Intracellular proteinases of invertebrates: calcium-dependent and proteasome/ubiquitin-dependent systems

Fungal Secondary Metabolites as Inhibitors of the Ubiquitin-Proteasome System

The ubiquitin–proteasome system (UPS) is the major non-lysosomal pathway responsible for regulated degradation of intracellular proteins in eukaryotes. As the principal proteolytic pathway in the cytosol and the nucleus, the UPS serves two main functions: the quality control function (i.e., removal of damaged, misfolded, and functionally incompetent proteins) and a major regulatory function (i.e., targeted degradation of a variety of short-lived regulatory proteins involved in cell cycle control, signal transduction cascades, and regulation of gene expression and metabolic pathways). Aberrations in the UPS are implicated in numerous human pathologies such as cancer, neurodegenerative disorders, autoimmunity, inflammation, or infectious diseases. Therefore, the UPS has become an attractive target for drug discovery and development. For the past two decades, much research has been focused on identifying and developing compounds that target specific components of the UPS. Considerable effort has been devoted to the development of both second-generation proteasome inhibitors and inhibitors of ubiquitinating/deubiquitinating enzymes. With the feature of unique structure and bioactivity, secondary metabolites (natural products) serve as the lead compounds in the development of new therapeutic drugs. This review, for the first time, summarizes fungal secondary metabolites found to act as inhibitors of the UPS components.

Acquisition of obligate mutualist symbionts during the larval stage is not beneficial for a coral host

Theory suggests that the direct transmission of beneficial endosymbionts (mutualists) from parents to offspring (vertical transmission) in animal hosts is advantageous and evolutionarily stable, yet many host species instead acquire their symbionts from the environment (horizontal acquisition). An outstanding question in marine biology is why some scleractinian corals do not provision their eggs and larvae with the endosymbiotic dinoflagellates that are necessary for a juvenile's ultimate survival. We tested whether the acquisition of photosynthetic endosymbionts (family Symbiodiniaceae) during the planktonic larval stage was advantageous, as is widely assumed, in the ecologically important and threatened Caribbean reef-building coral Orbicella faveolata. Following larval acquisition, similar changes occurred in host energetic lipid use and gene expression regardless of whether their symbionts were photosynthesizing, suggesting the symbionts did not provide the energetic benefit characteristic of the mutualism in adults. Larvae that acquired photosymbionts isolated from conspecific adults on their natal reef exhibited a reduction in swimming, which may interfere with their ability to find suitable settlement substrate, and also a decrease in survival. Larvae exposed to two cultured algal species did not exhibit differences in survival, but decreased their swimming activity in response to one species. We conclude that acquiring photosymbionts during the larval stage confers no advantages and can in fact be disadvantageous to this coral host. The timing of symbiont acquisition appears to be a critical component of a host's life history strategy and overall reproductive fitness, and this timing itself appears to be under selective pressure.

Immunoproteasome Subunits Are Required for CD8+ T Cell Function and Host Resistance to Brucella abortus Infection in Mice

The immunoproteasome is a specific proteasome isoform composed of three subunits, termed β1i, β2i, and β5i. Its proteolytic activity enhances the quantity and quality of peptides to be presented by major histocompatibility complex class I (MHC-I) molecules to CD8⁺ T cells. However, the role of the combined deficiency of the three immunoproteasome subunits in protective immunity against bacterial pathogens has not been investigated. In this study, we addressed the role of the immunoproteasome during infection by Brucella abortus, an intracellular bacterium that requires CD8⁺ T cell responses for the control of infection. Here, we demonstrate that immunoproteasome triple-knockout (TKO) mice were more susceptible to Brucella infection. This observed susceptibility was accompanied by reduced interferon gamma (IFN-γ) production by mouse CD4⁺ and CD8⁺ T lymphocytes. Moreover, the absence of the immunoproteasome had an impact on MHC-I surface expression and antigen presentation by dendritic cells. CD8⁺ T cell function, which plays a pivotal role in B. abortus immunity, also presented a partial impairment of granzyme B expression and, consequently, reduced cytotoxic activity. In conclusion, these results strongly suggest that immunoproteasome subunits are important components in host resistance to B. abortus infection by impacting both the magnitude and quality of CD8⁺ T cell responses.

The proteasomes of two marine decapod crustaceans, European lobster (Homarus gammarus) and Edible crab (Cancer pagurus), are differently impaired by heavy metals

The intracellular ubiquitin-proteasome system is a key regulator of cellular processes involved in the controlled degradation of short-living or malfunctioning proteins. Certain diseases and cellular dysfunctions are known to arise from the disruption of proteasome pathways. Trace metals are recognized stressors of the proteasome system in vertebrates and plants, but their effects on the proteasome of invertebrates are not well understood. Since marine invertebrates, and particularly benthic crustaceans, can be exposed to high metal levels, we studied the effects of in vitro exposure to Hg(2+), Zn(2+), Cu(2+), and Cd(2+) on the activities of the proteasome from the claw muscles of lobsters (Homarus gammarus) and crabs (Cancer pagurus). The chymotrypsin like activity of the proteasome of these two species showed different sensitivity to metals. In lobsters the activity was significantly inhibited by all metals to a similar extent. In crabs the activities were severely suppressed only by Hg(2+) and Cu(2+) while Zn(2+) had only a moderate effect and Cd(2+) caused almost no inhibition of the crab proteasome. This indicates that the proteasomes of both species possess structural characteristics that determine different susceptibility to metals. Consequently, the proteasome-mediated protein degradation in crab C. pagurus may be less affected by metal pollution than that of the lobster H. gammarus.

Biochemical markers of pollutant responses in macrozoobenthos from the White Sea: intracellular proteolysis

Coastal environments of Kandalaksha Gulf in the White Sea (Russia) despite nature conservation efforts are heavily influenced by human activities. Biological effects of complex environmental pollution, including organic substances, heavy metals, and oil hydrocarbons, were assessed in widely distributed marine invertebrates, Gammarus duebeni (Crustacea, Amphipoda) and Mytilus edulis (Mollusca, Bivalvia), collected from a series of anthropogenically-impacted areas and distanced reference sites in Kandalaksha Gulf. The parameters of intracellular protein degradation pathways such as cytosol calpain system and lysosomal cathepsins B (CatB) and cathepsin D (CatD) were studied. The response reactions observed in invertebrates vary in specificity and ranged from adaptive to destructive depending on the total contaminant level and the nature of predominant pollutant. The ecological relevance of studied parameters as biomarkers was confirmed by their ability to indicate both expose to pollutants and adverse effects at the organism level.

