event in uveal melanoma

Microsatellite instability (MSI) is a distinct tumour phenotype that is associated with alterations of DNA mismatch repair and is being increasingly reported in a number of hereditary and sporadic tumours. Numerous reports have suggested that melanocytic neoplasms, including cutaneous melanomas, frequently demonstrate low frequency MSI, whilst a small number of tumours exhibit high frequency MSI. Furthermore, loss of expression of DNA mismatch repair proteins has been associated with progression from benign to malignant disease in melanocytic neoplasms, but the presence or absence of mismatch repair defects in uveal melanomas has yet to be determined. This study was designed to establish whether MSI is a feature of these ocular melanomas. To investigate the prevalence of MSI in uveal melanomas, 52 tumours were analysed by polymerase chain reaction amplification of a panel of microsatellite markers selected for their ability to detect tumours exhibiting defects in DNA mismatch repair mechanisms. MSI was rarely detected in the 52 uveal melanomas analysed. All tumours demonstrated stable microsatellites at five of the six microsatellite markers tested (BAT26, BAT40, APC, D2S123 and Mfd15CA). Only one tumour showed the presence of a single unstable allele at a tetranucleotide marker (MYCL1). These data suggest that high frequency MSI does not occur in these tumours, and that low frequency MSI, in contrast to cutaneous melanoma, is a rare event in malignant melanomas of the uveal tract.

Microsatellite analysis in cutaneous malignant melanoma

The status and relevance of repetitive nucleotide sequences or microsatellite alterations in sporadic cutaneous melanoma has not been fully clarified. In this study we evaluated the presence of microsatellite alterations in a series of sporadic primary and metastatic melanomas in order to discover which genetic events may have a pathogenetic role in the development of this disease. Tumour samples were obtained from 21 patients with sporadic cutaneous melanoma, and from eight corresponding positive sentinel lymph nodes and one corresponding in-transit metastasis. In each specimen, selected neoplastic cells were procured by laser-assisted microdissection. Polymerase chain reaction-based microsatellite analysis was performed using a panel of 11 microsatellite markers, located at chromosome 2p, 4q, 9p, 16q, 17p and 21q. Overall, we found microsatellite alterations in five (23.8%) melanomas. Of these, one case showed alteration at marker D2S2182 and one at marker D17S261, whereas in another case alterations at three loci, D2S2182, D2S2291 and D9S171, were found. The fourth patient demonstrated an alteration at locus D9S171 both in the primary tumour and in the histologically positive sentinel lymph node. The fifth case was characterized by alterations at D2S2182 and at D17S250, whereas the corresponding in-transit metastasis showed the same alterations as the primary tumour and an additional alteration at IFN alpha. In conclusion, our study confirms previous observations that cutaneous melanomas demonstrate microsatellite alterations, although such instability occurs at a lower frequency than specific mismatch repair defects. Genetic analysis of metastatic lesions revealed that the same microsatellite alterations as in the primary tumour are seen, but additional genetic changes may develop during disease progression.

Microsatellite instability and its relevance to cutaneous tumorigenesis

Increasing evidence suggests that human tumors sequentially accumulate multiple mutations that cannot be explained by the low rates of spontaneous mutations in normal cells (2-3 mutations/cell). The mathematical models estimate that for the solid tumors to develop, as many as 6-12 mutations are required in each tumor cell. Therefore, to account for such high mutation rates, it is proposed that tumor cells are genetically unstable, i.e. they have genome-wide mutations at short repetitive DNA sequences called microsatellites. Microsatellite repeats are scattered throughout the human genome, primarily in the non-coding regions, and can give rise to variants with increased or reduced lengths, i.e. microsatellite instability (MSI). This instability has been reported in an increasing number of cutaneous tumors including: melanocytic tumors, basal cell carcinomas and primary cutaneous T-cell lymphomas. Moreover, MSI has been observed in skin tumors arising in the context of some hereditary disorders such as Muir-Torre syndrome, Von Recklinghausen's disease and disseminated superficial porokeratosis. While MSI in some of these disorders reflects underlying DNA replication errors, the mechanism of instability in others is still unknown. Thus far, MSI is considered to be a distinct tumorigenic pathway that reveals surprising versatility. The ramifications for cutaneous neoplasms warrant further investigation.

