Caveolin-1 influences mitochondrial plasticity and function in hepatic stellate cell activation.

Caveolin-1 (Cav-1) is an integral membrane protein present in all organelles, responsible for regulating and integrating multiple signals as a platform. Mitochondria are extremely adaptable to external cues in chronic liver diseases, and expression of Cav-1 may affect mitochondrial flexibility in hepatic stellate cells (HSCs) activation. We previously demonstrated that exogenous expression of Cav-1 was sufficient to increase some classical markers of activation in HSCs. Here, we aimed to evaluate the influence of exogenous expression and knockdown of Cav-1 on regulating the mitochondrial plasticity, metabolism, endoplasmic reticulum (ER)-mitochondria distance, and lysosomal activity in HSCs. To characterize the mitochondrial, lysosomal morphology, and ER-mitochondria distance, we perform transmission electron microscope analysis. We accessed mitochondria and lysosomal networks and functions through a confocal microscope and flow cytometry. The expression of mitochondrial machinery fusion/fission genes was examined by real-time polymerase chain reaction. Total and mitochondrial cholesterol content was measured using Amplex Red. To define energy metabolism, we used the Oroboros system in the cells. We report that GRX cells with exogenous expression or knockdown of Cav-1 changed mitochondrial morphometric parameters, OXPHOS metabolism, ER-mitochondria distance, lysosomal activity, and may change the activation state of HSC. This study highlights that Cav-1 may modulate mitochondrial function and structural reorganization in HSC activation, being a potential candidate marker for chronic liver diseases and a molecular target for therapeutic intervention.

A DNA repair-independent role for alkyladenine DNA glycosylase in alkylation-induced unfolded protein response.

Alkylating agents damage DNA and proteins and are widely used in cancer chemotherapy. While cellular responses to alkylation-induced DNA damage have been explored, knowledge of how alkylation affects global cellular stress responses is sparse. Here, we examined the effects of the alkylating agent methylmethane sulfonate (MMS) on gene expression in mouse liver, using mice deficient in alkyladenine DNA glycosylase (Aag), the enzyme that initiates the repair of alkylated DNA bases. MMS induced a robust transcriptional response in wild-type liver that included markers of the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) known to be controlled by XBP1, a key UPR effector. Importantly, this response is significantly reduced in the Aag knockout. To investigate how AAG affects alkylation-induced UPR, the expression of UPR markers after MMS treatment was interrogated in human glioblastoma cells expressing different AAG levels. Alkylation induced the UPR in cells expressing AAG; conversely, AAG knockdown compromised UPR induction and led to a defect in XBP1 activation. To verify the requirements for the DNA repair activity of AAG in this response, AAG knockdown cells were complemented with wild-type Aag or with an Aag variant producing a glycosylase-deficient AAG protein. As expected, the glycosylase-defective Aag does not fully protect AAG knockdown cells against MMS-induced cytotoxicity. Remarkably, however, alkylation-induced XBP1 activation is fully complemented by the catalytically inactive AAG enzyme. This work establishes that, besides its enzymatic activity, AAG has noncanonical functions in alkylation-induced UPR that contribute to cellular responses to alkylation.

Transcriptomic analysis reveals that mTOR pathway can be modulated in macrophage cells by the presence of cryptococcal cells.

Cryptococcus neoformans and Cryptococcus gattii are the etiological agents of cryptococcosis, a high mortality disease. The development of such disease depends on the interaction of fungal cells with macrophages, in which they can reside and replicate. In order to dissect the molecular mechanisms by which cryptococcal cells modulate the activity of macrophages, a genome-scale comparative analysis of transcriptional changes in macrophages exposed to Cryptococcus spp. was conducted. Altered expression of nearly 40 genes was detected in macrophages exposed to cryptococcal cells. The major processes were associated with the mTOR pathway, whose associated genes exhibited decreased expression in macrophages incubated with cryptococcal cells. Phosphorylation of p70S6K and GSK-3ß was also decreased in macrophages incubated with fungal cells. In this way, Cryptococci presence could drive the modulation of mTOR pathway in macrophages possibly to increase the survival of the pathogen.

Dipyridamole as a new drug to prevent Epstein-Barr virus reactivation.

Epstein-Barr virus (EBV) is a widely distributed gamma-herpesvirus that has been associated with various cancers mainly from lymphocytic and epithelial origin. Although EBV-mediated oncogenesis has been associated with viral oncogenes expressed during latency, a growing set of evidence suggested that antiviral treatments directed against EBV lytic phase may contribute to prevent some forms of cancers, including EBV-positive Post-Transplant Lymphoproliferative Diseases. It is shown here that dipyridamole (DIP), a safe drug with favorable and broad pharmacological properties, inhibits EBV reactivation from B-cell lines. DIP repressed immediate early and early genes expression mostly through its ability to inhibit nucleoside uptake. Considering its wide clinical use, DIP repurposing could shortly be evaluated, alone or in combination with other antivirals, to treat EBV-related diseases where lytic replication plays a deleterious role.

