HOPX is methylated and exerts tumour-suppressive function through Ras-induced senescence in human lung cancer.

HOPX acts as a tumour suppressor in various cancers. However, the regulation of HOPX in human lung cancer as well as the mechanism underlying its tumour-suppressive function has not yet been well elucidated. Here we investigated the epigenetic regulation and molecular mechanism by which HOPX exerts growth inhibitory effects. We found that HOPX was down-regulated in 12 out of 13 lung cancer cell lines and in 69 out of 120 primary lung tumours at mRNA and protein levels. Patients with lung adenocarcinoma (ADC) exhibited significantly more positive staining of HOPX protein compared with lung squamous cell carcinoma (SCC) (p =0.036). Again in ADC, patients with higher HOPX expression had a significantly longer disease-free survival (p =0.001). Methylation analysis showed that down-regulation of HOPX was associated with DNA methylation (p =0.011). To analyse the function of HOPX in lung cancer cells, stable transfection with an expression vector of HOPX was performed. It turned out that HOPX inhibited tumour cell proliferation rate, migration, and invasion, and, more interestingly, forced expression of HOPX enhanced cellular senescence via activation of oncogenic Ras and the downstream MAPK pathway, which in turn led to decreased MDM2 and increased p21. On the contrary, knockdown of HOPX by siRNA resulted in reduced Ras activity, inactivation of the MAPK pathway, and decreased p21 levels, accompanied by reduced cellular senescence. Additionally, the HOPX-induced senescence pathway was also active in human bronchial epithelial cells. Taken together, our data suggest that down-regulation of HOPX was related to DNA methylation and that HOPX exerts tumour-suppressive activity by oncogenic Ras-induced cellular senescence in lung cancer cells.

The p53 target gene desmocollin 3 acts as a novel tumor suppressor through inhibiting EGFR/ERK pathway in human lung cancer.

Desmosomes are intercellular junctions that confer strong cell-cell adhesion. Altered expression of desmocollin 3 (DSC3), a member of the desmosomal cadherin family, was found in various cancers; however, its functional involvement in carcinogenesis has not yet been elucidated. Expression/localization of DSC3 was analyzed by real-time reverse transcription-PCR, western blotting, immunofluorescence and immunohistochemistry. Methylation status of DSC3 was examined by demethylation tests, methylation-specific PCR and bisulfite sequencing. It turned out that downregulation of DSC3 in lung cancer cells was associated with DNA hypermethylation. In primary lung tumors, DSC3 was a potential diagnostic marker for lung squamous cell carcinoma, and DSC3 DNA hypermethylation was correlated with poor clinical outcome. To investigate the effect of the tumor suppressor gene p53 on DSC3, transient transfection with a wild-type p53-expression vector was performed. Overexpression of p53 resulted in an increased expression of DSC3 in a DSC3-unmethylated lung cancer cell line H2170, but not in H1299, a DSC3-methylated cell line. However, combination of p53 transfection with demethylation agent 5-aza-2'-deoxycytidine treatment led to increased expression of DSC3 in H1299 cells. Furthermore, functional studies after stable transfection of a DSC3 expression vector showed that ectopic expression of DSC3 inhibited cell proliferation, anchorage-independent growth, migration, as well as invasion, and most interestingly led to reduced phosphorylation levels of extracellular signal-regulated kinase1/2. Taken together, our data suggested that DSC3 acts as a novel tumor suppressor gene through inhibition of epidermal growth factor receptor/extracellular signal-regulated kinase signaling in lung cancer cells.

The diagnostic value of cytokeratin 5/6, 14, 17, and 18 expression in human non-small cell lung cancer.

