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An autocrine VEGF/VEGFR2 and p38 signaling loop confers resistance to 4-hydroxytamoxifen in MCF-7 breast cancer cells
Department of Oncology/Pathology, Karolinska Biomics Center, Karolinska Institutet, Stockholm, Sweden.
Department of Oncology/Pathology, Karolinska Biomics Center, Karolinska Institutet, Stockholm, Sweden.
Department of Pharmacology, University of Oslo, Oslo, Norway.
Department of Oncology/Pathology, Karolinska Biomics Center, Karolinska Institutet, Stockholm, Sweden.
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2008 (English)In: Molecular Cancer Research, ISSN 1541-7786, E-ISSN 1557-3125, Vol. 6, no 10, 1630-1638 p.Article in journal (Refereed) Published
Abstract [en]

Tamoxifen, a partial estrogen receptor antagonist, is part of the standard treatment of both primary and advanced breast cancers. However, significant proportions of breast cancers are either de novo resistant or develop tamoxifen resistance during the course of treatment through mechanisms which have been only partly characterized. We have previously found that high vascular endothelial growth factor (VEGF) or VEGF receptor 2 (VEGFR2) expression and concomitant high p38 mitogen-activated protein kinase activity within breast cancers predict a poor outcome for tamoxifen-treated patients. Here, we have molecularly dissected how VEGF/VEGFR2 and p38 are linked, and contribute to tamoxifen resistance within breast cancer using a MCF-7 BC cell model with different 4-hydroxytamoxifen (4-OHT) responsiveness. We report that MCF-7 breast cancer cell lines with tamoxifen resistance have increased secretion of VEGF and increased signaling through VEGFR2 compared with parental MCF-7 cells. 4-OHT treatment caused the ablation of VEGF secretion in parental MCF-7 cells, whereas in the tamoxifen-resistant subline, a VEGF/ VEGFR2 signaling loop was still evident upon treatment. Increased basal levels of total and phosphorylated p38 were observed in tamoxifen-resistant cells. Pharmacologic inhibition of p38 reduced the proliferation of both tamoxifen-responsive and tamoxifen-resistant cells and showed an additive growth-inhibitory effect in combination with 4-OHT. A connection between VEGF/ VEGFR2 and p38 signaling was identified by VEGF and VEGFR2 knockdown, which equally reduced both the total and the active forms of p38 in tamoxifen-resistant cells. Taken together, our results suggest that decreased sensitivityto 4-OHT is caused by a death-protecting VEGF/VEGFR2 and p38 growth factor loop in breast cancer cells. Inhibition of these signaling pathways may be beneficial to overcome tamoxifen resistance. Copyright © 2008 American Association for Cancer Research.

Place, publisher, year, edition, pages
2008. Vol. 6, no 10, 1630-1638 p.
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Medical and Health Sciences
URN: urn:nbn:se:liu:diva-50142DOI: 10.1158/1541-7786.MCR-07-2172OAI: diva2:271038
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2010-05-24

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