Expression of ICAD-l and ICAD-S in human brain tumor and its cleavage upon activation of apoptosis by anti-Fas antibody

Alterations in Molecular Profiles Affecting Glioblastoma Resistance to Radiochemotherapy: Where Does the Good Go?

Simple Summary

Glioblastoma is a type of brain cancer that remains incurable. Despite multiple past and ongoing preclinical studies and clinical trials, involving adjuvants to the conventional therapy and based on molecular targeting, no relevant benefit for patients’ survival has been achieved so far. The current first-line treatment regimen is based on ionizing radiation and the monoalkylating compound, temozolomide, and has been administered for more than 15 years. Glioblastoma is extremely resistant to most agents due to a mutational background that elicits quick response to insults and adapts to microenvironmental and metabolic changes. Here, we present the most recent evidence concerning the molecular features and their alterations governing pathways involved in GBM response to the standard radio-chemotherapy and discuss how they collaborate with acquired GBM’s resistance.

Abstract

Glioblastoma multiforme (GBM) is a brain tumor characterized by high heterogeneity, diffuse infiltration, aggressiveness, and formation of recurrences. Patients with this kind of tumor suffer from cognitive, emotional, and behavioral problems, beyond exhibiting dismal survival rates. Current treatment comprises surgery, radiotherapy, and chemotherapy with the methylating agent, temozolomide (TMZ). GBMs harbor intrinsic mutations involving major pathways that elicit the cells to evade cell death, adapt to the genotoxic stress, and regrow. Ionizing radiation and TMZ induce, for the most part, DNA damage repair, autophagy, stemness, and senescence, whereas only a small fraction of GBM cells undergoes treatment-induced apoptosis. Particularly upon TMZ exposure, most of the GBM cells undergo cellular senescence. Increased DNA repair attenuates the agent-induced cytotoxicity; autophagy functions as a pro-survival mechanism, protecting the cells from damage and facilitating the cells to have energy to grow. Stemness grants the cells capacity to repopulate the tumor, and senescence triggers an inflammatory microenvironment favorable to transformation. Here, we highlight this mutational background and its interference with the response to the standard radiochemotherapy. We discuss the most relevant and recent evidence obtained from the studies revealing the molecular mechanisms that lead these cells to be resistant and indicate some future perspectives on combating this incurable tumor.

The role of the DFF40/CAD endonuclease in genomic stability

Maintenance of genomic stability in cells is primordial for cellular integrity and protection against tumor progression. Many factors such as ultraviolet light, oxidative stress, exposure to chemical reagents, particularly mutagens and radiation, can alter the integrity of the genome. Thus, human cells are equipped with many mechanisms that prevent these irreversible lesions in the genome, as DNA repair pathways, cell cycle checkpoints, and telomeric function. These mechanisms activate cellular apoptosis to maintain DNA stability. Emerging studies have proposed a new protein in the maintenance of genomic stability: the DNA fragmentation factor (DFF). The DFF40 is an endonuclease responsible of the oligonucleosomal fragmentation of the DNA during apoptosis. The lack of DFF in renal carcinoma cells induces apoptosis without oligonucleosomal fragmentation, which poses a threat to genetic information transfer between cancerous and healthy cells. In this review, we expose the link between the DFF and genomic instability as the source of disease development.

Decreased Expression of Inhibitor of Caspase-Activated DNase (ICAD) in Renal Cell Carcinoma - Tissue Microarray of Human Samples

