Cytosolic activation of cathepsins mediates parvovirus H-1-induced killing of cisplatin and TRAIL-resistant glioma cells

Gliomas are often resistant to the induction of apoptotic cell death as a result of the development of survival mechanisms during astrocyte malignant transformation. In particular, the overexpression of Bcl-2-family members interferes with apoptosis initiation by DNA-damaging agents (e.g., cisplatin) or soluble death ligands (e.g., TRAIL). Using low-passage-number cultures of glioma cells, we have shown that parvovirus H-1 is able to induce death in cells resistant to TRAIL, cisplatin, or both, even when Bcl-2 is overexpressed. Parvovirus H-1 triggers cell death through both the accumulation of lysosomal cathepsins B and L in the cytosol of infected cells and the reduction of the levels of cystatin B and C, two cathepsin inhibitors. The impairment of either of these effects protects glioma cells from the viral lytic effect. In normal human astrocytes, parvovirus H-1 fails to induce a killing mechanism. In vivo, parvovirus H-1 infection of rat glioma cells intracranially implanted into recipient animals triggers cathepsin B activation as well. This report identifies for the first time cellular effectors of the killing activity of parvovirus H-1 against malignant brain cells and opens up a therapeutic approach which circumvents their frequent resistance to other death inducers.     

Activation of a helper and not regulatory human CD4+ T cell response by oncolytic H-1 parvovirus

Background

H-1 parvovirus (H-1 PV), a rodent autonomous oncolytic parvovirus, has emerged as a novel class of promising anticancer agents, because of its ability to selectively find and destroy malignant cells. However, to probe H-1 PV multimodal antitumor potential one of the major prerequisites is to decipher H-1 PV direct interplay with human immune system, and so prevent any risk of impairment.

Methodology/Principal findings

Non activated peripheral blood mononuclear cells (PBMCs) are not sensitive to H-1 PV cytotoxic effect. However, the virus impairs both activated PBMC proliferation ability and viability. This effect is related to H-1 PV infection as evidenced by Western blotting detection of H-1 PV main protein NS1. However, TCID50 experiments did not allow newly generated virions to be detected. Moreover, flow cytometry has shown that H-1 PV preferentially targets B lymphocytes. Despite seeming harmful at first sight, H-1 PV seems to affect very few NK cells and CD8+ T lymphocytes and, above all, clearly does not affect human neutrophils and one of the major CD4+ T lymphocyte subpopulation. Very interestingly, flow cytometry analysis and ELISA assays proved that it even activates human CD4+ T cells by increasing activation marker expression (CD69 and CD30) and both effective Th1 and Th2 cytokine secretion (IL-2, IFN-γ and IL-4). In addition, H-1 PV action does not come with any sign of immunosuppressive side effect. Finally, we have shown the efficiency of H-1 PV on xenotransplanted human nasopharyngeal carcinoma, in a SCID mouse model reconstituted with human PBMC.

Conclusions/Significance

Our results show for the first time that a wild-type oncolytic virus impairs some immune cell subpopulations while directly activating a Helper CD4+ T cell response. Thus, our data open numerous gripping perspectives of investigation and strongly argue for the use of H-1 PV as an anticancer treatment.     

Transformation of human cells by oncogenic viruses supports permissiveness for parvovirus H-1 propagation.

Parvovirus H-1 has been shown to suppress spontaneous and chemically or virally induced tumorigenesis in hamsters. In human cell culture systems propagation of H-1 is restricted to transformed cells, which are killed by H-1 infection, in contrast to normal diploid cells, which are nonpermissive for H-1. By analyzing the permissiveness of a variety of human cells for H-1, it was determined that the majority of tested transformed or immortalized cells which were permissive for H-1 contained the DNA of oncogenic viruses (human papillomavirus, simian virus 40, adenovirus, hepatitis B virus, Epstein-Barr virus, and human T-cell lymphotropic virus type I). Of six transformed cell lines negative for persisting tumor virus DNA, only two were permissive for H-1, while two were semipermissive and two were nonpermissive. Thus, persistence and expression of tumor virus functions appears to promote full permissiveness for H-1 in human cells. However, neither expression of genes of specific viral genomes nor the transformed state of apparently virus-free cells alone was sufficient to render human cells permissive for H-1. Therefore, the effect of tumor virus functions on H-1 in transformed cells seems to be indirect, probably mediated by cellular factors which are induced or switched off during the transformation process. It appears that similar factors are induced or switched off by 5-azacytidine or calcium phosphate, both known inducers of cellular gene expression.     

