DNA methylation regulates Microtubule-associated tumor suppressor 1 in human non-small cell lung carcinoma

Microtubule associated tumor suppressor 1 (MTUS1) has been recognized as a tumor suppressor gene in multiple cancers. However, the molecular mechanisms underlying the regulation of MTUS1 are yet to be investigated. This study aimed to clarify the significance of DNA methylation in silencing MTUS1 expression. We report that MTUS1 acts as tumor suppressor in non-small cell lung carcinoma (NSCLC). Analysis of in silico database and subsequent knockdown of DNMT1 suggested an inverse correlation between DNMT1 and MTUS1 function. Interestingly, increased methylation at MTUS1 promoter is associated with low expression of MTUS1. Treatment with DNA methyltransferases (DNMTs) inhibitor, 5-aza-2′-deoxycytidine (AZA) leads to both reduced promoter methylation accompanied with enrichment of H3K9Ac and enhanced MTUS1 expression. Remarkably, knockdown of MTUS1 showed increased proliferation and migration of NSCLC cells in contrast to diminished proliferation and migration, upon treatment with AZA. We concluded that low expression of MTUS1 correlates to DNA methylation and histone deacetylation in human NSCLC.     

Silencing of Discoidin Domain Receptor-1 (DDR1) Concurrently Inhibits Multiple Steps of Metastasis Cascade in Gastric Cancer

Accumulating evidence suggests that a unique set of receptor tyrosine kinases, known as discoidin domain receptors (DDRs), plays a role in cancer progression by interacting with the surrounding collagen matrix. In this study, we investigated the expression and role of DDR1 in human gastric cancer metastasis. Proliferation, migration, invasion, and tube formation assays were conducted in DDR1-expressing MKN74 gastric cancer cells and corresponding DDR1-silenced cells. The effects of DDR1 on tumor growth and metastasis were examined in orthotopically implanted and experimental liver metastasis models in nude mice. The expression of DDR1 in surgical specimens was analyzed by immunohistochemistry. DDR1 was expressed in human gastric cancer cell lines, and its expression in human gastric tumors was associated with poor prognosis. Among seven gastric cancer cell lines, MKN74 expressed the highest levels of DDR1. DDR1-silenced MKN74 cells showed unaltered proliferation activity. In contrast, migration, invasion, and tube formation were significantly reduced. When examined in an orthotopic nude mouse model, DDR1-silenced implanted tumors significantly reduced angiogenesis and lymphangiogenesis, thereby leading to reductions in lymph node metastasis and liver metastasis. In a model of experimental liver metastasis, DDR1-silenced cells almost completely inhibited liver colonization and metastasis. DDR1 deficiency led to reduced expression of the genes encoding vascular endothelial growth factor (VEGF)-A, VEGF-C, and platelet-derived growth factor-B. These results suggest that DDR1 is involved in gastric cancer tumor progression and that silencing of DDR1 inhibits multiple steps of the gastric cancer metastasis process.     

Crk II silencing down-regulates IGF-IR and inhibits migration and invasion of prostate cancer cells

Crk (C10 regulator of kinase) adaptor proteins are highly expressed in many types of human cancers and often contribute to aggressive cancer phenotypes. Crk II, a member of CRK family, has been reported to regulate cell migration and metastasis in breast cancer cells. However, its role in other cancer types has not been reported. In this study, we investigated the molecular function of Crk II in prostate cancer (PCa) cells (CWR-22rv1) in vitro and using a mouse tumor model. Results showed that Crk II knockdown by shRNA-mediated silencing (Crk II-shRNA) in the PCa cells significantly inhibited both cancer cell migration and invasion in cell culture study. Crk II-shRNA cancer cells also significantly decreased colony formation in vitro, but had no significant reduction of tumor volume after 4 weeks of cancer cell xenografting in vivo when compared to the scramble control. Interestingly, Crk II-shRNA cancer cells showed a greatly reduced level of insulin-like growth factor 1 receptor (IGF-1R) and decreased signaling of the IGF-1R/PI3K/Akt axis upon IGF-1 ligand stimulation. A close interaction between Crk II and IGF-1R was demonstrated upon co-immunoprecipitation of IGF-1R with Crk II protein. Further, treatment of cells with either proteosomal degradation or protein synthesis inhibitor showed higher proportion of ubiquitin-associated IGF-1R and faster degradation of IGF-1R in Crk II-shRNA cells in comparison with that in the control cancer cells. Taken together, these data suggest that Crk II plays an important role in the regulation of IGF-1R protein stability and affects downstream of IGF-1R signaling pathways. Therefore, targeting Crk-II can block IGF-1R growth signaling and suppress cancer cell invasion and progression.     

