A model for random genetic damage directing selection of diploid or aneuploid tumours

Program in Bioinformatics and Proteomics/Genomics, The University of Toledo, Toledo, OH, USA.
Cell Proliferation (Impact Factor: 3.12). 06/2011; 44(3):212-23. DOI: 10.1111/j.1365-2184.2011.00746.x
Source: PubMed


To test whether genetic instability may determine whether tumours become aneuploid or diploid.
We have identified genes needed for cell survival or replication by combining Affymetrix gene expression array data from 12 experimental cell lines with in silico GEO+GNF and expO databases. Specific loss of heterozygosis (LOHs), chromosomal abnormalities (called derivative chromosomes) and numbers of normal homologues were identified by SNP and SKY analyses. Random gene losses were calculated under the assumption that bi-allelic MMR gene inactivation causes a 20-fold increase in rate of gene loss.
There were ∼1.23 × 10(4) genes widely dispersed throughout the genome and possibly expressed by all cells for survival or proliferation, many of these genes performed housekeeping functions. Conservation of the genes may explain the complete haploid genomes found for 15 different cell types and derivative chromosomes selectively retained in aneuploid cancer cell lines after LOH formations, and normal homologue losses. Loss of cell survival/replication genes was calculated to be higher in colon stem cells of carriers of MMR gene mutations than carriers of APC gene mutations.
Random loss of cell survival/replication genes was calculated to be low enough for colon stem cells with APC gene mutations to 'select' LOH and derivative chromosome combinations favouring tumour cell proliferation. However, cell survival/replication gene loss was calculated to be too high for colonic stem cells lacking MMR genes to survive chromosomal instability, explaining why MMR mutations only produce tumours with diploid chromosome cells.

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    • "Some of these haploid genes may be haplo-insufficient and unable to produce enough mRNA for optimal gene function (Birchler et al., 2007). Thus, the 50% increase in mRNA levels found for the PC- 3 and SUIT-2 gene cancer genes (Fig. 7) may allow haplo-insufficient genes to produce enough mRNA for normal cell growth (Bazeley et al., 2011) or to raise the mRNAs of genes selected in oncogene and non-oncogene addictions in order to increase the numbers of rate-limiting proteins and thereby promote tumor growth (Dai and Lu, 2008; Luo et al., 2009; Ruggero, 2009) . In either case, molecular attacks against the transcription amplification mechanism(s) selected in a given cancer may have therapeutic benefits either by allowing latent, growth retarding effects of haploinsufficient genes to emerge and/or by decreasing the numbers of other crucial mRNA transcripts needed for tumor cell proliferation. "
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    ABSTRACT: The relative mRNA levels of differentially expressed (DE) and housekeeping (HK) genes of six aneuploid cancer lines with large-scale genomic changes identified by SNP/SKY analysis were compared with similar genes in diploid cells. The aneuploid cancer lines had heterogeneous genomic landscapes with subdiploid, diploid, and supradiploid regions and higher overall gene copy numbers compared with diploid cells. The mRNA levels of the haploid, diploid, and triploid HK genes were found to be higher after correction of easily identifiable mRNA measurement errors. Surprisingly, diploid and aneuploid HK gene mRNA levels were the same by standard expression array analyses, despite the higher copy numbers of the cancer cell HK genes. This paradoxical result proved to be due to inaccurate inputs of true intra-cellular mRNAs for analysis. These errors were corrected by analyzing the expression intensities of DE and HK genes in mRNAs extracted from equal cell numbers (50:50) of intact cancer cell and lymphocyte mixtures. Correction for both mRNA extraction/sample normalization errors and total gene copy numbers found the SUIT-2 and PC-3 cell lines' cancer genes both had ∼50% higher mRNA levels per single allele than lymphocyte gene alleles. These increased mRNA levels for single transcribed cancer alleles may restore functional mRNA levels to cancer genes rendered haplo-insufficient by the genetic instability of cancer. © 2013 Wiley Periodicals, Inc.
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    ABSTRACT: Chromosomal changes are widespread in the vast majority of colon carcinomas and aneuploidy is an established prognostic factor. However, this knowledge so far has no influence on tumor classification. We reported a morphology-based classification scheme, the core classification, that correlates with DNA ploidy. In particular, tripolar mitoses were identified as surrogate markers of a near triploid DNA content. In addition, a survey on chromosome numbers and survival rates in carcinomas suggested that triploidy as a particular state of aneuploidy may be correlated with a more aggressive tumor phenotype. We therefore aimed to analyze DNA ploidy in the colorectal adenoma-carcinoma sequence. The study collection consisted of 15 adenomas and 15 adenocarcinomas of 10 patients. Some of them showed a morphological transition between benign and malignant tumor components which were selectively analyzed by DNA measurements. In addition, we assessed the morphological parameters of the core classification. The main findings of the study may be summarized as follows. 1) DNA ploidy changes are already consistently detectable in colon adenomas. They are usually associated with hyperdiploidy. 2) Adenoma tissue adjacent to carcinomas, however, may carry a hypodiploid DNA content while the nearby carcinoma samples were hyperdiploid. Hypodiploidy may thus represent a transition state to near triploid carcinomas. 3) The size of tumor nuclei and mitoses usually reflects the ploidy level of colon tumors. Specifically, triploid mitoses may point to a near triploid DNA content. 4) Triploidy per se cannot be equated with tumor aggressiveness as it may already be found in adenocarcinoma in situ. 5) Tripolar and tetrapolar mitoses in invasive colon cancer, however, are potential indicators of an advanced chromosomal instability and seemed to be associated with advanced tumor stages. We present data that hypodiploidy may represent a transition state from adenoma to carcinoma in a subset of colorectal tumors and that near-triploidy may be associated with a more aggressive course of the disease. However, the interpretation of tripolar mitoses and triploidy is largely dependent on the cell type (benigne vs. malignant) and tissue context (invasive vs. non-invasive cancer). Furthermore, its interpretation may be distinct for different tumor stages and histotypes. Aneuploidy and multipolar mitoses are frequent findings in cancer cells. Their relevance for tumor biology deserves further studies.
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