Lipid raft-dependent endocytosis of close homolog of adhesion molecule L1 (CHL1) promotes neuritogenesis

CHL1 plays a dual role by either promoting or inhibiting neuritogenesis. We report here that neuritogenesis-promoting ligand-dependent cell surface clustering of CHL1 induces palmitoylation and lipid raft-dependent endocytosis of CHL1. We identify βII spectrin as a binding partner of CHL1, and we show that partial disruption of the complex between CHL1 and βII spectrin accompanies CHL1 endocytosis. Inhibition of the association of CHL1 with lipid rafts by pharmacological disruption of lipid rafts or by mutation of cysteine 1102 within the intracellular domain of CHL1 reduces endocytosis of CHL1. Endocytosis of CHL1 is also reduced by nifedipine, an inhibitor of the L-type voltage-dependent Ca(2+) channels. CHL1-dependent neurite outgrowth is reduced by inhibitors of lipid raft assembly, inhibitors of voltage-dependent Ca(2+) channels, and overexpression of CHL1 with mutated cysteine Cys-1102. Our results suggest that ligand-induced and lipid raft-dependent regulation of CHL1 adhesion via Ca(2+)-dependent remodeling of the CHL1-βII spectrin complex and CHL1 endocytosis are required for CHL1-dependent neurite outgrowth.

Key amino acid residues of ankyrin-sensitive phosphatidylethanolamine/phosphatidylcholine-lipid binding site of βI-spectrin

It was shown previously that an ankyrin-sensitive, phosphatidylethanolamine/phosphatidylcholine (PE/PC) binding site maps to the N-terminal part of the ankyrin-binding domain of β-spectrin (ankBDn). Here we have identified the amino acid residues within this domain which are responsible for recognizing monolayers and bilayers composed of PE/PC mixtures. In vitro binding studies revealed that a quadruple mutant with substituted hydrophobic residues W1771, L1775, M1778 and W1779 not only failed to effectively bind PE/PC, but its residual PE/PC-binding activity was insensitive to inhibition with ankyrin. Structure prediction and analysis, supported by in vitro experiments, suggests that “opening” of the coiled-coil structure underlies the mechanism of this interaction. Experiments on red blood cells and HeLa cells supported the conclusions derived from the model and in vitro lipid-protein interaction results, and showed the potential physiological role of this binding. We postulate that direct interactions between spectrin ankBDn and PE-rich domains play an important role in stabilizing the structure of the spectrin-based membrane skeleton.

Circulating leptin and inflammatory response in esophageal cancer, esophageal cancer-related cachexia-anorexia syndrome (CAS) and non-malignant CAS of the alimentary tract

We investigated the association between esophageal cancer and cachexia-anorexia syndrome (CAS) of the alimentary tract and leptin, an adipocytokine crucial for body weight regulation, a modulator of inflammatory/immune response, implication of which in cancer and CAS development remains debatable. Circulating leptin was measured in 135 esophageal cancer patients (51 non-cachectic and 84 cachectic) and 83 controls (63 non-cachectic and 20 cachectic) and referred to cancer stage, CAS, and inflammatory and nutritional indices. Leptin was down-regulated in cancer patients and cachectic controls as compared to non-cachectic controls, with more pronounced hypoleptinemia in advanced cancers. Leptin correlated directly with BMI, TNF-alpha, albumin, and hemoglobin and indirectly with IL-6, IL-8, and hsCRP. The correlations, except for hsCRP, were more pronounced in females. BMI alone (females) and BMI and hsCRP (males) were independent predictors of leptin explaining over 60% of its variability. Following adjustment for BMI and gender, cancer-related CAS but not cancer itself negatively affected leptin. Leptin and BMI were independently associated with cancer-related and non-malignant CAS with diagnostic accuracy of 93% in identifying subjects with CAS. Pro-inflammatory, angiogenic and mitogenic properties of leptin do not seem to be important for esophageal cancer development but hypoleptinemia, independently from co-occurring reduction of adiposity, appears to be strongly associated with esophageal cancer-related CAS and non-malignant CAS of the alimentary tract.