Silencing of Atp6v1c1 Prevents Breast Cancer Growth and Bone Metastasis

Previous studies have shown that Atp6v1c1, a regulator of the assembly of the V0 and V1 domains of the V-ATPase complex, is up-regulated in metastatic oral tumors. Despite these studies, the function of Atp6v1c1 in tumor growth and metastasis is still unknown. Atp6v1c1''s expression in metastatic oral squamous cell carcinoma indicates that Atp6v1c1 has an important function in cancer growth and metastasis. We hypothesized that elevated expression of Atp6v1c1 is essential to cancer growth and metastasis and that Atp6v1c1 promotes cancer growth and metastasis through activation of V-ATPase activity. To test this hypothesis, a Lentivirus-mediated RNAi knockdown approach was used to study the function of Atp6v1c1 in mouse 4T1 mammary tumor cell proliferation and migration in vitro and cancer growth and metastasis in vivo. Our data revealed that silencing of Atp6v1c1 in 4T1 cancer cells inhibited lysosomal acidification and severely impaired 4T1 cell growth, migration, and invasion through Matrigel in vitro. We also show that Atp6v1c1 knockdown with Lenti-c1s3, a lentivirus targeting Atp6v1c1 for shRNA mediated knockdown, can significantly inhibit 4T1 xenograft tumor growth, metastasis, and osteolytic lesions in vivo. Our study demonstrates that Atp6v1c1 may promote breast cancer growth and bone metastasis through regulation of lysosomal V-ATPase activity, indicating that Atp6v1c1 may be a viable target for breast cancer therapy and silencing of Atp6v1c1 may be an innovative therapeutic approach for the treatment and prevention of breast cancer growth and metastasis.     

Protease Nexin-1 affects the migration and invasion of C6 glioma cells through the regulation of urokinase Plasminogen Activator and Matrix Metalloproteinase-9/2

Protease Nexin-1 (PN-1) or Serpine2 is a physiological regulator of extracellular proteases as thrombin and urokinase (uPA) in the brain. Besides, PN-1 is also implicated in some human cancers and further identified as a substrate for Matrix Metalloproteinase (MMP)-9, a key enzyme in tumor invasiveness. Our aim was to study the role of PN-1 in the migration and invasive potential of glioma cells, using the rat C6 glioma cell line as stable clones transfected with pAVU6 + 27 vector expressing PN-1 short-hairpin RNA. We find that PN-1 knockdown enhanced the in vitro migration and invasiveness of C6 cells which also showed a strong gelatinolytic activity by in situ zymography. PN-1 silencing did not alter prothrombin whereas increased uPA, MMP-9 and MMP-2 expression levels and gelatinolytic activity in a conditioned medium from stable C6 cells. Selective inhibitors for MMP-9 (Inhibitor I), MMP-2 (Inhibitor III) or exogenous recombinant PN-1 added to the culture medium of C6 silenced cells restored either the migration and invasive ability or gelatinolytic activity thus validating the specificity of PN-1 silencing strategy. Phosphorylation levels of extracellular signal-related kinases (Erk1/2 and p38 MAPK) involved in MMP-9 and MMP-2 signaling were increased in PN-1 silenced cells. This study shows that PN-1 affects glioma cell migration and invasiveness through the regulation of uPA and MMP-9/2 expression levels which contribute to the degradation of extracellular matrix during tumor invasion.     

BMP2-induction of FN14 promotes protumorigenic signaling in gynecologic cancer cells

We previously reported that bone morphogenetic protein (BMP) signaling promotes tumorigenesis in gynecologic cancer cells. BMP2 enhances proliferation of ovarian and endometrial cancer cells via c-KIT induction, and triggers epithelial-mesenchymal transition (EMT) by SNAIL and/or SLUG induction, leading to increased cell migration. However, the downstream effectors of BMP signaling in gynecological cancer cells have not been clearly elucidated. In this study, we performed RNA-sequencing of Ishikawa endometrial and SKOV3 ovarian cancer cells after BMP2 stimulation, and identified TNFRSF12A, encoding fibroblast growth factor-inducible 14 (FN14) as a common BMP2-induced gene. FN14 knockdown suppressed BMP2-induced cell proliferation and migration, confirmed by MTS and scratch assays, respectively. In addition, FN14 silencing augmented chemosensitivity of SKOV3 cells. As a downstream effector of BMP signaling, FN14 modulated both c-KIT and SNAIL expression, which are important for growth and migration of ovarian and endometrial cancer cells. These results support the notion that the tumor promoting effects of BMP signaling in gynecological cancers are partially attributed to FN14 induction.     

