An N-terminal 78 amino acid truncation of REIC/Dkk-3 effectively induces apoptosis

PD-1 blockade augments CD8+ T cell dependent antitumor immunity triggered by Ad-SGE-REIC in Egfr-mutant lung cancer

OBJECTIVES

No immunotherapeutic protocol has yet been established in never-smoking patients with lung cancer harboring driver oncogenic mutations, such as epidermal growth factor receptor (EGFR) mutations. The immunostimulatory effect of Ad-REIC, a genetically engineered adenovirus vector expressing a tumor suppressor gene, reduced expression in immortalized cells (REIC), has been investigated in clinical trials for various solid tumors. However, the immunostimulatory effect of the Ad-REIC in EGFR-mutant lung cancer with a non-inflamed tumor microenvironment (TME) has not been explored.

MATERIALS AND METHODS

We used a syngeneic mouse model developed by transplanting Egfr-mutant lung cancer cells into single or double flanks of C57BL/6J mice. Ad-SGE-REIC, a 2nd-generation vector with an enhancer sequence, was injected only into the tumors from one flank, and its antitumor effects were assessed. Tumor-infiltrating cells were evaluated using immunohistochemistry or flow cytometry. The synergistic effects of Ad-SGE-REIC and PD-1 blockade were also examined.

RESULTS

Injection of Ad-SGE-REIC into one side of the tumor induced not only a local antitumor effect but also a bystander abscopal effect in the non-injected tumor, located on the other flank. The number of PD-1⁺CD8⁺ T cells increased in both injected and non-injected tumors. PD-1 blockade augmented the local and abscopal antitumor effects of Ad-SGE-REIC by increasing the number of CD8⁺ T cells in the TME of Egfr-mutant tumors. Depletion of CD8⁺ cells reverted the antitumor effect, suggesting they contribute to antitumor immunity.

CONCLUSION

Ad-SGE-REIC induced systemic antitumor immunity by modifying the TME status from non-inflamed to inflamed, with infiltration of CD8⁺ T cells. Additionally, in Egfr-mutant lung cancer, this effect was enhanced by PD-1 blockade. These findings pave the way to establish a novel combined immunotherapy strategy with Ad-SGE-REIC and anti-PD-1 antibody for lung cancer with a non-inflamed TME.

Dickkopf-3: An Update on a Potential Regulator of the Tumor Microenvironment

Dickkopf-3 (Dkk-3) is a member of the Dickkopf family protein of secreted Wingless-related integration site (Wnt) antagonists that appears to modulate regulators of the host microenvironment. In contrast to the clear anti-tumorigenic effects of Dkk-3-based gene therapies, the role of endogenous Dkk-3 in cancer is context-dependent, with elevated expression associated with tumor promotion and suppression in different settings. The receptors and effectors that mediate the diverse effects of Dkk-3 have not been characterized in detail, contributing to an ongoing mystery of its mechanism of action. This review compares the various functions of Dkk-3 in the tumor microenvironment, where Dkk-3 has been found to be expressed by subpopulations of fibroblasts, endothelial, and immune cells, in addition to epithelial cells. We also discuss how the activation or inhibition of Dkk-3, depending on tumor type and context, might be used to treat different types of cancers.

Expression of tumor suppressor REIC/Dkk-3 by a newly improved adenovirus vector with insertion of a hTERT promoter at the 3'-side of the transgene

