Overexpression of ARF1 is associated with cell proliferation and migration through PI3K signal pathway in ovarian cancer

Arf1 promotes porcine intestinal epithelial cell proliferation via the mTORC1 signaling pathway

The promotion of gut health, a pervasive problem in modern animal husbandry, positively affects organismal health, productivity, and economics. Porcine intestinal epithelial cells (IPEC-J2) continuously proliferate to maintain intestinal homeostasis, including barrier, immune, and absorptive functions. Gut homeostasis is fundamental to organismal health. ADP-ribosylation factor 1 (Arf1), a small GTPase, plays a crucial role in coordinating mTORC1 in response to nutrients, especially amino acid availability in the gut. mTORC1 is the central hub of proliferation. Thus, it seems likely that Arf1 promotes IPEC-J2 cell proliferation. However, the exact role of Arf1 in the porcine gut remains unclear. Therefore, we evaluated the functional role and possible mechanisms of Arf1 in the porcine intestine through Arf1 overexpression and knockdown in IPEC-J2 cells. Arf1 overexpression and knockdown significantly enhanced and inhibited, respectively, IPEC-J2 cell viability, and PCNA expression varied with Arf1 expression. Moreover, the proportion of Ki67-positive cells was significantly greater in the Arf1-overexpressing group than in the control group. These results suggest that Arf1 improves IPEC-J2 cell proliferation. The underlying mechanism was explored by Western blotting. Arf1 overexpression and knockdown significantly enhanced and suppressed, respectively, the levels of p-S6K1 and p-RPS6, which are key downstream targets of the mTORC1 signaling pathway. Collectively, our findings reveal the role of the Arf1-mTORC1 axis in IPEC-J2 cell proliferation and its potential function in regulating intestinal homeostasis and health.

Targeting guanine nucleotide exchange factors for novel cancer drug discovery

INTRODUCTION

Guanine nucleotide exchange factors (GEFs) regulate the activation of small GTPases (G proteins) of the Ras superfamily proteins controlling cellular functions. Ras superfamily proteins act as 'molecular switches' that are turned 'ON' by guanine exchange. There are five major groups of Ras family GTPases: Ras, Ran, Rho, Rab and Arf, with a variety of different GEFs regulating their GTP loading. GEFs have been implicated in various diseases including cancer. This makes GEFs attractive targets to modulate signaling networks controlled by small GTPases.

AREAS COVERED

In this review, the roles and mechanisms of GEFs in malignancy are outlined. The mechanism of guanine exchange activity by GEFs on a small GTPase is illustrated. Then, some examples of GEFs that are significant in cancer are presented with a discussion on recent progress in therapeutic targeting efforts using a variety of approaches.

EXPERT OPINION

Recently, GEFs have emerged as potential therapeutic targets for novel cancer drug development. Targeting small GTPases is challenging; thus, targeting their activation by GEFs is a promising strategy. Most GEF-targeted drugs are still in preclinical development. A deeper biological understanding of the underlying mechanisms of GEF activity and utilizing advanced technology are necessary to enhance drug discovery for GEFs in cancer.

THUMPD3-AS1 inhibits ovarian cancer cell apoptosis through the miR-320d/ARF1 axis

