Expression of activated M-Ras in a murine mammary epithelial cell line induces epithelial-mesenchymal transition and tumorigenesis

Aberrant expression of MRAS and HEG1 as the biomarkers for osimertinib resistance in LUAD

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) are the most applied targeted therapy for EGFR-mutant lung adenocarcinoma (LUAD). The third-generation EGFR-TKI, osimertinib, is widely used throughout lung cancer treatment, with single or combination modes. One of the main barriers in osimertinib treatment is the acquired resistance and mechanisms are not fully understood. Gene expression other than genetic mutations might predict drug response and mediate resistance occurrence. We analyzed six datasets of osimertinib-resistant LUAD cells from the Gene Expression Omnibus (GEO) database and identified two hub genes, named MRAS and HEG1. We found that the expression mode of MRAS/HEG1 in LUAD was osimertinib-dependent and contributed to drug resistance. We also explored potential mechanisms of hub genes related osimertinib resistance and emphasized the M2 infiltration involved. Moreover, potential therapeutic agents conquering MRAS/HEG1-related resistance were also identified. In conclusion, MRAS and HEG1 might be responsible for osimertinib resistance and could be promising prognostic biomarkers for osimertinib response in LUAD, which might provide insights into therapeutic strategies.

MRAS in coronary artery disease-Unchartered territory

Genome-wide association studies (GWAS) have identified coronary artery disease (CAD) susceptibility locus on chromosome 3q22.3. This locus contains a cluster of several genes that includes muscle rat sarcoma virus (MRAS). Common MRAS variants are also associated with CAD causing risk factors such as hypertension, dyslipidemia, obesity, and type II diabetes. The MRAS gene is an oncogene that encodes a membrane-bound small GTPase. It is involved in a variety of signaling pathways, regulating cell differentiation and cell survival (mitogen-activated protein kinase [MAPK]/extracellular signal-regulated kinase and phosphatidylinositol 3-kinase) as well as acute phase response signaling (tumor necrosis factor [TNF] and interleukin 6 [IL6] signaling). In this review, we will summarize the role of genetic MRAS variants in the etiology of CAD and its comorbidities with the focus on tissue distribution of MRAS isoforms, cell type/tissue specificity, and mode of action of single nucleotide variants in MRAS associated complex traits. Finally, we postulate that CAD risk variants in the MRAS locus are specific to smooth muscle cells and lead to higher levels of MRAS, particularly in arterial and cardiac tissue, resulting in MAPK-dependent tissue hypertrophy or hyperplasia.

Classical RAS proteins are not essential for paradoxical ERK activation induced by RAF inhibitors

RAF inhibitors unexpectedly induce ERK activation in normal and oncogenic RAS tumor cells, making them unsuitable for treating RAS-driven cancers. The precise mechanism of this paradox is not fully understood but is believed to be RAS dependent. In this study, we discovered that classical RAS proteins are not essential for RAF inhibitor-induced ERK activation in H/N/KRAS-less mouse embryonic fibroblasts. We further showed that the MRAS/SHOC2 complex is required for the classical RAS-independent paradoxical ERK activation. Our findings provide new insights into the mechanism of paradoxical ERK activation by RAF inhibitors, and they have important therapeutic implications for developing effective RAF inhibitors.

RAF inhibitors unexpectedly induce ERK signaling in normal and tumor cells with elevated RAS activity. Paradoxical activation is believed to be RAS dependent. In this study, we showed that LY3009120, a pan-RAF inhibitor, can unexpectedly cause paradoxical ERK activation in KRAS^G12C-dependent lung cancer cell lines, when KRAS is inhibited by ARS1620, a KRAS^G12C inhibitor. Using H/N/KRAS-less mouse embryonic fibroblasts, we discovered that classical RAS proteins are not essential for RAF inhibitor-induced paradoxical ERK signaling. In their absence, RAF inhibitors can induce ERK phosphorylation, ERK target gene transcription, and cell proliferation. We further showed that the MRAS/SHOC2 complex is required for this process. This study highlights the complexity of the allosteric RAF regulation by RAF inhibitors, and the importance of other RAS-related proteins in this process.

The Role of R-Ras Proteins in Normal and Pathologic Migration and Morphologic Change

The contributions that the R-Ras subfamily [R-Ras, R-Ras2/teratocarcinoma 21 (TC21), and M-Ras] of small GTP-binding proteins make to normal and aberrant cellular functions have historically been poorly understood. However, this has begun to change with the realization that all three R-Ras subfamily members are occasionally mutated in Noonan syndrome (NS), a RASopathy characterized by the development of hematopoietic neoplasms and abnormalities affecting the immune, cardiovascular, and nervous systems. Consistent with the abnormalities seen in NS, a host of new studies have implicated R-Ras proteins in physiological and pathologic changes in cellular morphology, adhesion, and migration in the cardiovascular, immune, and nervous systems. These changes include regulating the migration and homing of mature and immature immune cells, vascular stabilization, clotting, and axonal and dendritic outgrowth during nervous system development. Dysregulated R-Ras signaling has also been linked to the pathogenesis of cardiovascular disease, intellectual disabilities, and human cancers. This review discusses the structure and regulation of R-Ras proteins and our current understanding of the signaling pathways that they regulate. It explores the phenotype of NS patients and their implications for the R-Ras subfamily functions. Next, it covers recent discoveries regarding physiological and pathologic R-Ras functions in key organ systems. Finally, it discusses how R-Ras signaling is dysregulated in cancers and mechanisms by which this may promote neoplasia.