OBJECTIVES: The expression patterns of cytokeratin (CK) filaments in human epithelial neoplasms are complex and distinctive. The aims of this study were to analyze CK expression and to evaluate the diagnostic application of CKs in human non-small cell lung cancer (NSCLC). METHODS: mRNA expression of CK5, CK6, CK14, CK15, CK17, and CK19 was analyzed by Northern blotting. Protein expression of CK5/6, CK7, CK14, CK17, and CK18 was evaluated by immunohistochemistry on tissue microarrays. RESULTS: Northern blotting showed that CKs were highly expressed in human bronchial epithelial cells and/or small airway epithelial cells. In NSCLC cell lines, the expression pattern of CKs was heterogeneous. Regarding protein expression of CKs in 95 primary lung tumors, expression of CK5/6, CK14, and CK17 proteins was increased in squamous cell carcinomas compared to adenocarcinomas (ADC; p = 0.001, p = 0.030, and p = 0.001, respectively), and higher expression was significantly associated with lower grading (p = 0.006, p = 0.002, and p = 0.001, respectively), while increased expression of CK7 and CK18 was observed in ADC (p = 0.001, respectively). CONCLUSIONS: Our data suggest that CK5/6, CK7, CK14, CK17, and CK18 have diagnostic value in the subclassification of NSCLC.

Decreased PITX1 homeobox gene expression in human lung cancer.

The PITX1 (pituitary homeobox 1) gene has essential roles in human development and has been considered a tumor suppressor in various cancers. However, in lung cancer the role of PITX1 remains to be elucidated. In this study, we analyzed the expression of PITX1 at both mRNA and protein levels in human lung cancer. The reduced PITX1 expression was found in cancer cell lines test compared to normal human bronchial epithelia cells (HEBC) and small airway epithelia cells (SAEC) by Northern blot analysis and RT-PCR as well as Western blot analysis. In primary lung tissues, PITX1 mRNA was found to be downregulated in the majority of tumors compared with normal lung tissues. An association between the lack of PITX1 mRNA expression and higher tumor grade was observed. A tissue microarray containing 135 primary lung carcinomas was analyzed by immunohistochemistry. Eighty-four cases (62%) exhibited no expression of PITX1 and the lower expression of PITX1 was significantly linked to higher tumor stages. Additionally, PITX1 was found to be upregulated in lung cancer cell lines H2228 and H526 after they were exposed to a differentiation modifying agent 5-bromodeoxyuridine (BrdU). Since homeobox genes are known to transcriptionally regulate key cellular processes and associated with differentiation and carcinogenesis, we suggest that PITX1 might be linked to lung cancer development and progression.

Decreased expression of insulin-like growth factor binding protein 7 in human colorectal carcinoma is related to DNA methylation.

PURPOSE: Insulin-like growth factor binding protein 7 (IGFBP-7) is considered a tumor suppressor in various cancers, but its role in colorectal cancer (CRC) is still uncertain. The aims of this study were to analyze the IGFBP-7 expression, and explore the mechanism responsible for the inactivation of IGFBP-7 in CRC. METHODS: mRNA expression was studied by RT-PCR and Northern blot analysis of cultured cells. Methylation status was analyzed by treatment with 5-aza-2'-deoxycytidine followed by sequencing of PCR products of sodium bisulfite-treated genomic DNA. IGFBP-7 protein expression was evaluated by immunohistochemistry (IHC) on tissue microarrays. RESULTS: mRNA expression was lost in six out of eight CRC cell lines as compared to normal colon cells. DNA methylation was found in the region of exon 1 and intron 1 of IGFBP-7. In tumor tissue, 107 out of 279 samples showed a negative expression of IGFBP-7 by IHC, which was significantly associated with poor prognosis. The analysis of 37 paired cancerous and normal mucosa samples confirmed the downregulation in the tumors, but revealed variable basal expression levels of IGFBP-7 in normal mucosal samples. CONCLUSIONS: DNA methylation is a mechanism responsible for IGFBP-7 gene silencing providing a target for therapeutic intervention of this tumor suppressor gene.

Characterization of {gamma}-aminobutyric acid type A receptor-associated protein, a novel tumor suppressor, showing reduced expression in breast cancer.