Characterization of proteolytic activities during intestinal regeneration of the sea cucumber, Holothuria glaberrima

Proteolysis carried out by different proteases control cellular processes during development and regeneration. Here we investigated the function of the proteasome and other proteases in the process of intestinal regeneration using as a model the sea cucumber Holothuria glaberrima. This echinoderm possesses the ability to regenerate its viscera after a process of evisceration. Enzymatic activity assays showed that intestinal extracts at different stages of regeneration possessed chymotrypsin-like activity. This activity was inhibited by i) MG132, a reversible inhibitor of chymotrypsin and peptidylglutamyl peptidase hydrolase (PGPH) activities of the proteasome, ii) E64d, a permeable inhibitor of cysteine proteases and iii) TPCK, a serine chymotrypsin inhibitor, but not by epoxomicin, an irreversible and potent inhibitor of all enzymatic activities of the proteasome. To elucidate the role which these proteases might play during intestinal regeneration, we carried out in vivo experiments injecting MG132, E64d and TPCK into regenerating animals. The results showed effects on the size of the regenerating intestine, cell proliferation and collagen degradation. These findings suggest that proteolysis by several proteases is important in the regulation of intestinal regeneration in H. glaberrima.

[Proteases of calpain family in water invertebrates and fish]

The activity of Ca2+-dependent proteases, or calpains (EC 3.4.22.17), in a wide range of aquatic invertebrates (Oligochaeta, Hirudinea, Crustacea, Insecta, Gastropoda, Bivalvia) and vertebrates (Osteichthyes) was estimated. Detected molecular properties ofcalpains from the tissues of different species allow considering the complication of their structural organization and regulatory mechanisms between invertebrates and vertebrates in comparative-evolutionary aspect. Certain conclusions can be drawn about changes in the functional role of this proteolytic system in the cell metabolism.

Transcriptome comparison of susceptible and resistant wheat in response to powdery mildew infection

Powdery mildew (Pm) caused by the infection of Blumeria graminis f. sp. tritici (Bgt) is a worldwide crop disease resulting in significant loss of wheat yield. To profile the genes and pathways responding to the Bgt infection, here, using Affymetrix wheat microarrays, we compared the leaf transcriptomes before and after Bgt inoculation in two wheat genotypes, a Pm-susceptible cultivar Jingdong 8 (S) and its near-isogenic line (R) carrying a single Pm resistant gene Pm30. Our analysis showed that the original gene expression status in the S and R genotypes of wheat was almost identical before Bgt inoculation, since only 60 genes exhibited differential expression by P = 0.01 cutoff. However, 12 h after Bgt inoculation, 3014 and 2800 genes in the S and R genotype, respectively, responded to infection. A wide range of pathways were involved, including cell wall fortification, flavonoid biosynthesis and metabolic processes. Furthermore, for the first time, we show that sense-antisense pair genes might be participants in wheat-powdery mildew interaction. In addition, the results of qRT-PCR analysis on several candidate genes were consistent with the microarray data in their expression patterns. In summary, this study reveals leaf transcriptome changes before and after powdery mildew infection in wheat near-isogenic lines, suggesting that powdery mildew resistance is a highly complex systematic response involving a large amount of gene regulation.

Pitfalls in invertebrate proteasome assays

The ubiquitin-proteasome system controls a variety of essential intracellular processes through directed protein turnover. The invertebrate proteasome has recently gained increasing interest with respect to central physiological processes and pathways in different taxa. A pitfall in proteasome-activity assays, represented by the trypsin-like, the chymotrypsin-like, or the caspase-like site, lies in the fact that most commonly-used experimental substrates are susceptible to degradation by non-proteasomal proteolytic enzymes, which can lead to erroneous interpretation of activity data obtained. Through the use of a proteasome-specific inhibitor, epoxomicin, we could show that the shares of proteasomal and non-proteasomal activities in the degradation of a model polypeptide substrate for the chymotrypsin-like activity vary considerably between invertebrate taxa. Crustacean muscle tissue and hemocytes showed almost exclusively proteasomal activity. In yeast, approximately 90% of total proteolytic activity can be attributed to the proteasome. In contrast, proteasomal activity comprises only 20-60% of the total proteolytic activity in bivalve tissues. These results reveal that, without verification of the shares of proteasomal and non-proteasomal activities in crude extracts through the use of highly specific inhibitors, common proteasomal enzyme assays should be used and interpreted with caution.

The autoimmune disease-associated PTPN22 variant promotes calpain-mediated Lyp/Pep degradation associated with lymphocyte and dendritic cell hyperresponsiveness

A variant of the PTPN22-encoded Lyp phosphatase (Lyp620W) confers risk for autoimmune disease, but the mechanisms underlying this association remain unclear. We show here that mice expressing the Lyp variant homolog Pep619W manifest thymic and splenic enlargement accompanied by increases in T-cell number, activation and positive selection and in dendritic- and B-cell activation. Although Ptpn22 (Pep) transcript levels were comparable in Pep619W and wild-type Pep619R mice, Pep protein levels were dramatically reduced in the mutant mice, with Pep619W protein being more rapidly degraded and showing greater association with and in vitro cleavage by calpain 1 than Pep619R. Similarly, levels of the Lyp620W variant were decreased in human T and B cells, and its calpain binding and cleavage were increased relative to wild-type Lyp620R. Thus, calpain-mediated degradation with consequently reduced Lyp/Pep expression and lymphocyte and dendritic cell hyperresponsiveness represents a mechanism whereby Lyp620W may increase risk for autoimmune disease.

Participation of the sperm proteasome during in vitro fertilisation and the acrosome reaction in cattle

In this work, we have investigated the role of the bovine sperm proteasome during in vitro fertilisation (IVF) and the acrosome reaction (AR). Motile spermatozoa, obtained by a swim-up method in Sperm-Talp medium, were capacitated for 3.5 h and incubated in the presence or absence of the specific proteasome inhibitor epoxomicin for 30 and 60 min. Then, the spermatozoa were co-incubated with mature bovine cumulus oocytes and after 48 h the cleavage rate of inseminated oocytes was evaluated. In addition, we evaluated the participation of the sperm proteasome during the progesterone-induced AR. Capacitated spermatozoa were incubated for 30 min with or without epoxomicin, then progesterone was added and the ARs were evaluated using the dual fluorescent staining technique 'Hoechst and chlortetracycline'. The results indicate that the proteasome inhibitor decreased the cleavage rate of oocytes inseminated with treated spermatozoa. In addition, acrosomal exocytosis levels were statistically significantly higher in the samples treated with the AR inducer progesterone than in control samples in the absence of the inducer. However, the progesterone-induced AR was significantly reduced by previous treatment of the spermatozoa with epoxomicin (P < 0.001). These observations indicate that the bovine sperm proteasome participates in the IVF and AR processes.