Mitoxantrone changes spectrin-aminophospholipid interactions

Understanding drug-membrane and drug-membrane protein interactions would be a crucial step towards understanding the action and biological properties of anthracyclines, as the cell membrane with its integral and peripheral proteins is the first barrier encountered by these drugs. In this paper, we briefly describe mitoxantrone-monolayer and mitoxantrone-bilayer interactions, focusing on the effect of mitoxantrone on the interactions between erythroid or nonerythroid spectrin with phosphatidylethanolamine-enriched mono- and bilayers. We found that mitoxantrone markedly modifies the interaction of erythroid and nonerythroid spectrins with phosphatidylethanolamine/phosphatidylcholine (PE/PC) monolayers. The change in delta pi induced by spectrins is several-fold larger in the presence of 72 nM mitoxantrone than in its absence: spectrin/mitoxantrone complexes induced a strong compression of the monolayer. Spin-labelling experiments showed that spectrin/mitoxantrone complexes caused significant changes in the order parameter measured using a 5'-doxyl stearate probe in the bilayer, but they practically did not affect the mobility of 16'-doxyl stearate. These results indicate close-to-surface interactions/penetrations without significant effect on the mid-region of the hydrophobic core of the bilayer. The obtained apparent equilibrium dissociation constants indicated relatively similar mitoxantrone-phospholipid and mitoxantrone-spectrin (erythroid and nonerythroid) binding affinities. These results might in part, explain the effect of mitoxantrone on spectrin distribution in the living cells.

Evaluation of 8-hydroxydeoxyguanosine, thiobarbituric acid-reactive substances and total antioxidant status as possible disease markers in oesophageal malignancies

OBJECTIVES

Evaluation of oxidative stress and diagnostic utility of its markers in oesophageal squamous cell carcinoma (OSCC).

DESIGN

Serum 8-hydroxydeoxyguanosine, thiobarbituric acid-reactive substances (TBARS) and total antioxidant status (TAS) were measured in OSCC (n=75), non-malignant oesophageal diseases (n=30), and healthy subjects (n=79). Three months following oesophagectomy the measurements were repeated.

RESULTS

Exclusively in OSCC, 8-hydroxydeoxyguanosine and TBARS were elevated. TAS was reduced in non-malignancies compared to controls, and in OSCC compared to non-malignancies and controls. Only 8-hydroxydeoxyguanosine was associated with disease progression, lymph node involvement in particular. All indices were good indicators of cancer presence (ROC analysis) and normalized following oesophagectomy. A positive linear relationship between 8-hydroxydeoxyguanosine and TBARS, and negative non-linear between TAS and both 8-hydroxydeoxyguanosine and TBARS was demonstrated.

CONCLUSION

OSCC is associated with oxidative stress, attenuated following oesophagectomy. Consumption of serum antioxidants prevents accumulation of oxidatively modified molecules in non-malignancies. High accuracy of oxidative stress markers in indicating cancer presence warrants further investigation on their possible application as discriminatory markers and in monitoring treatment efficacy.

Structural insight into an ankyrin-sensitive lipid-binding site of erythroid beta-spectrin

It was recently shown that the region within beta-spectrin responsible for interactions with ankyrin includes a lipid-binding site which displayed sensitivity to inhibition by ankyrin. We studied its structure by constructing a series of single and double spin-labeled beta-spectrin-derived peptides and analyzing their spin-spin distances via electron paramagnetic resonance spectroscopy and the Fourier deconvolution method. The results indicate that the whole ankyrin-sensitive lipid-binding site of beta-spectrin exhibits a helical conformation revealing a distinct 3(10)-helix contribution at its N-terminus. The start of the helix was located five residues upstream along the sequence compared to the theoretical predictions. A model based on the obtained data provides direct evidence that the examined lipid-binding site is a highly amphipathic helix, which is correlated with the specific conformation of its N-terminal fragment.