Loss of heterozygosity, microsatellite instability, and mismatch repair protein alterations in the radial growth phase of cutaneous malignant melanomas

Little is known about genomic alterations during development of the radial growth phase (RGP) of cutaneous malignant melanomas (CMMs). In this investigation polymerase chain reaction-based microsatellite assays were applied to analyze 13 RGP-CMMs with 18 microsatellite markers at six chromosomal regions: 1p, 3p, 4q, 6q, 9p, and 10q. Loss of heterozygosity (LOH) was found in eight cases (62%), at 9p22, 1p36, and 10q11, suggesting the presence of tumor-suppressor genes at these regions. LOH was encountered frequently at the interferon-alpha (31%) and D10S249 loci (15%). Low-level microsatellite instability (MSI) (11-16% of investigated loci unstable) was noted in three cases (23%). Two MSI banding patterns were seen: band shift and the presence of additional bands. To investigate the underlying mechanisms of the low-level MSI pattern, we analyzed the lesions for expression of mismatch repair (MMR) proteins with immunoperoxidase methods and mouse monoclonal antibodies. The average percentages of positively stained cells for human MutL homolog 1 (hMLH1), human MutS homolog 2 (hMSH2), and human MutS homolog 6 (hMSH6) in RGP-CMM (75.6 +/- 3.4%, 67.20 +/- 7.71%, and 76.6 +/- 2.1%, respectively) were reduced compared with benign nevi. No statistically significant differences in MMR protein expression were found between microsatellite-stable and low-level MSI lesions (P = 0.173, P = 0.458, and P = 0.385 for hMLH1, hMSH2, and hMSH6, respectively). There was a direct correlation between values for percentages of positively stained cells for hMSH2 and hMSH6 (r = +0.9, P = 0.03), suggesting that common mechanisms regulate their expression. In conclusion, LOH, MSI, and reduced MMR protein expression appear to be present in at least some RGP-CMMs and may play a role in their pathogenesis. Further studies are necessary to support these finding and to determine their diagnostic and prognostic significance.

Cytogenetic characterization of complex karyotypes in seven established melanoma cell lines by multiplex fluorescence in situ hybridization and DAPI banding

We report the use of multiplex fluorescence in situ hybridization (M-FISH) to resolve chromosomal aberrations in seven established melanoma cell lines with hypotriploid to hypertetraploid complex karyotypes. By simultaneous identification of all human chromosomes in single FISH experiments using a set of 52 directly labeled, whole chromosome painting probes, cryptic chromosomal translocations and the origin of unclear chromosomal material in structural rearranged and marker chromosomes could be identified, refining the tumor karyotypes in all seven cell lines. The number of structural aberrations in each cell line assigned with combined M-FISH and DAPI banding analysis ranged from 15 to 45. Altogether, 275 breakpoints could be assigned to defined chromosomal regions or bands. The chromosome arms 1p, 6q, 7p, 9p, and 11q which are known to be nonrandomly associated with melanoma tumorigenesis, were frequently involved in chromosomal breaks and/or copy number changes. This study also demonstrated the practical usefulness of combining M-FISH with conventional cytogenetic banding techniques for the characterization of complex tumor karyotypes with massive genomic alterations.

Loss of heterozygosity analysis of cutaneous melanoma and benign melanocytic nevi: laser capture microdissection demonstrates clonal genetic changes in acquired nevocellular nevi

The molecular pathology of the common nevocellular nevus (NCN) and its relationship to the genetic model of malignant melanoma (MM) progression has not been fully characterized. We used laser capture microdissection of archival formalin-fixed material to study 34 melanocytic lesions (19 MM and 15 NCN). Twelve of the 15 NCN were acquired, 3 of which were congenital; none had dysplastic features. Ten polymorphic markers on five chromosomal regions (1p36, 6q22-23.3, 8p22-24, 10q23, and 11q23) were selected for loss of heterozygosity (LOH) analysis, based on previous studies demonstrating involvement in MM pathogenesis and progression. Loss of heterozygosity at any allelic locus was observed in 18 of 19 (95%) MM and in 9 of 15 (60%) NCN. Of the three congenital nevi analyzed, none showed LOH at any informative locus. The frequency of allelic loss was highest in the MM at 6q22-23.3 (64%), followed by 10q23 (62%), 8p22-24 (43%), 11q23 (43%), and 1p36 (13%). In the 15 NCN, the most frequent allelic losses were detected at 6q22-23.3 (29%), 1p36 (27%), and 10q23 (25%), with lower frequencies of LOH at 11q23 (10%) and 8p22-24 (7%). LOH at a single polymorphic marker, D6S1038, was detected in 70% of the MM and in 36% of the NCN, suggesting the presence of putative tumor-suppressor genes (TSGs) critical in melanocytic neoplasia at 6q22-23.3. The presence of clonal genetic alterations in acquired NCN justifies their classification as a benign neoplasm. The pattern of LOH in NCN is not random; rather, the relative frequencies of LOH at the chromosomal regions examined are consistent with a multistep model of MM progression that begins with NCN. Molecular analysis of NCN reiterates established epidemiologic and morphologic notions that NCN are precursor lesions for MM.