Strategic Developments & Future Perspective on Gene Therapy for Breast Cancer: Role of mTOR and Brk/ PTK6 as Molecular Targets

Breast cancer is a serious health issue and a major concern in biomedical research. Alteration in major signaling (viz. PI3K-AKT-mTOR, Ras-Raf-MEK-Erk, NF-kB, cyclin D1, JAK-STAT, Wnt, Notch, Hedgehog signaling and apoptotic pathway) contributes to the development of major subtypes of mammary carcinoma such as HER2 positive, TNBC, luminal A and B and normal-like breast cancer. Further, mutation and expression parameters of different genes involved in the growth and development of cells play an important role in the progress of different types of carcinoma, making gene therapy an emerging new therapeutic approach for the management of life-threatening diseases like cancer. The genetic targets (oncogenes and tumor suppressor genes) play a major role in the formation of a tumor. Brk/PTK6 and mTOR are two central molecules that are involved in the regulation of numerous signaling related to cell growth, proliferation, angiogenesis, survival, invasion, metastasis, apoptosis, and autophagy. Since these two proteins are highly upregulated in mammary carcinogenesis, this can be used as targeted genes for the treatment of breast cancer. However, not much work has been done on them. This review highlights the therapeutic significance of Brk and mTOR and their associated signaling in mammary carcinogenesis, which may provide a strategy to develop gene therapy for breast cancer management.

M-Ras is Muscle-Ras, Moderate-Ras, Mineral-Ras, Migration-Ras, and Many More-Ras

The Ras family of small GTPases comprises about 36 members in humans. M-Ras is related to classical Ras with regard to its regulators and effectors, but solely constitutes a subfamily among the Ras family members. Although classical Ras strongly binds Raf and highly activates the ERK pathway, M-Ras less strongly binds Raf and moderately but sustainedly activates the ERK pathway to induce neuronal differentiation. M-Ras also possesses specific effectors, including RapGEFs and the PP1 complex Shoc2-PP1c, which dephosphorylates Raf to activate the ERK pathway. M-Ras is highly expressed in the brain and plays essential roles in dendrite formation during neurogenesis, in contrast to the axon formation by R-Ras. M-Ras is also highly expressed in the bone and induces osteoblastic differentiation and transdifferentiation accompanied by calcification. Moreover, M-Ras elicits epithelial-mesenchymal transition-mediated collective and single cell migration through the PP1 complex-mediated ERK pathway activation. Activating missense mutations in the MRAS gene have been detected in Noonan syndrome, one of the RASopathies, and MRAS gene amplification occurs in several cancers. Furthermore, several SNPs in the MRAS gene are associated with coronary artery disease, obesity, and dyslipidemia. Therefore, M-Ras carries out a variety of cellular, physiological, and pathological functions. Further investigations may reveal more functions of M-Ras.

Mechanisms and consequences of subcellular RNA localization across diverse cell types

Essentially all cells contain a variety of spatially restricted regions that are important for carrying out specialized functions. Often, these regions contain specialized transcriptomes that facilitate these functions by providing transcripts for localized translation. These transcripts play a functional role in maintaining cell physiology by enabling a quick response to changes in the cellular environment. Here, we review how RNA molecules are trafficked within cells, with a focus on the subcellular locations to which they are trafficked, mechanisms that regulate their transport and clinical disorders associated with misregulation of the process.

MRAS: A Close but Understudied Member of the RAS Family

MRAS is the closest relative to the classical RAS oncoproteins and shares most regulatory and effector interactions. However, it also has unique functions, including its ability to function as a phosphatase regulatory subunit when in complex with SHOC2 and protein phosphatase 1 (PP1). This phosphatase complex regulates a crucial step in the activation cycle of RAF kinases and provides a key coordinate input required for efficient ERK pathway activation and transformation by RAS. MRAS mutations rarely occur in cancer but deregulated expression may play a role in tumorigenesis in some settings. Activating mutations in MRAS (as well as SHOC2 and PP1) do occur in the RASopathy Noonan syndrome, underscoring a key role for MRAS within the RAS-ERK pathway. MRAS also has unique roles in cell migration and differentiation and has properties consistent with a key role in the regulation of cell polarity. Further investigations should shed light on what remains a relatively understudied RAS family member.

RNA-sequencing reveals long-term effects of silver nanoparticles on human lung cells

Despite a considerable focus on the adverse effects of silver nanoparticles (AgNPs) in recent years, studies on the potential long-term effects of AgNPs are scarce. The aim of this study was to explore the effects of AgNPs following repeated low-dose, long-term exposure of human bronchial epithelial cells. To this end, the human BEAS-2B cell line was exposed to 1 µg/mL AgNPs (10 nm) for 6 weeks followed by RNA-sequencing (RNA-Seq) as well as genome-wide DNA methylation analysis. The transcriptomics analysis showed that a substantial number of genes (1717) were differentially expressed following AgNP exposure whereas only marginal effects on DNA methylation were observed. Downstream analysis of the transcriptomics data identified several affected pathways including the ‘fibrosis’ and ‘epithelial-mesenchymal transition’ (EMT) pathway. Subsequently, functional validation studies were performed using AgNPs of two different sizes (10 nm and 75 nm). Both NPs increased collagen deposition, indicative of fibrosis, and induced EMT, as evidenced by an increased invasion index, anchorage independent cell growth, as well as cadherin switching. In conclusion, using a combination of RNA-Seq and functional assays, our study revealed that repeated low-dose, long-term exposure of human BEAS-2B cells to AgNPs is pro-fibrotic, induces EMT and cell transformation.

