Oncogene amplification in neoplastic development and progression of human cancers

Increased dosage of cellular oncogenes resulting from amplification of DNA is a frequent genetic abnormality of tumor cells. Certain types of human tumors carry a specific amplified cellular oncogene at frequencies of up to 50 to 60%. Human neuroblastoma has been prototypic for a contribution of amplification to tumorigenesis, and evidence is emerging that amplification may be an early event involved in a malignant form of this cancer. It is unclear at which stage amplification plays a role in other cancers. Amplification of cellular oncogenes is a good predictor for clinical outcome in some human malignancies and is a paradigm for the application of oncogene research in a clinical context.     

Integrative genomics identifies RAB23 as an invasion mediator gene in diffuse-type gastric cancer

Recurrent genomic amplifications and deletions are frequently observed in primary gastric cancers (GC). However, identifying specific oncogenes and tumor suppressor genes within these regions can be challenging, as they often cover tens to hundreds of genes. Here, we combined high-resolution array-based comparative genomic hybridization (aCGH) with gene expression profiling to target genes within focal high-level amplifications in GC cell lines, and identified RAB23 as an amplified and overexpressed Chr 6p11p12 gene in Hs746T cells. High RAB23 protein expression was also observed in some lines lacking RAB23 amplification, suggesting additional mechanisms for up-regulating RAB23 besides gene amplification. siRNA silencing of RAB23 significantly reduced cellular invasion and migration in Hs746T cells, whereas overexpression of RAB23 enhanced cellular invasion in AGS cells. RAB23 amplifications in primary gastric tumors were confirmed by both fluorescence in situ hybridization and genomic qPCR, and in two independent patient cohorts from Hong Kong and the United Kingdom RAB23 expression was significantly associated with diffuse-type GC (dGC) compared with intestinal-type GC (iGC). These results provide further evidence that dGC and iGC likely represent two molecularly distinct tumor types, and show that investigating focal chromosomal amplifications by combining high-resolution aCGH with expression profiling is a powerful strategy for identifying novel cancer genes in regions of recurrent chromosomal aberration.     

Genomic and expression analysis of the 8p11-12 amplicon in human breast cancer cell lines

Gene amplification is an important mechanism of oncogene activation in breast and other cancers. Characterization of amplified regions of the genome in breast cancer has led to the identification of important oncogenes including erbB-2/HER-2, C-MYC, and fibroblast growth factor receptor (FGFR) 2. Chromosome 8p11-p12 is amplified in 10-15% of human breast cancers. The putative oncogene FGFR1 localizes to this region; however, we show evidence that FGFR inhibition fails to slow growth of three breast cancer cell lines with 8p11-p12 amplification. We present a detailed analysis of this amplicon in three human breast cancer cell lines using comparative genomic hybridization, traditional Southern and Northern analysis, and chromosome 8 cDNA microarray expression profiling. This study has identified new candidate oncogenes within the 8p11-p12 region, supporting the hypothesis that genes other than FGFR1 may contribute to oncogenesis in breast cancers with proximal 8p amplification.     

Predicting breast cancer risk: implications of a “weak” family history

Published guidelines adopted in many countries recommend that women whose family history of breast cancer places them at a risk ≥1.7 times that of the age-matched general population, should be considered for inclusion in special surveillance programmes. However validation of risk assessment models has been called for as a matter of urgency. The databases of the four Scottish Familial Breast Cancer clinics and the Scottish Cancer Registry have been searched to identify breast cancers occurring among 1,125 women aged 40–56, with family histories placing them below the “moderate” level of genetic risk. The observed incidence over 6 years was compared with age-specific data for the Scottish population. Our findings confirm that when there are two affected relatives (one first degree) the relative risk (RR) exceeds 1.7 regardless of their ages at diagnosis. When only one (first degree) relative was affected at any age from 40 to 55, the RR does not reach 1.7 if that relative was a mother but exceeds it if the relative was a sister. The probable explanation is that sisters are more likely than mother/daughter pairs to share homozygosity for a risk allele. Surveillance programmes might therefore accommodate sisters of women affected before age 55. Evidence that “low penetrance” alleles contributing to breast cancer risk may be recessive should be taken into account in strategies for identifying them. All the authors are from the Scottish Cancer Family Clinical Centres.     

