Tiam1 Overexpression Research Articles

Decreased Tiam1-mediated Rac1 activation is responsible for impaired directional persistence of chondrocyte migration in microtia.

The human auricle has a complex structure, and microtia is a congenital malformation characterized by decreased size and loss of elaborate structure in the affected ear with a high incidence. Our previous studies suggest that inadequate cell migration is the primary cytological basis for the pathogenesis of microtia, however, the underlying mechanism is unclear. Here, we further demonstrate that microtia chondrocytes show a decreased directional persistence during cell migration. Directional persistence can define a leading edge associated with oriented movement, and any mistakes would affect cell function and tissue morphology. By the screening of motility-related genes and subsequent confirmations, active Rac1 (Rac1-GTP) is identified to be critical for the impaired directional persistence of microtia chondrocytes migration. Moreover, Rho guanine nucleotide exchange factors (GEFs) and Rho GTPase-activating proteins (GAPs) are detected, and overexpression of Tiam1 significantly upregulates the level of Rac1-GTP and improves directional migration in microtia chondrocytes. Consistently, decreased expression patterns of Tiam1 and active Rac1 are found in microtia mouse models, Bmp5se/J and Prkralear-3J/GrsrJ. Collectively, our results provide new insights into microtia development and therapeutic strategies of tissue engineering for microtia patients.

MiR-590-5p/Tiam1-mediated glucose metabolism promotes malignant evolution of pancreatic cancer by regulating SLC2A3 stability

BackgroundT lymphoma invasion and metastasis 1 (Tiam1) is a tumor related gene that specifically activates Rho-like GTPases Rac1 and plays a critical role in the progression of various malignancies. Glycolysis plays an important role in cancer progression, it is crucial for supplying energy and producing metabolic end products, which can maintain the survival of tumor cells. As yet, however, the mechanism of Tiam1 in glycolysis reprogramming of pancreatic cancer (PC) remains to be clarified. Here, we investigated the functional role of Tiam1 in PC cell proliferation, metastasis and glycolysis reprogramming. It is expected to provide a new direction for clinical treatment.MethodsThe clinical relevance of Tiam1 was evaluated in 66 patients with PC, the effect of Tiam1 on cell proliferation was detected via 5-Ethynyl-2′-deoxyuridine (EdU) and colony formation. The ability of cell migration was detected by the wound healing and Transwell. Quantitative real time polymerase chain reaction (qRT-PCR) and luciferase reporter gene experiments clarify the regulatory relationship of miR-590-5p inhibiting Tiam1. Detection of the molecular mechanism of Tiam1 regulating glucose metabolism reprogramming in PC by glucose metabolism kit. RNA sequencing and Co-Immunoprecipitation (CoIP) have identified glucose transporter protein 3 (SLC2A3) as a key downstream target gene for miR-590-5p/Tiam1.ResultsWe found that Tiam1 expression increased in PC tissues and was associated with lymph node metastasis. The silencing or exogenous overexpression of Tiam1 significantly altered the proliferation, invasion, and angiogenesis of PC cells through glucose metabolism pathway. In addition, Tiam1 could interact with the crucial SLC2A3 and promote the evolution of PC in a SLC2A3-dependent manner. Moreover, miR-590-5p was found to exacerbate the PC cell proliferation, migration and invasion by targeting Tiam1. Furthermore, the reversing effects on proliferation, migration and invasion were found in PC cells with miR-590-5p/Tiam1 overexpression after applying glucose metabolism inhibition.ConclusionsOur findings demonstrate the critical role of Tiam1 in PC development and the miR-590-5p/Tiam1/SLC2A3 signaling pathway may serve as a target for new PC therapeutic strategies.Graphical

ALKBH5 inhibits thyroid cancer progression by promoting ferroptosis through TIAM1-Nrf2/HO-1 axis.