Identification of multiple forms of the noncapsid parvovirus protein NCVP1 in H-1 parvovirus-infected cells.

Analysis of extracts of H-1 parvovirus-infected cells with virus-specific antiserum led to the identification of two forms of the noncapsid virus protein NCVP1. These two proteins had apparent molecular weights of 84,000 (NCVP1) and 92,000 (NCVP1') and were structurally related, based on their immunological reactivity and on peptide map analysis. Both of these proteins appeared early in the virus infection, about the same time that capsid proteins appeared. NCVP1' was a highly phosphorylated protein which was apparently derived from NCVP1 via a post-translational event. Phosphoserine was the predominant phosphorylated amino acid in NCVP1' and appeared to be localized in one site or a few sites on the protein. The possible involvement of these noncapsid proteins in parvovirus DNA replication is discussed.     

Analysis of the protein-protein interactions in the parvovirus H-1 capsid.

The structure of the icosahedral capsid of the H-1 parvovirus was probed by chemical cross-linking methods. Treatment of empty capsids with high-molecular-weight polyethylene glycols resulted in irreversible aggregation of the minor capsid protein VP1. Multimers of VP1 containing at least five and perhaps six molecules were obtained, but only with empty capsids and not with the full, DNA-containing virus. Cross-linking of the empty capsids with dimethylsuberimidate confirmed the assignments of the products formed after treatment with polyethylene glycol. With dimethylsuberimidate the most abundant product was a heterologous dimer containing VP1 and the major capsid protein VP2'. A small amount of homologous VP2' dimer was also obtained, but the majority of VP2' remained unreacted even at high concentrations of dimethylsuberimidate. The capsid proteins of the full virus, on the other hand, were completely unreactive to dimethylsuberimidate. The data suggest that the minor protein VP1 may be clustered in the capsid and perhaps composes one or two of the morphological units of the icosahedral shell.     

Direct and indirect effects of ultraviolet light on the mutagenesis of parvovirus H-1 in human cells.

U.v. radiation is directly mutagenic for the single-stranded DNA parvovirus H-1 propagated in human cells. Mutation induction in the progeny of u.v.-irradiated virus increased linearly with the dose and could be ascribed neither to an increased number of rounds of viral replication nor to the indirect activation of an inducible cellular mutator activity by the u.v.-damaged virus. The level of mutagenesis among the descendants of both unirradiated and u.v.-damaged H-1 was enhanced if the host cells had been exposed to sublethal doses of u.v. light before infection. This indirect enhancement of viral mutagenesis in pre-irradiated cells was maximal at multiplicities lower than 0.2 infectious particles/cell. The frequency of mutations resulting from cell pre-irradiation was only slightly higher for u.v.-irradiated than for intact virus. Thus, the induced cellular mutator appeared to be mostly untargeted in the dose range given to the virus. U.v.-irradiation of the cells also enhanced the mutagenesis of u.v.-irradiated herpes simplex virus, a double-stranded DNA virus ( Lytle and Knott , 1982).     

Reactivation of gamma-ray irradiated parvovirus H-1 in cells of patients with ataxia telangiectasia and Huntington's chorea

Parvovirus H-1 was used to probe the cellular radiosensitivity of two human degeneration syndromes AT and HC. No difference in the survival of gamma irradiated H-1 was detected between skin fibroblasts from such patients and from a normal individual. However, AT and normal cells were distinguished by the fact that the reactivation of irradiated H-1 could be increased by UV or X-irradiation of the latter but not of the former cells.     

Pool and synthesis of phosphoribosylpyrophosphate in rat embryo cells infected with X14 or H-1 parvovirus

In rat embryo cell cultures infected with X14 or H-1 parvovirus the PRPP pool and the PRPP synthetase activity have been assayed. A radiometric method, prepared by Authors, based on the conversion of [6-14C) orotate to [6-14C) UMP by the mixed enzyme orotate phosphoribosyltransferase and orotidylate decarboxylase and on the separation of UMP by ascending chromatography, has been utilized. The PRPP pool and te PRPP synthetase activity appeared nearly unmodified in the cells infected with X14 or H-1 parvovirus compared to the mock-infected cells. Therefore, the lowered pyrimidine nucleotide synthesis in infected cells, shown in previous studies, may depend, rather than on the diminished PRPP pool, on the lower PRPP utilization; in fact, some inhibition by metabolites, that may be removed by added PRPP, might occur in the infected cells.     

