Arl4c expression in colorectal and lung cancers promotes tumorigenesis and may represent a novel therapeutic target

Chemically Modified Antisense Oligonucleotide Against ARL4C Inhibits Primary and Metastatic Liver Tumor Growth

ADP-ribosylation factor-like 4c (ARL4C) is identified as a small GTP-binding protein, which is expressed by Wnt and EGF signaling and plays an important role in tubulogenesis of cultured cells and the ureters. ARL4C is little expressed in adult tissues, but it is highly expressed in lung cancer and colorectal cancer and shown to represent a molecular target for cancer therapy based on siRNA experiments. This study revealed that ARL4C is highly expressed in primary hepatocellular carcinoma (HCC) tumors and colorectal cancer liver metastases, and that ARL4C expression is associated with poor prognosis for these cancers. Chemically modified antisense oligonucleotides (ASO) against ARL4C effectively reduced ARL4C expression in both HCC and colorectal cancer cells and inhibited proliferation and migration of these cancer cells in vitro ARL4C ASOs decreased the PIK3CD mRNA levels and inhibited the activity of AKT in HCC cells, suggesting that the downstream signaling of ARL4C in HCC cells is different from that in lung and colon cancer cells. In addition, subcutaneous injection of ARL4C ASO was effective in reducing the growth of primary HCC and metastatic colorectal cancer in the liver of immunodeficient mice. ARL4C ASO accumulated in cancer cells more efficiently than the surrounding normal cells in the liver and decreased ARL4C expression in the tumor. These results suggest that ARL4C ASO represents a novel targeted nucleic acid medicine for the treatment of primary and metastatic liver cancers.

ARL4C stabilized by AKT/mTOR pathway promotes the invasion of PTEN-deficient primary human glioblastoma

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) deficiency in primary human glioblastoma (GBM) is associated with increased invasiveness and poor prognosis with unknown mechanisms. Therefore, how loss of PTEN promotes GBM progression remains to be elucidated. Herein, we identified that ADP-ribosylation factor like-4C (ARL4C) was highly expressed in PTEN-deficient human GBM cells and tissues. Mechanistically, loss of PTEN stabilized ARL4C protein due to AKT/mTOR pathway-mediated inhibition of ARL4C ubiquitination. Functionally, ARL4C enhanced the progression of GBM cells in vitro and in vivo. Moreover, microarray profiling and GST pull-down assay identified that ARL4C accelerated tumor progression via RAC1-mediated filopodium formation. Importantly, targeting PTEN potently inhibited GBM tumor progression in vitro and in vivo, whereas overexpression of ARL4C reversed the tumor progression impaired by PTEN overexpression. Clinically, analyses with patients' specimens validated a negative correlation between PTEN and ARL4C expression. Elevated ARL4C expression but PTEN deficiency in tumor was associated with poorer disease-free survival and overall survival of GBM patients. Taken together, ARL4C is critical for PTEN-deficient GBM progression and acts as a novel prognostic biomarker and a potential therapeutic candidate. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

p63-Dependent Dickkopf3 Expression Promotes Esophageal Cancer Cell Proliferation via CKAP4

Dickkopf3 (DKK3) is a secretory protein that belongs to the DKK family, but exhibits structural divergence from other family members, and its corresponding receptors remain to be identified. Although DKK3 has been shown to have oncogenic functions in certain cancer types, the underlying mechanism by which DKK3 promotes tumorigenesis remains to be clarified. We show here that DKK3 stimulates esophageal cancer cell proliferation via cytoskeleton-associated protein 4 (CKAP4), which acts as a receptor for DKK3. DKK3 was expressed in approximately 50% of tumor lesions of esophageal squamous cell carcinoma (ESCC) cases; simultaneous expression of DKK3 and CKAP4 was associated with poor prognosis. Anti-CKAP4 antibody inhibited both binding of DKK3 to CKAP4 and xenograft tumor formation induced by ESCC cells. p63, a p53-related transcriptional factor frequently amplified in ESCC, bound to the upstream region of the DKK3 gene. Knockdown of p63 decreased DKK3 expression in ESCC cells, and reexpression of DKK3 partially rescued cell proliferation in p63-depleted ESCC cells. Expression of ΔNp63α and DKK3 increased the size of tumor-like esophageal organoids, and anti-CKAP4 antibody inhibited growth of esophageal organoids. Taken together, these results suggest that the DKK3-CKAP4 axis might serve as a novel molecular target for ESCC.Significance: In esophageal cancer, findings identify DKK3 as a poor prognostic indicator and demonstrate CKAP4 inhibition as an effective therapeutic strategy. Cancer Res; 78(21); 6107-20. ©2018 AACR.

