GIT1 promotes lung cancer cell metastasis through modulating Rac1/Cdc42 activity and is associated with poor prognosis

The Discovery of GIT1/β-Pix Inhibitors: Virtual Screening and Biological Evaluation of New Small-molecule Compounds with Anti-invasion Effect in Gastrointestinal Neoplasms

Background and Objective

GIT1 (G-protein-coupled receptor kinase interacting protein-1) has been found to be highly related with cancer cell invasion and metastasis in many cancer types. β-Pix (p21-activated kinase-interacting exchange factor) is one of the proteins that interact with GIT1. Targeting GIT1/β-Pix complex might be a potential therapeutic strategy for interfering cancer metastasis. However, at present, no well-recognized small-molecule inhibitor targeting GIT1/β-Pix is available. Thus, we aim to discover novel GIT1/β-Pix inhibitors with simple scaffold, high activity and low toxicity to develop new therapeutic strategies to restrain cancer metastasis.

Methods

GIT1/β-Pix inhibitors were identified from ChemBridge by virtual screening. Briefly, the modeling of GIT1 was performed and the establishment of GIT1/β-Pix binding pocket enabled the virtual screening to identify the inhibitor. In addition, direct binding of the candidate molecules to GIT1 was detected by biolayer interferometry (BLI) to discover the hit compound. Furthermore, the inhibitory effect on invasion of stomach and colon cancer cells in vitro was carried out by the transwell assay and detection of epithelial-mesenchymal transition (EMT)-related proteins. Finally, the binding mode of hit compound to GIT1 was estimated by molecular dynamics simulation to analyze the key amino residues to guide further optimization.

Results

We selected the top 50 compounds from the ChemBridge library by virtual screening. Then, by skeleton similarity analysis nine compounds were selected for further study. Furthermore, the direct interaction of nine compounds to GIT1 was detected by BLI to obtain the best affinitive compound. Finally, 17302836 was successfully identified (KD = 84.1±2.0 μM). In vitro tests on 17302836 showed significant anti-invasion effect on gastric cancer and colorectal cancer.

Conclusion

We discovered a new GIT1/β-Pix inhibitor (17302836) against gastrointestinal cancer invasion and metastasis. This study provides a promising candidate for developing new GIT1/β-Pix inhibitors for tumor treatment.

Ras superfamily GTPase activating proteins in cancer: Potential therapeutic targets?

To search more therapeutic strategies for Ras-mutant tumors, regulators of the Ras superfamily involved in the GTP/GDP (guanosine triphosphate/guanosine diphosphate) cycle have been well concerned for their anti-tumor potentials. GTPase activating proteins (GAPs) provide the catalytic group necessary for the hydrolysis of GTPs, which accelerate the switch by cycling between GTP-bound active and GDP-bound inactive forms. Inactivated GAPs lose their function in activating GTPase, leading to the continuous activation of downstream signaling pathways, uncontrolled cell proliferation, and eventually carcinogenesis. A growing number of evidence has shown the close link between GAPs and human tumors, and as a result, GAPs are believed as potential anti-tumor targets. The present review mainly summarizes the critically important role of GAPs in human tumors by introducing the classification, function and regulatory mechanism. Moreover, we comprehensively describe the relationship between dysregulated GAPs and the certain type of tumor. Finally, the current status, research progress, and clinical value of GAPs as therapeutic targets are also discussed, as well as the challenges and future direction in the cancer therapy.

GIT1 protects against breast cancer growth through negative regulation of Notch

Hyperactive Notch signalling is frequently observed in breast cancer and correlates with poor prognosis. However, relatively few mutations in the core Notch signalling pathway have been identified in breast cancer, suggesting that as yet unknown mechanisms increase Notch activity. Here we show that increased expression levels of GIT1 correlate with high relapse-free survival in oestrogen receptor-negative (ER(-)) breast cancer patients and that GIT1 mediates negative regulation of Notch. GIT1 knockdown in ER(-) breast tumour cells increased signalling downstream of Notch and activity of aldehyde dehydrogenase, a predictor of poor clinical outcome. GIT1 interacts with the Notch intracellular domain (ICD) and influences signalling by inhibiting the cytoplasm-to-nucleus transport of the Notch ICD. In xenograft experiments, overexpression of GIT1 in ER(-) cells prevented or reduced Notch-driven tumour formation. These results identify GIT1 as a modulator of Notch signalling and a guardian against breast cancer growth.

Notch signalling is reported to be hyperactivated in oestrogen receptor-negative (ER-) breast cancer. Here the authors show that G protein-coupled receptor kinase-interacting protein 1 (GIT1) negatively regulates Notch signalling and tumour growth in ER- breast cancer by blocking Notch ICD nuclear translocation.

Mouse-INtraDuctal (MIND): an in vivo model for studying the underlying mechanisms of DCIS malignancy

Due to widespread adoption of screening mammography, there has been a significant increase in new diagnoses of ductal carcinoma in situ (DCIS). However, DCIS prognosis remains unclear. To address this gap, we developed an in vivo model, Mouse-INtraDuctal (MIND), in which patient-derived DCIS epithelial cells are injected intraductally and allowed to progress naturally in mice. Similar to human DCIS, the cancer cells formed in situ lesions inside the mouse mammary ducts and mimicked all histologic subtypes including micropapillary, papillary, cribriform, solid, and comedo. Among 37 patient samples injected into 202 xenografts, at median duration of 9 months, 20 samples (54%) injected into 95 xenografts showed in vivo invasive progression, while 17 (46%) samples injected into 107 xenografts remained non-invasive. Among the 20 samples that showed invasive progression, nine samples injected into 54 xenografts exhibited a mixed pattern in which some xenografts showed invasive progression while others remained non-invasive. Among the clinically relevant biomarkers, only elevated progesterone receptor expression in patient DCIS and the extent of in vivo growth in xenografts predicted an invasive outcome. The Tempus XT assay was used on 16 patient DCIS formalin-fixed, paraffin-embedded sections including eight DCISs that showed invasive progression, five DCISs that remained non-invasive, and three DCISs that showed a mixed pattern in the xenografts. Analysis of the frequency of cancer-related pathogenic mutations among the groups showed no significant differences (KW: p > 0.05). There were also no differences in the frequency of high, moderate, or low severity mutations (KW; p > 0.05). These results suggest that genetic changes in the DCIS are not the primary driver for the development of invasive disease. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

G-Protein-Coupled Receptor Kinase-Interacting Protein 1 (GIT1) Promotes Head and Neck Squamous Cell Carcinoma Metastases via Activating the PI3K/AKT/mTOR Signal Pathway

OBJECTIVE

GIT1 is identified as a novel tumor oncogene in breast cancer. In this article, we aimed to explore the role of GIT1 in the progression of head and neck squamous cell carcinoma (HNSCC).

