Microsatellite alteration at chromosome 11 in primary human nasopharyngeal carcinoma in Taiwan

Histocompatibility locus antigens regions contribute to the ethnicity bias of Epstein-Barr virus-associated nasopharyngeal carcinoma in higher-incidence populations

Nasopharyngeal carcinoma (NPC) is one the most confusing and rare malignancy in most part of the world with significantly high occurrence in some populations of Southeast Asia, North Africa and Alaska. Apart from the dietary and environmental factors, NPC is well-associated with Epstein-Barr virus (EBV) infection in these ethnic groups. However, the internal molecular mechanism(s) for such association in specific populations is not known till date. Polymorphisms in the genes of histocompatibility locus antigens (HLA) are reported in NPC, but association of any particular polymorphism with ethnicity is not established yet. Here, we report a set of HLA polymorphisms in EBV-infected NPC samples from Northeast Indian population. These polymorphisms might play an important role for the lack of proper immune function against EBV infection and thus, eventually, for NPC generation in endemic populations like those of Northeast India.

Frequent concomitant epigenetic silencing of the stress-responsive tumor suppressor gene CADM1, and its interacting partner DAL-1 in nasal NK/T-cell lymphoma

Nasal NK/T-cell lymphoma (NL) is a rare but clinically important entity of lymphoma. Its preferential incidence in Orientals but not Caucasians suggests possible genetic predisposition. 11q deletion is common in NL, indicating certain tumor suppressor genes (TSGs) at this locus involved in its pathogenesis. We investigated the expression and methylation of an 11q23.2 TSG, CADM1 (or TSLC1), and its partner DAL-1 (or EPB41L3) in NL. Methylation and silencing of CADM1 were detected in 2 NL and 4 of 8 (50%) of non-Hodgkin lymphoma (NHL) cell lines, but not in normal NK cells and normal PBMC. Absence of CADM1 protein was also detected in NL cell lines. 5-aza-2'-deoxycytidine (Aza) demethylation or genetic knockout of both DNMT1 and 3B genes restored CADM1 and DAL-1 expression. CADM1 methylation was further detected in 36 of 45 (80%) of NL tumors. Concomitantly, DAL-1 was epigenetically inactivated in NL cell lines and virtually all the tumors with methylated CADM1. A significant correlation between the methylation of both genes was found (p < 0.0001). Homozygous deletion of CADM1 was detected in only 3 of 18 (17%) of tumors. The stress-response of CADM1 was abolished when its promoter becomes methylated. Our results demonstrate a frequent, predominant epigenetic silencing of CADM1 and DAL-1 in NL, which likely play a synergic role in NL pathogenesis.

Investigation of allelic imbalances on chromosome 3p in nasopharyngeal carcinoma in Tunisia: high frequency of microsatellite instability in patients with early-onset of the disease

Tunisia is one of the world's intermediate risk areas for nasopharyngeal carcinoma (NPC). Loss of heterozygosity (LOH) on the short arm of chromosome 3 (3p) is the most frequent genetic change reported in NPC from endemic areas. In the present study, we investigate the incidence of LOH and microsatellite instability (MSI) on chromosome 3p in 49 microdissected primary NPC specimens and corresponding non-cancerous tissues from Tunisian patients using six microsatellite polymorphic markers. LOH at one or more markers was observed in 40 out of 48 informative cases (83.3%). The markers D3S1038 at 3p25.2-26.1 and D3S1076 at 3p21.1-21.2 have showed the highest frequency of LOH (51.3%), followed by D3S1067 at 3p14.3-21.1 (48.7%), D3S1568 at 3p21.3 (47.4%), D3S659 at 3p13 (15.3%), and D3S1228 at 3p14.1-14.2 (11%). Interestingly, MSI at one or more microsatellite markers was observed in 15 cases (31.2%). The highest frequency of MSI was presented by D3S1568 (18.4%), D3S1067 (17.9%), and D3S1038 (12.8%). With regard to clinicopathological features, LOH was found to be less common in young patients (under 25 years) than in adults (p=0.04), whereas MSI was found to be more frequent in patients under 45 years than in older patients (p=0.006). No significant correlation was found between LOH or MSI and the other clinicopathological features investigated including, gender, tumor size, lymph node metastasis, UICC clinical stage, and histological subtype. This study revealed different patterns of allelic imbalance on chromosome 3P in NPC between age groups in Tunisia, and suggests an alteration in the DNA mismatch repair machinery that may be, in part, responsible of the early age onset form of this disease in North African populations. More attention should be given to the mismatch repair system in the juvenile form of this disease in future studies.