Activation of the Dickkopf1-CKAP4 pathway is associated with poor prognosis of esophageal cancer and anti-CKAP4 antibody may be a new therapeutic drug

Aberrant expression of the secretory protein Dickkopf1 (DKK1) is associated with poor prognosis of esophageal squamous cell carcinoma (ESCC), but the underlying mechanism of how DKK1 is involved in aggressiveness of ESCC is not clear. In this study, we show that cytoskeleton-associated protein 4 (CKAP4) functions as a DKK1 receptor in ESCC cells. Immunohistochemical analyses of ESCC revealed that both DKK1 and CKAP4 are minimally expressed in associated normal esophageal squamous mucosa of non-tumor regions, but strongly expressed in tumor lesions. Forty-six of 119 cases (38.7%) were positive for both DKK1 and CKAP4. Those expressing both proteins showed poor prognosis and relapse-free survival. Multivariate analysis demonstrated that expression of both proteins was the poor prognostic factor. The Cancer Genome Atlas data set indicated that the mRNA levels of DKK1 and CKAP4 are significantly elevated in the tumor lesions compared to non-tumor regions. DKK1 bound to CKAP4 at endogenous levels. DKK1 induced the internalization of CKAP4 from and its recycling to the plasma membrane. AKT was activated in ESCC cells in which DKK1 was highly expressed and CKAP4 was localized to the plasma membrane. Knockdown of either DKK1 or CKAP4 inhibited AKT activity and cell proliferation in vitro and xenograft tumor formation. Wild-type CKAP4 or DKK1, but not a DKK1 mutant that was unable to bind to CKAP4, rescued phenotypes induced by CKAP4 or DKK1 knockdown, respectively. The anti-CKAP4 antibody also inhibited AKT activity and suppressed xenograft tumor formation. In contrast, in ESCC cells in which DKK1 was marginally expressed, knockdown of CKAP4 or anti-CKAP4 antibody affected neither AKT activity nor cell proliferation. These findings suggest that the DKK1-CKAP4 pathway promotes ESCC cell proliferation and that CKAP4 might represent a novel therapeutic target for ESCCs expressing both DKK1 and CKAP4.

Epigenetic upregulation of ARL4C, due to DNA hypomethylation in the 3'-untranslated region, promotes tumorigenesis of lung squamous cell carcinoma

ADP-ribosylation factor (ARF)-like 4c (ARL4C) expression, induced by a combination of Wnt/β-catenin and EGF/Ras signaling, has been demonstrated to form epithelial morphogenesis. ARL4C overexpression, due to Wnt/β-catenin and EGF/Ras signaling alterations, was involved in tumorigenesis. It was also reported that ARL4C expression correlates with DNA hypomethylation in the 3’-untranslated region (UTR) of ARL4C gene during lymphogenesis. The current study was conducted to investigate the expression and functions of ARL4C due to DNA hypomethylation in lung and tongue cancers. Immunohistochemical analyses of tissue specimens obtained from lung and tongue squamous cell carcinoma (SCC) patients revealed that ARL4C is not observed in non-tumor regions, but is strongly expressed at high frequencies in tumor lesions. Although inhibition of Wnt/β-catenin or Ras/MAP kinase signaling did not decrease ARL4C expression in NCI-H520 lung SCC cells, ARL4C DNA was clearly hypomethylated in the 3’-UTR. Ten-eleven translocation methylcytosine dioxygenase (TET) enzyme, which mediates DNA demethylation, was highly expressed in NCI-H520 cells. Knockout of TET family proteins (TET1-3) in NCI-H520 cells reduced 5-hydroxymethylcytosine (5hmC) levels and promoted DNA methylation in the 3’-UTR, leading to the decrease in ARL4C expression and ARL4C-mediated cellular migration. In tumor lesions of ARL4C-positive lung SCC, 5hmC was frequently detected and DNA methylation in the 3’-UTR of ARL4C gene was lower than in non-tumor regions, which were consistent with the Cancer Genome Atlas dataset. These results suggest that ARL4C is expressed due to hypomethylation in the 3’-UTR for certain types of cancers and that ARL4C methylation status is involved in cancer cell function.

Identification of ARL4C as a Peritoneal Dissemination-Associated Gene and Its Clinical Significance in Gastric Cancer

BACKGROUND

In gastric cancer (GC), peritoneal dissemination (PD) occurs frequently and is incurable. In this study, we aimed to identify PD-associated genes in GC.

