Microarray-based Analyses of Hypoxia-induced Transcriptional Changes in Breast Cancer Cell Lines

摘要

Tumour hypoxia is a common characteristic of many solid human tumours, and is associated with a poor prognosis in various types of cancer. Metabolic changes occur when cells are exposed to low oxygen pressure; however, little is known about the mechanisms underlying malignant transformation and/or progression caused by hypoxia. Materials and Methods: We monitored global gene expression changes caused by hypoxia in four breast cancer cell lines using 27K cDNA microarrays. Cells were grown under hypoxic and normoxic conditions, and were harvested at four different time points. All genes were assigned to patterns (up, down, or unchanged) across the time points, followed by ontological mapping to investigate significant associations between genes belonging to specific patterns and Gene Ontology categories. Furthermore, we investigated genomic regions upstream of regulated genes for the presence of known regulatory motifs. Results: Several common effects of hypoxia were seen in the breast cancer cell lines, such as an increase in glycolytic metabolism; however, the response to hypoxia varied greatly between the cell lines. Oestrogen receptor (ER)-positive breast cancer cells displayed a partially unique response to hypoxia compared to ER-negative cells. Similarly, unique changes in e.g. RNA metabolism and DNA repair were seen in a BRCA1-deficient cell line. Whereas an enrichment of genes containing the HIF-1 binding site sequence was found among genes regulated by hypoxia in two of the cell lines investigated, this sequence was also identified in a considerable fraction of non-regulated genes. Conclusion: Global gene expression profiling of the cellular response to hypoxia revealed a multitude of novel mechanisms and functions affected by hypoxia in breast cancer cell lines. The findings also suggest a high degree of diversity in this response depending on the genetic background of the tumour cells. Specifically, down-regulation of genes involved in DNA repair mechanisms in a BRCAl-deficient cell line may reflect the crucial role played by the BRCA1 protein in instances of DNA damage, e.g. during hypoxia.