Epstein-Barr virus-encoded EBNA1 regulates cellular gene transcription and modulates the STAT1 and TGFbeta signaling pathways

The Epstein-Barr virus (EBV)-encoded EBNA1 protein is expressed in all virus-associated tumors where it plays an essential role in the maintenance, replication and transcription of the EBV genome. Transcriptional profiling of EBNA1-expressing carcinoma cells demonstrated that EBNA1 also influences the expression of a range of cellular genes including those involved in translation, transcription and cell signaling. Of particular interest was the ability of EBNA1 to enhance expression of STAT1 and sensitize cells to interferon-induced STAT1 activation with resultant enhancement of major histocompatibility complex expression. A negative effect of EBNA1 on the expression of TGFbeta1-responsive betaig-h3 and PAI-1 genes was confirmed at the protein level in EBV-infected carcinoma cells. This effect resulted from the ability of EBNA1 to repress TGFbeta1-induced transcription via a reduction in the interaction of SMAD2 with SMAD4. More detailed analysis revealed that EBNA1 induces a lower steady-state level of SMAD2 protein as a consequence of increased protein turnover. These data show that EBNA1 can influence cellular gene transcription resulting in effects that may contribute to the development of EBV-associated tumors.

Microsatellite Instability in Nasopharyngeal and Lymphoepithelial Carcinomas of the Head and Neck

Lymphoepithelial carcinoma (LEC) is a descriptive diagnosis for an undifferentiated carcinoma that has a typical morphologic appearance of large vesicular cells with prominent nucleoli and infiltrating lymphocytes. Tumors with this histopathologic appearance in the head and neck can be categorized as either those that occur in endemic areas, such as Southeast Asia and are associated with Epstein-Barr virus (EBV) infection, or those that occur in other countries and are less commonly associated with EBV. The molecular changes in endemic EBV-related LEC have been fairly well studied and include both alterations in tumor suppressor genes and 1 report of high levels of microsatellite instability. In nonendemic LECs arising in western countries, there is very little data related to molecular mutational profiles. In this study, we examined 19 cases of LEC from the United States for evidence of microsatellite instability at the DNA level and for alterations in the DNA mismatch repair (MMR) system at the immunohistochemical staining level. Only 3/19 cases showed high-level microsatellite instability and only 1 of these showed an alteration in the DNA MMR protein expression hMLH1. These data suggest that alterations in DNA MMR system are not a common mechanism of tumorigenesis in LEC of the head and neck in a nonendemic country.

Allelic imbalance at chromosome 11 in head and neck squamous cell carcinoma in an Indian patient population

BACKGROUND

Genetic instability of chromosome 11 is a frequent event in many solid tumours, including head and neck squamous cell carcinoma (HNSCC).

AIMS

To perform allelic imbalance analysis of cytogenetically mapped altered regions of human chromosome 11 in patients with HNSCC from eastern India.

METHODS

Genomic alterations were investigated using highly polymorphic microsatellite markers in both HNSCC and leukoplakia tissues.

RESULTS

Microsatellite markers D11S1758 from 11p13-15 and D11S925 from 11q23.3-24 had the highest frequency (38% and 32%, respectively) of loss of heterozygosity among all the markers analysed. Allelic loss at the marker D11S925 was seen in both leukoplakia and in all stages of HNSCC tumour tissues suggesting that it is an early event in HNSCC tumorigenesis. Microsatellite size alteration was also found to be high (> 20%) in several markers. In leukoplakia samples microsatellite instability was seen at a higher frequency than loss of the allele, indicating such alterations might initiate the process of tumorigenesis in HNSCC.

CONCLUSIONS

The high rate of chromosomal alterations at 11q21-24 in HNSCC suggests the presence of a putative tumour suppressor gene in this region.

Genome-wide analyses on loss of heterozygosity in head and neck squamous cell carcinomas

Head and neck squamous cell carcinoma (HNSCC) is a frequent malignancy with a poor survival rate. Identifying the tumor suppressor gene (TSG) loci by genomic studies is an important step to uncover the molecular mechanisms involved in HNSCC pathogenesis. We therefore performed comprehensive analyses on loss of heterozygosity (LOH) using a genome-wide panel of 191 microsatellite markers in 22 HNSCC samples. We found 53 markers with significantly high LOH (>30%) on 21 chromosomal arms; the highest values of those were observed on 3p, 9p, 13q, 15q, and 17p, corresponding to D3S2432 (67%), D9S921-D9S925 (67%) and GATA62F03 (86%), D13S1493 (60%), D15S211 (62%), and D17S1353 (88%), respectively. Fifteen hot spots of LOH were defined in 13 chromosomal arms: 2q22-23, 4p15.2, 4q24-25, 5q31, 8p23, 9p23-24, 9q31.3, 9q34.2, 10q21, 11q21-22.3, 14q11-13, 14q22.3, 17p13, 18q11, and 19q12 as loci reported previously in HNSCCs. Furthermore, we identified five novel hot spots of LOH on three chromosomal arms in HNSCC at 2q33 (D2S1384), 2q37 (D2S125), 8q12-13 (D8S1136), 8q24 (D8S1128), and 15q21 (D15S211). In conclusion, our comprehensive allelotype analyses have unveiled and confirmed a total of 20 possible TSG loci that could be involved in the development of HNSCC. These results provide useful clues for identification of putative TSGs involved in HNSCC by fine mapping of the suspected regions and subsequent analysis for functional genes.