Prognostic and therapeutic implications of mTORC1 and Rictor expression in human breast cancer

The mammalian target of rapamycin (mTOR) plays a key role in the regulation of cellular metabolism, growth and proliferation. It forms two multi-protein complexes known as complex 1 (mTORC1) and 2 (mTORC2). Raptor and Rictor are the core proteins for mTORC1 and mTORC2, respectively. This study examines the relationship between mTORC1, Rictor and Raptor mRNA expression and human breast cancer. Furthermore, the correlation between mTORC1 and hTERT was investigated. Breast cancer tissues (n=150) and normal tissues (n=31) were analysed using reverse transcription and quantitative PCR. Transcript levels were correlated with clinicopathological data. Higher mTOR expression was noted in breast cancer tissue (P=0.0018), higher grade tumours (grade 2 vs. 3, P=0.047), in ductal tumours (P=0.0014), and was associated with worse overall survival (P=0.01). Rictor expression was significantly higher in background breast tissues compared with tumours and was inversely related to the Nottingham Prognostic Index (NPI1 vs. 2, P=0.03) and tumour grade (grade 1 vs. 3, P=0.01) and was associated with better overall (P=0.037) and disease-free survival (P=0.048). The mRNA expression of Raptor was higher in tumours compared with normal tissues. Furthermore, the expression of Raptor was associated with a higher tumour grade (grade 1 vs. 3, P=0.027). A highly significant positive correlation between mTOR and hTERT (P<0.00001) was observed. These observations are consistent with the role of mTORC1 in the anti-apoptosis pathway and suggest that selective inhibitors of mTORC1 may be more efficacious in human breast cancer. Our findings support the hypothesis that mTORC1 is an important upregulator of telomerase in breast cancer.

P1-05-05: Prognostic Utility of Histone Modifier Gene Expression Profiles in Human Breast Cancer

Background: Gene expression is stringently controlled under physiological conditions by epigenetic mechanisms, including the specific methylation of cytosine residues within CpG dinucleotides and orchestrated adjustments in the histone dependent organisation of chromatin. The organisation of DNA within the chromatin template depends upon highly conserved histone proteins, the properties of which continue to exceed the simplistic packaging role originally assigned to them. Histone modifier enzymes impart a dynamic histone code and specific permutations have significant implications for chromatin topology and the functional configuration of promoters. This study follows our initial report describing potential tumour suppressor function associated with the histone methyltransferase SETD2 in human breast cancer. The objective was to evaluate the expression profiles of sixteen additional histone modifier genes in women with primary operable breast cancer within a well annotated cohort with extended follow-up.

Methods: Primary breast cancer tissues (n= 127) and adjacent benign/normal tissues (n=33) underwent RNA extraction and reverse transcription. The transcript levels of histone modifier genes were evaluated using real-time quantitative PCR, these included: histone acetyltransferases (CREBBP), Class 1 (HDAC1 and HDAC2), II (HDAC5) and III (SIRT1) histone deacetylases and histone methyltransferases (SUV39H1 and SUV39H2) amongst others. Transcript levels were analysed against a range of clinico-pathological variables, including: tumour size, grade, nodal involvement, histological subtype, receptor status, TNM stage, Nottingham Prognostic Index, disease free and overall survival over a 10 year follow-up period.

Results: Transcript levels of the histone modifier genes in breast cancer tissues differed significantly from non-malignant samples (HDAC5, HDAC1, KDM4A and KDM6A). Amongst breast cancers, significant differences in transcript levels were associated with established pathological parameters and prognostic indices: tumour grade (KAT5, HDAC1, KDM4A, SUV39H1 and KDM6A), receptor status (KAT5, SMYD3 and KDM1A), histological type (KAT5, KDM5C, MYST1, KDM4A and MLL), TNM stage (SUV39H1, KAT2B, KDM1A, KDM4A, KDM5C, MYST1, HDAC5 and KAT5), Nottingham Prognostic Index (KDM5C, MLL, MYST1 and SMYD3), disease free survival (SUV39H1, SMYD3, HDAC5, KDM6A, HDAC1, KDM1A, KDM4A, MYST1, KDM5C, KAT5 and MLL) and overall survival (MYST1). Interestingly, significant correlations were also identified between the differential expression profiles of particular histone modifying genes.

Conclusion: The expression profiles of histone modifier genes differ significantly between breast cancer tissues and normal/benign samples. Particular expression profiles in breast cancer are significantly associated with established pathological parameters, prognostic indices, disease free and overall survival. The biological significance and clinical relevance of altered expression of specific histone modifier genes and particular permutations of misexpression remain to be fully elucidated and further study is warranted. Epigenetic signatures derived from histone modifier genes may offer utility as biomarkers and histone modifier enzymes have potential for targeted therapeutic strategies.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-05-05.

Evidence for a tumour suppressor function of SETD2 in human breast cancer: a new hypothesis

BACKGROUND

SET domain containing protein 2 (SETD2) is a histone methyltransferase that is involved in transcriptional elongation. We previously demonstrated SETD2 to be a potential tumour suppressor gene in breast cancer. The aim of this study was to compare SETD2 expression in breast cancer with that in adjacent non-cancerous breast tissue (ANCT) in paired samples. A hypothesis is proposed that explains the mode of action of SETD2 as a tumour suppressor gene.

MATERIALS AND METHODS

Paired samples of tumour and adjacent non-cancerous tissue (ANCT) from 25 patients were analysed. The levels of transcription of SETD2 were determined using quantitative polymerase chain reaction and normalized against cytokeratin 19. Immunohistochemical staining with appropriate antibodies against SETD2 protein was also performed in selected samples.

RESULTS

Levels of SETD2 mRNA were significantly higher in ANCT when compared to those in tumour samples (p=0.01). Immunohistochemistry also demonstrated a higher protein expression in ANCT.

CONCLUSION

This study offers further evidence that SETD2 behaves like a tumour suppressor gene. Our hypothesis links SETD2 mode of action with telomerase regulation through human telomerase reverse transcriptase (hTERT). Several studies have emphasised the importance of histone methylation of hTERT promotor in telomerase regulation. SETD2 function of histone methylation could be the missing link in this chain which could explain the potential tumour suppressor function of SETD2.

Evidence of a tumour suppressor function for DLEC1 in human breast cancer

DLEC1 (deleted in lung and oesophageal cancer), located on 3p22.3, is a candidate tumour suppressor gene in lung, esophageal, and renal cancer. The aim of this study was determine whether the mRNA expression levels of DLEC1 were consistent with a tumour suppressive function.

MATERIALS AND METHODS

A total of 153 samples were analysed. The levels of transcription of DLEC1 were determined using quantitative PCR and normalised against (CK19). Transcript levels within breast cancer specimens were compared to normal background tissues.

RESULTS

Levels of transcription were lower [corrected] in tumour samples compared to adjacent non cancerous tissue (ANCT) samples but this was not statistically significant (median 0.167 vs. 0.03; p=0.138). DLEC1 expression levels were significantly lower in samples from patients who developed metastasis, local recurrence, or died of breast cancer when compared to those who were disease free for >10 years (p=0.041).

DISCUSSION

These findings are consistent with a possible tumour suppressor function of DLEC1 in breast cancer.

The mRNA expression of SETD2 in human breast cancer: correlation with clinico-pathological parameters

Background

SET domain containing protein 2 (SETD2) is a histone methyltransferase that is involved in transcriptional elongation.

There is evidence that SETD2 interacts with p53 and selectively regulates its downstream genes. Therefore, it could be implicated in the process of carcinogenesis. Furthermore, this gene is located on the short arm of chromosome 3p and we previously demonstrated that the 3p21.31 region of chromosome 3 was associated with permanent growth arrest of breast cancer cells. This region includes closely related genes namely: MYL3, CCDC12, KIF9, KLHL18 and SETD2. Based on the biological function of these genes, SETD2 is the most likely gene to play a tumour suppressor role and explain our previous findings.

Our objective was to determine, using quantitative PCR, whether the mRNA expression levels of SETD2 were consistent with a tumour suppressive function in breast cancer. This is the first study in the literature to examine the direct relationship between SETD2 and breast cancer.

Methods

A total of 153 samples were analysed.

The levels of transcription of SETD2 were determined using quantitative PCR and normalized against (CK19).

Transcript levels within breast cancer specimens were compared to normal background tissues and analyzed against conventional pathological parameters and clinical outcome over a 10 year follow-up period.

Results

The levels of SETD2 mRNA were significantly lower in malignant samples (p = 0.0345) and decreased with increasing tumour stage.

SETD2 expression levels were significantly lower in samples from patients who developed metastasis, local recurrence, or died of breast cancer when compared to those who were disease free for > 10 years (p = 0.041).

