Mesenchymal stem cells protect breast cancer cells through regulatory T cells: role of mesenchymal stem cell-derived TGF-beta.

Mesenchymal stem cells (MSCs) have been shown to support breast cancer growth. Because MSCs also increase the frequency of regulatory T cells (T(regs)), this study tested the hypothesis that human MSCs, via Tregs, protect breast cancer cells (BCCs) from immune clearance MSCs suppressed the proliferation of PBMCs when the latter were exposed to gamma-irradiated BCCs. Similarly, MSCs showed significant inhibition of PBMC migration toward BCCs and a corresponding decrease in CXCL12. MSCs also inhibited NK cell and CTL functions, which correlated with reduced numbers of CD8(+) and CD56(+) cells compared with parallel cultures without MSCs. The reduced NK and CTL activities correlated with a decrease in intracellular and secreted granzyme B. To explain these immunosuppressive findings, we compared T(reg) levels after coculture with MSCs and found an approximately 2-fold increase in T(regs), with associated decreases in antitumor Th1 cytokines and increases in Th2 cytokines. MSC-derived TGF-beta1 was largely responsible for the increase in T(regs) based on knockdown studies. In the presence of T(reg) depletion, PBMC proliferation and effector functions were partially restored. Together, these studies show an MSC-mediated increase in T(regs) in cocultures of PBMCs and BCCs. The results could be explained, in part, by the increase in Th2-type cytokines and MSC-generated TGF-beta1. These findings demonstrate immune protection by MSCs to BCCs. The reduction in immune cell proliferation and recruitment mediated by MSCs has implications for treatment of breast cancer with chemotherapy.

Mesenchymal stem cells in early entry of breast cancer into bone marrow.

BACKGROUND: An understanding of BC cell (BCC) entry into bone marrow (BM) at low tumor burden is limited when compared to highly metastatic events during heavy tumor burden. BCCs can achieve quiescence, without interfering with hematopoiesis. This occurs partly through the generation of gap junctions with BM stroma, located close to the endosteum. These events are partly mediated by the evolutionary conserved gene, Tac1. METHODOLOGY/PRINCIPAL FINDINGS: This study focuses on the role of mesenchymal stem cells (MSCs), Tac1, SDF-1 and CXCR4 in BCC entry into BM. The model is established in studies with low numbers of tumor cells, and focuses on cancer cells with low metastatic and invasion potential. This allowed us to recapitulate early event, and to study cancer cells with low invasive potential, even when they are part of larger numbers of highly metastatic cells. A novel migration assay showed a facilitating role of MSCs in BCC migration across BM endothelial cells. siRNA and ectopic expression studies showed a central role for Tac1 and secondary roles for SDF-1alpha and CXCR4. We also observed differences in the mechanisms between low invasive and highly metastatic cells. The in vitro studies were verified in xenogeneic mouse models that showed a preference for low invasive BCCs to BM, but comparable movement to lung and BM by highly metastatic BCCs. The expressions of Tac1 and production of SDF-1alpha were verified in primary BCCs from paired samples of BM aspirates and peripheral blood. CONCLUSIONS/SIGNIFICANCE: MSC facilitate BCC entry into BM, partly through Tac1-mediated regulation of SDF-1alpha and CXCR4. We propose a particular population of BCC with preference for BM could be isolated for characterization. This population might be the subset that enter BM at an early time period, and could be responsible for cancer resurgence and resistance to current therapies.

Stromal-derived factor-1alpha induces a non-canonical pathway to activate the endocrine-linked Tac1 gene in non-tumorigenic breast cells.