Muscle RAS oncogene homolog (MRAS) recurrent mutation in Borrmann type IV gastric cancer

The prognosis of patients with Borrmann type IV gastric cancer (Type IV) is extremely poor. Thus, there is an urgent need to elucidate the molecular mechanisms underlying the oncogenesis of Type IV and to identify new therapeutic targets. Although previous studies using whole-exome and whole-genome sequencing have elucidated genomic alterations in gastric cancer, none has focused on comprehensive genetic analysis of Type IV. To discover cancer-relevant genes in Type IV, we performed whole-exome sequencing and genome-wide copy number analysis on 13 patients with Type IV. Exome sequencing identified 178 somatic mutations in protein-coding sequences or at splice sites. Among the mutations, we found a mutation in muscle RAS oncogene homolog (MRAS), which is predicted to cause molecular dysfunction. MRAS belongs to the Ras subgroup of small G proteins, which includes the prototypic RAS oncogenes. We analyzed an additional 46 Type IV samples to investigate the frequency of MRAS mutation. There were eight nonsynonymous mutations (mutation frequency, 17%), showing that MRAS is recurrently mutated in Type IV. Copy number analysis identified six focal amplifications and one homozygous deletion, including insulin-like growth factor 1 receptor (IGF1R) amplification. The samples with IGF1R amplification had remarkably higher IGF1R mRNA and protein expression levels compared with the other samples. This is the first report of MRAS recurrent mutation in human tumor samples. Our results suggest that MRAS mutation and IGF1R amplification could drive tumorigenesis of Type IV and could be new therapeutic targets.

A new role for the PI3K/Akt signaling pathway in the epithelial-mesenchymal transition

Tumor metastasis is not only a sign of disease severity but also a major factor causing treatment failure and cancer-related death. Therefore, studies on the molecular mechanisms of tumor metastasis are critical for the development of treatments and for the improvement of survival. The epithelial-mesenchymal transition (EMT) is an orderly, polygenic biological process that plays an important role in tumor cell invasion, metastasis and chemoresistance. The complex, multi-step process of EMT involves multiple regulatory mechanisms. Specifically, the PI3K/Akt signaling pathway can affect the EMT in a variety of ways to influence tumor aggressiveness. A better understanding of the regulatory mechanisms related to the EMT can provide a theoretical basis for the early prediction of tumor progression as well as targeted therapy.

An MRAS, SHOC2, and SCRIB complex coordinates ERK pathway activation with polarity and tumorigenic growth

SHOC2 is mutated in Noonan syndrome and plays a key role in the activation of the ERK-MAPK pathway, which is upregulated in the majority of human cancers. SHOC2 functions as a PP1-regulatory protein and as an effector of MRAS. Here we show that SHOC2 and MRAS form a complex with SCRIB, a polarity protein with tumor suppressor properties. SCRIB functions as a PP1-regulatory protein and antagonizes SHOC2-mediated RAF dephosphorylation through a mechanism involving competition for PP1 molecules within the same macromolecular complex. SHOC2 function is selectively required for the malignant properties of tumor cells with mutant RAS, and both MRAS and SHOC2 play a key role in polarized migration. We propose that MRAS, through its ability to recruit a complex with paradoxical components, coordinates ERK pathway spatiotemporal dynamics with polarity and that this complex plays a key role during tumorigenic growth.

MRAS GTPase is a novel stemness marker that impacts mouse embryonic stem cell plasticity and Xenopus embryonic cell fate

Pluripotent mouse embryonic stem cells (mESCs), maintained in the presence of the leukemia inhibitory factor (LIF) cytokine, provide a powerful model with which to study pluripotency and differentiation programs. Extensive microarray studies on cultured cells have led to the identification of three LIF signatures. Here we focus on muscle ras oncogene homolog (MRAS), which is a small GTPase of the Ras family encoded within the Pluri gene cluster. To characterise the effects of Mras on cell pluripotency and differentiation, we used gain- and loss-of-function strategies in mESCs and in the Xenopus laevis embryo, in which Mras gene structure and protein sequence are conserved. We show that persistent knockdown of Mras in mESCs reduces expression of specific master genes and that MRAS plays a crucial role in the downregulation of OCT4 and NANOG protein levels upon differentiation. In Xenopus, we demonstrate the potential of Mras to modulate cell fate at early steps of development and during neurogenesis. Overexpression of Mras allows gastrula cells to retain responsiveness to fibroblast growth factor (FGF) and activin. Collectively, these results highlight novel conserved and pleiotropic effects of MRAS in stem cells and early steps of development.