Although primary localised tumours of renal cell carcinoma (RCC) can be treated relatively successfully with surgery, metastatic RCC has poor prognosis because of late diagnosis and resistance to therapies. In the present study, we were interested in profiling the protein expression of “inhibitor of caspase-activated DNase” (ICAD), an apoptosis inhibitor, in kidney cancer and its paired normal kidney. Immunohistochemistry with automated batch staining and morphometry using digital pathology were used to compare ICAD in 121 RCC specimens with their paired normal kidney tissue. Tissue microarray of formalin-fixed, paraffin-embedded archival tissue was used. Intensity and localisation of ICAD were compared between normal and cancer samples, and against grading within the cancers. The results demonstrated that, in this cohort, ICAD was highly expressed in the proximal tubular epithelium of normal kidney, and significantly decreased in clear cell RCC tissue (p < 0.05) as well as other subtypes of RCC (p < 0.01) compared with normal kidney. There was a tendency towards nuclear localisation of ICAD in clear cell RCC, but not in other subtypes of RCC. No significant association was found between ICAD intensity and grade of RCC. In summary, down-regulation of ICAD occurs in RCC. ICAD normally inhibits DNA fragmentation and apoptosis; thus, its down-regulation was unexpected in a cancer known for its resistance to apoptosis. However, these RCC samples were from primary, not metastatic, RCC sites, and down-regulated ICAD may be part of a progressive pathway that promotes RCC metastasis.

siRNA-mediated knock-down of DFF45 amplifies doxorubicin therapeutic effects in breast cancer cells

PURPOSE

RNA interference (RNAi) has become a promising tool for cancer therapy. Small interfering RNAs (siRNAs) can synergistically enhance the cell killing effects of drugs used in cancer treatment. Here we examined the effects of siRNA-mediated DNA fragmentation factor 45 (DFF45) gene silencing on breast cancer cell viability, cell cycle arrest, and apoptosis in the presence and absence of doxorubicin.

METHODS

We designed three siRNAs, which target different regions of the DFF45 mRNA. Gene silencing was confirmed by real time RT-PCR and Western blot analyses. The impact of DFF45 siRNA, doxorubicin, and their combination on the viability, cell cycle and apoptosis of T-47D and MDA-MB-231 breast cancer cells were determined by MTT, PI staining, annexin V binding, caspase-3 activity, DNA laddering, and chromatin condensation assays.

RESULTS

Based on flow cytometric analyses, we found that silencing of DFF45 alone had little effect on apoptosis, especially in T-47D cells. However, when used in combination with doxorubicin (0.33 μM) a significant increase (P < 0.05) in apoptosis was observed in T-47D and MDA-MB-231 cells, i.e., ~2.5- and 3-fold, respectively. Caspase-3 activity, chromatin condensation, as well as DNA laddering supported increased apoptosis in the combinatorial treatment. Cell cycle arrest in both cell lines occurred at lower levels after siRNA + doxorubicin treatment compared to doxorubicin only.

CONCLUSIONS

Our data indicate that DFF45 gene silencing, when applied in combination with doxorubicin, may offer a novel therapeutic strategy for the treatment of breast cancer.

Identification and characterization of the human inhibitor of caspase-activated DNase gene promoter

DNA fragmentation factor is a heterodimer complex of the nuclease CAD and its specific inhibitor ICAD, which can be activated during apoptosis to induce DNA fragmentation. Although ICAD expression levels have been quantified in a variety of human cancer cells, the mechanism of ICAD gene regulation remains unknown. In this study, we identified a 106-bp TATA-less region upstream of the transcription start site as a basal promoter of the human ICAD gene. An E-Box motif, which binds transcription factors of the basic helix-loop-helix/leucine zipper family, is responsible for transcriptional activity, as demonstrated using mutated promoter-reporters. A chromatin immunoprecipitation assay further demonstrated that Myc binds to an endogenous ICAD promoter. The functional importance of Myc in the regulation of ICAD transcription was also demonstrated by knock-down of c-Myc and N-Myc gene expression, as well as their ectopic expression. Structural analysis of the human ICAD promoter and identification of factors which regulate its activity might further our understanding of the biological role of ICAD with respect to regulation of apoptosis and cancer development.

