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Gene expression profiles of Herceptin-resistant breast cancer cells

ABSTRACT: Herceptin (trastuzumab) is a humanized monoclonal antibody targeted to the Her2 receptor tyrosine kinase. Despite a robust response rate to Herceptin-based therapies in Her2-positive patients, resistance frequently arises within one year of the initial response. To address the mechanism of Herceptin resistance, we selected clonal variants of Her2-positive BT474 human breast cancer cells (BT/HerR) that are highly resistant to the anti-proliferative effects of Herceptin in the presence of 0.2 uM or 1.0 uM Herceptin. Our original report on these cell lines demonstrated sustained PI3K/Akt signaling and sensitivity to PI3K inhibitors in BT/HerR cells in the presence of Herceptin, suggesting dysregulation of that pathway as an essential component of Herceptin-resistant proliferation. To address the mechanism by which BT/HerR cells and their PI3K/Akt signaling pathway became resistant to Herceptin, we analyzed gene expression profiles of two clones (BT/HerR1.0C and BT/HerR 1.0E) that were selected in 1.0 uM Herceptin and two clones (BT/HerR0.2D and BT/HerR 0.2J) that were selected in 0.2 uM Herceptin, in comparison to the Herceptin sensitive BT474 parent cells. Total cellular RNAs were extracted from BT474 (control) and four BT/HerR subclones, two that were originally selected in 1.0 uM Herceptin and two that were originally selected in 0.2 uM Herceptin. Two RNA samples independently prepared from each clone were analyzed.

ORGANISM(S): Homo sapiens

SUBMITTER: Gu L

PROVIDER: S-ECPF-GEOD-15043 | biostudies-other | 2009

REPOSITORIES: biostudies-other

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Project description:Resistance to endocrine therapy agents has presented a clinical obstacle in the treatment of hormone-dependent breast cancer. Our laboratory has initiated a study of microRNA regulation of signaling pathways that may result in breast cancer progression on aromatase inhibitors (AI). Microarray analysis of microRNA expression identified 115 significantly regulated microRNAs, of which 49 microRNAs were believed to be hormone-responsive. Within the AI-resistant cells, microRNAs were differentially expressed between the steroidal and non-steroidal AI-resistant lines. Also, a group of microRNAs were inversely expressed in the AI-resistant lines versus LTEDaro and tamoxifen-resistant. We focused our work on hsa-miR-128a which was hormone-responsive and up-regulated in the letrozole-resistant cell lines. Human miR-128a was shown to negatively target TGFBRI protein expression by binding to the 3’UTR region of the gene. Loss of TGFBRI resulted in compromised sensitivity to the growth inhibitory effects of TGFB in the letrozole-resistant lines. Inhibition of endogenous miR-128a resulted in re-sensitization of the letrozole-resistant lines to TGFB growth inhibitory effects. This data suggests that the hormone-responsive miR-128a can modulate TGFB signaling and survival of the letrozole-resistant cell lines. To our knowledge, this is the first study to address the role of microRNA regulation as well as TGFB signaling in AI-resistant breast cancer cell lines. We believe that in addition to estrogen-modulation of gene expression, hormone-regulated microRNAs may provide an additional level of post-transcriptional regulation of signaling pathways critically involved in breast cancer progression and AI-resistance. To look at microRNA expression profiles of breast cancer cell lines derived from MCF-7 cells that are resistant to endocrine therapy agents. MCF-7 cells that overexpress aromatase (MCF-7aro) were cultured long-term in the presence of endocrine therapy agents until cells acquired resistance. Three different aromatase inhibitors (letrozole, anastrozole or exemestane) were used, as well as the ER antagonist tamoxifen, or the hormone-free long-term estrogen deprived cells (LTED). Three replicates of the control cells (MCF-7aro) and all resistant cells were used for microarray experiments. Total of 23 samples were analyzed by microarray.

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Gene expression profiles of Herceptin-resistant breast cancer cells

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