Conclusion

This study demonstrates a compelling trend for SETD2 transcription levels to be lower in cancerous tissues and in patients who developed progressive disease. These findings are consistent with a possible tumour suppressor function of this gene in breast cancer.

Evidence of a tumour suppressive function of E2F1 gene in human breast cancer

BACKGROUND

The E2F family of transcription factors are key regulators of genes involved in cell cycle progression, cell fate determination, DNA damage repair and apoptosis. E2F1 is unique in that it contributes both to the control of cellular proliferation and cellular death. Furthermore, unlike other E2Fs, E2F1 responds to various cellular stresses. This study aimed to examine the level of mRNA expression of E2F1 gene in normal and malignant breast tissue and correlate the level of expression to tumour stage.

MATERIALS AND METHODS

One hundred and twenty-seven breast cancer tissue and 33 normal tissues were analyzed. Levels of transcription of E2F1 were determined using real-time quantitative PCR, normalized against CK19. Levels of expression were analyzed against TNM stage, nodal involvement, tumour grade and distant metastasis.

RESULTS

The levels of E2F1 mRNA were lower in malignant tissues. They declined further with increasing TNM stage. This became statistically significant when TNM stages 3 and 4 were compared to TNM stages 1 and 2 disease (TNM1 vs. TNM3 p = 0.032; TNM1 vs. TNM4 p = 0.032; TNM2 vs. TNM3 p = .019; TNM2 vs. TNM4 p = 0.021). The levels of E2F1 also fell with increasing tumour grade, when comparing grade 2 and 3 with grade 1, however, the differences were not statistically significant.

CONCLUSION

These results are highly suggestive of the role of E2F1 as a tumour suppressive gene in human breast cancer.

HTERT mRNA expression correlates with matrix metalloproteinase-1 and vascular endothelial growth factor expression in human breast cancer: a correlative study using RT-PCR

BACKGROUND

Telomerase activity has been significantly associated with nodal metastasis and cellular proliferation in human breast cancer, indicating that its degree of expression has some form of vital control over the invasive nature of the malignancy concerned. Of the telomerase subunits, the reverse transcriptase (hTERT) is the main determinant of enzyme activity. Vascular endothelial growth factors (VEGF)-C and (VEGF)-D, matrix metalloprotease type 1 (MMP-1) and protease-activated receptors (PARs) have all been linked to promotion of tumour invasiveness and metastatic dissemination. This study aims to examine the association between hTERT transcription and that of VEGF-D, VEGF-C, MMP-1, PAR1a and PAR1b through a correlative analysis of the mRNA transcripts of these genes in human breast cancer.

MATERIALS AND METHODS

Breast cancer tissues (n = 116) and normal tissues (n-31) were collected immediately after surgery and stored at -80 degrees C until use. The level of hTERT transcripts from the prepared DNA from the above samples was determined using real time-quantitative PCR based on the Amplifluor technology. The levels of the transcript were generated from a standard that was simultaneously amplified with the samples. Normalisation against cytokeratin 19 (CK19) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was also carried out.

RESULTS

There was a positive correlation between hTERT mRNA expression (after CK19 normalisation) with both VEGF-D and MMP-1 in human breast cancer. PAR1 was seen to correlate with hTERT (after GAPDH normalisation) with a highly significant correlation with PAR1a alone. However there was no correlation between hTERT transcription and VEGF-C or with PAR1b alone.

CONCLUSION

Our findings suggest that hTERT is a potential up-regulator of MMP-1, PAR1 and VEGF-D expression and this may explain its apparent control over the invasiveness and metastasis of the malignancy concerned.

hTERT mRNA expression is associated with a poor clinical outcome in human breast cancer

BACKGROUND

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. hTERT (human telomerase reverse transcriptase) gene is the rate-limiting determinant of telomerase reactivation. The present study aims to quantitatively measure the expression of hTERT mRNA in human breast cancer, examine the association between hTERT and the clinicopathological characteristics of the cancer specimens including the Nottingham Prognostic Index (NPI) and to explore the relationship between hTERT expression and clinical outcome.

MATERIALS AND METHODS

RNA was extracted from 116 breast carcinomas and 31 matched adjacent non-cancerous tissue (ANCT). hTERT mRNA expression was estimated by reverse transcriptase-PCR (RT-PCR) and Taqman methodology.

RESULTS

hTERT mRNA was present in all of the cancerous specimens (mean=0.1701, median=0.0205) and most ANCT specimens with levels being 2.6 times higher in the cancerous tissue than in ANCT (mean=0.156 vs. 0.68, p=0.18). The mean mRNA levels increased with NPI scores (0.0816 for NPI 1, 0.1186 for NPI 2 and 0.68 for NPI 3), however this failed to reach statistical significance (P-values= 0.33 for NPI 1 vs. 2, 0.27for NPI2 vs. 3 and 0.24 for NPI 1 vs. 3). hTERT levels also increased with increasing tumour's grade (mean= 0.0459 for grade 1, 0.111for grade 2, and 0.27 for grade 3) but this trend did not reach a statistical significance. Low levels of hTERT were associated with mucinous carcinoma compared with ductal (p=0.023) and lobular (p=0.021) types. hTERT mRNA levels were higher in patients who had recurrent disease or died from breast cancer compared with those who remained alive without disease after a median follow up of 6 years (p=0.0026).

CONCLUSION

High hTERT mRNA levels are associated with a poor clinical outcome in human breast cancer and should be included as a prognostic marker in future validation studies.

hTERT protein expression is independent of clinicopathological parameters and c-Myc protein expression in human breast cancer

Background

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. The hTERT (human telomerase reverse transcriptase) subunit seems to be the rate-limiting determinant of telomerase and knowledge of factors controlling hTERT transcription may be useful in therapeutic strategies. The hTERT promoter contains binding sites for c-Myc and there is some experimental and in vitro evidence that c-Myc may increase hTERT expression. We previously reported no correlation between c-Myc mRNA expression and hTERT mRNA or telomerase activity in human breast cancer. This study aims to examine the correlation between hTERT expression as determined by immunohistochemistry and c-Myc expression, lymph node status, and tumour size and grade in human breast cancer.

Materials and methods

The immunohistochemical expression of hTERT and c-Myc was investigated in 38 malignant breast tumours. The expression of hTERT was then correlated with the lymph node status, c-Myc expression and other clinicopathological parameters of the tumours.

Results

hTERT expression was positive in 27 (71%) of the 38 tumours. 15 (79%) of 19 node positive tumours were hTERT positive compared with 11 (63%) of 19 node negative tumours. The expression was higher in node positive tumours but this failed to reach statistical significance (p = 0.388). There was no significant association with tumour size, tumour grade or c-Myc expression. However, hTERT expression correlated positively with patients' age (correlation coefficient = 0.415, p = 0.0097).

Conclusion

hTERT protein expression is independent of lymph node status, tumour size and grade and c-Myc protein expression in human breast cancer

Evidence for a Tumour Suppressive Function of APRG1 in Breast Cancer

INTRODUCTION

Deletion mapping studies have shown that genes in the region 3p21.3 are often deleted in epithelial malignancies. Although the regions deleted differ between individual cancers there appears to be a specificity for the type of malignancy produced. As a result this area of chromosome 3 is thought to contain multiple tumour suppressor genes. The present study concentrates on one gene in that region, APRG1. This gene codes for a protein, which has been implicated in cell membrane interactions. The aim was to determine using quantitative PCR whether the levels of this gene were negatively correlated with clinical outcome in breast cancer.

METHODS

One hundred and twenty tumour tissues and 33 normal tissues were analyzed. Levels of transcription of APRG1 were determined using real-time quantitative PCR. APRG1 expression was normalized against CK19. Levels of expression were analyzed against staging, nodal involvement, grade, distant metastasis and survival over a 6 year follow up period.

RESULTS

Levels of APRG1 mRNA were lower in malignant tissues. They fell further with increasing stage using the TNM classification This became statistically significant when TNM stages 3 and 4 were compared to TNM 1 (p = 0.0046, p = 0.04, t-test). They were lower in those with positive nodes although this did not reach statistical significance. There was a statistically significant reduction in APRG1 in grade 3 tumours cf. grade 1 (p = 0.0081). APRG1 expression was highly negatively correlated with progressive disease: alive with metastasis (p = 0.0069), local recurrence (p = 0.0055), died of breast cancer (p = 0.11), all progressive disease (p = 0.035).

CONCLUSION

This study shows a compelling trend for APRG1 transcription levels to be lower in malignant tissues and lower still in those patients who develop progressive disease. There was also a statistically significant difference in APRG1 levels between grade 3 and grade 1 tumours. These results are highly suggestive of APRG1 acting as a tumour suppressor gene.

