Phosphorylation of the pro-apoptotic protein BAD on serine 155, a novel site, contributes to cell survival

Poly-β-thioester-Based Cross-Linked Nanocarrier for Cancer Cell Selectivity over Normal Cells and Cellular Apoptosis by Triggered Release of Parthenolide, an Anticancer Drug

Breast cancer is the most prevalent and aggressive type of cancer, causing high mortality rates in women globally. Many drawbacks and side effects of the current chemotherapy force us to develop a robust chemotherapeutic system that can deal with off-target hazards and selectively combat cancer growth, invasiveness, and cancer-initiating cells. Here, a pH-responsive cross-linked nanocarrier (140-160 nm) endowed with poly-β-thioester functionality (CBAPTL) has been sketched and fabricated for noncovalent firm encapsulation of anticancer drug, parthenolide (PTL) at physiological pH (7.4), which enables sustain release of PTL at relevant endosomal pH (∼5.0-5.3). For this, a bolaamphiphilic molecule integrated with β-thioester and acrylate functionality was synthesized to fabricate the pH-responsive poly-β-thioester-based cross-linked nanocarrier via Michael addition click reactions in water. The poly-β-thioester functionality of CBAPTL hydrolyzes at endosomal acidic conditions, thus leading to the selective release of PTL inside the cancer cell. Cross-linked nanocarriers exhibit high serum stability, dilution insensitivity, and targeted cellular uptake at tumor microenvironment (TME), contrasting normal cells. In vitro study using human MCF-7 breast cancer cells demonstrated that CBAPTL exhibited selective cytotoxicity, reduced clonogenic potential, increased reactive oxygen species (ROS) generation, and arrested the progression of the cell cycle at the G0/G1 phase efficiently. CBAPTL induced apoptosis via downregulating pro-proliferative protein Bcl-2 and upregulating proapoptotic proteins p53, BAD, p21, and cleaved PARP-1. CBAPTL inhibited proliferating signaling by suppressing AKT phosphorylation and p38 expression. CBAPTL also blocked the invasion and migration of MCF-7 cells. CBAPTL effectively inhibits primary and secondary mammosphere formation, thereby preventing cancer-initiating cells' growth. Conversely, CBAPTL has negligible effect on human red blood cells (RBCs) and peripheral blood mononuclear cells (PBMCs). These findings highlight the superior efficacy of CBAPTL compared to PTL alone in suppressing cancer cell growth, inducing apoptosis, and preventing invasiveness of MCF-7 cells. Thus, CBAPTL could be considered a possible selective chemotherapeutic cargo against breast cancer without affecting normal cells.

Non-Canonical Roles of Apoptotic Caspases in the Nervous System

Caspases are a family of cysteine proteases that predominantly cleave their substrates after aspartic acid residues. Much of what we know of caspases emerged from investigation a highly conserved form of programmed cell death called apoptosis. This form of cell death is regulated by several caspases, including caspase-2, caspase-3, caspase-7, caspase-8 and caspase-9. However, these “killer” apoptotic caspases have emerged as versatile enzymes that play key roles in a wide range of non-apoptotic processes. Much of what we understand about these non-apoptotic roles is built on work investigating how “killer” caspases control a range of neuronal cell behaviors. This review will attempt to provide an up to date synopsis of these roles.

Protein Kinase A in Human Retina: Differential Localization of Cβ, Cα, RIIα, and RIIβ in Photoreceptors Highlights Non-redundancy of Protein Kinase A Subunits

Protein kinase A (PKA) signaling is essential for numerous processes but the subcellular localization of specific PKA regulatory (R) and catalytic (C) subunits has yet to be explored comprehensively. Additionally, the localization of the Cβ subunit has never been spatially mapped in any tissue even though ∼50% of PKA signaling in neuronal tissues is thought to be mediated by Cβ. Here we used human retina with its highly specialized neurons as a window into PKA signaling in the brain and characterized localization of PKA Cα, Cβ, RIIα, and RIIβ subunits. We found that each subunit presented a distinct localization pattern. Cα and Cβ were localized in all cell layers (photoreceptors, interneurons, retinal ganglion cells), while RIIα and RIIβ were selectively enriched in photoreceptor cells where both showed distinct patterns of co-localization with Cα but not Cβ. Only Cα was observed in photoreceptor outer segments and at the base of the connecting cilium. Cβ in turn, was highly enriched in mitochondria and was especially prominent in the ellipsoid of cone cells. Further investigation of Cβ using RNA BaseScope technology showed that two Cβ splice variants (Cβ4 and Cβ4ab) likely code for the mitochondrial Cβ proteins. Overall, our data indicates that PKA Cα, Cβ, RIIα, and RIIβ subunits are differentially localized and are likely functionally non-redundant in the human retina. Furthermore, Cβ is potentially important for mitochondrial-associated neurodegenerative diseases previously linked to PKA dysfunction.

Essential role of glucokinase in the protection of pancreatic β cells to the glucose energetic status

Energy sensing is indispensable to balance anabolic and catabolic processes for the maintenance of cell viability. Pancreatic β cells are especially relevant because of their involvement in the coordination of insulin secretion when glucose concentration arises in the local milieu. In this work, we uncover the increased susceptibility of pancreatic β cells to cell death in response to different energy stressors. Upon glucose decline, from 25 to 5 mM, caused by stimulation with either 2-deoxyglucose or metformin, only pancreatic β cells showed an increase in cell death. Very interestingly, when we transfected either mouse insulinoma cell or human embryo kidney cells with a phospho-mutant form of B cell lymphoma 2 associated agonist of cell death at serine 155 (BAD S155D), an increase in the pro-survival factor B cell lymphoma 2 was detected in pancreatic β cells and not in human embryonic kidney cells in the presence of the energetic stressors. This data suggests that the protective capacity of this mutant form is only present in cells that present glucokinase. In contrast, upon hyperactivation of mechanistic target of rapamycin complex 1 signaling by knocking-down tuberous sclerosis complex protein, we observed increased susceptibility to cell death in response to energy stress in both pancreatic and non-pancreatic β cells. Therefore, mechanistic target of rapamycin complex 1 signaling presents a dual effect on cell viability. On the one hand, a chronic inhibition of mechanistic target of rapamycin complex 1 activity in response to the energy status is deleterious for pancreatic β cells, being attenuated by the overexpression of B cell lymphoma 2 associated agonist of cell death S155D. On the other hand, mechanistic target of rapamycin complex 1 hyperactivity provokes a susceptibility to energetic stress-induced cell death. Taken together, these results may open potential implications for the use of glucokinase activators or mechanistic target of rapamycin complex 1 modulators for the maintenance of pancreatic β cells for longer periods of time avoiding its loss in different pathologies such as type 2 diabetes mellitus.

Attenuation of diabetic cardiomyopathy by relying on kirenol to suppress inflammation in a diabetic rat model

Diabetic cardiomyopathy is characterized by diabetes‐induced myocardial abnormalities, accompanied by inflammatory response and alterations in inflammation‐related signalling pathways. Kirenol, isolated from Herba Siegesbeckiae, has potent anti‐inflammatory properties. In this study, we aimed to investigate the cardioprotective effect of kirenol against DCM and underlying the potential mechanisms in a type 2 diabetes mellitus model. Kirenol treatment significantly decreased high glucose‐induced cardiofibroblasts proliferation and increased the cardiomyocytes viability, prevented the loss of mitochondrial membrane potential and further attenuated cardiomyocytes apoptosis, accompanied by a reduction in apoptosis‐related protein expression. Kirenol gavage could affect the expression of pro‐inflammatory cytokines in a dose‐dependent manner but not lower lipid profiles, and only decrease fasting plasma glucose, fasting plasma insulin and mean HbA1c levels in high‐dose kirenol‐treated group at some time‐points. Left ventricular dysfunction, hypertrophy, fibrosis and cell apoptosis, as structural and functional abnormalities, were ameliorated by kirenol administration. Moreover, in diabetic hearts, oral kirenol significantly attenuated activation of mitogen‐activated protein kinase subfamily and nuclear translocation of NF‐κB and Smad2/3 and decreased phosphorylation of IκBα and both fibrosis‐related and apoptosis‐related proteins. In an Electrophoretic mobility shift assay, the binding activities of NF‐κB, Smad3/4, SP1 and AP‐1 in the nucleus of diabetic myocardium were significantly down‐regulated by kirenol treatment. Additionally, high dose significantly enhanced myocardial Akt phosphorylation without intraperitoneal injection of insulin. Kirenol may have potent cardioprotective effects on treating for the established diabetic cardiomyopathy, which involves the inhibition of inflammation and fibrosis‐related signalling pathways and is independent of lowering hyperglycaemia, hyperinsulinemia and lipid profiles.