M-Ras induces Ral and JNK activation to regulate MEK/ERK-independent gene expression in MCF-7 breast cancer cells

Constitutive activation of M-Ras has previously been reported to cause morphologic and growth transformation of murine cells, suggesting that M-Ras plays a role in tumorigenesis. Cell transformation by M-Ras correlated with weak activation of the Raf/MEK/ERK pathway, although contributions from other downstream effectors were suggested. Recent studies indicate that signaling events distinct from the Raf/MEK/ERK cascade are critical for human tumorigenesis. However, it is unknown what signaling events M-Ras triggers in human cells. Using constitutively active M-Ras (Q71L) containing additional mutations within its effector-binding loop, we found that M-Ras induces MEK/ERK-dependent and -independent Elk1 activation as well as phosphatidylinositol 3 kinase (PI3K)/Akt and JNK/cJun activation in human MCF-7 breast cancer cells. Among several human cell lines examined, M-Ras-induced MEK/ERK-independent Elk1 activation was only detected in MCF-7 cells, and correlated with Rlf/M-Ras interaction and Ral/JNK activation. Supporting a role for M-Ras signaling in breast cancer, EGF activated M-Ras and promoted its interaction with endogenous Rlf. In addition, constitutive activation of M-Ras induced estrogen-independent growth of MCF-7 cells that was dependent on PI3K/Akt, MEK/ERK, and JNK activation. Thus, our studies demonstrate that M-Ras signaling activity differs between human cells, highlighting the importance of defining Ras protein signaling within each cell type, especially when designing treatments for Ras-induced cancer. These findings also demonstrate that M-Ras activity may be important for progression of EGFR-dependent tumors.

Charting the NF-κB pathway interactome map

Inflammation is part of a complex physiological response to harmful stimuli and pathogenic stress. The five components of the Nuclear Factor κB (NF-κB) family are prominent mediators of inflammation, acting as key transcriptional regulators of hundreds of genes. Several signaling pathways activated by diverse stimuli converge on NF-κB activation, resulting in a regulatory system characterized by high complexity. It is increasingly recognized that the number of components that impinges upon phenotypic outcomes of signal transduction pathways may be higher than those taken into consideration from canonical pathway representations. Scope of the present analysis is to provide a wider, systemic picture of the NF-κB signaling system. Data from different sources such as literature, functional enrichment web resources, protein-protein interaction and pathway databases have been gathered, curated, integrated and analyzed in order to reconstruct a single, comprehensive picture of the proteins that interact with, and participate to the NF-κB activation system. Such a reconstruction shows that the NF-κB interactome is substantially different in quantity and quality of components with respect to canonical representations. The analysis highlights that several neglected but topologically central proteins may play a role in the activation of NF-κB mediated responses. Moreover the interactome structure fits with the characteristics of a bow tie architecture. This interactome is intended as an open network resource available for further development, refinement and analysis.

Targeting EGFR in Triple Negative Breast Cancer

Our preliminary data show that erlotinib inhibits Triple-negative breast cancer (TNBC) in a xenograft model. However, inhibition of metastasis by erlotinib is accompanied by nonspecific effects because erlotinib can inhibit other kinases; thus, more direct targets that regulate TNBC metastasis need to be identified to improve its therapeutic efficacy.

Ras-association domain family 1C protein promotes breast cancer cell migration and attenuates apoptosis

Background

The Ras association domain family 1 (RASSF1) gene is a Ras effector encoding two major mRNA forms, RASSF1A and RASSF1C, derived by alternative promoter selection and alternative mRNA splicing. RASSF1A is a tumor suppressor gene. However, very little is known about the function of RASSF1C both in normal and transformed cells.

Methods

Gene silencing and over-expression techniques were used to modulate RASSF1C expression in human breast cancer cells. Affymetrix-microarray analysis was performed using T47D cells over-expressing RASSF1C to identify RASSF1C target genes. RT-PCR and western blot techniques were used to validate target gene expression. Cell invasion and apoptosis assays were also performed.

Results

In this article, we report the effects of altering RASSF1C expression in human breast cancer cells. We found that silencing RASSF1C mRNA in breast cancer cell lines (MDA-MB231 and T47D) caused a small but significant decrease in cell proliferation. Conversely, inducible over-expression of RASSF1C in breast cancer cells (MDA-MB231 and T47D) resulted in a small increase in cell proliferation. We also report on the identification of novel RASSF1C target genes. RASSF1C down-regulates several pro-apoptotic and tumor suppressor genes and up-regulates several growth promoting genes in breast cancer cells. We further show that down-regulation of caspase 3 via overexpression of RASSF1C reduces breast cancer cells' sensitivity to the apoptosis inducing agent, etoposide. Furthermore, we found that RASSF1C over-expression enhances T47D cell invasion/migration in vitro.

Conclusion

Together, our findings suggest that RASSF1C, unlike RASSF1A, is not a tumor suppressor, but instead may play a role in stimulating metastasis and survival in breast cancer cells.

M-Ras is activated by bone morphogenetic protein-2 and participates in osteoblastic determination, differentiation, and transdifferentiation

The small GTPase M-Ras is highly expressed in the central nervous system and plays essential roles in neuronal differentiation. However, its other cellular and physiological functions remain to be elucidated. Here, we clarify the novel functions of M-Ras in osteogenesis. M-Ras was prominently expressed in developing mouse bones particularly in osteoblasts and hypertrophic chondrocytes. Its expression was elevated in C3H/10T1/2 (10T1/2) mesenchymal cells and in MC3T3-E1 preosteoblasts during differentiation into osteoblasts. Treatment of C2C12 skeletal muscle myoblasts with bone morphogenetic protein-2 (BMP-2) to bring about transdifferentiation into osteoblasts also induced M-Ras mRNA and protein expression. Moreover, the BMP-2 treatment activated the M-Ras protein. Stable expression of the constitutively active M-Ras(G22V) in 10T1/2 cells facilitated osteoblast differentiation. M-Ras(G22V) also induced transdifferentiation of C2C12 cells into osteoblasts. In contrast, knockdown of endogenous M-Ras by RNAi interfered with osteoblast differentiation in 10T1/2 and MC3T3-E1 cells. Osteoblast differentiation in M-Ras(G22V)-expressing C2C12 cells was inhibited by treatment with inhibitors of p38 MAP kinase (MAPK) and c-Jun N-terminal kinase (JNK) but not by inhibitors of MAPK and ERK kinase (MEK) or phosphatidylinositol 3-kinase. These results imply that M-Ras, induced and activated by BMP-2 signaling, participates in the osteoblastic determination, differentiation, and transdifferentiation under p38 MAPK and JNK regulation.