Lipid-binding role of βII-spectrin ankyrin-binding domain

It is known that erythroid and non-erythroid spectrins binding of vesicles and monolayers containing PE proved sensitive to inhibition by red blood cell ankyrin. We now show that the bacterially-expressed recombinant peptides representing betaII(brain)-spectrin's ankyrin-binding domain and its truncated mutants showed lipid-binding activity, although only those containing a full-length amino terminal fragment showed high to moderate affinity towards phospholipid mono- and bilayers and a substantial sensitivity of this binding to inhibition by ankyrin. These results are in accordance with our published data on betaI-spectrin's ankyrin-binding domain [Hryniewicz-Jankowska A, et al. Mapping of ankyrin-sensitive, PE/PC mono- and bilayer binding site in erythroid beta-spectrin. Biochem J 2004;382:677-85]. Moreover, we tested also the effect of transient transfection of living cells of several cell-lines with vectors coding for GFP-conjugates including betaII and also betaI full-length ankyrin-binding domain and their truncated fragments on the membrane skeleton organization. The transfection with constructs encoding full-length ankyrin-binding domain of betaII and betaI spectrin resulted in increased aggregation of membrane skeleton and its punctate appearance in contrast to near normal appearance of membrane skeleton of cells transiently transfected with GFP control or construct encoding ankyrin-binding domain truncated at their N-terminal region. Our results therefore indicate the importance of N-terminal region for lipid-binding activity of the beta-spectrin ankyrin-binding domain and its substantial role in maintaining the spectrin-based skeleton distribution.

Oxidative DNA damage and total antioxidant status in serum of patients with esophageal squamous cell carcinoma

BACKGROUND/AIMS

Oxidative stress is connected with activation of somatic mutations and rates of cell proliferation existing in cancer tissue. High level of reactive oxygen species is a mutagenic factor for DNA damage. Antioxidants are the components of the cellular defense mechanism against reactive oxygen molecules. The aim of our study was to analyze DNA peroxidation products' concentration and total antioxidant level in serum of the patients with esophageal squamous cell carcinoma before and after esophagectomy. We examined these parameters as markers of cancer development.

METHODOLOGY

We tested 18 patients (2 woman and 16 men, mean age 59.4 years) with esophageal squamous cell cancer before and after esophagectomy and 12 healthy people as a control group. Concentrations of 8-OHdG and enzymatic antioxidants level were analyzed in serum. Data were statistically analyzed by Mann-Whitney test.

RESULTS

We observed statistically significant higher concentrations of 8-OHdG and significant lower levels of enzymatic antioxidants in the patients with cancer in comparison to the control group. After esophagectomy we observed normalization of these parameters. In four patients the level of total antioxidants was low and 8-OHdG concentration was high during the whole time of treatment. These patients had disease progression.

CONCLUSIONS

Estimation of serum 8-OHdG concentration and total antioxidant status may be helpful for monitoring cancer therapy in patients with esophageal squamous cell cancer.

Spectrin-phospholipid interactions. Existence of multiple kinds of binding sites?

The object of this paper is to review briefly the studies on the interactions of erythroid and non-erythroid spectrins with lipids in model and natural membranes. An important progress on the identification of lipid-binding sites has recently been made although many questions remain still unanswered. In particular, our understanding of the physiological role of such interactions is still limited. Another important issue is the occurrence of spectrins in membrane rafts, how they are attached to the raft and what is their function in rafts.