METHODS

GIT1 expression in HNSCC was detected by RT-qPCR, immunohistochemistry assay, and Western blot. HNSCC cell proliferation, migration, and invasion were examined by CCK-8 assay, Wound healing assay, and Transwell assay, respectively. Cell apoptosis was detected by flow cytometric analysis.

RESULTS

In our study, GIT1 was notably upregulated in HNSCC tissues and cells. Moreover, GIT1 expression level had positive corelation with pathological grade and nodal status of HNSCC. Functional experiments showed that knockdown of GIT1 restrained HNSCC proliferation, invasion, migration, and EMT and facilitated cell apoptosis. Furthermore, GIT1 knockdown was found to restrain HNSCC tumor growth and lung metastasis. Additionally, PI3K/AKT/mTOR signal pathway inhibitors suppressed the effect of GIT1 on HNSCC cell progression.

CONCLUSION

GIT1 was upregulated in HNSCC and facilitated HNSCC cell progression by inducing PI3K/AKT/mTOR signal pathway. Therefore, we suggested that GIT1 might be a potential target for HNSCC treatment.

GIT1 overexpression promotes epithelial-mesenchymal transition and predicts poor prognosis in hepatocellular carcinoma

Globally, hepatocellular carcinoma (HCC) is one of the most common causes of cancer-associated mortalities. It has a high rate of metastasis and recurrence, which predict a poor prognosis. G-protein-coupled receptor (GPCR)-kinase interacting protein-1 (GIT1) is a multifunctional scaffold protein that mediates the progression of various tumors. Studies have correlated GIT1 with HCC, however, these correlations have not been fully elucidated. Therefore, we aimed at evaluating the expression of GIT1 in HCC tissues and cells, and to investigate its role and potential mechanisms in HCC progression. The expression levels of GIT1 in HCC tissues and other cancers was determined by using the Oncomine and TCGA databases. Functional analysis of GIT1 in HCC was evaluated through in vitro and in vivo experiments, whereby, HCC cells were transfected with synthetically overexpressed and short hairpin RNA (shRNA) lentivirus-mediated plasmids. Kaplan-Meier and Cox regression methods were used to establish the associations between GIT1 and clinical outcomes of 158 HCC patients. GIT1 was found to be elevated in HCC tissues where it promoted the invasion, migration, and proliferation of HCC cells. Moreover, the overexpression of GIT1 prompted epithelial-mesenchymal transition (EMT) by activating extracellular regulated kinase 1/2 (ERK1/2) pathway, which was shown to be reversed by SCH772984, a specific ERK1/2 inhibitor. GIT1 was also found to be associated with malignant features of HCC, leading to a poorer prognosis. In conclusion, GIT1 promotes HCC progression by inducing EMT and may reflect the course of HCC patients.

UBTF facilitates melanoma progression via modulating MEK1/2-ERK1/2 signalling pathways by promoting GIT1 transcription

Background

UBTF is an HMGB-box DNA binding protein and a necessary Pol I/Pol II basal transcription factor. It has been found that UBTF involves in carcinogenesis and progression of a few cancers. Nevertheless, the the biological function and potential molecular mechanism of UBTF in melanoma are still not clear and need to be clarified.

Methods

UBTF and GIT1 expressions in melanoma specimens and cell lines were examined by quantitative real-time PCR (qRT-PCR) and Western blot. MTT and colony formation assays were used to investigate the effects of UBTF and GIT1 on melanoma cell proliferation. Cell cycle and apoptosis assays were detected by flow cytometry. Tumor formation assay was used to analyze the effect of UBTF on melanoma growth. Bioinformatics predicting, chromatin immunoprecipitation (ChIP)-qRT-PCR and reporter gene assay were fulfilled for verifing GIT1 as UBTF targeting gene.

Results

Here we reported that UBTF mRNA and protein expressions were upregulated in primary melanoma specimens and cell lines. UBTF overexpression facilitated melanoma cell proliferation and cell cycle progression and restrained. Silencing UBTF suppressed cell multiplication, cell cycle progression and tumor growth, and promoted apoptosis. UBTF expression was positively related with GIT1 expression in human melanoma tissues. It was verified that UBTF promoted GIT1 transcription in melanoma cells through binding to the promoter region of GIT1. Furthermore, GIT1 overexpression promoted melanoma cell growth and suppressed apoptosis. Knockdown of GIT1 inhibited cell multiplication and induced apoptosis. Overexpression of GIT1 eliminated the effects of silencing UBTF on melanoma cells. Importantly, UBTF activated MEK1/2-ERK1/2 signalling pathways by upregulating GIT1 expression.

Conclusions

Our study demonstrates that UBTF promotes melanoma cell proliferation and cell cycle progression by promoting GIT1 transcription, thereby activating MEK1/2-ERK1/2 signalling pathways. The findings indicate that UBTF plays a crucial function in melanoma and may be a potential therapeutic target for the treatment of this disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02237-8.

Liquid-Liquid Phase Separation at the Plasma Membrane-Cytosol Interface: Common Players in Adhesion, Motility, and Synaptic Function

Networks of scaffold proteins and enzymes assemble at the interface between the cytosol and specific sites of the plasma membrane, where these networks guide distinct cellular functions. Some of these plasma membrane-associated platforms (PMAPs) include shared core components that are able to establish specific protein-protein interactions, to produce distinct supramolecular assemblies regulating dynamic processes as diverse as cell adhesion and motility, or the formation and function of neuronal synapses. How cells organize such dynamic networks is still an open question. In this review we introduce molecular networks assembling at the edge of migrating cells, and at pre- and postsynaptic sites, which share molecular players that can drive the assembly of biomolecular condensates. Very recent experimental evidence has highlighted the emerging role of some of these multidomain/scaffold proteins belonging to the GIT, liprin-α and ELKS/ERC families as drivers of liquid-liquid phase separation (LLPS). The data point to an important role of LLPS: (i) in the formation of PMAPs at the edge of migrating cells, where LLPS appears to be involved in promoting protrusion and the turnover of integrin-mediated adhesions, to allow forward cell translocation; (ii) in the assembly of the presynaptic active zone and of the postsynaptic density deputed to the release and reception of neurotransmitter signals, respectively. The recent results indicate that LLPS at cytosol-membrane interfaces is suitable not only for the regulation of active cellular processes, but also for the continuous spatial rearrangements of the molecular interactions involved in these dynamic processes.

Overexpression of microRNA-19a-3p promotes lymph node metastasis of esophageal squamous cell carcinoma via the RAC1/CDC42-PAK1 pathway

BACKGROUND

A tendency towards extensive regional lymph node metastasis (LNM) is a typical clinical characteristic of esophageal squamous cell carcinoma (ESCC). Up-regulated microRNA (miR)-19a-3p was verified as a predictor of LNM in ESCC in previous microarray analyses, but the underlying mechanisms remain unclear. Here, in vitro experiments were performed to confirm the effect of miR-19a-3p on promoting LNM and to explore the underlying mechanisms.

