No abstract

Although metastasis is the leading cause of cancer-related death, it is not clear why some patients with localized cancer develop metastatic disease after complete resection of their primary tumor. Such relapses have been attributed to tumor cells that disseminate early and remain dormant for prolonged periods of time; however, little is known about the control of these disseminated tumor cells. Here, we have used a spontaneous mouse model of melanoma to investigate tumor cell dissemination and immune control of metastatic outgrowth. Tumor cells were found to disseminate throughout the body early in development of the primary tumor, even before it became clinically detectable. The disseminated tumor cells remained dormant for varying periods of time depending on the tissue, resulting in staggered metastatic outgrowth. Dormancy in the lung was associated with reduced proliferation of the disseminated tumor cells relative to the primary tumor. This was mediated, at least in part, by cytostatic CD8 + T cells, since depletion of these cells resulted in faster outgrowth of visceral metastases. Our findings predict that immune responses favoring dormancy of disseminated tumor cells, which we propose to be the seed of subsequent macroscopic metastases, are essential for prolonging the survival of early stage cancer patients and suggest that therapeutic strategies designed to reinforce such immune responses may produce marked benefits in these patients. IntroductionMetastatic disease is the major cause of death by cancer (1, 2). Metastasis is a complex multistage process that requires cancer cells within the primary tumor to invade the local tissue and enter the blood or lymphatic vessels. Tumor cells need to survive in the circulation and migrate across vessel walls in order to colonize new sites and grow to form secondary tumors (3). The traditional view has been that tumor cell dissemination occurs late in cancer development (4-6); however, this notion has recently been challenged. Several expression profiling studies (7-10) suggest that the propensity of cancer cells to metastasize is acquired relatively early during tumor progression (reviewed in ref. 11). In addition, examination of bone marrow from early stage cancer patients without overt metastases (reviewed in refs. 12 and 13) and tumorbearing mice (14) revealed that disseminated tumor cells (DTCs) are present at much earlier time points than expected. We now need to understand the significance of these DTCs. Specifically, we must determine how early DTCs contribute to clinically relevant macrometastases and identify the mechanisms involved in the development, maintenance, and breakdown of dormancy.Transplanted tumor models in rodents are often used to study metastasis, with most of our current knowledge of cancer cell dissemination being drawn from xenograft models. However, these models often fail to recapitulate the gradual process of tumorigenesis that is observed in humans, and, in the case of immuno-

Iron homeostasis requires subtle control systems, as iron is both essential and toxic. In Aspergillus nidulans, iron represses iron acquisition via the GATA factor SreA, and induces iron-dependent pathways at the transcriptional level, by a so far unknown mechanism. Here, we demonstrate that iron-dependent pathways (e.g., heme biosynthesis) are repressed during iron-depleted conditions by physical interaction of HapX with the CCAAT-binding core complex (CBC). Proteome analysis identified putative HapX targets. Mutual transcriptional control between hapX and sreA and synthetic lethality resulting from deletion of both regulatory genes indicate a tight interplay of these control systems. Expression of genes encoding CBC subunits was not influenced by iron availability, and their deletion was deleterious during iron-depleted and iron-replete conditions. Expression of hapX was repressed by iron and its deletion was deleterious during irondepleted conditions only. These data indicate that the CBC has a general role and that HapX function is confined to iron-depleted conditions. Remarkably, CBC-mediated regulation has an inverse impact on the expression of the same gene set in A. nidulans, compared with Saccharomyces cerevisae.