Restoration of E-cadherin cell-cell junctions requires both expression of E-cadherin and suppression of ERK MAP kinase activation in Ras-transformed breast epithelial cells

E-cadherin is a main component of the cell-cell adhesion junctions that play a principal role in maintaining normal breast epithelial cell morphology. Breast and other cancers that have up-regulated activity of Ras are often found to have down-regulated or mislocalized E-cadherin expression. Disruption of E-cadherin junctions and consequent gain of cell motility contribute to the process known as epithelial-to-mesenchymal transition (EMT). Enforced expression of E-cadherin or inhibition of Ras-signal transduction pathway has been shown to be effective in causing reversion of EMT in several oncogene-transformed and cancer-derived cell lines. In this study, we investigated MCF10A human breast epithelial cells and derivatives that were transformed with either activated H-Ras or N-Ras to test for the reversion of EMT by inhibition of Ras-driven signaling pathways. Our results demonstrated that inhibition of mitogen-activated protein kinase (MAPK) kinase, but not PI3-kinase, Rac, or myosin light chain kinase, was able to completely restore E-cadherin cell-cell junctions and epithelial morphology in cell lines with moderate H-Ras expression. In MCF10A cells transformed by a high-level expression of activated H-Ras or N-Ras, restoration of E-cadherin junction required both the enforced reexpression of E-cadherin and suppression of MAPK kinase. Enforced expression of E-cadherin alone did not induce reversion from the mesenchymal phenotype. Our results suggest that Ras transformation has at least two independent actions to disrupt E-cadherin junctions, with effects to cause both mislocalization of E-cadherin away from the cell surface and profound decrease in the expression of E-cadherin.

Localized Rho GTPase activation regulates RNA dynamics and compartmentalization in tumor cell protrusions

mRNA trafficking and local protein translation are associated with protrusive cellular domains, such as neuronal growth cones, and deregulated control of protein translation is associated with tumor malignancy. We show here that activated RhoA, but not Rac1, is enriched in pseudopodia of MSV-MDCK-INV tumor cells and that Rho, Rho kinase (ROCK), and myosin II regulate the microtubule-independent targeting of RNA to these tumor cell domains. ROCK inhibition does not affect pseudopodial actin turnover but significantly reduces the dynamics of pseudopodial RNA turnover. Gene array analysis shows that 7.3% of the total genes analyzed exhibited a greater than 1.6-fold difference between the pseudopod and cell body fractions. Of these, only 13.2% (261 genes) are enriched in pseudopodia, suggesting that only a limited number of total cellular mRNAs are enriched in tumor cell protrusions. Comparison of the tumor pseudopod mRNA cohort and a cohort of mRNAs enriched in neuronal processes identified tumor pseudopod-specific signaling networks that were defined by expression of M-Ras and the Shp2 protein phosphatase. Pseudopod expression of M-Ras and Shp2 mRNA were diminished by ROCK inhibition linking pseudopodial Rho/ROCK activation to the localized expression of specific mRNAs. Pseudopodial enrichment for mRNAs involved in protein translation and signaling suggests that local mRNA translation regulates pseudopodial expression of less stable signaling molecules as well as the cellular machinery to translate these mRNAs. Pseudopodial Rho/ROCK activation may impact on tumor cell migration and metastasis by stimulating the pseudopodial translocation of mRNAs and thereby regulating the expression of local signaling cascades.

Fra-1 regulates vimentin during Ha-RAS-induced epithelial mesenchymal transition in human colon carcinoma cells

The process of epithelial mesenchymal transition, whereby cells acquire molecular alterations and fibroblastic features, is a fundamental process of embryogenesis and cancer invasion/metastasis. The mechanisms responsible for epithelial mesenchymal transition remain elusive. Human tumors frequently establish constitutively activated RAS signaling, which contributes to the malignant phenotype. In an effort to dissect distinct RAS isoform specific functions, we previously established human colon cell lines stably overexpressing activated Harvey-RAS (Ha-RAS) and Kirsten-RAS (Ki-RAS). Using these, we observed that only oncogenic Ha-RAS overexpression resulted in morphologic and molecular changes suggestive of epithelial to mesenchymal transition. We showed that vimentin, a key molecule of epithelial mesenchymal transition, was differentially regulated between Ha-RAS and Ki-RAS leading to a Ha-RAS specific induction of a migratory phenotype and eventually epithelial to mesenchymal transition. We demonstrated that the AP-1 sites in vimentin promoter could be involved in this regulation. A potential role of FRA-1 was suggested in the regulation of vimentin during the Ha-RAS-induced epithelial to mesenchymal transition, in association with colon cell migration. Our results therefore propose that in colon cells, the induction of epithelial mesenchymal transition by oncogenic Ha-RAS could occur through the overexpression of proteins like FRA-1 and vimentin.

