Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0006142 (breast cancer)
 160,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Rho family GTPases RhoA, RhoB, and RhoC regulate the actin cytoskeleton, cell movement, and cell growth. Unlike Ras, up-regulation or overexpression of these GDP/GTP binding molecular switches, but not activating point mutations, has been associated with human cancer. Although they share over 85% sequence identity, RhoA, RhoB, and RhoC appear to play distinct roles in cell transformation and metastasis. In NIH 3T3 cells, RhoA or RhoB overexpression causes transformation whereas RhoC increases the cell migration rate. To specifically target RhoA, RhoB, or RhoC function, we have generated a set of chimeric molecules by fusing the RhoGAP domain of p190, a GTPase-activating protein that accelerates the intrinsic GTPase activity of all three Rho GTPases, with the C-terminal hypervariable sequences of RhoA, RhoB, or RhoC. The p190-Rho chimeras were active as GTPase-activating proteins toward RhoA in vitro, co-localized with the respective active Rho proteins, and specifically down-regulated Rho protein activities in cells depending on which Rho GTPase sequences were included in the chimeras. In particular, the p190-RhoA-C chimera specifically inhibited RhoA-induced transformation whereas p190-RhoC-C specifically reversed the migration phenotype induced by the active RhoC. In human mammary epithelial-RhoC breast cancer cells, p190-RhoC-C, but not p190-RhoA-C or p190-RhoB-C, reversed the anchorage-independent growth and invasion phenotypes caused by RhoC overexpression. In the highly metastatic A375-M human melanoma cells, p190-RhoC-C specifically reversed migration, and invasion phenotypes attributed to RhoC up-regulation. Thus, we have developed a novel strategy utilizing RhoGAP-Rho chimeras to specifically down-regulate individual Rho activity and demonstrate that this approach may be applied to multiple human tumor cells to reverse the growth and/or invasion phenotypes associated with disregulation of a distinct subtype of Rho GTPase.
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PMID:A novel strategy for specifically down-regulating individual Rho GTPase activity in tumor cells. 1293 57

We have characterized the cDNA for a Rho GTPase activating protein (GAP) mapping to chromosome 13q12. The cDNA was characterized by determining the complete sequence of a 4.8 kb cDNA clone that represents the 5' untranslated region (UTR), the translated region, and the 3' UTR. The protein has a sterile alpha-motif (SAM), a distinct GAP domain, and a conserved START (StAR related lipid transfer) domain. The cDNA has 5 instability motifs (ATTTA) in the 3' UTR and one motif in the translated region between GAP and START domains. The RhoGAP transcript is truncated in some breast carcinoma cell lines and it has low expression in other breast cancer cell lines as compared to a normal breast cell line. We have previously observed the absence of RhoGAP transcript in a breast tumor specimen. A GST-fusion of the RhoGAP was tested for its specificity on RhoA, Cdc42, and Rac1. The protein was most active for RhoA. Transfection of RhoGAP into MCF7 cells significantly inhibited cell growth. The introduction of the RhoGAP construct into MDAMB231 cells that had previously been transfected with a p21 construct did not affect cell proliferation, indicating the involvement of p21 in Rho-mediated proliferation of cancer cells. NIH3T3 cells overexpressing RhoGAP showed considerable inhibition of stress fiber formation. Several cDNAs were identified as RhoGAP interactors by using the yeast two-hybrid assay system. These cDNAs correspond to SWI/SNF, alpha-tubulin, HMG CoA reductase, and TAX1 binding protein (TAX1BP1). The interaction with HMG CoA reductase may partially explain the growth inhibition of breast carcinoma cells by statin class of cholesterol lowering drugs. The biological significance of the interacting proteins is discussed in the context of their involvement in tumorigenesis. Our results indicate that loss of RhoGAP or its altered activity suppresses the growth of breast tumor cells. The presence of various motifs in RhoGAP and its interaction with several other proteins suggest that the protein may regulate Rho signaling in multiple ways and possibly function in a Rho-independent manner.
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PMID:Chromosome 13q12 encoded Rho GTPase activating protein suppresses growth of breast carcinoma cells, and yeast two-hybrid screen shows its interaction with several proteins. 1498 79