p53-Bad: A Novel Tumor Suppressor/Proapoptotic Factor Hybrid Directed to the Mitochondria for Ovarian Cancer Gene Therapy

Clinical trials involving p53 gene therapy for ovarian cancer failed due to the dominant negative inhibition of wild-type p53 and multiple genetic aberrations in ovarian cancer. To overcome this problem, we have designed a more potent chimeric gene fusion, called p53-Bad, that combines p53 with the mitochondrial pro-apoptotic factor Bad. Unlike wild-type p53, which acts as a nuclear transcription factor, this novel p53-Bad construct has multiple unique mechanisms of action including a direct and rapid apoptotic effect at the mitochondria. The mitochondrial localization, transcription activity, and apoptotic activity of the constructs were tested. The results suggest that p53 can be effectively targeted to the mitochondria by controlling the phosphorylation of pro-apoptotic Bad, which can only localize to the mitochondria when Ser-112 and Ser-136 of Bad are unphosphorylated. By introducing S112A and S136A mutations, p53-Bad fusion cannot be phosphorylated at these two sites and always localizes to the mitochondria. p53-Bad constructs also have superior activity over p53 and Bad alone. The apoptotic activity is consistent in many ovarian cancer cell lines regardless of the endogenous p53 status. Both p53 and the BH3 domain of Bad contribute to the superior activity of p53-Bad. Our data suggests that p53-Bad fusions are capable of inducing apoptosis and should be further pursued for gene therapy for ovarian cancer.

Secretin Prevents Apoptosis in the Developing Cerebellum Through Bcl-2 and Bcl-xL

Secretin (SCT) is involved in a variety of physiological processes and has been implicated in preventing apoptosis during brain development. However, little is known about the molecular mechanism underlying its neuroprotective effects. The B cell lymphoma 2 (Bcl-2) family proteins, such as Bcl-2 and Bcl-xL, determine the commitment of neurons to apoptosis. In SCT knockout mice, we found reduced transcript levels of anti-apoptotic genes Bcl-2 and Bcl-xL, but not of pro-apoptotic gene Bax, in the developing cerebellum. SCT treatment on ex vivo cultured cerebellar slices triggered a time-dependent increase of Bcl-2 and Bcl-xL expression. This SCT-induced transcriptional regulation of Bcl-2 and Bcl-xL was dependent on the cyclic AMP (cAMP) response element-binding protein (CREB), which is a key survival factor at the convergence of multiple signaling cascades. We further demonstrated that activation of CREB by SCT was mediated by cAMP/protein kinase A (PKA) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1/2 (ERK1/2) cascades. These findings, collectively, provide an uncharacterized signaling cascade for SCT-mediated neuronal survival, in which SCT promotes the key anti-apoptotic elements Bcl-2 and Bcl-xL in the intrinsic death pathway through PKA- and ERK-regulated CREB phosphorylation.

Linc00659, a long noncoding RNA, acts as novel oncogene in regulating cancer cell growth in colorectal cancer

Background

Colorectal cancer (CRC) is one of the most common cancers and causes of cancer-related death worldwide. In patients with CRC, metastasis is a crucial problem that leads to treatment failure and is the primary cause of the lethality of colon cancer. Long noncoding RNAs (lncRNAs) have recently emerged as critical molecules in the development, cell growth, apoptosis, and metastasis of CRC.

Method

We investigated the transcriptome profiles of human lncRNAs in the primary tumor tissues and in the corresponding normal mucosa of two patients with CRC by using a microarray approach. The expression levels of lncRNAs were verified in colon cancer by real-time PCR. Using bioinformatics approach to illustrate putative biological function of Linc00659 in colon cancer. The effects of Linc00659 on cell growth, proliferation, cell cycle and apoptosis were studies by in vitro assays.

Results

Our data revealed that compared with adjacent normal tissues, 201 lncRNAs were deregulated (fold change ≥ 4 or ≤ 0.25) in CRC tissues. Among them, the expression levels of Linc00659 were significantly increased in colon cancer, and high expression levels were correlated with poor survival in patients with CRC. Bioinformatics analysis results indicated that Linc00659 was significantly coexpressed with cycle-related genes in CRC. Linc00659 expression knockdown could significantly suppress colon cancer cell growth by impairing cell cycle progression. In addition, our results showed that Linc00659 expression knockdown could accelerate cell apoptosis in colon cancer cells treated with chemotherapy drugs. Meanwhile, our results also demonstrated that silencing of Linc00659 expression leads to cell growth inhibition and induced apoptosis, possibly by suppressing PI3K-AKT signaling in colon cancer.

Conclusion

Linc00659 is a novel oncogenic lncRNA involved in colon cancer cell growth by modulating the cell cycle. Our findings give an insight into lncRNA regulation and provide an application for colon cancer therapy.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0821-1) contains supplementary material, which is available to authorized users.

Design and Profiling of a Subcellular Targeted Optogenetic cAMP-Dependent Protein Kinase

Although the cAMP-dependent protein kinase (PKA) is ubiquitously expressed, it is sequestered at specific subcellular locations throughout the cell, thereby resulting in compartmentalized cellular signaling that triggers site-specific behavioral phenotypes. We developed a three-step engineering strategy to construct an optogenetic PKA (optoPKA) and demonstrated that, upon illumination, optoPKA migrates to specified intracellular sites. Furthermore, we designed intracellular spatially segregated reporters of PKA activity and confirmed that optoPKA phosphorylates these reporters in a light-dependent fashion. Finally, proteomics experiments reveal that light activation of optoPKA results in the phosphorylation of known endogenous PKA substrates as well as potential novel substrates.

Bad phosphorylation as a target of inhibition in oncology

Bcl-2 agonist of cell death (BAD) is a BH3-only member of the Bcl-2 family which possesses important regulatory function in apoptosis. BAD has also been shown to possess many non-apoptotic functions closely linked to cancer including regulation of glycolysis, autophagy, cell cycle progression and immune system development. Interestingly, BAD can be either pro-apoptotic or pro-survival depending on the phosphorylation state of three specific serine residues (human S75, S99 and S118). Expression of BAD and BAD phosphorylation patterns have been shown to influence tumor initiation and progression and play a predictive role in disease prognosis, drug response and chemosensitivity in various cancers. This review aims to summarize the current evidence on the functional role of BAD phosphorylation in human cancer and evaluate the potential utility of modulating BAD phosphorylation in cancer.