METHODS

KYSE-150 and TE-1 cell lines were transfected with lentiviral vectors to inhibit miR-19a-3p (LV-miR-19a-3p-inhibition), and cell proliferation, invasion, and migration were assessed. Target genes of miR-19a-3p were identified by sequencing analysis and quantitative reverse transcription PCR (qRT-PCR); Western blotting was performed to confirm targets and explore the potential mechanisms underlying the effect of miR-19a-3p on LNM.

RESULTS

miR-19a-3p had no effect on ESCC cell proliferation, whereas miR-19a-3p overexpression promoted the invasion and migration of ESCC cells. qRT-PCR verification and western blot analysis showed that LV-miR-19a-3p-inhibition downregulated cell division cycle 42 (CDC42), Rac family small GTPase 1 (RAC1), and p21 activated kinase 1 (PAK1).

CONCLUSIONS

Overexpression of miR-19a-3p increased the invasion and migration of ESCC cells via the RAC1/CDC42-PAK1 pathway, suggesting that this pathway mediates the effect of miR-19a-3p on promoting LNM in ESCC.

Hydrogen gas represses the progression of lung cancer via down-regulating CD47

Hydrogen gas (H₂) has been identified to play an anti-tumor role in several kinds of cancers, but the molecular mechanisms remain largely unknown. In our previous study, our project group found that H₂ could decrease the expression of CD47 in lung cancer A549 cells via the next-generation sequencing, indicating that CD47 might be involved in H₂-mediated lung cancer repression. Therefore, the present study aimed to explore the effects of CD47 on H₂-induced lung cancer repression. Western blotting and real-time PCR (RT-PCR) assays were used to detect the levels of proteins and mRNAs, respectively. Cell proliferation, invasion, migration and apoptosis were detected by using the cell counting kit-8 (CCK-8), Transwell chambers, wound healing and flow cytometry assays, respectively. The results showed that H₂ treatment caused decreases in the expression levels of CD47 and cell division control protein 42 (CDC42) in a dose-dependent manner. Up-regulation of CD47 abolished H₂ roles in promoting lung cancer cell apoptosis and repressing cell growth, invasion and migration in both A549 and H1975 cell lines. However, knockdown of CD47 enhanced H₂ role in lung cancer inhibition. Moreover, we also observed that H₂ treatment induced obvious inhibitions in the expression levels of CDC42 and CD47 in mice tumor tissues, as well as reinforced macrophage-mediated phagocytosis in A549 and H1975 cells. In conclusion, the current study reveals that H₂ inhibits the progression of lung cancer via down-regulating CD47, which might be a potent method for lung cancer treatment.

Exosomal miR-122-5p inhibits tumorigenicity of gastric cancer by downregulating GIT1

BACKGROUND

microRNAs (miRNAs) are non-coding RNAs with important roles in the progression of human cancers, including gastric cancer. Exosomes are extracellular vesicles, which could transfer numerous noncoding RNAs, such as miRNAs. Here, in our study, we intended to investigate the role of exosomal miR-122-5p in gastric cancer progression.

METHODS

Exosomes were isolated utilizing commercial kit or ultracentrifugation. Biomarkers of exosomes or epithelia-mesenchymal transition (EMT) were monitored by western blot. Expression levels of miR-122-5p and G-protein-coupled receptor kinase interacting protein-1 (GIT1) were evaluated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) or western blot. Cell proliferation and apoptosis were assessed by colony formation assay, methyl thiazolyl tetrazolium assay and flow cytometry. Cell metastasis was evaluated via Transwell assay. The interaction between miR-122-5p and GIT1 was validated by dual-luciferase reporter assay. Furthermore, tumor growth in vivo was detected by xenograft assay.

RESULTS

Exosomes were successfully isolated. MiR-122-5p was downregulated in exosomes derived from the serum of gastric cancer patients. Exosomal miR-122-5p could hinder gastric cancer cell proliferation and metastasis in vitro and tumor growth in vivo. Knockdown of GIT1 also inhibited gastric cancer cell proliferation and metastasis. Exosomal miR-122-5p targeted GIT1 to alter cellular behaviors of gastric cancer cells.

CONCLUSION

Exosomal miR-122-5p suppressed gastric cancer progression by targeting GIT1.

Dysregulation of miR-638 in the progression of cancers

MicroRNA (miRNA) is a form of short, single-stranded and non-coding RNA that is important in regulating the post-transcriptional modification of multiple downstream targets. Many miRNAs have been reported to involve in controlling the progression of human diseases, and one of them is miR-638, which play essential roles in regulating the development of human cancer. By targeting the 3'-ends of its targets, miR-638 can regulate cellular processes including proliferation, invasion, metastases, angiogenesis, apoptosis and inflammation. This review was aimed to summarize current findings on the roles of miR-638 in different human cancers based on the results from various in vitro, in vivo and clinical studies. The biogenesis process and tissue expression, followed by the roles of miR-638 in regulating the development of various human cancers by targeting different downstream targets were covered in this review. The potential applications and challenges of employing miR-638 as cancer biomarker and therapeutic agent were also discussed.

Decreased long non-coding RNA lincFOXF1 indicates poor progression and promotes cell migration and metastasis in osteosarcoma

Long non‐coding RNAs have been demonstrated to be important regulators of various cancers, though the precise mechanisms remain unclear. Although lincFOXF1 has been reported to act as a tumour suppressor, its function and underlying mechanisms in osteosarcoma have not yet been explored. We employed quantitative real‐time polymerase chain reaction (qRT‐PCR) to evaluate the expression of lincFOXF1 and GAPDH in osteosarcoma tissues and cell lines, and colony‐formation, CCK8, wound‐healing, and transwell assays were conducted to analyse the proliferation, migration, and invasion capacity of osteosarcoma cells. Subcellular localization analysis by fractionation and RNA immunoprecipitation assays were performed to elucidate the mechanism responsible for lincFOXF1‐mediated phenotypes of osteosarcoma cells. The results revealed that lincFOXF1 expression is significantly decreased and strongly related to Enneking stage as well as metastasis in osteosarcoma patients. Further experiments showed that lincFOXF1 inhibits the migration, invasion and metastasis of cells in vitro and vivo. Mechanistic investigation demonstrated that lincFOXF1 physically binds to EZH2, a polycomb repressive complex 2 (PRC2) component, and a search for downstream targets suggested that G‐protein‐coupled receptor kinase‐interacting protein 1 (GIT1) is involved in the lincFOXF1‐mediated repression of osteosarcoma cells migration and invasion. Moreover, GIT1 expression is inversely correlated with lincFOXF1 in osteosarcoma. The present findings indicate that lincFOXF1 is involved in the progression of osteosarcoma through binding with EZH2, further regulating GIT1 expression. Our results suggest that lincFOXF1 may serve as a biomarker and therapeutic target for osteosarcoma patients.

