Dana M. Brantley

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

TGF-βs are potent inhibitors of epithelial cell proliferation. However, in established carcinomas, autocrine/paracrine TGF-β interactions can enhance tumor cell viability and progression. Thus, we studied the effect of a soluble Fc:TGF-β type II receptor fusion protein (Fc:TβRII) on transgenic and transplantable models of breast cancer metastases. Systemic administration of Fc:TβRII did not alter primary mammary tumor latency in MMTV-Polyomavirus middle T antigen transgenic mice. However, Fc:TβRII increased apoptosis in primary tumors, while reducing tumor cell motility, intravasation, and lung metastases. These effects correlated with inhibition of Akt activity and FKHRL1 phosphorylation. Fc:TβRII also inhibited metastases from transplanted 4T1 and EMT-6 mammary tumors in syngeneic BALB/c mice. Tumor microvessel density in a mouse dorsal skin window chamber was unaffected by Fc:TβRII. Therefore, blockade of TGF-β signaling may reduce tumor cell viability and migratory potential and represents a testable therapeutic approach against metastatic carcinomas.

Soluble Eph A receptors inhibit tumor angiogenesis and progression in vivo

The Eph family of receptor tyrosine kinases and their ligands, known as ephrins, play a crucial role in vascular development during embryogenesis. The function of these molecules in adult angiogenesis has not been well characterized. Here, we report that blocking Eph A class receptor activation inhibits angiogenesis in two independent tumor types, the RIP-Tag transgenic model of angiogenesis-dependent pancreatic islet cell carcinoma and the 4T1 model of metastatic mammary adenocarcinoma. Ephrin-A1 ligand was expressed in both tumor and endothelial cells, and EphA2 receptor was localized primarily in tumor-associated vascular endothelial cells. Soluble EphA2-Fc or EphA3-Fc receptors inhibited tumor angiogenesis in cutaneous window assays, and tumor growth in vivo. EphA2-Fc or EphA3-Fc treatment resulted in decreased tumor vascular density, tumor volume, and cell proliferation, but increased cell apoptosis. However, EphA2-Fc had no direct effect on tumor cell growth or apoptosis in culture, yet inhibited migration of endothelial cells in response to tumor cells, suggesting that the soluble receptor inhibited blood vessel recruitment by the tumor. These data provide the first functional evidence for Eph A class receptor regulation of pathogenic angiogenesis induced by tumors and support the function of A class Eph receptors in tumor progression.

The ephrins and Eph receptors in angiogenesis

Eph receptors are a unique family of receptor tyrosine kinases that play critical roles in embryonic patterning, neuronal targeting, vascular development and adult neovascularization. Engagement of Eph receptors by ephrin ligands mediates critical steps of angiogenesis, including juxtacrine cell-cell contacts, cell adhesion to extracellular matrix, and cell migration. Recent evidence from in vitro angiogenesis assays and analysis of mice deficient for one or more members of the Eph family establishes the role of Eph signaling in sprouting angiogenesis and blood vessel remodeling during vascular development. Furthermore, elevated expression of Eph receptors and ephrin ligands is associated with tumors and associated tumor vasculature, suggesting that Eph receptors and their ephrin ligands also play critical roles in tumor angiogenesis and tumor growth. This review will focus on the relevance of Eph receptor signaling in embryonic and adult neovascularization, and possible contributions to tumor growth and metastasis.

Inhibition of NF-kappaB activity results in disruption of the apical ectodermal ridge and aberrant limb morphogenesis.

In Drosophila, the Dorsal protein establishes the embryonic dorso–ventral axis during development. Here we show that the vertebrate homologue of Dorsal, nuclear factor-kappa B (NF-κB), is vital for the formation of the proximo–distal organizer of the developing limb bud, the apical ectodermal ridge (AER). Transcription of the NF-κB proto-oncogene c-rel is regulated, in part, during morphogenesis of the limb bud by AER-derived signals such as fibroblast growth factors. Interruption of NF-κB activity using viral-mediated delivery of an inhibitor results in a highly dysmorphic AER, reduction in overall limb size, loss of distal elements and reversal in the direction of limb outgrowth. Furthermore, inhibition of NF-κB activity in limb mesenchyme leads to a reduction in expression of Sonic hedgehog and Twist but derepresses expression of the bone morphogenetic protein-4 gene. These results are the first evidence that vertebrate NF-κB proteins act to transmit growth factor signals between the ectoderm and the underlying mesenchyme during embryonic limb formation.

