Inhibition of nucleolar function and morphological change by adriamycin associated with heat shock protein 70 accumulation

The nucleolus: a central response hub for the stressors that drive cancer progression

The nucleolus is a sub-nuclear body known primarily for its role in ribosome biogenesis. Increased number and/or size of nucleoli have historically been used by pathologists as a prognostic indicator of cancerous lesions. This increase in nucleolar number and/or size is classically attributed to the increased need for protein synthesis in cancer cells. However, evidences suggest that the nucleolus plays critical roles in many cellular functions in both normal cell biology and disease pathologies, including cancer. As new functions of the nucleolus are elucidated, there is mounting evidence to support the role of the nucleolus in regulating additional cellular functions, particularly response to cellular stressors, maintenance of genome stability, and DNA damage repair, as well as the regulation of gene expression and biogenesis of several ribonucleoproteins. This review highlights the central role of the nucleolus in carcinogenesis and cancer progression and discusses how cancer cells may become “addicted” to nucleolar functions.

Development and characterization of an in vitro model of colorectal adenocarcinoma with MDR phenotype

The major cause of failure in cancer chemotherapy is the development of multidrug resistance (MDR), and the characterization of biological factors involved in this response to therapy is particularly needed. A doxorubicin-resistant HCT-8/R clone was selected from sensitive parental cells and characterized analyzing several parameters (cell cycle phase distribution, apoptotic activity, expression, distribution and functionality of the P-gp efflux pump, the response to other chemotherapy agents, its ultrastructural features, invasiveness, and transcriptomic profile). HCT-8/R cells showed a peculiar S phase distribution, characterized by a single pulse of proliferation, resistance to drug-mediated apoptosis, increased expression and functionality of P-gp and overexpression of stem cell markers (CD44 and aldehyde dehydrogenase 1A2). At the ultrastructural level, HCT-8/R presented a greater cell volume and several intracytoplasmic vesicles respect to HCT-8. Moreover, the resistant clone was characterized by cross resistance to other cytotoxic drugs and a greater capacity for migration and invasion, compared to parental cells. Our data reinforce the concept that the MDR phenotype in HCT-8/R cells is multifactorial and involves multiple mechanisms, representing an interesting tool to understand the biological basis of MDR and to test strategies that overcome resistance to chemotherapy.

The nucleolus as a fundamental regulator of the p53 response and a new target for cancer therapy

BACKGROUND

Recent studies have highlighted the fundamental role that key oncogenes such as MYC, RAS and PI3K occupy in driving RNA Polymerase I transcription in the nucleolus. In addition to maintaining essential levels of protein synthesis, hyperactivated ribosome biogenesis and nucleolar function plays a central role in suppressing p53 activation in response to oncogenic stress. Consequently, disruption of ribosome biogenesis by agents such as the small molecule inhibitor of RNA Polymerase I transcription, CX-5461, has shown unexpected, potent, and selective effects in killing tumour cells via disruption of nucleolar function leading to activation of p53, independent of DNA damage.

SCOPE OF REVIEW

This review will explore the mechanism of DNA damage-independent activation of p53 via the nucleolar surveillance pathway and how this can be utilised to design novel cancer therapies.

MAJOR CONCLUSION AND GENERAL SIGNIFICANCE

Non-genotoxic targeting of nucleolar function may provide a new paradigm for treatment of a broad range of oncogene-driven malignancies with improved therapeutic windows. This article is part of a Special Issue entitled: Translation and Cancer.

Hsp70 regulates the doxorubicin-mediated heart failure in Hsp70-transgenic mice

The aim of this study was to investigate the potential protective effect of the Hsp70 protein in the cardiac dysfunction induced by doxorubicin (DOX) and the mechanisms of its action. For this purpose, we used both wild-type mice (F1/F1) and Hsp70-transgenic mice (Tg/Tg) overexpressing human HSP70. Both types were subjected to chronic DOX administration (3 mg/kg intraperitoneally every week for 10 weeks, with an interval from weeks 4 to 6). Primary cell cultures isolated from embryos of these mice were also studied. During DOX administration, the mortality rate as well as weight reduction were lower in Tg/Tg compared to F1/F1 mice (P < 0.05). In vivo cardiac function assessment by transthoracic echocardiography showed that the reduction in left ventricular systolic function observed after DOX administration was lower in Tg/Tg mice (P < 0.05). The study in primary embryonic cell lines showed that the apoptosis after incubation with DOX was reduced in cells overexpressing Hsp70 (Tg/Tg), while the apoptotic pathway that was activated by DOX administration involved activated protein factors such as p53, Bax, caspase-9, caspase-3, and PARP-1. In myocardial protein extracts from identical mice with DOX-induced heart failure, the particular activated apoptotic pathway was confirmed, while the presence of Hsp70 appeared to inhibit the apoptotic pathway upstream of the p53 activation. Our results, in this DOX-induced heart failure model, indicate that Hsp70 overexpression in Tg/Tg transgenic mice provides protection from myocardial damage via an Hsp70-block in p53 activation, thus reducing the subsequent apoptotic mechanism.