Cholesterol affects spectrin–phospholipid interactions in a manner different from changes resulting from alterations in membrane fluidity due to fatty acyl chain composition

We previously showed that erythrocyte and brain spectrins bind phospholipid vesicles and monolayers prepared from phosphatidylethanolamine and phosphatidylserine and their mixtures with phosphatidylcholine (Review: A.F. Sikorski, B. Hanus-Lorenz, A. Jezierski, A. R. Dluzewski, Interaction of membrane skeletal proteins with membrane lipid domain, Acta Biochim. Polon. 47 (2000) 565). Here, we show how changes in the fluidity of the phospholipid monolayer affect spectrin-phospholipid interaction. The presence of up to 10%-20% cholesterol in the PE/PC monolayer facilitates the penetration of the monolayer by both types of spectrin. For monolayers constructed from mixtures of PI/PC and cholesterol, the effect of spectrins was characterised by the presence of two maxima (at 5 and 30% cholesterol) of surface pressure for erythroid spectrin, and a single maximum (at 20% cholesterol) for brain spectrin. The binding assay results indicated a small but easily detectable decrease in the affinity of erythrocyte spectrin for FAT-liposomes prepared from a PE/PC mixture containing cholesterol, and a 2- to 5-fold increase in maximal binding capacity (B(max)) depending on the cholesterol content. On the other hand, the results from experiments with a monolayer constructed from homogenous synthetic phospholipids indicated an increase in deltapi change with the increase in the fatty acyl chain length of the phospholipids used to prepare the monolayer. This was confirmed by the results of a pelleting experiment. Adding spectrins into the subphase of raft-like monolayers constructed from DOPC, SM and cholesterol (1/1/1) induced an increase in surface pressure. The deltapi change values were, however, much smaller than those observed in the case of a natural PE/PC (6/4) monolayer. An increased binding capacity for spectrins of liposomes prepared from a "raft-like" mixture of lipids could also be concluded from the pelleting assay. In conclusion, we suggest that the effect of membrane lipid fluidity on spectrin-phospholipid interactions is not simple but depends on how it is regulated, i.e., by cholesterol content or by the chemical structure of the membrane lipids.

Protein 4.1, a component of the erythrocyte membrane skeleton and its related homologue proteins forming the protein 4.1/FERM superfamily

The review is focused on the domain structure and function of protein 4.1, one of the proteins belonging to the membrane skeleton. The protein 4.1 of the red blood cells (4.1R) is a multifunctional protein that localizes to the membrane skeleton and stabilizes erythrocyte shape and membrane mechanical properties, such as deformability and stability, via lateral interactions with spectrin, actin, glycophorin C and protein p55. Protein 4.1 binding is modulated through the action of kinases and/or calmodulin-Ca2+. Non-erythroid cells express the 4.1R homologues: 4.1G (general type), 4.1B (brain type), and 4.1N (neuron type), and the whole group belongs to the protein 4.1 superfamily, which is characterized by the presence of a highly conserved FERM domain at the N-terminus of the molecule. Proteins 4.1R, 4.1G, 4.1N and 4.1B are encoded by different genes. Most of the 4.1 superfamily proteins also contain an actin-binding domain. To date, more than 40 members have been identified. They can be divided into five groups: protein 4.1 molecules, ERM proteins, talin-related molecules, protein tyrosine phosphatase (PTPH) proteins and NBL4 proteins. We have focused our attention on the main, well known representatives of 4.1 superfamily and tried to choose the proteins which are close to 4.1R or which have distinct functions. 4.1 family proteins are not just linkers between the plasma membrane and membrane skeleton; they also play an important role in various processes. Some, such as focal adhesion kinase (FAK), non-receptor tyrosine kinase that localizes to focal adhesions in adherent cells, play the role in cell adhesion. The other members control or take part in tumor suppression, regulation of cell cycle progression, inhibition of cell proliferation, downstream signaling of the glutamate receptors, and establishment of cell polarity; some are also involved in cell proliferation, cell motility, and/or cell-to-cell communication.