Molt cycle regulation of protein synthesis in skeletal muscle of the blackback land crab, Gecarcinus lateralis, and the differential expression of a myostatin-like factor during atrophy induced by molting or unweighting

In decapod crustaceans, claw muscle undergoes atrophy in response to elevated ecdysteroids while thoracic muscle undergoes atrophy in response to unweighting. The signaling pathways that regulate muscle atrophy in crustaceans are largely unknown. Myostatin is a negative regulator of muscle growth in mammals, and a myostatin-like cDNA is preferentially expressed in muscle of the land crab, Gecarcinus lateralis (Gl-Mstn). Contrary to prediction, levels of Gl-Mstn mRNA decreased dramatically in both the claw closer and weighted thoracic muscles when molting was induced by either eyestalk ablation (ESA) or multiple limb autotomy (MLA). However, the effect of molt induction was greater in the claw muscle. By late premolt, Gl-Mstn mRNA in the claw muscle decreased 81% and 94% in ESA and MLA animals, respectively, and was negatively correlated with ecdysteroids. Gl-Mstn mRNA in thoracic muscle decreased 68% and 82% in ESA and MLA animals, respectively, but was only weakly correlated with ecdysteroid. Claw and thoracic muscles also differed to varying extents in the expression of ecdysteroid receptor (Gl-EcR and Gl-RXR), elongation factor-2 (Gl-EF-2), and calpain T (Gl-CalpT) in response to molt induction, but levels of the four transcripts were not correlated with ecdysteroid. The downregulation of Gl-Mstn expression in premolt claw muscle coincided with 11- and 13-fold increases in protein synthesis in the myofibrillar and soluble protein fractions, respectively. Furthermore, the rate of the increase in the synthesis of soluble proteins was greater than that of myofibrillar proteins during early premolt (1.4:1, soluble:myofibrillar), but the two were equivalent during late premolt. By contrast, Gl-Mstn mRNA increased 3-fold and Gl-CalpT mRNA decreased 40% in unweighted thoracic muscle; there was little or no effect on Gl-EF-2, Gl-EcR, and Gl-RXR mRNA levels. These data indicate that Gl-Mstn expression is negatively regulated by both ecdysteroids and load-bearing contractile activity. The downregulation of Gl-Mstn in claw muscle may induce the elevated protein turnover associated with remodeling of the contractile apparatus during molt-induced atrophy. The upregulation of Gl-Mstn in unweighted thoracic muscle suggests that this factor is also involved in disuse atrophy when hemolymph ecdysteroid levels are low.

Proteomic identification of differentially expressed and phosphorylated proteins in epidermis involved in larval-pupal metamorphosis of Helicoverpa armigera

BACKGROUND

Metamorphosis is an important process in the life cycle of holometabolous insects and is regulated by insect hormones. During metamorphosis, the epidermis goes through a significant transformation at the biochemical and molecular levels.

RESULTS

To identify proteins and phosphoproteins involved in this process, we separated and compared epidermal protein profiles between feeding larvae and metamorphically committed larvae using two-dimensional gel electrophoresis and Pro-Q Diamond Phosphoprotein Staining. Sixty-one spots showing differential expression and/or phosphorylation were analyzed by mass spectrometry and eighteen proteins were proved related to larval-pupal transformation. Eight of them were further examined at the mRNA level by Reverse Transcription Polymerase Chain Reaction (RT-PCR) and two of them were examined at the protein level by Western blot. Calponin was highly expressed in the metamorphic epidermis and phosphorylated by protein kinase C.

CONCLUSION

Our results suggest that the expression and phosphorylation of these proteins may play important roles in coordinating the biochemical processes involved in larval-pupal metamorphosis.

Sperm-surface ATP in boar spermatozoa is required for fertilization: relevance to sperm proteasomal function

Extracellular ATP has been implicated in a number of cellular events, including mammalian sperm function. The complement of ATP-dependent sperm proteins includes six subunits of the 26S proteasome, a multi-subunit protease specific to ubiquitinated substrate-proteins. Proteolysis of ubiquitinated proteins by the 26S proteasome is necessary for the success of mammalian fertilization, including but not limited to acrosomal exocytosis (AE) and sperm-zona pellucida (ZP) penetration. The 26S proteasome is uniquely present on the sperm acrosomal surface during mammalian, ascidian, and invertebrate fertilization. The proteasome is a multi-subunit protease complex of approximately 2 MDa composed of the 19S regulatory complex and a 20S proteolytic core. Integrity of the 19S complex is maintained by six 19S ATPase subunits (PSMC1 through PSMC6). Consequently, we hypothesized that fertilization will be blocked by the depletion of sperm-surface associated ATP (ssATP). Depletion of ssATP by the Solanum tuberosum apyrase, a 49 kDa, non-cell permeant enzyme, significantly reduced the ATP content measured by an adapted luminescence-ATP assay from which all permeabilizing agents were excluded. Addition of active apyrase to porcine in vitro fertilization (IVF) medium caused a concentration dependent reduction in the overall fertilization rate. No such outcomes were observed in control groups using heat-inactivated apyrase. Apyrase treatment altered the band pattern of 19S ATPase subunits PSMC1 (Rpt2) and PSMC4 (Rpt3) in Western blotting, suggesting that it had an effect on the integrity of the sperm proteasomal 19S complex. Apyrase only altered the proteasomal core activities slightly, since these activities are not directly dependent on external ATP. In contrast, sperm treatment with MG132, a specific inhibitor of the proteasomal core chymotrypsin-like activity, inhibited the target proteolytic activity, but also induced a compensatory elevation in proteasomal peptidyl-glutamyl peptide hydrolase activity. Altogether, the present data provide an important missing piece of evidence in support of the ssATP-dependent, proteasomal-proteolytic model of sperm-ZP interactions.

Participation of the human sperm proteasome in the capacitation process and its regulation by protein kinase A and tyrosine kinase

The proteasome is a multicatalytic cellular complex present in human sperm that plays a significant role during several steps of mammalian fertilization. Here, we present evidence that the proteasome is involved in human sperm capacitation. Aliquots of highly motile sperm were incubated with proteasome inhibitors MG132 or epoxomicin. The percentage of capacitated sperm, the chymotrypsin-like activity of the proteasome, cAMP content, and the pattern of protein phosphorylation were assayed by using the chlortetracycline hydrochloride assay, a fluorogenic substrate, the cAMP enzyme immunoassay kit, and Western blot analysis, respectively. Our results indicate that treatment of sperm with proteasome inhibitors blocks the capacitation process, does not alter cAMP concentration, and changes the pattern of protein phosphorylation. To elucidate how proteasome activity is regulated during capacitation, sperm were incubated with: 1) tyrosine kinase (TK) inhibitors (genistein or herbimycin A); 2) protein kinase (PK) A inhibitors or activators (H89 and Rp-cAMPS, and 8-Br-cAMP, respectively); or 3) PKC inhibitors (tamoxifen or staurosporin) at different capacitation times. The chymotrypsin-like activity and degree of phosphorylation of the proteasome were then assayed. The results indicate that sperm treatment with TK and PKA inhibitors significantly decreases the chymotrypsin-like activity of the proteasome during capacitation. Immunoprecipitation and Western blot results suggest that the proteasome is phosphorylated during capacitation in a TK- and PKA-dependent pathway. In conclusion, we suggest that the sperm proteasome participates in the capacitation process, and that its activity is modulated by PKs.

