Cytoskeleton and Associated Proteins: Pleiotropic JNK Substrates and Regulators

This review extensively reports data from the literature concerning the complex relationships between the stress-induced c-Jun N-terminal kinases (JNKs) and the four main cytoskeleton elements, which are actin filaments, microtubules, intermediate filaments, and septins. To a lesser extent, we also focused on the two membrane-associated cytoskeletons spectrin and ESCRT-III. We gather the mechanisms controlling cytoskeleton-associated JNK activation and the known cytoskeleton-related substrates directly phosphorylated by JNK. We also point out specific locations of the JNK upstream regulators at cytoskeletal components. We finally compile available techniques and tools that could allow a better characterization of the interplay between the different types of cytoskeleton filaments upon JNK-mediated stress and during development. This overview may bring new important information for applied medical research.

α-Fodrin in Cytoskeletal Organization and the Activity of Certain Key Microtubule Kinesins

Cortical cytoskeletal proteins are significant in controlling various cellular mechanisms such as migration, cell adhesion, intercellular attachment, cellular signaling, exo- and endocytosis and plasma membrane integrity, stability and flexibility. Our earlier studies involving in vitro and ex vivo approaches led us to identify certain undiscovered characteristics of α-fodrin, a prominent cortical protein. The conventional functions attributed to this protein mainly support the plasma membrane. In the present study, we utilized a global protein expression analysis approach to detect underexplored functions of this protein. We report that downregulation of α-fodrin in glioblastoma cells, U-251 MG, results in upregulation of genes affecting the regulation of the cytoskeleton, cell cycle and apoptosis. Interestingly, certain key microtubule kinesins such as KIF23, KIF2B and KIF3C are downregulated upon α-fodrin depletion, as validated by real-time PCR studies.

A Na,K-ATPase-Fodrin-Actin Membrane Cytoskeleton Complex is Required for Endothelial Fenestra Biogenesis

Fenestrae are transcellular plasma membrane pores that mediate blood–tissue exchange in specialised vascular endothelia. The composition and biogenesis of the fenestra remain enigmatic. We isolated and characterised the protein composition of large patches of fenestrated plasma membrane, termed sieve plates. Loss-of-function experiments demonstrated that two components of the sieve plate, moesin and annexin II, were positive and negative regulators of fenestra formation, respectively. Biochemical analyses showed that moesin is involved in the formation of an actin–fodrin submembrane cytoskeleton that was essential for fenestra formation. The link between the fodrin cytoskeleton and the plasma membrane involved the fenestral pore protein PV-1 and Na,K-ATPase, which is a key regulator of signalling during fenestra formation both in vitro and in vivo. These findings provide a conceptual framework for fenestra biogenesis, linking the dynamic changes in plasma membrane remodelling to the formation of a submembrane cytoskeletal signalling complex.

Binding of alpha-fodrin to gamma-tubulin accounts for its role in the inhibition of microtubule nucleation

Non-erythroid spectrin or fodrin is present as part of the γ-tubulin ring complex (γ-TuRC) in brain tissue and brain derived cells. Here, we show that fodrin, which is otherwise known for providing structural support to the cell membrane, interacts directly with γ-tubulin within the γ-TuRC through a GRIP2-like motif. Turbidometric analysis of microtubule polymerization with nucleation-potent γ-TuRC isolated from HEK-293 cells that lack fodrin and the γ-TuRC from goat brain that contains fodrin shows inefficiency of the latter to promote nucleation. The involvement of fodrin was confirmed by the reduction in the microtubule polymerization efficiency of HEK-293 derived γ-TuRCs upon addition of purified brain fodrin. Thus, the interaction of fodrin with gamma-tubulin is responsible for its inhibitory effect on γ-tubulin mediated microtubule nucleation.