Orexin-A Protects Human Neuroblastoma SH-SY5Y Cells Against 6-Hydroxydopamine-Induced Neurotoxicity: Involvement of PKC and PI3K Signaling Pathways

Parkinson's disease (PD) is a common neurodegenerative disorder that is characterized by progressive and selective death of dopaminergic neurons. Multifunctional neuropeptide orexin-A is involved in many biological events of the body. It has been shown that orexin-A has protective effects in neurodegenerative disease such as PD. However, its cellular mechanisms have not yet been fully clarified. Here, we investigated the intracellular signaling pathway of orexin-A neuroprotection in 6-hydroxydopamine (6-OHDA)-induced SH-SY5H cells damage as an in vitro model of PD. The cells were incubated with 150 μM 6-OHDA, and the viability was examined by 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2-tetrazolium bromide (MTT) assay. Mitochondrial membrane potential and intracellular calcium were measured by fluorescent probes. Western blotting was also used to determine cyclooxygenase type 2 (COX-2), nuclear factor erythroid 2 related factor 2 (Nrf2), and HSP70 protein levels. The data showed that 6-OHDA has decreasing effects on cell viability, Nrf2, and HSP70 protein expression and increases the level of mitochondrial membrane potential, intracellular calcium, and COX-2 protein. Orexin-A (500 pM) significantly attenuated the 6-OHDA-induced cell damage. Furthermore, Orexin-A significantly prevented the mentioned effects of 6-OHDA on SH-SY5Y cells. Orexin 1 receptor antagonist (SB3344867), PKC, and PI3-kinase (PI3K) inhibitors (chelerythrin and LY294002, respectively) could suppress the orexin-A neuroprotective effect. In contrast, blockage of PKA by a selective inhibitor (KT5720) had no effects on the orexin protection. The results suggest that orexin-A protective effects against 6-OHDA-induced neurotoxicity are performed via its receptors, PKC and PI3K signaling pathways.

Biochemical and biophysical investigations of the interaction between human glucokinase and pro-apoptotic BAD

The glycolytic enzyme glucokinase (GCK) and the pro-apoptotic protein BAD reportedly reside within a five-membered complex that localizes to the mitochondria of mammalian hepatocytes and pancreatic β-cells. Photochemical crosslinking studies using a synthetic analog of BAD’s BH3 domain and in vitro transcription/translation experiments support a direct interaction between BAD and GCK. To investigate the biochemical and biophysical consequences of the BAD:GCK interaction, we developed a method for the production of recombinant human BAD. Consistent with published reports, recombinant BAD displays high affinity for Bcl-xL (K_D = 7 nM), and phosphorylation of BAD at S118, within the BH3 domain, abolishes this interaction. Unexpectedly, we do not detect association of recombinant, full-length BAD with recombinant human pancreatic GCK over a range of protein concentrations using various biochemical methods including size-exclusion chromatography, chemical cross-linking, analytical ultracentrifugation, and isothermal titration calorimetry. Furthermore, fluorescence polarization assays and isothermal titration calorimetry detect no direct interaction between GCK and BAD BH3 peptides. Kinetic characterization of GCK in the presence of high concentrations of recombinant BAD show modest (<15%) increases in GCK activity, observable only at glucose concentrations well below the K_0.5 value. GCK activity is unaffected by BAD BH3 peptides. These results raise questions as to the mechanism of action of stapled peptide analogs modeled after the BAD BH3 domain, which reportedly enhance the V_max value of GCK and stimulate insulin release in BAD-deficient islets. Based on our results, we postulate that the BAD:GCK interaction, and any resultant regulatory effect(s) upon GCK activity, requires the participation of additional members of the mitochondrial complex.

The mystery of BCL2 family: Bcl-2 proteins and apoptosis: an update

Apoptosis is a critically important biological process that plays an essential role in cell fate and homeostasis. An important component of the apoptotic pathway is the family of proteins commonly known as the B cell lymphoma-2 (Bcl-2). The primary role of Bcl-2 family members is the regulation of apoptosis. Although the structure of Bcl-2 family of proteins was reported nearly 10 years ago, however, it still surprises us with its structural and functional complexity and diversity. A number of studies have demonstrated that Bcl-2 family influences many other cellular processes beyond apoptosis which are generally independent of the regulation of apoptosis, suggesting additional roles for Bcl-2. The disruption of the regulation of apoptosis is a causative event in many diseases. Since the Bcl-2 family of proteins is the key regulator of apoptosis, the abnormalities in its function have been implicated in many diseases including cancer, neurodegenerative disorders, ischemia and autoimmune diseases. In the past few years, our understanding of the mechanism of action of Bcl-2 family of proteins and its implications in various pathological conditions has enhanced significantly. The focus of this review is to summarize the current knowledge on the structure and function of Bcl-2 family of proteins in apoptotic cellular processes. A number of drugs have been developed in the past few years that target different Bcl-2 members. The role of Bcl-2 proteins in the pathogenesis of various diseases and their pharmacological significance as effective molecular therapeutic targets is also discussed.

Myricetin exerts anti-proliferative, anti-invasive, and pro-apoptotic effects on esophageal carcinoma EC9706 and KYSE30 cells via RSK2

Myricetin, a common dietary flavonoid, is widely distributed in fruits and vegetables and is used as a health food supplement based on its anti-tumor properties. However, the effect and mechanisms of myricetin in esophageal carcinoma are not fully understood. Here, we demonstrated the effect of myricetin on the proliferation, apoptosis, and invasion of the esophageal carcinoma cell lines EC9706 and KYSE30 and explored the underlying mechanism and target protein(s) of myricetin. CCK-8 assay, transwell invasion assay, wound-healing assay, cell cycle analysis, and apoptosis assay were used to evaluate the effects of myricetin on cell proliferation, invasion, and apoptosis. Nude mouse tumor xenograft model was built to understand the interaction between myricetin and NTD RSK2. Pull-down assay was used to verify molecular mechanism. Myricetin inhibited proliferation and invasion and induced apoptosis of EC9706 and KYSE30 cells. Moreover, myricetin was shown to bind RSK2 through the NH2-terminal kinase domain. Finally, myricetin inhibited EC9706 and KYSE30 cell proliferation through Mad1 and induced cell apoptosis via Bad. Myricetin inhibits the proliferation and invasion and induces apoptosis in EC9706 and KYSE30 cells via RSK2. Myricetin exerts anti-proliferative, anti-invasive, and pro-apoptotic effects on esophageal carcinoma EC9706 and KYSE30 cells via RSK2. Our results provide novel insight into myricetin as a potential agent for the prevention and treatment of esophageal carcinoma.

Phosphodiesterase type 4 inhibitor rolipram improves survival of spiral ganglion neurons in vitro

Sensorineural deafness is caused by damage of hair cells followed by degeneration of the spiral ganglion neurons and can be moderated by cochlear implants. However, the benefit of the cochlear implant depends on the excitability of the spiral ganglion neurons. Therefore, current research focuses on the identification of agents that will preserve their degeneration. In this project we investigated the neuroprotective effect of Rolipram as a promising agent to improve the viability of the auditory neurons. It is a pharmaceutical agent that acts by selective inhibition of the phosphodiesterase 4 leading to an increase in cyclic AMP. Different studies reported a neuroprotective effect of Rolipram. However, its significance for the survival of SGN has not been reported so far. Thus, we isolated spiral ganglion cells of neonatal rats for cultivation with different Rolipram concentrations and determined the neuronal survival rate. Furthermore, we examined immunocytologically distinct proteins that might be involved in the neuroprotective signalling pathway of Rolipram and determined endogenous BDNF by ELISA. When applied at a concentration of 0.1 nM, Rolipram improved the survival of SGN in vitro. According to previous studies, our immunocytological data showed that Rolipram application induces the phosphorylation and thereby activation of the transcription factor CREB. This activation can be mediated by the cAMP-PKA-signalling pathway as well as via ERK as a part of the MAP-kinase pathway. However, only in cultures pre-treated with BDNF, an endogenous increase of BDNF was detected. We conclude that Rolipram has the potential to improve the vitality of neonatal auditory nerve cells in vitro. Further investigations are necessary to prove the effect of Rolipram in vivo in the adult organism after lesion of the hair cells and insertion of cochlear implants.

Antisense oligonucleotide suppression of human IGF-1R inhibits the growth and survival of in vitro cultured epithelial ovarian cancer cells

Background

Preclinical evaluation of the anti-neoplastic activity of antisense oligonucleotide (AS) suppression of human insulin-like growth factor I receptor (IGF-IR) in human epithelial ovarian cancer (EOC).