As a critical catalytic subunit of N6-methyladenosine (m6A) modification in messenger RNA, ALKBH5 has been reported to affect the progression of numerous tumors. However, the functions and mechanisms of ALKBH5 in thyroid cancer remain largely unknown. Relative mRNA and protein levels in thyroid cancer tissues and cells were detected by qRT-PCR and western blot, respectively. The proliferation and viability were evaluated using colony formation and CCK-8 assays. Intracellular ironlevel was measured by an iron colorimetric assay kit. ROS level was determined using CellRox Green reagent. TIAM1 mRNA m6A level was detected by MeRIP. Xenograft tumor growth was performed to examine the role of ALKBH5 in thyroid tumor growth in vivo. ALKBH5 was decreased in thyroid cancer tissues and cells. ALKBH5 overexpression inhibited thyroid cancer cell proliferation and increased the levels of Fe2+ and ROS and reduced the proteins expression of GPX4 and SLC7A11. Furthermore, overexpression of ALKBH5 inhibited TIAM1 expression by m6A modification, and overexpression of TIAM1 reversed the regulatory of oe-ALKBH5 on cell proliferation and ferroptosis in thyroid cancer. In addition, TIAM1 was elevated in thyroid cancer, and TIAM1 knockdown repressed thyroid cancer cell proliferation and promoted ferroptosis through regulating Nrf2/HO-1 axis. In addition, in vivo evidences also showed that ALKBH5 suppressed thyroid cancer progression by decreasing the m6A level of TIAM1. Our findings suggested that ALKBH5 inhibited thyroid cancer progression by inducing ferroptosis through m6A-TIAM1-Nrf2/HO-1 axis, suggesting ALKBH5 might be a potential target molecule for the treatment and diagnosis of thyroid cancer.

The RAC1 activator Tiam1 regulates centriole duplication through controlling PLK4 levels.

ABSTRACTCentriole duplication is tightly controlled to maintain correct centriole number through the cell cycle. Key to this is the regulated degradation of PLK4, the master regulator of centriole duplication. Here, we show that the Rac1 guanine nucleotide exchange factor (GEF) Tiam1 localises to centrosomes during S-phase, where it is required for the maintenance of normal centriole number. Depletion of Tiam1 leads to an increase in centrosomal PLK4 and centriole overduplication, whereas overexpression of Tiam1 can restrict centriole overduplication. Ultimately, Tiam1 depletion leads to lagging chromosomes at anaphase and aneuploidy, which are potential drivers of malignant progression. The effects of Tiam1 depletion on centrosomal PLK4 levels and centriole overduplication can be rescued by re-expression of both wild-type Tiam1 and catalytically inactive (GEF*) Tiam1, but not by Tiam1 mutants unable to bind to the F-box protein βTRCP (also known as F-box/WD repeat-containing protein 1A) implying that Tiam1 regulates PLK4 levels through promoting βTRCP-mediated degradation independently of Rac1 activation.

Tumor-associated mesenchymal stem cells promote hepatocellular carcinoma metastasis via a DNM3OS/KDM6B/TIAM1 axis.

Tumor-associated mesenchymal stem cells (MSCs) play a critical role in the growth and metastasis of hepatocellular carcinoma (HCC). However, the mechanism underlying the crosstalk between MSCs and HCC cells is not completely understood. Here, HCC cells were treated with or without conditioned medium of MSCs (CM-MSC), and examined for differential expression of long non-coding RNAs (lncRNAs). Knockdown and overexpression experiments were conducted to explore the function of the lncRNA DNM3OS in MSC-induced HCC growth and metastasis. CM-MSC treatment led to a concentration-dependent induction of DNM3OS in HCC cells. DNM3OS was significantly upregulated in HCC compared to adjacent liver tissues. High DNM3OS expression was associated with TNM stage, vascular invasion, and poor prognosis of HCC patients. Silencing of DNM3OS inhibited HCC cell proliferation and invasion in vitro and tumorigenesis and metastasis in vivo. Overexpression of DNM3OS enhanced HCC cell proliferation, invasion, and metastasis. Biochemically, DNM3OS was mainly localized in the nucleus and physically interacted with KDM6B. The association of DNM3OS with KDM6B induced the expression of TIAM1 through reduction of H3K27me3 at the TIAM1 promoter. TIAM1 overexpression restored the proliferation and invasion of DNM3OS-depleted HCC cells. Our data delineate a mechanism by which MSCs accelerate HCC growth and metastasis through a DNM3OS/KDM6B/TIAM1 axis.

Up-Regulation of Tiam1 Promotes the Radioresistance of Laryngeal Squamous Cell Carcinoma Through Activation of the JNK/ATF-2 Signaling Pathway.

PurposeOur previous study has revealed that T-lymphoma invasion and metastasis-inducing factor 1 (Tiam1) overexpression are significantly associated with aggressive behavior and poor prognosis in patients with laryngeal squamous cell carcinoma (LSCC). However, the influence of Tiam1 in the radioresistance of LSCC and its mechanism have never been elucidated.Materials and MethodsWestern blotting was used to confirm the relationship between Tiam1 and the JNK/ATF-2 signaling pathway. To explore the specific functions of Tiam1 and JNK/ATF-2 signaling pathway on the proliferation and apoptosis of LSCC after radiation, cloning formation assay and flow cytometry were conducted in vitro, and the experiments on a xenograft mouse model and TUNEL assay were performed in vivo.ResultsWestern blotting indicated that Tiam1 can regulate the JNK/ATF-2 signaling pathway through the influence of the activity of JNK and ATF-2. Up-regulation of Tiam1 could promote proliferation and inhibit apoptosis of LSCC after radiation both in vitro and in vivo. Moreover, the down-regulation of the JNK/ATF-2 signaling pathway reduced the radioresistance of LSCC caused by Tiam1 up-regulation.ConclusionThese results suggest that the up-regulation of Tiam1 expression can promote the radioresistance of LSCC through activation of the JNK/ATF-2 signaling pathway.