Functional Relevance of Missense Mutations Affecting the N-Terminal Part of Shank3 Found in Autistic Patients

Genetic defects in SHANK genes are associated with autism. Deletions and truncating mutations suggest haploinsufficiency for Shank3 as a major cause of disease which may be analyzed in appropriate Shank deficient mouse models. Here we will focus on the functional analysis of missense mutations found in SHANK genes. The relevance of most of these mutations for Shank function, and their role in autism pathogenesis is unclear. This is partly due to the fact that mutations spare the most well studied functional domains of Shank3, such as the PDZ and SAM domains, or the short proline-rich motifs which are required for interactions with postsynaptic partners Homer, Cortactin, dynamin, IRSp53 and Abi-1. One set of mutations affects the N-terminal part, including the highly conserved SPN domain and ankyrin repeats. Functional analysis from several groups has indicated that these mutations (e.g., R12C; L68P; R300C, and Q321R) interfere with the critical role of Shank3 for synapse formation. More recently the structural analysis of the SPN-ARR module has begun to shed light on the molecular consequences of mutations in the SPN of Shank3. The SPN was identified as a Ras association domain, with high affinities for GTP-bound, active forms of Ras and Rap. The two autism related mutations in this part of the protein, R12C and L68P, both abolish Ras binding. Further work is directed at identifying the consequences of Ras binding to Shank proteins at postsynaptic sites.

Bicalutamide enhances fodrin-mediated apoptosis through calpain in LNCaP

Prostate cancer is the most common cancer in men, and before it progresses and metastasizes, the anticancer drug bicalutamide is often administered to patients. Many cases of androgen-dependent prostate cancer develop resistance during treatment with bicalutamide. Therefore, the effect of bicalutamide on androgen-dependent LNCaP prostate cancer cells is of clinical interest. The aim of this study was to demonstrate the effects of the anticancer drug bicalutamide on LNCaP prostate cancer cells by using a proteomics approach. Based on the results, 314 proteins were differentially expressed between the LNCaP and LNCaP treated with bicalutamide. The apoptosis pathway associated with differentially expressed proteins was shown in the Kyoto Encyclopedia of Gene and Genome pathway mapper. The Kyoto Encyclopedia of Gene and Genome pathway mapper results revealed that the fodrin-mediated apoptosis pathway is associated with the actions of bicalutamide and Western blotting was performed to validate these results. Impact statement We studied bicalutamide's anticancer action by using proteomics. The effect of bicalutamide on androgen-exposed LNCaP cells was also studied. KEGG identified >1.8-fold differentially expressed proteins between test group cells. KEGG mapper showed fodrin-mediated apoptosis involvement in bicalutamide's action. The anticancer effects of bicalutamide, which was further confirmed using Western blotting. Therefore, this drug is a potential candidate for understanding bicalutamide's effect on LNCaP and fodrin can be used as a biomarker monitoring status in metastatic carcinoma.

The Differential Organization of F-Actin Alters the Distribution of Organelles in Cultured When Compared to Native Chromaffin Cells

Cultured bovine chromaffin cells have been used extensively as a neuroendocrine model to study regulated secretion. In order to extend such experimental findings to the physiological situation, it is necessary to study mayor cellular structures affecting secretion in cultured cells with their counterparts present in the adrenomedullary tissue. F-actin concentrates in a peripheral ring in cultured cells, as witnessed by phalloidin–rodhamine labeling, while extends throughout the cytoplasm in native cells. This result is also confirmed when studying the localization of α-fodrin, a F-actin-associated protein. Furthermore, as a consequence of this redistribution of F-actin, we observed that chromaffin granules and mitochondria located into two different cortical and internal populations in cultured cells, whereas they are homogeneously distributed throughout the cytoplasm in the adrenomedullary tissue. Nevertheless, secretion from isolated cells and adrenal gland pieces is remarkably similar when measured by amperometry. Finally, we generate mathematical models to consider how the distribution of organelles affects the secretory kinetics of intact and cultured cells. Our results imply that we have to consider F-actin structural changes to interpret functional data obtained in cultured neuroendocrine cells.

Induction of anti-Ro60/anti-La by immunisation with spectrin and induction of anti-spectrin by immunisation with Ro60 and 4-hydroxy-2-nonenal-modified Ro60 immunisation

OBJECTIVES

The Ro ribonucleoprotein particle, targeted in systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS), includes Ro60 (SSA) and La (SSA) autoantigens. Anti-Ro60 occurs in SLE and SS. The importance of α-fodrin and spectrin as well as anti-Ro and anti-fodrin/spectrin antibodies in SS and SLE, led us to hypothesise that rabbit immunisation with Ro60 or 4-hydroxy-2-nonenal-modified Ro60 would induce anti-spectrin. In addition, we hypothesised that antibodies to Ro60 and La will develop in animals immunised with spectrin.

METHODS

Two NZW rabbits each were immunised with 4-hydroxy-2-nonenal-modified Ro60 or unmodified Ro60. Methods used included ELISA, including an inside-out RBC membrane ELISA, and Crithidia lucilae assays.