Vimentin and epithelial-mesenchymal transition in human breast cancer--observations in vitro and in vivo

Breast cancer is a highly prevalent disease among women worldwide. While the expression of certain proteins within these tumours is used for prognosis and selection of therapies, there is a continuing need for additional markers to be identified. A considerable amount of current literature, based predominantly on cell culture systems, suggests that a major mechanism responsible for the progression of breast cancer is due to tumour cells losing their epithelial features and gaining mesenchymal properties. These events are proposed to be very similar to the epithelial-mesenchymal transition (EMT) process that has been well characterised in embryonic development. For the developmental and putative cancer EMT, the cell intermediate filament status changes from a keratin-rich network which connects to adherens junctions and hemidesmosomes, to a vimentin-rich network connecting to focal adhesions. This review summarises observations of vimentin expression in breast cancer model systems, and discusses the potential role of EMT in human breast cancer progression, and the prognostic usefulness of vimentin expression.

Characterization of R-ras3/m-ras null mice reveals a potential role in trophic factor signaling

R-Ras3/M-Ras is a member of the RAS superfamily of small-molecular-weight GTP-binding proteins. Previous studies have demonstrated high levels of expression in several regions of the central nervous system, and a constitutively active form of M-Ras promotes cytoskeletal reorganization, cellular transformation, survival, and differentiation. However, the physiological functions of M-Ras during embryogenesis and postnatal development have not been elucidated. By using a specific M-Ras antibody, we demonstrated a high level of M-Ras expression in astrocytes, in addition to neurons. Endogenous M-Ras was activated by several trophic factors in astrocytes, including epidermal growth factor (EGF), basic fibroblast growth factor, and hepatocyte growth factor. Interestingly, M-Ras activation by EGF was more sustained compared to prototypic Ras. A mouse strain deficient in M-Ras was generated to investigate its role in development. M-Ras null mice appeared phenotypically normal, and there was a lack of detectable morphological and neurological defects. In addition, primary astrocytes derived from Mras(-/-) mice did not appear to display substantial alterations in the activation of both the mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways in response to trophic factors.

Transcription factor snail modulates hormone expression in established endocrine pancreatic cell lines

The development of differentiated cells from undifferentiated progenitor cells is one of the central tenets of developmental biology. However, under conditions of tissue morphogenesis, regeneration, and cancer, this process of development is reversed and fully differentiated cells transition to an undifferentiated phenotype. Here we present evidence that the zinc-finger transcription factor Snail modulates this transition in differentiated pancreatic endocrine cell lines. During passage and growth of these cell lines, Snail expression is induced in a subset of cells within the culture, concomitant with a decrease in insulin and/or glucagon expression. As the cells cluster and exit the cell division cycle, nuclear levels of Snail are reduced and hormone expression is resumed. Snail represses proinsulin and proglucagon gene transcription, and reduction of Snail levels by small interfering RNA treatment increases proinsulin gene expression. We propose that Snail modulates the dynamic balance between differentiated and dedifferentiated cells allowing their migration and proliferation. These findings may be relevant to providing approaches for the enhancement of beta-cell growth in individuals with diabetes mellitus.

Distinct molecular mechanisms underlying clinically relevant subtypes of breast cancer: gene expression analyses across three different platforms

Background

Gene expression profiling has been used to define molecular phenotypes of complex diseases such as breast cancer. The luminal A and basal-like subtypes have been repeatedly identified and validated as the two main subtypes out of a total of five molecular subtypes of breast cancer. These two are associated with distinctly different gene expression patterns and more importantly, a significant difference in clinical outcome. To further validate and more thoroughly characterize these two subtypes at the molecular level in tumors at an early stage, we report a gene expression profiling study using three different DNA microarray platforms.

Results

Expression data from 20 tumor biopsies of early stage breast carcinomas were generated on three different DNA microarray platforms; Applied Biosystems Human Genome Survey Microarrays, Stanford cDNA Microarrays and Agilent's Whole Human Genome Oligo Microarrays, and the resulting gene expression patterns were analyzed. Both unsupervised and supervised analyses identified the different clinically relevant subtypes of breast tumours, and the results were consistent across all three platforms. Gene classification and biological pathway analyses of the genes differentially expressed between the two main subtypes revealed different molecular mechanisms descriptive of the two expression-based subtypes: Signature genes of the luminal A subtype were over-represented by genes involved in fatty acid metabolism and steroid hormone-mediated signaling pathways, in particular estrogen receptor signaling, while signature genes of the basal-like subtype were over-represented by genes involved in cell proliferation and differentiation, p21-mediated pathway, and G1-S checkpoint of cell cycle-signaling pathways. A minimal set of 54 genes that best discriminated the two subtypes was identified using the combined data sets generated from the three different array platforms. These predictor genes were further verified by TaqMan^® Gene Expression assays.

