Allelic imbalance at chromosome 17p13.3 (YNZ22) in breast cancer is independent of p53 mutation or p53 overexpression and is associated with poor prognosis at medium-term follow-up

Gain-of-Function Activity of Mutant p53 in Lung Cancer through Up-Regulation of Receptor Protein Tyrosine Kinase Axl

p53 mutations are present in up to 70% of lung cancer. Cancer cells with p53 mutations, in general, grow more aggressively than those with wild-type p53 or no p53. Expression of tumor-derived mutant p53 in cells leads to up-regulated expression of genes that may affect cell growth and oncogenesis. In our study of this aggressive phenotype, we have investigated the receptor protein tyrosine kinase Axl, which is up-regulated by p53 mutants at both RNA and protein levels in H1299 lung cancer cells expressing mutants p53-R175H, -R273H, and -D281G. Knockdown of endogenous mutant p53 levels in human lung cancer cells H1048 (p53-R273C) and H1437 (p53-R267P) led to a reduction in the level of Axl as well. This effect on Axl expression is refractory to the mutations at positions 22 and 23 of p53, suggesting that p53's transactivation domain may not play a critical role in the up-regulation of Axl gene expression. Chromatin immunoprecipitation (ChIP) assays carried out with acetylated histone antibodies demonstrated induced histone acetylation on the Axl promoter region by mutant p53. Direct mutant p53 nucleation on the Axl promoter was demonstrated by ChIP assays using antibodies against p53. The Axl promoter has a p53/p63 binding site, which however is not required for mutant p53-mediated transactivation. Knockdown of Axl by Axl-specific RNAi caused a reduction of gain-of-function (GOF) activities, reducing the cell growth rate and motility rate in lung cancer cells expressing mutant p53. This indicates that for lung cancer cell lines with mutant p53, GOF activities are mediated in part through Axl.

Acute lymphoblastic leukemia in a patient with Miller-Dieker syndrome

A 15-month-old girl with Miller-Dieker syndrome, a contiguous gene deletion syndrome involving chromosome 17p13.3 and resulting in lissencephaly, was diagnosed with precursor B-cell acute lymphoblastic leukemia. Cytogenetic analysis identified both the previously detected 17p13.3 deletion and additional complex numerical and structural abnormalities, including loss of chromosome 9, isochromosome 9q and interstitial deletion of 20q. This is, to our knowledge, the first report of acute leukemia in the setting of Miller-Dieker syndrome. Herein we review the literature regarding Miller-Dieker syndrome, with particular attention to the presence of several candidate tumor suppressor genes within the deleted material.

TP53 mutations are associated with a particular pattern of genomic imbalances in breast carcinomas

TP53 mutations play an important role in the development of several cancers and are present in 20-40% of all breast carcinomas, contributing to increased genomic instability. In order to address the relationship of mutated TP53 to genomic complexity, the present study analysed 61 breast carcinomas for TP53 mutations and compared mutation status with the pattern of genomic imbalances as assessed by comparative genomic hybridization (CGH). Twenty per cent of the present series of breast carcinomas harboured TP53 mutations. An increasing number of abnormalities, as identified by CGH (higher genomic complexity), correlated significantly with mutant TP53. Among the chromosome arms most commonly altered (in more than 20% of the tumours), loss of 8p and gain of 8q were associated with TP53 mutations, whereas loss of 16q was associated with wild-type TP53. By performing supervised hierarchical clustering analysis of the CGH data, a cluster of chromosome imbalances was observed that showed differences between wild-type and mutant TP53 cases. Among these, loss of chromosome arm 5q revealed the strongest correlation with altered TP53. To investigate further the most commonly deleted region of 5q, gene expression patterns from two publicly available microarray data sets of breast carcinomas were evaluated statistically. The expression data sets identified potential target genes, including genes involved in ubiquitination and the known TP53 target CSPG2. The genomic complexity of breast carcinomas as assessed by CGH is associated with TP53 mutation status; breast cancers with TP53 mutations display more complex genomes than do those with wild-type TP53. The pattern of genomic imbalances associated with mutant TP53 is non-random, with loss of chromosome arm 5q being particularly closely associated with TP53 mutations.

Dissecting the molecular mechanisms of human cancer: Translating laboratory advances into clinical practice

There are multiple molecular mechanisms involved in human cancers with many genes involved, complex interactions and a variety of ways to examine them. Some events are already emerging as clinically important; others will turn out to be bystanders. By focussing on key genes, such as p53, the clinical implications of genetic changes and the pathways they link into are becoming apparent. Using the complex methodologies now available allied to disciplines such as mathematics we are improving our understanding of malignancy. This is beginning to impact on the management of patients with cancer; meanwhile, a good surgical operation performed timeously is still the best chance a patient has of a cure for most types of solid cancers.

