[Show abstract][Hide abstract] ABSTRACT: The stromal microenvironment and particularly the macrophage component of primary tumors influence their malignant potential. However, at the metastatic site the role of these cells and their mechanism of actions for establishment and growth of metastases remain largely unknown.
Using animal models of breast cancer metastasis, we show that a population of host macrophages displaying a distinct phenotype is recruited to extravasating pulmonary metastatic cells regardless of species of origin. Ablation of this macrophage population through three independent means (genetic and chemical) showed that these macrophages are required for efficient metastatic seeding and growth. Importantly, even after metastatic growth is established, ablation of this macrophage population inhibited subsequent growth. Furthermore, imaging of intact lungs revealed that macrophages are required for efficient tumor cell extravasation.
These data indicate a direct enhancement of metastatic growth by macrophages through their effects on tumor cell extravasation, survival and subsequent growth and identifies these cells as a new therapeutic target for treatment of metastatic disease.
[Show abstract][Hide abstract] ABSTRACT: Genetic depletion of macrophages in Polyoma Middle T oncoprotein (PyMT)-induced mammary tumors in mice delayed the angiogenic switch and the progression to malignancy. To determine whether vascular endothelial growth factor A (VEGF-A) produced by tumor-associated macrophages regulated the onset of the angiogenic switch, a genetic approach was used to restore expression of VEGF-A into tumors at the benign stages. This stimulated formation of a high-density vessel network and in macrophage-depleted mice, was followed by accelerated tumor progression. The expression of VEGF-A led to a massive infiltration into the tumor of leukocytes that were mostly macrophages. This study suggests that macrophage-produced VEGF regulates malignant progression through stimulating tumor angiogenesis, leukocytic infiltration and tumor cell invasion.
[Show abstract][Hide abstract] ABSTRACT: The development of a tumor vasculature or access to the host vasculature is a crucial step for the survival and metastasis of malignant tumors. Although therapeutic strategies attempting to inhibit this step during tumor development are being developed, the biological regulation of this process is still largely unknown. Using a transgenic mouse susceptible to mammary cancer, PyMT mice, we have characterized the development of the vasculature in mammary tumors during their progression to malignancy. We show that the onset of the angiogenic switch, identified as the formation of a high-density vessel network, is closely associated with the transition to malignancy. More importantly, both the angiogenic switch and the progression to malignancy are regulated by infiltrated macrophages in the primary mammary tumors. Inhibition of the macrophage infiltration into the tumor delayed the angiogenic switch and malignant transition whereas genetic restoration of the macrophage population specifically in these tumors rescued the vessel phenotype. Furthermore, premature induction of macrophage infiltration into premalignant lesions promoted an early onset of the angiogenic switch independent of tumor progression. Taken together, this study shows that tumor-associated macrophages play a key role in promoting tumor angiogenesis, an essential step in the tumor progression to malignancy.
[Show abstract][Hide abstract] ABSTRACT: In mice, the uterus becomes transiently receptive to the hatched blastocyst on the day of implantation to allow its attachment to the luminal epithelium and subsequent invasion into the uterus. This uterine preparation for implantation is regulated by estradiol-17beta and progesterone, acting through their transcription factor receptors. Using ovariectomized mice treated with physiological regimens of these hormones, combined with methods to isolate RNA specifically from the uterine epithelium followed by transcriptome analysis on cDNA microarrays, 222 genes whose transcript abundance was specifically increased by estradiol-17beta and progesterone treatment were identified. Gene ontology analysis revealed an emphasis on genes involved with immune responses, extracellular matrix metabolism, and cell-to-cell communication. In situ hybridization to uterine sections isolated through the first 6 d of pregnancy identified novel sets of genes such as Bach, Myd88, Cd14, Isg20, and Lrp2 whose expression was restricted to the uterine epithelium during the implantation window. Particularly notable was the expression of the mRNA for members of the signaling pathway from the Toll-like receptors to its downstream targets such as Irg-1. The identification of these genes showing a cell type hormonally regulated pattern of expression in the uterus suggests novel functions for them during implantation.
[Show abstract][Hide abstract] ABSTRACT: In the uterus, progesterone (P4) acts early in G1 as a physiological inhibitor of estradiol-17beta (E2)-induced epithelial cell proliferation. Gene expression profiling of uterine epithelial cell RNA isolated 3 h after hormonal treatment of ovariectomized mice revealed the co-coordinate down-regulation by P4 of >20 genes whose functions are associated with DNA replication. This group included all of the minichromosome maintenance (MCM) proteins that are required for DNA replication licensing. E2 regulated loading of these MCM proteins onto chromatin in parallel with its induction of DNA synthesis. E2 caused this chromatin loading by retention of MCM proteins in the nucleus and through the induction of the loading factor Cdt1, which is necessary for the MCM heterohexamer to bind to the origin of DNA replication. P4 dramatically reduced the binding of the MCMs to chromatin by a number of mechanisms. First, MCM mRNA and protein abundance was down-regulated. Second, P4 inhibited the E2 induction of Cdt1. Third, P4 treatment sequestered the normally nuclear MCM proteins into the cytoplasm. This reduced MCM binding resulted in the complete inhibition of E2-induced DNA synthesis by P4. These data reveal mechanisms not only for female sex steroid hormone action but also in the regulation of DNA replication licensing.
Preview · Article · Oct 2006 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The mammalian cell cycle is regulated by the cyclin/cyclin-dependent kinase (CDK) phosphorylation of the retinoblastoma (pRB) family of proteins. Cyclin D1 with its CDK4/6 partners initiates the cell cycle and acts as the link between extracellular signals and the cell cycle machinery. Estradiol-17beta (E2) stimulates uterine epithelial cell proliferation, a process that is completely inhibited by pretreatment with progesterone (P4). Previously, we identified cyclin D1 localization as a key point of regulation in these cells with E2 causing its nuclear accumulation and P4 retaining it in the cytoplasm with the resultant inhibition of pRB phosphorylation. Here we show that E2 stimulates phosphoinositide 3-kinase to activate phosphokinase B/AKT to effect an inhibitory phosphorylation of glycogen synthase kinase (GSK-3beta). This pathway is suppressed by P4. Inhibition of the GSK-3beta activity in P4-treated uteri by the specific inhibitor, LiCl, reversed the nuclear accumulation of cyclin D1 and in doing so, caused pRB phosphorylation and the induction of downstream genes, proliferating cell nuclear antigen and Ki67. Conversely, inhibition of phosphoinositide 3 kinase by LY294002 or Wortmanin reversed the E2-induced GSK-3beta Ser9 inhibitory phosphorylation and blocked nuclear accumulation of cyclin D1. These data show the reciprocal actions of E2 and P4 on the phosphoinositide 3-kinase through to the GSK-3beta pathway that in turn regulates cyclin D1 localization and cell cycle progression. These data reveal a novel signaling pathway that links E2 and P4 action to growth factor-mediated signaling in the uterus.
No preview · Article · Sep 2005 · Molecular Endocrinology