Adenoviral vector-mediated RTVP-1 gene-modified tumor cell-based vaccine suppresses the development of experimental prostate cancer

Virus-inspired strategies for cancer therapy

The intentional use of viruses for cancer therapy dates back over a century. As viruses are inherently immunogenic and naturally optimized delivery vehicles, repurposing viruses for drug delivery, tumor antigen presentation, or selective replication in cancer cells represents a simple and elegant approach to cancer treatment. While early virotherapy was fraught with harsh side effects and low response rates, virus-based therapies have recently seen a resurgence due to newfound abilities to engineer and tune oncolytic viruses, virus-like particles, and virus-mimicking nanoparticles for improved safety and efficacy. However, despite their great potential, very few virus-based therapies have made it through clinical trials. In this review, we present an overview of virus-inspired approaches for cancer therapy, discuss engineering strategies to enhance their mechanisms of action, and highlight their application for overcoming the challenges of traditional cancer therapies.

A new personalized vaccine strategy based on inducing the pyroptosis of tumor cells in vivo by transgenic expression of a truncated GSDMD N-terminus

The variability and heterogeneity of tumor antigens and the tumor-driven development of immunosuppressive mechanisms leading to tumor escape from established immunological surveillance. Here, the tumor cells were genetically modified to achieve an inducible overexpression of the N-terminal domain of gasdermin D (GSDMD-NT) and effectively cause pyroptosis under a strict control. Pyroptotic tumor cells release damage-associated molecular patterns (DAMPs) and inflammatory cytokines to promote the maturation and migration of bone marrow-derived dendritic cells (BMDCs). Furthermore, local tumor delivery, and preventive or therapeutic subcutaneous immunization of the modified cells, followed by the induction of GSDMD-NT expression, significantly stimulated both the systemic and local responses of antitumor immunity, and reprogrammed the tumor microenvironment, leading to the dramatic suppression of tumor growth in mice. This study has explored the application potency of inducing the pyroptosis of tumor cells in the field of tumor immunotherapy, especially for developing a new and promising personalized tumor vaccine.

GLIPR1 and SPARC expression profile reveals a signature associated with prostate Cancer Brain metastasis

Despite advances in treatment of lethal prostate cancer, the incidence of prostate cancer brain metastases is increasing. In this sense, we analyzed the molecular profile, as well as the functional consequences involved in the reciprocal interactions between prostate tumor cells and human astrocytes. We observed that the DU145 cells, but not the LNCaP cells or the RWPE-1 cells, exhibited more pronounced, malignant and invasive phenotypes along their interactions with astrocytes. Moreover, global gene expression analysis revealed several genes that were differently expressed in our co-culture models with the overexpression of GLIPR1 and SPARC potentially representing a molecular signature associated with the invasion of central nervous system by prostate malignant cells. Further, these results were corroborated by immunohistochemistry and in silico analysis. Thus, we conjecture that the data here presented may increase the knowledge about the molecular mechanisms associated with the invasion of CNS by prostate malignant cells.

Glioma pathogenesis-related protein 1 performs dual functions in tumor cells

Glioma pathogenesis-related protein 1 (GLIPR1) was identified as an oncoprotein in some cancer types including gliomas, breast cancers, melanoma cancers, and Wilms tumors, but as a tumor suppressor in some other types of cancers, such as prostate cancers, lung cancers, bladder cancers, and thyroid cancers. In gliomas, GLIPR1 promotes the migration and invasion of glioma cells by interaction with the actin polymerization regulator Neural Wiskott-Aldrich syndrome protein (N-WASP) and then abolishes the negative effects of Heterogeneous nuclear ribonuclear protein K (hnRNPK). In prostate cancers, high levels of GLIPR1 induce apoptosis and destruction of oncoproteins. In lung cancers, overexpression of GLIPR1 inhibits the growth of lung cancer cells partially through inhibiting the V-ErbB avian erythroblastic leukemia viral oncogene homolog3 (ErbB3) pathway. However, the mechanisms that GLIPR1 performs its function in other tumors still remain unclear. The tumor suppressing role of GLIPR1 has been explored to the cancer treatment. The adenoviral vector-mediated Glipr1 (AdGlipr1) gene therapy and the GLIPR1-transmembrane domain deleted (GLIPR1-ΔTM) protein therapy both showed antitumor activities and stimulated immune response in prostate cancers. Whether GLPIR1 can be used to treat other tumors is an important topic to be explored. Among which, whether GLPIR1 can be used to treat lung cancer by atomizing inhalation is the key topic we care about. If it does, this therapy has a wide application prospect and is a great progression in lung cancer treatment.