The prognostic value of Tiam1 correlates with its roles in epithelial-mesenchymal transition progression and angiogenesis in lung adenocarcinoma.

BackgroundTiam1 has been identified as an oncogene and acts as an activator of GTPase Rac. Tiam1 was reported to be a promoter of cancer progression in various cancer types, while in lung adenocarcinoma, its mechanism of action is poorly understood.Materials and MethodsImmunohistochemistry staining and Western blot assay were used to determine Tiam1 expression in lung adenocarcinoma tissues, and its association with prognosis was determined by statistical analysis. We depleted Tiam1 in both A549 and H1975 cancer cell lines. Carboxyfluorescein diacetate succinimidyl ester staining and colony formation assays were used to evaluate its impact on cell proliferation ability after depletion. Transwell migration assay and wound healing assays were performed to determine its impact on migration ability of both cell lines. Western blot assay and immunofluorescence staining were used to analyze the association between Tiam1 and epithelial–mesenchymal transition (EMT) progression. Tube formation assay and vasculogenic mimicry assay were used to show the impact of Tiam1 depletion on cancer angiogenesis.ResultsIn this study, we demonstrated that Tiam1 overexpression in lung adenocarcinoma was significantly associated with advanced tumor grade and poor prognosis. In vitro assays indicated that Tiam1 depletion significantly inhibited cell proliferation, colony formation, and migration capacities in A549 and H1975 cells. Further investigations revealed that Tiam1 plays an important role in EMT program enhancement, angiogenesis, and accelerated tumor progression. Notably, Tiam1 depletion in cancer cells strongly inhibited human umbilical vein endothelial cell angiogenesis and vasculogenic mimicry capacities of both cancer cell lines.ConclusionTiam1 overexpression is associated with lung adenocarcinoma progression and may indicate poor prognosis. Tiam1 accelerated tumor progression due to EMT and angiogenesis enhancement. Our data may provide a novel therapeutic target for lung adenocarcinoma.

Abstract 5226: Tiam1 is a key modulator of chemoresistance in colorectal cancer

Abstract Purpose: Emerging evidence indicates that a small subpopulation of cancer cells with stem cell-like properties are responsible for acquisition of drug resistance in colorectal cancer (CRC). Intriguingly, the acquisition of such a stem-like state and subsequent drug resistance has been shown to be induced by the tumor microenvironment. In particular, cancer associated fibroblasts (CAFs) have been identified as a key component of tumor microenvironment which promote cancer stemness. Wnt signaling is a well-recognized pathway that drives self-renewal, and recently one of the Wnt-responsive genes, Tiam1, a guanine nucleotide exchange factor specific for Rac1, was shown to be overexpressed in CRC and associated with an aggressive cancer phenotype. Herein, we have investigated Tiam1 as a key modulator of chemoresistance in CRC. Methods: Tiam1 expression was assessed in resected CRC tissues from 300 patients who did or did not respond to chemotherapy. We used siRNA and CRISPR/CAS9 approach in three cell lines and animal models to examine whether inhibition of Tiam1 affects chemosensitivity in CRC. In addition, we established CRC patient derived-CAFs and examined whether the drug sensitivity of CRC cells was altered by supplementation of CAF-derived conditioned medium. Results: High Tiam1 expression significantly correlated with poor prognosis in CRC patients (P=0.032), and emerged as an independent prognostic factor (HR 5.06, 95% CI 1.10-23.2, P=0.038). In addition, Tiam1 overexpression is associated with patients who did not respond to chemotherapy (P=0.0005). We demonstrated that siRNA-mediated inhibition of Tiam1 enhanced sensitivity to three chemotherapeutic drugs (5-fluorouracil, oxaliplatin and irinotecan), and reduced tumor invasiveness in HCT116, SW480 and SW620 cell lines. Silencing of Tiam1 resulted in downregulation of stemness-related genes and spheroid formation ability. Furthermore, we validated that Tiam1-knockdown enhanced drug sensitivity and decreased the expression of stemness-related genes in xenograft tumors. Finally, we illustrated that the conditioned medium (CM) derived from CAFs led to increased stemness and chemoresistance in CRC cells through Tiam1 overexpression, and silencing of Tiam1 in CAFs resulted in reversal of stemness and chemoresistance properties. From a mechanistic standpoint, the target genes of Wnt signaling were also upregulated during co-culture with CM in CRC cells. Conclusion: We have firstly demonstrated that Tiam1 is overexpressed in CRC patients who did not respond to chemotherapeutic drugs; and furthermore, high Tiam1 expression emerged as an independent prognostic factor in CRC. Mechanistically, CAFs enhanced CRC chemoresistance through Tiam1 overexpression. Collectively, these results suggest that Tiam1 suppression in stroma may sensitize CRC cells to chemotherapeutic agents, suggesting that Tiam1 may be an attractive therapeutic target in colorectal cancer. Citation Format: Daisuke Izumi. Tiam1 is a key modulator of chemoresistance in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5226.