WNT5A expression in human breast cancer

The Wnt family encodes secreted signaling molecules involved in cell adhesion and, by implication, cell growth. Wnt5a has been shown to behave as a putative oncogene and also as a tumour suppressor gene. This is a reflection of its role within a multi-step pathway and in the variety of ways in which its production can be stimulated or switched off. Wnt genes can be functionally separated into two classes; those that activate the canonical Wnt/beta-catenin pathway and those that activate the Wnt/Ca++ pathway. Wnt5a signals through frizzled receptors and, depending upon which frizzled receptor is present, may activate either pathway. Therefore the observed function of Wnt5a is entirely dependent upon its context, hence the confusion over its role in tumorigenesis. This study examines Wnt5a mRNA expression using RT-PCR in human breast cancer.

MATERIALS AND METHODS

One hundred and twenty malignant breast tumours and 33 normal breast tissues were analysed. The levels of transcription of Wnt5a were determined using real-time quantitative PCR. Levels of expression were analysed against staging, nodal involvement, grade, distant metastasis and survival over a 6-year follow-up period.

RESULTS

Levels of Wnt5a mRNA were lower in tumours than in normal tissue (mean values: 107 vs. 62.7). They fell further with increasing stage using the Nottingham Prognostic Index. This became statistically significant when NPI3 was compared to normal tissue (p=0.043, t-test). There was a trend towards lower levels of Wnt5a in those with progressive disease, however, this did not reach statistical significance. In patients with ER-negative disease, lower levels of Wnt5a were significantly associated with a worse clinical outcome (p=0.016).

CONCLUSION

There is a trend for mRNA levels to be lower in cancerous tissue and lower still in those showing more aggressive behaviour. This is consistent with the hypothesis that Wnt5a is a tumour suppressor gene with potential clinical applications.

Mutational effects of retrovirus insertion on the genome of V79 cells by an attenuated retrovirus vector: implications for gene therapy

Attenuated retroviruses are currently the most widely used vectors in clinical gene therapy because of their potential to effect stable and permanent gene transfer. Since gene delivery is accompanied by random insertion of foreign genetic material into the recipient chromosomal DNA, the potential for insertional mutagenesis exists. In this study, we used a defective retrovirus vector containing a selectable marker, the hygromycin phosphotransferase gene, to investigate the mutagenic effects of vector integration on the mammalian genome. V79 Chinese hamster cells were infected with virus supernatants or by coculture with virus producer cells, and provirus insertion events occurred at low and high frequencies, respectively. The frequency of hprt mutagenesis was increased by a factor of 2.3 over the spontaneous hprt mutation frequency only following multiple provirus insertions/cell genome. Multiple provirus insertions (>3/genome) resulted in instability at the hprt locus in 63% of the virally induced hprt mutants, as indicated by rearrangements at the molecular level, whereas no rearrangements were found when the provirus copy number was 1-2/genome. To demonstrate direct proviral involvement in mutagenesis, the defective MLV vector was retrieved along with flanking genomic hprt sequences from one mutant, and localized within intron 5 of the hprt gene. These data suggest that provirus copy number is a key factor when considering the potential hazards of using retrovirus vectors for gene therapy.

hTERT mRNA expression correlates with telomerase activity in human breast cancer

AIMS

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. hTERT (human telomerase reverse transcriptase) gene seems to be the rate-limiting determinant of telomerase reactivation. hTERT mRNA expression was reported to correlate with telomerase activity in cell lines and some human tumours. However the correlation between telomerase activity and hTERT mRNA expression has not been previously examined in human breast cancer. The present study aims to quantitatively measure the expression of hTERT mRNA and telomerase activity in human breast cancer and examine the relationship between these parameters. Furthermore the associations with other parameters including estrogen receptor (ER) and progesterone receptor (PgR) status, DNA ploidy, and S-phase fraction (SPF) are also examined.

METHODS

RNA was extracted from 18 breast carcinomas and hTERT mRNA expressions were estimated by reverse transcriptase-PCR (RT-PCR) and Taqman methodology. These tumours had already been analysed for ER and PgR status using ligand-binding assays and had had their DNA ploidy and S-phase fractions measured by flow cytometry. Telomerase activity had already been determined by using a modified telomeric repeat and amplification protocol (TRAP) assay.

RESULTS

The expression of hTERT mRNA in the breast tumours ranged between 1.3 and 2.7 x 10(7) copy numbers per micro g of cellular RNA (the median value was 2.7x10(5) and the mean was 3.1 x 10(6)). Telomerase activity was between 0 and 246 units of Total Protein Generated (TPG), where one unit of TPG was equal to 600 molecules, of telomerase substrate primers extended by at least three telomeric repeats. The median level of TPG was 60 units and the mean level was 81 units). Telomerase activity was found to significantly correlate with hTERT expression (r(s)=0.51112, P=0.0302). There was no significant correlation between hTERT and other parameters.

CONCLUSION

hTERT mRNA expression significantly correlates with telomerase activity in human breast cancer. This is consistent with the hypothesis that hTERT is the catalytic and rate-limiting determinant subunit of the enzyme.

Human squamous cell carcinomas lose a mortality gene from chromosome 6q14.3 to q15

Normal human keratinocytes possess a finite replicative lifespan. Most advanced squamous cell carcinomas (SCCs), however, are immortal, a phenotype that is associated with p53 and INK4A dysfunction, high levels of telomerase and loss of heterozygosity (LOH) at several genetic loci, suggestive of the dysfunction of other mortality genes. We show here that human chromosome 6 specifically reduces the proliferation or viability of a human SCC line, BICR31, possessing LOH across the chromosome. This was determined by an 88% reduction in colony yield (P<0.001), following the reintroduction of an intact normal chromosome 6 by monochromosome transfer. Deletion analysis of immortal segregants using polymorphic markers revealed the loss of a 2.9 Mbp interval, centred on marker D6S1045 at 6q14.3-q15, in 6/19 segregants. Crucially, allelic losses of this region were not identified in control hybrids constructed between chromosome 6 and the BICR6 SCC cell line that is heterozygous for chromosome 6 and which showed no reduction in colony formation relative to the control chromosome transfers. This indicates that the minimally deleted region at D6S1045 is not the result of fragile sites, a recombination hot spot, or a feature of the monochromosome transfer technique. LOH of D6S1045 was found in 2/9 immortal SCC lines and was part of a minimally deleted region of line BICR19. Furthermore, allelic imbalance, consistent with LOH, was detected in 3/17 advanced SCCs of the tongue. These results suggest the existence of a suppressor of SCC immortality and tumour development at chromosome 6q14.3-q15, which is important to a subset of human SCCs.

hTERT expression in human breast cancer and non-cancerous breast tissue: correlation with tumour stage and c-Myc expression

Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell division and maintains chromosomal length and stability thus leading to cellular immortalisation. hTERT (human telomerase reverse transcriptase) gene is the rate-limiting determinant of telomerase reactivation. The present study aims to quantitatively measure the expression of hTERT mRNA in human breast cancer, adjacent non-cancerous tissue (ANCT) and benign breast lesions, examine the association between hTERT and the clinicopathological characteristics of the cancer specimens and to explore the relationship between c-Myc and hTERT expressions. RNA was extracted from 49 breast carcinomas, 46 matched ANCT, and eight fibroadenomas. hTERT and c-Myc mRNA expressions were estimated by reverse transcriptase-PCR (RT-PCR) and Taqman methodology. hTERT mRNA was present in all of the cancerous and most of ANCT specimens with levels being much higher in the cancerous tissue than in ANCT. The ratio of hTERT mRNA in tumour to that in ANCT was 2011 (95% confidence interval 373-10,853, P < 0.0001). There was no significant association between tumour hTERT expression and patient's age, tumour size, grade, nodal metastasis, estrogen receptor (ER) positivity, lymphovascular (LVI) or c-Myc expression. However, there was a weak but significant negative correlation between hTERT expression and progesterone receptor (PR) status (p = 0.04) in tumours. hTERT mRNA expression was also significantly higher in carcinomas (median = 2.61 x 10(6)) than in fibroadenomas (median = 424).We conclude that hTERT mRNA expression is significantly higher in human breast cancer than in non-cancerous breast tissue suggesting that hTERT has a potential role in breast cancer diagnosis. The hTERT mRNA levels in tumour do not seem to be associated with the patient's age or advanced tumour stage. Furthermore, hTERT mRNA expression does not correlate with c-Myc mRNA expression in breast cancer.

