Cleavage of nucleolin and AgNOR proteins during apoptosis induced by anticancer drugs in human salivary gland cells

Argentic staining reveals changes in cerebellar tissue organisation by prenatal glucocorticoid administration in rats

It was almost 150 years ago that Golgi revolutionised histology with silver-based stains. Major advances in knowledge of the nervous system became possible because of silver impregnations. Silver staining combined with classical histological staining, cytochemistry methods, and electron microscopy is useful for studying mechanisms and components at subcellular, cellular, and tissue levels. Despite the advantages of silver staining, its use has decreased over time. The aim of this work was to use argentic staining to study the cerebellar effects of controversial prenatal glucocorticoid (GC) therapy. At postnatal day 12 (P12), the cerebellum of corticosterone (CC)-treated rats impregnated with AgNOR staining exhibited diminished thickness of the external granule layer (EGL) and irregular Purkinje cell arrangement. There was a greater number of nucleoli and nucleolar organiser regions (NORs) in 24% of Purkinje cells. Cerebellar granule neuron progenitor (CGNP) cells of the EGL showed a decrease in cellular density (confirmed by proliferating cell nuclear antigen [PCNA] immunolocalization) and NORs. At postnatal day 6 (P6), the Golgi-Kopsch technique allowed us to observe disturbances in the distribution pattern of CGNP cells (during proliferation, migration, and differentiation) and premature growth of the Bergmann glia. Our findings reveal disturbances in the cerebellar development program with early cellular and tissue changes.

MMP7-mediated cleavage of nucleolin at Asp255 induces MMP9 expression to promote tumor malignancy

Nucleolin (NCL) participates in DNA transcription, ribosomal biogenesis and the regulation of RNA stability. However, the contribution of NCL to tumor development is still not clear. Herein, we found that NCL expression correlated with poor prognosis in lung cancer patients. Overexpressed NCL was predominantly cleaved to C-terminal truncated NCL (TNCL). In lung cancer formation, activation of the epidermal growth factor receptor pathway induced NCL expression, and also the expression of matrix metalloproteinase (MMP) 7, which then cleaved NCL at Asp255 to generate TNCL of 55 kDa. TNCL increased the expression of several oncogenes, including MMP9, anaplastic lymphoma kinase (ALK), HIF1a and CBLB, and decreased the expression of tumor suppressors including BRD4, PCM1, TFG and KLF6 by modulating mRNA stability through binding to the 3'-untranslated regions of their transcripts, thus ultimately enhancing metastasis activity. In conclusion, this study identified a novel role of the cleavage form of NCL generated by MMP7 in stabilizing MMP9 mRNA. We also provide a new insight that MMP7 not only cleaves the extracellular matrix to promote tumor invasion but also cleaves NCL, which augment oncogenesis. Blocking NCL cleavage may provide a useful new strategy for lung cancer therapy.

Targeting G-quadruplexes in gene promoters: a novel anticancer strategy?

G-quadruplexes are four-stranded DNA structures that are over-represented in gene promoter regions and are viewed as emerging therapeutic targets in oncology, as transcriptional repression of oncogenes through stabilization of these structures could be a novel anticancer strategy. Many gene promoter G-quadruplexes have physicochemical properties and structural characteristics that might make them druggable, and their structural diversity suggests that a high degree of selectivity might be possible. Here, we describe the evidence for G-quadruplexes in gene promoters and discuss their potential as therapeutic targets, as well as progress in the development of strategies to harness this potential through intervention with small-molecule ligands.

The C-terminus of nucleolin promotes the formation of the c-MYC G-quadruplex and inhibits c-MYC promoter activity

Nucleolin, the most abundant nucleolar phosphoprotein of eukaryotic cells, is known primarily for its role in ribosome biogenesis and cell proliferation. It is, however, a multifunctional protein that, depending on the cellular context, can drive either cell proliferation or apoptosis. Our laboratory recently demonstrated that nucleolin can function as a repressor of c-MYC transcription by binding to and stabilizing the formation of a G-quadruplex structure in a region of the c-MYC promoter responsible for controlling 85-90% of c-MYC's transcriptional activity. In this study, we investigate the structural elements of nucleolin that are required for c-MYC repression. The effect of nucleolin deletion mutants on the formation and stability of the c-MYC G-quadruplex, as well as c-MYC transcriptional activity, was assessed by circular dichroism spectropolarimetry, thermal stability, and in vitro transcription. Here we report that nucleolin's RNA binding domains 3 and 4, as well as the arginine-glycine-glycine (RGG) domain, are required to repress c-MYC transcription.