Elevated expression of Tiam1 is associated with poor prognosis and promotes tumor progression in pancreatic cancer

ObjectiveT-cell lymphoma invasion and metastasis inducing factor 1 (Tiam1) is known to be involved in tumor progression. However, its molecular roles and mechanism in pancreatic ductal adenocarcinoma (PDAC) remain unclear. The purpose of this study is to determine Tiam1 expression levels and investigate its underlying molecular mechanism in PDAC.Materials and methodsTiam1 protein expression levels in PDAC tissues were examined using immunohistochemistry. Tiam1 expression was confirmed in pancreatic cancer (PC) cells by Western blot and immunofluorescence staining. Tiam1-silenced PC cells were created using short interfering RNA. Subsequently, colony formation, scratch, and migration and invasion assays were carried out to explore the molecular mechanisms of Tiam1 in PC cells.ResultsThe results indicated that Tiam1 expression was significantly higher in PDAC tissues than in paired non-tumor tissues, and overexpression of Tiam1 was significantly correlated with histological grade (P=0.040) and lymph node metastasis (P=0.031) in PDAC. The PDAC patients with high Tiam1 expression had significantly lower 5-year overall survival than patients with low Tiam1 expression. More importantly, univariate and multivariate analysis suggested that Tiam1 expression, along with lymph node metastasis, is a significant independent prognostic factor for patients with PDAC. Furthermore, we also demonstrated that the downregulation of Tiam1 was associated with decreased cell proliferation and reduced migratory and invasive capability.ConclusionHigh expression of Tiam1 plays a significant role in the progression of PDAC and may be a potential biomarker of poor prognosis as well as a therapeutic target.

Clinical implication of Tiam1 overexpression in the prognosis of patients with serous ovarian carcinoma.

T lymphoma invasion and metastasis 1 (Tiam1), a guanine nucleotide exchange factor, was originally identified as an invasion- and metastasis-inducing gene in T lymphoma cells. High expression levels of the human Tiam1 gene have been found in numerous human malignancies, suggesting a potential role as a modifier of tumor initiation and progression. However, little is known about the status of Tiam1 in ovarian carcinoma. The present study aimed to investigate the clinicopathological significance of high Tiam1 expression in serous ovarian carcinoma. Immunohistochemical staining for Tiam1 was performed in 182 patients with serous ovarian carcinoma, in 76 patients with ovarian borderline tumors and in 72 patients with benign ovarian tumors. Immunofluorescence staining was also performed to detect the subcellular localization of Tiam1 protein in SK-OV-3 ovarian carcinoma cells. The correlations between high Tiam1 expression and the clinicopathological features of the ovarian carcinomas were evaluated by the χ2 test and Fisher's exact test. The overall survival (OS) rates were calculated by the Kaplan-Meier method, and the association between prognostic factors and patient survival was analyzed by the Cox proportional hazard model. Tiam1 protein showed a cytoplasmic and nuclear staining pattern in ovarian carcinoma. Strongly-positive Tiam1 protein expression was observed in 59.3% (108/182) of ovarian carcinomas, which was significantly higher than in benign serous tumors (12.5%; 9/72). Moreover, the rate of strongly-positive Tiam1 expression in borderline serous tumors (31.6%; 24/76) was also significantly higher than that in benign serous tumors. High Tiam1 protein expression was closely associated with a high histological grade, metastasis, advanced clinical stage and lower OS rates in ovarian carcinoma. Multivariate analysis indicated that Tiam1 was an independent prognostic factor, along with metastasis and clinical stage, in patients with ovarian carcinoma. In conclusion, Tiam1 expression is strongly associated with grade and outcome in ovarian carcinoma, and may serve as a useful molecular marker for clinical management.