Conclusion

We have identified and validated the two main previously defined clinically relevant subtypes, luminal A and basal-like, in a small set of early stage breast carcinomas. Signature genes characterizing these two subtypes revealed that distinct molecular mechanisms might have been pre-programmed at an early stage in different subtypes of the disease. Our results provide further evidence that these breast tumor subtypes represent biologically distinct disease entities and may require different therapeutic strategies. Finally, validated by multiple gene expression platforms, including quantitative PCR, the set of 54 predictor genes identified in this study may define potential prognostic molecular markers for breast cancer.

siRNA gelsolin knockdown induces epithelial-mesenchymal transition with a cadherin switch in human mammary epithelial cells

Epithelial-mesenchymal transition (EMT) describes a process occurring during development and oncogenesis by which epithelial cells obtain fibroblast-like properties and show reduced cell adhesion and increased motility. In this report, we demonstrated typical EMT in human mammary epithelial MCF10A small interfering (si)RNA gelsolin-knockdown cells. EMT was characterized by fibroblastic morphology, loss of contact inhibition and focus formation in monolayer growth, enhanced motility and invasiveness in vitro, increased actin filaments, overexpression of RAC, activation of both extracellular signal-regulated kinase and AKT, inactivation of glycogen synthase kinase-3, conversion of cadherin from the E- to N-type and induction of the transcription factor Snail. These results suggested that gelsolin functions as a switch that controls E- and N-cadherin conversion via Snail, and demonstrated that its knockdown leads to EMT in human mammary epithelial cells and possibly to the development of human mammary tumors.

Caveolin-1 deficiency (-/-) conveys premalignant alterations in mammary epithelia, with abnormal lumen formation, growth factor independence, and cell invasiveness

During breast cancer development, the luminal space of the mammary acinar unit fills with proliferating epithelial cells that exhibit growth factor-independence, cell attachment defects, and a more invasive fibroblastic phenotype. Here, we used primary cultures of mammary epithelial cells derived from genetically engineered mice to identify caveolin-1 (Cav-1) as a critical factor for maintaining the normal architecture of the mammary acinar unit. Isolated cultures of normal mammary epithelial cells retained the capacity to generate mammary acini within extracellular matrix. However, those from Cav-1 (-/-) mice exhibited defects in three-dimensional acinar architecture, including disrupted lumen formation and epidermal growth factor-independent growth due to hyperactivation of the p42/44 mitogen-activated protein kinase cascade. In addition, Cav-1-null mammary epithelial cells deprived of exogenous extracellular matrix underwent a spontaneous epithelial-mesenchymal transition, with reorganization of the actin cytoskeleton, and E-cadherin redistribution. Mechanistically, these phenotypic changes appear to be caused by increases in matrix metalloproteinase-2/9 secretion and transforming growth factor-beta/Smad-2 hyperactivation. Finally, loss of Cav-1 potentiated the ability of growth factors (hepatocyte growth factor and basic fibroblast growth factor) to induce mammary acini branching, indicative of a more invasive fibroblastic phenotype. Thus, a Cav-1 deficiency profoundly affects mammary epithelia by modulating the activation state of important signaling cascades. Primary cultures of Cav-1-deficient mammary epithelia will provide a valuable new model to study the spatial/temporal progression of mammary cell transformation.

Expression of activated M-Ras in hemopoietic stem cells initiates leukemogenic transformation, immortalization and preferential generation of mast cells

Cultures of purified hemopoietic stem cells transduced with an activated mutant of M-Ras contained abnormal cells that, despite the presence of only low levels of growth factors, generated large, dense colonies of macrophages and blast cells. Cells from these colonies survived and grew continuously in the absence of growth factors and generated clonal cell-lines that were mainly composed of well-differentiated mast cells, with a low frequency of undifferentiated cells. When transplanted into sublethally irradiated syngeneic mice, four out of four such clones gave rise to a systemic mastocytosis and mast-cell leukemia. However, the donor clones also generated low percentages of cells with the morphological and cell-surface characteristics of erythrocytes, granulocytes, monocytes and T- and B-lymphocytes. These data indicate that signals downstream of activated M-Ras are sufficient to transform hemopoietic stem cells, and while preserving their capacity to generate other cell-lineages in vivo, result in preferential generation of mast cells.

Epithelial-mesenchymal transition in development and cancer: role of phosphatidylinositol 3' kinase/AKT pathways

Epithelial-mesenchymal transition (EMT) is an important process during development by which epithelial cells acquire mesenchymal, fibroblast-like properties and show reduced intercellular adhesion and increased motility. Accumulating evidence points to a critical role of EMT-like events during tumor progression and malignant transformation, endowing the incipient cancer cell with invasive and metastatic properties. Several oncogenic pathways (peptide growth factors, Src, Ras, Ets, integrin, Wnt/beta-catenin and Notch) induce EMT and a critical molecular event is the downregulation of the cell adhesion molecule E-cadherin. Recently, activation of the phosphatidylinositol 3' kinase (PI3K)/AKT axis is emerging as a central feature of EMT. In this review, we discuss the role of PI3K/AKT pathways in EMT during development and cancer with a focus on E-cadherin regulation. Interactions between PI3K/AKT and other EMT-inducing pathways are presented, along with a discussion of the therapeutic implications of modulating EMT in order to achieve cancer control.

Cyclooxygenase-2 overexpression in MCF-10F human breast epithelial cells inhibits proliferation, apoptosis and differentiation, and causes partial transformation

To investigate the effects of cyclooxygenase-2 (COX-2) overexpression on breast cancer development, we stably transfected MCF-10F human breast epithelial cells with an expression vector containing human COX-2 cDNA oriented in the sense (10F-S) or antisense (10F-AS) direction. As expected, 10F-S cells expressed elevated levels of COX-2 protein, whereas this protein was undetectable in the 10F-AS cells. Prostaglandin E(2) production in these cells reflected COX-2 levels. The 10F-S cells had a significantly decreased rate of proliferation compared to 10F-AS or parental cells, and a delay in progression through the G(1) phase of the cell cycle. COX-2 overexpression also caused resistance to detachment-induced apoptosis (anoikis) as well as an inhibition of differentiation in cells cultured in Matrigel. Furthermore, after approximately 20 passages in culture, 10F-S cells developed fibroblast-like features, expressed vimentin, and formed foci of dense growth when cultured at confluence, suggesting that the cells were undergoing epithelial to mesenchymal transition (EMT). The 10F-S cells, however, were unable to grow in soft agar or form tumors in nude mice, suggesting that they were only partially transformed. Our observations suggest that COX-2 overexpression in human breast epithelial cells will predispose the mammary gland to carcinogenesis.

