CrkI and CrkII function as key signaling integrators for migration and invasion of cancer cells

Carcinogen-altered genes in rat esophagus positively modulated to normal levels of expression by both black raspberries and phenylethyl isothiocyanate

Our recent study identified 2,261 dysregulated genes in the esophagi of rats that received a 1-week exposure to the carcinogen N-nitrosomethylbenzylamine (NMBA). We further reported that 1,323 of these genes were positively modulated to near-normal levels of expression in NMBA-treated animals that consumed dietary phenylethyl isothiocyanate (PEITC), a constituent of cruciferous vegetables. Herein, we report our results with companion animals that were fed a diet containing 5% freeze-dried black raspberries (BRB) instead of PEITC. We found that 462 of the 2,261 NMBA-dysregulated genes in rat esophagus were restored to near-normal levels of expression by BRB. Further, we have identified 53 NMBA-dysregulated genes that are positively modulated by both PEITC and BRB. These 53 common genes include genes involved in phase I and II metabolism, oxidative damage, and oncogenes and tumor suppressor genes that regulate apoptosis, cell cycling, and angiogenesis. Because both PEITC and BRB maintain near-normal levels of expression of these 53 genes, their dysregulation during the early phase of NMBA-induced esophageal cancer may be especially important in the genesis of the disease.

MicroRNA-126 inhibits invasion in non-small cell lung carcinoma cell lines

Crk is a member of a family of adaptor proteins that are involved in intracellular signal pathways altering cell adhesion, proliferation, and migration. Increased expression of Crk has been described in lung cancer and associated with increased tumor invasiveness. MicroRNAs (miRNAs) are a family of small non-coding RNAs (approximately 21-25 nt long) that are capable of targeting genes for either degradation of mRNA or inhibition of translation. Crk is a predicted putative target gene for miR-126. Over-expression of miR126 in a lung cancer cell line resulted in a decrease in Crk protein without any alteration in the associated mRNA. These lung cancer cells exhibit a decrease in adhesion, migration, and invasion. Decreased cancer cell invasion was also evident following targeted knockdown of Crk. MiR-126 alters lung cancer cell phenotype by inhibiting adhesion, migration, and invasion and the effects on invasion may be partially mediated through Crk regulation.

Signaling through ShcA is required for transforming growth factor beta- and Neu/ErbB-2-induced breast cancer cell motility and invasion

Cooperation between the Neu/ErbB-2 and transforming growth factor beta (TGF-beta) signaling pathways enhances the invasive and metastatic capabilities of breast cancer cells; however, the underlying mechanisms mediating this synergy have yet to be fully explained. We demonstrate that TGF-beta induces the migration and invasion of mammary tumor explants expressing an activated Neu/ErbB-2 receptor, which requires signaling from autophosphorylation sites located in the C terminus. A systematic analysis of mammary tumor explants expressing Neu/ErbB-2 add-back receptors that couple to distinct signaling molecules has mapped the synergistic effect of TGF-beta-induced motility and invasion to signals emanating from tyrosine residues 1226/1227 and 1253 of Neu/ErbB-2. Given that the ShcA adaptor protein is known to interact with Neu/ErbB-2 through these residues, we investigated the importance of this signaling molecule in TGF-beta-induced cell motility and invasion. The reduction of ShcA expression rendered cells expressing activated Neu/ErbB-2, or add-back receptors signaling specifically through tyrosines 1226/1227 or 1253, unresponsive to TGF-beta-induced motility and invasion. In addition, a dominant-negative form of ShcA, lacking its three known tyrosine phosphorylation sites, completely abrogates the TGF-beta-induced migration and invasion of breast cancer cells expressing activated Neu/ErbB-2. Our results implicate signaling through the ShcA adaptor as a key component in the synergistic interaction between these pathways.