Ovarian cancer is one of the most common gynecologic malignancies that has a poor prognosis. THUMPD3-AS1 is an oncogenic long noncoding RNA (lncRNA) in several cancers. Moreover, miR-320d is downregulated and inhibited proliferation in ovarian cancer cells, whereas ARF1 was upregulated and promoted the malignant progression in epithelial ovarian cancer. Nevertheless, the role of THUMPD3-AS1 in ovarian cancer and the underlying mechanism has yet to be elucidated. Human normal ovarian epithelial cells (IOSE80) and ovarian cancer cell lines (CAVO3, A2780, SKOV3, OVCAR3, and HEY) were adopted for in vitro experiments. The functional roles of THUMPD3-AS1 in cell viability and apoptosis were determined using CCK-8, flow cytometry, and TUNEL assays. Western blot was performed to assess the protein levels of ARF1, Bax, Bcl-2, and caspase 3, whereas RT-qPCR was applied to measure ARF1 mRNA, THUMPD3-AS1, and miR-320d levels. The targeting relationship between miR-320d and THUMPD3-AS1 or ARF1 was validated with dual luciferase assay. THUMPD3-AS1 and ARF1 were highly expressed in ovarian cancer cells, whereas miR-320d level was lowly expressed. THUMPD3-AS1 knockdown was able to repress cell viability and accelerate apoptosis of OVCAR3 and SKOV3 cells. Also, THUMPD3-AS1 acted as a sponge of miR-320d, preventing the degradation of ARF1. MiR-320d downregulation reversed the tumor suppressive function induced by THUMPD3-AS1 depletion. Additionally, miR-320d overexpression inhibited ovarian cancer cell viability and accelerated apoptosis, which was overturned by overexpression of ARF1. THUMPD3-AS1 inhibited ovarian cancer cell apoptosis by modulation of miR-320d/ARF1 axis. The discoveries might provide a prospective target for ovarian cancer treatment.

Distinct role of TGN-resident clathrin adaptors for Vps21p activation in the TGN-endosome trafficking pathway

Clathrin-mediated vesicle trafficking plays central roles in post-Golgi transport. In yeast (Saccharomyces cerevisiae), the AP-1 complex and GGA adaptors are predicted to generate distinct transport vesicles at the trans-Golgi network (TGN), and the epsin-related proteins Ent3p and Ent5p (collectively Ent3p/5p) act as accessories for these adaptors. Recently, we showed that vesicle transport from the TGN is crucial for yeast Rab5 (Vps21p)-mediated endosome formation, and that Ent3p/5p are crucial for this process, whereas AP-1 and GGA adaptors are dispensable. However, these observations were incompatible with previous studies showing that these adaptors are required for Ent3p/5p recruitment to the TGN, and thus the overall mechanism responsible for regulation of Vps21p activity remains ambiguous. Here, we investigated the functional relationships between clathrin adaptors in post-Golgi-mediated Vps21p activation. We show that AP-1 disruption in the ent3Δ5Δ mutant impaired transport of the Vps21p guanine nucleotide exchange factor Vps9p transport to the Vps21p compartment and severely reduced Vps21p activity. Additionally, GGA adaptors, the phosphatidylinositol-4-kinase Pik1p and Rab11 GTPases Ypt31p and Ypt32p were found to have partially overlapping functions for recruitment of AP-1 and Ent3p/5p to the TGN. These findings suggest a distinct role of clathrin adaptors for Vps21p activation in the TGN-endosome trafficking pathway.

KLHL14: A Novel Prognostic Biomarker and Therapeutic Target for Ovarian Cancer

Ovarian cancer (OV) is a gynaecological malignancy that poses a serious risk to the health status of women. To date, effective molecular markers are unavailable for the diagnosis and management of ovarian malignancies. In this study, we aimed to investigate the molecular markers associated with the development of this cancer. We used bioinformatic analysis to determine the molecules and genes related to ovarian cancer using the gene expression profiling interactive analysis (GEPIA) and the cancer genome Atlas (TCGA) databases. In addition, we examined the genes and mechanisms underlying ovarian cancer. Our results showed that the KLHL14 gene is overexpressed in some cancers. An increase in the KLHL14 expression indicates a poor prognosis in patients with ovarian cancer. Results of immune cell infiltration analysis and half-maximal inhibitory concentration (IC50) analysis provide novel insights into the treatment of ovarian cancer. KLHL14 is anticipated to emerge as a novel molecular marker specifically for ovarian carcinoma.

