Project description:Basal-like and triple negative breast cancer (TNBC) share common molecular features, poor prognosis and a propensity for metastasis to the brain. Amplification of EGFR occurs in ~50% of basal-like breast cancer and mutations in the epidermal growth factor receptor (EGFR) have been reported in up to ~ 10% of Asian TNBC patients. In non-small cell lung cancer several different mutations in the EGFR tyrosine kinase domain confer sensitivity to receptor tyrosine kinase inhibitors, but the tumourigenic potential of EGFR mutations in breast cells and their potential for targeted therapy is unknown. Constructs containing wild type, G719S or E746-A750 deletion mutant forms of EGFR were transfected into the ‘near normal’ MCF10A breast cells and their tumorigenic derivative, MCF10CA1a. These transfected lines were used to investigate the effects of EGFR over-expression and mutation on proliferation, migration, invasion, response to gefitinib, and tumour formation in vivo. We also carried out copy number analysis and whole exome sequencing of the MCF10A and MCF10CA1a cell lines. Both activating mutations of EGFR increased the proliferative ability of MCF10A and MCF10CA1a cell lines, and increased the anchorage-independent growth and sensitivity to gefitinib in MCF10A cells. In addition, the EGFR-E746-A750 deletion increased the migratory and invasive abilities of the MCF10CA1a cell line in vitro, and greatly increased the formation and growth of MCF10CA1a tumours in vivo. Compared to MCF10A cells, MCF10CA1a cells had large regions of gain on chromosome 9 and the long arm of chromosome 3, deletion in the short arm of chromosome 7, and mutations in many genes implicated in cancer. The EGFR E746-A750 deletion mutation, and to a lesser extent G719S, greatly enhance the oncogenic properties of MCF10A cell line, and increase sensitivity to gefitinib. Although the addition of EGFR E746-A750 renders the MCF10CA1a cells more tumourigenic in vivo it is not accompanied by increased sensitivity to gefitinib, perhaps because of additional mutations, including the PIK3CA H1047R mutation, that the MCF10CA1a cell line has acquired. Screening TNBC/basal-like breast cancer for EGFR mutations may prove useful for directing therapy but, as in non-small cell lung cancer cancer, accompanying mutations in PIK3CA may confer gefitinib resistance.

Project description:Transcription and processing of histone mRNAs occurs at subnuclear domains known as Histone Locus Bodies (HLBs). Although it is known that higher-order chromatin organization is dysregulated in cancer, structural alterations within HLB across breast cancer progression are unclear. Differential expression across known as MCF10, a basal triple negative breast cancer progression model, followed by pathway analysis demonstrated many alterations in signaling cascades known to be related to proliferation. Positional gene enrichment identified the hist1 gene locus at chromosome 6p22 as the most significantly altered cluster of genes from the normal-like MCF10A to premalignant MCF10AT1. The malignant MCF10CA1a had a more varied expression pattern across the hist1 locus. Within this region there are three subclusters of hist1 genes which were generally upregulated while intervening genes were more frequently downregulated. Extending these findings to TCGA breast tumors revealed that normal adjacent tissue had lower expression within the subclusters than their matched tumor samples. Moreover, the expression pattern within the hist1 locus comparing normal versus tumors recapitulated a very similar pattern to that comparing 10A to AT1 or CA1a. Since the hist1 locus is transcribed and processed at a specific subnuclear microenvironment, the higher order chromatin organization of this locus may be a critical component of its regulation. We addressed whether CTCF, a key chromatin organizing protein, may play a role in organizing the hist1 HLB. Immunofluorescence for CTCF along with NPAT, a protein which decorates this locus, identified that CTCF may tether the hist1 HLB to the nuclear matrix. All three subclusters reside within a single topologically associating domain wherein interacting loops are bound by CTCF. Inter-subcluster interactions are lost in the premalignant AT1. Consistent with the varied expression across the hist1 HLB in CA1a, inter-subcluster interactions are regained in the malignant state. These data suggest a transient state in highly proliferative breast cancer cells in which the hist1 HLB is dynamically reorganized.

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High-resolution changes in chromatin organization throughout breast cancer progression

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