The Role of ARF Family Proteins and Their Regulators and Effectors in Cancer Progression: A Therapeutic Perspective

The Adenosine diphosphate-Ribosylation Factor (ARF) family belongs to the RAS superfamily of small GTPases and is involved in a wide variety of physiological processes, such as cell proliferation, motility and differentiation by regulating membrane traffic and associating with the cytoskeleton. Like other members of the RAS superfamily, ARF family proteins are activated by Guanine nucleotide Exchange Factors (GEFs) and inactivated by GTPase-Activating Proteins (GAPs). When active, they bind effectors, which mediate downstream functions. Several studies have reported that cancer cells are able to subvert membrane traffic regulators to enhance migration and invasion. Indeed, members of the ARF family, including ARF-Like (ARL) proteins have been implicated in tumorigenesis and progression of several types of cancer. Here, we review the role of ARF family members, their GEFs/GAPs and effectors in tumorigenesis and cancer progression, highlighting the ones that can have a pro-oncogenic behavior or function as tumor suppressors. Moreover, we propose possible mechanisms and approaches to target these proteins, toward the development of novel therapeutic strategies to impair tumor progression.

MicroRNA-760 acts as a tumor suppressor in gastric cancer development via inhibiting G-protein-coupled receptor kinase interacting protein-1 transcription

BACKGROUND

Gastric cancer (GC) has become a serious threat to people's health. Accumulative evidence reveals that dysregulation of numerous microRNAs (miRNAs) has been found during malignant formation. So far, the role of microRNA-760 (miR-760) in the development of GC is largely unknown.

AIM

To measure the expression level of miR-760 in GC and investigate its role in gastric tumorigenesis.

METHODS

Real-time quantitative polymerase chain reaction and Western blot analysis were used to measure the expression of miR-760 and G-protein-coupled receptor kinase interacting protein-1 (GIT1). Cell growth was detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) and cell colony formation assays. Apoptosis was assessed by flow cytometric analysis. The relationship between miR-760 and GIT1 was verified by luciferase reporter assay.

RESULTS

The results showed that the expression of miR-760 was decreased in GC and associated with poor clinical outcomes in GC patients. Furthermore, miR-760 restrained cell proliferation and cell colony formation and induced apoptosis in GC cells. In addition, miR-760 directly targeted GIT1 and negatively regulated its expression in GC. GIT1 was upregulated in GC and predicted a worse prognosis in GC patients. We also found that upregulation of GIT1 weakened the inhibitory effect of miR-760 in GC.

CONCLUSION

In conclusion, miR-760 targets GIT1 to inhibit cell growth and promote apoptosis in GC cells. Our data demonstrate that miR-760 may be a potential target for the treatment of GC.

Overexpression of BZW1 is an independent poor prognosis marker and its down-regulation suppresses lung adenocarcinoma metastasis

The basic leucine zipper and the W2 domain-containing protein 1 (BZW1) plays a key role in the cell cycle and transcriptionally control the histone H4 gene during G1/S phase. Since cellular proliferation rates are frequently dysregulated in human cancers, we identified the characteristics of BZW1 in cancer cells and analyzed its prognostic value in lung cancer patients. By searching public databases, we found that high BZW1 expression was significantly correlated with poor survival rate in non-small cell lung cancer (NSCLC), especially in lung adenocarcinoma. Similar trends were also shown in an array comprising NSCLC patient tissue. Knockdown of BZW1 inhibited cell metastatic ability, but did not affect the cell proliferation rate of NSCLC cells. From transcriptomics data mining, we found that coordination between BZW1 and EGFR overexpression was correlated with a worse outcome for lung cancer patients. In summary, BZW1 expression serves as an independent prognostic factor of NSCLC, especially in lung adenocarcinoma. Overexpression of BZW1 in lung cancer cells revealed a novel pathway underlying the induction of lung cancer metastasis.

Amyloid precursor protein and its phosphorylated form in non-small cell lung carcinoma

Amyloid precursor protein (APP) is a well-known to be involved in the development of Alzheimer's disease and harbors several phosphorylation sites in its cytoplasmic domain. APP has been also proposed as one of the molecules involved in cell proliferation and invasion in several human malignancies. However, the roles of APP including its phosphorylated form (p-APP) have remained largely unexplored in non-small cell lung carcinoma (NSCLC). Therefore, in this study, we first examined both APP and p-APP expressions and then explored the association between p-APP/APP status and clicopathological parameters in NSCLC. The number of APP-positive cases was 24/91 (26%) in adenocarcinomas (Ad) and 16/35 (46%) in squamous cell carcinomas (Sq), respectively. p-APP-positive cases in Ad and Sq were 28 (31%) and 17 (49%), respectively. In Ad cases, both APP and p-APP were significantly associated with clinical stages (APP and p-APP), pathologic T (p-APP), and pathologic N (APP and p-APP) of the cases examined. In Sq cases, there were no significant associations between APP status and any of the clinicopathological parameters examined with an exception of the significant correlation of p-APP with lymphatic invasion. APP status was not significantly associated with overall survival (OS) of Ad patients but a significant association was detected between p-APP-positive cases and OS of these patients (p < 0.0001). In Sq cases, both APP- (p = 0.01) and p-APP-positive (p = 0.04) groups were also significantly associated with adverse clinical outcome. These results did firstly demonstrate that APP, in particular, p-APP, is considered a potent prognostic factor for both Ad and Sq lung carcinoma patients. However, APP signaling including its phosphorylation signal are considered different between these two types of NSCC cells and further investigations are required for clarification.

LSCDFS-MKL: A multiple kernel based method for lung squamous cell carcinomas disease-free survival prediction with pathological and genomic data

Lung squamous cell carcinoma (SCC) is a fatal disease in both male and female, for which current treatments are inadequate. Surgical resection is regarded as the cornerstone of treatment for patients with lung SCC, but even for the same stage patients, the wide spectrum of disease-free survival (DFS) times exits. Therefore, how to improve the DFS prediction performance of lung SCC becomes one major research area. In this study, we proposed a novel method called LSCDFS-MKL, which was on the basis of multiple kernel learning to predict DFS of lung SCC. In LSCDFS-MKL, we first efficiently integrated pathological images and genomic data (copy number aberration, gene expression, protein expression) from lung SCC. The results of LSCDFS-MKL between different types of data show that the features extracted from pathological images play an important role in DFS prediction of lung SCC. Then we compared our method LSCDFS-MKL with other existing methods and performance analysis indicates that LSCDFS-MKL has a significantly better performance than other prediction methods. After that, we applied the proposed method on different stage stratums and the performance demonstrates that LSCDFS-MKL remains efficient in DFS prediction of lung SCC patients. Finally, we performed LSCDFS-MKL on an independent validation dataset and the accuracy of DFS prediction achieves 100%, which is promising.

