Mitochondrial regulation of cell death: mitochondria are essential for procaspase 3-p21 complex formation to resist Fas-mediated cell death

CIP/KIP and INK4 families as hostages of oncogenic signaling

CIP/KIP and INK4 families of Cyclin-dependent kinase inhibitors (CKIs) are well-established cell cycle regulatory proteins whose canonical function is binding to Cyclin-CDK complexes and altering their function. Initial experiments showed that these proteins negatively regulate cell cycle progression and thus are tumor suppressors in the context of molecular oncology. However, expanded research into the functions of these proteins showed that most of them have non-canonical functions, both cell cycle-dependent and independent, and can even act as tumor enhancers depending on their posttranslational modifications, subcellular localization, and cell state context. This review aims to provide an overview of canonical as well as non-canonical functions of CIP/KIP and INK4 families of CKIs, discuss the potential avenues to promote their tumor suppressor functions instead of tumor enhancing ones, and how they could be utilized to design improved treatment regimens for cancer patients.

Nonsteroidal anti-inflammatory drugs sensitize epithelial cells to Clostridioides difficile toxin-mediated mitochondrial damage

Clostridioides difficile damages the colonic mucosa through the action of two potent exotoxins. Factors shaping C. difficile pathogenesis are incompletely understood but are likely due to the ecological factors in the gastrointestinal ecosystem, mucosal immune responses, and environmental factors. Little is known about the role of pharmaceutical drugs during C. difficile infection (CDI), but recent studies have demonstrated that nonsteroidal anti-inflammatory drugs (NSAIDs) worsen CDI. The mechanism underlying this phenomenon remains unclear. Here, we show that NSAIDs exacerbate CDI by disrupting colonic epithelial cells (CECs) and sensitizing cells to C. difficile toxin-mediated damage independent of their canonical role of inhibiting cyclooxygenase (COX) enzymes. Notably, we find that NSAIDs and C. difficile toxins target the mitochondria of CECs and enhance C. difficile toxin-mediated damage. Our results demonstrate that NSAIDs exacerbate CDI by synergizing with C. difficile toxins to damage host cell mitochondria. Together, this work highlights a role for NSAIDs in exacerbating microbial infection in the colon.

The Mechanism of Two Benzaldehydes from Aspergillus terreus C23-3 Improve Neuroinflammatory and Neuronal Damage to Delay the Progression of Alzheimer's Disease

Alzheimer's disease (AD), a neurodegenerative disease, is the most common cause of dementia in humans worldwide. Although more in-depth research has been carried out on AD, the therapeutic effect of AD is not as expected, and natural active substances are increasingly sought after by scientists. In the present study, we evaluated two benzaldehydes from a coral-derived Aspergillus terreus strain C23-3, their anti-neuroinflammatory activity in microglia (BV-2), and their neuroprotective activity and mechanisms in hippocampal neuronal cells (HT-22). These include the protein expression of iNOS, COX-2, MAPKs pathways, Tau protein-related pathways, caspases family-related signaling pathways. They also include the levels of TNF-α, IL-6, IL-18 and ROS, as well as the level of mitochondrial oxidative stress and neuronal cell apoptosis. The results showed that both benzaldehydes were effective in reducing the secretion of various inflammatory mediators, as well as pro-inflammatory factors. Among these, benzaldehyde 2 inhibited mitochondrial oxidative stress and blocked neuronal cell apoptosis through Tau protein-related pathways and caspases family-related signaling pathways, thereby inhibiting β-amyloid (Aβ)-induced neurological damage. This study reveals that benzaldehyde 2 has potential as a therapeutic agent for Alzheimer's disease, and offers a new approach to the high-value use of marine natural products.

HSF1 and Its Role in Huntington's Disease Pathology

PURPOSE OF REVIEW

Heat shock factor 1 (HSF1) is the master transcriptional regulator of the heat shock response (HSR) in mammalian cells and is a critical element in maintaining protein homeostasis. HSF1 functions at the center of many physiological processes like embryogenesis, metabolism, immune response, aging, cancer, and neurodegeneration. However, the mechanisms that allow HSF1 to control these different biological and pathophysiological processes are not fully understood. This review focuses on Huntington's disease (HD), a neurodegenerative disease characterized by severe protein aggregation of the huntingtin (HTT) protein. The aggregation of HTT, in turn, leads to a halt in the function of HSF1. Understanding the pathways that regulate HSF1 in different contexts like HD may hold the key to understanding the pathomechanisms underlying other proteinopathies. We provide the most current information on HSF1 structure, function, and regulation, emphasizing HD, and discussing its potential as a biological target for therapy.

DATA SOURCES

We performed PubMed search to find established and recent reports in HSF1, heat shock proteins (Hsp), HD, Hsp inhibitors, HSF1 activators, and HSF1 in aging, inflammation, cancer, brain development, mitochondria, synaptic plasticity, polyglutamine (polyQ) diseases, and HD.

STUDY SELECTIONS

Research and review articles that described the mechanisms of action of HSF1 were selected based on terms used in PubMed search.

RESULTS

HSF1 plays a crucial role in the progression of HD and other protein-misfolding related neurodegenerative diseases. Different animal models of HD, as well as postmortem brains of patients with HD, reveal a connection between the levels of HSF1 and HSF1 dysfunction to mutant HTT (mHTT)-induced toxicity and protein aggregation, dysregulation of the ubiquitin-proteasome system (UPS), oxidative stress, mitochondrial dysfunction, and disruption of the structural and functional integrity of synaptic connections, which eventually leads to neuronal loss. These features are shared with other neurodegenerative diseases (NDs). Currently, several inhibitors against negative regulators of HSF1, as well as HSF1 activators, are developed and hold promise to prevent neurodegeneration in HD and other NDs.

CONCLUSION

Understanding the role of HSF1 during protein aggregation and neurodegeneration in HD may help to develop therapeutic strategies that could be effective across different NDs.

Ethanolic extract of Ya-nang (Tiliacora triandra) leaf powder induces apoptosis in cholangiocarcinoma cell lines via induction of hyperacetylation and inhibition of growth signaling

Objective

To develop alternative medicine for reducing undesired side effects of chemotherapy in CCA patients, the anticancer activity of Tiliacora triandra leaf powder ethanolic (TLPE) extract against cholangiocarcinoma cell lines was investigated.

Methods

Antiproliferation was studied using the MTT assay while apoptosis induction and cell cycle arrest were analyzed by flow cytometry. The levels of key proteins and phenolic acid content were analyzed by western blotting and reversed-phase HPLC, respectively.

Results

TLPE extract inhibited CCA cell growth in a dose- and time-dependent manner, with IC₅₀ values of 7.86 ± 0.05 µg/ml for KKU-M213B cells and 8.59 ± 0.36 µg/ml for KKU-100 cells at an exposure time of 72 h. TLPE extract inhibited the growth of CCA cell lines by inducing apoptosis of both cell lines and causing an increased population of KKU-100 cells at G0/G1 phase. TLPE extract up-regulated Ac-H3 but down-regulated p-ERK, p53, Bax, CDK4 and Bcl2 expressions in KKU-M213B cells. TLPE extract up-regulated Ac-H3, p21 and Bax but down-regulated p-ERK, p53, CDK4 and Bcl2 expressions in KKU-100 cells. Additionally, phenolic acids including p-hydroxybenzoic, vanillic, syringic, p-coumaric, ferulic and sinapinic acids were identified.

Conclusion

These results suggest the possibility of developing T. triandra leaf powder ethanolic extract as a chemotherapeutic or chemoprevention agent for cholangiocarcinoma.

Full Mitochondrial Genomes Reveal Species Differences between the Venerid Clams Ruditapes philippinarum and R. variegatus

In natural sea areas along the coast of China, venerid clams Ruditapes philippinarum and R. variegatus exhibit similar adult shell forms and are especially difficult to distinguish as spat and juveniles. This study used comparative mitochondrial genome analysis to reveal differences between these species. The results showed that: (1) the mitochondrial genomes of R. philippinarum and R. variegatus share a large number of similar gene clusters arranged in consistent order, yet they also display noncommon genes, with both gene rearrangements and random losses found; (2) the 13 protein-coding genes in R. philippinarum as well as two-fold and four-fold degenerate sites in R. variegatus have an evident AT bias; (3) the Ka/Ks ratio of the mitochondrial ATP8 gene was significantly higher in R. philippinarum than in R. variegatus, and an analysis of selection pressure revealed that the mitochondrial NADH dehydrogenase subunit 2 gene and NADH dehydrogenase subunit 6 gene of R. variegatus were under great selective pressure during its evolution; and finally, (4) the two species clustered into one branch on a phylogenetic tree, further affirming their phylogenetic closeness. Based on these results, we speculate that the species differences between R. variegatus and R. philippinarum are largely attributable to adaptive evolution to the environment. The present findings provide a reference for the development of germplasm identification.

