pRb2/p130 gene overexpression induces astrocyte differentiation

Effector mechanisms of sunitinib-induced G1 cell cycle arrest, differentiation, and apoptosis in human acute myeloid leukaemia HL60 and KG-1 cells

Acute myeloid leukaemia (AML) is a heterogeneous disease with dismal outcome. Sunitinib is an orally active inhibitor of multiple tyrosine kinase receptors approved for renal cell carcinoma and gastrointestinal stromal tumour that has also been studied for AML in several clinical trials. However, the precise mechanism of sunitinib action against AML remains unclear and requires further investigation. For this purpose, this study was conducted using human AML cell lines (HL60 and KG-1) and AML patients' mononucleated cells. Sunitinib induced G1 phase arrest associated with decreased cyclin D1, cyclin D3, and cyclin-dependent kinase (Cdk)2 and increased p27(Kip1), pRb1, and p130/Rb2 expression and phosphorylated activation of protein kinase C alpha and beta (PKCα/β). Selective PKCα/β inhibitor treatment abolished sunitinib-elicited AML differentiation, suggesting that PKCα/β may underlie sunitinib-induced monocytic differentiation. Furthermore, sunitinib increased pro-apoptotic molecule expression (Bax, Bak, PUMA, Fas, FasL, DR4, and DR5) and decreased anti-apoptotic molecule expression (Bcl-2 and Mcl-1), resulting in caspase-2, caspase-3, caspase-8, and caspase-9 activation and both death receptor and mitochondria-dependent apoptosis. Taken together, these findings provide evidence that sunitinib targets AML cells through both differentiation and apoptosis pathways. More clinical studies are urgently needed to demonstrate its optimal clinical applications in AML.

N-(4-Hydroxyphenyl) retinamide potentiated paclitaxel for cell cycle arrest and apoptosis in glioblastoma C6 and RG2 cells

Glioblastoma grows aggressively due to its ability to maintain abnormally high potentials for cell proliferation. The present study examines the synergistic actions of N-(4-hydroxyphenyl) retinamide (4-HPR) and paclitaxel (PTX) to control the growth of rat glioblastoma C6 and RG2 cell lines. 4-HPR induced astrocytic differentiation that was accompanied by increased expression of the tight junction protein e-cadherin and sustained down regulation of Id2 (member of inhibitor of differentiation family), catalytic subunit of rat telomerase reverse transcriptase (rTERT), and proliferating cell nuclear antigen (PCNA). Flow cytometric analysis showed that the microtubule stabilizer PTX caused cell cycle deregulation due to G2/M arrest. This in turn could alter the fate of kinetochore-spindle tube dynamics thereby halting cell cycle progression. An interesting observation was the induction of G1/S arrest by a combination of 4-HPR and PTX, altering the G2/M arrest induced by PTX alone. This was further ratified by the upregulation of tumor suppressor protein retinoblastoma, which repressed the expression of the key signaling moieties to induce G1/S arrest. Collectively, the combination of 4-HPR and PTX diminished the survival factors (e.g., rTERT, PCNA, and Bcl-2) to make glioblastoma cells highly prone to apoptosis with activation of cysteine proteases (e.g., calpain, cathepsins, caspase-8, caspase-3). Hence, the combination of 4-HPR and PTX can be considered as an effective therapeutic strategy for controlling the growth of heterogeneous glioblastoma cell populations.

A SAGE study of apolipoprotein E3/3, E3/4 and E4/4 allele-specific gene expression in hippocampus in Alzheimer disease

