TIAM-1 regulates polarized protrusions during dorsal intercalation in the Caenorhabditis elegans embryo through both its GEF and N-terminal domains.

Mediolateral cell intercalation is a morphogenetic strategy used throughout animal development to reshape tissues. Dorsal intercalation in the Caenorhabditis elegans embryo involves the mediolateral intercalation of two rows of dorsal epidermal cells to create a single row that straddles the dorsal midline, and thus is a simple model to study cell intercalation. Polarized protrusive activity during dorsal intercalation requires the C. elegans Rac and RhoG orthologs CED-10 and MIG-2, but how these GTPases are regulated during intercalation has not been thoroughly investigated. In this study, we characterized the role of the Rac-specific guanine nucleotide exchange factor (GEF) TIAM-1 in regulating actin-based protrusive dynamics during dorsal intercalation. We found that TIAM-1 can promote formation of the main medial lamellipodial protrusion extended by intercalating cells through its canonical GEF function, whereas its N-terminal domains function to negatively regulate the generation of ectopic filiform protrusions around the periphery of intercalating cells. We also show that the guidance receptor UNC-5 inhibits these ectopic filiform protrusions in dorsal epidermal cells and that this effect is in part mediated via TIAM-1. These results expand the network of proteins that regulate basolateral protrusive activity during directed rearrangement of epithelial cells in animal embryos.

Deficiency in SPOP-mediated ubiquitination and degradation of TIAM1 promotes gastric cancer progression.

It was well known that SPOP is highly mutated in various cancers especially the prostate cancer and SPOP mutation dramatically impaired its tumor suppressive function. However, the detailed role and underlying mechanisms of SPOP in regulating the growth of gastric cancer is not fully studied. Here, we found that Cullin3SPOP promoted the ubiquitination and degradation of TIAM1 protein in gastric cancer setting. Gastric cancer and prostate cancer derived SPOP mutation failed to suppress the proliferation, migration and invasion of gastric cancer cells partially due to the elevated level of TIAM1 protein. Notably, SPOP protein were negatively associated with TIAM1 protein in human gastric cancer tissue specimens. In conclusion, our results elucidate a molecular mechanism by which SPOP regulates the stability of TIAM1, and further demonstrate that SPOP inhibits the progression of gastric cancer by promoting the ubiquitination and degradation of TIAM1 protein.

A TIAM1-TRIM28 complex mediates epigenetic silencing of protocadherins to promote migration of lung cancer cells.

Lung cancer is the leading cause of cancer deaths. Its high mortality is associated with high metastatic potential. Here, we show that the RAC1-selective guanine nucleotide exchange factor T cell invasion and metastasis-inducing protein 1 (TIAM1) promotes cell migration and invasion in the most common subtype of lung cancer, non-small-cell lung cancer (NSCLC), through an unexpected nuclear function. We show that TIAM1 interacts with TRIM28, a master regulator of gene expression, in the nucleus of NSCLC cells. We reveal that a TIAM1-TRIM28 complex promotes epithelial-to-mesenchymal transition, a phenotypic switch implicated in cell migration and invasion. This occurs through H3K9me3-induced silencing of protocadherins and by decreasing E-cadherin expression, thereby antagonizing cell-cell adhesion. Consistently, TIAM1 or TRIM28 depletion suppresses the migration of NSCLC cells, while migration is restored by the simultaneous depletion of protocadherins. Importantly, high nuclear TIAM1 in clinical specimens is associated with advanced-stage lung adenocarcinoma, decreased patient survival, and inversely correlates with E-cadherin expression.

TIAM1 acts as an actin organization regulator to control adipose tissue-derived pericyte cell fate.

Pericytes are multipotent mesenchymal precursor cells that demonstrate tissue-specific properties. In this study, by comparing human adipose tissue- and periosteum-derived pericyte microarrays, we identified T cell lymphoma invasion and metastasis 1 (TIAM1) as a key regulator of cell morphology and differentiation decisions. TIAM1 represented a tissue-specific determinant between predispositions for adipocytic versus osteoblastic differentiation in human adipose tissue-derived pericytes. TIAM1 overexpression promoted an adipogenic phenotype, whereas its downregulation amplified osteogenic differentiation. These results were replicated in vivo, in which TIAM1 misexpression altered bone or adipose tissue generation in an intramuscular xenograft animal model. Changes in pericyte differentiation potential induced by TIAM1 misexpression correlated with actin organization and altered cytoskeletal morphology. Small molecule inhibitors of either small GTPase Rac1 or RhoA/ROCK signaling reversed TIAM1-induced morphology and differentiation in pericytes. In summary, our results demonstrate that TIAM1 regulates the cellular morphology and differentiation potential of human pericytes, representing a molecular switch between osteogenic and adipogenic cell fates.

