Role of the calpain–calpastatin system in the density-dependent growth arrest

Oversupplying metabolizable protein in late gestation for beef cattle: effects on prepartum BW, ruminal fermentation, nitrogen balance, and skeletal muscle catabolism

The objective of the study was to determine the effect of oversupplying MP during late gestation on maternal BW, ruminal fermentation, nitrogen balance, and skeletal muscle catabolism. Crossbred Hereford heifers (n = 24) were assigned to a control treatment designed to meet MP requirements (CON) or a treatment providing 133% of the MP requirement (HMP). Heifers were individually fed their treatment from day -55 ± 3 relative to parturition and DMI was summarized by week. BW was measured on day -55 ± 3, -41 ± 3, -27 ± 3, and -8 ± 3. Ruminal digesta samples were collected on day -34 ± 5 and -15 ± 4 for short-chain fatty acid and ammonia-N (NH3-N) concentration. Plasma was collected the day prior to ruminal digesta samples and analyzed for plasma urea-N. Nitrogen balance was measured over a 6-d period starting on day -34 ± 4 and -15 ± 4. Following completion of the N balance periods, muscle biopsies were collected from the longissimus dorsi and analyzed for abundance of proteins relating to skeletal muscle catabolism. Data were analyzed as a randomized complete block (date of parturition) design with repeated measures using the MIXED procedure of SAS. Heifers fed HMP increased conceptus-corrected BW by a greater magnitude than CON at day -8 relative to -55 and -41 (treatment × day, P < 0.01). DMI increased (P < 0.01) by 18% on week -2 compared to -8, but then decreased (P < 0.01) by 8.0% for week -1. N-intake, apparent N digestion, N excretion, and N retention (g/d) were all greater (P < 0.01) for HMP heifers than CON but did not differ when expressed as a proportion of N intake. Ruminal NH3-N decreased (treatment × day, P < 0.01) as parturition approached for HMP (10.1 to 8.6 mg/dL); whereas, NH3-N was not affected for CON (1.0 to 1.3 mg/dL). Consequently, plasma urea-N was greater (P < 0.01) for HMP heifers (15.0 vs. 7.5 mg/dL). Heifers fed HMP had improved (P < 0.01) DM, OM, and NDF digestibility relative to CON heifers. The abundance of calpastatin was greater (P = 0.03) and calpain tended to be greater (P = 0.085) for CON cows compared to HMP. Feeding greater quantities of MP during late gestation may improve ruminal fermentation, N balance, and improve BW gain prepartum.

Interference with Ca2+-Dependent Proteolysis Does Not Alter the Course of Muscle Wasting in Experimental Cancer Cachexia

Protein hypercatabolism significantly contributes to the onset and progression of muscle wasting in cancer cachexia. In this regard, a major role is played by the ATP-ubiquitin-proteasome-dependent pathway and by autophagy. However, little is known about the relevance of the Ca²⁺-dependent proteolytic system. Since previous results suggested that this pathway is activated in the skeletal muscle of tumor hosts, the present study was aimed to investigate whether inhibition of Ca²⁺-dependent proteases (calpains) may improve cancer-induced muscle wasting. Two experimental models of cancer cachexia were used, namely the AH-130 Yoshida hepatoma and the C26 colon carcinoma. The Ca²⁺-dependent proteolytic system was inhibited by treating the animals with dantrolene or by overexpressing in the muscle calpastatin, the physiologic inhibitor of Ca²⁺-dependent proteases. The results confirm that calpain-1 is overexpressed and calpastatin is reduced in the muscle of rats implanted with the AH-130 hepatoma, and show for the first time that the Ca²⁺-dependent proteolytic system is overactivated also in the C26-bearing mice. Yet, administration of dantrolene, an inhibitor of the Ca²⁺-dependent proteases, did not modify tumor-induced body weight loss and muscle wasting in the AH-130 hosts. Dantrolene was also unable to reduce the enhancement of protein degradation rates occurring in rats bearing the AH-130 hepatoma. Similarly, overexpression of calpastatin in the tibialis muscle of the C26 hosts did not improve muscle wasting at all. These observations suggest that inhibiting a single proteolytic system is not a good strategy to contrast cancer-induced muscle wasting. In this regard, a more general and integrated approach aimed at targeting the catabolic stimuli rather than the proteolytic activity of a single pathway would likely be the most appropriate therapeutic intervention.

Role of calpain-1 in the early phase of experimental ALS

Elevation in [Ca(2+)]i and activation of calpain-1 occur in central nervous system of SOD1(G93A) transgenic mice model of amyotrophic lateral sclerosis (ALS), but few data are available about the early stage of ALS. We here investigated the level of activation of the Ca(2+)-dependent protease calpain-1 in spinal cord of SOD1(G93A) mice to ascertain a possible role of the protease in the aetiology of ALS. Comparing the events occurring in the 120 day old mice, we found that [Ca(2+)]i and activation of calpain-1 were also increased in the spinal cord of 30 day old mice, as indicated by the digestion of some substrates of the protease such as nNOS, αII-spectrin, and the NR2B subunit of NMDA-R. However, the digestion pattern of these proteins suggests that calpain-1 may play different roles depending on the phase of ALS. In fact, in spinal cord of 30 day old mice, activation of calpain-1 produces high amounts of nNOS active species, while in 120 day old mice enhanced-prolonged activation of calpain-1 inactivates nNOS and down-regulates NR2B. Our data reveal a critical role of calpain-1 in the early phase and during progression of ALS, suggesting new therapeutic approaches to counteract its onset and fatal course.