Methods

Ovarian cancer cells from 36 patients with EOC were investigated under serum-free tissue culture conditions. IGF-I production was evaluated by standard ELISA. IGF-IR and phosphorylated IRS-1, AKT, and MAP kinase expression and protein levels were evaluated by immunohistochemistry and Western blotting. Cancer cell growth and proliferation assays were performed in triplicates using MTT assay. Apoptosis was evaluated by TUNNEL assay.

Results

All ovarian cancer tissue samples tested produced IGF-I and expressed IGF-IR, supporting the existence of an autocrine loop. Treatment of primary ovarian cancer cell lines with an IGF-1R AS inhibited growth and proliferation and decreased clonogenicity in soft agar assay. AS treatment was demonstrated to inhibit the expression of IGF-1R and decrease the concentration of phosphorylated IRS-1, AKT, and MAP kinase signaling protein downstream of the IGF-IR. We also observed that the IGF-1R AS sensitized cancer cell lines to cisplatin in vitro through the PI3K pathway.

Conclusions

IGF-IR enhances the proliferation and tumorigenicity of human ovarian cancer cells and inhibition of IGF-IR by AS oligonucleotide treatment potentiates the activity of cisplatin in vitro. Therefore, IGF-1R is a potential molecular target in ovarian cancer.

Function of survivin in trophoblastic cells of the placenta

BACKGROUND

Preeclampsia is one of the leading causes of maternal and perinatal mortality and morbidity worldwide and its pathogenesis is not totally understood. As a member of the chromosomal passenger complex and an inhibitor of apoptosis, survivin is a well-characterized oncoprotein. Its roles in trophoblastic cells remain to be defined.

METHODS

The placental samples from 16 preeclampsia patients and 16 well-matched controls were included in this study. Real-time PCR, immunohistochemistry and Western blot analysis were carried out with placental tissues. Primary trophoblastic cells from term placentas were isolated for Western blot analysis. Cell proliferation, cell cycle analysis and immunofluorescence staining were performed in trophoblastic cell lines BeWo, JAR and HTR-8/SVneo.

RESULTS

The survivin gene is reduced but the protein amount is hardly changed in preeclamptic placentas, compared to control placentas. Upon stress, survivin in trophoblastic cells is phosphorylated on its residue serine 20 by protein kinase A and becomes stabilized, accompanied by increased heat shock protein 90. Depletion of survivin induces chromosome misalignment, abnormal centrosome integrity, and reduced localization and activity of Aurora B at the centromeres/kinetochores in trophoblastic metaphase cells.

CONCLUSIONS

Our data indicate that survivin plays pivotal roles in cell survival and proliferation of trophoblastic cells. Further investigations are required to define the function of survivin in each cell type of the placenta in the context of proliferation, differentiation, apoptosis, angiogenesis, migration and invasion.

Mitochondrial phosphorylation in apoptosis: flipping the death switch

SIGNIFICANCE

Apoptosis is a complex cellular process subject to multiple layers of regulation. One such layer of regulation includes post-translational modifications, including acetylation and phosphorylation. In particular, phosphorylation of proteins directly implicated in the apoptotic process has been extensively documented. Importantly, these phosphorylation events often have functional consequences, affecting the onset of apoptotic cell death.

RECENT ADVANCES

Large-scale proteomics studies have identified multiple novel phosphorylation sites on proteins involved in the apoptotic process. The delineation of the regulation and functional consequences of these phosphorylation events will be important in understanding the regulatory complexity of apoptosis.

CRITICAL ISSUES

Multiple mitochondrial-localized proteins involved in apoptosis are functionally affected by phosphorylation, which can ultimately dictate whether a cell lives or dies. The dynamic interplay between these phosphorylated proteins and their regulatory enzymes is critical for understanding the complex cellular decision to undergo apoptosis.

FUTURE DIRECTIONS

Detailed analysis of the kinetic and spatial regulation of phosphorylation events on apoptotic proteins, as well as how these dynamics influence the cell death process, will illuminate the complex interplay between the network of proteins that control the decision to undergo cell death.

Anoikis molecular pathways and its role in cancer progression

Anoikis is a programmed cell death induced upon cell detachment from extracellular matrix, behaving as a critical mechanism in preventing adherent-independent cell growth and attachment to an inappropriate matrix, thus avoiding colonizing of distant organs. As anchorage-independent growth and epithelial-mesenchymal transition, two features associated with anoikis resistance, are vital steps during cancer progression and metastatic colonization, the ability of cancer cells to resist anoikis has now attracted main attention from the scientific community. Cancer cells develop anoikis resistance due to several mechanisms, including change in integrins' repertoire allowing them to grow in different niches, activation of a plethora of inside-out pro-survival signals as over-activation of receptors due to sustained autocrine loops, oncogene activation, growth factor receptor overexpression, or mutation/upregulation of key enzymes involved in integrin or growth factor receptor signaling. In addition, tumor microenvironment has also been acknowledged to contribute to anoikis resistance of bystander cancer cells, by modulating matrix stiffness, enhancing oxidative stress, producing pro-survival soluble factors, triggering epithelial-mesenchymal transition and self-renewal ability, as well as leading to metabolic deregulations of cancer cells. All these events help cancer cells to inhibit the apoptosis machinery and sustain pro-survival signals after detachment, counteracting anoikis and constituting promising targets for anti-metastatic pharmacological therapy. This article is part of a Special Section entitled: Cell Death Pathways.

14-3-3 proteins are essential signalling hubs for beta cell survival

AIMS/HYPOTHESIS

Diabetes is characterised by pancreatic beta cell death and dysfunction, resulting from unbalanced pro-survival and pro-death signalling. The 14-3-3 proteins are molecular adaptors that integrate numerous signalling pathways, including the v-raf-leukaemia viral oncogene 1 (RAF1)/B cell leukaemia/lymphoma 2 (BCL-2)-associated agonist of cell death (BAD) pathway, which we have previously implicated in insulin-dependent beta cell survival. Nevertheless, the roles of 14-3-3 proteins in beta cell fate and function have not been investigated.

METHODS

We examined the abundance, localisation, modulation and roles of 14-3-3 proteins using quantitative RT-PCR, immunoblot or imaging. MIN6 cells or mouse islets cells were manipulated with inhibitors, short interfering RNA (siRNA) or plasmids overexpressing 14-3-3.

RESULTS

We first characterised the abundance and subcellular location of all seven 14-3-3 isoforms in mouse and human beta cells. Most isoforms were cytoplasmic, except 14-3-3σ, which appeared to be nuclear. Analysis of 14-3-3 abundance under stress conditions revealed distinct modulation in mouse islets and MIN6 cells. Generalised 14-3-3 inhibition promoted apoptosis and dysfunction, and siRNA-mediated knockdown revealed isoform-specific roles in caspase-3-dependent beta cell apoptosis, with a clear role for 14-3-3ζ. Overabundance of 14-3-3ζ sequestered BAD-BCL2-associated X protein (BAX) from mitochondria, attenuated Dp5 (also known as Hrk) and Puma (also known as Bbc3) induction, and increased survival in response to pro-inflammatory cytokines or thapsigargin. Anti-apoptotic insulin treatment increased the sequestration of BAD/BAX by 14-3-3ζ. BAD mutants that were unable to bind 14-3-3ζ localised to mitochondria and induced apoptosis.

CONCLUSIONS/INTERPRETATION

This first study of the 14-3-3 family in beta cells revealed specific regulation, localisation and anti-apoptotic roles among the isoforms. Focus on 14-3-3ζ revealed its importance in preventing BAD-BAX mitochondrial localisation and protecting beta cells from multiple stresses. Thus, some 14-3-3 proteins are pro-survival signalling hubs.

Getting away with murder: how does the BCL-2 family of proteins kill with immunity?

The adult human body produces approximately one million white blood cells every second. However, only a small fraction of the cells will survive because the majority is eliminated through a genetically controlled form of cell death known as apoptosis. This review places into perspective recent studies pertaining to the BCL-2 family of proteins as critical regulators of the development and function of the immune system, with particular attention on B cell and T cell biology. Here we discuss how elegant murine model systems have revealed the major contributions of the BCL-2 family in establishing an effective immune system. Moreover, we highlight some key regulatory pathways that influence the expression, function, and stability of individual BCL-2 family members, and discuss their role in immunity. From lethal mechanisms to more gentle ones, the final portion of the review discusses the nonapoptotic functions of the BCL-2 family and how they pertain to the control of immunity.