APOE4 allele is a major risk factor for late-onset Alzheimer disease (AD). The mechanism of action of APOE in AD remains unclear. To study the effects of APOE alleles on gene expression in AD, we have analyzed the gene transcription patterns of human hippocampus from APOE3/3, APOE3/4, APOE4/4 AD patients and normal control using Serial Analysis of Gene Expression (SAGE). Using SAGE, we found gene expression patterns in hippocampus of APOE3/4 and APOE4/4 AD patients differ substantially from those of APOE3/3 AD patients. APOE3/4 and APOE4/4 allele expression may activate similar genes or gene pools with associated functions. APOE4 AD alleles activate multiple tumor suppressors, tumor inducers and negative regulator of cell growth or repressors that may lead to increased cell arrest, senescence and apoptosis. In contrast, there is decreased expression of large clusters of genes associated with synaptic plasticity, synaptic vesicle docking and fusing and axonal/neuronal outgrowth. In addition, reduction of neurotransmitter receptors and Ca2+ homeostasis, disruption of multiple signal transduction pathways, loss of cell protection, and perhaps most notably, mitochondrial oxidative phosphorylation/energy metabolism are associated with APOE3/4 and APOE4/4 AD alleles. These findings may help define the mechanisms that APOE4 contribute that increase risk for AD and identify new candidate genes conferring susceptibility to AD.

RB and RB2/P130 genes cooperate with extrinsic signals to promote differentiation of rat neural stem cells

Mechanisms governing commitment and differentiation of the cells of the nervous system begin to be elucidated: how extrinsic and intrinsic components are related remains poorly understood. To investigate this issue, we overexpressed genes of the retinoblastoma (Rb) family RB and RB2/p130, which play an important role during nerve cell maturation, in rat neural stem cells (NSCs). Immunostaining of neurons, astrocytes and oligodendrocytes in cultures overexpressing pRb or pRb2/p130 revealed that these genes affect lineage specification of differentiating NSCs. We observed modifications in percentage of differentiated cells indicating a shift towards the phenotype induced by culture conditions. Results were confirmed by detection of the expression levels of differentiation markers by RT-PCR. Analysis of BrdU incorporation and detection of an early marker of apoptosis suggest that the effect of pRb and pRb2/p130 overexpression is not dependent on the inhibition of cell proliferation, nor does it rely on the regulation of cell survival. Our findings suggest that Rb family genes are involved in fate determination of the cells of the nervous system. However, their role seems subsidiary to that of the extrinsic signals that promote lineage specification and appear to be mediated by a direct effect on the acquisition of a specific phenotype.

Rb family proteins as modulators of gene expression and new aspects regarding the interaction with chromatin remodeling enzymes

The pRb family proteins (pRb1/105, p107, pRb2/p130), collectively referred to as pocket proteins, are believed to function primarily as regulators of the mammalian cell cycle progression, and suppressors of cellular growth and proliferation. In addition, different studies suggest that these pocket proteins are also involved in development and differentiation of various tissues. Several lines of evidence indicate that generally pRb-family proteins function through their effect on the transcription of E2F-regulated genes. In fact, each of Rb family proteins binds to distinct members of the E2F transcription factors, which regulate the expression of genes whose protein products are necessary for cell proliferation and to drive cell-cycle progression. Nevertheless, pocket proteins can affect the G1/S transition through E2F-independent mechanisms. More recently, a broad range of evidences indicate that pRb-family proteins associate with a wide variety of transcription factors and chromatin remodeling enzymes forming transcriptional repressor complexes that control gene expression. This review focuses on the complex regulatory mechanisms by which pRb-family proteins tell genes when to switch on and off.

Differences in apolipoprotein E3/3 and E4/4 allele-specific gene expression in hippocampus in Alzheimer disease

Apolipoprotein E4 (APOE4) allele is a major risk factor for late-onset familial and sporadic Alzheimer disease (AD). The mechanism of action of APOE in the etiology of AD remains unclear. Using gene expression (microarray) analysis of human hippocampus from APOE3/3 AD and APOE4/4 AD cases, we found different gene transcription patterns between APOE4/4 and APOE3/3 AD cases. The expression of APOE4/4 alleles, in comparison to APOE3/3, is associated with upregulation of multiple gene transcripts encoding cell growth suppresser or arrest, signal transduction, myelinogenesis, cell adhesion and migration, heavy metal metabolism and detoxification. Whereas the APOE4 gene expression is associated with downregulation of gene transcripts involved in mitochondrial oxidative phosphorylation and energy metabolism, synaptic vesicle docking and fusing, and synaptic plasticity compared to APOE3. These mechanisms may contribute increased risk for AD and for cognitive dysfunction in AD patients who carry the APOE4 allele(s).