METHODS

We identified a PD-associated gene using three GC datasets: highly disseminated peritoneal GC cell lines, the Singapore dataset and The Cancer Genome Atlas (TCGA) dataset. We assessed the clinicopathological significance of the gene expression using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and performed immunohistochemical analysis for the gene in our patient cohort. We also performed survival analyses of the gene in our patient cohort, the Singapore dataset and the GSE62254 datasets. Moreover, gene set enrichment analysis (GSEA) was performed using the Singapore and TCGA datasets. Finally, in vitro experiments such as invasion/migration assays, immunofluorescence staining of actin filaments, epidermal growth factor (EGF) treatment analysis, and gene expression analysis were conducted using three gene-knockdown GC cell lines (AGS, 58As9, MKN45).

RESULTS

ADP-ribosylation factor-like 4c (ARL4C) was identified as a PD-associated gene, and immunohistochemical analysis showed that ARL4C was overexpressed in GC cells. High ARL4C expression was associated with the depth of invasion (p < 0.01) and PD (p < 0.05) and was a poor prognostic factor (p < 0.05) in our patient cohort, the Singapore dataset and the GSE62254 dataset. ARL4C expression positively correlated with the epithelial-mesenchymal transition (EMT) gene set in GSEA. Moreover, ARL4C knockdown reduced invasion/migration capacity, SLUG expression, and the formation of lamellipodia or filopodia in AGS and 58As9 cells. Finally, EGF treatment increased ARL4C expression in MKN45 cells.

CONCLUSIONS

ARL4C was associated with PD and was a poor prognostic factor in GC, possibly through promoting invasive capacity by activation of both EMT and motility.

ADP-ribosylation factor-like 4C binding to filamin-A modulates filopodium formation and cell migration

Filamin-A plays a key role in tumorigenesis as well as the metastatic progression of prostate cancer, ovarian cancer, and gastric carcinoma. In this study, we identified filamin-A as a novel effector of Arl4C and showed that binding between Arl4C and FLNa modulates the formation of filopodia and cell migration by promoting activation of Cdc42.

Changes in cell morphology and the physical forces that occur during migration are generated by a dynamic filamentous actin cytoskeleton. The ADP-ribosylation factor–like 4C (Arl4C) small GTPase acts as a molecular switch to regulate morphological changes and cell migration, although the mechanism by which this occurs remains unclear. Here we report that Arl4C functions with the actin regulator filamin-A (FLNa) to modulate filopodium formation and cell migration. We found that Arl4C interacted with FLNa in a GTP-dependent manner and that FLNa IgG repeat 22 is both required and sufficient for this interaction. We also show that interaction between FLNa and Arl4C is essential for Arl4C-induced filopodium formation and increases the association of FLNa with Cdc42-GEF FGD6, promoting cell division cycle 42 (Cdc42) GTPase activation. Thus our study revealed a novel mechanism, whereby filopodium formation and cell migration are regulated through the Arl4C-FLNa–mediated activation of Cdc42.

Intestinal cancer progression by mutant p53 through the acquisition of invasiveness associated with complex glandular formation

Tumor suppressor TP53 is frequently mutated in colorectal cancer (CRC), and most mutations are missense type. Although gain-of-functions by mutant p53 have been demonstrated experimentally, the precise mechanism for malignant progression in in vivo tumors remains unsolved. We generated Apc^Δ716 Trp53^LSL•R270H villin-CreER compound mice, in which mutant p53^R270H was expressed in the intestinal epithelia upon tamoxifen treatment, and examined the intestinal tumor phenotypes and tumor-derived organoids. Mutant Trp53^R270H, but not Trp53-null mutation accelerated submucosal invasion with generation of desmoplastic microenvironment. The nuclear accumulation of p53 was evident in Apc^Δ716 Trp53^R270H/R270H homozygous tumors like human CRC. Although p53 was distributed to the cytoplasm in Apc^Δ716 Trp53^+/R270H heterozygous tumors, it accumulated in the nuclei at the invasion front, suggesting a regulation mechanism for p53 localization by the microenvironment. Importantly, mutant p53 induced drastic morphological changes in the tumor organoids to complex glandular structures, which was associated with the acquisition of invasiveness. Consistently, the branching scores of human CRC that carry TP53 mutations at codon 273 significantly increased in comparison with those of TP53 wild-type tumors. Moreover, allografted Apc^Δ716 Trp53^R270H/R270H organoid tumors showed a malignant histology with an increased number of myofibroblasts in the stroma. These results indicate that nuclear-accumulated mutant p53^R270H induces malignant progression of intestinal tumors through complex tumor gland formation and acquisition of invasiveness. Furthermore, RNA sequencing analyses revealed global gene upregulation by mutant p53^R270H, which was associated with the activation of inflammatory and innate immune pathways. Accordingly, it is possible that mutant p53^R270H induces CRC progression, not only by a cell intrinsic mechanism, but also by the generation or activation of the microenvironment, which may synergistically contribute to the acceleration of submucosal invasion. Therefore, the present study indicates that nuclear-accumulated mutant p53^R270H is a potential therapeutic target for the treatment of advanced CRCs.