Overexpression of RhoA or RhoC in breast cancer indicates a poor prognosis, due to increased tumor cell proliferation and invasion and tumor-dependent angiogenesis. Until now, the strategy of blockage of the Rho-signaling pathway has used either GGTI or HMG-CoA reductase inhibitors, but they are not specific to RhoA or RhoC inhibition. In this study, a new approach with anti-RhoA and anti-RhoC siRNAs was used to inhibit specifically RhoA or RhoC synthesis. Two transfections of either RhoA or RhoC siRNA (8.5 nM) into MDA-MB-231 human breast cancer cells or HMEC-1 endothelial cells induced extensive degradation of the target mRNA and led to a dramatic decrease in synthesis of the corresponding protein. In vitro, these siRNAs inhibited cell proliferation and invasion more effectively than conventional blockers of Rho cell signaling. Finally, in a nude mouse model, intratumoral injections of anti-RhoA siRNA (100 microl at 85 nM) every 3 days for 20 days almost totally inhibited the growth and angiogenesis of xenografted MDA-MB-231 tumors. One may infer from these observations that specific inhibition of the Rho-signaling pathway with siRNAs represents a promising approach for the treatment of aggressive breast cancers.
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PMID:Anti-RhoA and anti-RhoC siRNAs inhibit the proliferation and invasiveness of MDA-MB-231 breast cancer cells in vitro and in vivo. 1566 38

Advanced malignancies often exhibit increased concentrations of transforming growth factor-beta (TGF beta), which has been suggested to promote invasion and metastasis. While inhibition of epithelial cell proliferation in response to TGF beta is mainly mediated by the well-characterised Smad pathway, the molecular mechanism leading to TGF beta-induced invasiveness and metastasis are largely unknown. To elucidate these mechanisms, we compared TGF beta1 signalling in MCF-7 and the Smad4-negative MDA-MB-468 breast cancer cells. Both cell lines react to TGF beta1 treatment with decreased subcortical actin and increased numbers of focal contacts. TGF beta1-induced cell migration was strongly dependent on the activation of extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK). These mitogen-activated protein kinases were phosphorylated in response to TGF beta and subsequently translocated into focal contacts. Inhibition of the TGF beta type I receptor ALK5 slightly reduced phosphorylation of ERK in MCF-7 cells, but neither inhibited phosphorylation of ERK in MDA-MB-468 cells nor TGF beta1-induced migration of both cell lines. In contrast, ALK5 inhibition effectively blocked Smad2 phosphorylation. In addition to ERK and JNK, the monomeric GTPase RhoA was activated by TGF beta1 and necessary for TGF beta-induced migration. Taken together, our study identifies a role of ERK and JNK activation and association of activated MAPKs with focal complexes in TGF beta1-induced cell migration in epithelial cells. These TGF beta-dependent processes were mediated independently of Smad4.
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PMID:TGF beta-induced focal complex formation in epithelial cells is mediated by activated ERK and JNK MAP kinases and is independent of Smad4. 1584 68

Metastasis results from a sequence of selective events often involving interactions with elements of the tumor-specific physiological microenvironment. The low-serum component of this microenvironment confers increased motility and invasion in breast cancer cells by activating the Na+/H+ exchanger isoform 1 (NHE1). The present study was undertaken to characterize the signal transduction mechanisms underlying this serum deprivation-dependent activation of both the NHE1 and the concomitant invasive characteristics such as leading edge pseudopodia development and penetration of matrigel in breast cancer cell lines representing different stages of metastatic progression. Using pharmacological and genetic manipulation together with transport and kinase activity assays, we observe that the activation of the NHE1 and subsequent invasion by serum deprivation in metastatic human breast cells is coordinated by a sequential RhoA/p160ROCK/p38MAPK signaling pathway gated by direct protein kinase A phosphorylation and inhibition of RhoA. Fluorescence resonance energy transfer imaging of RhoA activity and immunofluorescence analysis of phospho-RhoA and NHE1 show that serum deprivation dynamically remodels the cell, forming long, leading edge pseudopodia and that this signal module is preferentially compartmentalized in these leading edge pseudopodia, suggesting a tight topographic relation of the signaling module to an invasion-specific cell structure.
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PMID:Protein kinase A gating of a pseudopodial-located RhoA/ROCK/p38/NHE1 signal module regulates invasion in breast cancer cell lines. 1584 33

