Activation of autophagy in mesenchymal stem cells provides tumor stromal support.

Recent studies have implicated multipotential mesenchymal stem cells (MSCs) as an aid to breast cancer cell proliferation and metastasis, partly as a result of the MSCs secretome. As the tumor gets beyond 2 mm in diameter, the stromal cells could undergo starvation due to the lack of sufficient nutrients in solid tumor microenvironment. In this study, we investigated the survival mechanisms used by stressed stromal cells in breast cancers. We used serum-deprived mesenchymal stem cells (SD-MSCs) and MCF-7 breast cancer cells as model system with a hypothesis that stromal cells in the nutrient-deprived core utilize survival mechanisms for supporting surrounding cells. We tested this hypothesis using in vivo tumor xenografts in immunodeficient mice, which indicated that SD-MSCs supported MCF-7 tumor growth by protection from apoptosis. Histochemical assays showed that SD-MSCs-injected tumors exhibited higher cellularity, decreased apoptosis and decreased differentiation. Beclin-1 staining indicated autophagic areas surrounded by actively proliferating cells. Furthermore, in vitro studies demonstrate that SD-MSCs survive using autophagy and secrete paracrine factors that support tumor cells following nutrient/serum deprivation. Western blot and immunocytochemistry analysis of SD-MSCs demonstrated upregulation and perinuclear relocation of autophagy key regulators such as beclin-1, ATG10, ATG12, MAP-LC3 and lysosomes. Electron microscopic analysis detected a time-dependent increase in autophagosome formation and HDAC6 activity assays indicated the upregulation of autophagy. Taken together, these data suggest that under nutrient-deprived conditions that can occur in solid tumors, stromal cells utilize autophagy for survival and also secrete anti-apoptotic factors that can facilitate solid tumor survival and growth.

[1]  M. Lacey,et al.  Adult human mesenchymal stem cells enhance breast tumorigenesis and promote hormone independence , 2010, Breast Cancer Research and Treatment.

[2]  K. Dalby,et al.  Targeting the pro-death and pro-survival functions of autophagy as novel therapeutic strategies in cancer , 2010, Autophagy.

[3]  J. Taylor,et al.  HDAC6 controls autophagosome maturation essential for ubiquitin‐selective quality‐control autophagy , 2010, The EMBO journal.

[4]  M. Dyer,et al.  Targeting autophagy potentiates tyrosine kinase inhibitor-induced cell death in Philadelphia chromosome-positive cells, including primary CML stem cells. , 2009, The Journal of clinical investigation.

[5]  P. Schoenlein,et al.  Autophagy facilitates the progression of ERα-positive breast cancer cells to antiestrogen resistance , 2009, Autophagy.

[6]  Russell G. Jones,et al.  Tumor suppressors and cell metabolism: a recipe for cancer growth. , 2009, Genes & development.

[7]  R. Pochampally,et al.  Epigenetic Reprogramming of IGF1 and Leptin Genes by Serum Deprivation in Multipotential Mesenchymal Stromal Cells , 2009, Stem cells.

[8]  W. Bursch,et al.  Cell death and autophagy: cytokines, drugs, and nutritional factors. , 2008, Toxicology.

[9]  H. Hsu,et al.  Regulation of estrogenic effects by beclin 1 in breast cancer cells. , 2008, Cancer research.

[10]  J. Stagg Mesenchymal Stem Cells in Cancer , 2008, Stem Cell Reviews.

[11]  Minoru Yoshida,et al.  HDAC6 a new cellular stress surveillance factor , 2008, Cell cycle.

[12]  Ross Tubo,et al.  Mesenchymal stem cells within tumour stroma promote breast cancer metastasis , 2007, Nature.

[13]  R. Pochampally,et al.  Angiogenic Effects of Human Multipotent Stromal Cell Conditioned Medium Activate the PI3K‐Akt Pathway in Hypoxic Endothelial Cells to Inhibit Apoptosis, Increase Survival, and Stimulate Angiogenesis , 2007, Stem cells.

[14]  L. Avery,et al.  Dual roles of autophagy in the survival of Caenorhabditis elegans during starvation. , 2007, Genes & development.