PTHrP promotes malignancy of human oral cancer cell downstream of the EGFR signaling

Parathyroid hormone-related protein (PTHrP) is detected in many aggressive tumors and involved in malignant conversion; however, the underlying mechanism remains obscure. Here, we identified PTHrP as a mediator of epidermal growth factor receptor (EGFR) signaling to promote the malignancies of oral cancers. PTHrP mRNA was abundantly expressed in most of the quiescent oral cancer cells, and was significantly upregulated by EGF stimulation via ERK and p38 MAPK. PTHrP silencing by RNA interference, as well as EGFR inhibitor AG1478 treatment, significantly suppressed cell proliferation, migration, and invasiveness. Furthermore, combined treatment of AG1478 and PTHrP knockdown achieved synergistic inhibition of malignant phenotypes. Recombinant PTHrP substantially promoted cell motility, and rescued the inhibition by PTHrP knockdown, suggesting the paracrine/autocrine function of PTHrP. These data indicate that PTHrP contributes to the malignancy of oral cancers downstream of EGFR signaling, and may thus provide a therapeutic target for oral cancer.     

Identification of RECQ1-regulated transcriptome uncovers a role of RECQ1 in regulation of cancer cell migration and invasion

The RECQ protein family of helicases has critical roles in protecting and stabilizing the genome. Three of the 5 known members of the human RecQ family are genetically linked with cancer susceptibility syndromes, but the association of the most abundant human RecQ homolog, RECQ1, with cellular transformation is yet unclear. RECQ1 is overexpressed in a variety of human cancers, indicating oncogenic functions. Here, we assessed genome-wide changes in gene expression upon knockdown of RECQ1 in HeLa and MDA-MB-231 cells. Pathway analysis suggested that RECQ1 enhances the expression of multiple genes that play key roles in cell migration, invasion, and metastasis, including EZR, ITGA2, ITGA3, ITGB4, SMAD3, and TGFBR2. Consistent with these results, silencing RECQ1 significantly reduced cell migration and invasion. In comparison to genome-wide annotated promoter regions, the promoters of genes downregulated upon RECQ1 silencing were significantly enriched for a potential G4 DNA forming sequence motif. Chromatin immunoprecipitation assays demonstrated binding of RECQ1 to the G4 motifs in the promoters of select genes downregulated upon RECQ1 silencing. In breast cancer patients, the expression of a subset of RECQ1-activated genes positively correlated with RECQ1 expression. Moreover, high RECQ1 expression was associated with poor prognosis in breast cancer. Collectively, our findings identify a novel function of RECQ1 in gene regulation and indicate that RECQ1 contributes to tumor development and progression, in part, by regulating the expression of key genes that promote cancer cell migration, invasion and metastasis.     

IgG silencing induces apoptosis and suppresses proliferation,migration and invasion in LNCaP prostate cancer cells

Immunoglobulin G (IgG) has been implicated in the progression of various cancers. This study explored the role of IgG in the proliferation, apoptosis, cell cycle and in vitro invasive properties of LNCaP prostate cancer cells. We used IGHG1 small interfering RNA to silence IgG1 expression in LNCaP cells. The efficacy of IgG1 gene knockdown was confirmed using qPCR and western blotting. The colony formation, proliferation, migration and invasion abilities of LNCaP cells after transfection were assessed using colony-forming, flow cytometry and transwell assays. The expressions of PCNA and caspase-3 proteins in LNCaP cells after transfection were detected with immunofluorescence staining and western blotting. IgG1 silencing significantly decreased the colony formation, survival, cell cycle progression, migration and invasion of LNCaP cells (p?<?0.05). IgG1 silencing also reduced the amount of the proliferation marker PCNA and induced formation of the apoptotic marker caspase-3 (p?<?0.05). Our results show that IgG1 produced by LNCaP cells confers advantages for tumor cell survival, proliferation, migration and invasion, suggesting that IgG1 is a potential target for prostate cancer treatment.     