17Beta-estradiol is carcinogenic in human breast epithelial cells

The association found between breast cancer development and prolonged exposure to estrogen suggests that this hormone is of etiologic importance in the causation of this disease. In order to prove this postulate, we treated the immortalized human breast epithelial cells (HBEC) MCF-10F with 17beta-estradiol (E(2)) for testing whether they express colony formation in agar methocel, or colony efficiency (CE), and loss of ductulogenesis in collagen matrix, phenotypes also induced by the carcinogen benz[a]pyrene (BP). MCF-10F cells were treated with 0.0, 0.007, 70nM, or 0.25mM of E(2) twice a week for 2 weeks. CE increased from 0 in controls to 6.1, 9.2, and 8.7 with increasing E(2) doses. Ductulogenesis was 75 +/- 4.9 in control cells; it decreased to 63.7 +/- 28.8, 41.3 +/- 12.4, and 17.8 +/- 5.0 in E(2)-treated cells, which also formed solid masses or spherical formations lined by a multilayer epithelium, whose numbers increased from 0 in controls to 18.5 +/- 6.7, 107 +/- 11.8 and 130 +/- 10.0 for each E(2) dose. MCF-10F cells were also treated with 3.7 microM of progesterone (P) and the CE was 3.39 +/- 4.05. At difference of E(2), P does not impaired the ductulogenic capacity. Genomic analysis revealed that E(2)-treated cells exhibited loss of heterozigosity in chromosome 11, as detected using the markers D11S29 and D11S912 mapped to 11q23.3 and 11q24.2-25, respectively These results also indicate that E(2), like the chemical carcinogen BP, induces in HBEC phenotypes indicative of neoplastic transformation.

High-frequency microsatellite instability is associated with defective DNA mismatch repair in human melanoma

Hereditary nonpolyposis colorectal cancers and a steadily increasing number of sporadic tumors display microsatellite instability. In colorectal tumors, high-frequency microsatellite instability is strictly associated with inactivation of the DNA mismatch repair genes hMSH2, hMLH1, or hPMS2, whereas mutations in the mismatch repair gene hMSH6 have been identified in a subset of tumors with low-frequency microsatellite instability. In addition to epithelial tumors of the colon, endometrium, and ovary, microsatellite instability has been reported to occur also in sporadic melanoma. The relationship between microsatellite instability and mismatch repair in melanoma cells, however, has not been investigated so far. In this study, we analyzed microsatellite instability, mismatch repair activity, and expression of the hMSH2, hMSH6, hMLH1, and hPMS2 proteins in five melanoma cell lines and in tumor specimens from which the cells were derived. Four cell lines displayed normal levels of mismatch repair activity and expressed all the mismatch repair proteins. The extracts of the fifth cell line lacked the hMLH1 and hPMS2 proteins, and were correspondingly deficient in the repair of DNA mismatches. This line displayed high-frequency microsatellite instability, whereas the four mismatch-repair-proficient cell lines displayed either no or low-frequency microsatellite instability. These findings could be confirmed in the tumor specimens, in that only the tumor that did not express hMLH1 and hPMS2 displayed high-frequency microsatellite instability. Our data are consistent with the hypothesis that in melanoma, similarly to epithelial tumors, only the high-frequency microsatellite instability phenotype is strictly dependent on a defective mismatch repair system. Further studies on a large series of tumor specimens are required to establish the frequency of mismatch repair loss in human melanoma.

Neoplastic transformation of human breast epithelial cells by estrogens and chemical carcinogens