GLIPR1 inhibits the proliferation and induces the differentiation of cancer-initiating cells by regulating miR-16 in osteosarcoma

Osteosarcoma is a common, highly malignant and metastatic bone cancer. Elucidation of the molecular mechanisms of osteosarcoma may further help us to understand the pathogenesis of the disease, and offer novel targets for effective therapies. Human glioma pathogenesis-related protein 1 (GLIPR1) has been found to be downregulated in human cancers. However, its roles have not been reported in osteosarcoma. In the present study, we demonstrated that GLIPR1 protein was downregulated in osteosarcoma. Its overexpression inhibited the proliferation, migration and invasion and induced the differentiation of cancer-initiating cells (CICs) in osteosarcoma. Moreover, GLIPR1 overexpression upregulated miR-16 in osteosarcoma cells. The upregulation suppressed proliferation, migration and invasion as well as induced differentiation of CICs in osteosarcoma. Thus, we conclude that GLIPR1 inhibited the proliferation, migration and invasion and induced the differentiation of CICs by regulating miR-16 in osteosarcoma. The present study provides direct evidence that GLIPR1 is a bona fide tumor suppressor and identified GLIPR1 and miR-16 as key components for regulating the proliferation, migration, invasion and CICs in osteosarcoma.

GLI pathogenesis-related 1 functions as a tumor-suppressor in lung cancer

Background

GLI pathogenesis-related 1 (GLIPR1) was originally identified in glioblastomas and its expression was also found to be down-regulated in prostate cancer. Functional studies revealed both growth suppression and proapoptotic activities for GLIPR1 in multiple cancer cell lines. GLIPR1’s role in lung cancer has not been investigated. Protein arginine methyltransferase 5 (PRMT5) is a protein arginine methyltransferase and forms a stoichiometric complex with the WD repeat domain 77 (WDR77) protein. Both PRMT5 and WDR77 are essential for growth of lung epithelial and cancer cells. But additional gene products that interact genetically or biochemichally with PRMT5 and WDR77 in the control of lung cancer cell growth are not characterized.

Methods

DNA microarray and immunostaining were used to detect GLIPR1 expression during lung development and lung tumorigenesis. GLIPR1 expression was also analyzed in the TCGA lung cancer cohort. The consequence of GLIPR1 on growth of lung cancer cells in the tissue culture and lung tumor xenografts in the nude mice was observed.

Results

We found that GLIPR1 expression is negatively associated with PRMT5/WDR77. GLIPR1 is absent in growing epithelial cells at the early stages of mouse lung development and highly expressed in the adult lung. Expression of GLIPR1 was down-regulated during lung tumorigenesis and its expression suppressed growth of lung cancer cells in the tissue culture and lung tumor xenografts in mice. GLIPR1 regulates lung cancer growth through the V-Erb-B avian erythroblastic leukemia viral oncogene homolog 3 (ErbB3).

Conclusions

This study reveals a novel pathway that PRMT5/WDR77 regulates GLIPR1 expression to control lung cancer cell growth and GLIPR1 as a potential therapeutic agent for lung cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-016-0508-4) contains supplementary material, which is available to authorized users.

Systemic GLIPR1-ΔTM protein as a novel therapeutic approach for prostate cancer

GLIPR1 is a p53 target gene known to be downregulated in prostate cancer, and increased endogenous GLIPR1 expression has been associated with increased production of reactive oxygen species, increased apoptosis, decreased c-Myc protein levels and increased cell cycle arrest. Recently, we found that upregulation of GLIPR1 in prostate cancer cells increases mitotic catastrophe through interaction with heat shock cognate protein 70 (Hsc70) and downregulation of Aurora kinase A and TPX2. In this study, we evaluated the mechanisms of recombinant GLIPR1 protein (glioma pathogenesis-related protein 1-transmembrane domain deleted [GLIPR1-ΔTM]) uptake by prostate cancer cells and the efficacy of systemic GLIPR1-ΔTM administration in a prostate cancer xenograft mouse model. GLIPR1-ΔTM was selectively internalized by prostate cancer cells, leading to increased apoptosis through reactive oxygen species production and to decreased c-Myc protein levels. Interestingly, GLIPR1-ΔTM was internalized through clathrin-mediated endocytosis in association with Hsc70. Systemic administration of GLIPR1-ΔTM significantly inhibited VCaP xenograft growth. GLIPR1-ΔTM showed no evidence of toxicity following elimination from mouse models 8 hr after injection. Our results demonstrate that GLIPR1-ΔTM is selectively endocytosed by prostate cancer cells, leading to increased reactive oxygen species production and apoptosis, and that systemic GLIPR1-ΔTM significantly inhibits growth of VCaP xenografts without substantial toxicity.