Silencing of CD44 Gene Expression in Human 143-B Osteosarcoma Cells Promotes Metastasis of Intratibial Tumors in SCID Mice

Osteosarcoma (OS) is the most frequent primary malignant bone cancer in children and adolescents with a high propensity for lung metastasis. Therefore, it is of great importance to identify molecular markers leading to increased metastatic potential in order to devise more effective therapeutic strategies that suppress metastasis, the major cause of death in OS. CD44, the principal receptor for the extracellular matrix component hyaluronan (HA), is frequently found overexpressed in tumor cells and has been implicated in metastatic spread in various cancer types. Here, we investigated the effects of stable shRNA-mediated silencing of CD44 gene products on in vitro and in vivo metastatic properties of the highly metastatic human 143-B OS cell line. In vitro, CD44 knockdown resulted in a 73% decrease in the adhesion to HA, a 57% decrease in the migration rate in a trans-filter migration assay, and a 28% decrease in the cells'' capacity for anchorage-independent growth in soft agar compared to the control cells, implicating that CD44 expression contributes to the metastatic activity of 143-B cells. However, making use of an orthotopic xenograft OS mouse model, we demonstrated that reduced CD44 expression facilitated primary tumor growth and formation of pulmonary metastases. The enhanced malignant phenotype was associated with decreased adhesion to HA and reduced expression of the tumor suppressor merlin in vivo. In conclusion, our study identified CD44 as a metastasis suppressor in this particular experimental OS model.     

ADAM9 silencing inhibits breast tumor cell invasion in vitro

ADAM9 (A Disintegrin And Metalloproteinase 9) is a member of the ADAM protein family which contains a disintegrin domain. This protein family plays key roles in many physiological processes, including fertilization, migration, and cell survival. The ADAM proteins have also been implicated in various diseases, including cancer. Specifically, ADAM9 has been suggested to be involved in metastasis. To address this question, we generated ADAM9 knockdown clones of MDA-MB-231 breast tumor cells using silencing RNAs that were tested for cell adhesion, proliferation, migration and invasion assays. In RNAi-mediated ADAM9 silenced MDA-MB-231 cells, the expression of ADAM9 was lower from the third to the sixth day after silencing and inhibited tumor cell invasion in matrigel by approximately 72% when compared to control cells, without affecting cell adhesion, proliferation or migration. In conclusion, the generation of MDA-MB-231 knockdown clones lacking ADAM9 expression inhibited tumor cell invasion in vitro, suggesting that ADAM9 is an important molecule in the processes of invasion and metastasis.     

Discoidin domain receptor 2 facilitates prostate cancer bone metastasis via regulating parathyroid hormone-related protein

Prostate cancer frequently metastasizes to the skeleton but the underlying mechanism remains largely undefined. Discoidin domain receptor 2 (DDR2) is a member of receptor tyrosine kinase (RTK) family and is activated by collagen binding. This study aimed to investigate the function and detailed mechanism of DDR2 in prostate cancer bone dissemination. Herein we found that DDR2 was strongly expressed in bone-metastatic prostate cancer cells and tissues compared to that in normal controls. Enhanced expression of constitutively activated DDR2 led to elevation in motility and invasiveness of prostate cancer cells, whereas knockdown of DDR2 through specific shRNA caused a dramatic repression. Knockdown of DDR2 in prostate cancer cells resulted in significant decrease in the proliferation, differentiation and function of osteoblast. Over-expression of DDR2 in prostate cancer cells resulted in notable acceleration of osteoclast differentiation and bone resorption, whereas knockdown of DDR2 exhibited the opposite effects. An intrabone injection bone metastasis animal model demonstrated that DDR2 promoted osteolytic metastasis in vivo. Molecular evidence demonstrated that DDR2 regulated the expression, secretion, and promoter activity of parathyroid hormone-related protein (PTHrP), via modulating Runx2 phosphorylation and transactivity. DDR2 was responsive to TGF-β and involved in TGF-β-mediated osteoclast activation and bone resorption. In addition, DDR2 facilitated prostate cancer cells adhere to type I collagen. This study reveals for the first time that DDR2 plays an essential role in prostate cancer bone metastasis. The mechanism disclosure may provide therapeutic targets for the treatment of prostate cancer.     