Extracellular, circulating proteasomes and ubiquitin - incidence and relevance

The ubiquitin-proteasome system is the major pathway for intracellular protein degradation and is also deeply involved in the regulation of most basic cellular processes. Its proteolytic core, the 20S proteasome, has found to be attached also to the cell plasma membrane and certain observations are interpreted as to suggest that they may be released into the extracellular medium, e.g. in the alveolar lining fluid, epididymal fluid and possibly during the acrosome reaction. Proteasomes have also been detected in normal human blood plasma and designated circulating proteasomes; these have a comparatively low specific activity, a distinct pattern of subtypes and their exact origin is still enigmatic. In patients suffering from autoimmune diseases, malignant myeloproliferative syndromes, multiple myeloma, acute and chronic lymphatic leukaemia, solid tumour, sepsis or trauma, respectively, the concentration of circulating proteasomes has been found to be elevated, to correlate with the disease state and has even prognostic significance. Similarly, ubiquitin has been discovered as a normal component of human blood and seminal plasma and in ovarian follicular fluid. Increased concentrations were measured in diverse pathological situations, not only in blood plasma but also in cerebrospinal fluid, where it may have neuroprotective effects. As defective spermatozoa are covered with ubiquitin in the epididymal fluid, extracellular ubiquitination is proposed to be a mechanism for quality control in spermatogenesis. Growing evidence exists also for a participation of extracellular proteasomes and ubiquitin in the fertilization process.

cDNA cloning, characterization, and developmental expression of the 20S proteasome alpha5 subunit in the Mediterranean fruit fly Ceratitis capitata

In the present study, we report the cDNA cloning, characterization, and developmental expression of the 20S proteasome alpha5 subunit from the Mediterranean fruit fly Ceratitis capitata (medfly). Using an RT-PCR fragment that corresponds to the amino-terminal region of the Drosophila melanogaster 20S proteasome alpha5 subunit, we isolated a 987-bp cDNA that encodes the complete coding region of the medfly ortholog, which was named CcPSMA5. CcPSMA5 consists of 241 amino acids and has a predicted molecular weight of 26.4 kDa and pI 4.75. Comparison of the CcPSMA5 amino acid sequence with the sequences of all known 20S proteasome alpha5 subunits from different organisms indicated that the medfly 20S proteasome alpha5 subunit has the strongest homology to that of Drosophila. In situ hybridization showed that the CcPSMA5 gene is mapped in the region 44B of chromosome 4. Northern blot hybridization analysis showed that the CcPSMA5 mRNA has a size of approximately 1.2 kb. High levels of the CcPSMA5 mRNA were detected in freshly laid eggs, indicating that they were maternally deposited. The mRNA expression pattern during medfly development suggests that the CcPSMA5 gene is upregulated before mid-embryogenesis and at the onset of metamorphosis.

Parasites, proteomics and performance: effects of gregarine gut parasites on dragonfly flight muscle composition and function

In previous work, we found that dragonflies infected with gregarine gut parasites have reduced muscle power output, loss of lipid oxidation in their flight muscles, and a suite of symptoms similar to mammalian metabolic syndrome. Here, we test the hypothesis that changes in muscle protein composition underlie the observed changes in contractile performance. We found that gregarine infection was associated with a 10-fold average reduction in abundance of a approximately 155 kDa fragment of muscle myosin heavy chain (MHC; approximately 206 kDa intact size). Insect MHC gene sequences contain evolutionarily conserved amino acid motifs predicted for calpain cleavage, and we found that calpain digestion of purified dragonfly MHC produced a peptide of approximately 155 kDa. Thus, gut parasites in dragonflies are associated with what appears to be a reduction in proteolytic degradation of MHC. MHC155 abundance showed a strong negative relationship to muscle power output in healthy dragonflies but either no relationship or a weakly positive relationship in infected dragonflies. Troponin T (TnT) protein isoform profiles were not significantly different between healthy and infected dragonflies but whereas TnT isoform profile was correlated with power output in healthy dragonflies, there was no such correlation in infected dragonflies. Multivariate analyses of power output based on MHC155 abundance and a principal component of TnT protein isoform abundances explained 98% of the variation in muscle power output in healthy dragonflies but only 29% when data from healthy and infected dragonflies were pooled. These results indicate that important, yet largely unexplored, functional relationships exist between (pathways regulating) myofibrillar protein expression and (post-translational) protein processing. Moreover, infection by protozoan parasites of the midgut is associated with changes in muscle protein composition (i.e. across body compartments) that, either alone or in combination with other unmeasured changes, alter muscle contractile performance.

Proteomic profiling of a parasitic wasp exposed to constant and fluctuating cold exposure

When insects are exposed to fluctuating thermal regimes (FTRs) (i.e., cold exposure alternating with periodic short pulses to high temperature), in contrast to constant low temperature (CLT), mortality due to accumulation of chill injuries is markedly reduced. To investigate the physiological processes behind the positive impact of FTR, based on a holistic approach, two-dimensional electrophoresis (2-DE) analysis were performed with the parasitic wasp Aphidius colemani. Parasitoid proteomes revealed 369 well-distinguishable protein spots, where the overall response to cold exposure was clearly specific to treatments (CLT versus FTR). The reduced mortality under FTR was associated with up-regulation of several proteins playing key roles in energy metabolism (glycolysis, TCA cycle, synthesis and conversion of ATP), protein chaperoning (Hsp70/Hsp90), and protein degradation (proteasome). Our results also support the idea that cytoskeleton components, particularly actin arrangement, could play a role in the higher survival rates of insects under FTR.

Muscle-specific calpain is localized in regions near motor endplates in differentiating lobster claw muscles

Calpains are Ca2+-dependent proteinases that mediate protein turnover in crustacean skeletal muscles. We used an antibody directed against lobster muscle-specific calpain (Ha-CalpM) to examine its distribution in differentiating juvenile lobster claw muscles. These muscles are comprised of both fast and slow fibers early in development, but become specialized into predominantly fast or exclusively slow muscles in adults. The transition into adult muscle types requires that myofibrillar proteins specific for fast or slow muscles to be selectively removed and replaced by the appropriate proteins. Using immunohistochemistry, we observed a distinct staining pattern where staining was preferentially localized in the fiber periphery along one side of the fiber. Immunolabeling with an antibody directed against synaptotagmin revealed that the calpain staining was greatest in the cytoplasm adjacent to synaptic terminals. In complementary analyses, we used sequence-specific primers with real-time PCR to quantify the levels of Ha-CalpM in whole juvenile claw muscles. These expression levels were not significantly different between cutter and crusher claws, but were positively correlated with the expression of fast myosin heavy chain. The anatomical localization of Ha-CalpM near motor endplates, coupled with the correlation with fast myofibrillar gene expression, suggests a role for this intracellular proteinase in fiber type switching.

Expression patterns of ubiquitin, heat shock protein 70, alpha-actin and beta-actin over the molt cycle in the abdominal muscle of marine shrimp Litopenaeus vannamei

Crustacean muscle growth is discontinuous due to molt cycle. To characterize molt-related gene expression patterns, we studied the mRNA levels of molecular chaperone-ubiquitin and heat shock protein 70 (Hsp 70) in comparison with muscle protein alpha-actin and beta-actin in marine shrimp Litopenaeus vannamei. Total RNA from abdominal muscle was isolated from 3-month-old animals in six different molt stages. The mRNA levels of target genes were detected by reverse-transcriptase-multiplex PCR and expressed as the ratio to elongation factor-1alpha. Ubiquitin mRNA levels were relatively steady over all stages of the molt cycle. Hsp70 levels were not detectable in early postmolt and late premolt stages, but showed a progressive increase from late postmolt to intermolt stages. Expression levels of alpha-actin gene were lower during postmolt, reached a plateau in intermolt and remained relatively high in premolt stage. Levels of beta-actin increased progressively from postmolt to intermolt, reaching a maximum value in premolt. Therefore, the mRNAs encoding for ubiquitin and Hsp 70 in abdominal muscle did not increase significantly in premolt stages, which is typically associated with claw muscle degradation. Muscle structural alpha-actin and cytoskeletal beta-actin were increased during intermolt and premolt stages, suggesting high muscle growth during these stages in the abdominal muscle of the L. vannamei.