Endoplasmic reticulum protein GliPR1 regulates G protein signaling and the cell cycle and is overexpressed in AML

Glioma pathogenesis‑related protein 1 (GliPR1) is a pleiotropic protein involved in cell proliferation, tumor growth and apoptosis. The aim of the present study was to further characterize GliPR1 in regard to its subcellular localization and its overall effect on cellular gene expression. Knockdown of GliPR1 and Affymetrix microarray mRNA expression analysis revealed 262 GliPR1‑dependent differentially expressed genes, of which 40 were induced and 222 were suppressed. Differentially expressed genes were overrepresented in five Gene Ontology categories: G protein signaling pathways, regulation of cyclin‑dependent protein kinase activity, ER to Golgi vesicle-mediated transport, axon guidance and dephosphorylation. GliPR1-EGFP fusion protein co‑localized with the endoplasmic reticulum (ER) or with cytoplasmic vesicles as demonstrated by confocal microscopy. GliPR1 expression was found to be significantly increased in acute myeloid leukemia (AML) bone marrow samples, while markedly reduced in acute lymphoblastic leukemia, unchanged in myelodysplastic syndrome and slightly decreased in chronic lymphocytic leukemia as well as in chronic myelocytic leukemia (CML) when compared to normal samples. GliPR1 was localized and involved in the ER secretory protein pathway. GliPR1 affects G protein signaling and cell cycle regulation. Based on the observed overexpression in AML samples, GliPR1 should be further explored as a potential target for AML.

Combined therapeutic effects of adenoviral vector-mediated GLIPR1 gene therapy and radiotherapy in prostate and bladder cancer models

OBJECTIVES

The objectives of this study are to explore the potential benefits of combining AdGlipr1 (or AdGLIPR1) gene therapy with radiotherapy using subcutaneous prostate and bladder cancer models.

MATERIALS AND METHODS

Combination adenoviral vector-mediated gene therapy and radiotherapy were applied to 178-2 BMA and TSU-Pr1 cells in vitro and colony formation and apoptosis were analyzed. In addition, combination therapies were administered to mice bearing subcutaneous 178-2 BMA and TSU-Pr1 tumors, and tumor growth suppression and survival extension were compared with the monotherapies (AdGlipr1/AdGLIPR1 and radiotherapy) or control vector Adv/CMV/βgal, as well as single-cycle treatment with 2-cycle treatment.

RESULTS

Combination treatment significantly suppressed colony formation and increased apoptosis in vitro. In vivo, combination therapy produced significant 178-2 BMA and TSU-Pr1 tumor growth suppression and survival extension compared with the monotherapies or the control. Further tumor growth suppression and survival extension were observed after 2 cycles of the combination treatment.

CONCLUSIONS

Combining AdGlipr1 (AdGLIPR1) with radiotherapy may achieve additive or synergistic tumor control in selected prostate and bladder tumors, and additional therapeutic effects may result with repeated treatment cycles.

Identification of GLIPR1 tumor suppressor as methylation-silenced gene in acute myeloid leukemia by microarray analysis

PURPOSE

To identify methylation-silenced genes in acute myeloid leukemia (AML).

METHODS

Microarray analyses were performed in AML cell line HL-60 cells exposed to the demethylating agent 5-aza-2dC. The methylation status and expression of glioma pathogenesis-related protein 1 (GLIPR1), one of highly induced genes by demethylation, were further detected in six hematopoietic malignancy cell lines and 260 bone marrow samples from leukemia patients and nonmalignant diseases as control, as well as pre-treated and post-treated bone marrow samples from 24 complete remission AML patients received chemotherapy using MS-PCR, bisulfite DNA sequencing, RT-PCR, and Western blotting.

RESULTS

One hundred and nine genes were significantly induced by demethylation in HL-60 cells, 12 genes of which were confirmed by RT-PCR. GLIPR1, a tumor suppressor gene, was frequently methylation-silenced in AML cell lines and AML patients, but not in the other hematopoietic malignancy cell lines and patients. The frequencies of methylation-silenced GLIPR1 in the pre-treatment were significantly higher than those in the post-treatment in complete remission AML patients.

