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Silence of chromosomal amplifications in colon cancer
Petra Platzer1, Madhvi B Upender, Keith Wilson
1Howard Hughes Medical Institute, Cleveland, Ohio 44106, USA.
Abstract:
Oncogene activation by gene amplification is a major pathogenetic mechanism in human cancer. Using comparative genomic hybridization, we determined that metastatic human colon cancers commonly acquire numerous extra copies of chromosome arms 7p, 8q, 13q, and 20q. We then examined the consequence of these amplifications on gene expression using DNA microarrays. Of 55,000 transcripts profiled, 2,146 were determined to map to one of the four common colon cancer amplicons and to also be expressed in normal or malignant colon tissues. Of these, only 81 transcripts (3.8%) demonstrated a 2-fold increase over normal expression among cancers bearing the corresponding chromosomal amplification. Chromosomal amplifications are common in colon cancer metastasis, but increased expression of genes within these amplicons is rare.
Insights
Metastatic colon cancers often gain extra chromosome copies, but genes within these amplified regions rarely show increased expression. This finding suggests a complex relationship between gene amplification and oncogene activation in cancer progression.
Area of Science:
- Oncology
- Genetics
- Genomics
Background:
- Gene amplification is a key driver of oncogene activation in human cancers.
- Metastatic colon cancers frequently exhibit chromosomal amplifications.
Purpose of the Study:
- To investigate the frequency and impact of gene amplifications on gene expression in metastatic colon cancer.
- To identify specific amplified chromosomal regions and their associated gene expression changes.
Main Methods:
- Comparative genomic hybridization (CGH) was used to identify common chromosomal amplifications in metastatic colon cancers.
- DNA microarrays were employed to profile gene expression across 55,000 transcripts.
- Analysis focused on genes mapping to commonly amplified regions (chromosome arms 7p, 8q, 13q, and 20q).
Main Results:
- Metastatic colon cancers frequently acquired extra copies of chromosome arms 7p, 8q, 13q, and 20q.
- Of 2,146 transcripts mapping to these amplicons, only 81 (3.8%) showed a 2-fold increase in expression compared to normal tissues.
- This indicates that increased gene expression within amplified regions is uncommon.
Conclusions:
- Chromosomal amplifications are prevalent in colon cancer metastasis.
- Despite frequent amplifications, the increased expression of genes within these amplified regions is rare.
- This suggests that chromosomal amplifications in colon cancer may not always lead to oncogene activation through simple gene dosage effects.