Dipyridamole impairs autophagic flux and exerts antiproliferative activity on prostate cancer cells.

Autophagy is a cellular bulk degradation process used as an alternative source of energy and metabolites and implicated in various diseases. Inefficient autophagy in nutrient-deprived cancer cells would be beneficial for cancer therapy making its modulation valuable as a therapeutic strategy for cancer treatment, especially in combination with chemotherapy. Dipyridamole (DIP) is a vasodilator and antithrombotic drug. Its major effects involve the block of nucleoside uptake and phosphodiestesase inhibition, leading to increased levels of intracellular cAMP. Here we report that DIP increases autophagic markers due to autophagic flux blockage, resembling autophagosome maturation and/or closure impairment. Treatment with DIP results in an increased number of autophagosomes and autolysosomes and impairs degradation of SQSTM1/p62. As blockage of autophagic flux decreases the recycling of cellular components, DIP reduced the intracellular ATP levels in cancer cells. Autophagic flux blockage was neither through inhibition of lysosome function nor blockage of nucleoside uptake, but could be prevented by treatment with a PKA inhibitor, suggesting that autophagic flux failure mediated by DIP results from increased intracellular levels of cAMP. Treatment with DIP presented antiproliferative effects in vitro alone and in combination with chemotherapy drugs. Collectively, these data demonstrate that DIP can impair autophagic degradation, by preventing the normal autophagosome maturation, and might be useful in combination anticancer therapy.

Late autophagy inhibitor chloroquine improves efficacy of the histone deacetylase inhibitor SAHA and temozolomide in gliomas.

Glioblastoma multiforme is the most aggressive type of primary brain tumor associated with few therapeutic opportunities and poor prognosis. In this study, we evaluated the efficacy of combining temozolomide (TMZ) with suberoylanilide hydroxamic acid (SAHA) - a specific histone deacetylases inhibitor - in glioma models in vitro and in vivo. In glioma cell lines, combined TMZ/SAHA promoted more cytotoxicity, G2/M arrest and apoptosis than either drugs alone. G2/M arrest was detected as soon as 24 h post drug exposure and preceded apoptosis, which occurred from 72 h treatment. TMZ and SAHA, alone or combined, also stimulated autophagy as evaluated by means of acridine orange staining and immunodetection of LC3I-II conversion and p62/SQSTM1 degradation. Time-course of autophagy accompanied G2/M arrest and preceded apoptosis, and blockage of late steps of autophagy with chloroquine (CQ) augmented SAHA/TMZ toxicity leading to apoptosis. In orthotopic gliomas in vivo, combined SAHA/TMZ showed better antitumor efficacy than either drugs alone, and adding CQ to the regimen improved antiglioma effects of SAHA and TMZ monotherapies without further benefit on combined SAHA/TMZ. In summary, the herein presented data suggest that autophagy acts as a protective response that impairs efficacy of SAHA and TMZ. Inhibiting autophagy termination with CQ may offer means to improve antitumor effects of SAHA and TMZ in gliomas and possibly other cancers.

Ratiometric analysis of Acridine Orange staining in the study of acidic organelles and autophagy.

Acridine Orange is a cell-permeable green fluorophore that can be protonated and trapped in acidic vesicular organelles (AVOs). Its metachromatic shift to red fluorescence is concentration-dependent and, therefore, Acridine Orange fluoresces red in AVOs, such as autolysosomes. This makes Acridine Orange staining a quick, accessible and reliable method to assess the volume of AVOs, which increases upon autophagy induction. Here, we describe a ratiometric analysis of autophagy using Acridine Orange, considering the red-to-green fluorescence intensity ratio (R/GFIR) to quantify flow cytometry and fluorescence microscopy data of Acridine-Orange-stained cells. This method measured with accuracy the increase in autophagy induced by starvation or rapamycin, and the reduction in autophagy produced by bafilomycin A1 or the knockdown of Beclin1 or ATG7. Results obtained with Acridine Orange, considering R/GFIR, correlated with the conversion of the unlipidated form of LC3 (LC3-I) into the lipidated form (LC3-II), SQSTM1 degradation and GFP-LC3 puncta formation, thus validating this assay to be used as an initial and quantitative method for evaluating the late step of autophagy in individual cells, complementing other methods.