Identification of TIAM1 as a Potential Synthetic-Lethal-like Gene in a Defined Subset of Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC), the most common type of liver cancer, has very poor outcomes. Current therapies often have low efficacy and significant toxicities. Thus, there is a critical need for the development of novel therapeutic approaches for HCC. We have developed a novel bioinformatics pipeline, which integrates genome-wide DNA methylation and gene expression data, to identify genes required for the survival of specific molecular cancer subgroups but not normal cells. Targeting these genes may induce cancer-specific "synthetic lethality". Initially, five potential HCC molecular subgroups were identified based on global DNA methylation patterns. Subgroup-2 exhibited the most unique methylation profile and two candidate subtype-specific vulnerability or SL-like genes were identified for this subgroup, including TIAM1, a guanine nucleotide exchange factor encoding gene known to activate Rac1 signalling. siRNA targeting TIAM1 inhibited cell proliferation in TIAM1-positive (subgroup-2) HCC cell lines but had no effect on the normal hepatocyte HHL5 cell line. Furthermore, TIAM1-positive/subgroup-2 cell lines were significantly more sensitive to the TIAM1/RAC1 inhibitor NSC23766 compared with TIAM1-negative HCC lines or the normal HHL5 cell line. The results are consistent with a synthetic lethal role for TIAM1 in a methylation-defined HCC subgroup and suggest it may be a viable therapeutic target in this subset of HCC patients.

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 iron level 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.

TIAM1-mediated synaptic plasticity underlies comorbid depression-like and ketamine antidepressant-like actions in chronic pain.

Chronic pain often leads to depression, increasing patient suffering and worsening prognosis. While hyperactivity of the anterior cingulate cortex (ACC) appears to be critically involved, the molecular mechanisms underlying comorbid depressive symptoms in chronic pain remain elusive. T cell lymphoma invasion and metastasis 1 (Tiam1) is a Rac1 guanine nucleotide exchange factor (GEF) that promotes dendrite, spine, and synapse development during brain development. Here, we show that Tiam1 orchestrates synaptic structural and functional plasticity in ACC neurons via actin cytoskeleton reorganization and synaptic N-methyl-d-aspartate receptor (NMDAR) stabilization. This Tiam1-coordinated synaptic plasticity underpins ACC hyperactivity and drives chronic pain-induced depressive-like behaviors. Notably, administration of low-dose ketamine, an NMDAR antagonist emerging as a promising treatment for chronic pain and depression, induces sustained antidepressant-like effects in mouse models of chronic pain by blocking Tiam1-mediated maladaptive synaptic plasticity in ACC neurons. Our results reveal Tiam1 as a critical factor in the pathophysiology of chronic pain-induced depressive-like behaviors and the sustained antidepressant-like effects of ketamine.

RASAL2 mediated the enhancement of YAP1/TIAM1 signaling promotes malignant phenotypes of pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a high incidence of metastasis and dismal prognosis. As a member of Gas-Gap gene, RASAL2 is involved in the hydrolysis of RAS-GTP to RAS-GDP and abnormal expression in human cancers. Here we firstly described the function of RASAL2 on PDAC to enrich the knowledge of RAS family.We interestingly observed that RASAL2 expression was upregulated in PDAC at both mRNA and protein levels, and high expression of RASAL2 predicted a poor prognosis in PDAC patients. Additionally, RASAL2 promoted malignant behaviors of PDAC in vitro and in vivo. To determine the mechanistic roles of RASAL2 signaling and its potential as a therapeutic target in PDAC, we clarified that RASAL2 could accumulate the TIAM1 expression in different level through inhibiting YAP1 phosphorylation, increased TIAM1 mRNA expression and suppressed ubiquitination of TIAM1 protein. In conclusion, RASAL2 enhances YAP1/TIAM1 signaling and promotes PDAC development and progression.

