Abstract
BackgroundCancer stem-like cells are proposed to sustain solid tumors by virtue of their capacity for self-renewal and differentiation to cells that comprise the bulk of the tumor, and have been identified for a variety of cancers based on characteristic clonal morphologies and patterns of marker gene expression.MethodsSingle cell cloning and spheroid culture studies were used to identify a population of cancer stem-like cells in the androgen-independent human prostate cancer cell line PC3.ResultsWe demonstrate that, under standard culture conditions, ~10% of PC3 cells form holoclones with cancer stem cell characteristics. These holoclones display high self-renewal capability in spheroid formation assays under low attachment and serum-free culture conditions, retain their holoclone morphology when passaged at high cell density, exhibit moderate drug resistance, and show high tumorigenicity in scid immunodeficient mice. PC3 holoclones readily form spheres, and PC3-derived spheres yield a high percentage of holoclones, further supporting their cancer stem cell-like nature. We identified one gene, FAM65B, whose expression is consistently up regulated in PC3 holoclones compared to paraclones, the major cell morphology in the parental PC3 cell population, and two genes, MFI2 and LEF1, that are consistently down regulated. This molecular profile, FAM65Bhigh/MFI2low/LEF1low, also characterizes spheres generated from parental PC3 cells. The PC3 holoclones did not show significant enriched expression of the putative prostate cancer stem cell markers CD44 and integrin α2β1. PC3 tumors seeded with holoclones showed dramatic down regulation of FAM65B and dramatic up regulation of MFI2 and LEF1, and unexpectedly, a marked increase in tumor vascularity compared to parental PC3 tumors, suggesting a role of cancer stem cells in tumor angiogenesis.ConclusionsThese findings support the proposal that PC3 tumors are sustained by a small number of tumor-initiating cells with stem-like characteristics, including strong self-renewal and pro-angiogenic capability and marked by the expression pattern FAM65Bhigh/MFI2low/LEF1low. These markers may serve as targets for therapies designed to eliminate cancer stem cell populations associated with aggressive, androgen-independent prostate tumors such as PC3.
Highlights
Cancer stem-like cells are proposed to sustain solid tumors by virtue of their capacity for self-renewal and differentiation to cells that comprise the bulk of the tumor, and have been identified for a variety of cancers based on characteristic clonal morphologies and patterns of marker gene expression
We find that PC3 holoclones are characterized by the novel expression pattern FAM65Bhigh/MFI2low/LEF1low, and that this molecular profile is reproduced in PC3 spheres, suggesting this expression pattern is a marker for tumor-initiating PC3 cells with cancer stem-like cells (CSCs) characteristics
Growth rates were similar for all three clone types and for parental PC3 cells when the cells were seeded at high cell density, whereas several of the paraclones grew at a slower rate when seeded at low density (Additional file 3), indicating a need for cell-cell communication for efficient growth in culture
Summary
Cancer stem-like cells are proposed to sustain solid tumors by virtue of their capacity for self-renewal and differentiation to cells that comprise the bulk of the tumor, and have been identified for a variety of cancers based on characteristic clonal morphologies and patterns of marker gene expression. Solid tumors are proposed to be sustained by a limited number of cancer stem-like cells (CSCs) with high potential for proliferation and the capacity to differentiate into cells that comprise the bulk of the tumor [1]. CSCs express characteristic patterns of cell surface markers. These markers include CD34+CD38- in the case of acute myeloid leukemia, CD44+CD24lowESA- in breast and pancreatic cancer, CD133+ in brain tumors and colon cancer, CD44+ in head and neck cancer and EpCAMhighCD44+CD166+ in colorectal cancer [7,8,9,10,11,12,13,14,15]. Several CSC markers mark normal adult stem cell populations [16,17,18,19,20], supporting the stem cell-like nature of CSCs
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