Vasopressin inhibits apoptosis in renal collecting duct cells

The peptide hormone arginine vasopressin (AVP) plays a critical role in regulating salt and water transport in the mammalian kidney. Recent studies have also demonstrated that AVP can promote cell survival in neuronal cells through V1 receptors. The current study addresses whether AVP can inhibit apoptosis in kidney collecting duct cells via V2 receptors and also explores the downstream signaling pathways regulating this phenomenon. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling analysis and caspase cleavage assays demonstrated that 1-desamino-8-d-arginine vasopressin (dDAVP) inhibited apoptosis induced by various agents (staurosporine, actinomycin D, and cycloheximide) in cultured mouse cortical collecting duct cells (mpkCCD). Incubation with dDAVP also inhibited apoptosis induced by the phosphatidylinositol 3-kinase (PI3K) pathway inhibitor LY294002, suggesting that the antiapoptotic effects of dDAVP are largely independent of PI3K signaling. The V2 receptor antagonist SR121463 completely abolished the antiapoptotic effects of dDAVP. In addition, incubation with 8-cpt-cAMP, a cell-permeable analog of cAMP, reproduced the antiapoptotic effects of dDAVP. Both dDAVP and 8-cpt-cAMP increased phosphorylation of proapoptotic Bcl-2 family members Bad and Bok. Bad phosphorylation at Ser-112 and Ser-155 is known to inhibit its proapoptotic activity. Preincubation with H89 blocked dDAVP-induced phosphorylation of both Bad and Bok, suggesting dependence on protein kinase A (PKA). This study provides evidence that AVP can inhibit apoptosis through the V2 receptor and downstream cAMP-mediated pathways in mammalian kidney. The antiapoptotic action of AVP may be relevant to a number of physiological and pathophysiological conditions including osmotic tolerance in the inner medulla, escape from AVP-induced antidiuresis, and polycystic kidney disease.

Dynamics of the G protein-coupled vasopressin V2 receptor signaling network revealed by quantitative phosphoproteomics

G protein-coupled receptors (GPCRs) regulate diverse physiological processes, and many human diseases are due to defects in GPCR signaling. To identify the dynamic response of a signaling network downstream from a prototypical G(s)-coupled GPCR, the vasopressin V2 receptor, we have carried out multireplicate, quantitative phosphoproteomics with iTRAQ labeling at four time points following vasopressin exposure at a physiological concentration in cells isolated from rat kidney. A total of 12,167 phosphopeptides were identified from 2,783 proteins, with 273 changing significantly in abundance with vasopressin. Two-dimensional clustering of phosphopeptide time courses and Gene Ontology terms revealed that ligand binding to the V2 receptor affects more than simply the canonical cyclic adenosine monophosphate-protein kinase A and arrestin pathways under physiological conditions. The regulated proteins included key components of actin cytoskeleton remodeling, cell-cell adhesion, mitogen-activated protein kinase signaling, Wnt/β-catenin signaling, and apoptosis pathways. These data suggest that vasopressin can regulate an array of cellular functions well beyond its classical role in regulating water and solute transport. These results greatly expand the current view of GPCR signaling in a physiological context and shed new light on potential roles for this signaling network in disorders such as polycystic kidney disease. Finally, we provide an online resource of physiologically regulated phosphorylation sites with dynamic quantitative data (http://helixweb.nih.gov/ESBL/Database/TiPD/index.html).

Cell surface adhesion molecules and adhesion-initiated signaling: understanding of anoikis resistance mechanisms and therapeutic opportunities

Cells express various cell surface adhesion molecules (receptors) that not only mechanically serve as contacting sites between the cell and extracellular matrix (ECM) or adjacent cells, but also initiate intracellular signaling pathways modulating important cellular events including survival and proliferation. Normal cells undergo apoptosis when lacking ECM attachment. This type of cell death has been termed anoikis. Anoikis can be viewed as a normal process which ensures tissue homeostasis and failure to execute the anoikis program or resistance to anoikis could result in adherent cells surviving under suspension condition and proliferating at ectopic sites where the matrix proteins are different from those the cells originally contact. Resistance to anoikis is emerging as a hallmark of metastatic cancers which enables cancer cells to disseminate to distant organs through systemic circulation. In this review, we will discuss the molecular basis of adhesion-initiated signaling, the impact of loss of cell-ECM adhesion on normal cell survival, the role of cancer cell aggregate formation via intercellular adhesion under non-adherent condition, and mechanisms of anoikis resistance developed in metastatic cancer cells. Understanding of these aspects will provide opportunities to find new potential molecular targets, and therapeutic strategies based on these findings will likely prove to be more specific and effective.

Kinase consensus sequences: a breeding ground for crosstalk

The best characterized examples of crosstalk between two or more different post-translational modifications (PTMs) occur with respect to histones. These examples demonstrate the critical roles that crosstalk plays in regulating cell signaling pathways. Recently, however, non-histone crosstalk has been observed between serine/threonine phosphorylation and the modification of arginine and lysine residues within kinase consensus sequences. Interestingly, many kinase consensus sequences contain critical arginine/lysine residues surrounding the substrate serine/threonine residue. Therefore, we hypothesize that non-histone crosstalk between serine/threonine phosphorylation and arginine/lysine modifications is a global mechanism for the modulation of cellular signaling. In this review, we discuss several recent examples of non-histone kinase consensus sequence crosstalk, as well as provide the biophysical basis for these observations. In addition, we predict likely examples of crosstalk between protein arginine methyltransferase 1 (PRMT1) and Akt and discuss the future implications of these findings.

Arginine methylation of BCL-2 antagonist of cell death (BAD) counteracts its phosphorylation and inactivation by Akt

Protein arginine methylation is a common posttranslational modification catalyzed by a family of the protein arginine methyltransferases (PRMTs). We have previously reported that PRMT1 methylates Forkhead box O transcription factors at two arginine residues within an Akt consensus phosphorylation motif (RxRxxS/T), and that this methylation blocks Akt-mediated phosphorylation of the transcription factors. These findings led us to hypothesize that the functional crosstalk between arginine methylation and phosphorylation could be extended to other Akt target proteins as well as Forkhead box O proteins. Here we identify BCL-2 antagonist of cell death (BAD) as an additional substrate for PRMT1 among several Akt target proteins. We show that PRMT1 specifically binds and methylates BAD at Arg-94 and Arg-96, both of which comprise the Akt consensus phosphorylation motif. Consistent with the hypothesis, PRMT1-mediated methylation of these two arginine residues inhibits Akt-mediated phosphorylation of BAD at Ser-99 in vitro and in vivo. We also demonstrate that the complex formation of BAD with 14-3-3 proteins, which occurs subsequent to Akt-mediated phosphorylation, is negatively regulated by PRMT1. Furthermore, PRMT1 knockdown prevents mitochondrial localization of BAD and its binding to the antiapoptotic BCL-X(L) protein. BAD overexpression causes an increase in apoptosis with concomitant activation of caspase-3, whereas PRMT1 knockdown significantly suppresses these apoptotic processes. Taken together, our results add a new dimension to the complexity of posttranslational BAD regulation and provide evidence that arginine methylation within an Akt consensus phosphorylation motif functions as an inhibitory modification against Akt-dependent survival signaling.

AMPK-induced activation of Akt by AICAR is mediated by IGF-1R dependent and independent mechanisms in acute lymphoblastic leukemia

Background

Children with Acute Lymphoblastic Leukemia (ALL) diagnosed with resistant phenotypes and those who relapse have a dismal prognosis for cure. In search for novel treatment strategies, we identified the AMP activated protein kinase (AMPK) as a potential drug target based on its effects on cell growth and survival. We have shown previously that AICAR-induced AMPK activation also induced a compensatory survival mechanism via PI3K/Akt signaling.