CONCLUSION

We identify 109 genes induced by demethylation in HL-60 cells, and demonstrate that GLIPR1 is a methylation-silenced gene in the AML patients, and may serve as a marker for monitoring disease activity during therapy in the AML patients. The data provide the important information for studying the pathogenesis of AML and discovering the target genes of methylating agents.

GLIPR1 suppresses prostate cancer development through targeted oncoprotein destruction

Downregulation of the proapoptotic p53 target gene glioma pathogenesis-related protein 1 (GLIPR1) occurs frequently in prostate cancer, but the functional meaning of this event is obscure. Here, we report the discovery of functional relationship between GLIPR1 and c-Myc in prostate cancer where c-Myc is often upregulated. We found that the expression of GLIPR1 and c-Myc were inversely correlated in human prostate cancer. Restoration of GLIPR1 expression in prostate cancer cells downregulated c-myc levels, inhibiting cell-cycle progression. Downregulation was linked to a reduction in β-catenin/TCF4-mediated transcription of the c-myc gene, which was caused by GLIPR1-mediated redistribution of casein kinase 1α (CK1α) from the Golgi apparatus to the cytoplasm where CK1α could phosphorylate β-catenin and mediate its destruction. In parallel, GLIPR1 also promoted c-Myc protein ubiquitination and degradation by glycogen synthase kinase-3α- and/or CK1α-mediated c-Myc phosphorylation. Notably, genetic ablation of the mouse homolog of Glipr1 cooperated with c-myc overexpression to induce prostatic intraepithelial neoplasia and prostate cancer. Together, our findings provide evidence for CK1α-mediated destruction of c-Myc and identify c-Myc S252 as a crucial CK1α phosphorylation site for c-Myc degradation. Furthermore, they reveal parallel mechanisms of c-myc downregulation by GLIPR1 that when ablated in the prostate are sufficient to drive c-Myc expression and malignant development.

GLIPR1 tumor suppressor gene expressed by adenoviral vector as neoadjuvant intraprostatic injection for localized intermediate or high-risk prostate cancer preceding radical prostatectomy

BACKGROUND

GLIPR1 is upregulated by p53 in prostate cancer cells and has preclinical antitumor activity. A phase I clinical trial was conducted to evaluate the safety and activity of the neoadjuvant intraprostatic injection of GLIPR1 expressing adenovirus for intermediate or high-risk localized prostate cancer before radical prostatectomy (RP).

METHODS

Eligible men had localized prostate cancer (T1-T2c) with Gleason score greater than or equal to 7 or prostate-specific antigen 10 ng/mL or more and were candidates for RP. Patients received the adenoviral vector expressing the GLIPR1 gene by a single injection into the prostate followed four weeks later by RP. Six viral particle (vp) dose levels were evaluated: 10(10), 5 × 10(10), 10(11), 5 × 10(11), 10(12), and 5 × 10(12) vp.

RESULTS

Nineteen patients with a median age of 64 years were recruited. Nine men had T1c, 4 had T2a, and 3 had T2b and T2c clinical stage. Toxicities included urinary tract infection (n = 3), flu-like syndrome (n = 3), fever (n = 1), dysuria (n = 1), and photophobia (n = 1). Laboratory toxicities were grade 1 elevated AST/ALT (n = 1) and elevations of PTT (n = 3, with 1 proven to be lupus anticoagulant). No pathologic complete remission was seen. Morphologic cytotoxic activity, induction of apoptosis, and nuclear p27(Kip1) upregulation were observed. Peripheral blood CD8(+), CD4(+), and CD3(+) T-lymphocytes were increased, with upregulation of their HLA-DR expression and elevations of serum IL-12.

CONCLUSIONS

The intraprostatic administration of GLIPR1 tumor suppressor gene expressed by an adenoviral vector was safe in men, with localized intermediate or high-risk prostate cancer preceding RP. Preliminary evidence of biologic antitumor activity and systemic immune response was documented.