GLI-mediated Keratin 17 expression promotes tumor cell growth through the anti-apoptotic function in oral squamous cell carcinomas

PURPOSE

Keratin 17 (KRT17) has been suggested as a potential diagnostic marker of squamous cell carcinoma including oral squamous cell carcinoma (OSCC). The current study was conducted to clarify the function of KRT17 and its expression mechanism in OSCC.

METHODS

Immunohistochemical analyses were carried out to examine the expression of KRT17, GLI family zinc finger (GLI)-1, GLI-2, or cleaved caspase-3 in OSCCs. The expression of KRT17, GLI-1, or GLI-2 was investigated among OSCC cell lines, and the effects of loss-of-function of KRT17 or GLI, using siRNA or inhibitor, on the cell growth of the OSCC cell line HSC-2 particularly with respect to apoptosis were examined.

RESULTS

Immunohistochemical analyses of tissue specimens obtained from 78 OSCC patients revealed that KRT17 was not observed in non-tumor regions but was strongly expressed at high frequencies in tumor regions. Knockdown of KRT17 increased the number of cleaved caspase-3-positive cells, leading to the reduction of cell number. Loss-of-function of GLI-1 or GLI-2 also increased the cell numbers of apoptotic cells positive for staining of Annexin-V and propidium iodide (PI) and the terminal deoxynucleotidyl transferase dUTP-biotin nick-end labeling (TUNEL) method, and induced DNA fragmentation. This inhibitory effect on cell growth was partially rescued by exogenous KRT17 expression. In the KRT17-positive regions in OSCCs, GLI-1 or GLI-2 was frequently detected, and the number of cells with cleaved caspase-3 positive was decreased.

CONCLUSIONS

KRT17 promotes tumor cell growth, at least partially, through its anti-apoptotic effect as a result of the KRT17 overexpression by GLIs in OSCC.

Arl4c is a key regulator of tubulogenesis and tumourigenesis as a target gene of Wnt-β-catenin and growth factor-Ras signalling

Epithelial tubular morphogenesis (tubulogenesis) is a fundamental morphogenetic process of many epithelial organs. In this developmental process, epithelial cells migrate, proliferate, polarize and differentiate towards surrounding mesenchymal tissue to form tubule structures. Although epithelial tissue structures are basically stable in the postnatal period, epithelial cells regain highly proliferative and invasive potentials within mesenchymal tissue during tumour formation (tumourigenesis). Therefore, there must be a common molecular basis orchestrating the cellular behaviours involved in both tubulogenesis and tumourigenesis. ADP-ribosylation factor (Arf)-like protein 4c (Arl4c), which belongs to the small GTP-binding protein family, is expressed by the simultaneous activation of Wnt-β-catenin and growth factor-Ras-mitogen-activated protein kinase signalling, was identified as an essential regulator of tubulogenesis. Arl4c expression was also involved in the tumour formation of colorectal and lung cancers. In this review, we focus on Arl4c as a novel Wnt signal target molecule that links epithelial tubulogenesis to tumourigenesis.

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.

CKAP4 is a Dickkopf1 receptor and is involved in tumor progression

Dickkopf1 (DKK1) is a secretory protein that antagonizes oncogenic Wnt signaling by binding to the Wnt coreceptor low-density lipoprotein receptor-related protein 6 (LRP6). DKK1 may also regulate its own signaling to promote cancer cell proliferation, but the mechanism is not understood. Here, we identified cytoskeleton-associated protein 4 (CKAP4) as a DKK1 receptor and evaluated CKAP4-mediated DKK1 signaling in cancer cell proliferation. We determined that DKK1 binds CKAP4 and LRP6 with similar affinity but interacts with these 2 receptors with different cysteine-rich domains. DKK1 induced internalization of CKAP4 in a clathrin-dependent manner, further supporting CKAP4 as a receptor for DKK1. DKK1/CKAP4 signaling activated AKT by forming a complex between the proline-rich domain of CKAP4 and the Src homology 3 domain of PI3K, resulting in proliferation of normal cells and cancer cells. Expression of DKK1 and CKAP4 was frequent in tumor lesions of human pancreatic and lung cancers, and simultaneous expression of both proteins in patient tumors was negatively correlated with prognosis and relapse-free survival. An anti-CKAP4 antibody blocked the binding of DKK1 to CKAP4, suppressed AKT activity in a human cancer cell line, and attenuated xenograft tumor formation in immunodeficient mice. Together, our results suggest that CKAP4 is a potential therapeutic target for cancers that express both DKK1 and CKAP4.