Oncolytic H-1 parvovirus binds to sialic acid on laminins for cell attachment and entry

H-1 parvovirus (H-1PV) is a promising anticancer therapy. However, in-depth understanding of its life cycle, including the host cell factors needed for infectivity and oncolysis, is lacking. This understanding may guide the rational design of combination strategies, aid development of more effective viruses, and help identify biomarkers of susceptibility to H-1PV treatment. To identify the host cell factors involved, we carry out siRNA library screening using a druggable genome library. We identify one crucial modulator of H-1PV infection: laminin γ1 (LAMC1). Using loss- and gain-of-function studies, competition experiments, and ELISA, we validate LAMC1 and laminin family members as being essential to H-1PV cell attachment and entry. H-1PV binding to laminins is dependent on their sialic acid moieties and is inhibited by heparin. We show that laminins are differentially expressed in various tumour entities, including glioblastoma. We confirm the expression pattern of laminin γ1 in glioblastoma biopsies by immunohistochemistry. We also provide evidence of a direct correlation between LAMC1 expression levels and H-1PV oncolytic activity in 59 cancer cell lines and in 3D organotypic spheroid cultures with different sensitivities to H-1PV infection. These results support the idea that tumours with elevated levels of γ1 containing laminins are more susceptible to H-1PV-based therapies.

Inhibition of HIF1α-Dependent Upregulation of Phospho-l-Plastin Resensitizes Multiple Myeloma Cells to Frontline Therapy

The introduction of novel frontline agents in multiple myeloma (MM), like immunomodulatory drugs and proteasome inhibitors, has improved the overall survival of patients. Yet, MM is still not curable, and drug resistance (DR) remains the main challenge. To improve the understanding of DR in MM, we established a resistant cell line (MOLP8/R). The exploration of DR mechanisms yielded an overexpression of HIF1α, due to impaired proteasome activity of MOLP8/R. We show that MOLP8/R, like other tumor cells, overexpressing HIF1α, have an increased resistance to the immune system. By exploring the main target genes regulated by HIF1α, we could not show an overexpression of these targets in MOLP8/R. We, however, show that MOLP8/R cells display a very high overexpression of LCP1 gene (l-Plastin) controlled by HIF1α, and that this overexpression also exists in MM patient samples. The l-Plastin activity is controlled by its phosphorylation in Ser5. We further show that the inhibition of l-Plastin phosphorylation restores the sensitivity of MOLP8/R to immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs). Our results reveal a new target gene of DR, controlled by HIF1α.

A high rate of telomeric sister chromatid exchange occurs in chronic lymphocytic leukaemia B-cells

Cancer cells protect their telomere ends from erosion through reactivation of telomerase or by using the Alternative Lengthening of Telomere (ALT) mechanism that depends on homologous recombination. Chronic lymphocytic leukaemia (CLL) B cells are characterized by almost no telomerase activity, shelterin deregulation and telomere fusions. To characterize telomeric maintenance mechanisms in B-CLL patients, we measured their telomere length, telomerase expression and the main hallmarks of the ALT activity i.e. C-circle concentration, an extra-chromosomal telomere repeat (ECTR), and the level of telomeric sister chromatid exchange (T-SCE) rate. Patients showed relative homogenous telomere length although almost no TERT transcript and nearly no C-circle were evidenced. Nevertheless, compared with normal B cells, B-CLL cells showed an increase in T-SCE rate that was correlated with a strong down-regulation of the topoisomerase III alpha (TOP3A) expression, involved in the dissolution of Holliday Junctions (HJ), together with an increased expression of SLX1A, SLX4, MUS81 and GEN1, involved in the resolution of HJ. Altogether, our results suggest that the telomere maintenance mechanism of B-CLL cells do not preferentially use telomerase or ALT. Rather, the rupture of the dissolvasome/resolvasome balance may increase telomere shuffling that could homogenize telomere length, slowing telomere erosion in this disease.