Ubiquitin C-terminal hydrolase-activity is involved in sperm acrosomal function and anti-polyspermy defense during porcine fertilization

The 26S proteasome, which is a multi-subunit protease with specificity for substrate proteins that are postranslationally modified by ubiquitination, has been implicated in acrosomal function and sperm-zona pellucida (ZP) penetration during mammalian fertilization. Ubiquitin C-terminal hydrolases (UCHs) are responsible for the removal of polyubiquitin chains during substrate priming for proteasomal proteolysis. The inhibition of deubiquitination increases the rate of proteasomal proteolysis. Consequently, we have hypothesized that inhibition of sperm acrosome-borne UCHs increases the rate of sperm-ZP penetration and polyspermy during porcine in vitro fertilization (IVF). Ubiquitin aldehyde (UA), which is a specific nonpermeating UCH inhibitor, significantly (P < 0.05) increased polyspermy during porcine IVF and reduced (P < 0.05) UCH enzymatic activity measured in motile boar spermatozoa using a specific fluorometric UCH substrate, ubiquitin-AMC. Antibodies against two closely related UCHs, UCHL1 and UCHL3, detected these UCHs in the oocyte cortex and on the sperm acrosome, respectively, and increased the rate of polyspermy during IVF, consistent with the UA-induced polyspermy surge. In the oocyte, UCHL3 was primarily associated with the meiotic spindle. Sperm-borne UCHL3 was localized to the acrosomal surface and coimmunoprecipitated with a peripheral acrosomal membrane protein, spermadhesin AQN1. Recombinant UCHs, UCHL3, and isopeptidase T reduced polyspermy when added to the fertilization medium. UCHL1 was detected in the oocyte cortex but not on the sperm surface, and was partially degraded 6-8 h after fertilization. Enucleated oocyte-somatic cell electrofusion caused polarized redistribution of cortical UCHL1. We conclude that sperm-acrosomal UCHs are involved in sperm-ZP interactions and antipolyspermy defense. Modulation of UCH activity could facilitate the management of polyspermy during IVF and provide insights into male infertility.

Analysis of serine proteases from marine sponges by 2-D zymography

Proteolytic activities isolated from the marine demosponges Geodia cydonium and Suberites domuncula were analyzed by 2-D zymography, a technique that combines IEF and zymography. After purification, a 200 kDa proteolytically active protein band was obtained from G. cydonium when analyzed in gelatin copolymerized 1-D zymograms. The enzymatic activity was quantified using alpha-N-benzoyl-D-arginine p-nitroanilide (BAPNA) as a substrate and corresponded to a serine protease. The protease activity was resistant to urea and SDS. DTT and 2-mercaptoethanol (2-ME) did not significantly change the protease activity, but induced a shift in molecular mass of the proteolytic band to lower M(r) values as detected by zymography. Under mild denaturing conditions, lower M(r) bands (<200 kDa) were identified in 1-D zymograms, suggesting that the protease is composed of subunits which retain the catalytic activity. After 2-D zymography, the protease from G. cydonium revealed a pI of 8.0 and an M(r) shift from 200 to 66 kDa. To contrast these results, a cytosolic sample from S. domuncula was analyzed. The proteolytic activity of this sponge after 2-D zymography corresponded to an M(r) of 40 kDa and a pI of 4.0. The biological function of both sponge proteases is not yet known. This study demonstrates that mild denaturing conditions required for IEF may alter the interpretation of the 2-D zymography, and care must be taken during sample preparation.

Effect of fibronectin on proteasome activity, acrosome reaction, tyrosine phosphorylation and intracellular calcium concentrations of human sperm

BACKGROUND

Previously we showed that the human sperm proteasome plays significant roles during mammalian fertilization. Here we studied the effect of fibronectin (Fn), an extracellular matrix protein present in the cumulus oophorus of the oocyte, on proteasome activity, acrosome reaction, intracellular calcium concentration ([Ca(2+)](i)) and protein tyrosine phosphorylation of human sperm.

METHODS

Aliquots of motile sperm were incubated for 15 min (T0), 5 h (T5) and 18 h (T18), at 37 degrees C, 5% CO(2) and 95% air with Fn (0-100 microg/ml). The chymotrypsin- and trypsin-like activity of the proteasome was measured using the fluorogenic substrates, Suc-Leu-Leu-Val-Tyr-AMC and Boc-Gln-Ala-Arg-AMC, respectively. At T18, sperm aliquots were incubated for 15 min with Fn and/or progesterone in the presence or absence of epoxomicin (a proteasome inhibitor). The percentage of viable acrosome reacted sperm was evaluated using the Fluorescein isothiocyanate (FITC)-labeled Pisum sativum agglutinin. Tyrosine phosphorylation was evaluated by western blot and [Ca(2+)](i) using fura 2.

RESULTS

Fn stimulated both enzymatic activities of the proteasome and the acrosome reaction of human sperm. Progesterone enhanced and epoxomicin drastically inhibited the effect of Fn. Fn treatment also increased the [Ca(2+)](i). Western blot analysis revealed that Fn increased tyrosine protein phosphorylation and that some proteasome subunits became tyrosine phosphorylated upon Fn treatment.

CONCLUSIONS

These results suggest that Fn activates the proteasome and induces the acrosome reaction in human sperm. This effect may involve binding with specific receptors (integrins) on the sperm surface and the activation of tyrosine kinases.

Three calpains and ecdysone receptor in the land crab Gecarcinus lateralis: sequences, expression and effects of elevated ecdysteroid induced by eyestalk ablation