Osteoactivin promotes breast cancer metastasis to bone

The skeleton is a preferred site of metastasis in patients with disseminated breast cancer. We have used 4T1 mouse mammary carcinoma cells, which metastasize to bone from the mammary fat pads of immunocompetent mice, to identify novel genes involved in this process. In vivo selection of parental cells resulted in the isolation of independent, aggressively bone metastatic breast cancer populations with reduced metastasis to the lung. Gene expression profiling identified osteoactivin as a candidate that is highly and selectively expressed in aggressively bone metastatic breast cancer cells. These cells displayed enhanced migratory and invasive characteristics in vitro, the latter requiring sustained osteoactivin expression. Osteoactivin depletion in these cells, by small interfering RNA, also lead to a loss of matrix metalloproteinase-3 expression, whereas forced osteoactivin expression in parental 4T1 cells was sufficient to elevate matrix metalloproteinase-3 levels, suggesting that this matrix metalloproteinase may be an important mediator of osteoactivin function. Overexpression of osteoactivin in an independent, weakly bone metastatic breast cancer cell model significantly enhanced the formation of osteolytic bone metastases in vivo. Finally, high levels of osteoactivin expression in primary human breast cancers correlate with estrogen receptor-negative status and increasing tumor grade. Thus, we have identified osteoactivin as a protein that is expressed in aggressive human breast cancers and is capable of promoting breast cancer metastasis to bone.

Geldanamycin Anisimycins Activate Rho and Stimulate Rho- and ROCK-Dependent Actin Stress Fiber Formation

Heat shock protein 90 (Hsp90) is a member of the heat shock family of molecular chaperones that regulate protein conformation and activity. Hsp90 regulates multiple cell signaling pathways by controlling the abundance and activity of several important protein kinases and cell cycle-related proteins. In this report, we show that inhibition of Hsp90 by geldanamycin or its derivative, 17-allylamino-17-desmethoxygeldamycin, leads to activation of the Rho GTPase and a dramatic increase in actin stress fiber formation in human tumor cell lines. Inactivation of Rho prevents geldanamycin-induced actin reorganization. Hsp90 inactivation does not alter the appearance of filopodia or lamellipodia and tubulin architecture is not visibly perturbed. Our observations suggest that Hsp90 has an important and specific role in regulating Rho activity and Rho-dependent actin cytoskeleton remodeling.

A systems biology approach for pathway level analysis

A common challenge in the analysis of genomics data is trying to understand the underlying phenomenon in the context of all complex interactions taking place on various signaling pathways. A statistical approach using various models is universally used to identify the most relevant pathways in a given experiment. Here, we show that the existing pathway analysis methods fail to take into consideration important biological aspects and may provide incorrect results in certain situations. By using a systems biology approach, we developed an impact analysis that includes the classical statistics but also considers other crucial factors such as the magnitude of each gene's expression change, their type and position in the given pathways, their interactions, etc. The impact analysis is an attempt to a deeper level of statistical analysis, informed by more pathway-specific biology than the existing techniques. On several illustrative data sets, the classical analysis produces both false positives and false negatives, while the impact analysis provides biologically meaningful results. This analysis method has been implemented as a Web-based tool, Pathway-Express, freely available as part of the Onto-Tools (http://vortex.cs.wayne.edu).

Signaling adaptor protein Crk is indispensable for malignant feature of glioblastoma cell line KMG4

Signaling adaptor protein Crk has been shown to be involved in pathogenesis of human cancers including brain tumor where Crk was reported to be overexpressed. In this study, we addressed whether Crk is indispensable for malignant phenotype of brain tumor. In 20 surgical specimens of glioma, mRNA of both CrkI and CrkII was found to be elevated in malignant tumor. To define a precise role of Crk, we have established Crk-knockdown cell lines of glioblastoma KMG4 by siRNA, and early phase of cell adhesion to laminin was found to be suppressed. Wound healing assay revealed the decreased cell motility in Crk knockdown cells, and suppression of both anchorage-dependent and -independent growth were demonstrated in these cells. Furthermore, in vivo tumor forming potential was also markedly suppressed. These results suggest that Crk is required for early attachment to laminin, cell motility, and growth of glioblastoma cell line KMG4.