Genetic analysis of the short splice variant of the inhibitor of caspase-activated DNase (ICAD-S) in chicken DT40 cells

We have studied the regulation of the caspase-Activated DNase (CAD) by its inhibitor, ICAD. To study the role of ICAD short and long splice forms ICAD-S and ICAD-L, respectively, in vivo, we constructed chicken DT40 cell lines in which the entire coding regions of ICAD alone or ICAD plus CAD were deleted. ICAD and ICAD/CAD double knock-outs lacked both DNA fragmentation and nuclear fragmentation after the induction of apoptosis. We constructed a model humanized system in which human ICAD-L and CAD proteins expressed in DT40 ICAD/CAD double knock-out cells could rescue both DNA fragmentation and stage II chromatin condensation. ICAD-S could not replace ICAD-L as a chaperone for folding active CAD in these cells. However, a modified version of ICAD-S, in which the two caspase-3 cleavage sites were replaced with two tobacco etch virus (TEV) protease cleavage sites (ICAD-S(2TEV)) and which was therefore resistant to caspase cleavage, did inhibit CAD activation upon induction of apoptosis in vivo. Moreover, ICAD-L(2TEV) was functional as a chaperone for the production of active CAD in DT40 cells. In extracts prepared from these cells, we were able to activate CAD by cleavage of ICAD-L(2TEV) with TEV protease under non-apoptotic conditions. Thus, ICAD appears to be the only functional inhibitor of CAD activation in these cell-free extracts. Taken together, these observations indicate that ICAD-S may function together with ICAD-L as a buffer to prevent inappropriate CAD activation, particularly in cells where ICAD-S is the dominant form of ICAD protein.

Cyclosporine a induces growth arrest or programmed cell death of human glioma cells

Human malignant gliomas are highly resistant to current therapeutic approaches. We previously demonstrated that cyclosporine A (CsA) induces an apoptotic cell death in rat C6 glioma cells. In the present study, we found the induction of growth arrest or cell death of human malignant glioma cells exposed to CsA. In studied glioma cells, an accumulation of p21Cip1/Waf1 protein, a cell cycle inhibitor, was observed following CsA treatment, even in the absence of functional p53 tumour suppressor. CsA induced a senescence-associated growth arrest, in U87-MG glioma cells with functional p53, while in U373 and T98G glioma cells with mutated p53, CsA treatment triggered cell death associated with alterations of cell morphology, cytoplasm vacuolation, and condensation of chromatin. In T98G cells this effect was completely abolished by simultaneous treatment with an inhibitor of protein synthesis, cycloheximide (CHX). Moreover, CsA-induced cell death was accompanied by activation of executory caspases followed by PARP cleavage. CsA treatment did not elevate fasL expression and had no effect on mitochondrial membrane potential. We conclude that CsA triggers either growth arrest or non-apoptotic, programmed cell death in human malignant glioma cells. Moreover, CsA employs mechanisms different to those in the action of radio- and chemotherapeutics, and operating even in cells resistant to conventional treatments. Thus, CsA or related drugs may be an effective novel strategy to treat drug-resistant gliomas or complement apoptosis-based therapies.

The effect of ICAD-S on the formation and intracellular distribution of a nucleolytically active caspase-activated DNase

We show here that co-expression of murine CAD with either ICAD-L or ICAD-S in Escherichia coli as well as mammalian cells leads to a functional DFF complex, which after caspase-3 activation releases a nucleolytically active DNase. The chaperone activity of ICAD-S is between one and two orders of magnitude less effective than that of ICAD-L, as deduced from cleavage experiments with different activated recombinant DFF complexes produced in E.coli. With nucleolytically active EGFP fusion proteins of CAD it is demonstrated that co-expression of ICAD-S, which lacks the C-terminal domain of ICAD-L, including the NLS, leads to a homogeneous intracellular distribution of the DNase in transfected cells, whereas co-expression of human or murine ICAD-L variants lacking the NLS leads to exclusion of EGFP-CAD from the nuclei in approximately 50% of cells. These results attribute a particular importance of the NLS in the long isoform of the inhibitor of CAD for nuclear accumulation of the DFF complex in living cells. It is concluded that ICAD-L and ICAD-S in vivo might function as tissue-specific modulators in the regulation of apoptotic DNA degradation by controlling not only the enzymatic activity but also the amount of CAD available in the nuclei of mammalian cells.