[15]  D. Klionsky,et al.  Autophagy and Human Disease , 2007, Cell cycle.

[16]  Sharon Y. R. Dent,et al.  HDAC6 modulates cell motility by altering the acetylation level of cortactin. , 2007, Molecular cell.

[17]  J. Tao,et al.  Bone marrow stromal cells prevent apoptosis of lymphoma cells by upregulation of anti-apoptotic proteins associated with activation of NF-κB (RelB/p52) in non-Hodgkin's lymphoma cells , 2007, Leukemia.

[18]  Darwin J. Prockop,et al.  Short-Term Exposure of Multipotent Stromal Cells to Low Oxygen Increases Their Expression of CX3CR1 and CXCR4 and Their Engraftment In Vivo , 2007, PloS one.

[19]  Yoshiharu Kawaguchi,et al.  HDAC6 deacetylation of tubulin modulates dynamics of cellular adhesions , 2007, Journal of Cell Science.

[20]  K. Tarte,et al.  Human mesenchymal stem cells isolated from bone marrow and lymphoid organs support tumor B-cell growth: role of stromal cells in follicular lymphoma pathogenesis. , 2007, Blood.

[21]  V. Schmithorst,et al.  Cerebral ischemia-hypoxia induces intravascular coagulation and autophagy. , 2006, The American journal of pathology.

[22]  C. Isidoro,et al.  Autophagy‐dependent cell survival and cell death in an autosomal dominant familial neurohypophyseal diabetes insipidus in vitro model , 2005, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[23]  R. Pochampally,et al.  Serum deprivation of human marrow stromal cells (hMSCs) selects for a subpopulation of early progenitor cells with enhanced expression of OCT-4 and other embryonic genes. , 2004, Blood.

[24]  W. Dalton,et al.  Bone marrow stromal-derived soluble factors and direct cell contact contribute to de novo drug resistance of myeloma cells by distinct mechanisms , 2003, Leukemia.

[25]  G. Fuertes,et al.  Role of proteasomes in the degradation of short-lived proteins in human fibroblasts under various growth conditions. , 2003, The international journal of biochemistry & cell biology.

[26]  Xiao-Fan Wang,et al.  HDAC6 is a microtubule-associated deacetylase , 2002, Nature.

[27]  E. Kubista,et al.  Influences of stroma-derived growth factors on the cytokine expression pattern of human breast cancer cell lines , 2002, Archives of Gynecology and Obstetrics.

[28]  Y. Uchiyama Autophagic cell death and its execution by lysosomal cathepsins. , 2001, Archives of histology and cytology.

[29]  J. Dewitte,et al.  Comet assay and early apoptosis. , 2001, Mutation research.

[30]  K. Öllinger,et al.  Nutrient Deprivation of Cultured Rat Hepatocytes Increases the Desferrioxamine-available Iron Pool and Augments the Sensitivity to Hydrogen Peroxide* , 1997, The Journal of Biological Chemistry.

[31]  M. Kimmel,et al.  Conflict of interest statement. None declared. , 2010 .

[32]  Hoyun Lee,et al.  Chloroquine and its analogs: a new promise of an old drug for effective and safe cancer therapies. , 2009, European journal of pharmacology.

[33]  E. Morselli,et al.  Control of autophagy by oncogenes and tumor suppressor genes , 2009, Cell Death and Differentiation.

[34]  J. Tao,et al.  Bone marrow stromal cells prevent apoptosis of lymphoma cells by upregulation of anti-apoptotic proteins associated with activation of NF-kappaB (RelB/p52) in non-Hodgkin's lymphoma cells. , 2007, Leukemia.

[35]  D. Wallwiener,et al.  Influence of stroma-derived growth factors on the estradiol-stimulated proliferation of human breast cancer cells. , 2004, European journal of gynaecological oncology.

[36]  M. Konopleva,et al.  Stromal cells prevent apoptosis of AML cells by up-regulation of anti-apoptotic proteins , 2002, Leukemia.

[37]  D. Yee,et al.  The insulin-like growth factors, their receptors, and their binding proteins in human breast cancer. , 1991, Cancer treatment and research.

[38]  D. Yee,et al.  Regulation of human breast cancer by secreted growth factors. , 1989, Acta oncologica.