Annamaria Gal

Sustained TGF beta exposure suppresses Smad and non-Smad signalling in mammary epithelial cells, leading to EMT and inhibition of growth arrest and apoptosis.

To better understand the dual, tumour-suppressive and tumour-promoting function of transforming growth factor-β (TGFβ), we analysed mammary epithelial NMuMG cells in response to short and long-term TGFβ exposure. NMuMG cells became proliferation-arrested and apoptotic after exposure to TGFβ for 2–5 days, whereas surviving cells underwent epithelial–mesenchymal transition (EMT). After chronic TGFβ exposure (2–3 weeks), however, NMuMG cells became resistant to proliferation arrest and apoptosis, showing sustained EMT instead (TD cells). EMT was fully reversed by a pharmacologic TGFβ-receptor-I kinase inhibitor or withdrawal of TGFβ for 6–12 days. Interestingly, both cell cycle arresting/proapoptotic (Smads, p38 kinase) and antiapoptotic, proliferation and EMT-promoting signalling pathways (PI3K–PKB/Akt, ERK) were co-suppressed to low, but significant levels. Except for PI3K-Akt, TGFβ-dependent downregulation of these signalling pathways in transdifferentiated (TD) cells was fully reversed upon TGFβ withdrawal, together with partial re-induction of proliferation arrest and apoptosis. Co-injection of non-tumorigenic NMuMG cells with tumour-forming CHO cells oversecreting exogenous TGFβ1 (CHO-TGFβ1) allowed outgrowth of epithelioid cells in CHO-TGFβ1 cell-induced tumours. These epithelial islands enhanced CHO-TGFβ1 tumour cell proliferation, possibly due to chemokines (for example, JE/MCP-1) secreted by NMuMG/TD cells. We conclude that suppression of antiproliferative, proapoptotic TGFβ signalling in TD cells may permit TGFβ-dependent proliferation, survival and EMT-enhancing signalling pathways to act at low levels. Thus, TGFβ may modulate its own signalling to facilitate switching from tumour suppression to tumour progression.

Evidence That Phosphatidylinositol 3-Kinase- and Mitogen-activated Protein Kinase Kinase-4/c-Jun NH2-terminal Kinase-dependent Pathways Cooperate to Maintain Lung Cancer Cell Survival

Cancer cells in which the PTEN lipid phosphatase gene is deleted have constitutively activated phosphatidylinositol 3-kinase (PI3K)-dependent signaling and require activation of this pathway for survival. In non-small cell lung cancer (NSCLC) cells, PI3K-dependent signaling is typically activated through mechanisms other than PTEN gene loss. The role of PI3K in the survival of cancer cells that express wild-type PTEN has not been defined. Here we provide evidence that H1299 NSCLC cells, which express wild-type PTEN, underwent proliferative arrest following treatment with an inhibitor of all isoforms of class I PI3K catalytic activity (LY294002) or overexpression of the PTEN lipid phosphatase. In contrast, overexpression of a dominant-negative mutant of the p85α regulatory subunit of PI3K (Δp85) induced apoptosis. Whereas PTEN and Δ85 both inhibited activation of AKT/protein kinase B, only Δp85 inhibited c-Jun NH2-terminal kinase (JNK) activity. Cotransfection of the constitutively active mutant Rac-1 (Val12), an upstream activator of JNK, abrogated Δp85-induced lung cancer cell death, whereas constitutively active mutant mitogen-activated protein kinase kinase (MKK)-1 (R4F) did not. Furthermore, LY294002 induced apoptosis of MKK4-null but not wild-type mouse embryo fibroblasts. Therefore, we propose that, in the setting of wild-type PTEN, PI3K- and MKK4/JNK-dependent pathways cooperate to maintain cell survival.

G-CSF rescues tumor growth and neo-angiogenesis during liver metastasis under host angiopoietin-2 deficiency

Suppression of neo‐angiogenesis is a clinically used anti‐tumor strategy with new targets such as angiopoietin‐2 (Ang2) being proposed. However, the functions of Ang2 in vascular remodeling, inflammation and tumor growth are not consistent. We examined effect of depletion of host Ang2 on liver colony formation using Ang2 deficient (Ang2−/−) mice. Surprisingly, the metastatic colonies formed in Ang2−/− mice were larger than those in the wild type. These colonies had greater vascular density with more pericyte coverage than the vessels in liver colonies in the wild type. Liver VEGF concentration in both genotypes was equivalent, and thus, the differences appeared VEGF independent. However, after colony formation, the serum concentration of granulocyte‐colony stimulating factor (G‐CSF) and CXCL1 in Ang2−/− mice was 12 and 6 times greater than after colony formation in wild type. Increase of these two cytokines was associated with two times greater numbers of neutrophils recruited to the liver. Two times more Tie2+/CD11b+/CD31− cells were present in the tumors in Ang2−/− than in the wild type livers. These results suggest that the depletion of host Ang2 induced compensatory VEGF‐independent angiogenic mechanisms and thus enhanced liver metastatic colony growth and colony vascularity. They further indicate organotypic differences in response to tumor metastasis. In contrast, Ang2 deficiency inhibited tumor growth during metastatic colony formation in the lung, consistent with the reports of decreased pulmonary seeding of tumor cells after pharmacological inhibition of Ang2. Further studies are thus required to assess the effects of pharmacological Ang2 blockade for cancer patients particularly in the liver.