Arf GAPs as Regulators of the Actin Cytoskeleton-An Update

Arf GTPase-activating proteins (Arf GAPs) control the activity of ADP-ribosylation factors (Arfs) by inducing GTP hydrolysis and participate in a diverse array of cellular functions both through mechanisms that are dependent on and independent of their Arf GAP activity. A number of these functions hinge on the remodeling of actin filaments. Accordingly, some of the effects exerted by Arf GAPs involve proteins known to engage in regulation of the actin dynamics and architecture, such as Rho family proteins and nonmuscle myosin 2. Circular dorsal ruffles (CDRs), podosomes, invadopodia, lamellipodia, stress fibers and focal adhesions are among the actin-based structures regulated by Arf GAPs. Arf GAPs are thus important actors in broad functions like adhesion and motility, as well as the specialized functions of bone resorption, neurite outgrowth, and pathogen internalization by immune cells. Arf GAPs, with their multiple protein-protein interactions, membrane-binding domains and sites for post-translational modification, are good candidates for linking the changes in actin to the membrane. The findings discussed depict a family of proteins with a critical role in regulating actin dynamics to enable proper cell function.

Inhibiting GIT1 reduces the growth, invasion, and angiogenesis of osteosarcoma

Background

GIT1, a scaffold protein with ubiquitous multi-domain, is involved in many cellular processes. In recent years, it was proved that GIT1 participated in various tumors’ growth or metastasis. However, the biological function of GIT1 in osteosarcoma is still unclear. In this study, we aimed to investigate the role and mechanism of GIT1 in osteosarcoma.

Materials and methods

Human osteosarcoma tissues were obtained to investigate the distribution of GIT1. Adequate osteosarcoma cells were stably infected with lentivirus to knockdown GIT1 level and then was used to carry out cell invasion and vascular endothelial growth factor (VEGF) assay in vitro. Orthotopic femoral osteosarcoma model was constructed to investigate the growth, invasion, and angiogenesis in vivo. Western blot was used to detect extracellular signal-regulated kinase (ERK1/2) activation and hypoxia-inducible factor-1 (HIF-1α) expression.

Results

In this study, we found that GIT1 was distributed in human osteosarcoma tissues and highly expressed in osteosarcoma (OS) cells. Knockdown of GIT1 inhibited cell invasion and VEGF release in vitro and suppressed tumor growth, invasion, and angiogenesis in vivo. Furthermore, knockdown of GIT1 substantially downregulated the protein levels of p-ERK and HIF-1α in OST cells and inhibition of p-ERK by PD98059 could significantly decrease the expression of HIF-1α and concentration of VEGF in GIT1-shRNA-treated cells.

Conclusion

GIT1 knockdown can effectively inhibit the growth, invasion, and angiogenesis of osteosarcoma. Thus, GIT1 might act as an oncogenic factor in osteosarcoma and could be a potential molecular target for osteosarcoma gene therapy.

Crosstalk between Rac1-mediated actin regulation and ROS production

The small RhoGTPase Rac1 is implicated in a variety of events related to actin cytoskeleton rearrangement. Remarkably, another event that is completely different from those related to actin regulation has the same relevance; the Rac1-mediated production of reactive oxygen species (ROS) through NADPH oxidases (NOX). Each outcome involves different Rac1 downstream effectors; on one hand, events related to the actin cytoskeleton require Rac1 to bind to WAVEs proteins and PAKs that ultimately promote actin branching and turnover, on the other, NOX-derived ROS production demands active Rac1 to be bound to a cytosolic activator of NOX. How Rac1-mediated signaling ends up promoting actin-related events, NOX-derived ROS, or both is poorly understood. Rac1 regulators, including scaffold proteins, are known to exert tight control over its functions. Hence, evidence of Rac1 regulatory events leading to both actin remodeling and NOX-mediated ROS generation are discussed. Moreover, cellular functions linked to physiological and pathological conditions that exhibit crosstalk between Rac1 outcomes are analyzed, while plausible roles in neuronal functions (and dysfunctions) are highlighted. Together, discussed evidence shed light on cellular mechanisms which requires Rac1 to direct either actin- and/or ROS-related events, helping to understand crucial roles of Rac1 dual functionality.

miR-675-5p enhances tumorigenesis and metastasis of esophageal squamous cell carcinoma by targeting REPS2

Recently H19 has been demonstrated to be up-regulated in esophageal squamous cell carcinoma (ESCC) and shown to be the precursor of miR-675 that encodes miR-675-5p conservatively. miR-675 is overexpressed in many human cancers; however, the function of miR-675-5p is largely unknown in ESCC. In this study, we found that miR-675-5p expression was significantly increased in ESCC tissues and cell lines and related with ESCC progression and poor prognosis. We also showed here that down-regulation of miR-675-5p in ESCC cells dramatically induced cell G1 arrest and reduced cell proliferation, colony formation, migration and invasion in vitro as well as tumorigenesis and tumor metastasis in vivo. We subsequently identified that REPS2 was a target gene of miR-675-5p. We found that inhibition of miR-675-5p up-regulated the expression of REPS2, inhibited RalBP1/RAC1/CDC42 signaling pathway. Inversely, interference of REPS2 abrogated the effect induced by miR-675-5p inhibition, which resembled the function of miR-675-5p up-regulation. Taken together, our findings suggested that miR-675-5p might play an oncogenic role in ESCC through RalBP1/RAC1/CDC42 signaling pathway by inhibiting REPS2 and might serve as a valuable prognostic biomarker and therapeutic target for ESCC patients.

Targeting of GIT1 by miR-149* in breast cancer suppresses cell proliferation and metastasis in vitro and tumor growth in vivo

Breast cancer remains a major cause of cancer-related death in women worldwide. Dysregulation of microRNAs (miRNAs) is involved in the initiation and progression of breast cancer. Moreover, it was found that GIT1 was widely involved in the development of many human cancers. Herein, we aimed to investigate the expression changes of miR-149* and GIT1 and the functional effects of miR-149*/GIT1 link in breast cancer. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot (WB) were used to examine the expression levels of miR-149* and GIT1. Dual luciferase reporter assay was utilized to confirm the target interaction between miR-149* and GIT1. The biological functions, including cell proliferation, invasion, and migration, of miR-149* and GIT1 were determined by MTT assay and Transwell assays, respectively. Eventually, the tumor xenograft model in nude mice injected with stable transfected MDA-MB-231 cells was established to verify the effects of miR-149* and GIT1 on tumor growth. Our results showed that miR-149* expression was decreased, whereas GIT1 expression was increased in clinical samples of breast cancer. Based on the inverse expression trend between miR-149* and GIT1, we further demonstrated that miR-149* indeed directly targets GIT1. Subsequently, it was observed that inhibition of miR-149* significantly promoted cell proliferation, invasion, and migration, but the ability of cell proliferation, invasion, and migration was obviously declined after silencing of GIT1 in MDA-MB-231 cells transfected with miR-149* mimic and/or si-GIT1. Finally, it was also found that elevated miR-149* decelerated the tumor growth, while restored GIT1 accelerated the tumor growth in nude mice after 35 days of tumor xenograft. Collectively, these findings concluded that miR-149* might exert a tumor suppressive role in breast cancer by targeting GIT1.