Sporadic breast cancer, the most common cancer diagnosed in American and Northern European women, is gradually increasing in incidence in most Western countries. Prevention would be the most efficient way of eradicating this disease. This goal, however, cannot be accomplished until the specific agent(s) or mechanisms that initiate the neoplastic process are identified. Experimental studies have demonstrated that mammary cancer is a hormone-dependent multistep process that can be induced by a variety of compounds and mechanisms, that is, hormones, chemicals, radiation, and viruses, in addition to or in combination with genetic factors. Although estrogens have been shown to play a central role in breast cancer development, their carcinogenicity on human breast epithelial cells (HBECs) has not yet been clearly demonstrated. Breast cancer initiates in the undifferentiated lobules type 1, which are composed of three cell types: highly proliferating cells that are estrogen-receptor negative (ER-), nonproliferating cells that are ER positive (ER+), and very few (<1%) ER+ cells that proliferate. Interestingly, endogenous 17beta-estradiol (E(2)) is metabolized by the cytochrome P450 enzyme isoforms CYP1A1 and CYP1B1, which also activate benzo[a]pyrene (B[a]P), a carcinogen contained in cigarette smoke. We postulate that if estrogens are carcinogenic in HBECs, they should induce the same transformation phenotypes induced by chemical carcinogens and ultimately genomic changes observed in spontaneously developing primary breast cancers. To test this hypothesis we compared the transforming potential of E(2) on the HBEC MCF-10F with that of B[a]P. Both E(2) and B[a]P induced anchorage-independent growth, colony formation in agar methocel, and loss of ductulogenic capacity in collagen gel, all parameters indicative of cell transformation. In addition, the DNA of E(2)-transformed cells expressed LOH in chromosome 11 at 11q23.3, 11q24.2-q25, and LOH at 13q12-q13. B[a]P-induced cell transformation was also associated with LOH at 13q12-q13 and at 17p13.2. The relevance of these findings is highlighted by the observation that E(2)- and B[a]P-induced genomic alterations in the same loci found in ductal hyperplasia, ductal carcinoma in situ, and invasive ductal carcinoma of the breast.

Molecular disorders in transitional vs. peripheral zone prostate adenocarcinoma

Loss of heterozygosity (LOH) and microsatellite instability (MSI) have been shown to be mechanisms for tumor-suppressor gene inactivation in human oncogenesis. In our study, we examined LOH and MSI using 16 polymorphic markers of DNA for chromosomes 1, 3, 7, 8, 10 and 11. Microdissected tumor samples were isolated from 32 patients, representing 11 foci of incidentally discovered prostate cancer of the transitional zone (TZ), 12 prostate cancer of the peripheral zone (PZ) and 10 of high-grade PIN. We found loss of heterozygosity in the TZ group in 91% of informative cases (10/11) with al least 1 marker compared to 58% of cases (7/12) in PZ group and 70% of cases (7/10) in the HGPIN group. Chromosome 7 showed the highest rate of allelic loss in all 3 categories, with loss of 43% of loci in PIN, 37% in TZ tumors and 31% in PZ tumors. At chromosome 11, LOH was detected in 26% of loci in the TZ group, in 7% of loci in the PZ group and in 13% of loci in the PIN group. On chromosome 8, the PZ and HGPIN group showed allelic loss in 22% and 21% of loci, respectively, compared to 10% detected in the TZ group. The TZ group showed a significant higher rate of allelic instability compared to that observed in tumor samples from the peripheral zone: 73% of cases (8/11) showed genetic alterations (RER+ phenotype) in at least 4 loci analyzed compared to 8% and 10% in the PZ and HGPIN groups, respectively (p = 0.0006). These data suggest that transitional zone carcinoma and peripheral zone carcinoma display distinct and specific genetic alterations in different chromosomes. This diversity may help explain biologic and clinical differences between carcinomas arising in these distinct zones of the prostate. Also our results strongly suggest that the RER+ mutator phenotype could be linked to early development of transitional zone prostate carcinoma.

Comprehensive analysis of 112 melanocytic skin lesions demonstrates microsatellite instability in melanomas and dysplastic nevi, but not in benign nevi

INTRODUCTION

the length of DNA repetitive sequences (microsatellite instability (MSI)) represent distinct tumorigenic pathways associated with several familial and sporadic tumors.

MATERIAL AND METHODS

To investigate the prevalence and frequency of MSI in melanocytic lesions, the polymerase chain reaction (PCR)-based microsatellite assay was used to examine formalin-fixed, paraffin-embedded tissues of 30 benign melanocytic nevi, 60 melanocytic dysplastic nevi (MDN), and 22 primary vertical growth phase cutaneous malignant melanomas (CMM). Twenty-four microsatellite markers at the 1p, 2p, 3p, 4q and 9p chromosomal regions were used.

RESULTS

MSI was found at 1p and 9p in MDN and CMM but not in benign melanocytic nevi. The overall prevalence of MSI was 17/60 (28%) in MDN and 7/22 (31%) in CMM. The frequency of MSI ranged from 2/24 (9%) to 4/24 (17%) and was most commonly found at D9S162. There was a statistically significant correlation between degree of atypia and frequency of MSI (p<0.001) in MDN. There were two MSI banding patterns: band shifts and additional bands.