Tumor growth and metastasis suppression by Glipr1 gene-modified macrophages in a metastatic prostate cancer model

We previously identified the mouse and human Glipr1 and GLIPR1/RTVP-1 (respectively) genes as direct p53 targets with proapoptotic activities in various cancer cell lines, including prostate cancer. Intratumoral injection of an adenoviral vector capable of efficient transduction and expression of Glipr1 (AdGlipr1) yielded promising therapeutic results in an orthotopic, metastatic mouse model of prostate cancer. AdGlipr1-transduced macrophages (Mϕ/Glipr1) generated greater surface expression of CD40, CD80, and MHC class II molecules and greater production of interleukin (IL)-12 and IL-6 in vitro than control macrophages did. Mechanistic analysis indicated that increased production of IL-12 in Mϕ/Glipr1 depends on activation of the p38 signaling cascade. Mϕ/Glipr1 injected into orthotopic 178-2BMA tumors in vivo resulted in significantly suppressed prostate tumor growth and spontaneous lung metastases and longer survival relative to those observed in control-treated mice. Furthermore, these preclinical data indicate the generation of systemic natural killer-cell activity and tumor-specific cytotoxic T-lymphocyte responses. Trafficking studies confirmed that intratumorally injected Mϕ/Glipr1 could migrate to draining lymph nodes. Overall, our data suggest that this novel gene-modified cell approach is an effective treatment avenue that induces antitumor immune responses in preclinical studies.

Glioma pathogenesis-related protein 1: tumor-suppressor activities and therapeutic potential

After glioma pathogenesis-related protein 1 (GLIPR1/Glipr1) was identified, the expression of GLIPR1 was shown to be down-regulated in human prostate cancer, owing in part to methylation in the regulatory region of this gene in prostate cancer cells. Additional studies showed that GLIPR1/Glipr1 expression is induced by DNA-damaging agents independent of p53. Functional analysis of GLIPR1 using in vitro and in vivo gene-transfer approaches revealed both growth suppression and proapoptotic activities for mouse Glipr1 and human GLIPR1 in multiple cancer cell lines. The proapoptotic activities were dependent on production of reactive oxygen species and sustained c-Jun-NH(2) kinase signaling. It was interesting that adenoviral vector-mediated Glipr1 (AdGlipr1) transduction into prostate cancer tissues using an immunocompetent orthotopic mouse model revealed additional biologic activities consistent with tumor-suppressor functions. Significantly reduced tumor-associated angiogenesis and direct suppression of endothelial-cell sprouting activities were documented. In addition, AdGlipr1 strongly stimulated antitumor immune responses that resulted in specific cytotoxic T-lymphocyte activities in this model. Glipr1-related antitumor immunostimulatory activities were confirmed and extended in subsequent studies. Administration of a novel Glipr1 genemodified tumor cell vaccine had significant antitumor activity in a mouse model of recurrent prostate cancer. In conclusion, restoration of GLIPR1 function in prostate cancer cells through GLIPR1 gene-based or GLIPR protein-based delivery methods may provide a safe and effective approach for targeted therapy for a range of malignancies.

Neoadjuvant therapy preceding prostatectomy for prostate cancer: rationale and current trials

Neoadjuvant therapy improves outcomes for a number of malignancies and provides intermediate pathologic outcomes, which correlate with long-term outcomes. Neoadjuvant androgen-deprivation therapy, alone or with docetaxel chemotherapy, preceding prostatectomy for localized prostate cancer is feasible and demonstrates pathologic activity, but evidence for improved long-term outcomes is lacking. Data in support of the further exploration of neoadjuvant therapy for localized prostate cancer preceding prostatectomy are reviewed. Ongoing randomized trials are elucidating the impact of neoadjuvant androgen deprivation combined with docetaxel chemotherapy on pathologic and long-term outcomes. The correlation of pathologic and biologic outcomes with long-term outcomes in this setting is unknown. The neoadjuvant therapy approach followed by prostatectomy is feasible with a wide array of agents and provides a paradigm for evaluating the activity, and mechanism of action and resistance to new treatments. This promising modality may aid the rapid development of novel therapeutic agents. A multidisciplinary approach involving oncologists, urologists and pathologists is critical to the success of this model.

Inhibition of HIV-1 replication by small interfering RNAs directed against glioma pathogenesis related protein (GliPR) expression

BACKGROUND

Previously, we showed that glioma pathogenesis related protein (GliPR) is induced in CEM T cells upon HIV-1 infection in vitro. To examine whether GliPR plays a role as HIV dependency factor (HDF), we tested the effect of GliPR suppression by siRNA on HIV-1 replication.

RESULTS

Induction of GliPR expression by HIV-1 was confirmed in P4-CCR5 cells. When GliPR was suppressed by siRNA, HIV-1 replication was significantly reduced as measured by HIV-1 transcript levels, HIV-1 p24 protein levels, and HIV-1 LTR-driven reporter gene expression, suggesting that GliPR is a cellular co-factor of HIV-1. Microarray analysis of uninfected HeLa cells following knockdown of GliPR revealed, among a multitude of gene expression alterations, a down-regulation of syndecan-1, syndecan-2, protein kinase C alpha (PRKCA), the catalytic subunit beta of cAMP-dependent protein kinase (PRKACB), nuclear receptor co-activator 3 (NCOA3), and cell surface protein CD59 (protectin), all genes having relevance for HIV-1 pathology.