Estimation of genotoxicity, apoptosis and oxidative stress induction by TiO2 nanoparticles and acrylamide subacute oral coadministration in mice

Acrylamide is used in the industry and can be a by-product of high-temperature food processing which has toxic potential in various tissues, and titanium dioxide nanoparticles (TiO₂NPs) are widely used in toothpaste, sweets, food perseveration, chewing gum and medicines. Consequently, humans are daily exposed to large amounts of acrylamide and TiO₂NPs mainly through food intake. However, limited studies are available on the effect of simultaneously intake of acrylamide and TiO₂NPs on the integrity of genomic DNA and the induction of apoptosis in brain tissues. Therefore, this study estimated the influence of acrylamide coadministration on TiO₂NPs induced genomic instability and oxidative stress in the brain tissues of mice. To achieve this, mice were orally administrated acrylamide (3 mg/kg b.w) or/and TiO₂NPs (5 mg/kg b.w) for two successive weeks (5 days per week). The comet assay results showed that concurrent oral administration of acrylamide and TiO₂NPs strongly induced single- and double stranded DNA breaks, and that the level of reactive oxygen species (ROS) was also highly elevated within neural cells after simultaneous oral intake of acrylamide and TiO₂NPs compared to those observed after administration of acrylamide or/TiO₂NPs alone. Moreover, oral co-administration of acrylamide with TiO₂NPs increased apoptotic DNA damage to neurons by upregulating the expression levels of P53, TNF-α, IL-6 and Presenillin-1 genes compared to groups administered TiO₂NPs. Therefore, from these results, the present study concluded that coadministration of acrylamide renders TiO₂NPs more genotoxic and motivates apoptotic DNA damage and oxidative stress induced by TiO₂NPs in brain cells, and thus it is recommended to avoid concurrent oral acrylamide administration with TiO₂NPs.

Modulation of Mitochondrial Respiration During Early Reperfusion Reduces Cardiac Injury in Donation After Circulatory Death Hearts

ABSTRACT

Donation after circulatory death (DCD) donors are a potential source for heart transplantation. The DCD process has unavoidable ischemia and reperfusion (I/R) injury, primarily mediated through mitochondria, which limits routine utilization of hearts for transplantation. Amobarbital (AMO), a transient inhibitor of the electron transport chain, is known to decrease cardiac injury following ex vivo I/R. We studied whether AMO treatment during reperfusion can decrease injury in DCD hearts. Sprague Dawley rat hearts subjected to 25 minutes of in vivo ischemia (DCD hearts), or control beating donor hearts, were treated with AMO or vehicle for the first 5 minutes of reperfusion, followed by Krebs-Henseleit buffer reperfusion for 55 minutes (for mitochondrial isolation) or 85 minutes (for infarct size determination). Compared with vehicle, AMO treatment led to decreased infarct size (25.2% ± 1.5% vs. 31.5% ± 1.5%; P ≤ 0.05) and troponin I release (4.5 ± 0.05 ng/mL vs. 9.3 ± 0.24 ng/mL, P ≤ 0.05). AMO treatment decreased H 2 O 2 generation with glutamate as complex I substrate in both subsarcolemmal mitochondria (SSM) (37 ± 3.7 pmol·mg -1 ·min -1 vs. 56.9 ± 4.1 pmol·mg -1 ·min -1 ; P ≤ 0.05), and interfibrillar mitochondria (IFM) (31.8 ± 2.8 pmol·mg -1 ·min -1 vs. 46 ± 4.8 pmol·mg -1 ·min -1 ; P ≤ 0.05) and improved calcium retention capacity in SSM (360 ±17.2 nmol/mg vs. 277 ± 13 nmol/mg; P ≤ 0.05), and IFM (483 ± 20 nmol/mg vs. 377± 19 nmol/mg; P ≤ 0.05) compared with vehicle treatment. SSM and IFM retained more cytochrome c with AMO treatment compared with vehicle. In conclusion, brief inhibition of mitochondrial respiration during reperfusion using amobarbital is a promising approach to decrease injury in DCD hearts.

Protective role of cytoplasmic p21Cip1/Waf1 in apoptosis of CDK4/6 inhibitor-induced senescence in breast cancer cells

Inhibition of CDK4/6 slows the cell cycle and induces senescence in breast cancer cells. However, senescent cancer cells promote invasion and metastasis. Several drugs reportedly target senescent cells, including ABT‐263 (navitoclax). We examined the effects of the CDK4/6 inhibitor abemaciclib and ABT‐263 on two human breast cancer cell lines. The abemaciclib and ABT‐263 combination additively decreased the viability of MDA‐MB‐231 cells, but not MCF‐7 cells. Also, the combination therapy‐induced caspase‐dependent apoptosis in MDA‐MB‐231 cells. Combination therapy with abemaciclib and ABT‐737, an ABT‐263 analog, significantly suppressed the in vivo growth of MDA‐MB‐231 with transient body‐weight loss. Given that p16^Ink4a and p21^Cip1/Waf1 are key factors in senescence and that both cell lines were negative for p16, the role of p21 in apoptosis of treated breast cancer cells was investigated. Although abemaciclib increased the cytoplasmic p21 level in both cell lines as a hallmark of senescence, the abemaciclib and ABT‐263 combination decreased it only in MDA‐MB‐231 cells. This decrease of p21 expression was relieved by caspase inhibition, and p21 was colocalized with caspase‐3 in the cytoplasm of MDA‐MB‐231 cells. Alternatively, small interfering RNA‐mediated knockdown of p21 rendered caspase‐3‐negative MCF‐7 cells susceptible to abemaciclib and ABT‐263, as well as TNF‐related apoptosis‐inducing ligand. Furthermore, a clinical database analysis showed that p21^high breast cancer patients had a poorer prognosis compared to p21^low patients. These results suggest that cytoplasmic p21 plays a protective role in apoptosis of CDK4/6 inhibitor‐induced senescent breast cancer cells.

Anastasis: Return Journey from Cell Death

For over 20 years, it has been a dogma that once the integrity of mitochondria is disrupted and proapoptotic proteins that are normally located in the intermembrane space of mitochondria appeared in the cytoplasm, the process of cell death becomes inevitable. However, it has been recently shown that upon removal of the death signal, even at the stage of disturbance in the mitochondria, cells can recover and continue to grow. This phenomenon was named anastasis. Here, we will critically discuss the present knowledge concerning the mechanisms of cell death reversal, or development of anastasis, methods for its detection, and what role signaling from different intracellular compartments plays in anastasis stimulation.

Functional genomics identifies new synergistic therapies for retinoblastoma

Local intravitreal or intra-arterial chemotherapy has improved therapeutic success for the pediatric cancer retinoblastoma (RB), but toxicity remains a major caveat. RB initiates primarily with RB1 loss or, rarely, MYCN amplification, but the critical downstream networks are incompletely understood. We set out to uncover perturbed molecular hubs, identify synergistic drug combinations to target these vulnerabilities, and expose and overcome drug resistance. We applied dynamic transcriptomic analysis to identify network hubs perturbed in RB versus normal fetal retina, and performed in vivo RNAi screens in RB1^null and RB1^wt;MYCN^amp orthotopic xenografts to pinpoint essential hubs. We employed in vitro and in vivo studies to validate hits, define mechanism, develop new therapeutic modalities, and understand drug resistance. We identified BRCA1 and RAD51 as essential for RB cell survival. Their oncogenic activity was independent of BRCA1 functions in centrosome, heterochromatin, or ROS regulation, and instead linked to DNA repair. RAD51 depletion or inhibition with the small molecule inhibitor, B02, killed RB cells in a Chk1/Chk2/p53-dependent manner. B02 further synergized with clinically relevant topotecan (TPT) to engage this pathway, activating p53-BAX mediated killing of RB but not human retinal progenitor cells. Paradoxically, a B02/TPT-resistant tumor exhibited more DNA damage than sensitive RB cells. Resistance reflected dominance of the p53-p21 axis, which mediated cell cycle arrest instead of death. Deleting p21 or applying the BCL2/BCL2L1 inhibitor Navitoclax re-engaged the p53-BAX axis, and synergized with B02, TPT or both to override resistance. These data expose new synergistic therapies to trigger p53-induced killing in diverse RB subtypes.