Role of piwi-interacting RNA-651 in the carcinogenesis of non-small cell lung cancer

Piwi-interacting RNAs (piRNAs/piRs) are small non-coding RNAs that can serve important roles in genome stability by silencing transposable genetic elements. piR651, one of these novel piRNAs, regulates a number of biological functions, as well as carcinogenesis. Previous studies have reported that piR651 is overexpressed in human gastric cancer tissues and in several cancer cell lines, including non-small cell lung cancer (NSCLC) cell lines. However, the role of piRNAs in carcinogenesis has not been clearly defined. In the present study, a small interfering RNA inhibitor of piR651 was transfected into the NSCLC A549 and HCC827 cell lines to evaluate the effect of piR651 on cell growth. The association between piR651 expression and apoptosis was evaluated by flow cytometry and western blot analysis. Wound-healing and Transwell migration and invasion assays were used to determine the effect of piR651 on the migration and invasion of NSCLC cell lines. The results revealed that inhibition of piR651 inhibited cell proliferation and significantly increased the apoptotic rate compared with the negative control (NC), as well as altering the expression of apoptosis-associated proteins. There were fewer migrating and invading cells in the piR651-inhibited group than in the NC group in the Transwell assays. Furthermore, in the wound-healing assay, the wound remained wider in the piR651 inhibitor group, suggesting decreased cell migration compared with that in the NC group. The results of the present study demonstrate that piR651 potentially regulates NSCLC tumorigenic behavior by inhibiting cell proliferation, migration and invasion and by inducing apoptosis. Therefore, piR651 is a potential cancer diagnosis marker.

Comparative Proteomics Analysis Identifies Cdc42-Cdc42BPA Signaling as Prognostic Biomarker and Therapeutic Target for Colon Cancer Invasion

Metastasis is one of the major causes of treatment failure in the patients with colon cancer. The aim of our study is to find key proteins and pathways that drive invasion and metastasis in colon cancer. Eight rounds of selection of cancer cells invading through matrigel-coated chamber were performed to obtain highly invasive colon cancer sublines HCT116-I8 and RKO-I8. Stable Isotope Labeling by Amino Acids in Cell Culture technology was used to identify the differently expressed proteins, and the proteomics data were analyzed by ingenuity pathway analysis. PAK1-PBD immunoprecipitation combined with Western blot were carried out to determine Cdc42 activity, and qRT-PCR and Western blot were used to determine gene expression. The functional role of Cdc42BPA and Cdc42 pathway in colon cancer invasion was studied by loss-of-function experiments including pharmacological blockade, siRNA knockdown, chamber invasion, and WST-1 assays. Human colon cancer tissue microarray was analyzed by immunohistochemistry for overexpression of Cdc42BPA and its correlation with clinicopathological parameters and patient survival outcomes. HCT116-I8 and RKO-I8 cells showed significantly stronger invasive potential as well as decreased E-cadherin and increased vimentin expressions compared with parental cells. The differently expressed proteins in I8 cells compared with parental cells were identified. Bioinformatics analysis of proteomics data suggested that Cdc42BPA protein and Cdc42 signaling pathway are important for colon cancer invasion, which was confirmed by experimental data showing upregulation of Cdc42BPA and higher expression of active GTP-bound form of Cdc42 in HCT116-I8 and RKO-I8 cells. Functionally, pharmacological and genetic blockade of Cdc42BPA and Cdc42 signaling markedly suppressed colon cancer cell invasion and reversed epithelial mesenchymal transition process. Furthermore, compared with adjacent normal tissues, Cdc42BPA expression was significantly higher in colon cancer tissues and further upregulated in metastatic tumors in lymph nodes. More importantly, Cdc42BPA expression was correlated with metastasis and poor survival of the patients with colon cancer. This study provides the first evidence that Cdc42BPA and Cdc42 signaling are important for colon cancer invasion, and Cdc42BPA has potential implications for colon cancer prognosis and treatment.

The Arf-GAP and protein scaffold Cat1/Git1 as a multifaceted regulator of cancer progression

Cool-associated tyrosine phosphorylated protein 1 (Cat1), also referred to as GPCR-kinase interacting protein 1 (Git1), is a ubiquitously expressed, multi-domain protein that is best known for regulating cell shape and migration. Cat1/Git1 functions as a GTPase activating protein (GAP) that inactivates certain members of the ADP-ribosylation factor (Arf) family of small GTPases. It is also a scaffold that brings together several signaling proteins at specific locations within the cell, ensuring their efficient activation. Here we will discuss what is known regarding the classical role of Cat1/Git1 in the regulation of cell morphology and migration, as well as highlight some more recent findings that suggest this interesting signaling/scaffolding protein may also contribute in unexpected ways to oncogenic transformation.

Cell Division Cycle 42 plays a Cell type-Specific role in Lung Tumorigenesis

Cell division cycle 42 (CDC42) plays important roles in polarity establishment and maintenance as well as cell cycle progression and cell division. Although disruption of cell polarity is a prerequisite in epithelial tumor initiation, the roles of CDC42 in tumorigenesis are still poorly understood. Here we find that Cdc42 deficiency inhibits the Kras^G12D-induced lung alveoli tumor formation, while conversely promotes bronchiole tumor formation in mice. Bronchial Cdc42 loss destroys contact inhibition potentially through cell polarity disruption, and results in increased tumor formation. In contrast, deletion of Cdc42 in alveoli cells prevents Kras^G12D-induced cell proliferation, which leads to reduced tumor formation. Further analyses of clinical specimens uncover a significant positive correlation between CDC42 and type II alveolar epithelial cells marker SP-A, indicating the potential importance of CDC42 in this specific subset of lung cancer. Collectively, we identify the lineage-specific function of CDC42 in lung tumorigenesis potentially through the regulation of cell polarity integrity.

Spatial intratumoural heterogeneity in the expression of GIT1 is associated with poor prognostic outcome in oestrogen receptor positive breast cancer patients with synchronous lymph node metastases

Background: The outcome for oestrogen receptor positive (ER+) breast cancer patients has improved greatly in recent years largely due to targeted therapy. However, the presence of involved multiple synchronous lymph nodes remains associated with a poor outcome. Consequently, these patients would benefit from the identification of new prognostic biomarkers and therapeutic targets. The expression of G-protein-coupled receptor kinase-interacting protein 1 (GIT1) has recently been shown to be an indicator of advanced stage breast cancer. Therefore, we investigated its expression and prognostic value of GIT1 in a cohort of 140 ER+ breast cancer with synchronous lymph node involvement.