Crustacean muscle has four calpain-like proteinase activities (CDP I, IIa, IIb and III) that are involved in molt-induced claw muscle atrophy, as they degrade myofibrillar proteins in vitro and in situ. Using PCR cloning techniques, three full-length calpain cDNAs (Gl-CalpB, Gl-CalpM and Gl-CalpT) were isolated from limb regenerates of the tropical land crab Gecarcinus lateralis. All three had highly conserved catalytic (dII) and C2-like (dIII) domains. Gl-CalpB was classified as a typical, or EF-hand, calpain, as the deduced amino acid sequence had a calmodulin-like domain IV in the C-terminus and was most similar to Drosophila calpains A and B. Based on its estimated mass (approximately 88.9 kDa) and cross-immunoreactivity with a polyclonal antibody raised against Dm-CalpA, Gl-CalpB may encode CDP IIb, which is a homodimer of a 95-kDa subunit. It was expressed in all tissues examined, including skeletal muscle, heart, integument, gill, digestive gland, hindgut, nerve ganglia, gonads and Y-organ (molting gland). Both Gl-CalpM and Gl-CalpT were classified as atypical, or non-EF-hand, calpains, as they lacked a domain IV sequence. Gl-CalpM was a homolog of Ha-CalpM from lobster, based on similarities in deduced amino acid sequence, estimated mass (approximately 65.2 kDa) and structural organization (both were truncated at the C-terminal end of dIII). It was expressed at varying levels in most tissues, except Y-organ. Gl-CalpT (approximately 74.6 kDa) was similar to TRA-3 in the nematode Caenorhabditis elegans; domain IV was replaced by a unique ;T domain' sequence. It was expressed in most tissues, except eyestalk ganglia and Y-organ. The effects of elevated ecdysteroid, induced by eyestalk ablation, on calpain and ecdysone receptor (Gl-EcR) mRNA levels in skeletal muscles were quantified by real-time PCR. At 1 day after eyestalk ablation, Gl-EcR and Gl-CalpT mRNA levels increased 15- and 19.3-fold, respectively, in claw muscle but not in thoracic muscle. At 3 days after eyestalk ablation, Gl-EcR and Gl-CalpT mRNA levels in claw muscle had decreased to 2.8-fold and 4.3-fold higher than those in intact controls, respectively, suggesting a feedback inhibition by ecdysteroid. There was no significant effect of eyestalk ablation on Gl-CalpB and Gl-CalpM mRNA levels. Gl-CalpT and Gl-EcR mRNA levels were significantly correlated in both claw and thoracic muscles from intact and eyestalk-ablated animals. The data suggest that Gl-CalpT is involved in initiation of claw muscle atrophy by ecdysteroids. Premolt reduction in claw muscle mass and concomitant remodeling of the sarcomere probably result from post-transcriptional regulation of calpains.

Proteasomes

The major enzyme system catalysing the degradation of intracellular proteins is the proteasome system. A central inner chamber of the cylinder-shaped 20 S proteasome contains the active site, formed by N-terminal threonine residues. The 20 S proteasomes are extremely inefficient in degrading folded protein substrates and therefore one or two multisubunit 19 S regulatory particles bind to one or both ends of the 20 S proteasome cylinder, forming 26 S and 30 S proteasomes respectively. These regulatory complexes are able to bind proteins marked as proteasome substrates by prior conjugation with polyubiquitin chains, and initiate their unfolding and translocation into the proteolytic chamber of the 20 S proteasome, where they are broken down into peptides of 3–25 amino acids. The polyubiquitin tag is removed from the substrate protein by the deubiquitinating activity of the 19 S regulator complex. Under conditions of an intensified immune response, many eukaryotic cells adapt by replacing standard 20 S proteasomes with immuno-proteasomes and/or generating the proteasome activator complex, PA28. Both of these adaptations change the protein-breakdown process for optimized generation of antigenic peptide epitopes that are presented by the class I MHCs. Hybrid proteasomes (19 S regulator–20 S proteasome–PA28) may have a special function during the immune response. The functions of other proteasome accessory complexes, such as PA200 and PI31 are still under investigation.

Role of the sperm proteasome during fertilization and gamete interaction in the mouse

In this work, we have investigated the role of the sperm proteasome during in vitro fertilization (IVF) and gamete interaction in the mouse. Proteasome activity was measured in extract and intact sperm using a specific substrate. In addition, sperm were treated with specific proteasome inhibitors and evaluated during IVF, binding to the zona pellucida, and progesterone- and zona pellucida-induced acrosome reactions. In other experiments, sperm membrane proteins were obtained resuspending them in Triton X-114, shaking vigorously and let standing by 4 hr. Soluble sperm proteins were partitioned in the aqueous phase and sperm membrane proteins in the detergent phase. In both phases, proteasome activity was measured. Labeling of cell surface sperm proteins was carried out with the cell-impermeable NHS-LC biotin, extracted with Triton X-114, and mixing with avidin-agarose beads. Nonpermeabilized sperm were incubated with an anti-proteasome monoclonal antibody and evaluated by indirect immunofluorescence. The results indicate that sperm extracts as well as intact sperm had proteasome activity; the sperm proteasome was involved in IVF, specifically during sperm-zona pellucida binding and the acrosome reaction; soluble sperm membrane proteins exhibited proteasome activity; biotin experiments indicated the presence of proteasomes on the sperm surface, which was corroborated by indirect immunofluorescence experiments. All these observations indicate that the mouse sperm proteasome participates in the binding to the zona pellucida and the acrosome reaction and that there is a pool of proteasomes located on the sperm head.

Eyestalk ablation has little effect on actin and myosin heavy chain gene expression in adult lobster skeletal muscles

The organization of skeletal muscles in decapod crustaceans is significantly altered during molting and development. Prior to molting, the claw muscles atrophy dramatically, facilitating their removal from the base of the claw. During development, lobster claw muscles exhibit fiber switching over several molt cycles. Such processes may be influenced by the secretion of steroid molting hormones, known collectively as ecdysteroids. To assay the effects of these hormones, we used eyestalk ablation to trigger an elevation of circulating ecdysteroids and then quantified myofibrillar mRNA levels with real-time PCR and myofibrillar protein levels by SDS-PAGE. Levels of myosin heavy chain (MHC) and actin proteins and the mRNA encoding them were largely unaffected by eyestalk ablation, but in muscles from intact animals, myofibrillar gene expression was modestly elevated in premolt and postmolt animals. In contrast, polyubiquitin mRNA was significantly elevated (about 2-fold) in claw muscles from eyestalk-ablated animals with elevated circulating ecdysteroids. Moreover, patterns of MHC and actin gene expression are significantly different among slow and fast claw muscles. Consistent with these patterns, the three muscle types differed in the relative amounts of myosin heavy chain and actin proteins. All three muscles also co-expressed fast and slow myosin isoforms, even in fibers that are generally regarded as exclusively fast or slow. These results are consistent with other recent data demonstrating co-expression of myosin isoforms in lobster muscles.

The calpain-system of Drosophila melanogaster: coming of age

Drosophila melanogaster is one of the most popular and powerful model organisms that help our understanding of mammalian (human) life processes at the molecular level. Calpains are Ca(2+)-activated cytoplasmic proteases thought to play multiple roles in intracellular signal processing by limited proteolysis of target substrate proteins, thereby changing their function. The calpain superfamily consists of 14 genes in mammals, but only 4 genes in Drosophila. One may assume that the calpain system, i.e. recognizing calpain-dependent life processes and identifying the substrates cleaved while exerting their functions, would prove easier to solve in Drosophila than in mammals. Recently, major progress has been made in characterizing Drosophila Calpain A, Calpain B and Calpain C. The fourth member, Calpain D (or SOL), was analyzed earlier. At this juncture, it seems justifiable to summarize our knowledge about the Drosophila enzymes, in comparison to the ubiquitous mammalian ones, as regards structure-function relations, mode of activation by Ca(2+) and other factors, inhibition, potential targeting, expression pattern in vivo, etc. Equipped with all this information, we may now embark on the genetic modification of family members, interpreting mutant phenotypes in terms of the cell biology of calpains.