Clinicopathological implications of Tiam1 overexpression in invasive ductal carcinoma of the breast.

BackgroundT-lymphoma invasion and metastasis-inducing protein 1 (Tiam1) has been implicated in tumor occurrence and progression. Recent studies have shown that high expression levels of Tiam1 protein appear to be associated with the progression of numerous human tumors. This study attempted to explore the role of Tiam1 protein in tumor progression and the prognostic evaluation of breast cancer.MethodsThe localization of the Tiam1 protein was determined in the MDA-MB-231 breast cancer cell line using immunofluorescence (IF) staining. In addition, a total of 283 breast tissue samples, including 153 breast cancer tissues, 67 ductal carcinoma in situ (DCIS) and 63 adjacent non-tumor breast tissues, were analyzed by immunohistochemical (IHC) staining of the Tiam1 protein. The correlation between Tiam1 expression and clinicopathological characteristics was evaluated by Chi-square test and Fisher’s exact tests. Disease-free survival (DFS) and 10-year overall survival (OS) rates were calculated by the Kaplan-Meier method. Additionally, univariate and multivariate analyses were performed by the Cox proportional hazards regression models.ResultsTiam1 protein showed a mainly cytoplasmic staining pattern in breast cancer cells; however, nuclear staining was also observed. Tiam1 protein expression was significantly higher in breast cancers (42.5 %, 65/153) and DCIS (40.3 %, 27/67) than in adjacent non-tumor tissues (12.7 %, 8/63). In addition, Tiam1 associated with tumor stage and Ki-67 expression, but negatively correlated with receptor tyrosine-protein kinase erbB-2 (Her2) expression. Moreover, survival analyses showed that DFS and 10-year OS rates were significantly lower in breast cancer patients with high Tiam1 expression than those with low Tiam1 expression. Univariate analysis suggested that molecular types, clinical stage, Her2 expression levels and Tiam1 expression levels were also significantly associated with DFS and 10-year OS rates of breast cancer patients. Furthermore, multivariate analysis suggested that Tiam1 expression is a significant independent prognostic factor along with tumor stage in patients with breast cancer.ConclusionsTiam1 expression is frequently up-regulated in breast cancer. Tiam1 expression correlated with clinicopathological parameters, suggesting that it may be a useful prognostic biomarker and potential therapeutic target for patients with breast cancer.

Overexpression of Tiam1 promotes the progression of laryngeal squamous cell carcinoma.

T-lymphoma invasion and metastasis‑inducing factor1 (Tiam1) has been reported in various types of human cancer, which play important roles in facilitating the meta-stasis of malignant tumor. However, the investigation of Tiam1 in laryngeal squamous-cell carcinoma is extremely rare. The aim of the present study was to assess Tiam1 expression and examine its function in tumorigenesis and the metastasis of laryngeal squamous cell carcinoma (LSCC) invitro. Tiam1 expression in 98 primary LSCC tissue specimens was analyzed by immunohistochemistry and correlated with clinicopathological parameters and patients' survival. To investigate the effects of Tiam1 on the progression of LSCC, Tiam1/C1199 plasmid was transfected into LSCC, and proliferation, apoptosis, migration and invasion of transfected cells were examined using MTT, flow cytometry, wound-healing and Transwell assay, respectively. The results showed that, Tiam1 was detected in all primary LSCC samples. Additionally, Tiam1 overexpression was closely correlated with tumor progression and patient survival. Tiam1 overexpression was statistically significant, and served as an independent predictor of prognosis for patients with LSCC. The upregulation of Tiam1 by Tiam1/C1199 plasmid had no effect on the prolife-ration of transfected cells, but decreased the apoptotic rate of transfected cells, while the ability of migration and invasion was increased. These results suggested that Tiam1 overexpression in LSCC is possibly involved in the promotion of migration and invasion, and is a promising therapeutic target in the prevention of the progression of LSCC.

Overexpression of Tiam1 is associated with malignant phenotypes of nasopharyngeal carcinoma.

