Silvia Palumbo

microRNA-17 regulates the expression of ATG7 and modulates the autophagy process, improving the sensitivity to temozolomide and low-dose ionizing radiation treatments in human glioblastoma cells

ATG7 is a key autophagy-promoting gene that plays a critical role in the regulation of cell death and survival of various cell types. We report here that microRNAs (miRNAs), a class of endogenous 22–24 nucleotide noncoding RNA molecules able to affect stability and translation of mRNA, may represent a novel mechanism for regulating ATG7 expression and therefore autophagy. We demonstrated that ATG7 is a potential target for miR-17, and this miRNA could negatively regulate ATG7 expression, resulting in a modulation of the autophagic status in T98G glioblastoma cells. Treatment of these tumor cells with the miR-17 mimic decreased, and with the antagomir increased, the expression of ATG7 protein. Dual luciferase reporter assay confirmed that a specific miR-17 binding sequence in the 3′-UTR of ATG7 contributed to the modulation of the expression of the gene by miR-17. Interestingly, our results showed that anti-miR-17 administration activated autophagy through autophagosome formation, as resulted by LC3B and ATG7 protein expression increase, and by the analysis of GFP-LC3 positive autophagosome vesicles in living cells. Furthermore, the autophagy activation by anti-miR-17 resulted in a decrease of the threshold resistance at temozolomide doses in T98G cells, while miR-17 modulation in U373-MG glioblastoma cells resulted in a sensitization to low ionizing radiation doses. Our study of the role of miR-17 in regulating ATG7 expression and autophagy reveals a novel function for this miRNA sequence in a critical cellular event with significant impacts in cancer development, progression and treatment.

Autophagy and ionizing radiation in tumors: The “survive or not survive” dilemma

Autophagy is a so‐called “self‐eating” system responsible for degrading long‐lived proteins and cytoplasmic organelles, whose products are recycled to maintain cellular homeostasis. This ability makes autophagy a good candidate for a survival mechanism in response to several stresses, including the tumor cell transformation. In particular, recent studies suggested that autophagy functions as a pro‐death mechanism within different tumor contexts. It is, however, widely reported that autophagy represents both a survival mechanism or contributes directly to cell death fate. This interplay of the autophagy functions has been observed in many types of cancers and, in some cases, autophagy has been demonstrated to both promote and inhibit antitumor drug resistance. From a therapeutical point of view, the effects of the modulation of the tumor cell autophagic status, in response to ionizing radiations, are presently of particular relevance in oncology. Accordingly, this review also provides a perspective view on future works for exploring the modulation of autophagic indices in tumor cells as a novel molecular‐based adjuvant strategy, in order to improve radiotherapy and chemotherapy effects in cancer patients. J. Cell. Physiol. 228: 1–8, 2013.

Different involvement of autophagy in human malignant glioma cell lines undergoing irradiation and temozolomide combined treatments.

Glioblastoma (GB) has a poor prognosis, despite current multimodality treatment. Beside surgical resection, adjuvant ionizing radiation (IR) combined with Temozolomide (TMZ) drug administration is the standard therapy for GB. This currently combined radio‐chemotherapy treatment resulted in glial tumor cell death induction, whose main molecular death pathways are still not completely deciphered. In this study, the autophagy process was investigated, and in vitro modulated, in two different GB cell lines, T98G and U373MG (known to differ in their radiosensitivity), after IR or combined IR/TMZ treatments. T98G cells showed a high radiosensitivity (especially at low and intermediate doses), associated with autophagy activation, assessed by Beclin‐1 and Atg‐5 expression increase, LC3‐I to LC3‐II conversion and LC3B‐GFP accumulation in autophagosomes of irradiated cells; differently, U373MG cells resulted less radiosensitive. Autophagy inhibition, using siRNA against BECN1 or ATG‐7 genes, totally prevented decrease in viability after both IR and IR/TMZ treatments in the radiosensitive T98G cells, confirming the autophagy involvement in the cytotoxicity of these cells after the current GB treatment, contrary to U373MG cells. However, rapamycin‐mediated autophagy, that further radiosensitized T98G, was able to promote radiosensitivty also in U373MG cells, suggesting a role of autophagy process in enhancing radiosensitivity. Taken together, these results might enforce the concept that autophagy‐associated cell death might constitute a possible adjuvant therapeutic strategy to enhance the conventional GB treatment. J. Cell. Biochem. 113: 2308–2318, 2012.

Emerging roles of microRNA in modulating cell-death processes in malignant glioma.