CONCLUSIONS

The data presented revealed the presence of low-frequency MSI (MSI-L) at the 1p and 9p regions in both MDN and CMM. Whether the MSI-L pattern reflects a defect in mismatch repair genes is still to be determined.

Detection of invasion-related chromosomal changes in highly and weakly invasive melanoma cell clones by a modified comparative genomic hybridization approach

Invasion is a key step in the systemic spread of tumour cells. The aim of this study was to investigate whether specific chromosomal aberrations in melanoma occur during acquisition of a strongly invasive phenotype. We previously selected highly and weakly invasive cell clones from the human melanoma cell line Mel Im. Both cell clones retained a stable phenotype over more than 40 passages, revealing a five-fold difference in their invasive potential in vitro. Direct comparative genomic hybridization (CGH) (modified CGH) of the two cell clones was used as a powerful tool to screen for different chromosomal aberrations in both clones. Standard CGH and fluorescence in situ hybridization (FISH) was performed to verify the results of this improved technique. In general, the CGH pattern showed a high degree of identity consistent with the fact that the cell lines represent subclones of the same cell line. However, a few defined changes between the two cell clones were observed, including loss of 1q21-qter, 4q, 11p14-pter, 19q and 20p in the highly invasive cell clone. Two of the regions (1q and 11p) have already been suggested to be involved in melanoma progression, whereas changes in the others have not been detected before. In summary, our direct CGH approach proved to be suitable for fast and direct comparison of two cell types and allowed the identification of two known and three novel chromosomal changes involved in the acquisition of a strongly invasive melanoma cell phenotype.

Carcinogenicity of estrogens in human breast epithelial cells

Epidemiological and clinical evidences indicate that breast cancer risk is associated with prolonged ovarian function that results in elevated circulating levels of steroid hormones. Principal among these is estrogen, which is associated with two important risk factors, early onset of menarche and late menopause. However, up to now there is no direct experimental evidence that estrogens are responsible of the initiation of human breast cancer. We postulate that if estrogens are causative agents of this disease, they should elicit in human breast epithelial cells (HBEC) genomic alterations similar to those exhibited by human breast cancers, such as DNA amplification and loss of genetic material representing tumor suppressor genes. These effects could result from binding of the hormone to its nuclear receptors (ER) or from its metabolic activation to reactive metabolites. This hypothesis was tested by treating with the natural estrogen 17beta-estradiol (E2) and the synthetic steroid diethylstilbestrol (DES) MCF-10F cells, a HBEC line that is negative for ER. Cells treated with the chemical carcinogen benzo (a) pyrene (BP) served as a positive control of cell transformation. BP-, E2-, and DES-treated MCF-10F cells showed increases in survival efficiency and colony efficiency in agar methocel, and loss of ductulogenic capacity in collagen gel. The largest colonies were formed by BP-treated cells, becoming progressively smaller in DES- and E2-treated cells. The loss of ductulogenic capacity was maximal in BP-, and less prominent in E2- and DES-treated cells. Genomic analysis revealed that E2- and DES-treated cells exhibited loss of heterozygosity in chromosomes 3 and 11, at 3p21, 3p21-21.2, 3p21.1-14.2, and 3p14.2 14.1, and at 11q23.3 and 11q23.1-25 regions, respectively. It is noteworthy that these loci are also affected in breast lesions, such as ductal hyperplasia, carcinoma in situ, and invasive carcinoma. Our data are the first ones to demonstrate that estrogens induce in HBEC phenotypic changes indicative of cell transformation and that those changes are associated with significant genomic alterations that might unravel new pathways in the initiation of breast cancer.

Localization of multiple melanoma tumor-suppressor genes on chromosome 11 by use of homozygosity mapping-of-deletions analysis