RESULTS

Commercial anti-spectrin sera bound significantly to Ro60 (OD 2.6 ± 0.1), Ro60 multiple antigenic peptides (MAPs) (3 out of 21 Ro60 MAPs), La (OD 4.4±0.5), and La fragments as well as to double stranded DNA but not to BSA (OD 0.6±0.1). Anti-spectrin binding to purified spectrin could be inhibited by spectrin (>95%), and Ro60 or La (70%). When the binding of anti-spectrin was tested against a nested set of La fragments we found that a N4 fragment representing the C-terminal 250 aa (aa 159 to 408) bound the strongest (OD=4.12) followed by a N9 fragment (the C-terminal 36aa; aa373 to 408 (OD=1.36). Also, significant anti-spectrin antibody levels were induced by Ro60 and HNE-modified Ro60 immunisation.

CONCLUSIONS

We found intermolecular epitope spreading from Ro60/La to spectrin and vice versa, and this may have pathological significance in these animal models of autoimmunity.

Comprehensive survey of p94/calpain 3 substrates by comparative proteomics--possible regulation of protein synthesis by p94

Calpain represents a family of Ca(2+)-dependent cytosolic cysteine proteases found in almost all eukaryotes and some bacteria, and is involved in a variety of biological phenomena, including brain function. Several substrates of calpain are aggressively proteolyzed under pathological conditions, e.g., in neurodegenerating processes, fodrin is proteolyzed by calpain. Because very small amounts of substrate are proteolyzed by calpain under normal biological conditions, the molecular identities of calpain substrates are largely unknown. In this study, an extensive survey of the substrates of p94/calpain 3 in COS7 cells was executed using iTRAQ(TM) labeling and 2-D LC-MALDI analysis. p94 was used because: (i) several p94 splicing variants are expressed in brain tissue even though p94 itself is a skeletal-muscle-specific calpain, and (ii) it exhibits Ca(2+)-independent activity in COS cells, which makes it useful for evaluating the effects of p94 protease activity on proteins without perturbing the cells. Our approach revealed several novel protein substrates for p94, including the substrates of conventional calpains, components of the protein synthesis system, and enzymes of the glycolytic pathway. The results demonstrate the usefulness and sensitivity of this approach for mining calpain substrates. A combination of this method with other analytical methods would contribute to elucidation of the biological relevance of the calpain family.

Clinical significance of autoantibodies recognizing Sjögren's syndrome A (SSA), SSB, calpastatin and alpha-fodrin in primary Sjögren's syndrome

The aim of our study was (i) to compare the clinical and biological characteristics of 148 (137 women, 11 men) primary Sjögren's syndrome (pSS) patients at diagnosis as a function of their sex and (ii) to assess the prognostic value of anti-calpastatin and anti-alpha-fodrin autoantibodies. In addition, the presence of anti-nuclear antibodies (ANA), anti-52- and 60-kDa Sjögren's syndrome A (SSA), anti-Sjögren's syndrome B (SSB), anti-cyclic citrullinated peptide (CCP) antibodies and rheumatoid factors (RF) of IgA, IgG and IgM isotypes was sought in sera collected at pSS onset. Raynaud's syndrome, significantly more frequent in women, was the only systemic manifestation of pSS whose frequency differed significantly as a function of the patient's sex (P = 0.02). ANA (P = 0.001) and anti-60-kDa SSA autoantibodies (P = 0.03) were significantly more common in women, while men never synthesized detectable levels of anti-SSB, anti-calpastatin or IgG anti-alpha-fodrin autoantibodies. In addition, anti-CCP autoantibodies were found in low percentages of pSS patients (4% F/18% M). The absence of autoantibodies does not exclude the diagnosis of pSS in men that will be based mainly on the anatomopathological findings of a minor salivary gland biopsy. Positivity of anti-60-kDa SSA, anti-SSB, anti-calpastatin, IgA and IgG anti-alpha-fodrin antibodies is not associated with pSS clinical and biological severity.