Developmental neurobiology and the origin of brain tumors

Our knowledge of the causes of brain tumors has steadily increased and is leading to a refined understanding of the signaling pathways that may be essential for tumor formation. At the same time, we are gaining insights into the developmental processes that regulate the formation of the diverse range of cell types in the normal brain. Interestingly, many of these pathways seem to overlap and suggest common mechanisms regulating tumor formation and cellular development. This overlap may also inform us about the nature of the cell of origin for different types of brain tumors. By appreciating the inter-relationship between tumor formation and development, we maybe able to design new therapeutics targeting tumors for new modes of treatment.

Expression of Rb2/p130 protein correlates with the degree of malignancy in gliomas

It has been reported that there is an inverse correlation between the immunohistochemical expression of Rb2/p130, a member of the retinoblastoma gene family, and the degree of malignancy in at least some histological types. In order to investigate the expression of this protein in gliomas, we evaluated 58 samples from patients with resected gliomas. We focused on the relationship between the degree of malignancy of the glioma and the immunohistochemical detection of Rb2/p130. Expression of Rb2/p130 was observed in 38 glioma specimens (65.5%), including a high expression level in low-grade glioma specimens (> 30% positive cells in 84% of tumors) and a low expression level in high-grade glioma specimens (> 30% positive cells in 12% of tumors). The most aggressive of the gliomas exhibited very low to undetectable levels of Rb2/p130. Moreover, we observed an inverse correlation between Rb2/p130 expression and the degree of malignancy. These findings suggest that the differentiation of gliomas might be partially mediated by the Rb2/p130 gene, and that Rb2/ p130 expression can additionally be an indicator of a better prognosis in patients with gliomas.

Ezh2 reduces the ability of HDAC1-dependent pRb2/p130 transcriptional repression of cyclin A

The polycomb group (PcG) proteins are known to be involved in maintaining the silenced state of several developmentally regulated genes. Enhancer of zeste homolog 2 (Ezh2), a member of this large protein family, has also been shown to be deregulated in different tumor types and its role, both as a potential primary effector and as a mediator of tumorigenesis, has become a subject of increased interest. We observed that Ezh2 binds to pRb2/p130, a member of the retinoblastoma family; as such, we were led to consider the possible ability of Ezh2 to modulate cell cycle progression. Both Ezh2 and pRb2/p130 repress gene expression by recruiting histone deacetylase (HDAC1), which decreases DNA accessibility for activating transcription factors. Additionally, we observed that Ezh2 interacts with the C-terminal region of pRb2/p130, essential for interaction with HDAC1. We show that Ezh2 is able to reverse pRb2/p130-HDAC1-mediated repression of the cyclin A promoter. This indicates a functional role of this complex in regulating cyclin A expression, known to be crucial in mediating cell cycle advancement. We also detected a significant decrease in the retention of HDAC1 activity associated with pRb2/p130 when Ezh2 was overexpressed. Finally, electromobility shift assays (EMSA) demonstrated that overexpression of Ezh2 caused the abrogation of the pRb2/p130-HDAC1 complex on the cyclin A promoter. These data, taken together, suggest that Ezh2 competes with HDAC1 in binding to pRb2/p130, disrupting their occupancy on the cyclin A promoter. In this study, we propose a new mechanism for the functional inactivation of pRb2/p130 that ultimately contributes to cell cycle progression and malignant transformation.