Mitochondrial Dysfunction in Huntington's Disease; Interplay Between HSF1, p53 and PGC-1α Transcription Factors

Huntington’s disease (HD) is a neurodegenerative disease caused by an expanded CAG repeat in the huntingtin (HTT) gene, causing the protein to misfold and aggregate. HD progression is characterized by motor impairment and cognitive decline associated with the preferential loss of striatal medium spiny neurons (MSNs). The mechanisms that determine increased susceptibility of MSNs to mutant HTT (mHTT) are not fully understood, although there is abundant evidence demonstrating the importance of mHTT mediated mitochondrial dysfunction in MSNs death. Two main transcription factors, p53 and peroxisome proliferator co-activator PGC-1α, have been widely studied in HD for their roles in regulating mitochondrial function and apoptosis. The action of these two proteins seems to be interconnected. However, it is still open to discussion whether p53 and PGC-1α dependent responses directly influence each other or if they are connected via a third mechanism. Recently, the stress responsive transcription factor HSF1, known for its role in protein homeostasis, has been implicated in mitochondrial function and in the regulation of PGC-1α and p53 levels in different contexts. Based on previous reports and our own research, we discuss in this review the potential role of HSF1 in mediating mitochondrial dysfunction in HD and propose a unifying mechanism that integrates the responses mediated by p53 and PGC-1α in HD via HSF1.

Roles of long noncoding RNAs in colorectal cancer metastasis

Colorectal cancer (CRC) is the 3^rd most common malignancies worldwide. Metastasis is responsible for more than 90% CRC patients' death. Long noncoding RNAs (lncRNAs) are an important class of transcribed RNA molecules greater than 200 nucleotides in length. With the development of whole genome sequencing technologies, they have been gained more attention. Accumulating evidences suggest that abnormal expression of lncRNAs in diverse diseases are involved in various biological functions such as proliferation, apoptosis, metastasis and differentiation by acting as epigenetic, splicing, transcriptional or post-transcriptional regulators. Aberrant expression of lncRNAs has also been found in CRC. Besides, recent studies have indicated that lncRNAs play important roles in tumourigenesis and cancer metastasis. They participate in the process of metastasis by activing or inhibiting the metastatic pathways. However, their functions on the development of cancer metastasis are poorly understood. In this review, we highlight the findings of roles for lncRNAs in CRC metastasis and review the metastatic pathways of lncRNAs leading to cancer metastasis in CRC, including escape of apoptosis, epithelial-mesenchymal transition (EMT), angiogenesis and invasion, migration and proliferation. Furthermore, we also discuss the potential clinical application of lncRNAs in CRC as diagnostic markers and therapeutic targets.

Peanut testa extracts possessing histone deacetylase inhibitory activity induce apoptosis in cholangiocarcinoma cells

Previous studies demonstrated that peanut testa extracts (KK4 and ICG15042) containing natural histone deacetylase (HDAC) inhibitors inhibited the growth of several human cancer cell lines via apoptosis induction. The aims of this study were to investigate the anti-proliferative effects and the mechanism(s) responsible for apoptosis induction mediated by these peanut testa extracts in human cholangiocarcinoma cell lines (KKU-M214 and KKU-100). The anti-proliferative effects were assessed by MTT assay. Apoptotic cell death and cell cycle arrest were analyzed by flow cytometry. The caspase activities were studied using colorimetric caspase activity assay and western blot analysis. Our results revealed that KK4 and ICG15042 extracts inhibited cell proliferation of both KKU-M214 and KKU-100 cells in a dose- and time-dependent manner, with IC₅₀ values of 38.28 ± 0.29 (KK4), 43.91 ± 1.94 (ICG15042) μg/mL for KKU-M214 and 78.40 ± 1.74 (KK4), 82.77 ± 0.94 (ICG15042) μg/mL for KKU-100 at 72 h. Apoptosis induction by these peanut testa extracts were observed in both KKU-M214 and KKU-100 cells in a concentration-dependent manner. Moreover, the percentage of cells in the sub-G1 phase was significantly increased in both KKU-M214 and KKU-100 cells. Cell cycle arrest was not observed in other cell cycle phases. Activation of caspases 8 and 3 were apparent integral parts of apoptosis induction in both cells. Both peanut testa extracts also caused down-regulation of p53, p21, Bcl-2 and pERK1/2 protein expression in these cells. These results suggest that peanut testa extracts may be potential anti-cancer agents for cholangiocarcinoma chemoprevention or chemotherapy.

Modulation of IGF2BP1 by long non-coding RNA HCG11 suppresses apoptosis of hepatocellular carcinoma cells via MAPK signaling transduction

Hepatocellular carcinoma (HCC) is a common malignancy of the liver. HCG11 is a member of long non-coding family, upregulation of which in HCC was proved by our previous study. In the present study, the role of HCG11 in the development of HCC was detected by focusing on the interaction between HCG11 and its target protein insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1). The expression status of HCG11 and IGF2BP1 was first investigated with clinical HCC samples. Then the expressions of HCG11 and IGF2BP1 were both inhibited in the human HCC cell line HepG2 and the cell viability, proliferation, apoptosis and metastasis potential of HepG2 cells were assessed. At molecular level, the expression levels of p-ERK, p-JNK, p-p38, p21 and cleaved caspase-3 were also determined to explain the pathways involved in the function of HCG11 in the progression of HCC. Expression of HCG11 and IGF2BP1 were significantly higher in HCC tissues than those in para-tumor tissues. Knockdown of both indicators led to decreased cell viability, proliferation, and migration ability in HepG2 cells while the cell apoptosis and G1 cell cycle arrest were induced after knockdown of HCG11 and IGF2BP1. In addition, suppressed activity of HCG11 and IGF2BP1 blocked the phosphorylation of anti-apoptosis factors, including ERK, JNK and p38 while the mitochondrial apoptosis in HCC cells was initiated by activation of p21 and cleaved caspase-3. HCG11 exerted its effect on HCC via interaction with IGF2BP1, leading to activation of MAPK signaling, which eventually promoted the progression of HCC.

The histone deacetylase inhibitor trichostatin a decreases lymphangiogenesis by inducing apoptosis and cell cycle arrest via p21-dependent pathways

Background

The formation of new lymphatic vessels provides an additional route for tumour cells to metastasize. Therefore, inhibiting lymphangiogenesis represents an interesting target in cancer therapy. First evidence suggests that histone deacetylase inhibitors (HDACi) may mediate part of their antitumor effects by interfering with lymphangiogenesis. However, the underlying mechanisms of HDACi induced anti-lymphangiogenic properties are not fully investigated so far and in part remain unknown.

Methods

Human lymphatic endothelial cells (LEC) were cultured in vitro and treated with or without HDACi. Effects of HDACi on proliferation and cell cycle progress were analysed by BrdU assay and flow cytometry. Apoptosis was measured by quantifying mono- and oligonucleosomes in the cytoplasmic fraction of cell lysates. In vitro lymphangiogenesis was investigated using the Matrigel short term lymphangiogenesis assay. The effects of TSA on cell cycle regulatory proteins and apoptosis-related proteins were examined by western blotting, immunofluorescence staining and semi-quantitative RT-PCR. Protein- and mRNA half-life of p21 were analysed by western blotting and quantitative RT-PCR. The activity of the p21 promoter was determined using a dual luciferase assay and DNA-binding activity of Sp1/3 was investigated using EMSA. Furthermore, siRNA assays were performed to analyse the role of p21 and p53 on TSA-mediated anti-lymphangiogenic effects.