Cancer-related identity and positive affect in survivors of prostate cancer

Introduction Despite a shift in the cancer culture and language used to describe individuals diagnosed with this disease, the extent to which individuals with cancer adopt a particular cancer-related identity and the impact of these identities in relation to their well-being is virtually unknown. Materials and methods Using a cross-sectional study design and a metropolitan tumor registry, a mail questionnaire to examine post-treatment quality of life was sent to prostate cancer (PCa) survivors. The sample consisted of 490 PCa survivors, ranging in age from 49–88 (M = 69.7; SD = 7.8), one to eight years after diagnosis. The outcome measure used in these analyses was the PANAS to assess positive and negative affect. Results The most frequently reported cancer-related identity was “someone who has had PCa” (57%). The least reported self view was “victim” (1%). Twenty-six percent of men self-identified as “survivors” while 6% thought of themselves as “cancer conquerors.” Only 9% self-identified as a “patient.” Multivariate analyses, adjusted for potential confounders, show respondents who identified themselves as “survivors” or “cancer conquerors” reported significantly higher scores on positive affect than men who self-identified as “patients” (p < .001). Conclusions Although the majority of respondents identified themselves as “someone who has had cancer,” identifying as a “survivor” or “someone who has conquered cancer” appears to have adaptive value for positive mood. Implications for cancer survivors Those who perceive themselves as survivors of prostate cancer may derive some benefit in well-being associated with this self assessment.     

Molecular classes of breast cancer and their clinical relevance

Hierarchical clustering of gene expression profiles has shown that breast cancers can be separated into subclasses characterized by distinct gene profiles. It has been known for decades that breast cancer may be classified into estrogen receptor-positive versus estrogen receptor-negative tumors and, more recently, it was discovered that breast cancer may be classified into tumors amplified versus not amplified for human epidermal growth factor receptor-2 (HER-2). Now, with the use of gene expression profiling, estrogen receptor-positive tumors can be separated into luminal A class and B class tumors, revealing different prognoses and most likely different endocrine sensitivity. Much effort has been focused on characterizing the “triple-negative” tumors (basal cell-like and normal breast cell-like classes). The finding that these tumors, similar to tumors among BRCA1/BRAC2 mutation carriers, may respond to poly(adenosine diphosphate ribose) polymerase inhibitors has led to a targeted therapy approach and suggests defects in DNA repair are also a characteristic of basal cell-like tumors in patients harboring wild-type BRCA1.     

Ability of circular extrachromosomal DNA molecules to carry amplified MYCN proto-oncogenes in human neuroblastomas in vivo

Amplification of the proto-oncogene MYCN (also known as N-myc) in neuroblastomas has been shown to correlate with both disease stage and prognosis, yet little is known about the DNA structures that carry amplified MYCN genes in neuroblastomas in vivo. We have used DNA irradiation and pulsed-field gel electrophoresis to analyze MYCN amplification structures in eight neuroblastomas from separate patients (four primary tumors and four metastatic lesions exhibiting MYCN amplification). Six of the eight neuroblastomas (three primary tumors and three metastatic lesions) exhibited MYCN DNA irradiation profiles consistent with the presence of circular extrachromosomal DNA amplification structures. Five neuroblastomas possessed amplification structures within the size range of double minute chromosomes, and one contained smaller DNA circles. Two neuroblastomas exhibited MYCN DNA irradiation patterns consistent with larger (presumably chromosomal) amplification structures. Multiple sizes of DNA circles were observed in the neuroblastomas of four different patients, implying in vivo multimerization of amplification structures. The presence of circular MYCN amplification structures in six of eight neuroblastomas examined suggests that circular DNA molecules are important structures in in vivo gene amplification.     