Balanced production of ribosome components is required for proper G1/S transition in Saccharomyces cerevisiae

Cell cycle regulation is a very accurate process that ensures cell viability and the genomic integrity of daughter cells. A fundamental part of this regulation consists in the arrest of the cycle at particular points to ensure the completion of a previous event, to repair cellular damage, or to avoid progression in potentially risky situations. In this work, we demonstrate that a reduction in nucleotide levels or the depletion of RNA polymerase I or III subunits generates a cell cycle delay at the G1/S transition in Saccharomyces cerevisiae. This delay is concomitant with an imbalance between ribosomal RNAs and proteins which, among others, provokes an accumulation of free ribosomal protein L5. Consistently with a direct impact of free L5 on the G1/S transition, rrs1 mutants, which weaken the assembly of L5 and L11 on pre-60S ribosomal particles, enhance both the G1/S delay and the accumulation of free ribosomal protein L5. We propose the existence of a surveillance mechanism that couples the balanced production of yeast ribosomal components and cell cycle progression through the accumulation of free ribosomal proteins. This regulatory pathway resembles the p53-dependent nucleolar-stress checkpoint response described in human cells, which indicates that this is a general control strategy extended throughout eukaryotes.

Skeletal Muscle for Endomyocardial Biopsy: Comparable Stress Response in Doxorubicin Cardio-myopathy

In the present study, we compared the cell damage response in skeletal and cardiac muscle tissue when exposed to doxorubicin. This was carried out by means of a less invasive informative substitute to endomyocardiac biopsy based on Hsp70 immunodetection and a subcellular analysis of the nucleolus. Male Sprague Dawley rats (62 g body weight) were randomly distributed into 3 group, the control and doxorubicin I and doxorubicin II groups, in which 15 and 25 mg/kg body weight of doxorubicin (0.1 ml, i.v.) was administered, respectively. After 15, 30, 45 and 60 minutes, portions of the left and right ventricle wall and interventricle wall, together with skeletal muscle from the posterior and anterior member, were prepared for Hsp70 immunodetection by Western blot analysis and ultrastructural study using the thin cut technique. Differential cell response between the control and treated groups was observed in Hsp70 immunodetection and at the subcellular level. In the control group, the Hsp70 recognition levels and typical normal nucleolar morphology were similar, while the treated groups showed variable-dependent Hsp70 recognition and segregation of nucleolar components, forming ring-like figures of a variable-independent nature. Comparison of cardiac and skeletal muscle tissue cell response to doxorubicin toxic aggression revealed parallelism in terms of Hsp70 accumulation in certain regions of both tissues (15 mg/kg body weight of doxorubicin), which suggests that replacing endomyocardiac biopsy analysis with skeletal muscle analysis may be a safe option.

Low-energy-loss electron microscopy of doxorubicin in human breast cancer MCF-7 cells: localization by color

The distribution of the anti-cancer drug doxorubicin (DOX) in human breast cancer MCF-7 cells was imaged directly by low-energy-loss electron microscopy (EM) without specific antibodies or heavy metal stains, using only the electron-induced molecular orbital excitation of the drug. Cells treated with DOX were examined live by confocal fluorescence microscopy and as very thin sections in an electron microscope equipped with an electron energy filter having an energy resolution of 1 eV. The distribution of DOX obtained by EM from pairs of images at energy losses of 3+/-1 eV and 10+/-1 eV agreed with fluorescence microscope observations, but provided much more detail, easily distinguishing localization between nuclear membrane and perimembrane compartments and between vacuolated nucleoli and perinucleolar chromatin. Treatment times up to 1h and DOX concentrations up to 30 microM indicated a progression of DOX ingress from higher concentrations in the nuclear membrane to labeling of the nucleolus. Subsequently DOX moved into perinucleolar chromatin and concentrated in perimembrane chromatin aggregations. Quantification of the DOX signal indicated a decay half-life of 320 e/A2 under electron irradiation, whereas each image at 3000 x required 10 e/A2. The results point to a new field of high resolution microanalysis: color electron microscopy.