Golgi Complex: A Signaling Hub in Cancer

The Golgi Complex is the central hub in the endomembrane system and serves not only as a biosynthetic and processing center but also as a trafficking and sorting station for glycoproteins and lipids. In addition, it is an active signaling hub involved in the regulation of multiple cellular processes, including cell polarity, motility, growth, autophagy, apoptosis, inflammation, DNA repair and stress responses. As such, the dysregulation of the Golgi Complex-centered signaling cascades contributes to the onset of several pathological conditions, including cancer. This review summarizes the current knowledge on the signaling pathways regulated by the Golgi Complex and implicated in promoting cancer hallmarks and tumor progression.

Role of the Mosaic Cisternal Maturation Machinery in Glycan Synthesis and Oncogenesis

Tumorigenesis is associated with the deregulation of multiple processes, among which the glycosylation of lipids and proteins is one of the most extensively affected. However, in most cases, it remains unclear whether aberrant glycosylation is a cause, a link in the pathogenetic chain, or a mere consequence of tumorigenesis. In other cases, instead, studies have shown that aberrant glycans can promote oncogenesis. To comprehend how aberrant glycans are generated it is necessary to clarify the underlying mechanisms of glycan synthesis at the Golgi apparatus, which are still poorly understood. Important factors that determine the glycosylation potential of the Golgi apparatus are the levels and intra-Golgi localization of the glycosylation enzymes. These factors are regulated by the process of cisternal maturation which transports the cargoes through the Golgi apparatus while retaining the glycosylation enzymes in the organelle. This mechanism has till now been considered a single, house-keeping and constitutive function. Instead, we here propose that it is a mosaic of pathways, each controlling specific set of functionally related glycosylation enzymes. This changes the conception of cisternal maturation from a constitutive to a highly regulated function. In this new light, we discuss potential new groups oncogenes among the cisternal maturation machinery that can contribute to aberrant glycosylation observed in cancer cells. Further, we also discuss the prospects of novel anticancer treatments targeting the intra-Golgi trafficking process, particularly the cisternal maturation mechanism, to control/inhibit the production of pro-tumorigenic glycans.

Cross Talk between ARF1 and RhoA Coordinates the Formation of Cytoskeletal Scaffolds during Chlamydia Infection

Chlamydia trachomatis is an obligate intracellular bacterium that has developed sophisticated mechanisms to survive inside its infectious compartment, the inclusion. Notably, Chlamydia weaves an extensive network of microtubules (MTs) and actin filaments to enable interactions with host organelles and enhance its stability. Despite the global health and economic burden caused by this sexually transmitted pathogen, little is known about how actin and MT scaffolds are integrated into an increasingly complex virulence system. Previously, we established that the chlamydial effector InaC interacts with ARF1 to stabilize MTs. We now demonstrate that InaC regulates RhoA to control actin scaffolds. InaC relies on cross talk between ARF1 and RhoA to coordinate MTs and actin, where the presence of RhoA downregulates stable MT scaffolds and ARF1 activation inhibits actin scaffolds. Understanding how Chlamydia hijacks complex networks will help elucidate how this clinically significant pathogen parasitizes its host and reveal novel cellular signaling pathways.

Plumbagin suppresses non-small cell lung cancer progression through downregulating ARF1 and by elevating CD8+ T cells

Non-small cell lung cancer (NSCLC) is one of the most frequently diagnosed cancers and the leading causes of cancer death worldwide. Therefore, new therapeutic agents are urgently needed to improve patient outcomes. Plumbagin (PLB), a natural sesquiterpene present in many Chinese herbal medicines, has been reported for its anti-cancer activity in various cancer cells. In this study, the effects and underlying mechanisms of PLB on the tumorigenesis of NSCLC were investigated. PLB dose-dependently inhibited the growth of NSCLC cell lines. PLB promoted ROS production, activated the endoplasmic reticulum (ER) stress pathway, and induced cell apoptosis, accompanied by the decreased expression level of ADP-ribosylation factor 1 (ARF1) in NSCLC cancer cells, and those effects of PLB could be reversed by the pretreatment with N-acetyl-L-cysteine (NAC). More importantly, the calcium chelator (BM) significantly reversed PLB-induced cell apoptosis. Furthermore, PLB significantly inhibited the growth of both H1975 xenograft and LLC1 tumors and exhibited antitumor activity by enhancing the number and the effector function of CD8+ T cells in KRASLA2 mice model and the LLC1 xenograft. Our findings suggest that PLB exerts potent antitumor activity against NSCLC in vitro and in vivo through ARF1 downregulation and induction of antitumor immune response, indicating that PLB is a new novel therapeutic candidate for the treatment of patients with NSCLC.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