Loss-of-heterozygosity (LOH) studies have implicated one or more chromosome 11 tumor-suppressor gene(s) in the development of cutaneous melanoma as well as a variety of other forms of human cancer. In the present study, we have identified multiple independent critical regions on this chromosome by use of homozygosity mapping of deletions (HOMOD) analysis. This method of analysis involved the use of highly polymorphic microsatellite markers and statistics to identify regions of hemizygous deletion in unmatched melanoma cell line DNAs. Regions of loss were defined by the presence of an extended region of homozygosity (ERH) at > or =5 adjacent markers and having a statistical probability of < or =.001. Significant ERHs were similar in nature to deletions identified by LOH analyses performed on uncultured melanomas, although a higher frequency of loss (24 [60%] of 40 vs. 16 [34%] of 47) was observed in the cell lines. Overall, six small regions of overlapping deletions (SROs) were identified on chromosome 11 flanked by the markers D11S1338/D11S907 (11p13-15.5 [SRO1]), D11S1344/D11S11385 (11p11.2 [SRO2]), D11S917/D11S1886 (11q21-22.3 [SRO3]), D11S927/D11S4094 (11q23 [SRO4]), AFM210ve3/D11S990 (11q24 [SRO5]), and D11S1351/D11S4123 (11q24-25 [SRO6]). We propose that HOMOD analysis can be used as an adjunct to LOH analysis in the localization of tumor-suppressor genes.

Microsatellite instability in benign skin lesions in hereditary non-polyposis colorectal cancer syndrome

The coexistence of cutaneous and extra-cutaneous malignancies within one family could be explained by shared genetic mechanisms such as common tumor suppressor gene mutations or oncogene activation, as well as mutations in DNA repair genes. Hereditary non-polyposis colorectal cancer syndrome (HNPCC) and its variant Muir-Torre syndrome (MTS) are caused by germline DNA mismatch repair gene mutations. Colonic and endometrial tumors from HNPCC patients exhibit microsatellite instability (MSI), as do sebaceous lesions in MTS. We recruited individuals from cancer prone families to determine if MSI is found in benign and malignant skin lesions and to assess whether MSI in the skin is predictive of genomic instability with susceptibility to tumors characteristic of HNPCC. One hundred and fifteen benign, dysplastic, and malignant skin lesions from 39 cancer prone families were analyzed. Thirteen benign skin lesions from three individuals belonging to two HNPCC pedigrees showed MSI. No mutations in hMSH2 and hMLH1 were found in two of the three individuals with RER + skin lesions. We found MSI in non-sebaceous non-dysplastic skin lesions in HNPCC pedigrees. MSI was not found in skin lesions within other family cancer syndromes. These results have important clinical implications as the detection of MSI in prevalent readily accessible skin lesions could form the basis of noninvasive screening for HNPCC families. It may also be a valuable tool in the search for new mismatch repair genes.

Genomic structure of the human PLZF gene

The human PLZF (promyelocytic leukaemia zinc finger) gene encodes a Krüppel-like zinc finger protein, which was identified via the reciprocal translocation t(11;17)(q23;q21) fusing it to the retinoic acid receptor alpha (RARalpha) gene in promyelocytic leukaemia. To determine its complete genomic organisation, we constructed a cosmid-map fully containing the hPLZF gene. The gene has seven exons, including a novel 5' untranslated exon, varying in size from 87 to 1358bp and spans at least 120kb. Flanking intronic sequences were identified and all splice acceptor and donor sites conformed to the gt/ag rule. Five polymorphic markers could be fine located in its vicinity. These data will facilitate mutation analysis of hPLZF in t(11;17) leukaemia cases, as well as assist mapping and loss-of-heterozygosity analysis. Here we have tested hPLZF as a possible candidate for the PGL1 locus involved in hereditary head and neck paragangliomas. However, mutation analysis revealed no aberration in 12 paraganglioma patients from different families.

Functional localization of a melanoma tumor suppressor gene to a small (< or = 2 Mb) region on 11q23

We have previously demonstrated the existence of a melanoma tumor suppressor gene(s) on the long arm of chromosome 11 through suppression of tumorigenicity assays. Although loss of heterozygosity studies also support this finding, only a large critical region (44 cM) has been identified to date on 11q22-25. To further localize a tumor suppressor gene(s) within this region, we have now generated and characterized nine melanoma microcell hybrids, each retaining an introduced fragment of 11q. Of the nine hybrids, four were suppressed for tumor formation in nude mice, while five formed tumors at the same rate as the parental melanoma cell line (UACC 903). Molecular analysis of the hybrids with 118 microsatellite markers narrowed the location of a putative suppressor gene to a small (< or =2 Mb) candidate region on 11q23 between the markers D11S1786 and D11S2077 and within the larger region frequently deleted in melanoma tumors and cell lines. While multiple tumor suppressor genes are likely to reside on 11q22-25, the presence of this region in all four suppressed hybrids supports the simplest model that a single locus is responsible for the suppressed phenotype observed in UACC 903.