Proteasomal activity in mammalian spermatozoa

The proteasome is a multicatalytic cellular complex, which possess three different enzymatic activities, trypsin-like, chymotrypsin-like, and peptidylglutamyl peptidase. Its function is to remove abnormal or aged proteins. Recently, it has been suggested the participation of the sperm proteasome during mammalian fertilization. In this study, we present evidence that indicates that sperm extracts from several mammalian species, including hamster, mice, rats, bovine, rabbits, and humans all possess proteasome activity. We characterized the three specific activities of the proteasome using specific synthetic substrates and specific proteasome inhibitors. The results indicates that the highest specific activity detected was in mouse sperm toward the trypsin substrates and it was 1,114% of the activity of human sperm toward the chymotrypsin substrate Suc-Leu-Leu-Val-Tyr-AMC (SLLVY-AMC, which was considered as 100%). In all cases, the lowest activity was toward substrates for the peptidylglutamyl peptidase hydrolyzing activity, and it was lowest for rabbit sperm (1.7% of the activity of human sperm toward the chymotrypsin substrate SLLVY-AMC). In addition, specific proteasome inhibitors were able to block all proteasome activities almost 100%, with the exception of clasto-Lactacystin beta-lactone upon rat sperm. All sperm extracts tested evidenced bands of about 29-32 kDa by Western blots using a monoclonal antibody against proteasome subunits alpha 1, 2, 3, 5, 6, and 7. In conclusion, sperm from several mammals possess enzymatic activities that correspond to the proteasome. The proteasome from the different species hold similar but distinctive enzymatic characteristics.

Non-traditional roles of ubiquitin–proteasome system in fertilization and gametogenesis

Fertilization and gametogenesis are key events in sexual reproduction. Our recent studies, together with several reports by other authors, demonstrated that the extracellular ubiquitin-proteasome system plays a role in fertilization and gametogenesis in addition to the traditional intracellular ubiquitin-proteasome system. Here, we summarize our recent results showing the importance of the extracellular ubiquitin-proteasome system in the sperm penetration through the vitelline coat of the egg during ascidian fertilization, together with our recent reports implicating the participation of a novel proteasome-associating complex PC530 in starfish oocyte maturation. We also describe the results by other authors showing the participation of the ubiquitin system both in the elimination of defective sperm in epididymis and in the elimination of paternal mitochondria in fertilized eggs. These are evidence of non-traditional extracellular functions of the ubiquitin system.

Extracellular localization of proteasomes in human sperm

The proteasome, a multienzymatic protease complex is present in human sperm. Here we present evidence indicating that the proteasome has an extracellular localization, on the plasma membrane of the sperm head. Motile sperm (>90%) in PBS were incubated with the proteasome inhibitors clasto-lactacystin beta-lactone or epoxomicin. Then, the substrate Suc-Leu-Leu-Val-Tyr-AMC (SLLVY-AMC) was added and the enzyme activity evaluated in a spectrofluorometer. Other aliquots were resuspended in Tyrode's medium and incubated at different concentrations for various times with or without inhibitors in the presence of 0.4% azocasein. Hydrolysis of azocasein was evaluated at 440 nm. In addition, sperm membrane proteins were obtained incubating the sperm with Triton X-114 or with 0.5 M KCl plus Triton X-100 and removing insoluble material by centrifugation at 5,000g for 40 min. Proteasomal activity was evaluated with SLLVY-AMC and its presence corroborated by Western blotting. Formaldehyde fixed, unpermeabilized sperm were incubated with anti-proteasome monoclonal antibodies and evaluated using indirect immunofluorescence. The effect of proteasome inhibitors upon the progesterone-induced acrosome reaction was also evaluated. Results indicated that (a) whole, intact sperm were able to hydrolyze the proteasome substrates SLLVY-AMC and azocasein; this activity was inhibited by proteasome inhibitors; (b) proteasomal activity was detected in soluble sperm membrane protein preparations and Western blotting revealed the presence of the proteasome in these fractions; (c) indirect immunofluorescence revealed staining of the head region, particularly of the post acrosomal region; and (d) the proteasome plays an important role during the acrosome reaction.

Cloning of a muscle-specific calpain from the American lobster Homarus americanus: expression associated with muscle atrophy and restoration during moulting

A cDNA (1977 bp) encoding a crustacean calpain (Ha-CalpM; GenBank accession no. AY124009) was isolated from a lobster fast muscle cDNA library. The open reading frame specified a 575-amino acid (aa) polypeptide with an estimated mass of 66.3 kDa. Ha-CalpM shared high identity with other calpains in the cysteine proteinase domain (domain II; aa 111-396) and domain III (aa 397-575), but most of the N-terminal domain (domain I; aa 1-110) was highly divergent. Domain II contained the cysteine, histidine and asparagine triad essential for catalysis, as well as two conserved aspartate residues that bind Ca(2+). In domain III an acidic loop in the C2-like region, which mediates Ca(2+)-dependent phospholipid binding, had an expanded stretch of 17 aspartate residues. Ha-CalpM was classified as a non-EF-hand calpain, as it lacked domain IV, a calmodulin-like region containing five EF-hand motifs. Northern blot analysis, relative reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR showed that Ha-CalpM was highly expressed in skeletal muscles, but at much lower levels in heart, digestive gland, intestine, integument, gill, nerve cord/thoracic ganglion and antennal gland. An antibody raised against a unique N-terminal sequence recognized a 62 kDa isoform in cutter claw and crusher claw closer muscles and a 68 kDa isoform in deep abdominal muscle. Ha-CalpM was distributed throughout the cytoplasm, as well as in some nuclei, of muscle fibers. Purification of Ha-CalpM showed that the 62 kDa and 68 kDa isoforms co-eluted from gel filtration and ion exchange columns at positions consistent with those of previously described Ca(2+)-dependent proteinase III (CDP III; 59 kDa). Ha-CalpM mRNA and protein did not change during the moulting cycle. The muscle-specific expression of Ha-CalpM and the ability of Ha-CalpM/CDP III to degrade myofibrillar proteins suggest that it is involved in restructuring and/or maintaining contractile structures in crustacean skeletal muscle.

Molt cycle–dependent molecular chaperone and polyubiquitin gene expression in lobster

Lobster claw muscle undergoes atrophy in correlation with increasing ecdysteroid (steroid molting hormone) titers during premolt. In vivo molecular chaperone (constitutive heat shock protein 70 [Hsc70], heat shock protein 70 [Hsp70], and Hsp90) and polyubiquitin messenger ribonucleic acid (mRNA) levels were examined in claw and abdominal muscles from individual premolt or intermolt lobsters. Polyubiquitin gene expression was assayed as a marker for muscle atrophy. Both Hsc70 and Hsp90 mRNA levels were significantly induced in premolt relative to intermolt lobster claw muscle, whereas Hsp70 mRNA levels were not. Hsp90 gene expression was significantly higher in premolt claw muscle when compared with abdominal muscle. Polyubiquitin mRNA levels were elevated in premolt when compared with intermolt claw muscle and significantly elevated relative to premolt abdominal muscle.