Loss of heterozygosity of a locus in the chromosomal region 17p13.3 is associated with increased cell proliferation in astrocytic tumors

We had previously reported that loss of heterozygosity (LOH) of the D17S379 locus on 17p13.3 was significantly more frequent in high-grade gliomas (anaplastic astrocytoma, AA; glioblastoma multiforme, GBM) than in those of a low-grade diffuse astrocytoma (DA); however, this was independent of alterations at the TP53 locus, We also showed that LOH of D17S379 was associated with positive staining for p53 protein on immunohistochemistry, but LOH of the TP53 gene had no such association. In this work we show that cell proliferation as determined by MIB-1 labeling index (LI) was significantly higher in tumors with LOH of D17S379 than those with no LOH (NLOH). In accord with our previous results, p53 protein immunopositivity was also associated with increased MIB-1 LI; however, we observed no such association of LI with TP53 LOH. The results further confirm that alteration of one or more putative tumor suppressor loci at 17p13.3 is associated with increased proliferation in astrocytic tumors.

Karyotypic aberrations of chromosomes 16 and 17 are related to survival in patients with breast cancer

BACKGROUND

Breast cancer has a high incidence and associated mortality rate, yet little is known of the sequence of genetic events that underlie the clinical course.

METHODS

The study was a comparative genomic hybridization analysis of 40 primary breast cancers with survival data at a mean of 8.4 years.

RESULTS

The mean number of aberrations was 9.0, with a mean of 5.5 gains and 3.5 deletions per tumour. The most common aberrations were: gain of 1q (27 of 40), 8q (19 of 40) and 17q (13 of 40), and deletion of 17p (12 of 40) and 8p (11 of 40). These results are consistent with a distinctive pattern of large-scale (karyotypic) genetic change in primary breast cancer.

CONCLUSION

The novel findings of this study were that only women who were disease-free had loss of 16q (E-cadherin) in association with a gain of 16p, and 17p13 (p53) loss combined with 17q12 (HER2) amplification was found only in the cancers of women who developed recurrent disease. The karyotypic changes seen in primary breast cancer seem to be associated with outcome and point to the underlying genetic events.

Evaluation of numeric alterations of chromosomes 1 and 17 by in situ hybridization in invasive breast carcinoma with clinicopathologic parameters

Breast cancer is a genetically complex disease and is frequently associated with nonrandom chromosomal alterations. The occurrence of aberrations involving chromosomes 1 and 17 in malignant tissues of breast cancer patients has not been studied systematically. The numeric aberrations of chromosomes 1 and 17 were detected by nonisotopic in situ hybridization on paraffin-embedded tissue sections from 44 invasive breast carcinomas (42 cases available for chromosome 17) and were correlated with clinicopathologic parameters, patients' survival, p53, and c-erbB-2 proteins. Chromosome 17 and 1 aneuploidy were observed in the majority of breast carcinomas with equal percentages of polysomy and monosomy for chromosome 17 and predominance of polysomy for chromosome 1. Monosomy of chromosome 17 was significantly associated with positive lymph nodes and negative estrogen receptor (ER) immunohistochemical expression. Patients with chromosome 17 monosomy were at greater risk of death. Ductal carcinoma displayed a greater percentage of chromosome 1 polysomy than lobular ones. A statistically significant association was demonstrated between chromosome 1 polysomy and higher nuclear grade. Patients with chromosome 1 aneuploidy were at greater risk of death, and especially those with ER negativity. Aneuploid patients with c-erbB-2(-)/PR(-) phenotype demonstrated lower survival rates. These data suggest a possible susceptibility of chromosome 17 to losses and gains and chromosome 1 to gains. Chromosome 17 monosomy and chromosome 1 aneuploidy may be useful prognostic markers in breast cancer patients.

Expression of the Hypermethylated in Cancer gene (HIC-1) is associated with good outcome in human breast cancer

A new cancer gene, HIC-1 (Hypermethylated in Cancer) telomeric to p53 on chromosome 17p may be of clinical importance in sporadic breast cancer. Regional DNA hypermethylation of 17p13.3 resulting in suppression of gene expression has been shown to precede 17p structural changes in human carcinogenesis. In addition, loss of heterozygosity studies have suggested clinically significant involvement of a gene on 17p13.3 associated with poor prognosis in breast cancer. Using RT-PCR analysis, we demonstrate that the MCF7 (wild type p53) cell line expressed HIC-1 transcripts but the MDAMB231 (mutant p53) cell line did not, suggesting loss of HIC-1 expression and p53 malfunction may be synergistic events in sporadic breast cancer. HIC-1 expression was examined using RT-PCR on RNA extracted from 50 primary untreated, human breast cancers and was detected in only 7/50 (14%) cancers. All seven patients with HIC-1 expression were alive without disease recurrence after 8 years follow-up and 5/7 had detectable p53 wild type mRNA expression. This suggests that retained HIC-1 expression may offer a survival advantage. However the seven cancers had 17p13.3 loss of heterozygosity (LOH; four patients), a feature previously associated with poor prognosis, or were homozygous (three patients) suggesting there may be two genes at 17p13.3 involved in breast carcinogenesis. Using a demethylating drug 5-aza-2'-deoxycytidine (DeoxyC), HIC-1 expression was restored in the MDAMB231 cells, also suggesting restoration of HIC-1 function by reversing HIC-1 hypermethylation may offer a therapeutic avenue in breast cancer.