Fibulin-3 sponges Tiam1 to manipulate MMP-7 activity through ß-catenin signaling in oral squamous cell carcinoma.

Oral squamous cell carcinoma (named OSCC) is considered the most frequent malignancy in oral cavity, which has become a rapid increasing problem for the global public health with unclear molecular mechanism. Previously, Tiam1 (T-lymphoma invasion and metastasis inducing factor 1) has been reported as a potential oncogene for OSCC. Here, we in-depth explored its signaling mechanism for the disorder. The mRNA and protein expression levels of primary differentially expressed genes (Tiam1, Fibulin-3, and MMP-7) were measured in different TNM stages of OSCC patients using RT-PCR and ELISA methods. Based on the analysis of human OSCC cell line CAL27, the relationships between these factors have been further investigated and the interactions were also examined. The luciferase reporter assay was established for the promoter region of MMP-7. Both the epithelial (E-cadherin) and mesenchymal protein markers (Vimentin and Snail) expressions were examined using western blotting. The mRNA and protein activities of Fibulin-3 declined as the increase of TNM stage. Inversely, the mRNA and protein levels of Tiam1 and MMP-7 elevated significantly as OSCC progressed. Tiam1 transfection in CAL27 cells stimulated the expression of MMP-7 by accelerating the nuclear translocation of ß-catenin, which was opposite to the functions of Fibulin-3. Moreover, Tiam1 interacted directly with Fibulin-3. The Tiam1 induced OSCC epithelial-mesenchymal transition (EMT) via MMP-7 activation, which was dependent on the direct binding of ß-catenin at the promoter region. Collectively, these results indicated that Tiam1 competed with Fibulin-3 for nuclear ß-catenin translocation, which subsequently stimulated MMP-7 expression by TCF-4 domain interaction following EMT initiation in OSCC development. Our systematical work hypothesized an innovative signaling cassette for OSCC progression, which provided beneficial references for future clinical study.

YAP1 induces invadopodia formation by transcriptionally activating TIAM1 through enhancer in breast cancer.

Yes-associated protein 1 (YAP1), a central component of the Hippo pathway, plays an important role in tumor metastasis; however, the underlying mechanism remains to be elucidated. Invadopodia are actin-rich protrusions containing multiple proteases and have been widely reported to promote cell invasiveness by degrading the extracellular matrix. In the present study, we report that YAP1 induces invadopodia formation and promotes tumor metastasis in breast cancer cells. We also identify TIAM1, a guanine nucleotide exchange factor, as a target of the YAP1-TEAD4 complex. Our results demonstrate that YAP1 could promote TEAD4 binding to the enhancer region of TIAM1, which activates TIAM1 expression, subsequently increasing RAC1 activity and inducing invadopodia formation. These findings reveal the functional role of Hippo signaling in the regulation of invadopodia and provide potential molecular targets for preventing tumor metastasis in breast cancer.

miR-21-5p/Tiam1-mediated glycolysis reprogramming drives breast cancer progression via enhancing PFKL stabilization.

T lymphoma invasion and metastasis 1 (Tiam1) as a tumor-associated gene specifically activates Rho-like GTPases Rac1 and implicates in the invasive phenotype of many cancers. Altering the glycolytic pathway is foreseen as a sound approach to trigger cancer regression. However, the mechanism of Tiam1 in breast cancer (BC) glycolysis reprogramming remains to be clarified. Here, we reported the Tiam1 high expression and prognostic significance in BC. In vitro and in vivo experimental assays identified the functional role of Tiam1 in promoting BC cell proliferation, metastasis and glycolysis reprogramming. Mechanistically, we showed for the first time that Tiam1 could interact with the crucial glycolytic enzyme phosphofructokinase, liver type (PFKL) and promote the evolution of BC in a PFKL-dependent manner. Moreover, miR-21-5p was found to exacerbate the BC proliferation and aggression by targeting Tiam1. Altogether, our study highlights the critical role of Tiam1 in BC development and that the miR-21-5p/Tiam1/PFKL signaling pathway may serve as a target for new anti-BC therapeutic strategies.

Dendrite regeneration in C. elegans is controlled by the RAC GTPase CED-10 and the RhoGEF TIAM-1.