Selective potentiation of drug cytotoxicity by NSAID in human glioma cells: the role of COX-1 and MRP.

Here, we report that nonsteroidal anti-inflammatory drugs (NSAID) enhance the cytotoxic effects of doxorubicin and vincristine in T98G human malignant glioma cells. The cytotoxicity of BCNU, cisplatin, VM26, camptothecin, and cytarabine is unaffected by NSAID. No free radical formation is induced by doxorubicin or vincristine in the absence or presence of NSAID. Doxorubicin and vincristine cytotoxicity in the absence or presence of NSAID are unaffected by free radical scavengers. Functional inhibitors of phospholipase A2 (PLA2), such as dexamethasone and quinacrine, do not mimick the effects of NSAID. T98G cells, but not LN-18, LN-229, LN-308, or A172 glioma cells, express cyclooxygenase (COX-1) and NSAID do not modulate drug cytotoxicity in the other cell lines, except T98G. Thus, augmentation of doxorubicin and vincristine cytotoxicity by NSAID correlates with COX-1 expression. However, ectopic expression of COX-1 in LN-229 cells does not induce the phenotype of T98G cells, indicating that COX-1 inhibition does not mediate the effects of NSAID on drug cytotoxicity. In contrast, a multidrug resistance (MDR) phenotype due to expression of the multidrug resistance-associated protein (MRP) is most prominent in T98G cells and is amenable to modulation by indomethacin, suggesting that inhibition of MRP is at least in partly responsible for the potentiation of doxorubicin and vincristine cytotoxicity by NSAID.     

Retargeting of rat parvovirus H-1PV to cancer cells through genetic engineering of the viral capsid

The rat parvovirus H-1PV is a promising anticancer agent given its oncosuppressive properties and the absence of known side effects in humans. H-1PV replicates preferentially in transformed cells, but the virus can enter both normal and cancer cells. Uptake by normal cells sequesters a significant portion of the administered viral dose away from the tumor target. Hence, targeting H-1PV entry specifically to tumor cells is important to increase the efficacy of parvovirus-based treatments. In this study, we first found that sialic acid plays a key role in H-1PV entry. We then genetically engineered the H-1PV capsid to improve its affinity for human tumor cells. By analogy with the resolved crystal structure of the closely related parvovirus minute virus of mice, we developed an in silico three-dimensional (3D) model of the H-1PV wild-type capsid. Based on this model, we identified putative amino acids involved in cell membrane recognition and virus entry at the level of the 2-fold axis of symmetry of the capsid, within the so-called dimple region. In situ mutagenesis of these residues significantly reduced the binding and entry of H-1PV into permissive cells. We then engineered an entry-deficient viral capsid and inserted a cyclic RGD-4C peptide at the level of its 3-fold axis spike. This peptide binds α(v)β(3) and α(v)β(5) integrins, which are overexpressed in cancer cells and growing blood vessels. The insertion of the peptide rescued viral infectivity toward cells overexpressing α(v)β(5) integrins, resulting in the efficient killing of these cells by the reengineered virus. This work demonstrates that H-1PV can be genetically retargeted through the modification of its capsid, showing great promise for a more efficient use of this virus in cancer therapy.     

MicroRNA-215 enhances invasion and migration by targeting retinoblastoma tumor suppressor gene 1 in high-grade glioma

Objective

To elucidate the molecular mechanism of microRNA-215 (miR-215) in the migration and invasion of high grade glioma.

Results

42 Patients were analysed for clinicopathological characteristics. qRT-PCR showed that miR-215 was up-regulated in glioma tissues compared with non-neoplastic brain tissues (P < 0.05). The up-regulated miR-215 was closely associated with high grade glioma (P < 0.01) and poor overall survival (P < 0.01). Transwell assay showed that re-expression of miR-215 enhanced migration and invasion of glioma cells. miR-215 also down-regulated retinoblastoma tumor suppressor gene 1 (RB1) expression by targeting its 3′-UTR. Reversely, re-expression of RB1 inhibited partial effect of miR-215 on migration and invasion in vitro.

Conclusions

Re-expression of miR-215 promoted cell migration and invasion of glioma by targeting RB1. miR-215 can thus be used as a biomarker for tumor progression and prognosis in human high grade glioma.