Chlortetracycline, a Novel Arf Inhibitor That Decreases the Arf6-Dependent Invasive Properties of Breast Cancer Cells

Breast cancer is a major disease for women worldwide, where mortality is associated with tumour cell dissemination to distant organs. While the number of efficient anticancer therapies increased in the past 20 years, treatments targeting the invasive properties of metastatic tumour cells are still awaited. Various studies analysing invasive breast cancer cell lines have demonstrated that Arf6 is an important player of the migratory and invasive processes. These observations make Arf6 and its regulators potential therapeutic targets. As of today, no drug effective against Arf6 has been identified, with one explanation being that the activation of Arf6 is dependent on the presence of lipid membranes that are rarely included in drug screening. To overcome this issue we have set up a fluorescence-based high throughput screening that follows overtime the activation of Arf6 at the surface of lipid membranes. Using this unique screening assay, we isolated several compounds that affect Arf6 activation, among which the antibiotic chlortetracycline (CTC) appeared to be the most promising. In this report, we describe CTC in vitro biochemical characterization and show that it blocks both the Arf6-stimulated collective migration and cell invasion in a 3D collagen I gel of the invasive breast cancer cell line MDA-MB-231. Thus, CTC appears as a promising hit to target deadly metastatic dissemination and a powerful tool to unravel the molecular mechanisms of Arf6-mediated invasive processes.

Downregulation of long non-coding RNA LINC00460 inhibits the proliferation, migration and invasion, and promotes apoptosis of pancreatic cancer cells via modulation of the miR-320b/ARF1 axis

Pancreatic adenocarcinoma (PAAD) ranks among the most lethal cancers worldwide with high mortality. A marked increase in the level of long non-coding RNA LINC00460 was reported in PAAD patients, in comparison with the healthy controls. However, the underlying mechanisms of the above phenomenon are not yet well understood. Hence, the present study was designed to investigate the molecular mechanism underlying the role of LINC00460 in proliferation, migration and invasion of pancreatic cancer (PC) cells. It was found in our study that LINC00460 knockdown inhibited SW1990 cell proliferation, migration and invasion and promoted its apoptosis. Moreover, miR-320b was targeted straight and its expression was downregulated by LINC00460, whose knockdown led to a reduction in ARF1 expression. Interestingly, miR-320b downregulation partly reversed the effect of LINC00460 knockdown on the proliferation, migration, invasion and apoptosis of SW1990 cells, as well as ARF1expression. In conclusion, LINC00460 knockdown inhibited the proliferation, migration and invasion, and promotes the apoptosis of SW1990 cells via modulation of the miR-320b/ARF1 axis. Thus, LINC00460 can be perceived as a promising target in the treatment of PAAD.

Cross-Kingdom Activation of Vibrio Toxins by ADP-Ribosylation Factor Family GTPases