Neurons are vulnerable to physical insults, which compromise the integrity of both dendrites and axons. Although several molecular pathways of axon regeneration are identified, our knowledge of dendrite regeneration is limited. To understand the mechanisms of dendrite regeneration, we used the PVD neurons in C. elegans with stereotyped branched dendrites. Using femtosecond laser, we severed the primary dendrites and axon of this neuron. After severing the primary dendrites near the cell body, we observed sprouting of new branches from the proximal site within 6 hours, which regrew further with time in an unstereotyped manner. This was accompanied by reconnection between the proximal and distal dendrites, and fusion among the higher-order branches as reported before. We quantified the regeneration pattern into three aspects-territory length, number of branches, and fusion phenomena. Axonal injury causes a retraction of the severed end followed by a Dual leucine zipper kinase-1 (DLK-1) dependent regrowth from the severed end. We tested the roles of the major axon regeneration signalling hubs such as DLK-1-RPM-1, cAMP elevation, let-7 miRNA, AKT-1, Phosphatidylserine (PS) exposure/PS in dendrite regeneration. We found that neither dendrite regrowth nor fusion was affected by the axon injury pathway molecules. Surprisingly, we found that the RAC GTPase, CED-10 and its upstream GEF, TIAM-1 play a cell-autonomous role in dendrite regeneration. Additionally, the function of CED-10 in epidermal cell is critical for post-dendrotomy fusion phenomena. This work describes a novel regulatory mechanism of dendrite regeneration and provides a framework for understanding the cellular mechanism of dendrite regeneration using PVD neuron as a model system.

Loss-of-function variants in TIAM1 are associated with developmental delay, intellectual disability, and seizures.

TIAM Rac1-associated GEF 1 (TIAM1) regulates RAC1 signaling pathways that affect the control of neuronal morphogenesis and neurite outgrowth by modulating the actin cytoskeletal network. To date, TIAM1 has not been associated with a Mendelian disorder. Here, we describe five individuals with bi-allelic TIAM1 missense variants who have developmental delay, intellectual disability, speech delay, and seizures. Bioinformatic analyses demonstrate that these variants are rare and likely pathogenic. We found that the Drosophila ortholog of TIAM1, still life (sif), is expressed in larval and adult central nervous system (CNS) and is mainly expressed in a subset of neurons, but not in glia. Loss of sif reduces the survival rate, and the surviving adults exhibit climbing defects, are prone to severe seizures, and have a short lifespan. The TIAM1 reference (Ref) cDNA partially rescues the sif loss-of-function (LoF) phenotypes. We also assessed the function associated with three TIAM1 variants carried by two of the probands and compared them to the TIAM1 Ref cDNA function in vivo. TIAM1 p.Arg23Cys has reduced rescue ability when compared to TIAM1 Ref, suggesting that it is a partial LoF variant. In ectopic expression studies, both wild-type sif and TIAM1 Ref are toxic, whereas the three variants (p.Leu862Phe, p.Arg23Cys, and p.Gly328Val) show reduced toxicity, suggesting that they are partial LoF variants. In summary, we provide evidence that sif is important for appropriate neural function and that TIAM1 variants observed in the probands are disruptive, thus implicating loss of TIAM1 in neurological phenotypes in humans.

Syndecan-4 affects myogenesis via Rac1-mediated actin remodeling and exhibits copy-number amplification and increased expression in human rhabdomyosarcoma tumors.

Skeletal muscle demonstrates a high degree of regenerative capacity repeating the embryonic myogenic program under strict control. Rhabdomyosarcoma is the most common sarcoma in childhood and is characterized by impaired muscle differentiation. In this study, we observed that silencing the expression of syndecan-4, the ubiquitously expressed transmembrane heparan sulfate proteoglycan, significantly enhanced myoblast differentiation, and fusion. During muscle differentiation, the gradually decreasing expression of syndecan-4 allows the activation of Rac1, thereby mediating myoblast fusion. Single-molecule localized superresolution direct stochastic optical reconstruction microscopy (dSTORM) imaging revealed nanoscale changes in actin cytoskeletal architecture, and atomic force microscopy showed reduced elasticity of syndecan-4-knockdown cells during fusion. Syndecan-4 copy-number amplification was observed in 28% of human fusion-negative rhabdomyosarcoma tumors and was accompanied by increased syndecan-4 expression based on RNA sequencing data. Our study suggests that syndecan-4 can serve as a tumor driver gene in promoting rabdomyosarcoma tumor development. Our results contribute to the understanding of the role of syndecan-4 in skeletal muscle development, regeneration, and tumorigenesis.