Changes in contractile properties of skeletal muscle during developmentally programmed atrophy and death

Skeletal muscle atrophy and death are protracted processes that accompany aging and pathological insults in mammals. The intersegmental muscles (ISMs) from the tobacco hawkmoth Manduca sexta are composed of giant fibers that undergo distinct hormonally-regulated programs of atrophy and death at the end of metamorphosis. Atrophy occurs during the 3 days preceding adult emergence and results in a 40% reduction of mass, whereas death takes place during the subsequent 30 h and results in the complete loss of the fibers. There are no significant changes in tetanic force or calcium sensitivity in skinned fiber preparations during atrophy. However, the size of caffeine-induced contractions fell by about 50%. With the onset of the death phase, dramatic reductions occur in ISM: tetanic force, twitch amplitude, resting potential, caffeine-induced contractions, calcium sensitivity, and Hill coefficients. Several lines of evidence suggest that ISM atrophy is caused by an increase in protein turnover without significant modification of fiber organization. In contrast, ISM death is accompanied by disorganization of the contractile apparatus and concomitant loss of contractile function.

Ubiquitin and actin expression in claw muscles of land crab, Gecarcinus lateralis, and American lobster, Homarus americanus: differential expression of ubiquitin in two slow muscle fiber types during molt-induced atrophy

The closer muscle of large-clawed decapod crustaceans undergoes a proecdysial (premolt) atrophy to facilitate withdrawal of the appendage at ecdysis. This atrophy involves the activation of both calcium-dependent (calpains) and ubiquitin (Ub)/proteasome-dependent proteolytic systems that break down proteins to reduce muscle mass. Moreover, the large slow-twitch (S(1)) fibers undergo a greater atrophy than the small slow-tonic (S(2)) fibers. Both polyUb mRNA and Ub-protein conjugates increase during claw muscle atrophy. In this study in situ hybridization and RT-PCR were used to determine the temporal and spatial expression of polyUb and alpha-actin. A cDNA encoding the complete sequence of lobster muscle alpha-actin was characterized; a probe synthesized from the cDNA provided a positive control for optimizing RT-PCR and in situ hybridization. PolyUb was expressed at low levels in claw closer muscle from anecdysial (intermolt) land crab. By early proecdysis (premolt; stage D(0)), polyUb mRNA levels increased in medial fibers that insert along the midline of the apodeme, with greater expression in S(1) than S(2), while levels remained low in peripheral fibers. By late proecdysis, polyUb mRNA decreased in central fibers, while mRNA increased in peripheral S(1) fibers. In contrast, alpha-actin was expressed in lobster claw muscles at relatively constant levels during the intermolt cycle. These results suggest that Ub/proteasome-dependent proteolysis contributes to enhanced turnover of myofibrillar proteins during claw closer muscle atrophy. Furthermore, atrophy is not synchronous within the muscle; it begins in medial fibers and then progresses peripherally.

Evaluation of aminoaciduria in severely traumatized patients

BACKGROUND

It has been documented in the literature that hypocalcemia, hypoaminoacidemia, and hyperaminoaciduria are sequelae of trauma. The aminoaciduria of patients with different types and severity of traumatic injuries was investigated.

METHODS

Eight severely traumatized patients (ISS range, 20-43 years) and eight age-, gender-, and weight-matched controls were studied. Plasma and urine were collected 2.5-72 h after admission. Quantification of 28 amino acids in plasma and urine was performed by reversed-phase high-performance liquid chromatography. Urine concentrations of amino acids were indexed to creatinine.

RESULTS

The patients' mean serum concentrations of 4 amino acids (arginine, threonine, isoleucine, and glutamine) were significantly decreased, 2 others (tryptophan and glutamic acid) were significantly increased, and 22 were unchanged (p-value< or =0.05). Fractional (urinary) excretion of 11 amino acids was increased in the patients. The patients' serum total calcium and albumin concentrations were decreased, but the mean ionized calcium concentration was not significantly different from the controls.

CONCLUSIONS

The results of this study showed that aminoaciduria involving many amino acids is common for patients with different traumatic injuries and that the aminoaciduria is correlated with a reduction of the total serum calcium concentration.

Thermal acclimation and stress in the American lobster, Homarus americanus: equivalent temperature shifts elicit unique gene expression patterns for molecular chaperones and polyubiquitin

Using homologous molecular probes, we examined the influence of equivalent temperature shifts on the in vivo expression of genes coding for a constitutive heat shock protein (Hsc70), heat shock proteins (Hsps) (Hsp70 and Hsp90), and polyubiquitin, after acclimation in the American lobster, Homarus americanus. We acclimated sibling, intermolt, juvenile male lobsters to thermal regimes experienced during overwintering conditions (0.4 +/- 0.3 degrees C), and to ambient Pacific Ocean temperatures (13.6 +/- 1.2 degrees C), for 4-5 weeks. Both groups were subjected to an acute thermal stress of 13.0 degrees C, a temperature shift previously found to elicit a robust heat shock response in ambient-acclimated lobsters. Animals were examined after several durations of acute heat shock (0.25-2 hours) and after several recovery periods (2-48 hours) at the previous acclimation temperature, following a 2-hour heat shock. Significant inductions in Hsp70, Hsp90, and polyubiquitin messenger RNA (mRNA) levels were found for the ambient-acclimated group. Alternatively, for the cold-acclimated group, an acute thermal stress over an equivalent interval resulted in no induction in mRNA levels for any of the genes examined. For the ambient-acclimated group, measurements of polyubiquitin mRNA levels showed that hepatopancreas, a digestive tissue, incurred greater irreversible protein damage relative to the abdominal muscle, a tissue possessing superior stability over the thermal intervals tested.

Environmental endocrine disruption in decapod crustacean larvae: hormone titers, cytochrome P450, and stress protein responses to heptachlor exposure

A variety of enzymes and other proteins are produced by organisms in response to xenobiotic exposures. Cytochrome P450s (CYP) are one of the major phase I-type classes of detoxification enzymes found in terrestrial and aquatic organisms ranging from bacteria to vertebrates. One of the primary functions of stress proteins (HSPs) is to aid in the recovery of damaged proteins by chaperoning their refolding. These and other biomarkers of xenobiotic exposure and resulting effects have not been studied in crustacean larvae. This information is of potential importance for environmental management and risk assessment. In this work, we have given Homarus americanus larvae single 24 h exposures to the cyclodiene pesticide heptachlor, a known environmental endocrine disruptor (EDC) on different days of the 1st larval instar. We followed these larvae during the first larval stage for effects on timing of ecdysis to 2nd stage, ecdysteroid molting hormone titers, and alterations in the levels of cytochrome P450 CYP45 and HSP70 proteins. Delays in ecdysis were correlated with alterations in ecdysteroid levels. This result provides clues that this pesticide may function as an environmental endocrine disruptor in crustaceans. CYP45 and HSP70 levels were significantly elevated for several days following heptachlor exposure. The elevation in HSP70 was prolonged depending on the day of pesticide exposure and this was directly related to the increase in mortality. These results demonstrate the utility of these measurements as potential biomarkers in crustacean larval developmental toxicology and EDC effects research.