MicroRNAs (miRNAs) are small noncoding RNA molecules that regulate protein expression by cleaving or repressing the translation of target mRNAs. In mammals, their function mainly represses the mRNA transcripts via imperfect complementary sequences in the 3′UTR of target mRNAs. Several miRNAs have been recently reported to be involved in modulation of different genes in tumors, including glioblastoma, the most frequent brain tumor in adults. Despite the improvements in treatments, survival of patients remains poor, and glioblastoma is one of the most lethal form of human cancer. To define novel strategies against this tumor, emerging research investigated miRNAs involvement in glioblastoma. In particular, this review is focused on miRNAs involved on the two principal programmed cell‐death, apoptosis and autophagy, recently described from the literature. Moreover, the discovery of miRNAs role in glioma cell‐death pathways has also revealed a new category of therapeutic targets, fundamental for this kind of tumor. J. Cell. Physiol. 229: 277–286, 2014.

Silencing of cellular prion protein (PrPC) expression by DNA-antisense oligonucleotides induces autophagy-dependent cell death in glioma cells.

Malignant gliomas are the most common and lethal primary central nervous system neoplasms. Several intriguing lines of evidence have recently emerged indicating that the cellular prion protein (PrPC) may exert neuro- and cyto-protective functions: PrPC overexpression protects cultured neurons and also tumor cell lines exposed to various pro-apoptotic stimuli while, on the contrary, PrPC silencing sensitizes Adriamycin-resistant human breast carcinoma cells to TRAIL-mediated cell death. In order to determine if PrPC is involved in the resistance of glial tumors to cell death, the effects of cellular prion protein downregulation by antisense approach were investigated in different human malignant glioma cell lines. PrPC downregulation induced profound morphological changes and significant cell death. In addition, a significant tumor volume reduction was noted after PrPC silencing in a EGFP-GL261 glioma murine model. Investigations of the molecular effects induced by PrPC silencing were carried out on T98G human glioma cells by analysing autophagic as well as typical apoptotic markers (nuclear morphology, caspase-3/7, p53 and PARP-1). The results indicated that apoptosis was not induced after PrPC downregulation while, on the contrary, electron microscopy analysis, and an accumulation of GFP-LC3-II in autophagosomal membranes of GFP-LC3 transfected cells, indicated a predominant activation of autophagy. PrPC silencing also led to induction of LC3-II, increase in Beclin-1 and a concomitant decrease in p62, Bcl-2 and in the phosphorylation of 4E-BP1, a target of mTOR autophagy signaling. In conclusion, our results show for the first time that interfering with the cellular prion protein expression could modulate autophagy-dependent cell death pathways in glial tumor cells.

Combined EGFR and autophagy modulation impairs cell migration and enhances radiosensitivity in human glioblastoma cells

Glioblastoma (GBM) remains the most aggressive and lethal brain tumor due to its molecular heterogeneity and high motility and invasion capabilities of its cells, resulting in high resistance to current standard treatments (surgery, followed by ionizing radiation combined with Temozolomide chemotherapy administration). Locus amplification, gene overexpression, and genetic mutations of epidermal growth factor receptor (EGFR) are hallmarks of GBM that can ectopically activate downstream signaling oncogenic cascades such as PI3K/Akt/mTOR pathway. Importantly, alteration of this pathway, involved also in the regulation of autophagy process, can improve radioresistance in GBM cells, thus promoting the aggressive phenotype of this tumor. In this work, the endogenous EGFR expression profile and autophagy were modulated to increase radiosensitivity behavior of human T98G and U373MG GBM cells. Our results primarily indicated that EGFR interfering induced radiosensitivity according to a decrease of the clonogenic capability of the investigated cells, and an effective reduction of the in vitro migratory features. Moreover, EGFR interfering resulted in an increase of Temozolomide (TMZ) cytotoxicity in T98G TMZ‐resistant cells. In order to elucidate the involvement of the autophagy process as pro‐death or pro‐survival role in cells subjected to EGFR interfering, the key autophagic gene ATG7 was silenced, thereby producing a transient block of the autophagy process. This autophagy inhibition rescued clonogenic capability of irradiated and EGFR‐silenced T98G cells, suggesting a pro‐death autophagy contribution. To further confirm the functional interplay between EGFR and autophagy pathways, Rapamycin‐mediated autophagy induction during EGFR modulation promoted further impairment of irradiated cells, in terms of clonogenic and migration capabilities. Taken together, these results might suggest a novel combined EGFR‐autophagy modulation strategy, to overcome intrinsic GBM radioresistance, thus improving the efficacy of standard treatments. J. Cell. Physiol. 229: 1863–1873, 2014.

AUTOCOUNTER, an ImageJ JavaScript to analyze LC3B-GFP expression dynamics in autophagy-induced astrocytoma cells

An ImageJ JavaScript, AUTOCOUNTER, was specifically developed to monitor and measure LC3B-GFP expression in living human astrocytoma cells, namely T98G and U373-MG. Discrete intracellular GFP fluorescent spots derived from transduction of a Baculovirus replication-defective vector (BacMam LC3B-GFP), followed by microscope examinations at different times. After viral transgene expression, autophagy was induced by Rapamycin administration and assayed in ph-p70S6K/ p70S6K and LC3B immunoblotting expression as well as by electron microscopy examinations. A mutated transgene, defective in LC3B lipidation, was employed as a negative control to further exclude fluorescent dots derived from protein intracellular aggregation. The ImageJ JavaScript was then employed to evaluate and score the dynamics changes of the number and area of LC3B-GFP puncta per cell in time course assays and in complex microscope examinations. In conclusion, AUTOCOUNTER enabled to quantify LC3B-GFP expression and to monitor dynamics changes in number and shapes of autophagosomal-like vesicles: it might therefore represent a suitable algorithmic tool for in vitro autophagy modulation studies.