Frequent allelic loss of the chromosomal region 17p13 in breast cancer has suggested that more tumor suppressor genes, besides p53, are located in this region. By doing suppression subtractive hybridization to detect differentially expressed genes between the breast cancer cell line CAL51 and a nontumorigenic microcell hybrid CAL/17-1, we identified the gene for the gamma-aminobutyric acid type A (GABA(A)) receptor associated protein (GABARAP), located on 17p13.1. GABARAP displayed high expression levels in the microcell hybrid CAL/17-1 but only weak expression in CAL51 and other breast cancer cell lines tested. Furthermore, we observed large vesicles in CAL/17-1 by immunofluorescence staining, whereas no signal could be detected in the tumor cell line. GABARAP mRNA expression and protein expression were significantly down-regulated in invasive ductal and invasive lobular carcinomas compared with normal breast tissue measured by semiquantitative reverse transcription-PCR and immunohistochemistry, respectively. We assessed that neither mutations in the coding region of the gene nor hypermethylation of CpG islands in the promoter region are responsible for loss of gene expression in CAL51; however, 5-aza-2'-deoxycytidine treatment was effective in gene up-regulation, suggesting a methylation-dependent upstream effect. Stable transfection of GABARAP into CAL51 resulted in an increase of gene expression and remarkably influenced the ability of colony formation in soft agar and the growth rate in vitro and, moreover, suppressed the tumorigenicity of the cells in nude mice. In summary, our data suggest that GABARAP acts via a vesicle transport mechanism as a tumor suppressor in breast cancer.

Differentially expressed genes associated with human lung cancer.

To investigate the gene expression of 9 cDNA clones generated by suppression subtraction hybridization (SSH), Northern blot analysis was performed on a panel of immortalized bronchial epithelial cell lines, lung cancer cell lines and normal human bronchial epithelial cells (HBEC). The clones were located on chromosomes 1q, 2q, 3p, 3q, 4q and 14q representing regions that are frequently affected by DNA imbalances as shown by comparative genomic hybridization (CGH). Two were unknown (H24, H103) whereas the others matched to the Pest-containing nuclear protein (H52), Rp11-767C1 gene (H134), the hypothetical gene AK025444 (H238), Guanine nucleotide binding protein (G protein)/alpha inhibiting activity polypeptide 2 (H268), Laminin gamma 1 (Y45), the DEAD (Asp-Glu-Ala-Asp/His) box polypeptide 9 (Y162) and the heat shock 90 kDa protein 1, alpha (Y238). Northern blot results indicated that all of the studied clones showed differential up- or down-regulation in immortalized cells and lung cancer cell lines. Of those, clone Y238 representing HSP90alpha showed a clearly over-expressed transcript. Subsequently, semi-quantitative RT-PCR was used to further confirm the over-expression of Y238, indicating that HSP90alpha was significantly over-represented in 49 primary lung tumors as compared to 14 normal lung samples (P<0.01). CGH showed that the majority of studied lung cancer cell lines (71.4%) carried an overrepresentation at 14q32 where HSP90alpha is located suggesting that it may be affected by DNA copy number changes. The further characterization of these clones will provide us with valuable information on its role in lung carcinogenesis and may help to develop new diagnostic or therapeutic targets for this lethal disease.

CGH pattern of esthesioneuroblastoma and their metastases.

Comparative genomic hybridization (CGH) was used to screen 22 esthesioneuroblastomas (ENB) from 12 patients including 12 primary tumors and 10 metastasis/recurrent lesions for chromosomal imbalances being the most extensive study so far. The analysis revealed a characteristic pattern consisting of deletions on chromosomes 3p and overrepresentations on 17q in up to 100% of cases. Other important alterations being detectable in more than 80% of cases were deletions on 1p, 3p/q, 9p, 10p/q along with overrepresentation on 17p13, 20p and 22q. Particularly striking was the pattern for chromosomes 3, 10 and 17q and 20 being affected almost exclusively by deletions or overrepresentations, respectively. Pronounced overrepresentations suggestive for high copy amplifications were seen on 1p34, 1q23-q31, 7p21, 7q31, 9p23-p24, 17q11-q22, 17q24-q25, 19, 20p, 20q13 and 22q13. Comparing tumor pairs from the same patient revealed a high concordance indicating clonality and confirming the genetic homogeneity of the tumor entity. The analysis of metastatic/recurrent lesions indicated a higher percentage of pronounced alterations, e.g., high copy DNA gains at 1q34-qter, 7q11, 9p23-p24, 9q34, 13q33-q34, 16p13.3, 16p11, 16q23-q24 and 17p13. The analysis furthermore suggested specific alterations, e.g., deletions of chromosome 11 and gains of 1p to be associated with metastasis formation and/or worse prognosis. Our results indicate that ENB is a distinct entity and provides criteria for its genetic distinction from other small round cell tumor types.