Incipient Alzheimer's disease: microarray correlation analyses reveal major transcriptional and tumor suppressor responses

The pathogenesis of incipient Alzheimer's disease (AD) has been resistant to analysis because of the complexity of AD and the overlap of its early-stage markers with normal aging. Gene microarrays provide new tools for addressing complexity because they allow overviews of the simultaneous activity of multiple cellular pathways. However, microarray data interpretation is often hindered by low statistical power, high false positives or false negatives, and by uncertain relevance to functional endpoints. Here, we analyzed hippocampal gene expression of nine control and 22 AD subjects of varying severity on 31 separate microarrays. We then tested the correlation of each gene's expression with MiniMental Status Examination (MMSE) and neurofibrillary tangle (NFT) scores across all 31 subjects regardless of diagnosis. These well powered tests revealed a major transcriptional response comprising thousands of genes significantly correlated with AD markers. Several hundred of these genes were also correlated with AD markers across only control and incipient AD subjects (MMSE > 20). Biological process categories associated with incipient AD-correlated genes were identified statistically (ease program) and revealed up-regulation of many transcription factor/signaling genes regulating proliferation and differentiation, including tumor suppressors, oligodendrocyte growth factors, and protein kinase A modulators. In addition, up-regulation of adhesion, apoptosis, lipid metabolism, and initial inflammation processes occurred, and down-regulation of protein folding/metabolism/transport and some energy metabolism and signaling pathways took place. These findings suggest a new model of AD pathogenesis in which a genomically orchestrated up-regulation of tumor suppressor-mediated differentiation and involution processes induces the spread of pathology along myelinated axons.

Strategies for cancer gene therapy

Gene therapy offers new opportunities for cancer treatment and prevention through the use of targeted, relatively nontoxic treatments that can identify, disable, and destroy malignant cells. This article reviews the principles behind oncogene inactivation, tumor suppressor gene replacement, inhibition of angiogenesis, immunopotentiation, molecular chemotherapy, and addition of drug resistance genes. The adcantages and limitations of viral and nonviral vectors for delivery of the therapeutic genes are presented.

Cell cycle regulation and neural differentiation

The general mechanisms that control the cell cycle in mammalian cells have been studied in depth and several proteins that are involved in the tight regulation of cell cycle progression have been identified. However, the analysis of which molecules participate in cell cycle exit of specific cell lineages is not exhaustive yet. Moreover, the strict relation between cell cycle exit and induction of differentiation has not been fully understood and seems to depend on the cell type. Several in vivo and in vitro studies have been performed in the last few years to address these issues in cells of the nervous system. In this review, we focus our attention on cyclin-cyclin-dependent kinase complexes, cyclin kinase inhibitors, genes of the retinoblastoma family, p53 and N-Myc, and we aim to summarize the latest evidence indicating their involvement in the control of the cell cycle and induction of differentiation in different cell types of the peripheral and central nervous systems. Studies on nervous system tumors and a possible contributory role in tumorigenesis of polyomavirus T antigen are reported to point out the critical contribution of some cell cycle regulators to normal neural and glial development.

EGF-responsive rat neural stem cells: molecular follow-up of neuron and astrocyte differentiation in vitro

Neural stem cells (NSCs) could be very useful for the "cell therapy" treatment of neurological disorders. For this reason basic studies aiming to well characterize the biology of NSCs are of great interest. We carried out a molecular and immunocytochemical analysis of EGF-responsive NSCs obtained from rat pups. After the initial growth of NSCs as floating neurospheres in EGF-containing medium, cells were plated on poly-L-ornithine-coated dishes either in the presence or absence of EGF. We followed cell differentiation and apoptosis for 21 days in vitro and analyzed the expression levels of some genes having a major role in these processes, such as pRB, pRB2/p130, p27, and p53. We observed that EGF impairs neuronal differentiation. Furthermore, in the absence of mitogens, apoptosis, which appeared to proceed through the "p53 network," was significantly lower than in the presence of EGF. The cyclin kinase inhibitor p27, while important for cell cycle exit, seemed dispensable for cell survival and differentiation.

Astrocyte differentiation states and glioma formation

Gliomas are the most common primary malignancy in human central nervous system. Many similarities in cell morphology and expression of markers exist between cancerous cells and normal undifferentiated progenitor cells. At the molecular level, many important gene products are causally implicated in both the glial differentiation process and glial neoplasm formation. These observations raise the question of to what degree cell differentiation state influences glioma formation. In this review, we discuss new insights into the parallels between glial differentiation and glioma formation as well as the potential application of differentiation-inducing therapy.