Role of 17p13.3 chromosomal region in determining p53 protein immunopositivity in human astrocytic tumors

Immunohistochemistry of p53 protein is being increasingly performed as a clinical service as well as in research for prediction of tumor behavior. Although early reports suggested that p53 immunopositivity was associated with p53 gene alterations, recent evidence indicates that this is not always true. Earlier, we had demonstrated the significant association of loss of heterozygosity (LOH) of the chromosomal region 17p13.3 with higher grades of human astrocytic tumors. This was independent of the heterozygosity status of p53. LOH of p53 was taken as an indicator of p53 gene alteration, which was substantiated by sequencing a subset of the tumors. In the present study, we report that p53 immunopositivity in 40 of the same set of tumors (five could not be evaluated because of paucity of tissue) was significantly associated with LOH of 17p13.3 region (Fisher's exact two-tailed, P = 0.012; odds ratio, 12) but not with LOH of p53 (Fisher's exact two-tailed, P = 0.324; odds ratio, 2.24). This indicates that the gene(s) on the 17p13.3 region of the human chromosome may be influencing the p53 immunopositivity status of glial tumors and possibly other tumors in general. This has great implications in interpreting p53 immunohistochemistry results of biopsies of various tumor types as due to p53 mutations alone. The study thus points to a new molecular correlate for p53 immuno-positivity in tumors.

Physical map of 17p13 and the genes adjacent to p53

Genetic lesions in the p53 tumor suppressor gene are the most frequently observed alterations in human cancers. Typically in tumors, one allele of the p53 gene is initially mutated, followed by deletion of the remaining wildtype allele. In human colon cancer, for example, approximately 70% of late stage tumors are hemizygous mutant p53. Since the precise gene environment surrounding the p53 gene is not known, the neighboring genes concomitantly lost with wildtype p53 deletion remain undetermined. A restriction enzyme map and clone array of 1.1 Mb surrounding the p53 gene were constructed using a combination of YAC, BAC, NotI linking, and NotI jumping clones. The resulting physical map and clone array include approximately 400 kb telomeric and 700 kb centromeric to the p53 gene. Sequence determination and analysis adjacent to NotI and AscI sites, indicative of CpG islands, allowed the rapid identification of numerous genes within the cloned region. Twenty-seven transcription units were identified, including 18 characterized genes. Limited analysis of primary human colon tumors, hemizygous for the p53 gene, indicates loss of the entire 1.1-Mb region upon deletion of wildtype p53.

An immunochemical analysis of mdm2 expression in human breast cancer and the identification of a growth-regulated cross-reacting species p170

mdm2 is a 491 amino acid nuclear protein which is involved in complex interactions with important cell-cycle and stress-response regulators including p53, Rb and E2F. Recent data implicate mdm2 in the regulation of both p53 activity and level, and burgeoning data suggest that mdm2 may be involved in human epithelial tumourigenesis, including breast cancer. In this study the expression of mdm2 protein has been investigated in a series of 54 human breast carcinomas using immunoblotting methods. Overexpression of the predominant p90 mdm2 isoform is common in breast cancer (54 per cent) and this is not frequently a consequence of gene amplification. There is no relationship between p90 expression and either p53 protein expression or p53 mutational status. Additional mdm2 immunoreactive species of differing mobilities are identifiable, greatly complicating the analysis. For example, a p170 form is seen in many breast cancer samples (44 per cent) using 2A10 but is not identified by 3G5. This 2A10 immunoreactive species, which is almost certainly not an mdm2 isoform, is a growth-regulated protein, being undetectable in resting peripheral blood lymphocytes and rising to high levels after PHA stimulation. In contrast to mdm2 (p90), p170 is not induced by DNA damage caused by UV light. p170 is identifiable in mdm2 null cells by immunoblotting and is detected as a nuclear protein. While mdm2 immunostaining studies are increasing, this report highlights the complexity of mdm2 analysis in vivo and emphasizes the need to correlate immunohistological and biochemical assays since, in some mdm2 (p90) negative tumours, nuclear immunoreactivity may be identified as a consequence of cross-reacting species such as p170.