[Abnormal metabolism of triglycerides fractions in chronic pancreatitis and results after the operation treatment]

This study was undertaken to determine how fats digestion processes were damaged due to chronic pancreatitis, and identify, whether lipid metabolism improved after surgical treatment the patients with chronic pancreatitis. Total lipids, triglycerides, diglycerides and free fatty acids levels in serum and stool were analysed, using chemical tests, thin-layer chromatography and electrophoresis of serum lipoproteins. The patients before the operations showed higher total lipids and triglycerides concentrations, and lower concentrations of diglycerides and free fatty acids in stool. These patients had high triglycerides, chylomicrons, VLDL, LDL-CH concentrations, and low-diglycerides, free fatty acids, HDL-CH concentrations in serum. These data were statistically significant. After the operations and substitution therapy it was observed normalization of the total lipids and lipids fractions levels in stool and in serum. Concentrations of LDL-CH and HDL-CH fractions were irregular. We conclude, that these lipids parameters could be used in diagnosing and monitoring the results of chronic pancreatitis surgical treatment.

Mapping of an ankyrin-sensitive, phosphatidylethanolamine/phosphatidylcholine mono- and bi-layer binding site in erythroid beta-spectrin

It has been shown previously that binding of vesicles and monolayers containing PE (phosphatidylethanolamine) by either erythroid or non-erythroid spectrin proved sensitive to inhibition by purified erythrocyte ankyrin. We tested the lipid-binding affinities of the purified ankyrin-binding domain of beta-spectrin and of its truncated mutants in four ways, by analysing: (1) penetration of 'loose' PE/PC (phosphatidylcholine) monolayers; (2) binding to liposomes in suspension; (3) competition with spectrin for liposomes; and (4) binding of a PE/PC monolayer in a surface plasmon resonance system. The results obtained indicated that the full-length ankyrin-binding domain bound PE/PC mono- and bi-layers with moderate affinity, penetrated monolayers and competed with spectrin for liposomes. Moreover, its truncated mutants that retained the N-terminal part, in contrast with those lacking eight or 38 N-terminal residues (which bound lipid mono- and bi-layers with lower affinity), bound PE/PC mono- and bi-layers with an affinity and capacity comparable with those of the full-length ankyrin-binding domain, and this activity was inhibited by purified erythrocyte ankyrin. The full-length domain, in contrast with the mutant lacking 38 N-terminal residues, induced a small increase in the fluidity of PE/PC membranes when probed with 5'-doxyl stearate, similar to the effect of purified spectrin. Therefore we conclude that the binding site for PE-rich lipids, which is sensitive to ankyrin inhibition, is located in a 38-residue N-terminal fragment of the beta-spectrin ankyrin-binding domain, and that the first eight residues play a key role in this activity.

Occurrence of lipid receptors inferred from brain and erythrocyte spectrins binding NaOH-extracted and protease-treated neuronal and erythrocyte membranes

It was previously shown in model systems that brain spectrin binds membrane phospholipids. In the present study, we analysed binding of isolated brain spectrin and red blood cell spectrin to red blood or neuronal membranes which had been treated as follows: (1). extracted with low ionic-strength solution, (2). the above membranes extracted with 0.1 M NaOH, and (3). membranes treated as above, followed by protease treatment and re-extraction with 0.1 M NaOH. It was found that isolated, NaOH-extracted, protease-treated neuronal and red blood cell membranes bind brain and red blood cell spectrin with moderate affinities similar to those obtained in model phospholipid membrane-spectrin interaction experiments. Moreover, this binding was competitively inhibited by liposomes prepared from membrane lipids. The presented results indicate the occurrence of receptor sites for spectrins that are extraction- and protease-resistant, therefore most probably of lipidic nature, in native membranes.

