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Cell Cycle 10:18, 3198-3207; September 15, 2011; © 2011 Landes Bioscience
Mesenchymal stem cell-secreted soluble signaling molecules potentiate tumor growth Wei Zhu,1 Ling Huang,1 Yahong Li,1 Hui Qian,1 Xiuhong Shan,2 Yongmin Yan,1 Fei Mao,1 Xiaosheng Wu3,* and Wen-Rong Xu1,4,* School of Medical Sciences and Laboratory Medicine; 2Department of Radiology; The Affiliated Renmin Hospital; 4Department of Clinical Laboratory Medicine; The Affiliated Hospital; Jiangsu University; Zhenjiang, China; 3Department of Immunology; Mayo Clinic; College of Medicine; Rochester, MN USA
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Key words: mesenchymal stem cell, soluble signaling molecules, tumor growth, mechanism, reprogramming, tumor-associated fibroblast, angiogenesis Abbreviations: MSC, mesenchymal stem cell; hMSC-CM, human mesenchymal stem cells conditioned-medium; TAF, tumor-associated fibroblast
In previous studies, we and others have shown that bone marrow mesenchymal stem cells (MSCs) are recruited to sites of growing tumors and promote tumor growth in mouse xenograft models, suggesting that interactions between MSCs and tumor cells may play an important role in this process. However, the exact mechanism remains unclear. In the present study, we investigated whether the physical presence or the continuous presence of MSCs is required for enhanced tumor growth, and we found that pretreatment of tumor cells SGC-7901 with a single dose of human MSC-conditioned medium (hMSC-CM) in vitro is sufficient to potentiate tumor growth comparable to the effect of MSC co-injection in vivo in mouse xenograft models. We further showed that significant tumor modifying activity is present in post-ultracentrifigation soluble fraction. Biochemical analysis suggests that hMSC-CM induces the expression of VEGF of tumor cells as well as the activation of RhoA-GTPase and ERK1/2. Furthermore, hMSC-CM-enhanced tumor growth is sustainable in serial transplantation, suggesting that MSC-secreted factors have profound effects on “reprogramming” of tumor growth. Our data provide new insights into the way in which MSCs modify tumor growth and offer a new and exciting opportunity to develop effective therapeutics for intercepting tumor progression.
©201 1L andesBi os c i enc e. Donotdi s t r i but e.
Introduction Mesenchymal stem cells (MSCs) are a heterogeneous subset of pluripotent adult progenitor cells derived from in vitro culture of bone marrow stromal cells. MSCs are necessary for the maintenance and regeneration of various types of connective tissues, including adipose tissue, bone, cartilage and muscle, and in this regard, it is believed that MSCs are present in various tissues and organs in vivo. Furthermore, recent studies have also shown that newly injected MSCs often relocalize to the bone marrow and to tissues/organs with inflammation as well as to sites of growing tumors, suggesting that MSCs play important roles in the modulation of immunity as well as tumor growth besides their functions in tissue repair.1-5 For a long time, it was thought that cancer is autonomous and self-sufficient, but this view has been challenged by recent studies showing that tumor growth, progression and metastasis are critically dependent on tumor-nurturing stroma. The stroma mainly consists of mesenchymal cell types, which are fibroblasts and myofibroblasts or tumor-associated fibroblasts (TAFs) which can be derived from MSCs.6-9 The stromal cells are mobilized into the circulation and incorporated into the tumor microenvironment.10-12 There has been speculation that MSCs may provide
tumor cells with continuous structural, functional and logistic support for rapid tumor growth, possibly through (1) the formation of tumor-nurturing niches, (2) the activation of angiogenesis by direct production of pro-angiogenic factors, (3) the modulation of tumor immune responses in the host and (4) the production of tumor-potentiating factors leading to enhanced tumor growth transiently or sustainably. Previously, we and others have shown that MSCs can significantly enhance the growth of tumor xenografts in mouse models regardless of whether the MSCs were co-injected in a cell mix with tumor cells or were injected separately at different anatomic sites from the site of tumor injection.13-17 It seems conceivable that MSCs may physically interact with tumor cells, possibly through the formation of a tumor-fostering structural milieu or through the secretion of tumor-promoting molecules at a significant local concentration. In this study, we aimed to address some of these questions by examining the effect of treatment of tumor cells with hMSCconditioned medium (hMSC-CM) on the development of tumor grafts. We observed that pretreatment of SGC-7901 tumor cells with a single dose of hMSC-CM in vitro is sufficient to support a robust tumor engraftment comparable to that of MSC coinjection in vivo. We also found that hMSC-CM potentiates tumor
*Correspondence to: Xiaosheng Wu or Wen-Rong Xu; Email:
[email protected] or
[email protected] Submitted: 05/10/11; Revised: 08/04/11; Accepted: 08/04/11 DOI: 10.4161/cc.10.18.17638 3198
Cell Cycle
Volume 10 Issue 18
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©201 1L andesBi os c i enc e. Donotdi s t r i but e. Figure 1. Pretreatment of tumor cells with hMSC-CM in vitro results in increased tumor growth in vivo. (A and B) The development of tumor xenografts after subcutaneous injection with untreated SGC-7901 cells, mixed SGC-7901 cells and hMSCs or hMSC-CM-treated SGC-7901 cells. (C) Tumor volume was evaluated in mice co-injected with mixed SGC-7901 cells and hMSCs, hMSC-CM-treated SGC-7901 cells, ultracentrifuged hMSC-CM-treated SGC-7901 cells or SGC-7901 cells alone. (D) Tumor volume was evaluated in secondary xenograft tumors from mice injected with hMSC-CM-treated SGC-7901 cells, ultracentrifuged hMSC-CM-treated SGC-7901 cells or untreated SGC-7901 cells alone.
cell growth, at least in part, through the activation of VEFG expression as well as the activation of RhoA GTPase and ERK1/2. Results Treatment of tumor cells with hMSC-CM significantly enhances tumor growth in mouse xenograft models. Whether MSCs promote tumor growth in mouse xenograft models by directly providing tumor-nurturing structural support, by secreting soluble tumor growth-promoting factors or through other mechanisms remains unknown. In an effort to answer these questions, we first treated SGC-7901 tumor cells with hMSC (characterized in Fig. S1 by their surface marker expression)conditioned medium (hMSC-CM) for 48 h, followed by subcutaneous injection of untreated SGC-7901 tumor cells alone, hMSC-CM-treated SGC-7901 tumor cells alone or untreated tumor cells mixed with hMSC into BALB/c-nu/nu mice. We
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found only two of six mice injected with untreated SGC-7901 cells alone developed small tumors 28 d after injection, while all six mice co-injected with SGC-7901 cells and hMSCs developed measurable tumors 8 d after injection. Strikingly, we found that all six mice injected with SGC-7901 cells pretreated with hMSC‑CM also developed measurable tumors by day 11, lagging only 3 d behind the co-injected mice (Fig. 1A). The mean tumor sizes in both the group injected with SGC-7901 cells pretreated with hMSC-CM and the group co-injected with hMSCs was greater than 300 mm3 at 25 d after injection, in sharp contrast to that in the control group (
