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UBC Theses and Dissertations

Y-box binding protein-1 (YB-1) is essential for the growth and survival of HER-2 over-expressing breast cancer cells Lee, Cathy


The human epidermal growth factor receptor (HER-2) is over-expressed in 20-30% of breast carcinomas and is a prognostic marker for poor patient outcome. We previously identified the transcription/translation factor Y-box binding protein-1 (YB-1) to be a novel substrate of AKT which binds to epidermal growth factor receptor (EGFR) and HER-2 promoters once phosphorylated (Wu J et al. 2006). YB-1 is over-expressed in approximately 40% of breast cancers; its expression is strongly correlated with HER-2 and is associated with poor patient survival. In order to gain a deeper understanding of the functional role of YB-1 in HER-2 over-expressing breast cancer, we silenced the expression of this factor in BT474-m1 and MDA-MB-453 cells. The loss of YB-1 inhibited the growth of BT474-m1 and MDA-MB-453 cells in monolayer and/or in soft agar. Consistent with this, we found a decrease in the expression of YB-1 responsive gene egfr and/or her-2 in BT474-m1 and MDA-MB-453 cells, which could begin to explain how growth is promoted by this factor. Furthermore, loss of YB-1 expression induced apoptosis in BT474-m1 cells. Beyond its role in tumor growth, YB-1 is also strongly linked to drug resistance. We therefore addressed whether it could play a part in Herceptin sensitivity. Herceptin is currently being used to treat patients with HER-2 positive breast cancer; however, only 30% of the patients respond to the therapy and many of them develop resistance within the first year of treatment. Therefore, it is of utmost importance to understand the biology of HER-2 over-expressing breast cancer to develop novel therapies that can benefit more patients. First we established that Herceptin inhibited BT474-m1 cell growth in anchorage-independent conditions whereas MDA-MB-453 cells were resistant to this treatment. We subsequently demonstrated that knock-down of YB-1 increased sensitivity of BT474-m1 cells to Herceptin while MDA-MB-453 cells failed to respond to the combination treatment. The mechanism for Herceptin resistance in MDA-MB-453 cells still remains elusive and requires further investigation. Thus far, we conclude that YB-1 is needed for the growth and survival of HER-2 positive BT474-m1 and MDA-MB-453 breast cancer cells by inducing members of the HER family.

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