Results

We found that HDACi inhibited cell proliferation and that the pan-HDACi TSA induced G0/G1 arrest in LEC. Cell cycle arrest was accompanied by up-regulation of p21, p27 and p53. Additionally, we observed that p21 protein accumulated in cellular nuclei after treatment with TSA. Moreover, we found that p21 mRNA was significantly up-regulated by TSA, while the protein and mRNA half-life remained largely unaffected. The promoter activity of p21 was enhanced by TSA indicating a transcriptional mechanism. Subsequent EMSA analyses showed increased constitutive Sp1/3-dependent DNA binding in response to HDACi. We demonstrated that p53 was not required for TSA induced p21 expression and growth inhibition of LECs. Interestingly, siRNA-mediated p21 depletion almost completely reversed the anti-proliferative effects of TSA in LEC. In addition, TSA induced apoptosis by cytochrome c release contributed to activating caspases-9, −7 and −3 and downregulating the anti-apoptotic proteins cIAP-1 and −2.

Conclusions

In conclusion, we demonstrate that TSA - a pan-HDACi - has distinct anti-lymphangiogenic effects in primary human lymphatic endothelial cells by activating intrinsic apoptotic pathway and cell cycle arrest via p21-dependent pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2807-y) contains supplementary material, which is available to authorized users.

The Growing Complexity of Cancer Cell Response to DNA-Damaging Agents: Caspase 3 Mediates Cell Death or Survival?

It is widely stated that wild-type p53 either mediates the activation of cell cycle checkpoints to facilitate DNA repair and promote cell survival, or orchestrates apoptotic cell death following exposure to cancer therapeutic agents. This reigning paradigm has been challenged by numerous discoveries with different human cell types, including solid tumor-derived cell lines. Thus, activation of the p53 signaling pathway by ionizing radiation and other DNA-damaging agents hinders apoptosis and triggers growth arrest (e.g., through premature senescence) in some genetic backgrounds; such growth arrested cells remain viable, secrete growth-promoting factors, and give rise to progeny with stem cell-like properties. In addition, caspase 3, which is best known for its role in the execution phase of apoptosis, has been recently reported to facilitate (rather than suppress) DNA damage-induced genomic instability and carcinogenesis. This observation is consistent with an earlier report demonstrating that caspase 3 mediates secretion of the pro-survival factor prostaglandin E₂, which in turn promotes enrichment of tumor repopulating cells. In this article, we review these and related discoveries and point out novel cancer therapeutic strategies. One of our objectives is to demonstrate the growing complexity of the DNA damage response beyond the conventional “repair and survive, or die” hypothesis.

Simultaneous deletion of p21Cip1/Waf1 and caspase-3 accelerates proliferation and partially rescues the differentiation defects of caspase-3 deficient hematopoietic stem cells

Specialized blood cells are generated through the entire life of an organism by differentiation of a small number of hematopoietic stem cells (HSC). There are strictly regulated mechanisms assuring a constant and controlled production of mature blood cells. Although such mechanisms are not completely understood, some factors regulating cell cycle and differentiation have been identified. We have previously shown that Caspase-3 is an important regulator of HSC homeostasis and cytokine responsiveness. p21cip1/waf1 is a known cell cycle regulator, however its role in stem cell homeostasis seems to be limited. Several reports indicate interactions between p21cip1/waf1 and Caspase-3 in a cell type dependent manner. Here we studied the impact of simultaneous depletion of both factors on HSC homeostasis. Depletion of both Caspase-3 and p21cip1/waf1 resulted in an even more pronounced increase in the frequency of hematopoietic stem and progenitor cells. In addition, simultaneous deletion of both genes revealed a further increase of cell proliferation compared to single knock-outs and WT control mice, while apoptosis or self-renewal ability were not affected in any of the genotypes. Upon transplantation, p21cip1/waf1-/- bone marrow did not reveal significant alterations in engraftment of lethally irradiated mice, while Caspase-3 deficient HSPC displayed a significant reduction of blood cell production. However, when both p21cip1/waf1 and Caspase-3 were eliminated this differentiation defect caused by Caspase-3 deficiency was abrogated.

RPLP1, a crucial ribosomal protein for embryonic development of the nervous system

Ribosomal proteins are pivotal to development and tissue homeostasis. RP Large P1 (Rplp1) overexpression is associated with tumorigenesis. However, the physiological function of Rplp1 in mammalian development remains unknown. In this study, we disrupted Rplp1 in the mouse germline and central nervous system (Rplp1^CNSΔ). Rplp1 heterozygosity caused body size reductions, male infertility, systemic abnormalities in various tissues and a high frequency of early postnatal death. Rplp1^CNSΔ</emph> newborn mice exhibited perinatal lethality and brain atrophy with size reductions of the neocortex, midbrain and ganglionic eminence. The Rplp1 knockout neocortex exhibited progenitor cell proliferation arrest and apoptosis due to the dysregulation of key cell cycle and apoptosis regulators (cyclin A, cyclin E, p21^CIP1, p27^KIP1, p53). Similarly, Rplp1 deletion in pMEFs led to proliferation arrest and premature senescence. Importantly, Rplp1 deletion in primary mouse embryonic fibroblasts did not alter global protein synthesis, but did change the expression patterns of specific protein subsets involved in protein folding and the unfolded protein response, cell death, protein transport and signal transduction, among others. Altogether, we demonstrated that the translation “fine-tuning” exerted by Rplp1 is essential for embryonic and brain development and for proper cell proliferation.

cAMP protects acute promyelocytic leukemia cells from arsenic trioxide-induced caspase-3 activation and apoptosis

More recently, arsenic trioxide (ATO), was integrated into acute promyelocytic leukemia (APL) treatment, showing high efficacy and tolerability in patients with both ATRA-sensitive and ATRA-resistant APL. ATO could induce apoptosis at relatively high concentrations (0.5 to 2.0 micromol/L) and partial differentiation at low concentrations (0.1 to 0.5 micromol/L) in leukemic promyelocytes. It is known that cAMP agonists enhance low-dose ATO-induced APL cells differentiation. Less well appreciated was the possible interaction between relatively high-doses of ATO and enhanced levels of cAMP in APL cells. Here, we show that elevation of cAMP levels by forskolin inhibited ATO-mediated apoptosis in APL-derived NB4 cells, and this inhibition could be averted by cell permeable cAMP-dependent protein kinase inhibitor (14-22) amide. Inactivating phosphorylation of the proapoptotic protein Bad at Ser118 and phosphorylation of the CREB proto-oncogene at Ser133 were observed upon elevation of cAMP levels in NB4 cells. Phosphorylation of these PKA target proteins is known to promote cell survival in AML cells. The ability of cAMP to endow the APL cells with survival advantage is of particular importance when cAMP agonists may be considered as adjuncts to APL therapy.

Comparison of cancer cell survival triggered by microtubule damage after turning Dyrk1B kinase on and off

Using a tubulin polymerization inhibitor and a tubulin polymerization/Dyrk1B dual inhibitor, we intentionally allowed or blocked the Dyrk1B-coordinated cell survival process in response to microtubule damage. By examining the resulting differential effects on cell function and phenotype, we have elucidated key molecular interactions involved in the Dyrk1B-coordinated cell survival process as well as the associated overall cellular impact. Dyrk1B activation that is induced by microtubule damage triggers microtubule stabilization and promotes the mitochondrial translocation of p21(Cip1/waf1) (referred to as p21 hereafter) to suppress apoptosis. These coordinated survival events rapidly repair microtubules, relieve cell G2/M arrest for 42% of the cells, suppress apoptosis for 27% of the cells, and increase cell viability by 10-fold. That is, the dual inhibitor is 10 times more potent in the inhibition of cancer cell viability. This approach affords a novel drug discovery strategy by targeting both the therapeutic targets and the associated cell survival pathway using a single therapeutic agent.