Induction of nucleolin translocation by acharan sulfate in A549 human lung adenocarcinoma

Acharan sulfate (AS), isolated from the giant African snail Achatina fulica, is a novel glycosaminoglycan, consisting primarily of the repeating disaccharide structure alpha-D-N-acetylglucosaminyl (1 --> 4) 2-sulfoiduronic acid. AS shows anti-tumor activity in vitro and in vivo. Despite this activity, AS is only weakly cytotoxic towards cancer cells. We examine the interactions between AS and cell-surface proteins in an effort to explain this anti-tumor activity. Using flow cytometry and affinity column chromatography, we confirm that AS has strong affinity to specific cell-surface proteins including nucleolin (NL) in A549 human lung adenocarcinomas. Surprisingly, we found the translocation of NL from nucleus to cytoplasm under the stimulation of AS (100 microg/ml) in vitro. Also, as NL exits the nucleus, the levels of growth factors such as bFGF and signaling cascade proteins, such as p38, p53, and pERK, are altered. These results suggest that the communication between AS and NL plays a critical role on signal transduction in tumor inhibition.

Nucleolin/C23 is a negative regulator of hydrogen peroxide-induced apoptosis in HUVECs

Nucleolin plays important roles in chromatin structure, rDNA transcription, rRNA maturation, nucleocytoplasmic transport, and ribosome assembly. Although it has been shown to be anti-apoptotic, the underlying mechanisms remain unclear. In the current study, we first examined endogenous nucleolin expression in response to oxidative stress-induced apoptosis in human umbilical vascular endothelial cells (HUVECs). Flow cytometry and caspase activity assays showed that H(2)O(2) treatment caused apoptosis of the cells; reverse-transcription polymerase chain reaction and Western blotting revealed the downregulation of nucleolin expression and increased protein cleavage during this process. Overexpression of nucleolin protein by transfecting cells with the full-length nucleolin cDNA inhibited apoptosis, but nucleolin deficiency brought about by transfection with antisense oligonucleotide increased apoptosis of HUVECs. Concurrently, the expression of the apoptotic protein gene Bax was also downregulated following nucleolin overexpression. All these results indicate an important negative regulatory role for nucleolin in the apoptosis of endothelial cells, likely involving the Bax pathway.

Regulation of stress-induced nuclear protein redistribution: a new function of Bax and Bak uncoupled from Bcl-x(L)

Apoptosis is regulated by changes in the subcellular distribution of pro- and anti-apoptotic proteins, among which are nuclear proteins such as histone H1 (H1) and nucleophosmin (NPM). These proteins were reported to translocate to the cytosol and mitochondria, and to facilitate apoptosis in response to apoptotic stressors. The significance of this stress-induced, nuclear protein redistribution and its exact molecular mechanism are poorly understood. We show here that in mouse embryonic fibroblasts (MEFs), different apoptotic stimuli induce H1, NPM and nucleolin, but not KAP-1 nuclear/cytoplasmic redistribution, which precedes the appearance of apoptotic features. Using MEFs deficient in Bax/Bak, Apaf-1 or caspase-9, as well as caspase inhibitors, we show that this redistribution requires Bax and Bak, but neither the apoptosome nor caspases. Furthermore, the BH3 mimetic ABT-737, which acts through Bax/Bak, also stimulates nuclear protein redistribution in a Bax/Bak-dependent manner. Re-expression of Bax or Bak in Bax/Bak-deficient MEFs restores nuclear redistribution during apoptosis. This is not accompanied by Bax or Bak N-terminus exposure and is not inhibited by Bcl-x(L) overexpression. These results identify, for the first time, a function of Bax/Bak that is insensitive to inhibition by Bcl-x(L) and most likely unrelated to their canonical, pore-forming activity on mitochondria.

Calpain-truncated CRMP-3 and -4 contribute to potassium deprivation-induced apoptosis of cerebellar granule neurons