Regulation of human telomerase activity: repression by normal chromosome 3 abolishes nuclear telomerase reverse transcriptase transcripts but does not affect c-Myc activity

Telomerase is required for the complete replication of chromosomal ends. In tumors, the human telomerase reverse transcriptase subunit (hTERT) is up-regulated, thereby removing a critical barrier for unlimited cell proliferation. To understand more about hTERT regulation, we measured hTERT RNA levels by quantitative reverse transcription (RT)-PCR. Telomerase-positive cell lines were found to contain between 0.2 and 6 molecules of spliced hTERT RNA per cell, whereas in telomerase-negative cells, the number of molecules was below the sensitivity of the assay (<0.004 molecules/cell). Intron-containing, immature hTERT RNA was observed only in nuclei of telomerase-positive cells, which suggests that hTERT RNA levels are transcriptionally regulated. Microcell transfer of a normal chromosome 3 into the human breast carcinoma cell line (21NT) abolishes telomerase activity and induces senescence. Endogenous hTERT transcripts were undetectable in the nuclei of 21NT-chromosome 3 hybrids, even in cells permanently expressing a transfected hTERT cDNA. However, chromosome 3 transfer did not affect the expression of green fluorescent protein reporter constructs driven by up to 7.4 kb of noncoding DNA flanking the 5' end of the hTERT gene. Because direct up-regulation of hTERT through c-Myc overexpression had previously been reported, we investigated whether chromosome 3 transfer affected c-Myc activity. An at least 30-fold reduction of immature intron-containing hTERT RNA was observed after the introduction of a normal chromosome 3, but expression levels of c-Myc, Mad1, and other c-Myc target genes were unchanged. Our results suggest that telomerase is regulated primarily at the level of hTERT transcription by complex mechanisms involving regulatory elements distant from the 5' flanking region, and that the putative hTERT repressor on chromosome 3 does not regulate the expression of hTERT through c-Myc or one of its coregulators.

Identification of tumor metastasis suppressor region on the short arm of human chromosome 20

Acquisition of metastatic ability by prostate cancer cells is the hallmark of their lethal trait and outcome. However, the genetic alterations underlying the clinical progression and pathogenesis of prostate cancer are not well understood. Several studies involving loss of heterozygosity (LOH) and comparative genomic hybridization analysis have identified distinctively altered regions on various human chromosomes, and genomic imbalance of chromosome 20 was implicated in progression and recurrence of prostate tumors. To examine the role of chromosome 20 in prostate neoplasms, we introduced this chromosome into highly metastatic rat prostate cancer cells using the microcell-mediated chromosome transfer technique. Introduction of the chromosome resulted in significant suppression of the metastatic ability of the hybrid cells, by as much as 98%, without any interference with the in vivo growth rate or tumorigenicity of primary tumor in SCID mice. Our STS-PCR analysis on 10 hybrid clones indicates that the suppressor activity of chromosome 20 is located in the p11.23-12 region. Further examination of the hybrid clones by experimental metastasis assay and histologic analysis as well as Matrigel invasion assay suggests the involvement of the suppressor region at an early stage of invasion and extravasation. We also investigated the status of the chromosome 20 suppressor region in pathology specimens from human prostate cancer patients and detected the frequent loss of this region in high-grade tumors. These results suggest the presence of a putative suppressor gene on human chromosome 20 that is functionally involved in development of prostate cancer metastases.

BRCA1 germline mutations in Cypriot breast cancer patients from 26 families with family history

Germline mutations in the BRCA1 gene are causative for a variable number of hereditary breast/ovarian cancers. The data presented in this study are based on genetic analysis of the BRCA1 gene in 49 DNA samples from breast cancer patients with a positive family history. A combination of manual direct DNA sequencing and SSCP analysis was used to screen the entire coding region of BRCA1. Overall 13 variants were detected which included 5 missense mutations, 3 polymorphisms and 5 intronic changes. Further genetic analysis of the 13 variants was carried out using 50 control DNA samples. Our results showed that 12 out of the 13 variants detected in the DNA of the patients group, were also present in the control group. It appears that the Greek Cypriot families studied so far have an unexpectebly low frequency of deleterious mutations in the BRCA1 gene. This is the first report on BRCA1 mutation analysis in Cyprus.

Telomerase suppression by chromosome 6 in a human papillomavirus type 16-immortalized keratinocyte cell line and in a cervical cancer cell line

BACKGROUND

High-risk human papillomavirus (HPV) types play a major role in the development of cervical cancer in vivo and can induce immortalization of primary human keratinocytes in vitro. Activation of the telomere-lengthening enzyme telomerase constitutes a key event in both processes. Because losses of alleles from chromosome 6 and increased telomerase activity have been observed in high-grade premalignant cervical lesions, we analyzed whether human chromosome 6 harbors a putative telomerase repressor locus that may be involved in HPV-mediated immortalization.

METHODS

Microcell-mediated chromosome transfer was used to introduce chromosomes 6 and 11 to the in vitro generated HPV type 16 (HPV16)-immortalized keratinocyte cell line FK16A and to the in vivo derived HPV16-containing cervical cancer cell line SIHA: Hybrid clones were analyzed for growth characteristics, telomerase activity, human telomerase reverse transcriptase (hTERT) and HPV16 E6 expression, and telomere length. FK16A hybrid clones were also transduced with an hTERT-containing retrovirus to examine the effect of ectopic hTERT expression on growth. Statistical tests were two-sided.

RESULTS

Introduction of human chromosome 6 but not of chromosome 11 to both cell lines yielded hybrid cells that demonstrated crisis-like features (i.e., enlarged and flattened morphology, vacuolation, and multinucleation) and underwent growth arrest after a marked lag period. In the chromosome 6 hybrid clones analyzed, telomerase activity and hTERT messenger RNA (mRNA) expression were statistically significantly reduced compared with those in the chromosome 11 hybrid clones (for telomerase activity, P =.004 for the FK16A hybrids and P =.039 for the SiHa hybrids; for hTERT mRNA expression, P =.003 for the FK16A hybrids). The observed growth arrest was associated with telomeric shortening. Ectopic expression of hTERT in FK16A cells could prevent the telomeric shortening-based growth arrest induced by chromosome 6.

CONCLUSIONS

Chromosome 6 may harbor a repressor of hTERT transcription, the loss of which may be involved in HPV-mediated immortalization.

Telomere length abnormalities in mammalian radiosensitive cells

Telomere lengths in radiosensitive murine lymphoma cells L5178Y-S and parental radioresistant L5178Y cells were measured by quantitative fluorescence in situ hybridization. Results revealed a 7-fold reduction in telomere length in radiosensitive cells (7 kb) in comparison with radioresistant cells (48 kb). Therefore, it was reasoned that telomere length might be used as a marker for chromosomal radiosensitivity. In agreement with this hypothesis, a significant inverse correlation between telomere length and chromosomal radiosensitivity was observed in lymphocytes from 24 breast cancer patients and 5 normal individuals. In contrast, no chromosomal radiosensitivity was observed in mouse cell lines that showed shortened telomeres, possibly reflecting differences in radiation responses between primary cells and established cell lines. Telomere length abnormalities observed in radiosensitive cells suggest that these two phenotypes may be linked.

Localization of a novel tumor metastasis suppressor region on the short arm of human chromosome 2

Much of the lethality of malignant neoplasms is attributable directly to their ability to develop secondary growths in organs at a distance from the primary tumor mass, whereas few patients die from their primary neoplasm. Little is known about the molecular mechanism of tumor metastasis, however, which is controlled by a variety of positive and negative factors. In the search for metastasis suppressor genes, we have used the microcell-mediated chromosome transfer method and a rat prostate tumor model in SCID mice. When human chromosome 2 was introduced into the highly metastatic rat prostatic tumor cell, AT6.1, the metastatic ability of this cell was significantly (>99%) decreased in animals. An STS-based PCR analysis for 8 hybrid clones indicates that the suppressor activity is located in the p25-22 region of the chromosome. Furthermore, the AT6.1 cell with human chromosome 2 showed a reduced ability to invade Matrigel, suggesting that the suppressor activity is involved in the step of tumor invasion during the progression of prostate cancer. We have also examined the status of the suppressor region on chromosome 2 in human prostate cancer specimens and found that this region was often lost in high-grade tumors. These results suggest that the putative suppressor gene on chromosome 2 is functionally involved in the progression of human prostate cancer. Genes Chromosomes Cancer 28:285-293, 2000.

hMSH6 deficiency and inactivation of the alphaE-catenin invasion-suppressor gene in HCT-8 colon cancer cells

Transition from an epithelioid (E) to a round (R) morphotype, in the human colon cancer cell line HCT-8, is associated with loss or truncation of alphaE-catenin and acquisition of invasiveness in organ culture. In E clones, like in parental HCT-8 cells, one allele of the alphaE-catenin gene (CTNNA1) is mutated. HCT-8 cells have also a 'Microsatelite Instability-High' (MSI-H) phenotype presumably due to a mutated hMSH6 gene. Fusion of E type cells doubles the wild type CTNNA1 alleles and prevents the loss of alphaE-catenin. Introduction of an extra chromosome 2, carrying a wild type hMSH6 gene, restores post-replicative mismatch repair and also prevents the frequent inactivation of the remaining wild type CTNNA1 allele.

