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To K.,Experimental Medicine Program | To K.,Child and Family Research Institute | Fotovati A.,Child and Family Research Institute | Reipas K.M.,Experimental Medicine Program | And 19 more authors.
Cancer Research | Year: 2010

Y-box binding protein-1 (YB-1) is an oncogenic transcription/translation factor expressed in >40% of breast cancers, where it is associated with poor prognosis, disease recurrence, and drug resistance. We questioned whether this may be linked to the ability of YB-1 to induce the expression of genes linked to cancer stem cells such as CD44 and CD49f. Herein, we report that YB-1 binds the CD44 and CD49f promoters to transcriptionally upregulate their expressions. The introduction of wild-type (WT) YB-1 or activated P-YB-1S102 stimulated the production of CD44 and CD49f in MDA-MB-231 and SUM 149 breast cancer cell lines. YB-1-transfected cells also bound to the CD44 ligand hyaluronan more than the control cells. Similarly, YB-1 was induced in immortalized breast epithelial cells and upregulated CD44. Conversely, silencing YB-1 decreased CD44 expression as well as reporter activity in SUM 149 cells. In mice, expression of YB-1 in the mammary gland induces CD44 and CD49f with associated hyperplasia. Further, activated mutant YB-1S102D enhances self-renewal, primary and secondary mammosphere growth, and soft-agar colony growth,. which were reversible via loss of CD44 or CD49f. We next addressed the consequence of this system on therapeutic responsiveness. Here, we show that paclitaxel induces P-YB-1S102 expression, nuclear localization of activated YB-1, and CD44 expression. The overexpression of WT YB-1 promotes mammosphere growth in the presence of paclitaxel. Importantly, targeting YB-1 sensitized the CD44High/CD24Low cells to paclitaxel. In conclusion, YB-1 promotes cancer cell growth and drug resistance through its induction of CD44 and CD49f. © 2010 American Association for Cancer Research. Source

Gwozdz A.M.,Experimental Medicine Program | Leung R.,Experimental Medicine Program | Wang H.,Experimental Medicine Program | Bang K.W.A.,St. Michaels Hospital | And 5 more authors.
Thrombosis and Haemostasis | Year: 2010

Exposure of procoagulant phosphatidylserine (PS) on the surface of activated platelets is not readily reversible and this may propagate thrombosis. Persistence of PS exposure may be attributed, at least in part, to a continued reduction of the activity of aminophospholipid translocase (APLT), that transports PS from the outer to the inner membrane leaflet. We investigated whether calpain is involved in the inhibition of APLT activity. In flow cytometric investigations, using the inhibitors calpeptin or E64d at a concentration that blocks calpain activation, we found that calpain is not responsible for the reduction in APLT activity that results in persistence of PS exposure. Unexpectedly, we found that the inhibitors had additional effects independent of blocking calpain. Incubation of resting platelets with calpeptin resulted in a subpopulation of platelets with increased intracellular Ca 2+ and persistent PS exposure. The inhibitors also increased the proportion of platelets with persistent PS exposure in suspensions stimulated with thrombin and/or collagen or the Ca2+-ionophore A23187 under conditions in which calpain was not activated or in which its activation was completely blocked; P-selectin expression on thrombin and/ or collagen-stimulated platelets was inhibited. Furthermore, in stimulated platelets, calpeptin increased the proportion of the PS-exposing platelets expressing a second apoptotic hallmark, collapsed mitochondrial inner membrane potential (Δψm). These additional effects of calpeptin on platelet regulation of intracellular Ca2+ levels and apoptotic-like events should be taken into account when it is used as an inhibitor of calpain. © Schattauer 2010. Source

Dhillon J.,Experimental Medicine Program | Dhillon J.,University of British Columbia | Astanehe A.,Experimental Medicine Program | Astanehe A.,University of British Columbia | And 6 more authors.
Oncogene | Year: 2010

The development of acquired resistance to trastuzumab remains a prevalent challenge in the treatment of patients whose tumors express human epidermal growth factor 2 (HER2). We previously reported that HER2 overexpressing breast cancers are dependent on Y-box binding protein-1 (YB-1) for growth and survival. As YB-1 is also linked to drug resistance in other types of cancer, we address its possible role in trastuzumab insensitivity. Employing an in vivo model of acquired resistance, we demonstrate that resistant cell lines have elevated levels of P-YB-1 S102 and its activating kinase P-RSK and these levels are sustained following trastuzumab treatment. Further, to demonstrate the importance of YB-1 in mediating drug resistance, the expression of the active mutant YB-1 S102D rendered the BT474 cell line insensitive to trastuzumab. Questioning the role of tumor-initiating cells (TIC) and their ability to escape cancer therapies, we investigate YB-1's role in inducing the cancer stem cell marker CD44. Notably, the resistant cells express more CD44 mRNA and protein compared with BT474 cells, which correlated with increased mammosphere formation. Expression of YB-1 S102D in the BT474 cells increase CD44 protein levels, resulting in enhanced mammosphere formation. Further, exposing BT474 cells to trastuzumab selected for a resistant sub-population enriched for CD44. Conversely, small intefering RNA inhibition of CD44 restored trastuzumab sensitivity in the resistant cell lines. Our findings provide insight on a novel mechanism employed by tumor cells to acquire the ability to escape the effects of trastuzumab and suggest that targeting YB-1 may overcome resistance by eliminating the unresponsive TIC population, rendering the cancer sensitive to therapy. © 2010 Macmillan Publishers Limited All rights reserved. Source

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