Methods: Immunohistochemistry was employed to assess GIT1 expression in a tissue microarray (TMA) containing duplicate non-adjacent cores with matched primary tumour and lymph node tissue (n=140). GIT1 expression in tumour cells was scored and statistical correlation analyses were carried out.

Results: The results revealed a sub-group of patients that displayed discordant expression of GIT1 between the primary tumour and the lymph nodes (i.e. spatial intratumoural heterogeneity). We observed that loss of GIT1 expression in the tumour cells of the metastasis was associated with a shorter time to recurrence, poorer overall survival, and a shorter median survival time. Moreover, multivariate analysis demonstrated that GIT1 expression was an independent prognostic indicator.

Conclusions: GIT1 expression enabled the identification of a sub-class of ER+ patients with lymph node metastasis that have a particularly poor prognostic outcome. We propose that this biomarker could be used to further stratify ER+ breast cancer patients with synchronous lymph node involvement and therefore facilitate adjuvant therapy decision making.

Expanding functions of GIT Arf GTPase-activating proteins, PIX Rho guanine nucleotide exchange factors and GIT-PIX complexes

The GIT proteins, GIT1 and GIT2, are GTPase-activating proteins (inactivators) for the ADP-ribosylation factor (Arf) small GTP-binding proteins, and function to limit the activity of Arf proteins. The PIX proteins, α-PIX and β-PIX (also known as ARHGEF6 and ARHGEF7, respectively), are guanine nucleotide exchange factors (activators) for the Rho family small GTP-binding protein family members Rac1 and Cdc42. Through their multi-domain structures, GIT and PIX proteins can also function as signaling scaffolds by binding to numerous protein partners. Importantly, the constitutive association of GIT and PIX proteins into oligomeric GIT-PIX complexes allows these two proteins to function together as subunits of a larger structure that coordinates two distinct small GTP-binding protein pathways and serves as multivalent scaffold for the partners of both constituent subunits. Studies have revealed the involvement of GIT and PIX proteins, and of the GIT-PIX complex, in numerous fundamental cellular processes through a wide variety of mechanisms, pathways and signaling partners. In this Commentary, we discuss recent findings in key physiological systems that exemplify current understanding of the function of this important regulatory complex. Further, we draw attention to gaps in crucial information that remain to be filled to allow a better understanding of the many roles of the GIT-PIX complex in health and disease.

Proteomic analysis reveals GIT1 as a novel mTOR complex component critical for mediating astrocyte survival

Smithson and Gutmann reveal that mTOR complex molecular composition varies in different somatic tissues. In astrocytes and neural stem cells, they identified G-protein-coupled receptor kinase interactor protein 1 (GIT1) as a novel mTOR-binding protein, creating a unique mTOR complex lacking Raptor and Rictor. GIT1 binding to mTOR was essential for mTOR-mediated astrocyte survival.

As a critical regulator of cell growth, the mechanistic target of rapamycin (mTOR) protein operates as part of two molecularly and functionally distinct complexes. Herein, we demonstrate that mTOR complex molecular composition varies in different somatic tissues. In astrocytes and neural stem cells, we identified G-protein-coupled receptor kinase-interacting protein 1 (GIT1) as a novel mTOR-binding protein, creating a unique mTOR complex lacking Raptor and Rictor. Moreover, GIT1 binding to mTOR is regulated by AKT activation and is essential for mTOR-mediated astrocyte survival. Together, these data reveal that mTOR complex function is partly dictated by its molecuflar composition in different cell types.

Methylation-mediated loss of SFRP2 enhances invasiveness of non-small cell lung cancer cells

The malignancy of non-small cell lung cancer (NSCLC) largely results from its invasive manner. Secreted frizzled-related proteins (SFRPs) have been recently found to suppress the invasiveness of some cancers. On the other hand, the methylation of SFRPs increases protein degradation to reduce the activity of SFRPs, resulting in increased tumor cell invasion and cancer metastasis. However, the role of SFRPs in the invasion of NSCLC has not been reported. Here we analyzed the regulation of SFRPs in NSCLC cells and its effects on cell invasion. We found that SFRP2 mRNA was significantly decreased and methylation of SFRP2 gene was significantly increased in NSCLC tissue, compared to the paired adjacent nontumor tissue. Moreover, SFRP2 expression was significantly decreased in NSCLC cell lines. In NSCLC cell lines, the SFRP2 expression would be restored by the demethylation of SFRP2 gene with 5'-aza-deoxycytidine in NSCLC cell lines, at the levels of both mRNA and protein. Thus, the cell invasion would be suppressed. Furthermore, the demethylation of SFRP2 gene appeared to inhibit Zinc Finger E-Box Binding Homeobox 1 (ZEB1) and matrix metallopeptidase 9 (MMP9), two key factors that enhance NSCLC cell invasion. Thus, SFRP2 may inhibit NSCLC invasion by suppressing ZEB1 and MMP9, while its methylation promotes NSCLC invasion.

Cool-associated Tyrosine-phosphorylated Protein 1 Is Required for the Anchorage-independent Growth of Cervical Carcinoma Cells by Binding Paxillin and Promoting AKT Activation

Cool-associated tyrosine-phosphorylated protein 1 (Cat-1) is a signaling scaffold as well as an ADP-ribosylation factor-GTPase-activating protein. Although best known for its role in cell migration, we recently showed that the ability of Cat-1 to bind paxillin, a major constituent of focal complexes, is also essential for the anchorage-independent growth of HeLa cervical carcinoma cells. Here we set out to learn more about the underlying mechanism by which Cat-paxillin interactions mediate this effect. We show that knocking down paxillin expression in HeLa cells promotes their ability to form colonies in soft agar, whereas ectopically expressing paxillin in these cells inhibits this transformed growth phenotype. Although knocking down Cat-1 prevents HeLa cells from forming colonies in soft agar, when paxillin is knocked down together with Cat-1, the cells are again able to undergo anchorage-independent growth. These results suggest that the requirement of Cat-1 for this hallmark of cellular transformation is coupled to its ability to bind paxillin and abrogate its actions as a negative regulator of anchorage-independent growth. We further show that knocking down Cat-1 expression in HeLa cells leads to a reduction in Akt activation, which can be reversed by knocking down paxillin. Moreover, expression of constitutively active forms of Akt1 and Akt2 restores the anchorage-independent growth capability of HeLa cells depleted of Cat-1 expression. Together, these findings highlight a novel mechanism whereby interactions between Cat-1 and its binding partner paxillin are necessary to ensure sufficient Akt activation so that cancer cells are able to grow under anchorage-independent conditions.

srGAP1 mediates the migration inhibition effect of Slit2-Robo1 in colorectal cancer

BACKGROUND

The neuronal guidance molecule Slit2 plays suppressive role in tumorigenesis and progression. We previously showed that Slit2-Robo1 inhibit cell migration in colorectal cancer (CRC). However, little is known about its downstream effectors in CRC. This study tries to identify whether the Slit-Robo Rho GTPase activating protein 1 (srGAP1) could mediate the inhibitory effect of Slit2-Robo1 on CRC cell migration.