The aim of the present study was to analyze the roles of T lymphoma invasion and metastasis 1 (Tiam1) in nasopharyngeal carcinoma (NPC) progression and its correlation with clinicopathological features, including the survival of patients with NPC. Tiam1 protein expression in NPC tissues was examined using immunohistochemistry. Reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence staining were performed to detect the expression of Tiam1 in 6 NPC cell lines. Stable Tiam1-overexpressing NPC cells using a transfection technique and Tiam1-silencing NPC cells using short hairpin RNA were constructed. Subsequently, MTT assay, plate and soft agar colony formation assays, cell adhesion, migration, invasion assays and experimental animal models were carried out to detect the biological functions of Tiam1 in vitro and in vivo. Immunohistochemical analysis revealed that Tiam1 had high expression in 96 of 140 (68.6%) paraffin-embedded archival NPC biopsies. Tiam1 overexpression was significantly associated with N classification (P=0.004), distant metastasis (P=0.042) and clinical stage (P=0.042). Patients with higher levels of Tiam1 expression had poorer overall survival (P=0.002). Multivariate analysis revealed that Tiam1 expression is an independent prognostic indicator for the overall survival of NPC patients. Using the approaches of exogenous overexpression and the knockdown of Tiam1 expression, respectively, it was confirmed that Tiam1 promoted cell proliferation, adhesion, invasion and migration in vitro and in vivo. These data support the notion that Tiam1 plays an important role in the progression of NPC, and the overexpression of Tiam1 is associated with malignant phenotypes of NPC.

Elevated expression of T-lymphoma invasion and metastasis inducing factor 1 in squamous-cell carcinoma of the head and neck and its clinical significance

PurposeT-lymphoma invasion and metastasis inducing factor 1 (Tiam1) overexpression has been reported in a variety of human cancers. However, the investigation of Tiam1 in squamous-cell carcinoma of the head and neck (SCCHN) is extremely rare. The aim of the present study is to assess Tiam1 expression and to explore its role in SCCHN. MethodsTiam1 expression in 119 primary SCCHN tissue specimens was analysed by immunohistochemistry and correlated with clinicopathological parameters and patients’ survival. Additionally, 12 paired SCCHN tissues were evaluated for Tiam1 expression by Western blotting. ResultsWestern blotting indicated that Tiam1 expression levels in SCCHN carcinomas were significantly higher than those in the corresponding paraneoplastic tissues (P<0.001). Immmunohistochemistry staining revealed that Tiam1 was detected in all primary tumour samples, moreover, Tiam1 overexpression was significantly correlated with lymph node metastasis (P<0.001), clinical stage (P<0.001), histological grade (P=0.001) and recurrence (P<0.001). Survival analysis demonstrated that high Tiam1 expression was significantly correlated with shorter disease-free survival and overall survival (both P<0.001). When combining the Tiam1 expression and lymph node status, Kaplan–Meier survival showed that patients with Tiam1 overexpression/lymph node metastasis (+) had both shorter disease-free and overall survival than others (both P<0.001). Multivariate Cox proportional hazards model analysis confirmed that lymph node metastasis, histological grade and Tiam1 overexpression were statistically significant, independent predictor of prognosis for patients with SCCHN. ConclusionTiam1 may contribute to SCCHN progression, and represent as a novel prognostic indicator as well as a potential therapeutic target for SCCHN.

Downregulation of T-cell lymphoma invasion and metastasis-inducing factor 1 induces cytoskeletal rearrangement and inhibits the invasive capacity of gastric cancer cells

T-cell lymphoma invasion and metastasis-inducing factor 1 (Tiam-1) is an important member of the diffuse B-cell lymphoma (Dbl) oncogene family. In a previous study, the overexpression of Tiam-1 protein was identified by immunohistochemistry in human gastric cancer tissues, indicating that Tiam-1 may represent a candidate biomarker of the invasive and metastatic capacity of gastric cancer and for patient prognosis. In the present study, in vitro adhesion selection was used to separate two subpopulations with high (MH) or low (ML) invasive and metastatic potential from the MKN-45 human gastric cancer cell line (M0). A positive correlation was observed between Tiam-l mRNA and protein expression levels and the invasive capacity of the cells using RT-PCR and quantitative cellular-ELISA, respectively. To determine the mechanism by which Tiam-1 affects the invasive capacities of gastric cancer cells, Tiam-1 expression was downregulated in the MH subclone by liposomal transfection of antisense oligodeoxynucleotides (ASODNs). Following 48 h of treatment with ASODNs (0.43 µM), Tiam-1 mRNA transcription and protein expression levels in MH cells was decreased by 80 and 24%, respectively, compared with untreated controls. In addition, the in vitro invasive potential of MH cells was suppressed by 60%. Morphological and ultrastructural observations also demonstrated that ASODN-treated MH cells exhibited a smooth surface with markedly reduced filopodia and microspikes, which resembled M0 and ML cells. In addition, cytoskeletal distribution was markedly altered from disordered to regular with reduced long filament-like structures, projections, pseudopodia on the cell surface and decreased actin bodies in the cytoplasm. Results of the current study indicate that the overexpression of Tiam-1 contributes to the invasive phenotypes of gastric cancer cells. These observations are likely to provide an improved insight into the biological mechanisms of Tiam-1 and promote the development of novel treatment strategies in gastric cancer.