Analysis of the RNA helicase A gene in human lung cancer.

In this study we investigated the RNA helicase A (RHA) gene localized on chromosome 1q25 in 15 lung cancer cell lines, 54 primary carcinomas, bronchial epithelial cells and normal lung. Both RT-PCR and real-time RT-PCR showed that RHA is over-expressed in tumour samples compared to normal lung tissues (p=0.01). There was a tendency for higher expression levels in small cell lung cancer compared to non-small cell carcinomas. Over-expression of Y-162 correlated with high grade tumours (p=0.023). However, there was no correlation with tumour stage and survival. Our observations are compatible with the role of RHA in lung cancer development.

[Evaluation of p63 expression in lung cancer by use of complementary DNA and tissue microarray].

OBJECTIVE: To study p63 expression at mRNA transcript and protein levels in human lung cancers, including squamous cell lung carcinoma (SCC), adenocarcinoma, large cell lung carcinoma (LCLC) and small cell lung carcinoma (SCLC), or the corresponding metastatic foci. The relationship of p63 expression and alterations in p63 locus at chromosomal 3q27-29 was also determined. METHODS: p63 gene expression in 72 cases of SCC, adenocarcinoma, LCLC and SCLC was analyzed by cDNA microarray technology. Tissue microarray of specimens from 150 cases of primary lung cancer was prepared for immunohistochemical study for p63 protein. Possible chromosomal alterations at the p63 locus in 70 cases of primary lung cancer were studied by comparative genomic hybridization (CGH) technology. RESULTS: p63 mRNA transcript expression was significantly increased by more than 10-fold in SCC, as compared with that in other histologic subtypes including adenocarcinoma, LCLC and SCLC. p63 mRNA expression in metastatic foci was also remarkably higher than that in their primary tumors (P < 0.001). Immunostaining showed that p63 protein expression was observed in 94.64% of SCC, whereas only one lung adenocarcinoma (1.79%) was positive. Immunopositivity was also demonstrated in 2 of the 4 LCLC cases studied. None of the SCLC cases was positive. There was a statistically significant difference in p63 expression between pT1 and pT2 tumors (P < 0.05). The CGH results showed that overrepresentation of p63 locus at chromosomal 3q27-29 was a typical finding in SCC. p63 immunopositivity also correlated significantly with pronounced gains of p63 locus at chromosomal 3q27-q29 (P < 0.000 1), suggesting that strong expression of p63 in lung SCC was associated with increased gene amplification. CONCLUSION: p63 may play a role in oncogenesis of human lung squamous cell carcinoma and development of metastasis.

[Study on relationship between p63 expression and 3q27-q29 alteration in non-small cell lung cancer].