New insights into p53 signaling and cancer cell response to DNA damage: implications for cancer therapy

Activation of the p53 signaling pathway by DNA-damaging agents was originally proposed to result either in cell cycle checkpoint activation to promote survival or in apoptotic cell death. This model provided the impetus for numerous studies focusing on the development of p53-based cancer therapies. According to recent evidence, however, most p53 wild-type human cell types respond to ionizing radiation by undergoing stress-induced premature senescence (SIPS) and not apoptosis. SIPS is a sustained growth-arrested state in which cells remain viable and secrete factors that may promote cancer growth and progression. The p21(WAF1) (hereafter p21) protein has emerged as a key player in the p53 pathway. In addition to its well-studied role in cell cycle checkpoints, p21 regulates p53 and its upstream kinase (ATM), controls gene expression, suppresses apoptosis, and induces SIPS. Herein, we review these and related findings with human solid tumor-derived cell lines, report new data demonstrating dynamic behaviors of p53 and p21 in the DNA damage response, and examine the gain-of-function properties of cancer-associated p53 mutations. We point out obstacles in cancer-therapeutic strategies that are aimed at reactivating the wild-type p53 function and highlight some alternative approaches that target the apoptotic threshold in cancer cells with differing p53 status.

Binding of carbon nanotube to BMP receptor 2 enhances cell differentiation and inhibits apoptosis via regulating bHLH transcription factors

Biomaterials that can drive stem cells to an appropriate differentiation level and decrease apoptosis of transplanted cells are needed in regenerative medicine. Nanomaterials are promising novel materials for such applications. Here we reported that carboxylated multiwalled carbon nanotube (MWCNT 1) promotes myogenic differentiation of mouse myoblast cells and inhibits cell apoptosis under the differentiation conditions by regulating basic helix-loop-helix transcription factors. MWCNT 1 attenuates bone morphogenetic protein receptor (BMPR) signaling activity by binding to BMPR2 and attenuating the phosphorylation of BMPR1. This molecular understanding allowed us to tune stem cell differentiation to various levels by chemical modifications, demonstrating human control of biological activities of nanoparticles and opening an avenue for potential applications of nanomaterials in regenerative medicine.

Stellettin A induces endoplasmic reticulum stress in murine B16 melanoma cells

Isomalabaricanes are a small class of rearranged triterpenoids obtained from marine sponges. Most of these are cytotoxic to tumor cells, but the underlying mechanism is not clear. In this study, it was demonstrated that stellettin A (1), obtained from Geodia japonica, inhibited the growth of B16F10 murine melanoma cells by the induction of endoplasmic reticulum stress and accumulation of unfolded proteins. Immunoblotting analysis revealed abnormal glycosylation patterns of two melanoma marker proteins, tyrosinase and tyrosinase-related protein 1, and the retention of these proteins in the endoplasmic reticulum. Compound 1 induced the upregulation of the unfolded protein chaperone, glucose-regulated protein 78, in a dose-dependent manner. Increase of autophagosome-associated protein light chain 3 (LC3) in a membrane-bound form (LC3II) and its immunofluorescence co-localization with tyrosinase suggest the possible removal of deglycosylated and unfolded proteins by autophagy of the cells. There was no change in either the expression of the apoptosis marker protein Bcl-2 or the appearance of apoptotic nuclei in 1-treated cells. Taken together, 1 is an endoplasmic reticulum stressor that inhibits the growth of B16 melanoma cells by induction of abnormal protein glycosylation and autophagy.

Celecoxib synergizes human pancreatic ductal adenocarcinoma cells to sorafenib-induced growth inhibition

BACKGROUND

Pancreatic ductal adenocarcinoma is frequently associated with aberrant activation of the Ras/Raf/MAPK pathway and cyclooxygenase-2 (COX-2) overexpression. This study evaluated the potential for combining the multikinase inhibitor sorafenib and the specific COX-2 inhibitor celecoxib as therapy in pancreatic ductal adenocarcinoma cells.

METHODS

BxPC-3, MIAPaCa-2, PANC-1 and AsPC-1 pancreatic adenocarcinoma cells were exposed to sorafenib and celecoxib combined treatment in vitro. Cell viability and various growth promoting and survival signaling pathways were monitored by MTT, flow cytometry and Western blotting.

RESULTS

Combined treatment with sorafenib and celecoxib synergistically inhibited pancreatic adenocarcinoma cell proliferation. This regimen produced combination index (CI) values between 0.67 and 0.92 for the various cell lines, indicating significant synergistic interactions between sorafenib and celecoxib, which also markedly inhibited the migratory capacity. The growth inhibition was associated with an accumulation of cells in the G(0)/G(1) phase of the cell cycle and induction of apoptosis. These changes were accompanied by a significant reduction of p21(WAF1/Cip1) levels, where celecoxib sensitized the cells to sorafenib-mediated p21(WAF1/Cip1) suppression.

CONCLUSION

These results suggest that combined treatment with sorafenib and celecoxib synergistically induce growth inhibition and apoptosis in pancreatic adenocarcinoma cells through a process involving p21(WAF1/Cip1) suppression.

TGF-β-activated kinase 1 promotes cell cycle arrest and cell survival of X-ray irradiated HeLa cells dependent on p21 induction but independent of NF-κB, p38 MAPK and ERK phosphorylations

Transforming growth factor-β-activated kinase 1 (TAK1) appears to play a role in inhibiting apoptotic death in response to multiple stresses. To assess the role of TAK1 in X-ray induced apoptosis and cell death, we irradiated parental and siRNA-TAK1-knockdown HeLa cells. Changes in gene expression levels with and without TAK1-knockdown were also examined after irradiation to elucidate the molecular mechanisms involved. After X-ray irradiation, cell death estimated by the colony formation assay increased in the TAK1-knockdown cells. Apoptosis induction, determined by caspase-3 cleavage, suggested that the increased radiosensitivity of the TAK1-knockdown cells could be partially explained by the induction of apoptosis. However, cell cycle analysis revealed that the percentage of irradiated cells in the G(2)/M-phase decreased, and those in the S- and SubG(1)-phases increased due to TAK1 depletion, suggesting that the loss of cell cycle checkpoint regulation may also be involved in the observed increased radiosensitivity. Interestingly, significant differences in the induction of NF-κB, p38 MAPK and ERK phosphorylation, the major downstream molecules of TAK1, were not observed in TAK1 knockdown cells compared to their parental control cells after irradiation. Instead, global gene expression analysis revealed differentially expressed genes after irradiation that bioinformatics analysis suggested are associated with cell cycle regulatory networks. In particular, CDKN1A (coding p21(WAF1)), which plays a central role in the identified network, was up-regulated in control cells but not in TAK1 knockdown cells after X-ray irradiation. Si-RNA knockdown of p21 decreased the percentage of cells in the G(2)/M phase and increased the percentage of cells in the S- and SubG(1)-phases after X-ray irradiation in a similar manner as TAK-1 knockdown. Taken together, these findings suggest that the role of TAK1 in cell death, cell cycle regulation and apoptosis after X irradiation is independent of NF-κB, p38 MAPK, and ERK phosphorylation, and dependent, in part, on p21 induction.

Role of p21 in SP600125-induced cell cycle arrest, endoreduplication, and apoptosis

The anti-cancer effect of the c-Jun N-terminal kinase (JNK) inhibitor SP600125 has been well evaluated in human cancer cells. However the role of p21 in SP600125-mediated G(2)/M distribution is not fully understood. Our results showed that the transcriptional activation of p21 by SP600125 is mediated through the proximal regions of multiple Sp1 sites in the p21 promoter following ERK-dependent phosphorylation of Sp1. In this process, p21 induces endoreduplication through the inhibition of cyclin E/Cdk2 activity at 24 h but does not directly regulate cyclin B1/Cdc2 activity. Furthermore, SP600125 induces the phosphorylation of p21 at Thr 145 through the PI3K/Akt pathway. Akt-mediated phosphorylation of p21 and protection of apoptosis are completely abolished by inhibitors of PI3K and Akt. In summary using time points, we identified the dual functions of p21 as an inhibitor of cell-cycle progression at 24 h and as an anti-apoptotic factor at 48 h.

p21(WAF1/CIP1) upregulation through the stress granule-associated protein CUGBP1 confers resistance to bortezomib-mediated apoptosis

Background

p21^WAF1/CIP1 is a well known cyclin-dependent kinase inhibitor induced by various stress stimuli. Depending on the stress applied, p21 upregulation can either promote apoptosis or prevent against apoptotic injury. The stress-mediated induction of p21 involves not only its transcriptional activation but also its posttranscriptional regulation, mainly through stabilization of p21 mRNA levels. We have previously reported that the proteasome inhibitor MG132 induces the stabilization of p21 mRNA, which correlates with the formation of cytoplasmic RNA stress granules. The mechanism underlying p21 mRNA stabilization, however, remains unknown.