Localization of a novel tumor metastasis suppressor region on the short arm of human chromosome 2

Much of the lethality of malignant neoplasms is attributable directly to their ability to develop secondary growths in organs at a distance from the primary tumor mass, whereas few patients die from their primary neoplasm. Little is known about the molecular mechanism of tumor metastasis, however, which is controlled by a variety of positive and negative factors. In the search for metastasis suppressor genes, we have used the microcell-mediated chromosome transfer method and a rat prostate tumor model in SCID mice. When human chromosome 2 was introduced into the highly metastatic rat prostatic tumor cell, AT6.1, the metastatic ability of this cell was significantly (>99%) decreased in animals. An STS-based PCR analysis for 8 hybrid clones indicates that the suppressor activity is located in the p25-22 region of the chromosome. Furthermore, the AT6.1 cell with human chromosome 2 showed a reduced ability to invade Matrigel, suggesting that the suppressor activity is involved in the step of tumor invasion during the progression of prostate cancer. We have also examined the status of the suppressor region on chromosome 2 in human prostate cancer specimens and found that this region was often lost in high-grade tumors. These results suggest that the putative suppressor gene on chromosome 2 is functionally involved in the progression of human prostate cancer. Genes Chromosomes Cancer 28:285-293, 2000.

Telomerase activity and lymphovascular invasion in breast cancer

BACKGROUND

Telomerase is a ribonucleoprotein enzyme that plays an important role in cell immortalization and carcinogenesis. Lymphovascular invasion (LVI) is a fundamental step in the process of breast cancer metastasis and is recognized as an important prognostic factor in patients with breast cancer.

METHODS

Using a PCR-based assay, telomerase activity was determined in 34 prospectively collected infiltrating breast carcinomas. Adjacent sections of the specimens were examined histologically by two experienced breast pathologists using light microscopy and haematoxylin & eosin staining.

RESULTS

Telomerase activity was detected in 24 (71%) of 34 breast tumours. Two (20%) of 10 telomerase-negative tumours had LVI compared with 14 (58.3%) of 24 telomerase-positive tumours. This association was statistically significant (P<0.05). Telomerase activity was also significantly associated with nodal metastases but not with tumour grade, tumour size or menopausal status.

CONCLUSIONS

Telomerase reactivation is significantly associated with LVI in breast cancer and may reflect the metastatic potential of the disease.

Telomerase activity in phyllodes tumours

AIMS

To investigate telomerase, a ribonucleoprotein that synthesizes telomeres. Recent evidence suggests that telomerase reactivation is associated with the acquisition of immortalization and malignancy.

METHODS

Using a sensitive PCR-based assay (the TRAP assay), we examined telomerase activity in two recurrent phyllodes tumours in two patients.

RESULTS

Both tumours expressed telomerase activity. Histological examination of the lesions, according to the criteria proposed by Azzopardi and Salvadori, revealed a malignant phyllodes tumour in one patient and a benign phyllodes tumour in the other patient.

CONCLUSIONS

Our findings suggest that telomerase activity may have a potential role as a prognostic marker in predicting the clinical behaviour of these rare tumours.

Telomerase activity in the human breast

Telomerase is a ribonucleoprotein enzyme which appears to play an important role in carcinogenesis. Telomerase reactivation seems to be associated with immortalization and malignancy. Using a PCR-based assay, we examined telomerase activity in 50 breast tissue specimens, prospectively obtained from 37 women undergoing elective breast surgery. The specimens examined included normal breast (n=13), benign breast lesions (n=5), ductal carcinoma in situ (n=8) and infiltrating ductal carcinoma (n=24). All normal breast, benign breast and DCIS specimens lacked telomerase activity. Sixteen (67%) of 24 infiltrating carcinomas. In infiltrating ductal cancer, there was a statistically significant association between telomerase activity and nodal metastasis. The present results indicate that telomerase activity is associated with acquisition of invasive malignancy in the human breast and may have a role in complementing cytopathological diagnosis. Telomerase activity as a prognostic marker should be included in future validation studies. In DCIS, telomerase activity may be a late event associated with invasion of the basement membrane.

Telomerase as an anti-cancer drug target: will it fulfil its early promise?

The discovery that the ribonucleoprotein telomerase is responsible for the immortality of human cancer cells represents a major advance in our quest to identify a distinguishing biochemical feature of the malignant phenotype that could be useful as a target for novel anti-cancer drug development. However, recent observations on telomere dynamics and cell lifespan using telomerase 'knockout' mouse models together with improved techniques to assay telomerase in normal human tissues have raised certain questions regarding potential side effects of anti-telomerase treatments. More importantly, such work has also demonstrated the propensity of mouse cell populations, in which telomerase has been experimentally inactivated, to generate immortal variants capable of maintaining their telomeres by alternative mechanisms. These recent findings and their implications for the potential success of anti-telomerase therapies are subjected to critical review. The wide differences between telomerase and telomere biology in mouse and human cells are highlighted, and the urgent need to obtain direct experimental evidence concerning the behaviour of a wide variety of human cancer cells under conditions of telomerase inhibition is stressed. It is concluded that, despite the caveats, the development of small molecule drugs that powerfully inhibit telomerase should remain a top priority area for those engaged in the rational design of novel cancer therapeutics.

The association between telomerase, histopathological parameters, and KI-67 expression in breast cancer

BACKGROUND

Telomerase is a ribonucleoprotein enzyme that appears to play an important role in carcinogenesis. Telomerase reactivation seems to be associated with immortalization and malignancy.

METHODS

Using a polymerase chain reaction (PCR)-based assay known as the TRAP (telomeric repeat and amplification protocol) assay, we examined telomerase activity in 60 breast specimens prospectively collected from 39 patients undergoing elective breast surgery in our center. The specimens included adjacent noncancerous breast (n = 21), benign breast disease (n = 5), and infiltrating carcinoma (n = 34). Ki-67 expression was determined in 32 invasive breast cancer specimens using immunohistochemistry techniques. The histopathological features were determined by light microscopy by an experienced breast pathologist.

RESULTS

Telomerase activity was detected in 24 (71%) of 34 infiltrating carcinomas. None of the adjacent noncancerous specimens nor the benign breast lesions expressed telomerase activity. Telomerase reactivation was significantly associated with nodal metastasis and Ki-67 expression. There was no significant association between telomerase activity and menopausal status, tumor grade, or tumor size.

CONCLUSIONS

Telomerase reactivation is associated with the acquisition of malignancy in the human breast. Telomerase activity is significantly associated with nodal metastasis and cellular proliferation as measured by Ki-67 expression in human breast cancer.

Telomerase activity and prognosis in breast cancer

AIMS

Telomerase is a ribonucleoprotein enzyme which appears to play an important role in carcinogenesis. Its reactivation is associated with the acquisition of immortalization and malignancy. The present study aims to examine the association between telomerase activity and prognosis in breast cancer.

METHODS

Using a PCR-based assay, we retrospectively examined telomerase activity in 45 frozen human breast cancer specimens. Telomerase activity was compared with histopathological and clinical data.

RESULTS

Telomerase activity was detected in 20 (44%) of 45 cases and was associated with advanced histopathological grade and tumour type (ductal vs. lobular). The association with these histological parameters was statistically significant (chi-squared test P<0.05). There was no significant difference in the overall survival rate (78 vs. 77%) or disease-free survival (73 vs. 69%) at 5 years (Kaplan-Meier method, log-rank test P>0.05).

CONCLUSIONS

The present results indicate that telomerase activity in human breast cancer is not associated with nodal status or disease outcome.

Genetic and functional analyses exclude mortality factor 4 (MORF4) as a keratinocyte senescence gene

Approximately 50% of immortal human keratinocyte lines show loss of heterozygosity of chromosome region 4q33-q34, and the reintroduction of chromosome 4 into one such line, BICR 6, causes proliferation arrest and features of replicative senescence. Recently, a candidate gene, mortality factor 4 (MORF4), was identified in this region and sequenced in 21 immortal keratinocyte lines. There were no mutations or deletions, and two of the seven lines that showed loss of heterozygosity at 4q33-q34 were heterozygous for MORF4 itself. Furthermore, the transfer of a chromosomal segment containing the entire MORF4 gene did not mimic the senescence effect of chromosome 4 in BICR 6. These results suggest that the inactivation of MORF4 is not required for human keratinocyte immortality.