METHODS

The protein expression of srGAP1 in clinical CRC tissues was tested by immunohistochemistry staining. Conditioned medium was prepared from HEK293 cells stably expressing Slit2-myc, Robo1-HA or RoboN (a soluble extracellular domain of Robo1). Immunoprecipitation (IP) was applied to check the interaction between Robo1 and srGAP1, and immunofluorescence (IF) was used to observe the subcellular localization of Robo1 and srGAP1. Small GTPase pull-down assay was used to determine the activity of Cdc42. A modified wound healing assay was performed to detect cell migration.

RESULTS

The protein expression of srGAP1 was remarkably decreased in 47.5% of CRC tissues compared with adjacent noncancerous tissues, and the decreased srGAP1 expression was associated with lymphatic invasion, poor tumor differentiation, high TNM stage, and poor survival (P < 0.05). IP and IF assays revealed that srGAP1 was a Robo1-interacting protein and exhibited similar dynamic subcellular distribution after Slit2 treatment in CRC cells. Small GTPase pull-down assay and migration assay indicated that Slit2-Robo1 signaling inhibited Cdc42 activity and CRC cell motility through srGAP1.

CONCLUSION

Downregulation of srGAP1 in CRC was associated with tumor progression and poor prognosis. srGAP1 is an important downstream molecule of Slit2 signalling in CRC, and mediates the anti-migration function of Slit2 by inhibiting Cdc42.

srGAP1 mediates the migration inhibition effect of Slit2-Robo1 in colorectal cancer

BACKGROUND

The neuronal guidance molecule Slit2 plays suppressive role in tumorigenesis and progression. We previously showed that Slit2-Robo1 inhibit cell migration in colorectal cancer (CRC). However, little is known about its downstream effectors in CRC. This study tries to identify whether the Slit-Robo Rho GTPase activating protein 1 (srGAP1) could mediate the inhibitory effect of Slit2-Robo1 on CRC cell migration.

METHODS

The protein expression of srGAP1 in clinical CRC tissues was tested by immunohistochemistry staining. Conditioned medium was prepared from HEK293 cells stably expressing Slit2-myc, Robo1-HA or RoboN (a soluble extracellular domain of Robo1). Immunoprecipitation (IP) was applied to check the interaction between Robo1 and srGAP1, and immunofluorescence (IF) was used to observe the subcellular localization of Robo1 and srGAP1. Small GTPase pull-down assay was used to determine the activity of Cdc42. A modified wound healing assay was performed to detect cell migration.

RESULTS

The protein expression of srGAP1 was remarkably decreased in 47.5% of CRC tissues compared with adjacent noncancerous tissues, and the decreased srGAP1 expression was associated with lymphatic invasion, poor tumor differentiation, high TNM stage, and poor survival (P < 0.05). IP and IF assays revealed that srGAP1 was a Robo1-interacting protein and exhibited similar dynamic subcellular distribution after Slit2 treatment in CRC cells. Small GTPase pull-down assay and migration assay indicated that Slit2-Robo1 signaling inhibited Cdc42 activity and CRC cell motility through srGAP1.

CONCLUSION

Downregulation of srGAP1 in CRC was associated with tumor progression and poor prognosis. srGAP1 is an important downstream molecule of Slit2 signalling in CRC, and mediates the anti-migration function of Slit2 by inhibiting Cdc42.

Emerging roles of RAC1 in treating lung cancer patients

The Ras-related C3 botulinum toxin substrate 1 (RAC1), a member of the Rho family of small guanosine triphosphatases, is critical for many cellular activities, such as phagocytosis, adhesion, migration, motility, cell proliferation, and axonal growth. In addition, RAC1 plays an important role in cancer angiogenesis, invasion, and migration, and it has been reported to be related to most cancers, such as breast cancer, gastric cancer, testicular germ cell cancer, and lung cancer. Recently, the therapeutic target of RAC1 in cancer has been investigated. In addition, some investigations have shown that inhibition of RAC1 can reverse drug-resistance in non-small cell lung cancer. In this review, we summarize the recent advances in understanding the role of RAC1 in lung cancer and the underlying mechanisms and discuss its value in clinical therapy.

Arf proteins in cancer cell migration

Members of the ADP-ribosylation factor (Arf) family of small GTP-binding (G) proteins regulate several aspects of membrane trafficking, such as vesicle budding, tethering and cytoskeleton organization. Arf family members, including Arf-like (Arl) proteins have been implicated in several essential cellular functions, like cell spreading and migration. These functions are used by cancer cells to disseminate and invade the tissues surrounding the primary tumor, leading to the formation of metastases. Indeed, Arf and Arl proteins, as well as their guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) have been found to be abnormally expressed in different cancer cell types and human cancers. Here, we review the current evidence supporting the involvement of Arf family proteins and their GEFs and GAPs in cancer progression, focusing on 3 different mechanisms: cell-cell adhesion, integrin internalization and recycling, and actin cytoskeleton remodeling.

MicroRNA-34c Suppresses Breast Cancer Migration and Invasion by Targeting GIT1

Abnormal expression of microRNAs plays important role in tumor metastasis. Migration and invasion of cancer cells accord for the metastasis and deterioration of breast cancer. However, the regulatory role of microRNAs in the invasion and migration of breast cancer cells has not completely understood yet. Here we found that microRNA-34c (miR-34c) was significantly downregulated in metastatic tissue of breast cancer. In vitro study showed that miR-34c negatively regulated GIT1 protein expression by binding to the 3'UTR of GIT1 mRNA. Consistently, GIT1 protein expression was found upregulated significantly in metastatic breast cancer. Moreover, miR-34c overexpression suppressed the expression of GIT1 protein, and this effect was restored by AMO-miR-34c in breast cancer cells. Overexpression of miR-34c suppressed cell migration and invasion in both MCF-7 and MDA-MD-231 breast cancer cells. Furthermore, knockdown of endogenous GIT1 expression reduced the migration and invasion of both two breast cancer cells. Collectively, miR-34c downregulation in breast cancer cells resulted in the upregulation of GIT1, which in turn enhanced the migration and invasion of breast cancer. This study highlights molecular mechanism of migration and invasion of breast cancer cells.