The chemokine Stromal-derived factor-1alpha (SDF-1alpha) interacts with seven transmembrane (TM) G-protein-coupled receptor (GPR), CXCR4. SDF-1alpha is linked to inflammation, chemoattraction, cancer metastasis, and hematopoiesis. Tachykinin (Tac1) peptides bind seven transmembrane (TM), GPR and are involved in tumor promotion. SDF-1alpha regulates Tac1 expression in non-tumorigenic breast cells through a bimodal pattern with repression at high levels through nuclear factor-kappa B (NFkappaB) activation. This study focuses on the mechanism of activation at low SDF-1alpha in MCF12A non-tumorigenic breast cells. Reporter gene assays with the 5' flanking region of Tac1 (exon 1 omitted) and co-transfection with the repressor of cAMP response element (CREB) (ICER), and transfection with the CRE sites mutated, verified critical roles for CRE sites in SDF-1alpha-mediated Tac1 activation. Western blots and functional assays with specific inhibitors indicated that SDF-1alpha phosphorylated CREB (P-CREB) via Galpha(i)2-PI3K-protein kinase C (PKC)zeta-p38-extracellular signal-regulated kinase (ERK) and no evidence of cAMP-PKA pathway. This observation is different from previous studies that reported CREB-phosphorylated PKA pathway in the activation of Tac1 in bone marrow stromal cells. This suggests cell specificity in Tac1 expression. In conclusion, this study reports on a non-canonical pathway in Tac1 activation by SDF-1alpha. This finding is significant, since Tac1 is relevant to breast cancer metastasis, to bone marrow where stromal cells have a significant facilitating function.

Nuclear factor-kappaB accounts for the repressor effects of high stromal cell-derived factor-1alpha levels on Tac1 expression in nontumorigenic breast cells.

Stromal cell-derived factor-1alpha (SDF-1alpha) is a CXC chemokine that interacts with CXCR4 receptor. Tac1 encodes peptides belonging to the tachykinins, including substance P. SDF-1alpha production is decreased in Tac1 knockdown breast cancer cells and is also reduced in these cancer cells following contact with bone marrow stroma when Tac1 expression is increased. Here, we report on the effects of relatively high and low SDF-1alpha levels on Tac1 expression in nontumorigenic breast cells MCF12A. Reporter gene assays, Northern analyses, and ELISA for substance P showed increased Tac1 expression at 20 and 50 ng/mL SDF-1alpha and reduced expression at 100 ng/mL. Omission of the untranslated region showed a dose-dependent effect of SDF-1alpha on reporter gene activity, suggesting that receptor desensitization cannot account for the suppressive effects at 100 ng/mL SDF-1alpha. Tac1 expression at high SDF-1alpha involves an intracellular signaling pathway that incorporates the activation of phosphatidylinositol 3-kinase-phosphoinositide-dependent kinase-1-AKT-nuclear factor-kappaB (NF-kappaB). The major repressive effect occurs via NF-kappaB located within exon 1. In summary, NF-kappaB is involved in the repression of Tac1 at higher levels of SDF-1alpha in MCF12A. These results are relevant to dysfunction of Tac1 in breast cancer cells and also provide insights on the behavior of breast cancer cells as they traverse across gradient changes of SDF-1alpha.

G-coupled protein receptors and breast cancer progression: potential drug targets.

Breast cancer remains a leading cause of death despite early screening and advances in medicine. Bone marrow metastasis often complicates the clinical picture by requiring more aggressive treatment and worsening long-term prognoses. Recent therapeutic targeting of hormonal receptors such as human epidermal growth factor receptor 2 and estrogen receptor has shown limited success in treating localized disease for those patients whose cancer cells are responsive. Although traditional approaches such as chemotherapy have demonstrated many successes, these agents fail to target quiescent cancer stem cells, which might have entered the bone marrow where they might be responsible for the quiescence population. Following years of clinical remission, these dormant cells could lead to secondary cancer resurgence. To date, little progress has been made in the development of targeted treatments for receptor negative and metastatic disease. In this review, we discuss the role of G-protein coupled receptors, including neurokinin-1, neurokinin-2 and chemokine receptor 4, as novel targets in the treatment of breast cancer.

Stromal derived growth factor-1alpha: another mediator in neural-emerging immune system through Tac1 expression in bone marrow stromal cells.