Functional evidence of novel tumor suppressor genes for cutaneous malignant melanoma

Losses of heterozygosity involving chromosomes 9 and 10 are frequent events in the development and progression of cutaneous malignant melanoma. To investigate whether specifically deleted chromosomal regions encode tumor suppressor genes (TSGs), we introduced normal chromosome 10 into the tumorigenic human metastatic melanoma cell line UACC-903 by microcell fusion. In addition, two chromosome 9 derivatives that were microdeleted in the region of the p16INK4A/p15INK4B locus were transferred to determine whether an additional melanoma TSG or TSGs reside on chromosome 9p, as indicated by previous melanoma allele loss studies. In comparison to parental cells, microcell hybrids generated with chromosomes 9 (microdeleted) and 10 displayed reduced anchorage-independent growth in soft agar and markedly reduced tumorigenicity in athymic (nu/nu) mice. These data define a TSG or TSGs that function independently of p15/p16 on chromosome 9 and provide evidence for a TSG (or TSGs) on chromosome 10 that may be important in melanoma development.

Telomerase repressor sequences on chromosome 3 and induction of permanent growth arrest in human breast cancer cells

BACKGROUND

Activation of the enzyme telomerase, which has been associated with cellular immortality, may constitute a key step in the development of human cancer. Telomerase is repressed in most normal human somatic cells. This study was conducted, using a genetic complementation approach, with the aim of identifying and mapping the genes responsible for repressing telomerase and, simultaneously, to establish the effect of experimentally induced telomerase repression on human tumor cell growth.

METHODS

Individual human chromosomes isolated from normal diploid cells and tagged with bacterial antibiotic resistance genes (for later selection) were introduced into cells of the human breast carcinoma cell line 21NT by means of microcell transfer. Selected hybrid clones were screened for telomerase activity by use of the polymerase chain reaction-based telomere repeat amplification protocol (TRAP) assay, and the proliferative fate of the hybrid clones was determined. Regions of the introduced chromosomes associated with telomerase repression were mapped using segregant hybrids and a deletion analysis that employed microsatellite DNA markers.

RESULTS

Strong repression of telomerase was observed following transfer of human chromosome 3 into 21NT cells but not after transfer of chromosomes 8, 12, or 20. The vast majority of hybrid clones with repressed telomerase entered permanent growth arrest after 10-18 population doublings. Deletion analysis of nonrepressed segregant monochromosome 3 hybrids indicated two regions on the short arm of chromosome 3 (3p21.3-p22 and 3p12-21.1) where telomerase regulator genes may be located.

CONCLUSIONS

Telomerase in human breast cancer cells is efficiently repressed by a gene or genes on normal human chromosome 3p, and this repression is associated with permanent growth arrest of the tumor cells.

Telomerase activity in melanoma and non-melanoma skin cancer

Telomeres are specialized structures consisting of repeat arrays of TTAGGGn located at the ends of chromosomes. They are essential for chromosome stability and, in the majority of normal somatic cells, telomeres shorten with each cell division. Most immortalized cell lines and tumours reactivate telomerase to stabilize the shortening chromosomes. Telomerase activation is regarded as a central step in carcinogenesis and, here, we demonstrate telomerase activation in premalignant skin lesions and also in all forms of skin cancer. Telomerase activation in normal skin was a rare event, and among 16 samples of normal skin (one with a history of chronic sun exposure) 12.5% (2 out of 16) exhibited telomerase activity. One out of 16 (6.25%) benign proliferative lesions, including viral and seborrhoeic wart samples, had telomerase activity. In premalignant actinic keratoses and Bowen's disease, 42% (11 out of 26) of samples exhibited telomerase activity. In the basal cell carcinoma and cutaneous malignant melanoma (CMM) lesions, telomerase was activated in 77% (10 out of 13) and 69% (22 out of 32) respectively. However, only 25% (3 out of 12) of squamous cell carcinomas (SCC) had telomerase activity. With the exception of one SCC sample, telomerase activity in a positive control cell line derived from a fibrosarcoma (HT1080) was not inhibited when mixed with the telomerase-negative SCC or CMM extracts, indicating that, overall, Taq polymerase and telomerase inhibitors were not responsible for the negative results. Mean telomere hybridizing restriction fragment (TRF) analysis was performed in a number of telomerase-positive and -negative samples and, although a broad range of TRF sizes ranging from 3.6 to 17 kb was observed, a relationship between telomerase status and TRF size was not found.

A telomere-independent senescence mechanism is the sole barrier to Syrian hamster cell immortalization

Reactivation of telomerase and stabilization of telomeres occur simultaneously during human cell immortalization in vitro and the vast majority of human cancers possess high levels of telomerase activity. Telomerase repression in human somatic cells may therefore have evolved as a powerful resistance mechanism against immortalization, clonal evolution and malignant progression. The comparative ease with which rodent cells immortalize in vitro suggests that they have less stringent controls over replicative senescence than human cells. Here, we report that Syrian hamster dermal fibroblasts possess substantial levels of telomerase activity throughout their culture life-span, even after growth arrest in senescence. In our studies, telomerase was also detected in uncultured newborn hamster skin, in several adult tissues, and in cultured fibroblasts induced to enter the post-mitotic state irreversibly by serum withdrawal. Transfection of near-senescent dermal fibroblasts with a selectable plasmid vector expressing the SV40 T-antigen gene resulted in high-frequency single-step immortalization without the crisis typically observed during the immortalization of human cells. Collectively, these data provide an explanation for the increased susceptibility of rodent cells to immortalization (and malignant transformation) compared with their human equivalents, and provide evidence for a novel, growth factor-sensitive, mammalian senescence mechanism unrelated to telomere maintenance.

SURF1, encoding a factor involved in the biogenesis of cytochrome c oxidase, is mutated in Leigh syndrome

Leigh Syndrome (LS) is a severe neurological disorder characterized by bilaterally symmetrical necrotic lesions in subcortical brain regions that is commonly associated with systemic cytochrome c oxidase (COX) deficiency. COX deficiency is an autosomal recessive trait and most patients belong to a single genetic complementation group. DNA sequence analysis of the genes encoding the structural subunits of the COX complex has failed to identify a pathogenic mutation. Using microcell-mediated chromosome transfer, we mapped the gene defect in this disorder to chromosome 9q34 by complementation of the respiratory chain deficiency in patient fibroblasts. Analysis of a candidate gene (SURF1) of unknown function revealed several mutations, all of which predict a truncated protein. These data suggest a role for SURF1 in the biogenesis of the COX complex and define a new class of gene defects causing human neurodegenerative disease.

Human chromosome 16 suppresses metastasis but not tumorigenesis in rat prostatic tumor cells

Genomic aberrations at the chromosome 16q arm are one of the most consistent abnormalities observed by loss of heterozygosity and comparative genomic hybridization analyses in human prostate cancer, suggesting that there are tumor suppressor or metastasis suppressor genes encoded by this chromosomal region. To functionally identify such suppressor genes, we have conducted microcell-mediated chromosome transfer to introduce human chromosome 16 into the highly metastatic Dunning rat prostatic cancer cell line, AT6.1. The metastatic ability of the resultant microcell hybrid clones was then tested in a standard spontaneous metastasis assay using SCID mice. When the microcell-mediated chromosome transfer hybrid cells containing whole human chromosome 16 were injected, the number of metastatic lesions in the lung was significantly reduced as much as 99% on average. Therefore, chromosome 16 has a strong activity to suppress the metastatic ability of AT6.1 cells while it did not affect the tumorigenesis and tumor growth rate. A PCR analysis of various microcell hybrid clones with sequence-tagged site markers indicates that the metastasis suppressor activity is located in the q24.2 region of chromosome 16. Our results are consistent with the previous finding that the region of human chromosome 16q has frequent loss of heterozygosity in prostate cancer patients and suggest that there is a metastasis suppressor gene in this region that may play an important role in the progression of prostate cancer.