Methodology/Principal Findings

We identified the stress granules component CUGBP1 as a factor required for p21 mRNA stabilization following treatment with bortezomib ( =  PS-341/Velcade). This peptide boronate inhibitor of the 26S proteasome is very efficient for the treatment of myelomas and other hematological tumors. However, solid tumors are sometimes refractory to bortezomib treatment. We found that depleting CUGBP1 in cancer cells prevents bortezomib-mediated p21 upregulation. FISH experiments combined to mRNA stability assays show that this effect is largely due to a mistargeting of p21 mRNA in stress granules leading to its degradation. Altering the expression of p21 itself, either by depleting CUGBP1 or p21, promotes bortezomib-mediated apoptosis.

Conclusions/Significance

We propose that one key mechanism by which apoptosis is inhibited upon treatment with chemotherapeutic drugs might involve upregulation of the p21 protein through CUGBP1.

Increased expression but not sensitivity to Fas/CD95 in glioblastoma cells depleted of mitochondrial DNA

Mitochondria and Fas (CD95) play a role in tumorigenicity and apoptosis. In the present study, the functional relationship of mitochondria to Fas in mediating apoptosis was investigated. Glioblastoma cells (DBTRGO5MG, U87) were depleted of mitochondrial DNA (mtDNA) by treatment with ethidium bromide (Rho(-) cells). Compared to Rho(+) cells, Rho(-) cells showed enhanced expression of Fas at the cell surface. Indeed, when Rho(+) cells were treated with mitochondrial respiratory chain complex inhibitors, Fas cell surface expression was noted to increase in a similar fashion to the depletion of mtDNA in both cell lines. However, when cells were evaluated for sensitivity to apoptosis using Fas-engagement, there was no difference between the Rho(+) and Rho(-) cells in either cell line. By contrast, sensitivity to the cytotoxic agent cis-diammine-dichloroplatinum (cisplatin) was markedly increased in the Rho(-) cells, which expressed higher levels of cell surface Fas. Expression of Fas is increased with the depletion of mtDNA and respiratory complex inhibitors. However, this increase in expression does not necessarily translate to an increase in sensitivity to Fas-engagement, although there is an increase in the sensitivity of depleted cells to cytotoxic agents such as cisplatin.

Activation of p21(CIP1/WAF1) in mammary epithelium accelerates mammary tumorigenesis and promotes lung metastasis

While p21 is well known to inhibit cyclin-CDK activity in the nucleus and it has also been demonstrated to have oncogenic properties in different types of human cancers. In vitro studies showed that the oncogenic function of p21is closely related to its cytoplasmic localization. However, it is unclear whether cytoplasmic p21 contributes to tumorigenesis in vivo. To address this question, we generated transgenic mice expressing the Akt-phosphorylated form of p21 (p21T145D) in the mammary epithelium. The results showed that Akt-activated p21 was expressed in the cytoplasm of mammary epithelium. Overexpression of Akt-activated p21 accelerated tumor onset and promoted lung metastasis in MMTV/neu mice, providing evidence that p21, especially cytoplasmic phosphorylated p21, has an oncogenic role in promoting mammary tumorigenesis and metastasis.

Cytoplasmic p21 expression levels determine cisplatin resistance in human testicular cancer

Platinum-based chemotherapies such as cisplatin are used as first-line treatment for many cancers. Although there is often a high initial responsiveness, the majority of patients eventually relapse with platinum-resistant disease. For example, a subset of testicular cancer patients still die even though testicular cancer is considered a paradigm of cisplatin-sensitive solid tumors, but the mechanisms of chemoresistance remain elusive. Here, we have shown that one key determinant of cisplatin-resistance in testicular embryonal carcinoma (EC) is high cytoplasmic expression of the cyclin-dependent kinase (CDK) inhibitor p21. The EC component of the majority of refractory testicular cancer patients exhibited high cytoplasmic p21 expression, which protected EC cell lines against cisplatin-induced apoptosis via CDK2 inhibition. Localization of p21 in the cytoplasm was critical for cisplatin resistance, since relocalization of p21 to the nucleus by Akt inhibition sensitized EC cell lines to cisplatin. We also demonstrated in EC cell lines and human tumor tissue that high cytoplasmic p21 expression and cisplatin resistance of EC were inversely associated with the expression of Oct4 and miR-106b seed family members. Thus, targeting cytoplasmic p21, including by modulation of the Oct4/miR-106b/p21 pathway, may offer new strategies for the treatment of chemoresistant testicular and other types of cancer.

Overexpression of p75(NTR) increases survival of breast cancer cells through p21(waf1)

The p75 neurotrophin receptor (p75(NTR)) plays a critical role in various neuronal and non-neuronal cell types by regulating cell survival, differentiation and proliferation. To evaluate the influence of p75(NTR) in breast cancer development, we have established and characterized breast cancer cells which stably overexpress p75(NTR). We showed that p75(NTR) overexpression per se promoted cell survival to apoptogens with a concomitant slowdown of cell growth. The pro-survival effect is associated with an increased expression of the inhibitor of apoptosis protein-1 (c-IAP1), a decrease of TRAIL-induced cleavage of PARP, procaspase 9 and procaspase 3, and a decrease of cytochrome C release from the mitochondria. The anti-proliferative effect is due to a cell accumulation in G0/G1, associated with a decrease of Rb phosphorylation and an increase of p21(waf1). Interestingly, inhibition of p21(waf1) with siRNA not only restores proliferation but also abolishes the pro-survival effect of p75(NTR), indicating the key role of p21(waf1) in the biological functions of p75(NTR). Finally, using a SCID mice xenograft model, we showed that p75(NTR) overexpression favors tumor growth and strongly increases tumor resistance to anti-tumoral treatment. Together, our findings suggest that p75(NTR) overexpression in breast tumor cells could favor tumor survival and contribute to tumor resistance to drugs. This provides a rationale to consider p75(NTR) as a potential target for the future design of innovative therapeutic strategies.

Examination of the expanding pathways for the regulation of p21 expression and activity

p21(Waf1/Cip1/Sdi1) was originally identified as an inhibitor of cyclin-dependent kinases, a mediator of p53 in growth suppression and a marker of cellular senescence. p21 is required for proper cell cycle progression and plays a role in cell death, DNA repair, senescence and aging, and induced pluripotent stem cell reprogramming. Although transcriptional regulation is considered to be the initial control point for p21 expression, there is growing evidence that post-transcriptional and post-translational regulations play a critical role in p21 expression and activity. This review will briefly discuss the activity of p21 and focus on current knowledge of the determinants that control p21 transcription, mRNA stability and translation, and protein stability and activity.

Single-cell analysis of p16(INK4a) and p21(WAF1) expression suggests distinct mechanisms of senescence in normal human and Li-Fraumeni Syndrome fibroblasts

Herein we used single-cell observation methods to gain insight into the roles of p16(INK4A) and p21(WAF1) (hereafter p16 and p21) in replicative senescence and ionizing radiation-induced accelerated senescence in human [normal, ataxia telangiectasia (AT) and Li-Fraumeni syndrome (LFS)] fibroblast strains. Cultures of all strains entered a state of replicative senescence at late passages, as evident from inhibition of growth, acquisition of flattened and enlarged cell morphology, and positive staining for senescence-associated beta-galactosidase. In addition, proliferating early-passage cultures of these strains exhibited accelerated senescence in response to ionizing radiation. Immunofluorescence microscopy revealed the heterogeneous expression of p16 in normal and AT fibroblast strains, with the majority of the cells exhibiting undetectable levels of p16 irrespective of in vitro culture age. Importantly, replicative senescence as well as accelerated senescence triggered by ionizing radiation were accompanied by sustained nuclear accumulation of p21, but did not correlate with p16 expression in p53-proficient (normal and AT) fibroblasts. In p53-deficient (LFS) fibroblasts, on the other hand, replicative senescence and ionizing radiation-triggered accelerated senescence strongly correlated with expression of p16 but not of p21. Furthermore, senescence in LFS fibroblasts was associated with genomic instability encompassing polyploidy. Our findings are compatible with a model in which p16 serves as a backup regulator of senescence, triggering this response preferentially in the absence of wild-type p53 activity. The possibility that one of the tumor-suppressor functions of p16 may be associated with genomic instability, preventing the emergence of malignant progeny from polyploid giant cells, is also supported by these results.