Rac-1 Superactivation Triggers Insulin-independent Glucose Transporter 4 (GLUT4) Translocation That Bypasses Signaling Defects Exerted by c-Jun N-terminal kinase (JNK)- and Ceramide-induced Insulin Resistance

Insulin activates a cascade of signaling molecules, including Rac-1, Akt, and AS160, to promote the net gain of glucose transporter 4 (GLUT4) at the plasma membrane of muscle cells. Interestingly, constitutively active Rac-1 expression results in a hormone-independent increase in surface GLUT4; however, the molecular mechanism and significance behind this effect remain unresolved. Using L6 myoblasts stably expressing myc-tagged GLUT4, we found that overexpression of constitutively active but not wild-type Rac-1 sufficed to drive GLUT4 translocation to the membrane of comparable magnitude with that elicited by insulin. Stimulation of endogenous Rac-1 by Tiam1 overexpression elicited a similar hormone-independent gain in surface GLUT4. This effect on GLUT4 traffic could also be reproduced by acutely activating a Rac-1 construct via rapamycin-mediated heterodimerization. Strategies triggering Rac-1 "superactivation" (i.e. to levels above those attained by insulin alone) produced a modest gain in plasma membrane phosphatidylinositol 3,4,5-trisphosphate, moderate Akt activation, and substantial AS160 phosphorylation, which translated into GLUT4 translocation and negated the requirement for IRS-1. This unique signaling capacity exerted by Rac-1 superactivation bypassed the defects imposed by JNK- and ceramide-induced insulin resistance and allowed full and partial restoration of the GLUT4 translocation response, respectively. We propose that potent elevation of Rac-1 activation alone suffices to drive insulin-independent GLUT4 translocation in muscle cells, and such a strategy might be exploited to bypass signaling defects during insulin resistance.

The adhesion-GPCR BAI1 regulates synaptogenesis by controlling the recruitment of the Par3/Tiam1 polarity complex to synaptic sites.

Excitatory synapses are polarized structures that primarily reside on dendritic spines in the brain. The small GTPase Rac1 regulates the development and plasticity of synapses and spines by modulating actin dynamics. By restricting the Rac1-guanine nucleotide exchange factor Tiam1 to spines, the polarity protein Par3 promotes synapse development by spatially controlling Rac1 activation. However, the mechanism for recruiting Par3 to spines is unknown. Here, we identify brain-specific angiogenesis inhibitor 1 (BAI1) as a synaptic adhesion GPCR that is required for spinogenesis and synaptogenesis in mice and rats. We show that BAI1 interacts with Par3/Tiam1 and recruits these proteins to synaptic sites. BAI1 knockdown results in Par3/Tiam1 mislocalization and loss of activated Rac1 and filamentous actin from spines. Interestingly, BAI1 also mediates Rac-dependent engulfment in professional phagocytes through its interaction with a different Rac1-guanine nucleotide exchange factor module, ELMO/DOCK180. However, this interaction is dispensable for BAI1's role in synapse development because a BAI1 mutant that cannot interact with ELMO/DOCK180 rescues spine defects in BAI1-knockdown neurons, whereas a mutant that cannot interact with Par3/Tiam1 rescues neither spine defects nor Par3 localization. Further, overexpression of Tiam1 rescues BAI1 knockdown spine phenotypes. These results indicate that BAI1 plays an important role in synaptogenesis that is mechanistically distinct from its role in phagocytosis. Furthermore, our results provide the first example of a cell surface receptor that targets members of the PAR polarity complex to synapses.

Up-regulation of T-lymphoma and metastasis gene 1 in gastric cancer and its involvement in cell invasion and migration

Background T-lymphoma and metastasis gene 1 (Tiam1) produces a guanine nucleotide exchange factor (GNEF) that regulates guanosine triphosphatase, which transforms guanosine diphosphate to guanosine triphosphate. Recently published data indicate that Tiam1 was associated with gastric cancer. The aim of this study was to investigate biological effects and potential mechanisms of Tiam1 in gastric carcinoma. Methods We analyzed the expression of Tiam1 in 114 pair-matched gastric neoplastic and adjacent non-neoplastic tissues by quantitative real-time PCR. We investigated Tiam1 expression and its prognostic value for gastric cancer. Furthermore, the functions of Tiam1 over-expression were analyzed with stable-expression Tiam1 plasmid in human gastric cancer cell lines. Results Tiam1 expression was significantly associated with cell differentiation and lymphatic metastasis; expression of Tiam1 mRNA was up-regulated in gastric cancer compared to pair-matched adjacent non-tumor tissues. Analyses of surgical tissue samples and 5-year survival of gastric cancer patients showed that those with strong Tiam1 expression had significantly shorter overall survival time than those with negative Tiam1 expression. Ectopic expression of Tiam1 promoted cell growth, migration and invasion of gastric cancer cells in vitro. Conclusions In gastric cancer cells, Tiam1 affects multiple properties associated with acquisition of the metastatic phenotype, and may be a marker of gastric cancer progression and metastasis in a subset of cancer.