Human chromosome 21 determines growth factor dependence in human/mouse B-cell hybridomas

Interleukin 6 (IL-6) serves as a growth factor for mouse plasmacytomas. As a model for IL-6-mediated growth of plasmacytomas, we study IL-6-dependent B-cell hybridomas, which can be generated through fusion of B lymphocytes with a plasmacytoma cell line, e.g., SP2/0. In the present report, we have investigated the peculiar behavior of B-cell hybridomas with respect to IL-6 dependence. We demonstrate that although newly generated hybridomas are IL-6 dependent, many hybridomas lose this dependency at frequencies as high as 50%, shortly after fusion. We speculated that the loss of IL-6-dependent growth is due to the well-known chromosomal instability of B-cell hybridomas. Consequently, loss of IL-6 dependence is the result of loss of a specific chromosome(s). This model implies the existence of an "IL-6 dependency" gene, the loss of which makes hybridomas capable of proliferating in the absence of IL-6. Because SP2/0 is IL-6 independent, the IL-6-dependent phenotype of B-cell hybridomas, and hence the IL-6 dependency gene, must be derived from the B lymphocyte. We have tested this model by generating human/mouse B-cell hybridomas through fusion of human B lymphocytes with SP2/0. We then analyzed the human chromosome content of 10 IL-6-dependent and 14 IL-6-independent subclones. From that analysis we concluded that the presence of human chromosome 21 correlated with IL-6 dependence. This correlation was confirmed by microcell fusion experiments in which a single copy of chromosome 21 was introduced into IL-6-independent hybridomas, resulting in reconstitution of the IL-6-dependent phenotype. We therefore conclude that chromosome 21 carries an IL-6 dependency gene.

Genetic control of telomerase and replicative senescence in human and rodent cells

The ribonucleoprotein telomerase is detectable in most human cancer cells and immortalized cells but is absent or inactive in the vast majority of normal counterparts. Repression of telomerase activity in human somatic cells, which leads to telomere shortening and replicative senescence, may have evolved as a protective mechanism against immortalization, unfettered clonal evolution and cancer. Rodent cells in culture are far more susceptible to immortalization and malignant progression than human cells. This can be explained by our observation that normal diploid rodent (hamster) fibroblasts possess active telomerase throughout their proliferative life span, and therefore they do not require a telomerase activation step during immortalization. Monochromosome transfer techniques have enabled us to identify powerful telomerase repressive activity specifically associated with the introduction of a single copy of human chromosome 3 into human carcinoma cells. Fine-structure deletion analysis of non-repressed hybrids has permitted us to map the position of the candidate telomerase repressor gene to 3p21.1-3p21.3. A strategy for isolating the gene has been developed involving a combination of fine-structure deletion mapping and functional gene transfer approaches. The availability of cloned telomerase repressor genes will advance our understanding of telomerase regulation in the human soma and its disruption during human cancer development.

The effect of different TP53 mutations on the chromosomal stability of a human colonic adenoma derived cell line with endogenous wild type TP53 activity, before and after DNA damage

We examined the effect of loss of wild type TP53 activity on the chromosomal stability of a human colonic adenoma derived cell line (designated AA/Cl) by studying transfected variants which express different TP53 mutations. Using gross chromosomal aberrations as a measure of instability, we studied metaphase spreads of a vector control cell line (AA/PCMV) and variants expressing the 143(Val-Ala) mutation, which retain endogenous wild type TP53 activity, or the 273(Arg-His) TP53 mutation, which acts as a dominant negative. It was found that the proportion of cells with more than 4% aberrations was significantly greater in the AA/273p53/B cell line (an approximate 5-Fold increase) than in the vector control or the AA/143p53/A cell line. To investigate whether loss of TP53 dependent checkpoints also predisposed the cells to accumulate persistent chromosomal aberrations after DNA damage, cells were exposed to 5 Gy gamma radiation. Regardless of TP53 status, cells with radiation induced chromosomal damage were eliminated through a TP53 independent mechanism, suggesting that loss of TP53 activity did not permit the survival of these cells. In contrast, when exposed to low level gamma radiation (0.2 Gy), decreased wild type TP53 function and/or expression of mutant TP53 protein led to increased radioresistance (both in the non-dominant as well as the dominant mutant expressing cell lines). These findings suggest that loss of TP53 activity and/or acquisition of specific TP53 mutations can increase chromosomal instability and resistance to low level DNA damage in human colonic adenoma cells. This study emphasises the different biological consequences of individual TP53 mutations on the genotype of premalignant colorectal epithelial cells and subsequent implications for tumorigenic progression.

Evidence for the inactivation of multiple replicative lifespan genes in immortal human squamous cell carcinoma keratinocytes

Human keratinocyte immortality is genetically recessive to the normal phenotype of limited replicative lifespan and appears to require the dysfunction of p53 and the cyclin D-Cdk inhibitor p16. In order to test for the inactivation of other candidate replicative lifespan genes in the immortal cells of human tumors, we developed a series of mortal and immortal keratinocyte cultures derived from neoplastic lesions of the head and neck which were amenable to molecular genetic analysis by the loss of heterozygosity (LOH) technique. The results indicate that keratinocyte immortalization in head and neck squamous cell carcinoma (SCC-HN) development involves the inactivation of at least two further pathways to senescence and four in all. Chromosomes 1, 4 and 7 carry genes representing immortality complementation groups C, B and D respectively and immortal keratinocytes showed LOH at either 4q32-q34 between D4S1554 and D4S171 (group B) or 7q31 (group D) but never 1q25 (group C). These results tentatively suggest that the genes responsible for the immortality complementation groups encode proteins on the same pathway to senescence. In addition, all of the immortal keratinocyte lines possessed high levels of telomerase activity and a suppressor of telomerase activity has been mapped to the short arm of chromosome 3p. Five out of eight lines showed LOH at 3p21.2-p21.3, a region which may carry a gene capable of suppressing SCC-HN telomerase. However, alternative mechanisms of telomerase reactivation were also suggested by our results. None of the above genetic alterations were seen in seven senescent neoplastic keratinocyte cultures. Other loci harbouring antiproliferative genes implicated in replicative lifespan showed few or no alterations and any alterations seen were additional to those described above.

The genetic basis of human keratinocyte immortalisation in squamous cell carcinoma development: the role of telomerase reactivation

Normal human keratinocytes have a finite replicative lifespan which culminates in senescence. Chromosomal telomere length may act as a mediator of replicative senescence, signalling cell cycle arrest in G1 when one or more telomeres become too short. Telomeric attrition in normal keratinocytes may be due to inadequate levels of telomerase activity and possibly also to oxidative damage. In advanced squamous cell carcinoma replicative senescence breaks down to yield immortal variants, in which several dominantly acting genes are functionally compromised, including p53 and the cyclin D-Cdk4/6 inhibitor CDKN2A/p16. The increased activity of both of these proteins would be expected to contribute to the G1 arrest in senescence and we have shown that levels of p16 are dramatically increased in senescent keratinocytes. In addition, two other genes which control a cell cycle G1 checkpoint independently of p53 and pRb appear dysfunctional. These genes are uncloned but map to chromosome 4q and 7q31.1 and appear to represent senescence complementation groups B and D, respectively. In immortal neoplastic keratinocytes, telomerase is strongly upregulated and there is evidence for a suppressor of the enzyme on the short arm of chromosome 3 mapping to 3p21.2-p21.3. We have also mapped the human telomerase RNA gene to 3q26.3 and found it to be overrepresented or amplified in a proportion of squamous cell tumours and cell lines. These observations may explain why isochromosome 3q is so common in human squamous carcinoma. None of these genetic alterations are seen in carcinomas which senesce and suggest that multiple genetic alterations are required for keratinocyte immortality.

The defect in the AT-like hamster cell mutants is complemented by mouse chromosome 9 but not by any of the human chromosomes

X-ray sensitive Chinese hamster V79 cells mutants, V-C4, V-E5 and V-G8, show an abnormal response to X-ray-induced DNA damage. Like ataxia telangiectasia (AT) cells, they display increased cell killing, chromosomal instability and a diminished inhibition of DNA synthesis following ionizing radiation. To localize the defective hamster gene (XRCC8) on the human genome, human chromosomes were introduced into the AT-like hamster mutants, by microcell mediated chromosome transfer. Although, none of the human chromosomes corrected the defect in these mutants, the defect was corrected by a single mouse chromosome, derived from the A9 microcell donor cell line. In four independent X-ray-resistant microcell hybrid clones of V-E5, the presence of the mouse chromosome was determined by fluorescent in situ hybridization, using a mouse cot-1 probe. By PCR analysis with primers specific for different mouse chromosomes and Southern blot analysis with the mouse Ldlr probe, the mouse chromosome 9, was identified in all four X-ray-resistant hybrid clones. Segregation of the mouse chromosome 9 from these hamster-mouse microcell hybrids led to the loss of the regained X-ray-resistance, confirming that mouse chromosome 9 is responsible for complementation of the defect in V-E5 cells. The assignment of the mouse homolog of the ATM gene to mouse chromosome 9, and the presence of this mouse chromosome only in the radioresistant hamster cell hybrids suggest that the hamster AT-like mutant are homologous to AT, although they are not complemented by hamster chromosome 11.