Results

In the present study, we further investigated the downstream signaling induced by AMPK activation in ALL cells. We found that AICAR-induced AMPK activation resulted in up-regulation of P-Akt (Ser473 and Thr308) and decrease of P-mTOR (Ser2448) expression and downstream signaling. We determined that activation of P-Akt (Thr308) was mediated by AMPK-induced IGF-1R activation via phosphorylation of the insulin receptor substrate-1 (IRS-1) at Ser794. Inhibition of IGF-1R signaling using the tyrosine kinase inhibitor HNMPA(AM)₃ resulted in significant decrease in P-IRS-1 (Ser794) and P-Akt (Thr308). Co-treatment of AICAR plus HNMPA(AM)₃ prevented AMPK-induced up-regulation of P-Akt (Thr308) but did not alter the activation of P-Akt (Ser473). Inhibition of AMPK using compound-C resulted in decreased P-Akt expression at both residues, suggesting a central role for AMPK in Akt activation. In addition, inhibition of IGF-1R signaling in ALL cells resulted in cell growth arrest and apoptosis. Additional Western blots revealed that P-IGF-1R (Tyr1131) and P-IRS-1 (Ser794) levels were higher in NALM6 (Bp-ALL) than CEM (T-ALL), and found differences in IGF-1R signaling within Bp-ALL cell line models NALM6, REH (TEL-AML1, [t(12;21)]), and SupB15 (BCR-ABL, [t(9;22)]). In these models, higher sensitivity to IGF-1R inhibitors correlated with increased levels of IGF-1R expression. Combined therapy simultaneously targeting IGF-1R, AMPK, Akt, and mTOR pathways resulted in synergistic growth inhibition and cell death.

Conclusions

Our study demonstrates that AMPK activates Akt through IGF-1R dependent and independent mechanisms. Co-targeting IGF-1R and related downstream metabolic and oncogenic signaling pathways represent a potential strategy for future translation into novel ALL therapies.

Molecular modeling of BAD complex resided in a mitochondrion integrating glycolysis and apoptosis

BAD (Bcl-2 antagonist of cell death) and GK (glucokinase) reside in a mitochondrial complex together with PKA and PP1 catalytic units (PKAc and PP1c) and WAVE-1 that integrates glycolysis and apoptosis. Our research results reveal that BAD is phosphorylated and inactivated on Ser 75 in a BAD-Bcl-xL complex by PKA (targeted to mitochondria through association with WAVE1), resulting in the dissociation of BAD and its binding to GK. Moreover, GK can interact with PP1c and also distinguish WAVE1. On the other hand, BAD is dephosphorylated and activated on Ser75 by PP1c, leading to the separation of PKAc and its binding to the regulatory (R) subunit of PKA which by the dimerization domain of its R subunit connects with WAVE1 linked with GK of the complex. This may be the reason of the complex existing in liver mitochondria, regardless of phosphorylated and dephosphorylated BAD. Additionally, GK like PKA may also prevent Bcl-xL from rebinding to BAD by phosphorylating BAD at Ser 118. The BAD complex model reveals that BAD and GK play key roles because of BAD as a substrate for the PKA-PP1 pair and by BH3 domain directly interacting with GK. This is helpful for our development and research of the molecular mechanism of BAD integrating glycolysis and apoptosis.

The role of zinc in the modulation of neuronal proliferation and apoptosis

Although a requirement of zinc (Zn) for normal brain development is well documented, the extent to which Zn can modulate neuronal proliferation and apoptosis is not clear. Thus, we investigated the role of Zn in the regulation of these two critical events. A low Zn availability leads to decreased cell viability in human neuroblastoma IMR-32 cells and primary cultures of rat cortical neurons. This occurs in part as a consequence of decreased cell proliferation and increased apoptotic cell death. In IMR-32 cells, Zn deficiency led to the inhibition of cell proliferation through the arrest of the cell cycle at the G₀/G₁ phase. Zn deficiency induced apoptosis in both proliferating and quiescent neuronal cells via the intrinsic apoptotic pathway. Reductions in cellular Zn triggered a translocation of the pro-apoptotic protein Bad to the mitochondria, cytochrome c release, and caspase-3 activation. Apoptosis is the resultant of the inhibition of the prosurvival extracellular-signal-regulated kinase, the inhibition of nuclear factor-kappa B, and associated decreased expression of antiapoptotic proteins, and to a direct activation of caspase-3. A deficit of Zn during critical developmental periods can have persistent effects on brain function secondary to a deregulation of neuronal proliferation and apoptosis.

Zinc deficiency and neurodevelopment: the case of neurons

Zinc is essential for normal brain development. Gestational severe zinc deficiency can lead to overt fetal brain malformations. Although not teratogenic, suboptimal zinc nutrition during gestation can have long-term effects on the offspring's nervous system. This article will review current knowledge on the role of zinc in modulating neurogenesis and neuronal apoptosis as well as the proposed underlying mechanisms. A decrease in neuronal zinc causes cell cycle arrest, which in part involves a deregulation of select signals (ERK1/2, p53, and NF-kappaB). Zinc deficiency also induces apoptotic neuronal death through the intrinsic (mitochondrial) pathway, which can be triggered by the activation of the zinc-regulated enzyme caspase-3, and as a consequence of abnormal regulation of prosurvival signals (ERK1/2 and NF-kappaB). Alterations in the finely tuned processes of neurogenesis, neuronal migration, differentiation, and apoptosis, which involve the developmental shaping of the nervous system, could have a long-term impact on brain health. Zinc deficiency during gestation, even at the marginal levels observed in human populations, could increase the risk for behavioral/neurological disorders in infancy, adolescence, and adulthood.

Apigenin induces apoptosis via downregulation of S-phase kinase-associated protein 2-mediated induction of p27Kip1 in primary effusion lymphoma cells

OBJECTIVE

The mechanisms that regulate mitogenic and antiapoptotic signals in primary effusion lymphoma (PEL) are not well known. In efforts to identify novel approaches to block the proliferation of PEL cells, we assessed the effect of apigenin (4',5,7-trihydroxyflavone), a flavonoid on a panel of PEL cell lines.

MATERIALS AND METHODS

We studied the effect of apigenin on four PEL cell lines. Apoptosis was measured by annexin V/PI dual staining and DNA laddering. Protein expression was measured by immunoblotting.

RESULTS

Apigenin induced apoptosis in PEL cell lines in a dose dependent manner. Such effects of apigenin appeared to result from suppression of constitutively active kinase AKT resulting in down-regulation of SKP2, hypo-phosphorylation of Rb and accumulation of p27Kip1. Apigenin treatment of PEL cells caused dephosphorylation of p-Bad protein leading to down regulation of the anti-apoptotic protein, Bcl-2 and an increase in Bax/Bcl2 ratio. Apigenin treatment also triggered Bax conformational change and subsequently translocation from cytosole to mitochondria causing loss of mitochondrial membrane potential with subsequent release of cytochrome c. Released cytochrome c onto the cytosole activated caspase-9 and caspase-3, followed by polyadenosin-5'-diphosphate-ribose polymerase (PARP) cleavage. Finally, treatment of PEL cells with apigenin down-regulated the expression of inhibitor of apoptosis protein (IAPs).

