ABSTRACT
Vascular endothelial cells are a critical component of the hematopoietic microenvironment that regulates blood cell production. Recent studies suggest the existence of functional cross-talk between hematologic malignancies and vascular endothelium. Here we show that human acute myeloid leukemia (AML) localizes to the vasculature in both patients and in a xenograft model. A significant number of vascular tissue-associated AML cells (V-AML) integrate into vasculature in vivo and can fuse with endothelial cells. V-AML cells acquire several endothelial cell-like characteristics, including the upregulation of CD105, a receptor associated with activated endothelium. Remarkably, endothelial-integrated V-AML shows an almost fourfold reduction in proliferative activity compared with non-vascular-associated AML. Primary AML cells can be induced to downregulate the expression of their hematopoietic markers in vitro and differentiate into phenotypically and functionally defined endothelial-like cells. After transplantation, these leukemia-derived endothelial cells are capable of giving rise to AML. These novel functional interactions between AML cells and normal endothelium along with the reversible endothelial cell potential of AML suggest that vascular endothelium may serve as a previously unrecognized reservoir for AML.
Subject(s)
Endothelium, Vascular/metabolism , Leukemia, Myeloid, Acute/physiopathology , Adult , Aged , Aged, 80 and over , Animals , Antigens, CD/metabolism , Cell Differentiation , Cell Line , Cell Survival , Cells, Cultured , Endoglin , Female , Humans , In Situ Hybridization, Fluorescence , Leukemia, Myeloid, Acute/metabolism , Male , Mice , Mice, Inbred NOD , Middle Aged , Neoplasm Transplantation , Phenotype , Receptors, Cell Surface/metabolism , Recurrence , Young AdultABSTRACT
MUC1 is a transmembrane mucin that was initially cloned from malignant mammary epithelial cells as a tumor antigen. More than 90% of human breast carcinomas overexpress MUC1. Numerous studies have demonstrated an interaction between MUC1 and other oncogenic proteins such as beta-catenin, erbB receptors and c-Src, but a functional role for MUC1 in transformation has not been identified. We previously reported the development of transgenic mice that overexpress human MUC1 in the mouse mammary gland (MMTV-MUC1). Analysis of these transgenic mice at an early age demonstrated the ability of MUC1 to potentiate EGF-dependent activation of MAP kinase signaling pathways in the lactating mammary gland. We now report that multiparous MMTV-MUC1 transgenic mice stochastically develop unifocal mammary gland carcinomas late in life. Molecular analysis of these tumors shows a tumor-specific coimmunoprecipitation between MUC1 and beta-catenin. Examination of the contralateral glands in MMTV-MUC1 transgenics demonstrates that the development of frank carcinomas is accompanied by a failure of multiparous glands to undergo postlactational involution. Furthermore, uniparous MMTV-MUC1 transgenic mice display decreased postlactational apoptosis, elevated whey acidic protein expression and aberrant pErk2 activation. These findings are the first to determine that MUC1 overexpression promotes in vivo transformation of the mammary gland.