Identification of human tumour suppressor genes by monochromosome transfer: rapid growth-arrest response mapped to 9p21 is mediated solely by the cyclin-D-dependent kinase inhibitor gene, CDKN2A (p16INK4A)

Microcell transfer of intact normal human chromosomes into immortal mouse and hamster fibroblast cell lines has revealed growth suppressive activity associated with a small sub-set of the human complement. Here, we describe the results of a detailed study aimed at identifying the gene or genes responsible for the rapid growth-arrest response obtained with human chromosome-9. Initially, STS-PCR deletion mapping of segregants arising in monochromosome transfer experiments was used successfully to localize the active sub-chromosomal region to 9p21. Subsequent fine-structure deletion mapping of previously uniformative hybrid segregants, employing additional markers between D9S162 and D9S171, provided strong evidence that the cyclin-dependent kinase (cdk) inhibitor gene CDKN2A (p16INK4A) was solely responsible for the chromosome-9 effect; 9p21 microdeletions in a significant proportion of segregant clones were restricted to a single CDKN2A exon. Transfection experiments with CDKN2A and CDKN2B cDNA expression vectors, using mouse A9 cells and three human malignant melanoma cell lines as recipients, provided further evidence in support of this hypothesis. Collectively, our results indicate that expression of human CDKN2A (controlled either by its natural regulatory elements, or by a cytomegalovirus promoter) is incompatible with in vitro proliferation in immortalized rodent cells and in human melanoma cell lines. The rapidity of the growth inhibitory effects of CDKN2A was inconsistent with a mode of action involving induction of replicative cell senescence via telomerase repression, but was consistent with a mechanism based on cell cycle arrest through cdk inhibition. The study described here has generated a panel of microdeleted monochromosome-9 donor hybrids which may prove valuable in functional investigations aimed at identifying other important tumour suppressor genes located on human chromosome-9.

Nongenotoxic carcinogens: development of detection methods based on mechanisms: a European project

While the accumulation of genetic changes in a somatic cell is considered essential for the genesis of a cancer, it has become clear that not all carcinogens are genotoxic, suggesting that some carcinogens indirectly participate in the generation of genetic changes during carcinogenesis. A European project funded by the European Community was thus conceived to study mechanisms of nongenotoxic aspects of carcinogenesis. Two main strategical approaches were adapted: (i) to study whether and how Syrian hamster embryo (SHE), Syrian hamster dermal (SHD) and BALB/c 3T3 cell transformation systems simulate in vivo carcinogenesis, and to examine whether they can detect nongenotoxic carcinogens; (ii) to study, refine and validate mechanisms-based end-points for detection of nongenotoxic carcinogens. For mechanisms-based research, the proposed end-points included gap junctional intercellular communication (GJIC) inhibition, altered expression of critical genes, immortalization and aberrant cell proliferation. We also selected model compounds commonly usable for various endpoints. Our major results can be summarized as follows: (1) SHE and BALB/c 3T3 transformation systems reflect both genotoxic and nongenotoxic carcinogenic events; they detect not only genotoxic but also many although not all, nongenotoxic carcinogens. This is further supported by the fact that both genotoxic and nongenotoxic carcinogens were able to immortalize SHD cells. (2) Many nongenotoxic carcinogens, although not all, inhibit GJIC in vitro as well as in vivo. Mechanistic studies suggest an important role of blocked GJIC in carcinogenesis and that different mechanisms are involved in inhibition of the communication by different agents used. However, inhibition of GJIC is not a prerequisite for the enhancement (or induction) of transformation of SHE or BALB/c 3T3 cells. (3) Among compounds examined, there was a good correlation between induction of micronuclei and cell transformation in SHE cells while no such correlation was found between the induction of cell transformation and ornithine decarboxylase activity. (4) Two transgenic mouse mutation assays (lacI and lacZ) were established and validated. The genotoxin dimethylnitrosamine was shown to be mutagenic to the liver in both assays. Ortho-anisidine, a bladder-specific carcinogen that was inactive in standard rodent genetic toxicity assays was uniquely mutagenic to the bladder of the transgenic mice. The peroxisome proliferator methyl clofenipate was established as nonmutagenic to the liver of both transgenic mice. That eliminated DNA damage as a cause of the liver tumours produced by this chemical and weakened the idea that induced cell division leads to mutation induction. (5) With an in vitro DNA replication model, it was found that DNA damage induced by genotoxic agents can be responsible for inhibition of DNA replication, while certain nongenotoxic agents such as phorbol esters increase DNA replication. (6) An attempt to use structure-activity relationship for subfamilies of nongenotoxic carcinogens, e.g., receptor-mediated carcinogens, has been initiated with some promising results. Our results support the idea that there are multiple nongenotoxic mechanisms in carcinogenesis, and that working hypothesis-oriented approaches are encouraged rather than simple screening of chemicals in developing test systems for the detection of nongenotoxic carcinogens.

Novel use of a selectable fusion gene as an "in-out" marker for studying genetic loss in mammalian cells

Recent demonstrations of loss of heterozygosity in a wide variety of human cancers suggest that large multilocus genetic deletions (presumably including tumor suppressor genes) constitute a major class of genetic alteration in human carcinogenesis. Here we show that a bifunctional fusion gene (Hytk), suitable for both positive and negative selection, is an effective marker for studying genetic loss in mammalian cells with minimal interference from point-mutational changes. Studies with a transgenic V79 cell line in which a single functional copy of Hytk was stably inserted into the genome in a retroviral vector showed that loss of the marker (and presumably flanking cellular genetic material) could be induced efficiently by ionizing radiation (gamma-rays and fast neutrons) but only weakly by the powerful point-mutagen benzo[a]pyrene diol epoxide. In a first application of the system, we provide evidence that radiation-induced loss can occur through an indirect mechanism after a high-frequency event. Collectively, our results suggest that the Hytk marker should be a valuable tool for studying genome position effects on the tolerance of genetic loss in cultured human cells that represent different stages in clonal evolution and tumor progression.

Mechanisms involved in the immortalization of mammalian cells by ionizing radiation and chemical carcinogens

Immortalization is a prerequisite for the clonal evolution and malignant transformation of normal mammalian cells in culture. In order to gain a mechanistic insight into the genetics of carcinogen-induced cellular immortality, a cell culture assay has been developed based on the use of freshly explanted Syrian hamster dermal (SHD) fibroblasts. The relative efficacies of a variety of chemical and physical carcinogens at immortalizing SHD cells (against a zero background of spontaneous immortalization) were compared. Ionizing radiation and nickel chloride appeared to be more effective as immortalizing agents than powerful point mutagens, suggesting (but not proving) that clastogenic damage may be more significant in the immortalization process than point mutation. Frequencies of induced immortality (10(-6)-10(-7)/treated cell) were arguably consistent with a direct mutational mechanism involving a single genetic target. However, detailed cytogenetic characterization of a panel of newly immortalized cell lines revealed no non-random chromosomal alterations in the cells at the level of G-banding. Furthermore, additional experiments with the SHD system have provided confirmatory evidence that immortalization can occur as an indirect consequence of carcinogen exposure following an induced high frequency change in the treated population, rather than through direct targeted mutagenesis. Previous somatic cell genetic studies have suggested the possibility that a target gene for immortalization exists on the human and Chinese hamster X chromosomes. Here we provide strong evidence that the normal SHD X chromosome displays powerful senescence-inducing properties when introduced, by microcell transfer, into newly immortalized SHD recipients. These results suggest that induction of the immortal phenotype in SHD cells by carcinogens results primarily from functional inactivation of a senescence gene which may be X-linked. One possible mechanism for senescence gene inactivation consistent with our observations is through a sub-microscopic interstitial genetic deletion. However, the considerable efficacy of nickel (a human carcinogen) as an immortalizing agent at nonmutagenic doses raises the alternative possibility that immortalization may occur through an epigenetic mechanism.

Construction and characterization of a highly stable human: rodent monochromosomal hybrid panel for genetic complementation and genome mapping studies

Human:rodent somatic cell hybrids carrying a single, intact, selectable human chromosome are valuable both for functional somatic cell genetic analysis and genome mapping procedures. Here, we describe the construction and detailed molecular cytogenetic characterization of a panel of 23 stable hybrids, representing all 22 human autosomes plus the X-chromosome. Individual normal human chromosomes have been tagged with a selectable fusion gene (Hytk) introduced into the chromosome in a small (4.2 kbp) retroviral vector. Use of the Hytk marker permits both positive and negative ("in-out") selection to be applied to the human chromosome in any mammalian cell background. The panel includes 18 new hybrids isolated by direct microcell transfer from normal human diploid fibroblasts into mouse A9 cells.