Kinesin superfamily protein 3 (KIF3) motor transports fodrin-associating vesicles important for neurite building

Kinesin superfamily proteins (KIFs) comprise several dozen molecular motor proteins. The KIF3 heterotrimer complex is one of the most abundantly and ubiquitously expressed KIFs in mammalian cells. To unveil the functions of KIF3, microinjection of function-blocking monovalent antibodies against KIF3 into cultured superior cervical ganglion (SCG) neurons was carried out. They significantly blocked fast axonal transport and brought about inhibition of neurite extension. A yeast two-hybrid binding assay revealed the association of fodrin with the KIF3 motor through KAP3. This was further confirmed by using vesicles collected from large bundles of axons (cauda equina), from which membranous vesicles could be prepared in pure preparations. Both immunoprecipitation and immunoelectron microscopy indicated the colocalization of fodrin and KIF3 on the same vesicles, the results reinforcing the evidence that the cargo of the KIF3 motor consists of fodrin-associating vesicles. In addition, pulse-labeling study implied partial comigration of both molecules as fast flow components. Taken together, the KIF3 motor is engaged in fast axonal transport that conveys membranous components important for neurite extension.

Changes in expression of the DNA repair protein complex DNA-dependent protein kinase after ischemia and reperfusion

Reperfusion of ischemic tissue causes an immediate increase in DNA damage, including base lesions and strand breaks. Damage is reversible in surviving regions indicating that repair mechanisms are operable. DNA strand breaks are repaired by nonhomologous end joining in mammalian cells. This process requires DNA-dependent protein kinase (DNA-PK), composed of heterodimeric Ku antigen and a 460,000 Da catalytic subunit (DNA-PKcs). In this study, a rabbit spinal cord model of reversible ischemia was used to demonstrate the effect of acute CNS injury on the activity and expression of DNA-dependent protein kinase. The DNA-binding activity of Ku antigen, analyzed by an electrophoretic mobility shift assay, increased during reperfusion after a short ischemic insult (15 min of occlusion), from which the animals recover neurological function. After severe ischemic injury (60 min of occlusion) and reperfusion that results in permanent paraplegia, Ku DNA binding was reduced. Protein levels of the DNA-PK components-Ku70, Ku80, and DNA-PKcs-were monitored by immunoblotting. After 60 min of occlusion, the amount of DNA-PKcs and the enzyme poly(ADP-ribose) polymerase (PARP) decreased with the same time course during reperfusion. Concurrently 150 and 120 kDa fragments were immunostained by an anti-DNA-PKcs monoclonal antibody. This antibody was shown to cross-react with alpha-fodrin breakdown products. The 120 kDa fodrin peptide is associated with caspase-3 activation during apoptosis. Both DNA-PKcs and PARP are also substrates for caspase-3-like activities. The results are consistent with a model in which after a short ischemic insult, DNA repair proteins such as DNA-PK are activated. After severe ischemic injury, DNA damage overwhelms repair capabilities, and cell death programs are initiated.

A protein factor that inhibits ATP-dependent glutamate and gamma-aminobutyric acid accumulation into synaptic vesicles: purification and initial characterization

Glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, is transported into and stored in synaptic vesicles. We have purified to apparent homogeneity a protein from brain cytosol that inhibits glutamate and gamma-aminobutyric acid uptake into synaptic vesicles and have termed this protein "inhibitory protein factor" (IPF). IPF refers to three distinct proteins with relative molecular weights of 138,000 (IPF alpha), 135,000 (IPF beta), and 132,000 (IPF gamma), respectively. Gel filtration and sedimentation data suggest that all three proteins share an elongated structure, identical Stokes radius (60 A), and identical sedimentation coefficient (4.3 S). Using these values and a partial specific volume of 0.716 ml/g, we determined the native molecular weight for IPF alpha to be 103,000. Partial sequence analysis shows that IPF alpha is derived from alpha fodrin, a protein implicated in several diverse cellular activities. IPF alpha inhibits ATP-dependent glutamate uptake into purified synaptic vesicles with an IC50 of approximately 26 nM, while showing no ability to inhibit ATP-independent uptake at concentrations up to 100 nM. Moreover, IPF alpha inhibited neither norepinephrine uptake into chromaffin vesicles nor Na+-dependent glutamate uptake into synaptosomes. However, IPF alpha inhibited uptake of gamma-aminobutyric acid into synaptic vesicles derived from spinal cord, suggesting that inhibition may not be limited to glutamatergic systems. We propose that IPF could be a novel component of a presynaptic regulatory system. Such a system might modulate neurotransmitter accumulation into synaptic vesicles and thus regulate the overall efficacy of neurotransmission.