ErbB2/Neu-Induced, Cyclin D1-Dependent Transformation Is Accelerated in p27-Haploinsufficient Mammary Epithelial Cells but Impaired in p27-Null Cells

ABSTRACT ErbB2/Neu destabilizes the cyclin-dependent kinase (Cdk) inhibitor p27 and increases expression of cyclin D1. Therefore, we studied the roles of p27 and cyclin D1 in ErbB2-mediated mammary epithelial cell transformation. Overexpression of ErbB2 or cyclin D1 in p27+/− primary murine mammary epithelial cells resulted in increased proliferation, cyclin D1 nuclear localization, and colony formation in soft agar compared to those in p27+/+ cells. In contrast, ErbB2- or cyclin D1-overexpressing p27−/− cells displayed reduced proliferation, anchorage-independent growth, Cdk4 activity, cyclin D1 expression, and cyclin D1 nuclear localization compared to wild-type cells. A cyclin D1 mutation in its nuclear export sequence (T286A) partially rescued nuclear localization of cyclin D1 in p27−/− cells but did not increase proliferation or Cdk4 kinase activity. Overexpression of E2F1, however, increased proliferation to the same degree in p27+/+ , p27+/− , and p27−/− cells. Mammary glands from MMTV (mouse mammary tumor virus)-neu/p27+/− mice exhibited alveolar hyperplasia, enhanced proliferation, decreased apoptosis, and accelerated tumor formation compared to MMTV-neu/p27+/+ glands. However, MMTV-neu/p27−/− glands showed decreased proliferation, cyclin D1 expression, and Cdk4 activity, as well as markedly prolonged tumor latency, compared to MMTV-neu/p27+/+ glands. These results suggest that p27+/− mammary epithelium may be more susceptible to oncogene-induced tumorigenesis, whereas p27-null glands, due to severely impaired cyclin D1/Cdk4 function, are more resistant to transformation.

Inhibition of VEGF-dependent multistage carcinogenesis by soluble EphA receptors.

Elevated expression of Eph receptors has long been correlated with the growth of solid tumors. However, the functional role of this family of receptor tyrosine kinases in carcinogenesis and tumor angiogenesis has not been well characterized. Here we report that soluble EphA receptors inhibit tumor angiogenesis and tumor progression in vivo in the RIP-Tag transgenic model of vascular endothelial growth factor (VEGF)-dependent multistage pancreatic islet cell carcinoma. Soluble EphA receptors delivered either by a transgene or an osmotic minipump inhibited the formation of angiogenic islet, a premalignant lesion, and reduced tumor volume of solid islet cell carcinoma. EphA2-Fc or EphA3-Fc treatment resulted in decreased tumor volume but increased tumor and endothelial cell apoptosis in vivo. In addition, soluble EphA receptors inhibited VEGF and betaTC tumor cell-conditioned medium-induced endothelial cell migration in vitro and VEGF-induced cornea angiogenesis in vivo. A dominant negative EphA2 mutant inhibited--whereas a gain-of-function EphA2 mutant enhanced--tumor cell-induced endothelial cell migration, suggesting that EphA2 receptor activation is required for tumor cell-endothelial cell interaction. These data provide functional evidence for EphA class receptor regulation of VEGF-dependent tumor angiogenesis, suggesting that the EphA signaling pathway may represent an attractive novel target for antiangiogenic therapy in cancer.

Dynamic expression and activity of NF-κB during post-natal mammary gland morphogenesis

The Rel/NF-kappaB family of transcription factors has been implicated in such diverse cellular processes as proliferation, differentiation, and apoptosis. As each of these processes occurs during post-natal mammary gland morphogenesis, the expression and activity of NF-kappaB factors in the murine mammary gland were examined. Immunohistochemical and immunoblot analyses revealed expression of the p105/p50 and RelA subunits of NF-kappaB, as well as the major inhibitor, IkappaBalpha, in the mammary epithelium during pregnancy, lactation, and involution. Electrophoretic mobility shift assay (EMSA) demonstrated that DNA-binding complexes containing p50 and RelA were abundant during pregnancy and involution, but not during lactation. Activity of an NF-kappaB-dependent luciferase reporter in transgenic mice was highest during pregnancy, decreased to near undetectable levels during lactation, and was elevated during involution. This highly regulated pattern of activity was consistent with the modulated expression of p105/p50, RelA, and IkappaBalpha.