BACKGROUND: Inflammatory breast cancer (IBC) is the most lethal form of locally invasive breast cancer known. However, very little information is available on the cellular mechanisms responsible for manifestation of the IBC phenotype. To understand the unique phenotype of IBC, we compared the motile and adhesive interactions of an IBC cell line, SUM 149, to the non-IBC cell line SUM 102. RESULTS: Our results demonstrate that both IBC and non-IBC cell lines exhibit similar adhesive properties to basal lamina, but SUM 149 showed a marked increase in adhesion to collagen I. In vitro haptotaxis assays demonstrate that SUM 149 was less invasive, while wound healing assays show a less in vitro migratory phenotype for SUM 149 cells relative to SUM 102 cells. We also demonstrate a role for Rho and E-cadherin in the unique invasive phenotype of IBC. Immunoblotting reveals higher E-cadherin and RhoA expression in the IBC cell line but similar RhoC expression. Rhodamine phalloidin staining demonstrates increased formation of actin stress fibers and larger focal adhesions in SUM 149 relative to the SUM 102 cell line. CONCLUSION: The observed unique actin and cellular architecture as well as the invasive and adhesive responses to the extracellular matrix of SUM 149 IBC cells suggest that the preference of IBC cells for connective tissue, possibly a mediator important for the vasculogenic mimicry via tubulogenesis seen in IBC pathological specimens. Overexpression of E-cadherin and RhoA may contribute to passive dissemination of IBC by promoting cell-cell adhesion and actin cytoskeletal structures that maintain tissue integrity. Therefore, we believe that these findings indicate a passive metastatic mechanism by which IBC cells invade the circulatory system as tumor emboli rather than by active migratory mechanisms.
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PMID:In vitro analysis of the invasive phenotype of SUM 149, an inflammatory breast cancer cell line. 1585 4

beta2-Chimerin is a member of the "non-protein kinase C" intracellular receptors for the second messenger diacylglycerol and the phorbol esters that is yet poorly characterized, particularly in the context of signaling pathways involved in proliferation and cancer progression. beta2-Chimerin possesses a C-terminal Rac-GAP (GTPase-activating protein) domain that accelerates the hydrolysis of GTP from the Rac GTPase, leading to its inactivation. We found that beta2-chimerin messenger levels are significantly down-regulated in human breast cancer cell lines as well as in breast tumors. Adenoviral delivery of beta2-chimerin into MCF-7 breast cancer cells leads to inhibition of proliferation and G(1) cell cycle arrest. Mechanistic studies show that the effect involves the reduction in Rac-GTP levels, cyclin D1 expression, and retinoblastoma dephosphorylation. Studies using the mutated forms of beta2-chimerin revealed that these effects were entirely dependent on its C-terminal GAP domain and Rac-GAP activity. Moreover, MCF-7 cells stably expressing active Rac (V12Rac1) but not RhoA (V14RhoA) were insensitive to beta2-chimerin-induced inhibition of proliferation and cell cycle progression. The modulation of G(1)/S progression by beta2-chimerin not only implies an essential role for Rac in breast cancer cell proliferation but also raises the intriguing possibility that diacylglycerol-regulated non-protein kinase C pathways can negatively impact proliferation mechanisms controlled by Rho GTPases.
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PMID:Rac-GAP-dependent inhibition of breast cancer cell proliferation by {beta}2-chimerin. 1586 13