NK cells use a variety of receptors to detect abnormal cells, including

Tumor microenvironment is characterized by chronic inflammation represented by infiltrating leukocytes and soluble mediators, which lead to a local and systemic immunosuppression associated with cancer progression. Here, we used the ret transgenic spontaneous murine melanoma model that mimics human melanoma. Skin tumors and metastatic lymph nodes showed increased levels of inflammatory factors such as IL-1β, GM-CSF, and IFN-γ, which correlated with tumor progression. Moreover, Gr1 + CD11b + myeloidderived suppressor cells (MDSCs), known to inhibit tumor reactive T cells, were enriched in melanoma lesions and lymphatic organs during tumor progression. MDSC infiltration was associated with a strong TCR ζ-chain down-regulation in all T cells. Coculturing normal splenocytes with tumor-derived MDSC induced a decreased T-cell proliferation and ζ-chain expression, verifying the MDSC immunosuppressive function and suggesting that the tumor inflammatory microenvironment supports MDSC recruitment and immunosuppressive activity. Indeed, upon manipulation of the melanoma microenvironment with the phosphodiesterase-5 inhibitor sildenafil, we observed reduced levels of numerous inflammatory mediators (e.g., IL-1β, IL-6, VEGF, S100A9) in association with decreased MDSC amounts and immunosuppressive function, indicating an antiinflammatory effect of sildenafil. This led to a partial restoration of ζ-chain expression in T cells and to a significantly increased survival of tumor-bearing mice. CD8 T-cell depletion resulted in an abrogation of sildenafil beneficial outcome, suggesting the involvement of MDSC and CD8 T cells in the observed therapeutic effects. Our data imply that inhibition of chronic inflammation in the tumor microenvironment should be applied in conjunction with melanoma immunotherapies to increase their efficacy.therapy | cytokines

In order to metastasize, cancer cells need to acquire a motile phenotype. Previously, development of this phenotype was thought to rely on the acquisition of selected, random mutations and thus would occur late in cancer progression. However, recent studies show that cancer cells disseminate early, implying the existence of a different, faster route to the metastatic motile phenotype. Using a spontaneous murine model of melanoma, we show that a subset of bone marrow-derived immune cells (myeloid-derived suppressor cells or MDSC) preferentially infiltrates the primary tumor and actively promotes cancer cell dissemination by inducing epithelial-mesenchymal transition (EMT). CXCL5 is the main chemokine attracting MDSC to the primary tumor. In vitro assay using purified MDSC showed that TGF-β, EGF, and HGF signaling pathways are all used by MDSC to induce EMT in cancer cells. These findings explain how cancer cells acquire a motile phenotype so early and provide a mechanistic explanation for the long recognized link between inflammation and cancer progression.

We report here on a novel metallothionein-I (MT)/ret transgenic mouse line in which skin melanosis, benign melanocytic tumor and malignant melanoma metastasizing to distant organs develop stepwise. The process of tumor development and its malignant transformation in this line may resemble that of the human giant congenital melanocytic nevus that is present at birth and that frequently gives rise to malignant melanoma during aging. We observed an increase in the expression level and activity of the ret transgene during the disease progression. That increase in transgene expression accompanied an activation of mitogen-activated protein kinases (MAPKs) and c-Jun as well as matrix metalloproteinases. These results suggest that progressive dysregulation of the expression level of the ret transgene might play a crucial role in the malignant transformation of melanocytic tumors developed in the MT/ret transgenic mouse line.

SUMMARY While the genetic control of renal branching morphogenesis has been extensively described, the cellular basis of this process remains obscure. GDNF/Ret signaling is required for ureter and kidney development, and cells lacking Ret are excluded from the tips of the branching ureteric bud in chimeric kidneys. Here, we find that this exclusion results from earlier, Ret-dependent cell rearrangements in the caudal Wolffian duct, which generate a specialized epithelial domain that later emerges as the tip of the primary ureteric bud. By juxtaposing cells with elevated or reduced Ret activity, we find that Wolffian duct cells compete, based on Ret signaling levels, to contribute to this domain. At the same time, the caudal Wolffian duct transiently converts from a simple to a pseudostratified epithelium, a process that does not require Ret. Thus, both Ret-dependent cell movements and Ret-independent changes in the Wolffian duct epithelium contribute to ureteric bud formation.