BAG6/BAT3 modulates autophagy by affecting EP300/p300 intracellular localization

We recently reported that BAG6/BAT3 (BCL2-associated athanogene 6) is essential for basal and starvation-induced autophagy in E18.5 bag6(-/-) mouse embryos and in mouse embryonic fibroblasts (MEFs) through the modulation of the EP300/p300-dependent acetylation of TRP53 and autophagy-related (ATG) proteins. We observed that BAG6 increases TRP53 acetylation during starvation and pro-autophagic TRP53-target gene expression. BAG6 also decreases the EP300 dependent-acetylation of ATG5, ATG7, and LC3-I, posttranslational modifications that inhibit autophagy. In addition, in the absence of BAG6 or when using a mutant of BAG6 exclusively located in the cytoplasm, autophagy is inhibited, ATG7 is hyperacetylated, TRP53 acetylation is abrogated, and EP300 accumulates in the cytoplasm indicating that BAG6 is involved in the regulation of the nuclear localization of EP300. We also reported that the interaction between BAG6 and EP300 occurs in the cytoplasm rather than the nucleus. Moreover, during starvation, EP300 is transported to the nucleus in a BAG6-dependent manner. We concluded that BAG6 regulates autophagy by controlling the localization of EP300 and its accessibility to nuclear (TRP53) and cytoplasmic (ATGs) substrates.

Bronchial airway gene expression in smokers with lung or head and neck cancer

Cigarette smoking is the major cause of cancers of the respiratory tract, including non-small cell lung cancer (NSCLC) and head and neck cancer (HNC). In order to better understand carcinogenesis of the lung and upper airways, we have compared the gene expression profiles of tumor-distant, histologically normal bronchial biopsy specimens obtained from current smokers with NSCLC or HNC (SC, considered as a single group), as well as nonsmokers (NS) and smokers without cancer (SNC). RNA from a total of 97 biopsies was used for gene expression profiling (Affymetrix HG-U133 Plus 2.0 array). Differentially expressed genes were used to compare NS, SNC, and SC, and functional analysis was carried out using Ingenuity Pathway Analysis (IPA). Smoking-related cancer of the respiratory tract was found to affect the expression of genes encoding xenobiotic biotransformation proteins, as well as proteins associated with crucial inflammation/immunity pathways and other processes that protect the airway from the chemicals in cigarette smoke or contribute to carcinogenesis. Finally, we used the prediction analysis for microarray (PAM) method to identify gene signatures of cigarette smoking and cancer, and uncovered a 15-gene signature that distinguished between SNC and SC with an accuracy of 83%. Thus, gene profiling of histologically normal bronchial biopsy specimens provided insight into cigarette-induced carcinogenesis of the respiratory tract and gene signatures of cancer in smokers.

Cooperative effects of Janus and Aurora kinase inhibition by CEP701 in cells expressing Jak2V617F

The Janus kinase 2 mutant V617F occurs with high frequency in myeloproliferative neoplasms. Further mutations affecting the Janus kinase family have been discovered mostly in leukaemias and in myeloproliferative neoplasms. Owing to their involvement in neoplasia, inflammatory diseases and in the immune response, Janus kinases are promising targets for kinase inhibitor therapy in these disease settings. Various quantitative assays including two newly developed screening assays were used to characterize the function of different small-molecule compounds in cells expressing Jak2V617F. A detailed comparative analysis of different Janus kinase inhibitors in our quantitative assays and the subsequent characterization of additional activities demonstrated for the first time that the most potent Jak2 inhibitor in our study, CEP701, also targets Aurora kinases. CEP701 shows a unique combination of both activities which is not found in other compounds also targeting Jak2. Furthermore, colony forming cell assays showed that Janus kinase 2 inhibitors preferentially suppressed the growth of erythroid colonies, whereas inhibitors of Aurora kinases preferentially blocked myeloid colony growth. CEP701 demonstrated a combined suppression of both colony types. Moreover, we show that combined application of a Janus and an Aurora kinase inhibitor recapitulated the effect observed for CEP701 but might allow for more flexibility in combining both activities in clinical settings, e.g. in the treatment of myeloproliferative neoplasms. The newly developed screening assays are high throughput compatible and allow an easy detection of new compounds with Janus kinase 2 inhibitory activity.

