Blockade of TGF-beta inhibits mammary tumor cell viability, migration, and metastases

Transforming growth factor beta signaling impairs Neu-induced mammary tumorigenesis while promoting pulmonary metastasis

The influence of transforming growth factor beta (TGF-beta) signaling on Neu-induced mammary tumorigenesis and metastasis was examined with transgenic mouse models. We generated mice expressing an activated TGF-beta type I receptor or dominant negative TGF-beta type II receptor under control of the mouse mammary tumor virus promoter. When crossed with mice expressing activated forms of the Neu receptor tyrosine kinase that selectively couple to the Grb2 or Shc signaling pathways the activated type I receptor increased the latency of mammary tumor formation but also enhanced the frequency of extravascular lung metastasis. Conversely, expression of the dominant negative type II receptor decreased the latency of Neu-induced mammary tumor formation while significantly reducing the incidence of extravascular lung metastases. These observations argue that TGF-beta can promote the formation of lung metastases while impairing Neu-induced tumor growth and suggest that extravasation of breast cancer cells from pulmonary vessels is a point of action of TGF-beta in the metastatic process.

Enhanced antitumor immunity in mice deficient in CD69

We investigated the in vivo role of CD69 by analyzing the susceptibility of CD69-/- mice to tumors. CD69-/- mice challenged with MHC class I- tumors (RMA-S and RM-1) showed greatly reduced tumor growth and prolonged survival compared with wild-type (WT) mice. The enhanced anti-tumor response was NK cell and T lymphocyte-mediated, and was due, at least in part, to an increase in local lymphocytes. Resistance of CD69-/- mice to MHC class I- tumor growth was also associated with increased production of the chemokine MCP-1, diminished TGF-beta production, and decreased lymphocyte apoptosis. Moreover, the in vivo blockade of TGF-beta in WT mice resulted in enhanced anti-tumor response. In addition, CD69 engagement induced NK and T cell production of TGF-beta, directly linking CD69 signaling to TGF-beta regulation. Furthermore, anti-CD69 antibody treatment in WT mice induced a specific down-regulation in CD69 expression that resulted in augmented anti-tumor response. These data unmask a novel role for CD69 as a negative regulator of anti-tumor responses and show the possibility of a novel approach for the therapy of tumors.

Stress and radiation-induced activation of multiple intracellular signaling pathways

Exposure of cells to a variety of stresses induces compensatory activations of multiple intracellular signaling pathways. These activations can play critical roles in controlling cell survival and repopulation effects in a stress-specific and cell type-dependent manner. Some stress-induced signaling pathways are those normally activated by mitogens such as the EGFR/RAS/PI3K-MAPK pathway. Other pathways activated by stresses such as ionizing radiation include those downstream of death receptors, including pro-caspases and the transcription factor NFKB. This review will attempt to describe some of the complex network of signals induced by ionizing radiation and other cellular stresses in animal cells, with particular attention to signaling by growth factor and death receptors. This includes radiation-induced signaling via the EGFR and IGFI-R to the PI3K, MAPK, JNK, and p38 pathways as well as FAS-R and TNF-R signaling to pro-caspases and NFKB. The roles of autocrine ligands in the responses of cells and bystander cells to radiation and cellular stresses will also be discussed. Based on the data currently available, it appears that radiation can simultaneously activate multiple signaling pathways in cells. Reactive oxygen and nitrogen species may play an important role in this process by inhibiting protein tyrosine phosphatase activity. The ability of radiation to activate signaling pathways may depend on the expression of growth factor receptors, autocrine factors, RAS mutation, and PTEN expression. In other words, just because pathway X is activated by radiation in one cell type does not mean that pathway X will be activated in a different cell type. Radiation-induced signaling through growth factor receptors such as the EGFR may provide radioprotective signals through multiple downstream pathways. In some cell types, enhanced basal signaling by proto-oncogenes such as RAS may provide a radioprotective signal. In many cell types, this may be through PI3K, in others potentially by NFKB or MAPK. Receptor signaling is often dependent on autocrine factors, and synthesis of autocrine factors will have an impact on the amount of radiation-induced pathway activity. For example, cells expressing TGFalpha and HB-EGF will generate protection primarily through EGFR. Heregulin and neuregulins will generate protective signals through ERBB4/ERBB3. The impact on radiation-induced signaling of other autocrine and paracrine ligands such as TGFbeta and interleukin 6 is likely to be as complicated as described above for the ERBB receptors.

Mechanisms in epithelial plasticity and metastasis: insights from 3D cultures and expression profiling

Most human tumors are of epithelial origin (carcinomas) and metastases from such tumors lead to >80% of all cancer deaths. In contrast to aberrant control of proliferation, cell cycle, apoptosis, angiogenesis, and lifespan, mechanisms involved in local invasion and metastasis are still insufficiently understood. We will review a set of (often conflicting) in vitro/in vivo data that suggest the existence of several types of epithelial cell plasticity changes towards a fibroblastoid, invasive phenotype, which increasingly emerge as crucial events during metastasis. New cellular models were identified, which form organotypic structures under near-physiological 3D-culture conditions in vitro as well as tumors/metastases in vivo. In these models, key proteins and signaling pathways were identified (e.g., TGFbeta, ERK/MAPK, PI3K, and PDGF), which specify distinct types of epithelial plasticity correlated with steps in cancer progression and metastasis. The existence of several distinct epithelial plasticity phenotypes is also strongly suggested by expression profiling of polysome-bound mRNA, yielding a better representation of the proteome than conventional expression profiling.