Stromal cell-derived growth factor-1alpha (SDF-1alpha) is a member of the CXC chemokines and interacts with the G protein, seven-transmembrane CXCR4 receptor. SDF-1alpha acts as a chemoattractant for immune and hemopoietic cells. The Tac1 gene encodes peptides belonging to the tachykinin family with substance P being the predominant member. Both SDF-1alpha and Tac1 peptides are relevant hemopoietic regulators. This study investigated the effects of SDF-1alpha on Tac1 expression in the major hemopoietic supporting cells, the bone marrow stroma, and addresses the consequence to hemopoiesis. Reporter gene assays with the 5' flanking region of Tac1 showed a bell-shaped effect of SDF-1alpha on luciferase activity with 20 ng/ml SDF-1alpha acting as stimulator, whereas 50 and 100 ng/ml SDF-1alpha acted as inhibitors. Gel shift assays and transfection with wild-type and mutant IkappaB indicate NF-kappaB as a mediator in the repressive effects at 50 and 100 ng/ml SDF-1alpha. Northern analyses and ELISA showed correlations among reporter gene activities, mRNA (beta-preprotachykinin I), and protein levels for substance P. Of relevance is the novel finding by long-term culture-initiating cell assays that showed an indirect effect of SDF-1alpha on hemopoiesis through substance P production. The results also showed neurokinin 1 and not neurokinin 2 as the relevant receptor. Another crucial finding is that substance P does not regulate the production of SDF-1alpha in stroma. The studies indicate that SDF-1alpha levels above baseline production in bone marrow stroma induce the production of substance P to stimulate hemopoiesis. Substance P, however, does not act as autocrine stimulator to induce the production of SDF-1alpha. This study adds SDF-1alpha as a mediator within the neural-immune-hemopoietic axis.

Oncogenic and metastatic properties of preprotachykinin-I and neurokinin-1 genes.

Breast cancer (BC) remains the cancer with highest mortality among women in the United States. Entry of BC cells (BCCs) in bone marrow (BM) leads to poor prognosis. This review discusses studies showing interactions between BCCs and BM stroma, consequently providing BCCs with advantages of survival within BM. Myc transcription factor is investigated as a link between the transforming properties of peptides derived from the preprotachykinin-I gene (PPT-I) and Neurokinin-1 (NK1) receptor. A co-culture method previously described to model early integration of BCC in BM is used to study timeline changes of PPT-I and TGF-beta using northern analyses and a bioassay, respectively. The results show changes of both genes in BCCs and BM stroma. Relevance of these changes to homeostasis in BM is discussed. Myc has been shown to link the expressions of TGF-beta1 and PPT-I in BCCs. We now show a role for Myc in the expression of NK1. PPT-I and the chemokine SDF-1alpha induce the expression of each other through an autocrine mechanism. Since a role for Myc in SDF-1alpha-PPT-I axis has not been studied, we speculate on this finding, based on the cell-homing property of SDF-1alpha. Since Myc could be oncogenic, it might be involved in the transforming properties of PPT-I and NK1 while SDF-1alpha could be involved in cell-homing of BCCs through the regulation of PPT-I. The findings are discussed in the context of other related reports.

SDF-1alpha regulation in breast cancer cells contacting bone marrow stroma is critical for normal hematopoiesis.

Breast cancer cells (BCCs) show preference for the bone marrow (BM). An animal model showed 2 populations of BCCs in the BM with regard to their cycling states. An in vitro model of early BC entry into BM showed normal hematopoiesis. Here, we show a critical role for BCC-derived SDF-1alpha in hematopoietic regulation. The studies used a coculture of BM stroma and BCCs (cell lines and stage II BCCs). Northern blots and enzyme-linked immunosorbent assay (ELISA) showed gradual decreases in SDF-1alpha production in BCCs as they contact BM stroma, indicating partial microenvironmental effects caused by stroma on the BCCs. SDF-1 knock-down BCCs and increased exogenous SDF-1alpha prevented contact inhibition between BCCs and BM stroma. Contact inhibition was restored with low SDF-1alpha levels. Long-term culture-initiating assays with CD34(+)/CD38(-)/Lin(-) showed normal hematopoiesis provided that SDF-1alpha levels were reduced in BCCs. Gap junctions (connexin-43 [CX-43]) were formed between BCCs and BM stroma, with concomitant interaction between CD34(+)/CD38(-)/Lin(-) and BM stroma but not with the neighboring BCCs. In summary, SDF-1alpha levels are reduced in BCCs that contact BM stroma. The low levels of SDF-1alpha in BCCs regulate interactions between BM stroma and hematopoietic progenitors, consequently facilitating normal hematopoiesis.