Tetraspanin in oncogenic epithelial-mesenchymal transition

Members of the L6 family of membrane proteins, a branch of the tetraspanin superfamily, are overexpressed in tumor cells from many types of cancers. However, direct evidence of their oncogenic activity has not been previously shown. In this issue of the JCI, Lee et al. demonstrate that overexpression of the tetraspanin superfamily member TM4SF5 in human hepatocellular carcinoma cells causes cellular phenotypic changes that resemble classical descriptions of epithelial-mesenchymal transition (EMT), with some unique aspects (see the related article beginning on page 1354). They also show that these TM4SF5-mediated effects trigger tumor formation when these cells are injected into mice. The study implicates TM4SF5, for the first time to our knowledge, in EMT oncogenic pathways of cancer progression.

Abstract 402: Plasticity of tumor associated macrophages in a metastatic melanoma model in the mouse

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Macrophages acquire different functional traits, with the pro-inflammatory, classically activated M1 and the tissue-repair, alternatively activated M2 phenotypes the best characterized to date. Tumor-associated macrophages (TAMs) have been described as alternatively activated and exert pro-tumoral activity. We investigated TAMs isolated from subcutaneous tumors and experimental lung metastases at an early (72 h) and late (3 wk) stage within a B16F10 mouse melanoma model. The macrophages were characterized according to their expression of genes, surface markers and secreted factors. Interestingly, the mRNA profile revealed both M1- and M2-associated gene expression in macrophages derived from s.c. melanoma, including Cxcl9, Cxcl11, Il-1a, Nos2, and Retnla (FIZZ-1), Arg-1 and Fn1, respectively. In early pulmonary metastases, we found that macrophages also expressed both pro-inflammatory (Il1b, Il12b, Ccl2), and anti-inflammatory (Ccl17 and Ccl22) cytokines and chemokines and other M1- and M2-associated genes, such as Cd40, Cd86, and Il27ra and Itgax (Cdd11c), respectively. Macrophages from late stage lung metastases displayed predominantly alternatively activated characteristics with Arg1, Retnla and Fn1 expression, but pro-inflammatory genes, such as Ccl2, Il1b and Cxcl10 were also induced/upregulated. We therefore suggest an intermediate phenotype of TAMs which does not fit the orthodox M1/M2 paradigm. To describe the mechanism by which macrophages are recruited to pulmonary metastases, we investigated chemokine receptor expression of macrophages infiltrating the lung. While Ccr2 was expressed at high level in macrophages associated with both the control and B16F10 metastases bearing lung, we found that Ccr1 and Ccr5 expression was induced after tumor cell challenge. The secretion profile of B16F10 cells revealed CCL5 (RANTES), a ligand for these receptors, secreted at high level, which suggests that CCL5 attracts macrophages to lung metastases via CCR1 and CCR5. The effect of anti-CCL5 antibody treatment, and s.c melanoma growth and pulmonary metastasis development in CCR1-/- and CCR5-/- mice will be discussed. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 402. doi:1538-7445.AM2012-402

The response of infiltrating and resident macrophages to melanoma challenge in the mouse lung: Involvement of the CC-chemokine axis in the recruitment of pro-tumoral macrophages.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC In a pulmonary metastasis model using B16F10 melanoma, we found monocyte/macrophage infiltration gradually increasing in the course of metastatic progression. The gene expression pattern of the infiltrating macrophages revealed an early (d3) inflammatory response that shifted to a tumor-promoting late response (d21). The pro-tumoral expression pattern was characterized by Arg1 and elevated expression of Ccl2, Vcam1, Vegfa, Stab1, Lyve1 and Ptgs2. In contrast, while enhancing their anti-inflammatory phenotype, resident lung (alveolar) macrophages also expressed pro-inflammatory genes, notably Il12b. We found at least three chemokine receptors involved in the recruitment of macrophages into the metastatic lung: CCR1, CCR2 and CCR5. The B16F10 cells secreted large quantities of RANTES which in turn activates CCR1 and CCR5, and thus contribute to macrophage chemotaxis. Infiltrating monocytes/macrophages, as well as alveolar macrophages, revealed an increased chemokine expression level in response to tumor challenge. These chemokines included the ligands for CCR1 and CCR5, Mip1α and Mip1β, thus providing a constant means of further macrophage recruitment. Interestingly, the expression of the CCR2 ligand, CCL2, was found strikingly increased by infiltrating monocytes/ macrophages, thus ensuring a positive feed-back loop for macrophage recruitment. In order to explore the involvement of CC chemokine receptors in pulmonary metastasis, we treated the mice with antagonists against CCR1, CCR5 and CCR2 after i.v. B16F10 challenge. The CCR1 and CCR5 antagonist treatments resulted in a 20% decrease in the number of lung colonies each. FACS analysis of the B16F10 colony bearing lungs revealed a distribution of macrophage subsets quite different from untreated lungs, highlighting the importance of CC-chemokine receptors in the recruitment of pro-tumoral macrophages. The effect of a CCR2 antagonist on lung colony formation will be discussed, together with its effect on the phenotype of macrophage subpopulations. Citation Format: Thomas T. Tapmeier, Annamaria Gal, Ruth J. Muschel. The response of infiltrating and resident macrophages to melanoma challenge in the mouse lung: Involvement of the CC-chemokine axis in the recruitment of pro-tumoral macrophages. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-324. doi:10.1158/1538-7445.AM2013-LB-324