MicroRNA-183 as a Novel Regulator Protects Against Cardiomyocytes Hypertrophy via Targeting TIAM1.

BACKGROUND: MicroRNAs serve as important regulators of the pathogenesis of cardiac hypertrophy. Among them, miR-183 is well documented as a novel tumor suppressor in previous studies, whereas it exhibits a downregulated expression in cardiac hypertrophy recently. The present study was aimed to examine the effect of miR-183 on cardiomyocytes hypertrophy. METHODS: Angiotensin II (Ang II) was used for establishment of cardiac hypertrophy model in vitro. Neonatal rat ventricular cardiomyocytes transfected with miR-183 mimic or negative control were further utilized for the phenotype analysis. Moreover, the bioinformatics analysis and luciferase reporter assays were used for exploring the potential target of miR-183 in cardiomyocytes. RESULTS: We observed a significant decreased expression of miR-183 in hypertrophic cardiomyocytes. Overexpression of miR-183 significantly attenuated the cardiomyocytes size morphologically and prohypertrophic genes expression. Moreover, we demonstrated that TIAM1 was a direct target gene of miR-183 verified by bioinformatics analysis and luciferase reporter assays, which showed a decreased mRNA and protein expression in the cardiomyocytes transfected with miR-183 upon Ang II stimulation. Additionally, the downregulated TIAM1 expression was required for the attenuated effect of miR-183 on cardiomyocytes hypertrophy. CONCLUSIONS: Taken together, these evidences indicated that miR-183 acted as a cardioprotective regulator for the development of cardiomyocytes hypertrophy via directly regulation of TIAM1.

TIAM1-RAC1 promote small-cell lung cancer cell survival through antagonizing Nur77-induced BCL2 conformational change.

Small-cell lung cancer (SCLC), an aggressive neuroendocrine malignancy, has limited treatment options beyond platinum-based chemotherapy, whereafter acquired resistance is rapid and common. By analyzing expression data from SCLC tumors, patient-derived models, and established cell lines, we show that the expression of TIAM1, an activator of the small GTPase RAC1, is associated with a neuroendocrine gene program. TIAM1 depletion or RAC1 inhibition reduces viability and tumorigenicity of SCLC cells by increasing apoptosis associated with conversion of BCL2 from its pro-survival to pro-apoptotic function via BH3 domain exposure. This conversion is dependent upon cytoplasmic translocation of Nur77, an orphan nuclear receptor. TIAM1 interacts with and sequesters Nur77 in SCLC cell nuclei and TIAM1 depletion or RAC1 inhibition promotes Nur77 translocation to the cytoplasm. Mutant TIAM1 with reduced Nur77 binding fails to suppress apoptosis triggered by TIAM1 depletion. In conclusion, TIAM1-RAC1 signaling promotes SCLC cell survival via Nur77 nuclear sequestration.

Identification of Rac guanine nucleotide exchange factors promoting Lgl1 phosphorylation in glioblastoma.

The protein Lgl1 is a key regulator of cell polarity. We previously showed that Lgl1 is inactivated by hyperphosphorylation in glioblastoma as a consequence of PTEN tumour suppressor loss and aberrant activation of the PI 3-kinase pathway; this contributes to glioblastoma pathogenesis both by promoting invasion and repressing glioblastoma cell differentiation. Lgl1 is phosphorylated by atypical protein kinase C that has been activated by binding to a complex of the scaffolding protein Par6 and active, GTP-bound Rac. The specific Rac guanine nucleotide exchange factors that generate active Rac to promote Lgl1 hyperphosphorylation in glioblastoma are unknown. We used CRISPR/Cas9 to knockout PREX1, a PI 3-kinase pathway-responsive Rac guanine nucleotide exchange factor, in patient-derived glioblastoma cells. Knockout cells had reduced Lgl1 phosphorylation, which was reversed by re-expressing PREX1. They also had reduced motility and an altered phenotype suggestive of partial neuronal differentiation; consistent with this, RNA-seq analyses identified sets of PREX1-regulated genes associated with cell motility and neuronal differentiation. PREX1 knockout in glioblastoma cells from a second patient did not affect Lgl1 phosphorylation. This was due to overexpression of a short isoform of the Rac guanine nucleotide exchange factor TIAM1; knockdown of TIAM1 in these PREX1 knockout cells reduced Lgl1 phosphorylation. These data show that PREX1 links aberrant PI 3-kinase signaling to Lgl1 phosphorylation in glioblastoma, but that TIAM1 is also to fill this role in a subset of patients. This redundancy between PREX1 and TIAM1 is only partial, as motility was impaired in PREX1 knockout cells from both patients.