Effects of Tiam 1 on Invasive Capacity of Gastric Cancer Cells in vitro and Underlying Mechanisms

To investigate changes in the invasive capacity of gastric cancer cells in vitro after expression inhibition of T lymphoma invasion and metastasis inducing factor 1 (Tiam 1) and underlying mechanisms. Using adhesion selection, two subpopulations with high (MH) or low (ML) invasive capacity were separated from the human gastric cancer cell line MKN-45 (M0). Tiam 1 antisense oligodeoxynucleotide (ASODN) was transfected into MH cells with liposomes, and expression of Tiam 1 mRNA and protein was determined by RT-PCR and quantitative cellular-ELISA. Changes in the cytoskeleton, invasive capacity in vitro and expression of ras-related C3 botulinum toxin substrate 1 (Rac 1), integrin β1 and matrix metalloproteinase 2 (MMP 2) between Tiam 1 ASODN transfected MH cells and non-transfected cells were observed by HE staining, cytoskeletal protein staining, scanning electron microscopy, Boyden chamber tests and cyto-immunohistochemistry. A positive correlation existed between the expression level of Tiam l mRNA or protein and the invasion capacity of gastric cancer cells. After ASODN treatment (0.43 μM for 48 h), Tiam 1 mRNA transcription and protein expression in MH cells were decreased by 80% and 24% respectively (P < 0.05), compared with untreated controls, while invasive capacity in vitro was suppressed by 60% (P < 0.05). Morphologic and ultrastructural observation also showed that ASODN-treated MH cells exhibited smooth surfaces with obviously reduced filopodia and microspikes, which resembled M0 and ML cells. Additionally, cytoskeletal distribution dramatically altered from disorder to regularity with reduced long filament-like structure, projections, pseudopodia on cell surface, and with decreased acitn-bodies in cytoplasm. After Tiam 1 ASODN treatment, the expression of Rac 1 and Integrin β1 in MH cells was not affected (P > 0.05), but that of MMP 2 in MH cells was significantly inhibited compared with untreated cells (P < 0.05). Over-expression of Tiam-1 contributes to the invasive phenotype of gastric cancer cells. Inhibition of Tiam 1 expression could impair the invasive capacity of gastric cancer cells through modulating reconstruction of the cytoskeleton and regulating expression of MMP 2.

Tiam1 is associated with hepatocellular carcinoma metastasis

We have previously demonstrated that overexpression of T lymphoma invasion and metastasis 1 (Tiam1) is correlated with poor prognosis in patients with hepatocellular carcinoma (HCC). In this study, we tried to further investigate the potential roles of Tiam1 in the progression of HCC in a larger set of samples. By detecting Tiam1 expression in 213 HCC patients, we observed that Tiam1 had a higher probability of being overexpressed in HCC patients with metastasis than those without metastasis (68.3% vs. 52.7%, p = 0.036). In addition, the cell line with high metastatic potential expressed more Tiam1 than did the cell line with low metastatic potential. Overexpression of Tiam1 was suggested to be significantly correlated with HCC metastasis. We stably upregulated Tiam1 expression in MHCC97L as well as knocked down Tiam1 expression in HCCLM6. We also investigated the effects of Tiam1 overexpression and knockdown on HCC cells proliferation, migration and invasion in vitro and on tumorigenicity and metastasis in vivo. Overexpression of Tiam1 increased proliferation, migration and invasion of MHCC97L cells, while knockdown of Tiam1 in HCCLM6 cells resulted in the reverse. In vivo functional studies showed upregulation of Tiam1 expression led to an enhancement of tumorigenicity and metastatic potential in mice. However, knockdown of Tiam1 expression exhibited nearly 2.2-fold retardation in tumor growth and great inhibition on tumor metastases. Our results indicate that Tiam1, as a metastasis-related gene, may contribute to HCC invasion and metastasis, and consequently, it may be a useful biomarker for therapeutic strategy and control in HCC treatment.