Novel HIV-1 therapeutics through targeting altered host cell pathways

The emergence of drug-resistant HIV-1 strains presents a challenge for the design of new drugs. Anti-HIV compounds currently in use are the subject of advanced clinical trials using either HIV-1 reverse transcriptase, viral protease or integrase inhibitors. Recent studies show an increase in the number of HIV-1 variants resistant to anti-retroviral agents in newly infected individuals. Targeting host cell factors involved in the regulation of HIV-1 replication might be one way to combat HIV-1 resistance to the currently available anti-viral agents. A specific inhibition of HIV-1 gene expression could be expected from the development of compounds targeting host cell factors that participate in the activation of the HIV-1 LTR promoter. Here we discuss how targeting the host can be accomplished either by using small molecules to alter the function of the host's proteins such as p53 or cdk9, or by utilizing new advances in siRNA therapies to knock down essential host factors such as CCR5 and CXCR4. Finally, we will discuss how the viral protein interactomes should be used to better design therapeutics against HIV-1.

The Cdk inhibitor p57(Kip2) controls LIM-kinase 1 activity and regulates actin cytoskeleton dynamics

The cyclin-dependent kinase inhibitor p57(Kip2) gene has been suggested to be a tumor suppressor gene, being inactivated in various cancer types, linked to tumor progression and poor patient outcome. Here, we report that p57(Kip2) interacts with the actin cytoskeleton modifying enzyme, LIM-kinase 1 (LIMK-1) but not LIMK-2. This interaction enhances activity of LIMK-1, independently of its activator Rho-associated kinase. This resulted in an increased phosphorylation and consequent inactivation of the actin depolymerization factor, cofilin. In accordance, selective p57(Kip2) expression promotes actin stress fiber formation in cancer cells. Fluorescence recovery after photobleaching analysis of fluorescent-labeled actin further demonstrated that p57(Kip2) expression results in reduction of actin protein mobile fraction, which affects its turnover rate in cell. Finally, we present evidence that the p57(Kip2) control of LIMK-1 ultimately affects cell mobility negatively. Thus, in addition to its established function in control of proliferation and cell death, these results indicate that p57(Kip2) is critical in the regulation of actin cytoskeleton dynamic and by this means migration ability of cancer cells.

Host biomarkers and biological pathways that are associated with the expression of experimental cerebral malaria in mice

Cerebral malaria (CM) is a primary cause of malaria-associated deaths among young African children. Yet no diagnostic tools are available that could be used to predict which of the children infected with Plasmodium falciparum malaria will progress to CM. We used the Plasmodium berghei ANKA murine model of experimental cerebral malaria (ECM) and high-density oligonucleotide microarray analyses to identify host molecules that are strongly associated with the clinical symptoms of ECM. Comparative expression analyses were performed with C57BL/6 mice, which have an ECM-susceptible phenotype, and with mice that have ECM-resistant phenotypes: CD8 knockout and perforin knockout mice on the C57BL/6 background and BALB/c mice. These analyses allowed the identification of more than 200 host molecules (a majority of which had not been identified previously) with altered expression patterns in the brain that are strongly associated with the manifestation of ECM. Among these host molecules, brain samples from mice with ECM expressed significantly higher levels of p21, metallothionein, and hemoglobin alpha1 proteins by Western blot analysis than mice unaffected by ECM, suggesting the possible utility of these molecules as prognostic biomarkers of CM in humans. We suggest that the higher expression of hemoglobin alpha1 in the brain may be associated with ECM and could be a source of excess heme, a molecule that is considered to trigger the pathogenesis of CM. Our studies greatly enhance the repertoire of host molecules for use as diagnostics and novel therapeutics in CM.

Ataxia telangiectasia mutated and p21CIP1 modulate cell survival of drug-induced senescent tumor cells: implications for chemotherapy

PURPOSE

Premature or stress-induced senescence is a major cellular response to chemotherapy in solid tumors and contributes to successful treatment. However, senescent tumor cells are resistant to apoptosis and may also reenter the cell cycle. We set out to find a means to specifically induce senescent tumor cells to undergo cell death and not to reenter the cell cycle that may have general application in cancer therapy.

EXPERIMENTAL DESIGN

We investigated the mechanisms regulating cell survival in drug-induced senescent tumor cells. Using immunofluorescence and flow cytometry-based techniques, we established the status of the ataxia telangiectasia mutated (ATM) signaling pathway in these cells. We assayed the requirement of ATM signaling and p21(CIP1) expression for survival in premature senescent tumor cells using pharmacologic inhibitors and antisense oligonucleotides.

RESULTS

The ATM/ATR (ATM- and Rad3-related) signaling pathway was found to be constitutively active in drug-induced senescent tumor cells. We found that blocking ATM/ATR signaling with pharmacologic inhibitors, including the novel ATM inhibitors KU55933 and CGK733, induced senescent breast, lung, and colon carcinoma cells to undergo cell death. We show that the mechanism of action of this effect is directly via p21(CIP1), which acts downstream of ATM. This is in contrast to the effects of ATM inhibitors on normal, untransformed senescent cells.

CONCLUSIONS

Blocking ATM and/or p21(CIP1) following initial treatment with a low dose of senescence-inducing chemotherapy is a potentially less toxic and highly specific treatment for carcinomas.

Involvement of p21 and FasL in induction of cell cycle arrest and apoptosis by neochamaejasmin A in human prostate LNCaP cancer cells

Neochamaejasmin A ( 1), a biflavonoid isolated from the roots of a traditional Chinese medicine, Stellera chamaejasme L., was shown to inhibit cellular (3)H-thymidine incorporation (IC 50 12.5 microg/mL) and subsequent proliferation of human prostate cancer LNCaP cells. Treatment of LNCaP cells with low doses of 1 (< or =6.25 microg/mL) suppressed DNA-binding activities of the transcription factors NFkappaB and AP-1 to the promoter of cyclin D and also inhibited expression of the cell cycle regulatory proteins cyclin D, proliferating cell nuclear antigen, and nucleolin, thus arresting cells in G 1 phase of the cell cycle. A lengthy exposure with higher doses of 1 (> or =12.5 microg/mL) revealed the production of reactive oxygen species, dissipation of the mitochondrial membrane potential, up-regulation of cyclin-dependent kinase inhibitor p21, and induction of cell apoptosis. An aggregation of Fas-procaspase 8-procaspase 3 and p21-procaspase 3 proteins by coimmunoprecipitation, immunoblotting analysis, and MALDI-mass spectrometry indicated the involvement of Fas and p21 in 1-mediated cytotoxicity, and pretreatment of cells with antisense FasL oligonucleotides partially abolished apoptosis. Thus, 1 blocked cell cycle progression at the G 1 phase by activating the p21 protein and ultimately promoting the Fas-caspase 8-caspase 3 apoptotic machinery.

Antiproliferative and survival properties of PMA in MCF-7 breast cancer cell

Although PKCs are assumed to be the main targets of phorbol esters (PMA), additional PMA effectors, such as chimaerins (a family of RacGTPase activating proteins) and RasGRP (exchange factor for Ras/Rap1), can counteract or strengthen the PKC pathways. In this study, we evaluated the proliferative behavior of PMA-treated MCF-7 breast cancer cell and found that: PMA induced growth arrest and inhibited cell death; PMA activated ERKs, which, in turn, induced p21; and inhibitors of ERK (PD98059) and PKC (GF109203X) prevented p21 induction and abolished the PMA survival effect. We conclude that PMA inhibits MCF-7 cell growth and simultaneously stimulates cell survival; both responses are linked to ERK-dependent and p53-independent p21 induction.