CONCLUSIONS

Altogether, these data suggest a novel function for apigenin, acting as a suppressor of AKT/PKB pathway in PEL cells, and raise the possibility that this agent may have a future therapeutic role in PEL and possibly other malignancies with constitutive activation of the AKT/PKB pathway.

p90 ribosomal S6 kinase 1 (RSK1) and the catalytic subunit of protein kinase A (PKA) compete for binding the pseudosubstrate region of PKAR1alpha: role in the regulation of PKA and RSK1 activities

Previously we showed that the inactive form of p90 ribosomal S6 kinase 1 (RSK1) interacts with the regulatory subunit, PKARIalpha, of protein kinase A (PKA), whereas the active RSK1 interacts with the catalytic subunit (PKAc) of PKA. Herein, we demonstrate that the N-terminal kinase domain (NTK) of RSK1 is necessary for interactions with PKARIalpha. Substitution of the activation loop phosphorylation site (Ser-221) in the NTK with the negatively charged Asp residue abrogated the association between RSK1 and PKARIalpha. This explains the lack of an interaction between active RSK1 and PKARIalpha. Full-length RSK1 bound to PKARIalpha with an affinity of 0.8 nm. The NTK domain of RSK1 competed with PKAc for binding to the pseudosubstrate region (amino acids 93-99) of PKARIalpha. Overexpressed RSK1 dissociated PKAc from PKARIalpha, increasing PKAc activity, whereas silencing of RSK1 increased PKAc/PKARIalpha interactions and decreased PKAc activity. Unlike PKAc, which requires Arg-95 and -96 in the pseudosubstrate region of PKARIalpha for their interactions, RSK1/PKARIalpha association requires all four Arg residues (Arg-93-96) in the pseudosubstrate site of PKARIalpha. A peptide (Wt-PS) corresponding to residues 91-99 of PKARIalpha competed for binding of RSK1 with PKARIalpha both in vitro and in intact cells. Furthermore, peptide Wt-PS (but not control peptide Mut-PS), by dissociating RSK1 from PKARIalpha, activated RSK1 in the absence of any growth factors and protected cells from apoptosis. Thus, by competing for binding to the pseudosubstrate region of PKARIalpha, RSK1 regulates PKAc activity in a cAMP-independent manner, and PKARIalpha by associating with RSK1 regulates its activation and its biological functions.

Regulation of protein kinase A activity by p90 ribosomal S6 kinase 1

Previously, we reported that the catalytic subunit of cAMP-dependent protein kinase (PKAc) binds to the active p90 ribosomal S6 kinase 1 (RSK1) (Chaturvedi, D., Poppleton, H. M., Stringfield, T., Barbier, A., and Patel, T. B. (2006) Mol. Cell. Biol. 26, 4586-4600). Herein, by overexpressing hemagglutinin-tagged RSK1 fragments in HeLa cells we have identified the region of RSK1 that is responsible for the interaction with PKAc. PKAc bound to the last 13 amino acids of RSK1, which overlaps the Erk1/2 docking site. This interaction between PKAc and RSK1 required the phosphorylation of Ser-732 in the C terminus of RSK1. Depending upon its phosphorylation status, RSK1 switched interactions between Erk1/2 and PKAc. In addition, a peptide corresponding to the last 13 amino acids of RSK1 with substitution of Ser-732 with Glu (peptide E), but not Ala (peptide A), decreased interactions between endogenous active RSK1 and PKAc. RSK1 attenuated the ability of cAMP to activate PKA in vitro and this modulation was abrogated by peptide E, but not by peptide A. Similarly, in intact cells, cAMP-mediated phosphorylation of Bcl-xL/Bcl-2-associated death promoter on Ser-115, the PKA site, was reduced when RSK1 was activated by epidermal growth factor, and this effect was blocked by peptide E, but not by peptide A. These findings demonstrate that interactions between endogenous RSK1 and PKAc in intact cells regulate the ability of cAMP to activate PKA and identify a novel mechanism by which PKA activity is regulated by the Erk1/2 pathway.

BAD: undertaker by night, candyman by day

The BH3-only pro-apoptotic proteins are upstream sensors of cellular damage that selectively respond to specific, proximal death and survival signals. Genetic models and biochemical studies indicate that these molecules are latent killers until activated through transcriptional or post-translational mechanisms in a tissue-restricted and signal-specific manner. The large number of BH3-only proteins, their unique subcellular localization, protein-interaction network and diverse modes of activation suggest specialization of their damage-sensing function, ensuring that the core apoptotic machinery is poised to receive input from a wide range of cellular stress signals. The apoptotic response initiated by the activation of BH3-only proteins ultimately culminates in allosteric activation of pro-apoptotic BAX and BAK, the gateway proteins to the mitochondrial pathway of apoptosis. From activation of BH3-only proteins to oligomerization of BAX and BAK and mitochondrial outer membrane permeabilization, an intricate network of interactions between the pro- and anti-apoptotic members of the BCL-2 family orchestrates the decision to undergo apoptosis. Beyond regulation of apoptosis, multiple BCL-2 proteins have recently emerged as active components of select homeostatic pathways carrying other cellular functions. This review focuses on BAD, which was the first BH3-only protein linked to proximal survival signals through phosphorylation by survival kinases. In addition to findings that delineated the physiological role of BAD in apoptosis and its dynamic regulation by phosphorylation, studies pointing to new roles for this protein in other physiological pathways, such as glucose metabolism, are highlighted. By executing its 'day' and 'night' jobs in metabolism and apoptosis, respectively, BAD helps coordinate mitochondrial fuel metabolism and the apoptotic machinery.

Identification of novel in vivo phosphorylation sites of the human proapoptotic protein BAD: pore-forming activity of BAD is regulated by phosphorylation

BAD is a proapoptotic member of the Bcl-2 protein family that is regulated by phosphorylation in response to survival factors. Although much attention has been devoted to the identification of phosphorylation sites in murine BAD, little data are available with respect to phosphorylation of human BAD protein. Using mass spectrometry, we identified here besides the established phosphorylation sites at serines 75, 99, and 118 several novel in vivo phosphorylation sites within human BAD (serines 25, 32/34, 97, and 124). Furthermore, we investigated the quantitative contribution of BAD targeting kinases in phosphorylating serine residues 75, 99, and 118. Our results indicate that RAF kinases represent, besides protein kinase A, PAK, and Akt/protein kinase B, in vivo BAD-phosphorylating kinases. RAF-induced phosphorylation of BAD was reduced to control levels using the RAF inhibitor BAY 43-9006. This phosphorylation was not prevented by MEK inhibitors. Consistently, expression of constitutively active RAF suppressed apoptosis induced by BAD and the inhibition of colony formation caused by BAD could be prevented by RAF. In addition, using the surface plasmon resonance technique, we analyzed the direct consequences of BAD phosphorylation by RAF with respect to association with 14-3-3 and Bcl-2/Bcl-X(L) proteins. Phosphorylation of BAD by active RAF promotes 14-3-3 protein association, in which the phosphoserine 99 represented the major binding site. Finally, we show here that BAD forms channels in planar bilayer membranes in vitro. This pore-forming capacity was dependent on phosphorylation status and interaction with 14-3-3 proteins. Collectively, our findings provide new insights into the regulation of BAD function by phosphorylation.

The PKARIalpha subunit of protein kinase A modulates the activation of p90RSK1 and its function

Previously, we showed that interactions between p90(RSK1) (RSK1) and the subunits of type I protein kinase A (PKA) regulate the activity of PKA and cellular distribution of active RSK1 (Chaturvedi, D., Poppleton, H. M., Stringfield, T., Barbier, A., and Patel, T. B. (2006) Mol. Cell Biol. 26, 4586-4600). Here we examined the role of the PKARIalpha subunit of PKA in regulating RSK1 activation and cell survival. In mouse lung fibroblasts, silencing of the PKARIalpha increased the phosphorylation and activation of RSK1, but not of RSK2 and RSK3, in the absence of any stimulation. Silencing of PKARIalpha also decreased the nuclear accumulation of active RSK1 and increased its cytoplasmic content. The increased activation of RSK1 in the absence of any agonist and changes in its subcellular redistribution resulted in increased phosphorylation of its cytoplasmic substrate BAD and increased cell survival. The activity of PKA and phosphorylation of BAD (Ser-155) were also enhanced when PKARIalpha was silenced, and this, in part, contributed to increased cell survival in unstimulated cells. Furthermore, we show that RSK1, PKA subunits, D-AKAP1, and protein phosphatase 2A catalytic subunit (PP2Ac) exist in a complex, and dissociation of RSK1 from D-AKAP1 by either silencing of PKARIalpha, depletion of D-AKAP1, or by using a peptide that competes with PKARIalpha for binding to AKAPs, decreased the amount of PP2Ac in the RSK1 complex. We also demonstrate that PP2Ac is one of the phosphatases that dephosphorylates RSK, but not ERK1/2. Thus, in unstimulated cells, the increased phosphorylation and activation of RSK1 after silencing of PKARIalpha or depletion of D-AKAP1 are due to decreased association of PP2Ac in the RSK1 complex.

