Oncotarget

Research Papers:

Sustained conditional knockdown reveals intracellular bone sialoprotein as essential for breast cancer skeletal metastasis

Marineta Kovacheva, Michael Zepp, Stefan M. Berger and Martin R. Berger _

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Oncotarget. 2014; 5:5510-5522. https://doi.org/10.18632/oncotarget.2132

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Abstract

Marineta Kovacheva1, Michael Zepp1, Stefan M. Berger2 and Martin R. Berger1

1 German Cancer Research Center (DKFZ), Toxicology and Chemotherapy Unit, Heidelberg, Germany

2 Central Institute of Mental Health, Department of Molecular Biology, Mannheim, Germany

Correspondence:

Martin R. Berger, email:

Keywords: breast cancer, skeletal metastasis, bone sialoprotein, conditional knockdown, BSP related signaling cascade

Received: March 14, 2014 Accepted: June 24, 2014 Published: June 26, 2014

Abstract

Increased bone sialoprotein (BSP) serum levels are related to breast cancer skeletal metastasis, but their relevance is unknown. We elucidated novel intracellular BSP functions by a conditional knockdown of BSP. Conditional MDA-MB-231 subclones were equipped with a novel gene expression cassette containing a tet-reg­ulated miRNA providing knockdown of BSP production. These clones were used to assess the effect of BSP on morphology, proliferation, migration, colony formation and gene expression in vitro, and on soft tissue and osteolytic le­sions in a xenograft model by three imaging methods. BSP knockdown caused significant anti-proliferative, anti-migratory and anti-clonogenic effects in vitro (p<0.001). In vivo, significant de­creases of soft tissue and osteolytic lesions (p<0.03) were recorded after 3 weeks of miRNA treatment, leading to complete remission within 6 weeks. Microarray data revealed that 0.3% of genes were modulated in response to BSP knockdown. Upregulated genes included the endoplasmic reticulum stress genes ATF3 and DDIT3, the tumor suppressor gene EGR1, ID2 (related to breast epithelial differentiation), c-FOS and SERPINB2, whereas the metastasis associated genes CD44 and IL11 were downregulated. Also, activation of apoptotic pathways was demonstrated. These results implicate that intracellular BSP is essential for breast cancer skeletal metastasis and a target for treating these lesions.


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