Increasing evidence shows that calpain-mediated proteolytic processing of a selective number of proteins plays an important role in neuronal apoptosis. Study of calpain-mediated cleavage events and related functions may contribute to a better understanding of neuronal apoptosis and neurodegenerative diseases. We, therefore, investigated the role of calpain substrates in potassium deprivation-induced apoptosis of cerebellar granule neurons (CGNs). Twelve previously known and seven novel candidates of calpain substrates were identified by 2-D DIGE and MALDI-TOF/TOF MS analysis. Further, the identified novel calpain substrates were validated by Western blot analysis. Moreover, we focused on the collapsin response mediator proteins (CRMP-1, -2, -3 and -4 isoforms) and found that CRMPs were proteolytically processed by calpain but not by caspase, both in vivo and in vitro. To clarify the properties of the calpain-mediated proteolysis of CRMPs, we constructed the deletion mutants of CRMPs for additional biochemical studies. In vitro cleavage assays revealed that CRMP-1, -2 and -4 were truncated by calpain at the C-terminus, whereas CRMP-3 was cleaved at the N-terminus. Finally, we assessed the role of CRMPs in the process of potassium deprivation-triggered neuronal apoptosis by overexpressing the truncated CRMPs in CGNs. Our data clearly showed that the truncated CRMP-3 and -4, but not CRMP-1 and -2, significantly induced neuronal apoptosis. These findings demonstrated that calpain-truncated CRMP-3 and -4 act as pro-apoptotic players when CGNs undergo apoptosis.

Changes in the status of nucleolus during long-term culturing of human HeLa cells

Changes in the immunocytochemical status of the nucleoli during long-term (6-8 months) in vitro culturing of HeLa (carcinoma of the cervix uteri) cells were described using new A3 monoclonal antibodies selectively reacting with human cell nucleoli. The appearance of cells with abnormal location of A3 antigen was paralleled by a significant increase of culture sensitivity to some external factors (protein synthesis inhibition and oxidative stress). The data indicate that location of one of the nucleolar antigens is an indicator of the qualitative status of HeLa cells in the culture.

Nucleolar development and allocation of key nucleolar proteins require de novo transcription in bovine embryos

The goal of the present study was to investigate whether key nucleolar proteins involved in ribosomal RNA (rRNA) transcription and processing are transcribed de novo or from maternally inherited messenger RNAs (mRNA) in bovine embryos, and to which extent de novo transcription of these proteins mRNA is required for the development of functional nucleoli during the major activation of the embryonic genome. Immunofluorescence for localization of key nucleolar proteins, autoradiography for detection of transcriptional activity, and transmission electron microscopy were applied to in vitro produced bovine embryos cultured from the 2-cell stage with or without (control groups) alpha-amanitin, which blocks the RNA polymerases II and III transcription and, thus the synthesis of mRNA. In the control groups, weak autoradiographic labeling was initially observed in the periphery of few nuclei at the 4-cell and the early 8-cell stage, and the entire nucleoplasm as well as nucleolus precursor bodies (NBBs) were prominently labelled in all late 8-cell stages. The NPBs displayed initial transformation into fibrillo-granular nucleoli. In the alpha-amanitin group, lack of autoradiographic labeling was seen at all developmental stages and disintegrated NPBs stage were found at the late 8-cell. Our immunofluorescence data indicate that RNA polymerase I, UBF, topoisomerase I and fibrillarin are transcribed de novo whereas nucleolin and nucleophosmin are maternally inherited as demonstrated by alpha -amanitin inhibition. However, localization of these two proteins to the nucleolar compartments was negatively affected by the alpha-amanitin treatment. Consequently, functional nucleoli were not established.

Actinomycin D upregulates proapoptotic protein Puma and downregulates Bcl-2 mRNA in normal peripheral blood lymphocytes

We have examined the ability of actinomycin D to induce apoptosis in human peripheral blood lymphocytes. Run-On assays were performed to specify the primary molecular damage, reverse transcription-PCR, Western blots and flow cytometry studies were performed to ascertain which proteins of the apoptosis machinery were affected to cause actinomycin D-induced cell death. Expression of 23 apoptosis-related genes was investigated. The down-regulation of ribosomal RNA synthesis caused by actinomycin D induced a mitochondria-dependent apoptosis. Although the expression of the majority of examined genes remained indifferent against actinomycin D activity, the cellular level of p53 protein increased, subsequently upregulating both Puma mRNA and protein. Puma-mediated mitochondrial apoptosis was accompanied by nucleolin cleavage and Bcl-2 mRNA destabilization. The stability of the cellular level of Bcl-2 protein independent of a mRNA decrease suggests that protection of Bcl-2 protein against proteasomal degradation can moderate the apoptotic process. In peripheral blood lymphocytes cultured in vitro, the apoptosis induced by a low concentration of actinomycin D (10 nmol/l) is dependent on p53 and Puma activation. This apoptotic pathway is demonstrated in peripheral blood lymphocytes for the first time. A different apoptotic pathway induced in peripheral blood lymphocytes using this drug has, however, been previously revealed by other authors. The combination of cell specificity and dose-dependent effects can likely play a decisive role in apoptosis observed in peripheral blood lymphocytes after genotoxic drug application.