Snail and Slug are major determinants of ovarian cancer invasiveness at the transcription level

OBJECTIVES

The transcriptional factors Snail and Slug have been reported to be important in cell migration during development and also during tumor metastasis. Their expression and role in ovarian cancer, hitherto unexplored, was examined to understand the molecular events in ovarian cancer metastases since the latter is responsible for the high degree of mortality associated with the disease.

METHODS

Ectopic expression of mSnail and mSlug in the epithelial ovarian cancer cell line SKOV3 was carried out and stable clones were selected. These were used to examine specific repression of the adherens, tight and desmosomal junction components by the two transcription factors. Furthermore, functional implications with respect to enhanced migration of cells, tumorigenecity and metastasis were also studied.

RESULTS

The ectopic expression of Snail or Slug resulted in epithelial-mesenchymal transition (EMT), enhanced motility, invasiveness and tumorigenecity in the cell line SKOV3. In addressing the mechanism by which Snail and Slug lead to loss of intercellular adhesion, specific repression of adherens junction components (E-cadherin and betacatenin), tight junction components (Occludin and ZO-1) and desmosomal junction components (Dsg2) were observed. Snail suppresses expression of adherens and tight junction components, while Slug suppresses expression of all the three junction components; concertedly, bringing down the intercellular adhesion between cells. Further activation of these transcriptional factors in hypoxic conditions revealed a rapid upregulation of Slug expression as an immediate reaction that probably triggers off a signaling cascade leading to Snail expression.

CONCLUSIONS

These results indicate distinct roles of the transcriptional factors Snail and Slug during ovarian cancer metastasis and cell survival through mediation of EMT.

Expression of a constitutively active mutant of M-Ras in normal bone marrow is sufficient for induction of a malignant mastocytosis/mast cell leukemia, distinct from the histiocytosis/monocytic leukemia induced by expression of activated H-Ras

Expression of constitutively activated M-Ras in normal murine bone-marrow cells was sufficient to induce the factor-independent, in vitro growth and differentiation of colonies of macrophages and neutrophils, and the generation of immortal lines of factor-independent mast cells, and, upon in vivo injection of the transduced cells, a fatal mastocytosis/mast-cell leukemia. In contrast, expression of constitutively activated H-Ras in bone-marrow cells resulted in the in vitro growth, in the absence of exogenous factors, of colonies that contained only macrophages and of lines of cells resembling dendritic cells, and, upon in vivo injection of the transduced cells, a fatal histiocytosis/monocytic leukemia. Macrophages generated by bone-marrow cells expressing activated M-Ras or activated H-Ras differed morphologically, the latter appearing more activated, a difference abrogated by an inhibitor of Erk activation. Inhibition of either Erk or PI3 kinase blocked the capacity of both activated M-Ras and activated H-Ras to support proliferation and viability. However, inhibition of p38 MAPK activity suppressed proliferation of bone-marrow cells expressing activated H-Ras, but enhanced that of bone-marrow cells expressing activated M-Ras. Thus, expression of either activated M-Ras or H-Ras in normal hematopoietic cells was sufficient for transformation but each resulted in the generation of distinct lineages of cells.

Multiple Aspects of the Phenotype of Mammary Epithelial Cells Transformed by Expression of Activated M-Ras Depend on an Autocrine Mechanism Mediated by Hepatocyte Growth Factor/Scatter Factor

Multiple aspects of the transformed phenotype induced in a murine mammary epithelial cell line scp-2 by expression of activated G22V M-Ras, including maintainance of cell number at low density, anchorage-independent growth, invasion of Matrigel, and secretion of matrix metalloproteinases (MMP) 2 and 9, were dependent on an autocrine mechanism. Conditioned medium from dense cultures of scp-2 cells expressing G22V M-Ras, but not from parental cells, induced activation of Erk and Akt in cells expressing G22V M-Ras, maintained the cell number and promoted anchorage-independent growth of cells expressing G22V M-Ras (although not the parental cells), and induced scattering of MDCK cells. The latter activities were blocked by neutralizing antibodies to hepatocyte growth factor/scatter factor (HGF/SF) and could be mimicked by HGF/SF. Anti-HGF/SF antibodies also inhibited invasion of Matrigel, and the production of MMP-2 and MMP-9, together with urokinase-type plasminogen activator, was secreted by G22V M-Ras scp-2 cells but not by parental cells. Invasion of Matrigel was blocked by an inhibitor of MMPs, BB94, and by the mitogen-activated protein kinase kinase 1/2 kinase inhibitor PD98059 but was only marginally affected by the phosphatidylinositol 3-kinase inhibitor LY294002. Autocrine HGF/SF was thus critical for expression of key features of the phenotype of mammary epithelial cells transformed by expression of activated M-Ras.