Determination of genes and microRNAs involved in the resistance to fludarabine in vivo in chronic lymphocytic leukemia

BACKGROUND

Chronic lymphocytic leukemia (CLL) cells are often affected by genomic aberrations targeting key regulatory genes. Although fludarabine is the standard first line therapy to treat CLL, only few data are available about the resistance of B cells to this purine nucleoside analog in vivo. Here we sought to increase our understanding of fludarabine action and describe the mechanisms leading to resistance in vivo. We performed an analysis of genomic aberrations, gene expression profiles, and microRNAs expression in CLL blood B lymphocytes isolated during the course of patients' treatment with fludarabine.

RESULTS

In sensitive patients, the differentially expressed genes we identified were mainly involved in p53 signaling, DNA damage response, cell cycle and cell death. In resistant patients, uncommon genomic abnormalities were observed and the resistance toward fludarabine could be characterized based on the expression profiles of genes implicated in lymphocyte proliferation, DNA repair, and cell growth and survival. Of particular interest in some patients was the amplification of MYC (8q) observed both at the gene and transcript levels, together with alterations of myc-transcriptional targets, including genes and miRNAs involved in the regulation of cell cycle and proliferation. Differential expression of the sulfatase SULF2 and of miR-29a, -181a, and -221 was also observed between resistant and sensitive patients before treatment. These observations were further confirmed on a validation cohort of CLL patients treated with fludarabine in vitro.

CONCLUSION

In the present study we identified genes and miRNAs that may predict clinical resistance of CLL to fludarabine, and describe an interesting oncogenic mechanism in CLL patients resistant to fludarabine by which the complete MYC-specific regulatory network was altered (DNA and RNA levels, and transcriptional targets). These results should prove useful for understanding and overcoming refractoriness to fludarabine and also for predicting the clinical outcome of CLL patients before or early during their treatment.

The histone deacetylase inhibitor MGCD0103 induces apoptosis in B-cell chronic lymphocytic leukemia cells through a mitochondria-mediated caspase activation cascade

Clinical trials have shown activity of the isotype-selective histone deacetylase (HDAC) inhibitor MGCD0103 in different hematologic malignancies. There are data to support the use of HDAC inhibitors in association with other cancer therapies. To propose a rational combination therapy, it is necessary to depict the molecular basis behind the cytotoxic effect of MGCD0103. In this study, we found that MGCD0103 was substantially more toxic in neoplastic B cells relative to normal cells, and we described the death pathways activated by MGCD0103 in B-cell chronic lymphocytic leukemia (CLL) cells from 32 patients. MGCD0103 decreased the expression of Mcl-1 and induced translocation of Bax to the mitochondria, mitochondrial depolarization, and release of cytochrome c in the cytosol. Caspase processing in the presence of the caspase inhibitor Q-VD-OPh and time course experiments showed that caspase-9 was the apical caspase. Thus, MGCD0103 induced the intrinsic pathway of apoptosis in CLL cells. Moreover, MGCD0103 treatment resulted in the activation of a caspase cascade downstream of caspase-9, caspase-dependent amplification of mitochondrial depolarization, activation of calpain, and Bax cleavage. We propose a model whereby the intrinsic pathway of apoptosis triggered by MGCD0103 in CLL is associated with a mitochondrial death amplification loop.

From molecular characteristics to cellular events in apoptosis-resistant HL-60 cells

The ability to induce apoptosis in tumor cells is critical to elicit a positive response to cytotoxic chemo-therapy. In this study, we investigated the effect of the topoisomerase I inhibitors camptothecin and SN-38, known to cause an unusual form of DNA damage, on apoptotic pathways using the leukemic cell line HL-60 and its vincristine-resistant variant HL-60 VCR. Both camptothecin and SN-38 induced high levels of apoptosis in sensitive cells when compared to the multidrug-resistant ones. Interestingly, a higher BCL-2/BAX ratio was observed in HL-60 VCR at the basal state and during treatments. Moreover, these cells which did not exhibit Bcr-abl translocation or bcrp efflux pump, overexpressed topoisomerase I protein. The data provide evidence that BCL-2 protein could protect HL-60 VCR from mitochondrial membrane depolarization and block ROS production in these cells. Finally, our results suggest that dysregulation of proteins associated with DNA replication and apoptotic process could contribute to the multidrug-resistance phenotype.