Expression of DNA repair proteins hMSH2, hMSH6, hMLH1, O6-methylguanine-DNA methyltransferase and N-methylpurine-DNA glycosylase in melanoma cells with acquired drug resistance

Malignant melanoma is well known for its primary unresponsiveness to chemotherapy. The mechanisms conferring this intrinsic resistance are unclear. In this study, we investigated the role of genes involved in DNA repair in a panel of human melanoma cell variants exhibiting low and high levels of resistance to 4 commonly used drugs in melanoma treatment, i.e., vindesine, etoposide, fotemustine and cisplatin. We show that in melanoma cells exhibiting resistance to cisplatin, etoposide and vindesine, the nuclear content of each of the DNA mismatch repair (MMR) proteins hMLH1, hMSH2 and hMSH6 was reduced by 30-70%. A decreased expression level of up to 80% of mRNAs encoding hMLH1 and hMSH2 was observed in drug-resistant melanoma cells selected for cisplatin, etoposide and fotemustine, while vindesine-selected cells showed only moderate reduction. In melanoma cells that acquired resistance to fotemustine, the amount of nuclear MMR proteins was nearly unaltered, whereas the activity of O6-methylguanine-DNA methyltransferase (MGMT) was considerably enhanced. Activity of N-methylpurine-DNA glycosylase (MPG) was not significantly altered in any of the drug-resistant melanoma cells. Our data indicate that modulation of both MMR components and MGMT expression level may contribute to the drug-resistant phenotype of melanoma cells.

Identification of two distinct deletion targets at 11q23 in cutaneous malignant melanoma

Karyotypic and molecular data indicate that genetic alterations of the long arm of chromosome 11 (11q) are involved in the pathogenesis of malignant melanoma as well as of other malignancies. We have shown previously, by analysis of loss of heterozygosity (LOH), that a tumor-suppressor gene playing an important role in malignant melanoma is likely to be located within a 51-cM region at 11q23. Its loss appeared to be a late event in tumor progression and an indicator of a less favorable clinical outcome. To further test this hypothesis on a larger set of tumors and to refine the region(s) of common allelic loss, we analyzed 21 polymorphic microsatellite repeats on 11q. A PCR-based assay for LOH was used to study normal and tumor tissues from 53 individuals with primary cutaneous malignant melanoma or metastatic disease. Our findings indicate that in cutaneous malignant melanoma there are at least 2 distinct regions of common allelic loss on 11q, one of them centered around marker APOC3 at 11q23.1-q23.2 delineated by markers D11S1347 and D11S4142 and spanning approximately 5 Mb and a second 3-Mb region around marker D11S925 at 11q23.3 delineated by markers D11S528 and D11S1345. Both regions have been described as deletion targets or as being included within larger allelic deletions detected in several other common tumor types. Thus, these 2 putative melanoma-suppressor loci are likely to harbor tumor-suppressor genes relevant to tumorigenesis of melanoma and a number of other common human malignancies.

Microsatellite instability in human cancer: a prognostic marker for chemotherapy?

The majority of tumors associated with the nonpolyposis form of familial colorectal cancer (HNPCC) shows a specific form of genetic instability which is manifested by length alterations of mono- or dinucleotide repeat sequences [e.g., (A)n or (CA)n]. This phenomenon was termed the RER+ (replication error-positive) phenotype, MSI or MIN (microsatellite instability), and found to result from defects in the cells' DNA mismatch repair system. This system recognizes and restores misincorporated bases or slippage errors which frequently occur during DNA replication. Loss of DNA mismatch repair therefore strongly accelerates the evolutionary process of mutagenesis and selection which underlies the development of cancer. In addition to mutation avoidance, DNA mismatch repair also plays a crucial role in the toxicity of a number of DNA-damaging drugs that are used in cancer chemotherapy. In experimental systems, mismatch-repair-deficient cells are highly tolerant to the methylating chemotherapeutic drugs streptozocin and temozolomide and, albeit to a lesser extent, to cisplatin and doxorubicin. These drugs are therefore expected to be less effective on mismatch-repair-deficient tumors in humans. MIN was also found in a substantial portion of sporadic (nonfamilial) human tumors. However, in many cases the extent of microsatellite instability was not as dramatic as found in HNPCC-related tumors and the underlying genetic defect is unclear. Therefore, while the mismatch repair status of tumors may become an important determinant in the choice of chemotherapeutic intervention, the significance of MIN in sporadic cancer remains elusive.