Phosphatidylinositol 3-Akt-kinase-dependent phosphorylation of p21(Waf1/Cip1) as a novel mechanism of neuroprotection by glucocorticoids

The role of glucocorticoids in the regulation of apoptosis remains incongruous. Here, we demonstrate that corticosterone protects neurons from apoptosis by a mechanism involving the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). In primary cortical neurons, corticosterone leads to a dose- and Akt-kinase-dependent upregulation with enhanced phosphorylation and cytoplasmic appearance of p21(Waf1/Cip1) at Thr 145. Exposure of neurons to the neurotoxin ethylcholine aziridinium (AF64A) results in activation of caspase-3 and a dramatic loss of p21(Waf1/Cip1) preceding apoptosis in neurons. These effects of AF64A are reversed by pretreatment with corticosterone. Corticosterone-mediated upregulation of p21(Waf1/Cip1) and neuroprotection are completely abolished by glucocorticoid and mineralocorticoid receptor antagonists as well as inhibitors of PI3- and Akt-kinase. Both germline and somatically induced p21(Waf1/Cip1) deficiency abrogate the neuroprotection by corticosterone, whereas overexpression of p21(Waf1/Cip1) suffices to protect neurons from apoptosis. We identify p21(Waf1/Cip1) as a novel antiapoptotic factor for postmitotic neurons and implicate p21(Waf1/Cip1) as the molecular target of neuroprotection by high-dose glucocorticoids.

The cell cycle inhibitor p57(Kip2) promotes cell death via the mitochondrial apoptotic pathway

The p57(Kip2) gene belongs to the Cip/Kip family of cyclin-dependent kinase (CDK) inhibitors and has been suggested to be a tumor suppressor gene, being inactivated in various types of human cancers. However, little is known concerning p57(Kip2) possible interplay with the apoptotic cell death machinery and its possible implication for cancer. Here, we report that selective p57(Kip2) expression sensitizes cancer cells to apoptotic agents such as cisplatin, etoposide and staurosporine (STS) via a mechanism, which does not require p57(Kip2)-mediated inhibition of CDK. Translocation of p57(Kip2) to mitochondria occurs within 20 min after STS application. In fact, p57(Kip2) primarily promotes the intrinsic apoptotic pathways, favoring Bax activation and loss of mitochondrial transmembrane potential, consequent release of cytochrome-c into cytosol, caspase-9 and caspase-3 activation. In accordance, Bcl2 overexpression or voltage-dependent anion channel (VDAC) inhibition is able to inhibit p57(Kip2) cell death promoting effect. Thus, in addition to its established function in control of proliferation, these results reveal a mechanism whereby p57(Kip2) influences the mitochondrial apoptotic cell death pathway in cancer cells.

Negative regulation of ASK1 by p21Cip1 involves a small domain that includes Serine 98 that is phosphorylated by ASK1 in vivo

The cyclin-dependent kinase inhibitor p21(Cip1) regulates multiple cellular functions and protects cells from genotoxic and other cellular stresses. Activation of apoptosis signal-regulating kinase 1 (ASK1) induced by inhibition of mTOR signaling leads to sustained phospho-c-Jun that is suppressed in cells with functional p53 or by forced expression of p21(Cip1). Here we show that small deletions of p21(Cip1) around S98 abrogate its association with ASK1 but do not affect binding to Cdk1, hence distinguishing between the cell cycle-regulating functions of p21(Cip1) and its ability to suppress activation of the ASK1/Jun N-terminal protein kinase (JNK) pathway. p21(Cip1) is phosphorylated in vitro by both ASK1 and JNK1 at S98. In vivo phosphorylation of p21(Cip1), predominantly carried out by ASK1, is associated with binding to ASK1 and inactivation of ASK1 kinase function. Binding of p21(Cip1) to ASK1 requires ASK1 kinase function and may involve phosphorylation of S98.

Glycogen synthase kinase 3beta phosphorylates p21WAF1/CIP1 for proteasomal degradation after UV irradiation

UV irradiation has been reported to induce p21(WAF1/CIP1) protein degradation through a ubiquitin-proteasome pathway, but the underlying biochemical mechanism remains to be elucidated. Here, we show that ser-114 phosphorylation of p21 protein by glycogen synthase kinase 3beta (GSK-3beta) is required for its degradation in response to UV irradiation and that GSK-3beta activation is a downstream event in the ATR signaling pathway triggered by UV. UV transiently increased GSK-3beta activity, and this increase could be blocked by caffeine or by ATR small interfering RNA, indicating ATR-dependent activation of GSK-3beta. ser-114, located within the putative GSK-3beta target sequence, was phosphorylated by GSK-3beta upon UV exposure. The nonphosphorylatable S114A mutant of p21 was protected from UV-induced destabilization. Degradation of p21 protein by UV irradiation was independent of p53 status and prevented by proteasome inhibitors. In contrast to the previous report, the proteasomal degradation of p21 appeared to be ubiquitination independent. These data show that GSK-3beta is activated by UV irradiation through the ATR signaling pathway and phosphorylates p21 at ser-114 for its degradation by the proteasome. To our knowledge, this is the first demonstration of GSK-3beta as the missing link between UV-induced ATR activation and p21 degradation.

p21 blocks irradiation-induced apoptosis downstream of mitochondria by inhibition of cyclin-dependent kinase-mediated caspase-9 activation

The role of the cyclin-dependent kinase (CDK) inhibitor p21 as a mediator of p53-induced growth arrest is well established. In addition, recent data provide strong evidence for new emerging functions of p21, including a role as a modulator of apoptosis. The mechanisms, however, by which p21 interferes with the death machinery, especially following ionizing radiation (IR), are largely unknown. Here, we report that IR induced caspase-9 and caspase-3 activation and subsequent apoptosis only in p21-deficient colon carcinoma cells, whereas similar treated wild-type cells were permanently arrested in the G(2)-M phase, correlating with the induction of cellular senescence. Interestingly, activation of the mitochondrial pathway, including caspase-2 processing, depolarization of the outer mitochondrial membrane, and cytochrome c release, was achieved by IR in both cell lines, indicating that p21 inhibits an event downstream of mitochondria but preceding caspase-9 activation. IR-induced p21 protein expression was restricted to the nucleus, and no evidence for a mitochondrial or cytoplasmic association was found. In addition, p21 did neither interact with caspase-3 or caspase-9, suggesting that these events are not required for the observed protection. Consistent with this assumption, we found that CDK inhibitors potently abrogated IR-induced caspase processing and activation without affecting mitochondrial events. In addition, in vitro caspase activation assays yielded higher caspase-3 activities in extracts of irradiated p21-deficient cells compared with extracts of similar treated wild-type cells. Thus, our results strongly indicate that p21 protects cells from IR-induced apoptosis by suppression of CDK activity that seems to be required for activation of the caspase cascade downstream of the mitochondria.

Proteomic analysis of factors released from p21-overexpressing tumour cells

The p21Waf1/Cip1/Sdi1 cyclin-dependent kinase inhibitor is a key regulator of cell cycle progression and has also been observed to influence the expression of genes associated with several age-related disorders. Previous work has shown that expression of p21 in tumour cells mediates an antiapoptotic and mitogenic paracrine effect, which is in contrast to the arrested state of p21-expressing cells. Here, we have employed SELDI-MS technology to characterise, at a proteomic level, factors released from HT-1080 human fibrosarcoma cells displaying inducible p21 expression. Conditioned media from induced and noninduced cells were profiled on a range of diverse ProteinChip arrays and subjected to SELDI-MS analysis. Evaluation of proteins binding onto IMAC, Q10 or CM10 surfaces led to the discovery of a number of putative p21-regulated factors. We further validated three p21-regulated proteins observed at 10.2, 11.7 and 13.4 kDa. Using Q Ceramic HyperD fractionation columns, we were able to selectively enrich for each of these three proteins. Subsequent SDS-PAGE and MS analysis of tryptic digests identified the 13.4 kDa protein as cystatin C and the 10.2 kDa protein as pro-platelet basic protein (PPBP). Judging by the apparent MW and the pI of the 11.7 kDa protein, we reasoned that it may be beta-2-microglobulin, which was confirmed by subsequent identification. Increased levels of cystatin C and beta-2-microglobulin in conditioned media from p21-expressing cells was confirmed by antibody capture experiments using anticystatin C and anti-beta-2-microglobulin antibodies on preactivated PS-20 arrays. Western blot analysis demonstrated increased expression of intracellular and extracellular cystatin C and beta-2-microglobulin in p21-expressing cells, compared to noninduced controls. Increased levels of PPBP were validated in cell lysates from p21-expressing cells. The three secreted factors that we have identified in this study, have all been shown previously to have growth modulating effects and, as such, may contribute to the observed mitogenic and anti-apoptotic paracrine activity of p21-expressing [corrected] cells.