DDR1 and DDR2 physical interaction leads to signaling interconnection but with possible distinct functions

ABSTRACT

Discoidin domain receptors 1 and 2 (DDR1 and DDR2) are members of the tyrosine kinase receptors activated after binding with collagen. DDRs are implicated in numerous physiological and pathological functions such as proliferation, adhesion and migration. Little is known about the expression of the two receptors in normal and cancer cells and most of studies focus only on one receptor. Western blot analysis of DDR1 and DDR2 expression in different tumor cell lines shows an absence of high co-expression of the two receptors suggesting a deleterious effect of their presence at high amount. To study the consequences of high DDR1 and DDR2 co-expression in cells, we over-express the two receptors in HEK 293T cells and compare biological effects to HEK cells over-expressing DDR1 or DDR2. To distinguish between the intracellular dependent and independent activities of the two receptors we over-express an intracellular truncated dominant-negative DDR1 or DDR2 protein (DDR1DN and DDR2DN). No major differences of Erk or Jak2 activation are found after collagen I stimulation, nevertheless Erk activation is higher in cells co-expressing DDR1 and DDR2. DDR1 increases cell proliferation but co-expression of DDR1 and DDR2 is inhibitory. DDR1 but not DDR2 is implicated in cell adhesion to a collagen I matrix. DDR1, and DDR1 and DDR2 co-expression inhibit cell migration. Moreover a DDR1/DDR2 physical interaction is found by co-immunoprecipitation assays. Taken together, our results show a deleterious effect of high co-expression of DDR1 and DDR2 and a physical interaction between the two receptors.     

Inhibition of DDR1 reduces invasive features of human A375 melanoma,HT29 colon carcinoma and SK-HEP hepatoma cells

ABSTRACT

DDR1 is a receptor tyrosine kinases for collagen and an adverse prognostic factor in primary and metastatic tumors.Despite this, DDR1 signaling and its functional consequences in tumor development remain unclear. RT-PCR and Western blot show that A375, colon carcinoma HT29 and liver carcinoma SK-HEP human cell lines express functional DDR1 that phosphorylates in response to collagen type I. Chemical inhibition of DDR1 phosphorylation or DDR1 mRNA silencing reduced AKT and ERK phosphorylation, expression of ICAM1 and VCAM1, Ki67 and secretion of MMP9. DDR1 silenced cells showed reduced adhesion to collagen type I, MMP-dependent invasion, and chemotactic and proliferative responses to collagen type I. Our work indicates an essential role for DDR1 signaling in key prometastatic features of collagen type I in human carcinoma cells.     

Discoidin domain receptors: A promising target in melanoma

The discoidin domain receptor 1 (DDR1) is a member of the receptor tyrosine kinase family that signals in response to collagen and that has been implicated in cancer progression. In the present study, we investigated the expression and role of DDR1 in human melanoma progression. Immunohistochemical staining of human melanoma specimens (n = 52) shows high DDR1 expression in melanoma lesions that correlates with poor prognosis. DDR1 expression was associated with the clinical characteristics of Clark level and ulceration and with BRAF mutations. Downregulation of DDR1 by small interfering RNA (siRNA) in vitro inhibited melanoma cells malignant properties, migration, invasion, and survival in several human melanoma cell lines. A DDR tyrosine kinase inhibitor (DDR1‐IN‐1) significantly inhibited melanoma cell proliferation in vitro, and ex vivo and in tumor xenografts, underlining the promising potential of DDR1 inhibition in melanoma.     

Targeting Insulin-Like Growth Factor 1 Receptor Inhibits Pancreatic Cancer Growth and Metastasis

Pancreatic cancer is one of the most lethal cancers. Increasing incidence and mortality indicates that there is still much lacking in detection and management of the disease. This is partly due to a lack of specific symptoms during early stages of the disease. Several growth factor receptors have been associated with pancreatic cancer. Here, we have investigated if an RNA interference approach targeted to IGF-IR could be effective and efficient against pancreatic cancer growth and metastasis. For that, we evaluated the effects of IGF-1R inhibition using small interfering RNA (siRNAs) on tumor growth and metastasis in HPAC and PANC-1 pancreatic cancer cell lines. We found that silencing IGF-1R inhibits pancreatic cancer growth and metastasis by blocking key signaling pathways such AKT/PI3K, MAPK, JAK/STAT and EMT. Silencing IGF-1R resulted in an anti-proliferative effect in PANC-1 and HPAC pancreatic cancer cell lines. Matrigel invasion, transwell migration and wound healing assays also revealed a role for IGF-1R in metastatic properties of pancreatic cancer. These results were further confirmed using Western blotting analysis of key intermediates involved in proliferation, epithelial mesenchymal transition, migration, and invasion. In addition, soft agar assays showed that silencing IGF-1R also blocks the colony forming capabilities of pancreatic cancer cells in vitro. Western blots, as well as, flow cytometric analysis revealed the induction of apoptosis in IGF-1R silenced cells. Interestingly, silencing IGF-1R also suppressed the expression of insulin receptor β. All these effects together significantly control pancreatic cancer cell growth and metastasis. To conclude, our results demonstrate the significance of IGF-1R in pancreatic cancer.     