GTP-mediated differentiation of the human K562 cell line: transient overexpression of GATA-1 and stabilization of the gamma-globin mRNA

Induction of specific gene expression may provide an alternative or a support to conventional cytotoxic chemotherapy of cancer, as well as to therapy for sickle cell diseases. In this respect, pharmacological induction of expression of the endogenous gamma-globin gene is a realistic approach to therapy of beta-globin disorders. Erythroid differentiation and inhibition of proliferation of the human CML K562 cell line was induced by guanosine 5'-triphosphate (GTP). The hemoglobin production in cells was correlated to an increase in alpha- and gamma-globin mRNA expression. At the transcriptional level, we showed that both the expression of the major erythroid transcription factor GATA-1 (protein and mRNA) and its binding capacity to the gamma-globin gene promoter was transiently increased. Moreover, GTP moderately stimulated the gamma-globin gene promoter after 48 h of treatment. At the post-transcriptional level, GTP treatment led to a drastic increase of the gamma-globin mRNA half-life. This stabilizing effect of GTP was mediated via the 3'-untranslated region (3'-UTR) of the gamma-globin mRNA. In conclusion, mechanism of GTP-mediated differentiation of K562 cells is linked to an early activation of gamma-globin gene transcription followed by a stabilization of its mRNA.

Factors contributing to the resistance to apoptosis induced by topoisomerase I inhibitors in vincristine resistant cells

The activity of numerous antineoplasic drugs is correlated with their capacity to induce the apoptotic process. In this study, apoptosis induced by the topoisomerase I (Topo I) inhibitors camptothecin (CPT) and the CPT-11 active metabolite SN-38 was evaluated on HL-60 cells and their multidrug resistant variant HL-60-Vincristine cells. Both CPT and SN-38 induced high levels of apoptosis in sensitive cells but very low levels in MDR cells. The role of the different genes and proteins usually implicated in the drug resistance phenomenon was studied. The Pgp independence of the two drugs was suggested by the lack of modulation of anti-Topo I effects with verapamil. Moreover CPT and SN-38 induced a strong decrease of mdr1 mRNA in MDR treated cells. MRP mRNA expression was very low in drug sensitive and resistant cells and decreased during treatments in both cell lines. However, MRP protein was not detected in control and MDR cells suggesting that this pump was probably not implicated in this resistance phenomenon. Topo I and BCL-2 proteins displayed a higher expression in MDR cells but only Topo I proteins decreased during treatments in the two cell lines. These data suggest that in addition to the classical multidrug resistance phenotype, dysregulation of proteins associated with DNA replication and apoptotic process could contribute to acquired resistance to a large panel of drugs, including those which are not considered as substrates for Pgp.

Two distinct modes of oncoprotein expression during apoptosis resistance in vincristine and daunorubicin multidrug-resistant HL60 cells

Apoptosis is a genetically regulated cell death process which results in a variety of morphological changes like chromatin condensation and DNA fragmentation. The decision between survival or death in response to an apoptotic stimulus is determined and regulated in part by oncoproteins which include proteins of the Bcl-2 family (bcl-2, bax, bcl-xL) and bcr-abl. We investigated the effect of these proteins on the induction of this phenomenon in human promyelocytic leukemic HL60 cells and two multidrug resistant homologues selected respectively with vincristine (HL60/VCR) and daunorubicin (HL60R/DNR). We show that sensitive cells at 1 micron and HL60/VCR cells at DNR IC50 were able to undergo apoptosis while HL60R/DNR did not even at much higher concentration of DNR. However, treatment with synthetic C2-ceramide did not sensitize HL60/DNR cells to apoptosis. Cell death through apoptosis or necrosis was accompanied by acidification of the cytosol without mitochondrial membrane depolarization. Western blotting analysis shows that bax is expressed at slightly elevated level in HL60S/VCR in comparison with the other cells lines. Bcl-2 is overexpressed in HL60/VCR but not in HL60R/DNR. However, this cell line displayed a higher expression of bcl-xL. Interestingly, bcr-abl, a dysregulated tyrosine kinase was detected only in HL60R/DNR cells. DNR at the IC50, has no effect on expression of the oncoproteins. These data suggest that in addition of the multidrug resistance phenotype, bcr-abl translocation and bcl-xL overexpression could also account for the development of resistance to cell death induced by anthracyclines in leukemic cells.

