Okadaic acid induced cyclin B1 expression and mitotic catastrophe in rat cortex

Id1 and Sonic Hedgehog Mediate Cell Cycle Reentry and Apoptosis Induced by Amyloid Beta-Peptide in Post-mitotic Cortical Neurons

Amyloid beta-peptide (Aβ), the neurotoxic component of senile plaques in Alzheimer's disease (AD) brains, is known to trigger cell cycle reentry in post-mitotic neurons followed by apoptosis. However, the underlying mechanisms remain unclear. Recently, we have reported that Aβs stimulate the expression of inhibitor of differentiation-1 (Id1) to induce sonic hedgehog (SHH) (Hung et al., Mol Neurobiol 53(2):793-809, 2016), and both are mitogens capable of triggering cell cycle progression. In this work, we tested the hypothesis that Aβ-induced Id1 and SHH contribute to cell cycle reentry leading to apoptosis in neurons. We found that Aβ triggered cell cycle progression in the post-mitotic neurons, as indicated by the increased expression of two G1-phase markers including cyclin D1 and phosphorylated retinoblastoma protein (pRb), two G2-phase markers such as proliferating cell nuclear antigen (PCNA) and incorporation of 5-bromo-2'-deoxyuridine (BrdU) into newly synthesized DNA, as well as the mitotic marker histone H3 phosphorylated at Ser-10. As expected, Aβ also enhanced caspase-3 cleavage in the cortical neurons. Id1 siRNA, the neutralization antibody against SHH (SHH-Ab), and the cyclin-dependent kinase (CDK)-4/6 inhibitor PD0332991 all attenuated, in part or in full, the Aβ-induced expression of these cell cycle markers. Indeed, exogenous recombinant Id1 protein and the biologically active N-terminal fragment of SHH (SHH-N) were both sufficient to enhance the expression of cell cycle markers independent of Aβ. Taken together, our results revealed the critical roles of Id1 and SHH mediating Aβ-dependent cell cycle reentry and subsequently caspase-dependent apoptosis in the fully differentiated post-mitotic neurons, at least in vitro.

U1 snRNP Alteration and Neuronal Cell Cycle Reentry in Alzheimer Disease

The aberrancy of U1 small nuclear ribonucleoprotein (snRNP) complex and RNA splicing has been demonstrated in Alzheimer's disease (AD). Importantly, the U1 proteopathy is AD-specific, widespread and early-occurring, thus providing a very unique clue to the AD pathogenesis. The prominent feature of U1 histopathology is its nuclear depletion and redistribution in the neuronal cytoplasm. According to the preliminary data, the initial U1 cytoplasmic distribution pattern is similar to the subcellular translocation of the spliceosome in cells undergoing mitosis. This implies that the U1 mislocalization might reflect the neuronal cell cycle-reentry (CCR) which has been extensively evidenced in AD brains. The CCR phenomenon explains the major molecular and cellular events in AD brains, such as Tau and amyloid precursor protein (APP) phosphorylation, and the possible neuronal death through mitotic catastrophe (MC). Furthermore, the CCR might be mechanistically linked to inflammation, a critical factor in the AD etiology according to the genetic evidence. Therefore, the discovery of U1 aberrancy might strengthen the involvement of CCR in the AD neuronal degeneration.

U1 snRNP Alteration and Neuronal Cell Cycle Reentry in Alzheimer Disease

The aberrancy of U1 small nuclear ribonucleoprotein (snRNP) complex and RNA splicing has been demonstrated in Alzheimer’s disease (AD). Importantly, the U1 proteopathy is AD-specific, widespread and early-occurring, thus providing a very unique clue to the AD pathogenesis. The prominent feature of U1 histopathology is its nuclear depletion and redistribution in the neuronal cytoplasm. According to the preliminary data, the initial U1 cytoplasmic distribution pattern is similar to the subcellular translocation of the spliceosome in cells undergoing mitosis. This implies that the U1 mislocalization might reflect the neuronal cell cycle-reentry (CCR) which has been extensively evidenced in AD brains. The CCR phenomenon explains the major molecular and cellular events in AD brains, such as Tau and amyloid precursor protein (APP) phosphorylation, and the possible neuronal death through mitotic catastrophe (MC). Furthermore, the CCR might be mechanistically linked to inflammation, a critical factor in the AD etiology according to the genetic evidence. Therefore, the discovery of U1 aberrancy might strengthen the involvement of CCR in the AD neuronal degeneration.

Upregulation of Cdh1 signaling in the hippocampus attenuates brain damage after transient global cerebral ischemia in rats

Cerebral ischemia is a major cause of brain dysfunction. The E3 ubiquitin ligase anaphase-promoting complex and its coactivator Cdh1 have been reported to be involved in the regulation of neuronal survival, differentiation, axonal growth and synaptic development in the central nervous system. However, its role in the ischemic brain and the underlying mechanisms remain poorly understood. The present study aimed to investigate the effects of Cdh1 overexpression on the ischemic rat brain by direct intra-hippocampal injection of lentivirus-delivered Cdh1 before transient global cerebral ischemia reperfusion. Spatial memory acquisition and retention were assessed using a Morris water maze task. Neuronal damage, glial activation, oxidative stress and the synaptic ultrastructure were also examined. The results indicated that a recombinant Cdh1-encoding lentiviral vector can upregulate the expression of Cdh1 in the rat hippocampus. Cdh1 overexpression increased the survival rates of rats, reversed the abnormal accumulation of cyclin B1, alleviated neuronal death, inhibited glial activation, mitigated oxidative stress, modulated synaptic plasticity and improved neurological deficits caused by ischemia. Our study indicates that targeting the Cdh1 signaling pathway in the hippocampus may provide a promising therapeutic strategy for the clinical treatment of transient global cerebral ischemia.