Rho GDP dissociation inhibitor (RhoGDI) plays an essential role in control of a variety of cellular functions through interactions with Rho family GTPases, including Rac1, Cdc42, and RhoA. RhoGDI is frequently overexpressed in human tumors and chemo-resistant cancer cell lines, raising the possibility that RhoGDI might play a role in the development of drug resistance in cancer cells. We found that overexpression of RhoGDI increased resistance of cancer cells (MDA-MB-231 human breast cancer cells and JLP-119 lymphoma cells) to the induction of apoptosis by two chemotherapeutic agents: etoposide and doxorubicin. Conversely, silencing of RhoGDI expression by DNA vector-mediated RNA interference (small interfering RNA) sensitized MDA-MB-231 cells to drug-induced apoptosis. Resistance to apoptosis was restored by reintroduction of RhoGDI protein expression. The mechanism for the anti-apoptotic activity of RhoGDI may derive from its ability to inhibit caspase-mediated cleavage of Rac1 GTPase, which is required for maximal apoptosis to occur in response to cytotoxic drugs. Taken together, the data show that RhoGDI is an anti-apoptotic molecule that mediates cellular resistance to these chemotherapy agents.
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PMID:Rho GDP dissociation inhibitor protects cancer cells against drug-induced apoptosis. 1602 5

Receptor tyrosine kinases of the Eph family are upregulated in several different types of cancer. One family member in particular, the EphA2 receptor, has been linked to breast, prostate, lung and colon cancer, as well as melanoma. However, mechanisms by which EphA2 contributes to tumor progression are far from clear. In certain tumor cell lines, EphA2 receptor is underphosphorylated, raising the question of whether ligand-induced receptor phosphorylation and its kinase activity play a role in oncogenesis. To test directly the role of EphA2 receptor phosphorylation/kinase activity in tumor progression, we generated EphA2 receptor variants that were either lacking the cytoplasmic domain or carrying a point mutation that inhibits its kinase activity. Expression of these EphA2 mutants in breast cancer cells resulted in decreased tumor volume and increased tumor apoptosis in primary tumors. In addition, the numbers of lung metastases were significantly reduced in both experimental and spontaneous metastasis models. Reduced tumor volume and metastasis are not due to defects in tumor angiogenesis, as there is no significant difference in tumor vessel density between wild-type tumors and tumors expressing EphA2-signaling-defective mutants. In contrast, tumor cells expressing the EphA2 mutants are defective in RhoA GTPase activation and cell migration. Taken together, these results suggest that receptor phosphorylation and kinase activity of the EphA2 receptor, at least in part, contribute to tumor malignancy.
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PMID:A kinase-dependent role for EphA2 receptor in promoting tumor growth and metastasis. 1610 80

In order to display the full metastatic phenotype, the cancer cell must acquire the ability to migrate. In breast cancer, we have previously shown that insulin-like growth factor I (IGF-I) enhances cell motility in the highly metastatic MDA-231BO cell line by activating the type I IGF receptor (IGF1R). This motility response requires activation of IRS-2 and integrin ligation. In order to identify the key molecules downstream of IRS-2, we examined several signaling pathways known to be involved in cell motility. Focal adhesion kinase (FAK) was not activated by IGF-I, but IGF-I caused redistribution of FAK away from focal adhesion plaques. IGF-I treatment of MDA-231BO cells activated RhoA and inhibition of Rho-kinase (ROCK) inhibited the IGF-mediated motility response. The mitogen activated protein kinase (MAPK), p38, was also activated by IGF-I and inhibition of p38 by SB203580 blocked IGF-I induced cell motility. ROCK inhibition with Y-27632 also inhibited p38 phosphorylation suggesting that p38 lies downstream of ROCK. Both Erk1,2 and phosphatidyl-3 kinase (PI3K) were required for IGF-I stimulated cell motility, but only PI3K appeared to be directly downstream of IGF-I. Thus, IGF-I activation of its receptor coordinates multiple signaling pathways required for cell motility. Defining the key molecules downstream of the type I IGF receptor may provide a basis for optimizing therapies directed at this target.
Breast Cancer Res Treat 2005 Sep
PMID:Multiple signaling pathways are activated during insulin-like growth factor-I (IGF-I) stimulated breast cancer cell migration. 1618 36


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