Paradoxes of the EphB4 receptor in cancer

Recent findings have started to uncover the intriguing roles of the Eph family of receptor tyrosine kinases in normal epithelial cells and during oncogenic transformation. This review focuses on EphB4, an Eph receptor that has both tumor-suppressing and tumor-promoting activities in breast cancer. Understanding the multifaceted role of EphB4 in tumorigenesis may allow the development of new anticancer therapies.

From Tpr-Met to Met, tumorigenesis and tubes

The receptor for hepatocyte growth factor (HGF)/scatter factor (SF), Met, controls a program of invasive epithelial growth through the coordination of cell proliferation and survival, cell migration and epithelial morphogenesis. This process is important during embryogenesis and for organ regeneration in the adult. However, when deregulated the HGF/SF-Met signaling axis contributes to tumorigenesis and metastasis. Studies on the oncogenic activation of the Met receptor have shed light on the molecular mechanisms underlying the oncogenic activation of receptor tyrosine kinase (RTKs). More than a decade ago, work on the Met related oncogene, Tpr-Met, revealed the mechanism for activation of RTK-derived oncogenes generated following chromosomal translocation. More recently, studies on the mechanisms of downregulation of the Met RTK highlight a role for loss of downregulation in RTK oncogenic activation.

eEF1A2 activates Akt and stimulates Akt-dependent actin remodeling, invasion and migration

eEF1A2 (eukaryotic protein elongation factor 1 alpha 2) is a protein translation factor that is likely a human oncogene by virtue of its capacity to transform mammalian cells and its high expression in tumors of the ovary, breast and lung. Here, we show that expression of eEF1A2 is sufficient to stimulate the formation of filopodia in BT549 human breast cancer cells and non-transformed Rat2 cells. Filopodia formation in eEF1A2-expressing cells is dependent on the activity of phosphatidylinositol-3 kinase (PI3K), and the ROCK and Akt kinases. Furthermore, eEF1A2 expression is sufficient to activate Akt in a PI3K-dependent fashion and inactivation of eEF1A2 by short interfering RNA reduces Akt activity. Using breast cancer cell line BT 549, we show that eEF1A2 expression stimulates cell migration and invasion in a largely PI3K- and Akt-dependent manner. These results suggest that eEF1A2 regulates oncogenesis through Akt and PI3K-dependent cytoskeletal remodeling.

Gab1 is required for cell cycle transition, cell proliferation, and transformation induced by an oncogenic met receptor

We have shown previously that either Grb2- or Shc-mediated signaling from the oncogenic Met receptor Tpr-Met is sufficient to trigger cell cycle progression in Xenopus oocytes. However, direct binding of these adaptors to Tpr-Met is dispensable, implying that another Met binding partner mediates these responses. In this study, we show that overexpression of Grb2-associated binder 1 (Gab1) promotes cell cycle progression when Tpr-Met is expressed at suboptimal levels. This response requires that Gab1 possess an intact Met-binding motif, the pleckstrin homology domain, and the binding sites for phosphatidylinositol 3-kinase and tyrosine phosphatase SHP-2, but not the Grb2 and CrkII/phospholipase Cgamma binding sites. Importantly, we establish that Gab1-mediated signals are critical for cell cycle transition promoted by the oncogenic Met and fibroblast growth factor receptors, but not by progesterone, the natural inducer of cell cycle transition in Xenopus oocytes. Moreover, Gab1 is essential for Tpr-Met-mediated morphological transformation and proliferation of fibroblasts. This study provides the first evidence that Gab1 is a key binding partner of the Met receptor for induction of cell cycle progression, proliferation, and oncogenic morphological transformation. This study identifies Gab1 and its associated signaling partners as potential therapeutic targets to impair proliferation or transformation of cancer cells in human malignancies harboring a deregulated Met receptor.