T-lymphoma invasion and metastasis 1 promotes invadopodia formation and is regulated by the PI3K/Akt signaling pathway in hepatocellular carcinoma.

At present, there are still many poorly understood aspects of the mechanisms underlying hepatocellular carcinoma (HCC) invasion and metastasis. Invadopodia are important structures for cancer cell invasion and metastasis. We determined that high T-lymphoma invasion and metastasis 1 (Tiam1) expression is associated with HCC invasion and metastasis and poor patient prognosis after surgery. Gain- and loss-of-function studies confirmed that Tiam1 promotes invadopodia formation in HCC by activating Rac1. A series of biochemical experiments confirmed that this effect is regulated by the PI3K/Akt signaling pathway. We also confirmed that PIP2 facilitates this effect. In summary, these findings reveal that Tiam1 plays an important role in invadopodia formation in HCC.

MiR-10b-5p inhibits tumorigenesis in gastric cancer xenograft mice model through down-regulating Tiam1.

The miR-10b-5p plays an important role in gastric cancer development but its exact effect on gastric cancer development in vivo has not been fully studied. We showed that miR-10b-5p inhibited the proliferation and migration of gastric cancer cells by down-regulating Tiam1 which was up-regulated in both gastric cancer cells and tissues. Gastric cancer xenograft experiment showed that lenti-miR-10b-5p treatment and agomir-10b-5p injection could significantly retard tumor growth and reduce tumor size and induced apoptosis. Therefore, our results elucidate the tumor suppressor role of miR-10b-5p in gastric cancer in which it acts as a negative regulator of Tiam1 and also provide a molecular mechanism for agomir-10b-5p to treat gastric cancer.

RBP-J promotes cell growth and metastasis through regulating miR-182-5p-mediated Tiam1/Rac1/p38 MAPK axis in colorectal cancer.

BACKGROUND: RBP-J is involved in number of cellular processes. However, the potential mechanisms of RBP-J on colorectal cancer (CRC) development have not been clearly defined. In this study, we aimed to investigate the role and molecular mechanism of RBP-J in CRC. METHODS: The expression levels of RBP-J and Tiam1 in CRC tissues and cells were evaluated by RT-qPCR or western blot. RBP-J was knocked down with sh-RBP-J or overexpressed by pcDNA3.1-RBP-J in CRC cells. Cell proliferation, migration and invasion abilities were analyzed by MTT, wound healing, and transwell assay, respectively. CHIP-qPCR, RIP and dual luciferase reporter assays were performed to confirm the interaction between miR-182-5p and RBP-J or Tiam1. Expression levels of p-p38 MAPK, p38 MAPK, Slug-1, Twist1 and MMP-9 were analyzed by western blot. G-LISA test was used to detect Rac1 activity. RESULTS: Our results showed that the expression of RBP-J and Tiam1 was significantly up-regulated in CRC tissues and cells. RBP-J overexpression promoted proliferation, migration and invasion of CRC cells. Moreover, RBP-J was found to directly target miR-182-5p promoter and positively regulate the Tiam1/Rac1/p38 MAPK signaling pathway in CRC cells. It was also proved that miR-182-5p can bind Tiam1 directly. Furthermore, experiments revealed that RBP-J could promote CRC cell proliferation, migration and invasion via miR-182-5p-mediated Tiam1/Rac1/p38 MAPK axis. In addition, knockdown of RBP-J reduced tumor growth and metastasis in CRC mice. CONCLUSION: RBP-J regulates CRC cell growth and metastasis through miR-182-5p mediated Tiam1/Rac1/p38 MAPK signaling pathway, implying potential novel therapeutic targets for CRC patients.