Reduced expression in immortalized cells (REIC)/Dickkopf-3 (Dkk-3) overexpression, induced using an adenovirus (Ad)-REIC, has been revealed to have a dramatic therapeutic effect on multiple types of cancer. To achieve an improved therapeutic effect from Ad-REIC on cancer, our group previously developed an enhanced gene expression system, the C-TSC cassette [cytomegalovirus (CMV)-RU5' located upstream (C); another promoter unit composed of triple tandem promoters, human telomerase reverse transcriptase (hTERT), simian virus 40 and CMV, located downstream of the cDNA (TSC); plus a polyadenylation (polyA) signal]. When applied to the conventional Ad-REIC, this novel system induced the development of an enhanced product, Ad-C-TSC-REIC, which exhibited a noticeable anticancer effect. However, there were difficulties in terms of Ad-C-TSC-REIC productivity in HEK293 cells, which are a widely used donor cell line for viral production. Productivity of Ad-C-TSC-REIC was significantly reduced compared with the conventional Ad-REIC, as the Ad-C-TSC-REIC had a significantly higher ability to induce apoptotic cell death of not only various types of cancer cell, but also HEK293 cells. The present study aimed to overcome this problem by modifying the C-TSC structure, resulting in an improved candidate: A C-T cassette (C: CMV-RU5' located upstream; T: another promoter unit composed of a single hTERT promoter, located downstream of the cDNA plus a polyA signal), which demonstrated gene expression comparable to that of the C-TSC system. The improved adenovirus REIC/Dkk-3 product with the C-T cassette, named Ad-C-T-REIC, exhibited a higher expression level of REIC/Dkk3, similar to that of Ad-C-TSC-REIC. Notably, the vector mitigated the cell death of donor HEK293 cells, resulting in a higher rate of production of its adenovirus. These results indicated that Ad-C-T-REIC has the potential to be a useful tool for application in cancer gene therapy.

Canine REIC/Dkk-3 interacts with SGTA and restores androgen receptor signalling in androgen-independent prostate cancer cell lines

Background

The pathological condition of canine prostate cancer resembles that of human androgen-independent prostate cancer. Both canine and human androgen receptor (AR) signalling are inhibited by overexpression of the dimerized co-chaperone small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA), which is considered to cause the development of androgen-independency. Reduced expression in immortalised cells (REIC/Dkk-3) interferes with SGTA dimerization and rescues AR signalling. This study aimed to assess the effects of REIC/Dkk-3 and SGTA interactions on AR signalling in the canine androgen-independent prostate cancer cell line CHP-1.

Results

Mammalian two-hybrid and Halo-tagged pull-down assays showed that canine REIC/Dkk-3 interacted with SGTA and interfered with SGTA dimerization. Additionally, reporter assays revealed that canine REIC/Dkk-3 restored AR signalling in both human and canine androgen-independent prostate cancer cells. Therefore, we confirmed the interaction between canine SGTA and REIC/Dkk-3, as well as their role in AR signalling.

Conclusions

Our results suggest that this interaction might contribute to the development of a novel strategy for androgen-independent prostate cancer treatment. Moreover, we established the canine androgen-independent prostate cancer model as a suitable animal model for the study of this type of treatment-refractory human cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1094-4) contains supplementary material, which is available to authorized users.

Tumor suppressor REIC/DKK-3 and co-chaperone SGTA: Their interaction and roles in the androgen sensitivity

REIC/DKK-3 is a tumor suppressor, however, its intracellular physiological functions and interacting molecules have not been fully clarified. Using yeast two-hybrid screening, we found that small glutamine-rich tetratricopeptide repeat-containing protein α (SGTA), known as a negative modulator of cytoplasmic androgen receptor (AR) signaling, is a novel interacting partner of REIC/DKK-3. Mammalian two-hybrid and pull-down assay results indicated that the SGTA-REIC/DKK-3 interaction involved the N-terminal regions of both REIC/DKK-3 and SGTA and that REIC/DKK-3 interfered with the dimerization of SGTA, which is a component of the AR complex and a suppressor of dynein motor-dependent AR transport and signaling. A reporter assay in human prostate cancer cells that displayed suppressed AR signaling by SGTA showed recovery of AR signaling by REIC/DKK-3 expression. Considering these results and our previous data that REIC/DKK-3 interacts with the dynein light chain TCTEX-1, we propose that the REIC/DKK-3 protein interferes with SGTA dimerization, promotes dynein-dependent AR transport and then upregulates AR signaling.

Properties of the feline tumour suppressor reduced expression in immortalized cells (REIC/Dkk-3)

Reduced expression in immortalized cells (REIC/Dkk-3), a member of the human Dickkopf (Dkk) family, is a growth suppressor in human and canine mammary tumours. Mammary gland tumours are common neoplasms with high malignancy in female cats. The purpose of this study was to clone the feline REIC/Dkk-3 homolog, investigate its expression in cell lines established from feline mammary gland tumours, and test its tumour suppressor function. Western blot analysis revealed that expression of the REIC/Dkk-3 protein was reduced in feline mammary carcinoma cell lines. Forced expression of REIC/Dkk-3 induced apoptosis in feline mammary tumour cell lines. These results demonstrate that REIC/Dkk-3 expression, which is downregulated in feline mammary tumour cell lines, results in the induction of apoptosis in these cells. Our findings suggest that feline REIC/Dkk-3 represents a potential molecular target for the development of therapies against feline mammary cancers.