Oncogenes expand during evolution to withstand somatic amplification

BackgroundCancer-related genes are under intense evolutionary pressure. We conjectured that gene size is an important determinant of amplification propensity for oncogenes and thus cancer susceptibility and therefore could be subject to natural selection.Patients and methodsGene information, including size and genomic locations, of all protein-coding genes were downloaded from Ensembl (release 87). Quantification of gene amplification was based on Genomic Identification of Significant Targets in Cancer scores obtained from available The Cancer Genome Atlas studies.ResultsOncogenes are larger in size as compared with non-cancer genes (mean size: 92.1 kb versus 61.4 kb;P < 0.0001) in the human genome, which is contributed by both increased total exon size (mean size: 4.6 kb versus 3.4 kb;P < 0.0001) and higher intronic content (mean %: 84.8 versus 78.0;P < 0.01). Such non-random size distribution and intronic composition are conserved in mouse and Drosophila (allP < 0.0001). Stratification by gene age indicated that young oncogenes have been subject to a stronger evolutionary pressure for gene expansion than their non-cancer counterparts. Pan-cancer analysis demonstrated that larger oncogenes were amplified to a lesser extent. Tumor-suppressor genes also moved toward small oncogenes in the course of evolution.ConclusionsOncogenes expand in size whereas tumor-suppressor genes move closer to small oncogenes in the course of evolution to withstand oncogenic somatic amplification. Our findings have shed new light on the previously unappreciated influence of gene size on oncogene amplification and elucidated how cancers have shaped our genome to its present configuration.     

Aromatase inhibitors: from bench to bedside and back

The development of the novel “third generation” aromatase inhibitors (anastrozole, letrozole) and inactivators (exemestane) is one of the most successful contemporary achievements in breast cancer therapy. While clinical studies evaluated toxicity and efficacy in metastatic disease, the endocrine effects of multiple compounds were evaluated in parallel, identifying the most potent aromatase inhibitors based on estrogen deprivation in plasma and tissue samples in addition to “total body aromatase inhibition” in vivo. Thus, “translational” studies have been of vital importance identifying the unique characteristics of these drugs. While first- and second generation aromatase inhibitors inhibit estrogen synthesis in vivo by up to 90%, third generation compounds like anastrozole, exemestane and letrozole were shown to cause ≥ 98% aromatase inhibition in humans. The present paper summarises and discusses the “translational research” that provided the background for the implementation of the third generation aromatase inhibitors and inactivators into large clinical trials and later on in clinical use. Finally, some of the major topics of currently ongoing translational research programs are presented. These programs focus on aromatase regulation in different tissues, mechanisms of resistance to aromatase inhibition and strategies to overcome resistance like combined therapy with aromatase inhibitors and intracellular signal transduction inhibitors. This article is based on an invited lecture delivered at the 15th Annual Meeting of the Japanese Breast Cancer Society, held in Yokohama 29–30 June 2007.     

Targeting MYCN IRES in MYCN‐amplified neuroblastoma with miR‐375 inhibits tumor growth and sensitizes tumor cells to radiation

The MYCN oncogene is amplified in 20% of neuroblastomas, leading to its overexpression at both the mRNA and protein levels. MYCN overexpression is strongly associated with advanced disease stage, rapid tumor progression and a worse prognosis. In the present study, we identified microRNA‐375 (miR‐375) as a negative regulator of MYCN: enforced expression of miR‐375 inhibited MYCN‐amplified neuroblastoma in vitro and in vivo. Upon searching the website miRbase for possible miR‐375 binding sites within the whole MYCN mRNA, we found that the MYCN 5′‐UTR had significant sequence complementarity to miR‐375, yet no complementary sequences existed within the MYCN 3′‐UTR and coding regions. Enforced overexpression of miR‐375 efficiently inhibited MYCN mRNA translation and protein synthesis, via an IRES‐dependent mechanism. In athymic nude mouse model with human MYCN‐amplified neuroblastoma, MYCN downregulation by miR‐375 led to inhibition of tumor cell growth and tumorigenicity. In particular, miR‐375‐regulated inhibition of MYCN translation was enhanced when MYCN‐amplified neuroblastoma cells were exposed to stress stimulation, such as ionizing irradiation (IR), resulting in a remarkable increase in the neuroblastoma''s sensitivity to IR‐induced cell death. Our results identified a novel mechanism by which IRES‐dependent translation of MYCN is repressed by miR‐375, particularly during cellular stress, highlighting a potential anticancer strategy: the development of miR‐375 as a novel therapeutic agent to treat MYCN‐amplified neuroblastoma.