CONCLUSIONS

The up-regulation of GliPR by HIV-1 and the early significant inhibition of HIV-1 replication mediated by knockdown of GliPR reveal GliPR as an important HIV-1 dependency factor (HDF), which may be exploited for HIV-1 inhibition.

The CAP superfamily: cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins--roles in reproduction, cancer, and immune defense

The cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) superfamily members are found in a remarkable range of organisms spanning each of the animal kingdoms. Within humans and mice, there are 31 and 33 individual family members, respectively, and although many are poorly characterized, the majority show a notable expression bias to the reproductive tract and immune tissues or are deregulated in cancers. CAP superfamily proteins are most often secreted and have an extracellular endocrine or paracrine function and are involved in processes including the regulation of extracellular matrix and branching morphogenesis, potentially as either proteases or protease inhibitors; in ion channel regulation in fertility; as tumor suppressor or prooncogenic genes in tissues including the prostate; and in cell-cell adhesion during fertilization. This review describes mammalian CAP superfamily gene expression profiles, phylogenetic relationships, protein structural properties, and biological functions, and it draws into focus their potential role in health and disease. The nine subfamilies of the mammalian CAP superfamily include: the human glioma pathogenesis-related 1 (GLIPR1), Golgi associated pathogenesis related-1 (GAPR1) proteins, peptidase inhibitor 15 (PI15), peptidase inhibitor 16 (PI16), cysteine-rich secretory proteins (CRISPs), CRISP LCCL domain containing 1 (CRISPLD1), CRISP LCCL domain containing 2 (CRISPLD2), mannose receptor like and the R3H domain containing like proteins. We conclude that overall protein structural conservation within the CAP superfamily results in fundamentally similar functions for the CAP domain in all members, yet the diversity outside of this core region dramatically alters target specificity and, therefore, the biological consequences.

Gene-modified bone marrow cell therapy for prostate cancer

There is a critical need to develop new and effective cancer therapies that target bone, the primary metastatic site for prostate cancer and other malignancies. Among the various therapeutic approaches being considered for this application, gene-modified cell-based therapies may have specific advantages. Gene-modified cell therapy uses gene transfer and cell-based technologies in a complementary fashion to chaperone appropriate gene expression cassettes to active sites of tumor growth. In this paper, we briefly review potential cell vehicles for this approach and discuss relevant gene therapy strategies for prostate cancer. We further discuss selected studies that led to the conceptual development and preclinical testing of IL-12 gene-modified bone marrow cell therapy for prostate cancer. Finally, we discuss future directions in the development of gene-modified cell therapy for metastatic prostate cancer, including the need to identify and test novel therapeutic genes such as GLIPR1.

Glioma pathogenesis-related protein 1 exerts tumor suppressor activities through proapoptotic reactive oxygen species-c-Jun-NH2 kinase signaling

Glioma pathogenesis-related protein 1 (GLIPR1), a novel p53 target gene, is down-regulated by methylation in prostate cancer and has p53-dependent and -independent proapoptotic activities in tumor cells. These properties suggest an important tumor suppressor role for GLIPR1, yet direct genetic evidence of a tumor suppressor function for GLIPR1 is lacking and the molecular mechanism(s), through which GLIPR1 exerts its tumor suppressor functions, has not been shown. Here, we report that the expression of GLIPR1 is significantly reduced in human prostate tumor tissues compared with adjacent normal prostate tissues and in multiple human cancer cell lines. Overexpression of GLIPR1 in cancer cells leads to suppression of colony growth and induction of apoptosis. Mice with an inactivated Glipr1 gene had significantly shorter tumor-free survival times than either Glipr1(+/+) or Glipr1(+/-) mice in both p53(+/+) and p53(+/-) genetic backgrounds, owing to their development of a unique array of malignant tumors. Mechanistic analysis indicated that GLIPR1 up-regulation increases the production of reactive oxygen species (ROS) leading to apoptosis through activation of the c-Jun-NH(2) kinase (JNK) signaling cascade. Thus, our results identify GLIPR1 as a proapoptotic tumor suppressor acting through the ROS-JNK pathway and support the therapeutic potential for this protein.