     

Mutation of lysine 405 to serine in the parvovirus H-1 NS1 abolishes its functions for viral DNA replication, late promoter trans activation, and cytotoxicity.

A consensus sequence in parvovirus nonstructural protein NS1 has been predicted to be an ATP-binding domain associated with an ATPase and a DNA helicase activity. To investigate the function of NS1 in viral gene expression, a site-directed mutagenesis converting NS1 lysine 405 to serine in parvovirus H-1 was carried out by the polymerase chain reaction. As shown previously, a parvovirus genome containing a deleted NS1 gene was excised from a bacterial plasmid and replicated when a wild-type NS1 gene was provided in trans but failed to be excised and replicate when the mutant NS1 gene was supplied. Interestingly, the serine 405 mutation totally lost the activity of trans activation on the virus late promoter (P38) in a chloramphenicol acetyltransferase (CAT) assay and it lost evidence for cytotoxicity in two tumor cell lines (HeLa Gey and NB324K). The serine 405 NS1 protein was translocated normally to the nucleus. These results suggest that the NS1 lysine 405 of H-1 in its putative purine nucleotide-binding site is essential for viral DNA replication and that this domain may be involved in the regulation of the P38 promoter by an unknown mechanism. The loss of NS1 cytotoxicity on tumor cells suggests that NS1 expression is the major cause of cell killing by parvoviruses, which may facilitate further study of the mechanism of oncosuppression by parvoviruses.     

Induction of differentiation by radiation and hyperthermia in neuroblastoma—glioma hybrid cells

The effects of either radiation or hyperthermia on the differentiation potential of NG108-15, a neuroblastoma-glioma hybrid cell line, were studied. After radiation and hyperthermia, the outgrowth of neurites from NG108-15 cells was potentiated, and polarizing current and voltage pulses induced a distinct action potential and a diphasic (inward following outward) current, respectively. An increase in the specific activity of acetylcholinesterase was also observed. In addition, both treatments induced an elevation of the concentration of intracellular calcium in some cells. The increase in intracellular calcium concentration caused by applying the calcium ionophore, A23187, induced differentiation. It is suggested that both the radiation- and the hyperthermia-induced increases of electrical excitability and acetylcholinesterase activity may have originated from an increase in intracellular Ca²⁺ concentration.     

Transformation by SV 40 virus sensitizes fibroblasts of human skin to the lytic action of H-1 parvovirus

Human skin fibroblasts which are naturally resistant to Parvovirus H-1 can be lysed by this virus after SV40 transformation. This observation raises the possibility that oncosuppression by Parvovirus involves a direct oncolytic effect.     

Enhancement of radiation cytotoxicity by UCN-01 in non-small cell lung carcinoma cells

Thoracic ionizing radiation is a standard component of combined-modality therapy for locally advanced non-small cell lung cancer. To improve low 5-year survival rates (5- 15%), new strategies for enhancing the effectiveness of ionizing radiation are needed. The kinase inhibitor UCN-01 has multiple cell cycle effects, including abrogation of DNA damage-induced S- and G(2)-phase arrest, which may limit DNA repair prior to mitosis. To test the hypothesis that therapy-induced cell cycle effects would have an impact on the efficacy of a combination of UCN-01 plus ionizing radiation, the cell cycle responses of the non-small cell lung cancer cell lines Calu1 (TP53-null) and A549 (wild-type TP53) to 2 Gy ionizing radiation were correlated with clonogenic survival after irradiation plus UCN-01. Irradiated cells were exposed to UCN-01 simultaneously and at 3-h increments after irradiation. In Calu1 cells but not A549 cells, sequence-dependent potentiation of radiation by UCN-01 was observed, with maximal interaction occurring when UCN-01 was administered 6 h after irradiation. This coincided with the postirradiation time with the greatest depletion of cells from G(1). Abrogation of G(2) arrest was observed regardless of TP53 status. The role of TP53 was investigated using siRNA to achieve gene silencing. These studies demonstrated that radiation plus UCN-01 was more effective in cells with diminished TP53 activity, associated with a reduced G(1) checkpoint arrest. These studies indicate that simultaneous elimination of multiple DNA damage-induced checkpoints in G(1), S and G(2) may enhance the effects of radiation and that drug scheduling may have an impact on clinical efficacy.