L1 and Alu elements are among the most active retroposons (mobile elements) in the human genome. Several human diseases, including certain forms of breast cancer and leukemia, are associated with L1 and Alu insertions in functionally important areas of the genome. We present data demonstrating that environmental pollutants, such as heavy metals, can stimulate L1 retrotransposition in a tissue culture system using two different types of assays. The response to these agents was equivalent when using a cell line with a stably integrated L1 vector (genomic) or a by introducing the L1 vector by transient transfection (episomal) of the cell. Reproducible results showed that mercury (HgS), cadmium (CdS), and nickel (NiO) increase the activity of L1 by an average of three (3) fold p<0.001. This observation is the first to link several carcinogenic agents with the increased retrotransposition activity of L1 as an alternate mechanism of generating genomic instability contributing to the process of carcinogenesis. Our results demonstrate that mobile element activation must be considered as one of the mechanisms when evaluating genomic damage/instability in response to environmental agents.

Purpose: Overexpression of transforming growth factor (TGF)-h has been implicated in promoting immune suppression, tumor angiogenesis, tumor cell migration, and invasion in many cancers, including carcinoma of the breast. Thus, targeted down-regulation of TGF-h1expression in breast cancer in situ and determination of its implications would provide new treatment approaches for disease management. Experimental Design: Small interfering RNA constructs targeting TGF-h1 were validated and used to develop clonal derivatives of the metastatic breast cancer cell line MDA-MB-435. The cells were used in several in vitro analyses, including migration, invasion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, apoptosis, and signaling assays. A wound-healing assay was used to determine migration of the cells in culture and a Boyden chamber transwell assay was used for invasion. Further, the clones were used in an in vivo mouse model for the kinetics of tumor growth and gene expression in the primary site and in lungs upon metastasis. Results: Inhibition of TGF-h1 expression in MDA-MB-435 cells showed a 35% decrease in migration and a 55% decrease in invasion in vitro, with a 50% increase in proliferation and no effect on apoptosis. In vivo analysis indicated a 90% decrease in the number of mice bearing macroscopic lung metastases; however, the primary tumors did not show any difference in the growth kinetics when compared with the parental MDA-MB-435 cells. Analysis of TGF-h signaling pathways in the clonal derivatives showed a decrease in Smad2 activation and an increase in AKT and extracellular signal-regulated kinase activation. Interestingly, analysis of TGF-h receptor expression showed a decrease in both receptor I and II expression in TGF-h1 silenced cells. These results suggest that inhibition of TGF-h1ligand may act as a negative feedback loop to disrupt the function of all TGF-h isoforms. Conclusions: Therapies targeting the TGF-h signaling pathway may be more effective in latestage disease to prevent organ metastasis but not primary tumor formation and may be combined with other tumor-targeted therapies normally limited by increased circulatingTGF-h levels.

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Background Although antiangiogenic therapy is a promising new line of therapy for prostate cancer, we recently reported that stable expression of endostatin arrested the progression of prostate cancer to poorly differentiated state and distant metastasis in TRAMP mice. However, the same therapy failed to provide any benefit when given either during or after the onset of metastatic switch. The present study determined the possible mechanisms behind the selective advantage of endostatin therapy in early stage disease. Methods Angiogenesis-related gene expression analysis was performed to identify target genes and molecular pathways involved in the therapy effects. Based on the results from in vivo studies, and recapitulation of the in vivo data in vitro using tumorigenic and non-tumorigenic human prostate cancer cells that are either androgen-sensitive or androgen-independent, analyses of possible mechanisms of the selective advantage of early treatment were performed using assays for cell proliferation, apoptosis, migration and cell signaling. The identified mechanisms were further confirmed in vivo. Results Results indicated that cells with high androgen receptor (AR) expression were more sensitive to endostatin treatment than androgen-independent cells with low or no AR expression. Endostatin was found to significantly downregulate the expression of growth factors, receptor tyrosine kinases, proteases, and AR both in vitro and in vivo only when the cells express high levels of AR. Cell proliferation was not influenced by endostatin treatment but migration was significantly affected only in androgen-sensitive cells. Targeted downregulation of AR prior to endostatin treatment in androgen sensitive cells and overexpression of AR in androgen independent cells indicated that the effect of endostatin via AR downregulation is mediated by a non-genotropic mechanism on Ras and RhoA pathways, and independently of AR on MAPK/ERK pathway. Conclusions These data indicate that systemically stable endostatin expression delays the onset of metastatic switch by acting on multiple pathways involving AR.

<div>Abstract<p><b>Purpose:</b> Overexpression of transforming growth factor (TGF)-β has been implicated in promoting immune suppression, tumor angiogenesis, tumor cell migration, and invasion in many cancers, including carcinoma of the breast. Thus, targeted down-regulation of TGF-β1 expression in breast cancer <i>in situ</i> and determination of its implications would provide new treatment approaches for disease management.</p><p><b>Experimental Design:</b> Small interfering RNA constructs targeting TGF-β1 were validated and used to develop clonal derivatives of the metastatic breast cancer cell line MDA-MB-435. The cells were used in several <i>in vitro</i> analyses, including migration, invasion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, apoptosis, and signaling assays. A wound-healing assay was used to determine migration of the cells in culture and a Boyden chamber transwell assay was used for invasion. Further, the clones were used in an <i>in vivo</i> mouse model for the kinetics of tumor growth and gene expression in the primary site and in lungs upon metastasis.</p><p><b>Results:</b> Inhibition of TGF-β1 expression in MDA-MB-435 cells showed a 35% decrease in migration and a 55% decrease in invasion <i>in vitro</i>, with a 50% increase in proliferation and no effect on apoptosis. <i>In vivo</i> analysis indicated a 90% decrease in the number of mice bearing macroscopic lung metastases; however, the primary tumors did not show any difference in the growth kinetics when compared with the parental MDA-MB-435 cells. Analysis of TGF-β signaling pathways in the clonal derivatives showed a decrease in Smad2 activation and an increase in AKT and extracellular signal-regulated kinase activation. Interestingly, analysis of TGF-β receptor expression showed a decrease in both receptor I and II expression in TGF-β1 silenced cells. These results suggest that inhibition of TGF-β1 ligand may act as a negative feedback loop to disrupt the function of all TGF-β isoforms.</p><p><b>Conclusions:</b> Therapies targeting the TGF-β signaling pathway may be more effective in late-stage disease to prevent organ metastasis but not primary tumor formation and may be combined with other tumor-targeted therapies normally limited by increased circulating TGF-β levels.</p></div>