BACKGROUND: To investigate the relationship of p63 expression and p63 locus at chromosomal 3q27-q29 in non-small cell lung cancer (NSCLC). METHODS: Chromosomal imbalance in 30 cases of squamous cell carcinoma (SCC) and 40 cases of adenocarcinoma of the lung were evaluated by comparative genomic hybridization (CGH) technology. A tissue microarray of specimens from 122 primary NSCLC specimens was employed and used for immunohistochemical detection of p63 protein expression. RESULTS: p63 positivity was found in 54 (44.26%) cases of NSCLC. p63 immunostaining was observed in 51 (86.44%) of 59 SCC, whereas only one adenocarcinoma (1.67%) showed immunoreactivity. Immunopositivity was seen in 2 (66.66%) of 3 large cell lung cancer (LCLC). No correlation existed between p63 protein expression and the age of patient, sex, tumor grading, tumor metastasis, prognosis (P > 0.05). The CGH results revealed that the gain of chromosome 3q27-q29 was identified in 32 (48.57%) of 70 NSCLC samples tested. Overrepresentation was detected in 24 cases of 30 SCC. In 40 adenocarcinoma, only 8 cases showed chromosome gain at chromosomal 3q27-q29. The comparison of p63 immunostaining with chromosomal alteration of 3q27-q29 demonstrated that pronounced gain was detected in 23 (95.83%) cases of 24 SCC with p63 immunopositivity. One case of adenocarcinoma that was p63 positive showed a chromosomal 3q27-q29 normal representation but not pronounced gain. CONCLUSIONS: The results suggest that p63 immuno-positivity correlates significantly with pronounced gains of the p63 locus at chromosomal 3q27-q29, and p63 gene amplification correlates with development and progression of lung SCC.

Molecular cytogenetic characterization of epithelioid hemangioendothelioma.

Epithelioid hemangioendothelioma (EHE) is a rare vascular tumor whose pathological diagnosis can be difficult. In the literature two cases of EHE were found to harbor a balanced t(1;3)(p36.3;q25) translocation, suggesting a characteristic chromosomal rearrangement as cause for the development of EHE. In this study, 14 cases of EHE were investigated by interphase fluorescence in situ hybridization (FISH) directed against the translocation breakpoint 1p36.3. A subset of cases was also analyzed by comparative genomic hybridization (CGH) and image cytometry. Five out of eight cases that could be successfully analyzed by FISH harbored a chromosomal break in the 1p36.3 region. The break-apart signals were present in diploid nuclei, and less frequently also in tetraploid nuclei. In the latter, the chromosomal break was present twice, suggesting that polyploidy occurred after the chromosomal alteration. DNA cytometry confirmed that tetraploid cells were present in most examined cases with one case indicating almost equal amounts of diploid and tetraploid tumor cells. CGH revealed single chromosomal imbalances of unclear significance. We could confirm that EHE may harbor a recurrent mutation involving the 1p36.3 chromosomal region thus supporting the notion that the t(1;3)(p36.3;q25) translocation is a relevant genetic finding in this tumor entity.

Core classification of head and neck squamous cell carcinomas: correlations between morphology, DNA ploidy and HPV infection.

AIMS: The study intended to reveal whether HPV infection is reflected by nuclear morphology and DNA cytometry parameters in head and neck squamous cell carcinomas (HNSCC). METHODS: In total, 39 HNSCC were selected for reanalysis by histomorphology applying the core classification, DNA cytometry and HPV detection. For the core classification, HE sections were assessed by a score system to evaluate the nuclear size, the mitosis size, their variabilities and the presence of tripolar or tetrapolar mitoses. HPV was analyzed by consensus PCR followed by a hybridization method for virus typing. Static DNA cytometry was applied on single cell suspension focusing particularly on the parameters DNA modal value, DNA index peak, DNA index mean, 2c deviation index and 5c exceeding rate. Statistical analysis was done by T-test or Fisher's exact test. RESULTS: The analysis revealed that HPV positive HNSCC had significantly smaller nuclei than HPV negative cases. Increasing values of the nuclear size and mitosis size were significantly associated with higher indices of the DNA cytometry analysis. CONCLUSIONS: The study confirms that the core classification can provide information on the ploidy of HNSCC and that HPV positive tumors represent a distinct morphological and genetic carcinoma subtype.

5-Bromodeoxyuridine induced differentiation of a human small cell lung cancer cell line is associated with alteration of gene expression.