Resistance to apoptosis induced by topoisomerase I inhibitors in multidrug-resistant HL60 leukemic cells

The induction of apoptosis by topoisomerase I inhibitors, camptothecin and SN38, was evaluated in drug-sensitive HL60 and multidrug-resistant (MDR) HL60-Vinc leukemic cells. MDR cells displayed a partial resistance to these apoptotic stimuli and this phenomenon was not modulated by verapamil. Basal free calcium concentrations were similar in both cell sublines and were not modified during treatment. Cytoplasmic pH was more acidic in sensitive cells than in MDR cells. Moreover, a significant acidification was obtained during the early stage of apoptosis in sensitive HL60 cells only. Basal Bcl-2 protein expression was found to be greater in MDR than in sensitive cells and was not modulated by apoptosis inducers. This increase of Bcl-2 in MDR cells could be due to the selection process as vincristine enhances Bcl-2 phosphorylation and expression in HL60 sensitive cells. MDR HL60-Vincristine cells therefore display a resistance to apoptosis induced by non-MDR drugs, possibly by Bcl-2 overexpression and inability of these drugs to mediate intracellular pH changes in these drug-resistant cells.

Image cytometry of early nuclear events during apoptosis induced by camptothecin in HL-60 leukemic cells

The nuclear morphological alterations occurring during apoptosis induced in human HL-60 cells by camptothecin were analyzed quantitatively by image cytometry. Two separate phases were identified during the apoptotic process. The first phase, observed between 0-2 h of incubation, consisted in the appearance of cells with an apparently decondensed chromatin. This phenomenon was blocked by the inhibitors of DNA fragmentation, TLCK and H7. In contrast, staurosporine and cytochalasin B, which inhibit apoptosis without any effect on DNA fragmentation in this system, did not prevent this morphological change. The second phase, observed after 3 h of culture, corresponded to the appearance of cells with very homogeneous and condensed chromatin. This phenomenon correlated with the detection of typical apoptotic cells with fragmented nuclei and was inhibited by all drugs (TLCK, H7, staurosporine, and cytochalasin B). These observations suggest that image cytometry allows the detection of subvisual microscopic events within the first hour after the induction of an apoptotic process and that the dissection of this process into several different phases might be associated with DNA fragmentation.

Analysis of DNA content in multidrug-resistant cells by image and flow cytometry

Nuclear DNA content was assessed in multidrug-resistant (MDR) cells by image and flow cytometry. Two human MDR cell lines (K562-Dox and CEM-VLB) obtained by in vitro drug selection and overexpressing mdr1 gene were compared to their respective sensitive counterparts (K562 and CCRF-CEM) and to the MDR hamster LR73-R cell line obtained by transfection of mouse mdr1 cDNA. Both cell lines obtained by selection displayed a decreased DNA content, as measured by image cytometry after Feulgen staining, or by flow cytometry after staining with propidium iodide, ethidium bromide, or Hoechst 33342. This decrease was not accompanied by changes in cell cycle phase distribution of cells. Moreover, image cytometry of cells stained after various hydrolysis times in 5 M HCl indicated that MDR cells displayed the same hydrolysis kinetics and sensitivity as drug-sensitive cells with a well-preserved stoichiometry of the Feulgen reaction. LR73-R cells transfected with mdr1 cDNA exhibited only a very limited change in propidium iodide staining as compared with sensitive LR73 cells, suggesting that mdr1 gene overexpression alone could not account for the alterations in DNA content observed in the selected MDR cells.