Gene Expression Analysis of an EGFR Indirectly Related Pathway Identified PTEN and MMP9 as Reliable Diagnostic Markers for Human Glial Tumor Specimens

In this study the mRNA levels of five EGFR indirectly related genes, EGFR, HB-EGF, ADAM17, PTEN, and MMP9, have been assessed by Real-time PCR in a panel of 37 glioblastoma multiforme specimens and in 5 normal brain samples; as a result, in glioblastoma, ADAM17 and PTEN expression was significantly lower than in normal brain samples, and, in particular, a statistically significant inverse correlation was found between PTEN and MMP9 mRNA levels. To verify if this correlation was conserved in gliomas, PTEN and MMP9 expression was further investigated in an additional panel of 16 anaplastic astrocytoma specimens and, in parallel, in different human normal and astrocytic tumor cell lines. In anaplastic astrocytomas PTEN expression was significantly higher than in glioblastoma multiforme, but no significant correlation was found between PTEN and MMP9 expression. PTEN and MMP9 mRNA levels were also employed to identify subgroups of specimens within the different glioma malignancy grades and to define a gene expression-based diagnostic classification scheme. In conclusion, this gene expression survey highlighted that the combined measurement of PTEN and MMP9 transcripts might represent a novel reliable tool for the differential diagnosis of high-grade gliomas, and it also suggested a functional link involving these genes in glial tumors.

Combined Epidermal Growth Factor Receptor and Beclin1 Autophagic Protein Expression Analysis Identifies Different Clinical Presentations, Responses to Chemo- and Radiotherapy, and Prognosis in Glioblastoma

Dysregulated EGFR in glioblastoma may inactivate the key autophagy protein Beclin1. Each of high EGFR and low Beclin1 protein expression, independently, has been associated with tumor progression and poor prognosis. High (H) compared to low (L) expression of EGFR and Beclin1 is here correlated with main clinical data in 117 patients after chemo- and radiotherapy. H-EGFR correlated with low Karnofsky performance and worse neurological performance status, higher incidence of synchronous multifocality, poor radiological evidence of response, shorter progression disease-free (PDFS), and overall survival (OS). H-Beclin1 cases showed better Karnofsky performance status, higher incidence of objective response, longer PDFS, and OS. A mutual strengthening effect emerges in correlative power of stratified L-EGFR and H-Beclin1 expression with incidence of radiological response after treatment, unifocal disease, and better prognosis, thus identifying an even longer OS group (30 months median OS compared to 18 months in L-EGFR, 15 months in H-Beclin1, and 11 months in all GBs) (P = 0.0001). Combined L-EGFR + H-Beclin1 expression may represent a biomarker in identifying relatively favorable clinical presentations and prognosis, thus envisaging possible EGFR/Beclin1-targeted therapies.

Altered cellular distribution and sub-cellular sorting of doppel (Dpl) protein in human astrocytoma cell lines

Doppel, a prion-like protein, is a GPI-membrane anchored protein generally not expressed in the Central Nervous System (CNS) of different mammalian species, including human. Nevertheless, in astrocytomas, a particular kind of glial tumors, the doppel encoding gene (PRND) is over-expressed and the corresponding protein product (Dpl) is ectopically localized in the cytoplasm of the tumor cells. In this study we have analysed the sub-cellular localization of Dpl using double-immunofluorescence staining and confocal microscopy examinations in two astrocytoma-derived human cell lines (IPDDC-A2 and D384-MG). Our results confirmed that Dpl is localized in the cytoplasm of the astrocytoma cells and indicated that it is mostly associated with Lamp-1 and Limp-2 positive lysosomal vesicles and, marginally, to the Golgi apparatus and other cellular organelles. Noticeably, none of the examined tumor cells showed a membrane-Dpl localization. The membrane-associated Dpl expression was restored after the transfection of the astrocytoma cells with mutated Dpl-expression vectors in its glycosylation sites. Additionally, Dpl showed altered expression and traffic using the acidotropic agent ammonium chloride, leading to the accumulation of Dpl in nascent exocytic vesicles. Altogether, these results indicated that in the astrocytic tumor cells Dpl has an altered biosynthetic trafficking, likely derived from abnormal post-translational processes: these modifications do not permit the localization of Dpl in correspondence of the plasma membrane and lead to its intracellular accumulation in the lysosomes. In these proteolytic compartments, the astrocytic tumor cells might provide to the degradation of the excess of a potentially cytotoxic Dpl product.