The cysteine-rich core domain of REIC/Dkk-3 is critical for its effect on monocyte differentiation and tumor regression

Reduced expression in immortalized cells (REIC)/Dickkopf (Dkk)-3 is a tumor-suppressor gene and has been studied as a promising therapeutic gene for cancer gene therapy. Intratumoral injection of an adenovirus vector carrying the human REIC/Dkk-3 gene (Ad-REIC) elicits cancer cell-specific apoptosis and anticancer immune responses. The cytokine-like effect of secretory REIC/Dkk-3 on the induction of dendritic cell (DC)-like cell differentiation from monocytes plays a role in systemic anticancer immunity. In the present study, we generated recombinant full-length and N-terminally truncated REIC/Dkk-3 to characterize the biological activity of the protein. During the purification procedure, we identified a 17 kDa cysteine-rich stable product (C17-REIC) showing limited degradation. Further analysis showed that the C17-REIC domain was sufficient for the induction of DC-like cell differentiation from monocytes. Concomitant with the differentiation of DCs, the REIC/Dkk-3 protein induced the phosphorylation of glycogen synthase kinase 3β (GSK-3β) and signal transducers and activators of transcription (STAT) at a level comparable to that of granulocyte/macrophage colony-stimulating factor. In a mouse model of subcutaneous renal adenocarcinoma, intraperitoneal injection of full-length and C17-REIC proteins exerted anticancer effects in parallel with the activation of immunocompetent cells such as DCs and cytotoxic T lymphocytes in peripheral blood. Taken together, our results indicate that the stable cysteine-rich core region of REIC/Dkk-3 is responsible for the induction of anticancer immune responses. Because REIC/Dkk-3 is a naturally circulating serum protein, the upregulation REIC/Dkk-3 protein expression could be a promising option for cancer therapy.

Molecular cloning and tumour suppressor function analysis of canine REIC/Dkk-3 in mammary gland tumours

REIC/Dkk-3, a member of the human Dickkopf (Dkk) family, plays a role as a suppressor of growth in several human cancers. In this study, the tumour suppression function of canine REIC/Dkk-3 was investigated. The full-length open reading frame of the canine REIC/Dkk-3 homologue was cloned and the tissue distribution of REIC/Dkk-3 mRNA was determined, along with the subcellular localisation of the REIC/Dkk-3 protein in canine cancer cell lines. Expression of REIC/Dkk-3 was lower in mammary gland tumours and in canine mammary carcinoma cell lines than in normal mammary gland tissue. Overexpression of REIC/Dkk-3 induced apoptosis in canine mammary carcinoma cell lines. These results show that expression of REIC/Dkk-3 is downregulated in canine mammary tumours and that one of the functions of this gene is induction of apoptosis.

Overexpression of Dickkopf-3 induces apoptosis through mitochondrial pathway in human colon cancer

AIM: To investigate the mechanisms of the biological roles of Dickkopf-3 (Dkk-3) in cell invasion, survival and apoptosis in colon cancer cells.

METHODS: Three human colon cancer cell lines, i.e., HT-29, LoVo and SW480, were used. Overexpression of Dkk-3 induced by pEGFP-N1-Dkk-3-GFP plasmid in LoVo cells was performed using Lipofectamine 2000 reagent. Reverse transcription polymerase chain reaction and Western blotting were performed to determine the mRNA and protein expression levels of Dkk-3, respectively. Cell proliferation assay, cell cycle analysis, hoechst 33258 assay and Matrigel invasion assay were performed on Dkk-3 overexpressing transfectants.

RESULTS: The mRNA and protein expressions of Dkk-3 in HT-29 (mRNA: 0.06 ± 0.02, protein: 0.06 ± 0.01) and LoVo (mRNA: 0.07 ± 0.02, protein: 0.07 ± 0.02) cells were significantly lower than that in SW480 cells (mRNA: 0.92 ± 0.04, protein: 0.69 ± 0.13; all P < 0.05), and the greatest levels of invasiveness was in LoVo cells. Dkk-3 overexpression inhibited the proliferation and invasion of LoVo cells and induced cell cycle arrest at G₀/G₁ phase and subsequent apoptosis, as indicated by increased chromatin condensation and fragments, upregulated Bax and cytochrome c protein, downregulated survivin and Bcl-2 protein, and the activation of caspase-3 and caspase-9. Furthermore, Dkk-3 overexpression reduced the accumulation of cytosolic fraction of β-catenin.