Pathogenic Vibrio species use many different approaches to subvert, attack, and undermine the host response. The toxins they produce are often responsible for the devastating effects associated with their diseases. These toxins target a variety of host proteins, which leads to deleterious effects, including dissolution of cell organelle integrity and inhibition of protein secretion. Becoming increasingly prevalent as cofactors for Vibrio toxins are proteins of the small GTPase families. ADP-ribosylation factor small GTPases (ARFs) in particular are emerging as a common host cofactor necessary for full activation of Vibrio toxins. While ARFs are not the direct target of Vibrio cholerae cholera toxin (CT), ARF binding is required for its optimal activity as an ADP-ribosyltransferase. The makes caterpillars floppy (MCF)-like and the domain X (DmX) effectors of the Vibrio vulnificus multifunctional autoprocessing repeats-in-toxin (MARTX) toxin also both require ARFs to initiate autoprocessing and activation as independent effectors. ARFs are ubiquitously expressed in eukaryotes and are key regulators of many cellular processes, and as such they are ideal cofactors for Vibrio pathogens that infect many host species. In this review, we cover in detail the known Vibrio toxins that use ARFs as cross-kingdom activators to both stimulate and optimize their activity. We further discuss how these contrast to toxins and effectors from other bacterial species that coactivate, stimulate, or directly modify host ARFs as their mechanisms of action.

Disease-related cellular protein networks differentially affected under different EGFR mutations in lung adenocarcinoma

It is unclear how epidermal growth factor receptor EGFR major driver mutations (L858R or Ex19del) affect downstream molecular networks and pathways. This study aimed to provide information on the influences of these mutations. The study assessed 36 protein expression profiles of lung adenocarcinoma (Ex19del, nine; L858R, nine; no Ex19del/L858R, 18). Weighted gene co-expression network analysis together with analysis of variance-based screening identified 13 co-expressed modules and their eigen proteins. Pathway enrichment analysis for the Ex19del mutation demonstrated involvement of SUMOylation, epithelial and mesenchymal transition, ERK/mitogen-activated protein kinase signalling via phosphorylation and Hippo signalling. Additionally, analysis for the L858R mutation identified various pathways related to cancer cell survival and death. With regard to the Ex19del mutation, ROCK, RPS6KA1, ARF1, IL2RA and several ErbB pathways were upregulated, whereas AURK and GSKIP were downregulated. With regard to the L858R mutation, RB1, TSC22D3 and DOCK1 were downregulated, whereas various networks, including VEGFA, were moderately upregulated. In all mutation types, CD80/CD86 (B7), MHC, CIITA and IFGN were activated, whereas CD37 and SAFB were inhibited. Costimulatory immune-checkpoint pathways by B7/CD28 were mainly activated, whereas those by PD-1/PD-L1 were inhibited. Our findings may help identify potential therapeutic targets and develop therapeutic strategies to improve patient outcomes.

miR-744-5p inhibits cellular proliferation and invasion via targeting ARF1 in epithelial ovarian cancer

miR-744-5p has been demonstrated to play an important role in cancer progression. However, the functions of miR-744-5p in epithelial ovarian cancer (EOC) are not well clarified. In this study, our aim was to investigate the role of miR-744-5p and its underlying molecular mechanism in cell progression of EOC. EOC clinical tissues and matched adjacent ovarian epithelial tissues were collected from 18 patients. Tissues and cell lines were analyzed by qPCR or Western blot to investigate the expression of miR-744-5p and ARF1 in EOC. Cell proliferative capacity was assessed by CCK8 and colony formation assays. Wound healing and transwell assays were performed to evaluate cell migration and invasion. The potential binding relation between miR-744-5p and IRF1 was demonstrated by dual luciferase report assay. The results showed that expression of miR-744-5p was low in EOC clinical tissues and cells. Overexpression of miR-744-5p inhibited proliferation, migration, and invasion of EOC cells. Further mechanistic study identified that ARF1 is a target of miR-744-5p, which is negatively correlated with the expression of miR-744-5p, and overexpression of ARF1 could reverse the inhibition of miR-744-5p on the proliferation, migration, and invasion of EOC cells. Taken together, our results indicated that miR-744-5p attenuated EOC progression via targeting IRF1, providing potential guidance for the clinical treatment of ovarian cancer.

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.