The tetraspanin CD151 is required for Met-dependent signaling and tumor cell growth

CD151, a transmembrane protein of the tetraspanin family, is implicated in the regulation of cell-substrate adhesion and cell migration through physical and functional interactions with integrin receptors. In contrast, little is known about the potential role of CD151 in controlling cell proliferation and survival. We have previously shown that β4 integrin, a major CD151 partner, not only acts as an adhesive receptor for laminins but also as an intracellular signaling platform promoting cell proliferation and invasive growth upon interaction with Met, the tyrosine kinase receptor for hepatocyte growth factor (HGF). Here we show that RNAi-mediated silencing of CD151 expression in cancer cells impairs HGF-driven proliferation, anchorage-independent growth, protection from anoikis, and tumor progression in xenograft models in vivo. Mechanistically, we found that CD151 is crucially implicated in the formation of signaling complexes between Met and β4 integrin, a known amplifier of HGF-induced tumor cell growth and survival. CD151 depletion hampered HGF-induced phosphorylation of β4 integrin and the ensuing Grb2-Gab1 association, a signaling pathway leading to MAPK stimulation and cell growth. Accordingly, CD151 knockdown reduced HGF-triggered activation of MAPK but not AKT signaling cascade. These results indicate that CD151 controls Met-dependent neoplastic growth by enhancing receptor signaling through β4 integrin-mediated pathways, independent of cell-substrate adhesion.     

Phosphorylation of DARPP-32 regulates breast cancer cell migration downstream of the receptor tyrosine kinase DDR1

Cell migration plays a central role in processes such as development, wound healing and cancer metastasis. Here we describe a novel interaction between DDR1, a receptor tyrosine kinase activated by collagen, and the phosphoprotein DARPP-32 in mammary epithelial cells. DARPP-32 expression was readily detected in non-transformed mammary cell lines, but was strongly reduced or even absent in breast tumor cell lines, such as MCF7. Transfection of MCF7 cells with DARPP-32 resulted in severely impaired cell migration, while DARPP-32 transfection into the DDR1-deficient breast cancer cell line MDA-MB-231 did not alter migration. Co-expression of both DDR1 and DARPP-32 in MDA-MB-231 cells inhibited migration, thereby supporting a critical role of the DDR1/DARPP-32 complex in motility. Mutational substitution of the phosphorylation sites Thr-34 or Thr-75 on DARPP-32 revealed that phosphorylation of Thr-34 is necessary for the ability of DARPP-32 to impair breast tumor cell migration. Thus, DARPP-32 signaling downstream of DDR1 is a potential new target for effective anti-metastatic breast cancer therapy.     

RhoGDIα-dependent balance between RhoA and RhoC is a key regulator of cancer cell tumorigenesis

RhoGTPases are key signaling molecules regulating main cellular functions such as migration, proliferation, survival, and gene expression through interactions with various effectors. Within the RhoA-related subclass, RhoA and RhoC contribute to several steps of tumor growth, and the regulation of their expression affects cancer progression. Our aim is to investigate their respective contributions to the acquisition of an invasive phenotype by using models of reduced or forced expression. The silencing of RhoC, but not of RhoA, increased the expression of genes encoding tumor suppressors, such as nonsteroidal anti-inflammatory drug-activated gene 1 (NAG-1), and decreased migration and the anchorage-independent growth in vitro. In vivo, RhoC small interfering RNA (siRhoC) impaired tumor growth. Of interest, the simultaneous knockdown of RhoC and NAG-1 repressed most of the siRhoC-related effects, demonstrating the central role of NAG-1. In addition of being induced by RhoC silencing, NAG-1 was also largely up-regulated in cells overexpressing RhoA. The silencing of RhoGDP dissociation inhibitor α (RhoGDIα) and the overexpression of a RhoA mutant unable to bind RhoGDIα suggested that the effect of RhoC silencing is indirect and results from the up-regulation of the RhoA level through competition for RhoGDIα. This study demonstrates the dynamic balance inside the RhoGTPase network and illustrates its biological relevance in cancer progression.