Expression of manganese superoxide disumutase influences chemosensitivity in esophageal and gastric cancers

The purpose of this study was to examine whether the increased sensitivity of cancer cells to adriamycin (ADM), which is known to produce superoxide radicals, was brought through suppressed manganese superoxide disumutase (MnSOD) expression in the presence of transforming growth factor beta1 (TGFbeta1). T.T., MKN28, and MKN45 cell lines were treated with TGFbeta1 before exposure to ADM. Athymic female mice bearing the MKN28 cells were treated with TGFbeta1, ADM, or TGFbeta1 + ADM. Pretreatment of T.T., MKN28, and MKN45 cell lines with TGFbeta1 resulted in increased sensitivity to ADM. In contrast, simultaneous exposure to TNFalpha, which increased MnSOD expression, decreased sensitivity of cancer cells to ADM. In vivo studies demonstrated that the combined administration of TGFbeta1 and ADM delayed tumor growth better than either treatment alone. Our results suggest that the synergistic antitumor effects of TGFbeta1 and ADM may be due to decreased MnSOD expression in cancer cells. Thus, combined administration of TGFbeta1 and ADM might prove useful for treatment of malignant disease.

Evidence of p53-dependent cross-talk between ribosome biogenesis and the cell cycle: effects of nucleolar protein Bop1 on G(1)/S transition

Bop1 is a novel nucleolar protein involved in rRNA processing and ribosome assembly. We have previously shown that expression of Bop1Delta, an amino-terminally truncated Bop1 that acts as a dominant negative mutant in mouse cells, results in inhibition of 28S and 5.8S rRNA formation and deficiency of newly synthesized 60S ribosomal subunits (Z. Strezoska, D. G. Pestov, and L. F. Lau, Mol. Cell. Biol. 20:5516-5528, 2000). Perturbation of Bop1 activities by Bop1Delta also induces a powerful yet reversible cell cycle arrest in 3T3 fibroblasts. In the present study, we show that asynchronously growing cells are arrested by Bop1Delta in a highly concerted fashion in the G(1) phase. Kinase activities of the G(1)-specific Cdk2 and Cdk4 complexes were downregulated in cells expressing Bop1Delta, whereas levels of the Cdk inhibitors p21 and p27 were concomitantly increased. The cells also displayed lack of hyperphosphorylation of retinoblastoma protein (pRb) and decreased expression of cyclin A, indicating their inability to progress through the restriction point. Inactivation of functional p53 abrogated this Bop1Delta-induced cell cycle arrest but did not restore normal rRNA processing. These findings show that deficiencies in ribosome synthesis can be uncoupled from cell cycle arrest and reveal a new role for the p53 pathway as a mediator of the signaling link between ribosome biogenesis and the cell cycle. We propose that aberrant rRNA processing and/or ribosome biogenesis may cause "nucleolar stress," leading to cell cycle arrest in a p53-dependent manner.

Enhancement of heat-induced heat shock protein (hsp)72 accumulation by doxorubicin (Dox) in vitro

Previous studies have shown that cellular thermotolerance develops in response to exposure to doxorubicin (Dox) and treatment with hyperthermia. In the present study, we evaluated the induction of thermotolerance and the accumulation of heat shock protein (hsp)72 after treatment with Dox and/or hyperthermia at 44 degrees C in Chinese hamster V-79 cells. Thermotolerance developed after exposure to Dox at 37 degrees C for 2 h in a dose-dependent manner. Western blot analysis showed no accumulation of hsp72 after exposure to Dox (0.2 microg/ml) for 2 h (lethal dose (LD)(15)). Hsp72 accumulated 12 h after hyperthermia at 44 degrees C for 35 min (LD(15)). However, when the cells were exposed to Dox (0.1 microg/ml) followed by heating at 44 degrees C for 25 min (LD(15)), accumulation of hsp72 was observed after 6 h. These results suggest that enhancement of induction of hsp72 accumulation by Dox may be involved in the development of thermotolerance induced by sequential treatment with Dox and hyperthermia.

Pharmacological hepatic preconditioning: involvement of 70-kDa heat shock proteins (HSP72 and HSP73) in ischaemic tolerance after intravenous administration of doxorubicin

BACKGROUND

Pharmacological preconditioning may induce a stress response which protects liver against ischaemia-reperfusion injury (IRI). The aim of this study was to determine, in an animal model, whether intravenous administration of doxorubicin induces heat shock proteins (HSPs) in liver tissue and facilitates liver tolerance to subsequent warm IRI.

METHODS

Male Wistar rats were used. Production of HSPs was determined in liver tissue sequentially after the injection of doxorubicin 1 mg/kg body-weight. Acquisition of tolerance for 30 min warm ischaemia and reperfusion of the liver was determined in animals pretreated (48 h beforehand) with doxorubicin, and in controls. Biochemical liver function and liver adenine nucleotide concentration 40 min after reperfusion and survival rate at 7 days after the ischaemic insult were recorded.

RESULTS

Expression of HSP72 and HSP73 in the liver was confirmed 48 h after doxorubicin administration. Biochemical parameters and survival rates were significantly better in pretreated animals than in controls.

CONCLUSION

These results indicate that doxorubicin has the potential to provide the liver with tolerance against IRI. A simultaneous increase of both HSP72 and HSP73 in liver tissue may explain the acquisition of tolerance following the administration of doxorubicin.