Up-regulated ADP-Ribosylation factor 3 promotes breast cancer cell proliferation through the participation of FOXO1

ADP-ribosylation factor 3 (ARF3) is a member of the KRAS proto-oncogene, GTPase(Ras) super-family of guanine nucleotide-binding proteins that mediates Golgi-related mitosis, but its role in malignant cells is unclear. In the present study, we found that mRNA and protein expression of ARF3 is up-regulated in breast cancer cells. Immunohistochemical analysis of 167 paraffin-embedded archived breast cancer tissues showed that ARF3 expression was localized primarily in the cytoplasm and was significantly up-regulated in malignant specimens compared to benign specimens. There were strong associations between ARF3 expression and clinicopathological characteristics in breast cancer. We also found that overexpressing ARF3 promoted, while silencing endogenous ARF3 inhibited, the proliferation of breast cancer cells by regulating cell cycle G1-S transition. Moreover, the pro-proliferative effect of ARF3 on breast cancer cells was associated with inactivation of the forkhead box O1 (FOXO1) transcription factor. ARF3 promotes breast cancer cell proliferation through the participation of FOXO1 and represents as a novel prognostic marker and therapeutic target for breast cancer.

LncRNA TP73-AS1 is a novel regulator in cervical cancer via miR-329-3p/ARF1 axis

Cervical cancer holds one of the highest morbidity and mortality in various types of cancers. It even leads to the most number of cancer-related deaths of women. A lot of research has indicated that the anomalous expression of long noncoding RNAs (lncRNAs) would induce carcinogenesis and is associated with poor prognosis of patients with cancer. However, the function and mechanism of many lncRNAs still call for further research. Tumor Protein P73 Antisense RNA 1 (TP73-AS1) is no exception. LncRNA TP73-AS1 has been found to promote cancer progressions in various cancers. It is upregulated in cervical cancer cells. The proliferation and migration ability of cervical cancer cells can also be boosted by TP73-AS1 in return. Meanwhile, miRNA-329-3p is downregulated in cervical cancer cells and could bind with both TP73-AS1 and ADP Ribosylation Factor 1 (ARF1). TP73-AS1 inhibited miR-329-3p expression while miR-329-3p inhibited ARF1 expression. More importantly, TP73-AS1 can positively regulate ARF1 expression. Based on all these experiments, TP73-AS1 regulates ARF1 expression by competitively binding with miR-329-3p, thus regulating cervical cancer progression. Further rescue assays confirmed TP73-AS1 regulates cervical cell proliferation and migration via miR-329-3p/ARF1. TP73-AS1 might serve as a novel regulator in cervical cancer.

Functional disruption of the Golgi apparatus protein ARF1 sensitizes MDA-MB-231 breast cancer cells to the antitumor drugs Actinomycin D and Vinblastine through ERK and AKT signaling

Increasing evidence indicates that the Golgi apparatus plays active roles in cancer, but a comprehensive understanding of its functions in the oncogenic transformation has not yet emerged. At the same time, the Golgi is becoming well recognized as a hub that integrates its functions of protein and lipid biosynthesis to signal transduction for cell proliferation and migration in cancer cells. Nevertheless, the active function of the Golgi apparatus in cancer cells has not been fully evaluated as a target for combined treatment. Here, we analyzed the effect of perturbing the Golgi apparatus on the sensitivity of the MDA-MB-231 breast cancer cell line to the drugs Actinomycin D and Vinblastine. We disrupted the function of ARF1, a protein necessary for the homeostasis of the Golgi apparatus. We found that the expression of the ARF1-Q71L mutant increased the sensitivity of MDA-MB-231 cells to both Actinomycin D and Vinblastine, resulting in decreased cell proliferation and cell migration, as well as in increased apoptosis. Likewise, the combined treatment of cells with Actinomycin D or Vinblastine and Brefeldin A or Golgicide A, two disrupting agents of the ARF1 function, resulted in similar effects on cell proliferation, cell migration and apoptosis. Interestingly, each combined treatment had distinct effects on ERK1/2 and AKT signaling, as indicated by the decreased levels of either phospho-ERK1/2 or phospho-AKT. Our results suggest that disruption of Golgi function could be used as a strategy for the sensitization of cancer cells to chemotherapy.

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.

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.