The initiation and progression of breast cancer is a complex process that is influenced by heterogeneous cell populations within the tumor microenvironment (TME). Although adipocytes have been shown to promote breast cancer development, adipocyte characteristics involved in this process remain poorly understood. In this study, we demonstrate enrichment of beige/brown adipose markers, contributed from the host as well as tumor cells, in the xenografts from breast cancer cell lines. In addition to uncoupling protein-1 (UCP1) that is exclusively expressed in beige/brown adipocytes, gene expression for classical brown (MYF5, EVA1 and OPLAH), as well as beige (CD137/TNFRSF9 and TBX1) adipocyte markers, were also elevated in the xenografts. Enrichment of beige/brown characteristics in the xenografts was independent of the site of implantation of the breast tumor cells. Early stages of xenografts showed an expansion of a subset of mammary cancer stem cells (MCSCs) that expressed PRDM16, a master regulator of brown adipocyte differentiation. Depletion of UCP1+ or Myf5+ cells significantly reduced tumor development. There was increased COX-2 (MT-CO2) expression, which is known to stimulate formation of beige adipocytes in early xenografts and treatment with a COX-2 inhibitor (SC236) reduced tumor growth. By contrast, treatment with factors that induce brown adipocyte differentiation in vitro led to larger tumors in vivo. A panel of xenografts derived from established breast tumor cells as well as patient-tumor tissues were generated that expressed key brown adipose tissue (BAT)-related markers and contained cells that morphologically resembled brown adipocytes. Implications This is the first report demonstrating that beige /brown adipocyte characteristics could play an important role in breast tumor development and suggest a potential target for therapeutic drug design.

BackgroundBreast cancer is a complex heterogeneous disease where many distinct subtypes are found. Younger African American (AA) women often present themselves with aggressive form of breast cancer with unique biology which is very difficult to treat. Better understanding the biology of AA breast tumors could lead to development of effective treatment strategies. Our previous studies indicate that AA but not Caucasian (CA) triple negative (TN) breast cancer cells were sensitive to nitrosative stress-induced cell death. In this study, we elucidate possible mechanisms that contribute to nitric oxide (NO)-induced apoptosis in AA TN breast cancer cells.MethodsBreast cancer cells were treated with various concentrations of long-acting NO donor, DETA-NONOate and cell viability was determined by trypan blue exclusion assay. Apoptosis was determined by TUNEL and caspase 3 activity as well as changes in mitochondrial membrane potential. Caspase 3 and Bax cleavage, levels of Cu/Zn superoxide dismutase (SOD) and Mn SOD was assessed by immunoblot analysis. Inhibition of Bax cleavage by Calpain inhibitor, and levels of reactive oxygen species (ROS) as well as SOD activity was measured in NO-induced apoptosis. In vitro and in vivo effect of NO treatment on mammary cancer stem cells (MCSCs) was assessed.Results and discussionNO induced mitocondria-mediated apoptosis in all AA but not in CA TN breast cancer cells. We found significant TUNEL-positive cells, cleavage of Bax and caspase-3 activation as well as depolarization mitochondrial membrane potential only in AA TN breast cancer cells exposed to NO. Inhibition of Bax cleavage and quenching of ROS partially inhibited NO-induced apoptosis in AA TN cells. Increase in ROS coincided with reduction in SOD activity in AA TN breast cancer cells. Furthermore, NO treatment of AA TN breast cancer cells dramatically reduced aldehyde dehydrogenase1 (ALDH1) expressing MCSCs and xenograft formation but not in breast cancer cells from CA origin.ConclusionsEthnic differences in breast tumors dictate a need for tailoring treatment options more suited to the unique biology of the disease.

<p>Images of xenografts, osmium stained sections, quantitation of lipids and immunohistochemistry.</p>

<p>Human breast tumors used in this study were according to the stage/grade</p>

<p>Images of xenografts, osmium stained sections, quantitation of lipids and immunohistochemistry.</p>