Peripheral monocytes and CD4+ cells are potential sources for increased circulating levels of TGF-beta and substance P in autoimmune myelofibrosis.

Myelofibrosis is an uncommon phenomenon associated with a variety of neoplastic and inflammatory processes. Although there is evidence that cytokines elaborated by clonal malignant hematopoietic cells are implicated in myelofibrosis in primary hematologic disorders, there has been little data to date on the pathophysiology of myelofibrosis in autoimmune disorders. Here we report a case of autoimmune myelofibrosis with pancytopenia. Peripheral blood monocytes and CD4-positive lymphocytes produced significantly elevated levels of transforming growth factor beta (TGF-beta) compared to similar cells from healthy volunteer controls. TGF-beta has been implicated in the pathogenesis of myelofibrosis associated with primary hematological malignancies. Furthermore, substance P, previously linked to myelofibrosis, was also detected in elevated levels in the patient's serum and correlated negatively with the levels of the patient's blood counts. These findings suggest a role for both TGF-beta and substance P in the pathophysiology of autoimmune myelofibrosis. This is the first report of deregulated production of TGF-beta by monocytes in the pathobiology of autoimmune myelofibrosis.

Stromal derived growth factor-1alpha as a beacon for stem cell homing in development and injury.

This review extrapolates the functions of SDF-1alpha and its receptor, CXCR4, as regulators of hematopoietic stem cells and discusses their potential roles in the development and regeneration of tissues. The discussion focuses on the repair of neural tissues while parallels are made with bone marrow hematopoietic stem cells. Overall, the organization links the basic biology of SDF-1alpha and CXCR4 to topics in medicine and show how any disease processes involving the SDF-1alpha-CXCR4 system could be central points in medicine. Discussions focused on potential therapies for SDF-1 and CXCR4 in clinical disorders. Breast and prostate cancers are selected as examples of solid tumors while leukemia is discussed as an example of hematological malignancies. Diffuse macular edema is discussed as potential therapy for a non-malignant disease.

An in vitro method to select malignant cells from surgical biopsies of breast cancer patients.

To date, breast cancer (BC) research is mainly studied with cell lines. These cells were passaged multiple times, acquiring phenotypes, additional mutations and epigenetic changes. These changes make the passaged cell lines different from the original malignancy. Thus cell lines, although useful as models could be improved with additional studies with primary BC. It is difficult to obtain malignant cells from breast tissues without contamination from surrounding healthy cells. Selection and expansion of malignant cells from surgical tissues have proved to be daunting tasks. This study describes a reliable and reproducible method for isolating and expanding malignant cells from surgical breast tissues. The method uses co-cultures with BM stroma to select for the cancer cells while the healthy cells undergo rapid cell death. Studies are described to show the cloning efficiencies and sensitivity of the method using surgical samples of varying sizes, different stages of BC, and samples from needle biopsies.

Tachykinins in the emerging immune system: relevance to bone marrow homeostasis and maintenance of hematopoietic stem cells.

The mammalian tachykinins mediate crosstalk within the neural-immune-hematopoietic axis. Hematopoiesis occurs in the adult bone marrow (BM) and it is described as the method by which the immune system is replenished by a finite number of hematopoietic stem cells (HSC). These cells are found in the BM close to the endosteum where the oxygen level is the lowest. The BM is also resident to mesenchymal stem cell (MSC). The functions of HSC depend on the MSC to generate the supporting stromal cells. This review discusses possible mechanisms by which the MSC act as the 'gatekeeper' in the BM and regulate immune cells in and out of the BM. The roles of the tachykinins are discussed in the context of homeostasis in the BM and as mediators of BM disruption. The involvement of the tachykinins within the BM microenvironment and the development of immune cells in the BM are explained.