Small cell lung cancer (SCLC) appears to arise from neuroendocrine cells with the potential to differentiate into a variety of lung epithelial cell lineages. In order to investigate molecular events underlying the cell type transition in SCLC, we treated a SCLC cell line H526 with a differentiation inducing agent 5-bromodeoxyuridine (BrdU). The treatment led to a dramatic conversion from suspension cells to adherent cells exhibiting an epithelioid phenotype, which remarkably reduced the ability of colony formation in soft agar and suppressed the tumor growth rate in nude mice. The phenotypic transition was consistent with upregulation of surfactant protein C (SFTPC), thyroid transcription factor 1 (TTF-1), Connexin 26 (Cx26), insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1), as well as homeobox genes LAGY, PITX1, and HOXB2. Our data suggest that BrdU induced cell differentiation could be linked to the development of a less aggressively phenotype in small cell lung cancer.

Homeobox gene HOP has a potential tumor suppressive activity in human lung cancer.

The homeobox containing gene HOP (Homeodomain Only Protein) was identified in the developing heart and lung where it functions downstream of Nkx2.5 and Nkx2.1 to modulate cardiac and lung gene expression. Previously, we found that HOP was downregulated in lung cancer. In this study, we constructed an expression vector containing the full-length cDNA of HOP and transfected it into a lung cancer cell line H2170. Stable transfection led to an increased expression of HOP confirmed by Northern blot analysis. HOP positive transfectants remarkably reduced the growth rate and the ability of anchorage-independent growth in soft agar, and moreover suppressed the tumor formation in nude mice compared to controls. Transient transfection of Nkx2.1 into H2170 resulted in the overexpression of HOP, and correspondingly, siRNA silencing of Nkx2.1 reduced the expression of HOP in lung cancer cells. Treatment with a differentiation modulating agent 5-bromodeoxyuridine (BrdU) led to restoration of HOP expression in a small cell lung cancer cell line H526. In 29 paired primary lung tumor samples, loss of heterozygosity (LOH) analysis was performed by using the 3 microsatellite markers D4S189, D4S231 and D4S392 around the region of chromosome 4q12 where HOP locates. LOH was only found in 4 out 23 cases (17.4%) indicating that allelic loss is a rare genetic event not responsible for the downregulation of HOP in lung cancer. Taken together, our data suggest that HOP is a potential tumor suppressor possibly involved in lung cancer differentiation, and functions downstream of Nkx2.1.

Downregulation of connexin 26 in human lung cancer is related to promoter methylation.

Cell-Cell communication via gap junctions plays a key role in carcinogenesis and in growth control. One of the gap junction proteins, Connexin 26 (Cx26) was considered as tumor suppressor in various cancers. In our study, the expression of Cx26 was analyzed in human lung cancer. The reduced mRNA expression was observed in 17 lung cancer cell lines examined by Northern blot analysis and RT-PCR. In 138 primary carcinomas comprising all subtypes analyzed by immunohistochemistry, 85 cases (62%) exhibited no expression of Cx26, whereas in other 53 cases the Cx26 staining was positive (38%). Additionally, an association between Cx26 protein expression and higher grading of tumors was found in whole tumor samples (p =0.028) but no statistically significant correlations could be observed with tumor stage, tumor size and node status. In squamous cell carcinoma, tumors with higher stage and grading were linked to higher expression of Cx26 (p = 0.015 and 0.017, respectively). To explore the mechanism responsible for the downregulation of Cx26, we treated 2 lung cancer cell lines H2170 and H226 with the demethylation agent 5-aza-2'-deoxycytidine and found the reexpression of Cx26 mRNA. Methylation status of these 2 cell lines was further analyzed by PCR amplification of bisulfite modified DNA and sequencing. A heterogeneous methylation pattern turned out. Our results suggest the inactivation of Cx26 in lung cancer may be explained by promoter methylation.

Chromosomal imbalances in wood dust-related adenocarcinomas of the inner nose and their associations with pathological parameters.