CONCLUSION: Dkk-3 overexpression induced apoptosis in human colon cancer possibly through the mitochondrial pathway. Dkk-3 may be involved in the Wnt/β-catenin signaling pathways in colon cancer.

Targeting the Wnt pathway in cancer: the emerging role of Dickkopf-3

Aberrant activation of the Wnt signaling pathway is a major trait of many human cancers. Due to its vast implications in tumorigenesis and progression, the Wnt pathway has attracted considerable attention at several molecular levels, also with respect to developing novel cancer therapeutics. Indeed, research in Wnt biology has recently provided numerous clues, and evidence is accumulating that the secreted Wnt antagonist Dickkopf-related protein 3 (Dkk-3) and its regulators may constitute interesting therapeutic targets in the most important human cancers. Based on the currently available literature, we here review the knowledge on the biological role of Dkk-3 as an antagonist of the Wnt signaling pathway, the involvement of Dkk-3 in several stages of tumor development, the genetic and epigenetic mechanisms disrupting DKK3 gene function in cancerous cells, and the potential clinical value of Dkk-3 expression/DKK3 promoter methylation as a biomarker and molecular target in cancer diseases. In conclusion, Dkk-3 rapidly emerges as a key player in human cancer with auspicious tumor suppressive capacities, most of all affecting apoptosis and proliferation. Its gene expression is frequently downregulated by promoter methylation in almost any solid and hematological tumor entity. Clinically, evidence is accumulating of Dkk-3 being both a potential tumor biomarker and effective anti-cancer agent. Although further research is needed, re-establishing Dkk-3 expression in cancer cells holds promise as novel targeted molecular tumor therapy.

Dickkopf3 overexpression inhibits pancreatic cancer cell growth in vitro

AIM: To elucidate the role of dickkopf3 (Dkk3) in human pancreatic cancer cell growth.

METHODS: Dkk3 mRNA and protein expression in human pancreatic cancer cell lines were detected by real-time reverse transcription polymerase chain reaction (real-time RT-PCR), Western blotting and immunofluorescence. Methylation of the Dkk3 promoter sequence was examined by methylation-specific polymerase chain reaction (MSP) and Dkk3 mRNA expression was determined by real-time RT-PCR after 5-aza-2’-deoxycytidine (5-aza-dC) treatment. The effects of Dkk3 on cancer cell proliferation and in vitro sensitivity to gemcitabine were investigated by CellTiter 96^® AQueous One Solution Cell Proliferation Assay (MTS) after transfecting the Dkk3 expression plasmid into human pancreatic cancer cells. The expression of β-catenin, phosphorylated extracellular signal-regulated protein kinases (pERK) and extracellular signal-regulated protein kinases (ERK) was also examined by real-time RT-PCR and Western blotting after upregulating Dkk3 expression in human pancreatic cancer cells.

RESULTS: The results show that the expression levels of both Dkk3 mRNA and protein were low in all pancreatic cancer cell lines tested. The Dkk3 promoter sequence was methylated in the MIA PaCa-2 and AsPC-1 cell lines, which showed reduced Dkk3 expression. These two cell lines, which initially had a methylated Dkk3 promoter, showed increased Dkk3 mRNA expression that was dependent upon the dosage and timing of the DNA demethylating agent, 5-aza-dC, treatment (P < 0.05 or P < 0.01). When Dkk3 expression was upregulated following the transfection of a Dkk3 expression plasmid into MIA PaCa-2 cells, the ability of cells to proliferate decreased (P < 0.01), and the expression of β-catenin and pERK was downregulated (P < 0.01). Sensitivity to gemcitabine was enhanced in Dkk3 expression plasmid-transfected cells.

CONCLUSION: Our findings, for the first time, implicate Dkk3 as a tumor suppressor in human pancreatic cancer, through the downregulation of β-catenin expression via the ERK-mediated pathway.