Paragangliomas of the head and neck region show complete loss of heterozygosity at 11q22-q23 in chief cells and the flow-sorted DNA aneuploid fraction

Nonchromaffin paragangliomas of the head and neck region, also known as glomus tumors, are usually benign neoplasms consisting of clusters of chief cells surrounded by sustentacular cells arranged in so-called 'Zellballen.' Most of the patients have a familial background. In a previous study, examining all chromosome arms, we found loss of heterozygosity (LOH) predominantly at the chromosome 11q22-q23 region, where the disease causing gene PGL1 has been located by linkage analysis. However, all tumors showed only partial loss of allele signal intensities, and it was not clear whether this represented allelic imbalance or cellular heterogeneity. In the current study, we have performed LOH analysis for the 11q22-q23 region on DNA-aneuploid tumor cells, enriched by flow sorting, and on purified chief cell fractions obtained by single-cell microdissection. Complete LOH was found for two markers (D11S560 and CD3D) in the flow-sorted aneuploid fractions, whereas no LOH was found in the diploid fractions of three tumors. The microdissected chief cells from two of these tumors also showed complete LOH for both markers, indicating that the chief cells are clonal proliferated tumor cells. These results indicate that the PGL1 gene is likely to be a tumor suppressor gene, which is inactivated according to the two-hit model of Knudson. Furthermore, it shows that chief cells are a major if not the sole neoplastic component of paragangliomas.

Localization of tumor suppressor activity important in nonsmall cell lung carcinoma on chromosome 11q

Loss of heterozygosity on chromosome 11q23 is observed at high frequency in human nonsmall cell lung carcinomas (NSCLCs), suggesting the presence of a tumor suppressor gene. Previous analysis of DNA from 79 patients identified a commonly deleted segment of 5 centimorgans. Complementation analysis was used to further localize a putative tumor suppressor gene. Three yeast artificial chromosome (YAC) clones spanning the minimal loss of heterozygosity region were modified, and spheroplast fusion was used to transfer them into human A549 NSCLC or murine Lewis lung carcinoma (LLC) cell lines. The resulting yeast x human hybrid cell lines containing an intact copy of a 1.6-Mb YAC, 939b12, showed reduced growth in vitro. Injection of parental A549 cells into athymic (nu/nu) mice resulted in tumor formation at 27 of 28 injection sites. In contrast, two independent 939b12-containing cell lines formed tumors at only 3 of 20 injection sites. 939b12 also suppressed tumor formation by LLC NSCLC cells in nude mice, but YACs 785e12 and 911f2, which flank 939b12, had no suppressor activity. Further localization of tumor suppression activity on 939b12 was accomplished by introduction of defined fragmentation derivatives into A549 cells and by analysis of YACs that were broken on transfer into LLC cells. This complementation approach localized tumor suppression activity to the central 700 kb of 939b12 and provides a functional assay for positional cloning of this tumor suppressor gene.

Atm-dependent interactions of a mammalian chk1 homolog with meiotic chromosomes

BACKGROUND

Checkpoint pathways prevent cell-cycle progression in the event of DNA lesions. Checkpoints are well defined in mitosis, where lesions can be the result of extrinsic damage, and they are critical in meiosis, where DNA breaks are a programmed step in meiotic recombination. In mitotic yeast cells, the Chk1 protein couples DNA repair to the cell-cycle machinery. The Atm and Atr proteins are mitotic cell-cycle proteins that also associate with chromatin during meiotic prophase I. The genetic and regulatory interaction between Atm and mammalian Chk1 appears to be important for integrating DNA-damage repair with cell-cycle arrest.

RESULTS

We have identified structural homologs of yeast Chk1 in human and mouse. Chk1(Hu/Mo) has protein kinase activity and is expressed in the testis. Chk1 accumulates in late zygotene and pachytene spermatocytes and is present along synapsed meiotic chromosomes. Chk1 localizes along the unsynapsed axes of X and Y chromosomes in pachytene spermatocytes. The association of Chk1 with meiotic chromosomes and levels of Chk1 protein depend upon a functional Atm gene product, but Chk1 is not dependent upon p53 for meiosis I functions. Mapping of CHK1 to human chromosomes indicates that the gene is located at 11q22-23, a region marked by frequent deletions and loss of heterozygosity in human tumors.

CONCLUSIONS

The Atm-dependent presence of Chk1 in mouse cells and along meiotic chromosomes, and the late pachynema co-localization of Atr and Chk1 on the unsynapsed axes of the paired X and Y chromosomes, suggest that Chk1 acts as an integrator for Atm and Atr signals and may be involved in monitoring the processing of meiotic recombination. Furthermore, mapping of the CHK1 gene to a region of frequent loss of heterozygosity in human tumors at 11q22-23 indicates that the CHK1 gene is a candidate tumor suppressor gene.