Comparative genomic hybridization (CGH) was used to screen 42 wood dust-related sinonasal adenocarcinomas for chromosomal alterations. The tumour collection comprised 39 papillary-tubular cylinder cell adenocarcinomas (PTCCs; six cases G1, 23 G2, and ten G3), two alveolar goblet cell adenocarcinomas (AGCs), and one signet ring cell adenocarcinoma (SRC), according to the Kleinsasser and Schroeder classification. Copy number changes were detected in 41 tumours (97.6%). The one carcinoma without imbalances was a PTCC-G1. DNA gains were most frequently seen on chromosomes 12p (83%), 7q (74%), 8q (71%), and 20q (71%), 11q (61%), 22 (59%), and 1q (52%). Pronounced overrepresentations suggestive of high copy amplifications were detected on 8q (15 cases, 36%), 7q (six cases, 14%), 20q (five cases, 12%), 13q14 (three cases, 7%), 1q22, 5p, 12p and 20 (two cases, 5% each), and 2q24, 3q13, 3q22, 7p, 14q12, and 16q13 (one case, each 2%). Frequent chromosomal losses occurred at 5q (81%), 18q (76%), 4 (74%), 8p (61%), 9p (60%), 6q and 17p (52% each), and 3p, 13q, and 21 (50% each). There was a quantitative as well as a qualitative increase of alterations from PTCC-G1 to PTCC-G2 and finally PTCC-G3, confirming the usefulness of histopathological grading. While PTCC-G1 carried only a few alterations, namely gains on chromosomes 17 and 7 as well as losses of 4q and 13q, PTCC-G2 already carried many of the above-mentioned alterations, while PTCC-G3 showed significantly more gains of 7q, 8q, and 12p, and losses of 8p and 17p. Additionally, the latter subgroup was particularly prone to carry pronounced DNA gains. These data provide further evidence for a recurrent pattern of chromosomal imbalances in sinonasal adenocarcinomas and highlight distinct aberrations that are associated with tumour differentiation and progression.

Identification of a novel homeobox-containing gene, LAGY, which is downregulated in lung cancer.

We have isolated a novel gene, lung cancer-associated gene Y (LAGY), by suppression subtractive hybridization. The nucleotide sequence of LAGY predicts a small protein of 73 amino acids containing a putative homeobox domain with a molecular mass of 8.1 kD. Multiple-tissue Northern blot analysis revealed that LAGY is present in human placenta, lung, brain, heart and skeletal muscle. Gene mapping locates LAGY on chromosome 4q11-13.1. The expression of LAGY mRNA was widely lost in 18 lung tumor cell lines comprising all major histological types, as shown by Northern blot analysis and semiquantitative reverse transcription-polymerase chain reaction. In an investigation of 72 primary lung tumors, this gene was significantly downregulated in tumors compared to 9 normal lung tissue samples. There was a significant reduction of LAGY expression in squamous cell carcinoma (SCC; n = 27) with increasing grade and stage. No expression was detectable in two high-grade SCCs or two small cell and large cell lung carcinomas (n = 4 for each). In adenocarcinoma (n = 37), expression was reduced; however, this did not reach statistical significance. Since homeodomain-containing genes are known to transcriptionally regulate key cellular processes and are associated with carcinogenesis, we suggest that LAGY might be linked to lung cancer development and progression.

Identification of differentially expressed genes in immortalized human bronchial epithelial cell line as a model for in vitro study of lung carcinogenesis.

Suppression subtractive hybridization (SSH) was applied to identify differentially expressed genes in the SV40LT immortalized human bronchial epithelial cell line Y-BE, with normal human bronchial epithelial cells (HBEC) as a control. Two cDNA libraries of up- and downregulated genes were generated, comprising 218 known genes and 131 unknown genes in total. The expression of 22 clones from the 2 libraries was investigated by Northern blot analysis, and 86.4% (19/22) of them showed differential expression between Y-BE cells and HBEC. Although the Y-BE cells are nontumorigenic in nude mice, Comparative genomic hybridization (CGH) detected some DNA imbalances in Y-BE cells that were similar to lung cancer cells. Our data demonstrate that the studied cell line Y-BE and SSH is a reliable approach for identifying new genes that are associated with immortalization and early tumor development that may help to understand the pathogenesis of lung cancer.