Role of protein kinase C-iota in transformed non-malignant RWPE-1 cells and androgen-independent prostate carcinoma DU-145 cells

Prostate cancer is one of the leading causes of death among men in the USA.

OBJECTIVE

In this study, we investigated the role of atypical protein kinase C-iota (PKC-iota) in androgen independent prostate DU-145 carcinoma cellscompared to transformed non-malignant prostate RWPE-1 cells.

MATERIALS AND METHODS

Western blotting and immunoprecipitations demonstrated that PKC-iotaisassociated with cyclin-dependent kinase activating kinase (CAK/Cdk7) in RWPE-1 cells, but not in DU-145 cells.

RESULTS

Treatment of prostate RWPE-1 cells with PKC-iota silencing RNA (siRNA) decreased cell viability,cell-cycle accumulation at G2/M phase, and phosphorylation of Cdk7 and Cdk2. In addition, PKC-iota siRNA treatment caused less phosphorylation ofBad at ser-155, ser-136, and greater Bad/Bcl-xL heterodimerization, leading to apoptosis. In DU-145 cells, PKC-iota was anti-apoptotic and was required for cell survival. Treatment with PKC-iota siRNA blocked increase in cell number, and inhibited G1/S transition by accumulation of cells in G0/G1phase. In addition to cell-cycle arrest, both RWPE-1 and DU-145 cells underwent apoptosis due to mitochondrial dysfunction and apoptosis cascades, such as release of cytochrome c,activation of caspase-7, and poly (ADP-ribose)polymerase (PARP) cleavage.

CONCLUSION

Our results suggest that PKC-iota is required for cell survival in both transformed non-malignant prostate RWPE-1 cells and androgen-independent malignant prostate DU-145 cells, whereas suppressing PKC-iota lead to apoptosis in DU-145 prostate cells.

Tumour cell survival signalling by the ERK1/2 pathway

Several advances in recent years have focused increasing attention on the role of the RAF-MEK-ERK1/2 pathway in promoting cell survival. The demonstration that BRAF is a human oncogene mutated at high frequency in melanoma, thyroid and colon cancer has provided a pathophysiological context, whilst the description of potent and highly selective inhibitors of BRAF or MEK has allowed a more informed and rational intervention in both normal and tumour cells. In addition, separate studies have uncovered new mechanisms by which the ERK1/2 pathway can control the activity or abundance of members of the BCL-2 protein family to promote cell survival. It is now apparent that various oncogenes co-opt ERK1/2 signalling to de-regulate these BCL-2 proteins and this contributes to, and even underpins, survival signalling in some tumours. New oncogene-targeted therapies allow direct or indirect inhibition of ERK1/2 signalling and can cause quite striking tumour cell death. In other cases, inhibition of the ERK1/2 pathway may be more effective in combination with other conventional and novel therapeutics. Here, we review recent advances in our understanding of how the ERK1/2 pathway regulates BCL-2 proteins to promote survival, how this is de-regulated in tumour cells and the opportunities this might afford with the use of new targeted therapies.

Epidermal growth factor abrogates hypoxia-induced apoptosis in cultured human trophoblasts through phosphorylation of BAD Serine 112

We tested the hypothesis that epidermal growth factor (EGF) limits hypoxia-induced apoptosis in cultured human trophoblasts by phosphorylation of the proapoptotic protein Bcl-2-associated death promoter (BAD). Cytotrophoblasts were isolated from placentas of uncomplicated pregnancies at 38-40 wk gestation. Primary trophoblasts or transfected JEG3 trophoblast cells were cultured in less than 1 or 20% oxygen in the presence or absence of EGF and signaling pathway inhibitors. BAD, green fluorescent protein (GFP)-BAD, 14-3-3, Bcl-X(L), and neoepitopes formed during apoptotic cleavage of cytokeratin 18 intermediate filaments were quantified using immunoblotting. Cultures immunostained by fluorescent antibodies were analyzed by confocal microscopy for BAD and GFP. Fluorescence resonance energy transfer was used to detect molecular interaction between endogenous BAD and GFP-BAD. We found EGF increased the phosphorylation of BADser112 under standard culture conditions. Whereas hypoxia enhanced apoptosis and increased phosphorylation of both BADser136 and BADser155, hypoxia diminished phosphorylation of BADser112, and this effect was reversible by EGF. Transfected GFP-BAD, which directly interacted with endogenous BAD by colocalization and fluorescence resonance energy transfer, enhanced hypoxia-induced apoptosis in JEG3 cells. EGF reduced apoptosis in hypoxic JEG3 cells that overexpressed GFP-BAD but not in cells overexpressing GFP-BAD that harbored a serine-to-alanine mutation at the 112 site. Coimmunoprecipitation studies showed that EGF reduced the proapoptotic interaction of BAD with Bcl-X(L). The effect of EGF on phosphorylation of BADser112 was dependent on the action of p38 MAPK. We conclude that EGF signals via p38 MAPK to increase phosphorylation of BADser112 and thereby limit trophoblast apoptosis.

Hepatic stress in hereditary tyrosinemia type 1 (HT1) activates the AKT survival pathway in the fah-/- knockout mice model

BACKGROUND/AIMS

The AKT survival pathway is involved in a wide variety of human cancers. We investigated the implication of this pathway in hereditary tyrosinemia type 1 (HT1), a metabolic disease exhibiting hepatocellular carcinoma (HCC), despite treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexadione (NTBC) which prevents liver damage. HT1 is an autosomal recessive disorder caused by accumulation of toxic metabolites due to a deficiency in fumarylacetoacetate hydrolase (FAH), the last enzyme in the catabolism of tyrosine.

METHODS

NTBC withdrawal in the murine fah(-/-) knockout model was used to analyze in vivo the correlation between pathophysiological, biochemical and histological features consistent with hepatocarcinogenesis and activation of the AKT survival pathway.

RESULTS

The HT1 stress initiated by NTBC discontinuation causes a progressive increase of liver and kidney pathophysiology. A stable activation of the AKT survival pathway is observed in the liver but not in kidneys of fah(-/-) mice. Hepatic survival is reinforced by inhibition of mitochondrial-mediated apoptosis through inactivation of Bad and induction of BCl-X(L) and BCl-2.

CONCLUSIONS

The chronic stress induced by liver disease in HT1 activates the AKT survival signal and inhibits intrinsic apoptosis to confer cell death resistance in vivo and favor hepatocarcinogenesis.

CaMKII and CaMKIV mediate distinct prosurvival signaling pathways in response to depolarization in neurons

By fusing the CaMKII-inhibitory peptide AIP to GFP, we constructed a specific and effective CaMKII inhibitor, GFP-AIP. Expression of GFP-AIP and/or dominant-inhibitory CaMKIV in cultured neonatal rat spiral ganglion neurons (SGNs) shows that CaMKII and CaMKIV act additively and in parallel to mediate the prosurvival effect of depolarization. Depolarization or expression of constitutively active CaMKII functionally inactivates Bad, indicating that this is one means by which CaMKII promotes neuronal survival. CaMKIV, but not CaMKII, requires CREB to promote SGN survival, consistent with the exclusively nuclear localization of CaMKIV and indicating that the principal prosurvival function of CaMKIV is activation of CREB. Consistent with this, a constitutively active CREB construct that provides a high level of CREB activity promotes SGN survival, although low levels of CREB activity did not do so. Also, in apoptotic SGNs, activation of CREB by depolarization is disabled, presumably as part of a cellular commitment to apoptosis.