Brain spectrin exerts much stronger effect on anionic phospholipid monolayers than erythroid spectrin

Red blood cell spectrin and its nonerythroid analogues are linked to integral proteins of the membrane by several skeletal protein receptors, such as ankyrin and protein 4.1 together with p55. However, there are also many reasons for believing that they are insufficient to engender all the properties that characterise the native membrane. Therefore, we are concerned with the mechanism by which brain spectrin interacts with phospholipids of the membrane bilayer. Brain and erythrocyte spectrin were shown previously to bind phospholipid vesicles as well as monolayers prepared from aminophospholipids: phosphatidylethanolamine and phosphatidylserine and their mixtures with phosphatidylcholine (PC). In the present study, it is shown that brain spectrin binds to monolayers prepared from anionic phospholipids, such as phosphatidylinositol (PI), phosphatidic acid (PA), phosphatidyl glycerol, diphosphatidylglycerol, and their mixtures with PC. Brain spectrin injected into the subphase to reach nanomolar concentration induced a substantial increase in the surface pressure of monolayers prepared from the phospholipids and their mixtures mentioned above, possibly by penetrating them. This effect is stronger in the case of monolayers prepared from anionic phospholipids alone and weaker when monolayers were prepared from mixtures with PC. The weakest effect was observed in the case of phosphatidylinositol-4,5-bisphosphate monolayers. An interaction of brain spectrin with monolayers prepared from anionic phospholipids (PI/PC 7:3 and PA/PC 7:3) was inhibited (PI/PC much stronger than PA/PC) by purified erythrocyte ankyrin, which indicates that the binding site for those lipids is located in the beta-subunit, possibly in, or in close proximity of, the ankyrin-binding site. In contrast, erythrocyte spectrin injected into the subphase induced a change in the surface pressure of monolayers prepared from anionic phospholipids, which was equal or smaller than the value of surface pressure change induced by protein without a monolayer. This effect was different from what had been observed previously for monolayers prepared from aminophospholipids and their mixtures with PC, and from the data for nonerythroid spectrin presented here.

Brain spectrin (fodrin) interacts with phospholipids as revealed by intrinsic fluorescence quenching and monolayer experiments

We demonstrate that phospholipid vesicles affect the intrinsic fluorescence of isolated brain spectrin. In the present studies we tested the effects of vesicles prepared from phosphatidylcholine (PtdCho) alone, in addition to vesicles containing PtdCho mixed with other phospholipids [phosphatidylethanolamine (PtdEtn) and phosphatidylserine] as well as from total lipid mixture extracted from brain membrane. The largest effect was observed with PtdEtn/PtdCho (3:2 molar ratio) vesicles; the effect was markedly smaller when vesicles were prepared from egg yolk PtdCho alone. Brain spectrin injected into a subphase induced a substantial increase in the surface pressure of monolayers prepared from phospholipids. Results obtained with this technique indicated that the largest effect is again observed with monolayers prepared from a PtdEtn/PtdCho mixture. The greatest effect was observed when the monolayer contained 50-60% PtdEtn in a PtdEtn/PtdCho mixture. This interaction occurred at salt and pH optima close to physiological conditions (0.15 M NaCl, pH7.5). Experiments with isolated spectrin subunits indicated that the effect of the beta subunit on the monolayer surface pressure resembled that measured with the whole molecule. Similarly to erythrocyte spectrin-membrane interactions, brain spectrin interactions with PtdEtn/PtdCho monolayer were competitively inhibited by isolated erythrocyte ankyrin. This also suggests that the major phospholipid-binding site is located in the beta subunit and indicates the possible physiological significance of this interaction.

Interaction of brain spectrin (fodrin) with phospholipids

Binding of brain spectrin to frozen and thawed liposomes was studied, using a pelleting assay, as a function of lipid composition. Saturable binding was observed for all lipid mixtures that included aminophospholipids, as well as for the total lipid of synaptic plasma membranes. Binding was strong and saturable, with dissociation constants in the nanomolar range. There were two pH optima at ca. 6.0 and 7.5 and a sharp ionic strength optimum, corresponding to physiological solvent conditions. No competition could be detected with extraneous globular proteins, serum albumin, and hemoglobin. The results imply a strong, direct interaction between brain spectrin and the neuronal plasma membrane in the cell.