LB100, a small molecule inhibitor of PP2A with potent chemo- and radio-sensitizing potential

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase that plays a significant role in mitotic progression and cellular responses to DNA damage. While traditionally viewed as a tumor suppressor, inhibition of PP2A has recently come to attention as a novel therapeutic means of driving senescent cancer cells into mitosis and promoting cell death via mitotic catastrophe. These findings have been corroborated in numerous studies utilizing naturally produced compounds that selectively inhibit PP2A. To overcome the known human toxicities associated with these compounds, a water-soluble small molecule inhibitor, LB100, was recently developed to competitively inhibit the PP2A protein. This review summarizes the pre-clinical studies to date that have demonstrated the anti-cancer activity of LB100 via its chemo- and radio-sensitizing properties. These studies demonstrate the tremendous therapeutic potential of LB100 in a variety of cancer types. The results of an ongoing phase 1 trial are eagerly anticipated.

Zinc and the aging brain

Alterations in trace element homeostasis could be involved in the pathology of dementia, and in particular of Alzheimer's disease (AD). Zinc is a structural or functional component of many proteins, being involved in numerous and relevant physiological functions. Zinc homeostasis is affected in the elderly, and current evidence points to alterations in the cellular and systemic distribution of zinc in AD. Although the association of zinc and other metals with AD pathology remains unclear, therapeutic approaches designed to restore trace element homeostasis are being tested in clinical trials. Not only could zinc supplementation potentially benefit individuals with AD, but zinc supplementation also improves glycemic control in the elderly suffering from diabetes mellitus. However, the findings that select genetic polymorphisms may alter an individual's zinc intake requirements should be taken into consideration when planning zinc supplementation. This review will focus on current knowledge regarding pathological and protective mechanisms involving brain zinc in AD to highlight areas where future research may enable development of new and improved therapies.

Small compound 6-O-angeloylplenolin induces mitotic arrest and exhibits therapeutic potentials in multiple myeloma

Background

Multiple myeloma (MM) is a disease of cell cycle dysregulation while cell cycle modulation can be a target for MM therapy. In this study we investigated the effects and mechanisms of action of a sesquiterpene lactone 6-O-angeloylplenolin (6-OAP) on MM cells.

Methodology/Principal Findings

MM cells were exposed to 6-OAP and cell cycle distribution were analyzed. The role for cyclin B1 to play in 6-OAP-caused mitotic arrest was tested by specific siRNA analyses in U266 cells. MM.1S cells co-incubated with interleukin-6 (IL-6), insulin-like growth factor-I (IGF-I), or bone marrow stromal cells (BMSCs) were treated with 6-OAP. The effects of 6-OAP plus other drugs on MM.1S cells were evaluated. The in vivo therapeutic efficacy and pharmacokinetic features of 6-OAP were tested in nude mice bearing U266 cells and Sprague-Dawley rats, respectively. We found that 6-OAP suppressed the proliferation of dexamethasone-sensitive and dexamethasone-resistant cell lines and primary CD138+ MM cells. 6-OAP caused mitotic arrest, accompanied by activation of spindle assembly checkpoint and blockage of ubiquitiniation and subsequent proteasomal degradation of cyclin B1. Combined use of 6-OAP and bortezomib induced potentiated cytotoxicity with inactivation of ERK1/2 and activation of JNK1/2 and Casp-8/-3. 6-OAP overcame the protective effects of IL-6 and IGF-I on MM cells through inhibition of Jak2/Stat3 and Akt, respectively. 6-OAP inhibited BMSCs-facilitated MM cell expansion and TNF-α-induced NF-κB signal. Moreover, 6-OAP exhibited potent anti-MM activity in nude mice and favorable pharmacokinetics in rats.

Conclusions/Significance

These results indicate that 6-OAP is a new cell cycle inhibitor which shows therapeutic potentials for MM.

Okadaic acid and dinophysis toxin 2 have differential toxicological effects in hepatic cell lines inducing cell cycle arrest, at G0/G1 or G2/M with aberrant mitosis depending on the cell line

Okadaic acid is one of the toxins responsible for the human intoxication known as diarrhetic shellfish poisoning, which appears after the consumption of contaminated shellfish. The main diarrhetic shellfish poisoning toxins are okadaic acid, dinophysistoxin-1, -2, and -3. In vivo, after intraperitoneal injection, dinophysistoxin-2 is approximately 40% less toxic than okadaic acid in mice. The cytotoxic and genotoxic effect of okadaic acid varies very significantly in different cell lines, so similar responses could be expected for dinophysistoxin-2. In order to determine whether this was the case, we studied the effect of okadaic acid and dinophysistoxin-2 in two hepatic cell lines (HepG2 and Clone 9). The cytotoxicity of these toxins, as well as their effects on the cell cycle and its regulation on both cell lines, were determined. Okadaic acid and dinophysistoxin-2 resulted to be equipotent in clone 9 cultures, while okadaic acid was more potent than dinophysistoxin-2 in HepG2 cell cultures. Both toxins had opposite effects on the cell cycle; they arrested the cell cycle of clone 9 cells in G2/M inducing aberrant mitosis while arresting the cell cycle of HepG2 in G0/G1. When the effect of the toxins on p53 subcellular distribution was studied, p53 was detected in the nuclei of both cell types. The effect of the toxins on the gene expression of cyclins and cyclin-dependent kinases was different for both cell lines. The toxins induced an increase in gene expression of cyclins A, B, and D in clone 9 cells while they induced a decrease in cyclins A and B in HepG2 cells. They also induced a decrease in cyclin-dependent kinase 1 in HepG2 cells.