Calpain inhibition promotes the rescue of F(508)del-CFTR in PBMC from cystic fibrosis patients

A basal calpain activity promotes the limited proteolysis of wild type (WT) cystic fibrosis conductance regulator (CFTR), inducing the internalization of the split channel. This process contributes to the regulation in the level of the active CFTR at the plasma membranes. In peripheral blood mononuclear cells (PBMC) from 16 healthy donors, the inhibition of calpain activity induces a 3-fold increase in the amount of active WT CFTR at the plasma membranes. Instead, in PBMC from cystic fibrosis (CF) patients, calpain activity is expressed at aberrant levels causing the massive removal of F⁵⁰⁸del-CFTR from the cell surface. In these patients, the inhibition of such abnormal proteolysis rescues physiological amounts of active mutated CFTR in 90% of the patients (25 over 28). The recovery of functional F⁵⁰⁸del-CFTR at the physiological location, in cells treated with a synthetic calpain inhibitor, indicates that F⁵⁰⁸del-CFTR folding, maturation, and trafficking operate in CF-PBMC at significant rate. Thus, an increase in the basal calpain activity seems primarily involved in the CFTR defect observed in various CF cells. Furthermore, in CF-PBMC the recovery of the scaffolding protein Na⁺/H⁺ exchanger regulatory factor 1 (NHERF-1), occurring following inhibition of the aberrant calpain activity, can contribute to rescue CFTR-functional clusters.

CFTR mutations altering CFTR fragmentation

Most CF (cystic fibrosis) results from deletion of a phenylalanine (F⁵⁰⁸) in the CFTR {CF transmembrane-conductance regulator; ABCC7 [ABC (ATP-binding cassette) sub-family C member 7]} which causes ER (endoplasmic reticulum) degradation of the mutant. Using stably CFTR-expressing BHK (baby-hamster kidney) cell lines we demonstrated that wild-type CTFR and the F508delCFTR mutant are cleaved into differently sized N- and C-terminal-bearing fragments, with each hemi-CFTR carrying its nearest NBD (nucleotide-binding domain), reflecting differential cleavage through the central CFTR R-domain. Similar NBD1-bearing fragments are present in the natively expressing HBE (human bronchial epithelial) cell line. We also observe multiple smaller fragments of different sizes in BHK cells, particularly after F508del mutation (ladder pattern). Trapping wild-type CFTR in the ER did not generate a F508del fragmentation fingerprint. Fragments change their size/pattern again post-mutation at sites involved in CFTR's in vitro interaction with the pleiotropic protein kinase CK2 (S511A in NBD1). The F508del and S511A mutations generate different fragmentation fingerprints that are each unlike the wild-type; yet, both mutants generate new N-terminal-bearing CFTR fragments that are not observed with other CK2-related mutations (S511D, S422A/D and T1471A/D). We conclude that the F508delCFTR mutant is not degraded completely and there exists a relationship between CFTR's fragmentation fingerprint and the CFTR sequence through putative CK2-interactive sites that lie near F508.

Calpastatin upregulation in Mycoplasma hyorhinis-infected cells is promoted by the mycoplasma lipoproteins via the NF-κB pathway

Mycoplasma hyorhinis frequently contaminates cultured cells, with effects on synthetic and metabolic pathways. We demonstrated for the first time that contamination of cells by a strain of M. hyorhinis (NDMh) results in increased levels of calpastatin (the endogenous inhibitor of the ubiquitous Ca(2+) -dependent protease calpain). We now show that the calpastatin upregulation by NDMh in neuroblastoma SH-SY5Y cells resides in the NDMh lipoprotein fraction (LPP), via the NF-κB transcription pathway. NF-κB activation requires dissociation of the cytoplasmic NF-κB/IκB complex followed by NF-κB translocation to the nucleus. NDMh-LPP induced translocation of the NF-κB RelA subunit to the nucleus and upregulated calpastatin. RelA translocation and calpastatin elevation were prevented when dissociation of the NF-κB/IκB complex was inhibited either by transfection with the non-phosphorylatable IκB mutant ΔNIκBα, or by using PS1145, an inhibitor of the IκB kinase (IKK complex). Increased calpastatin levels attenuate calpain-related amyloid-β-peptide and Ca(2+) -toxicity (these are central to the pathogenesis of Alzheimer's Disease). LPP-induced elevation of calpastatin provides an example of effects on non-inflammatory intracellular proteins, the outcome being significant alterations in host cell functions. Since calpastatin level is important in the control of calpain activity, mycoplasmal LPP may be of interest in treating some pathological processes involving excessive calpain activation.

Evidence for alteration of calpain/calpastatin system in PBMC of cystic fibrosis patients

We are here reporting that in peripheral blood mononuclear cells (PBMC) of patients homozygous for F508del-CFTR the calpain-calpastatin system undergoes a profound alteration. In fact, calpain basal activity, almost undetectable in control PBMC, becomes measurable at a significant extent in cells from cystic fibrosis (CF) patients, also due to a 40-60% decrease in both calpastatin protein and inhibitory activity. Constitutive protease activation in CF patients' cells induces a large accumulation of the mutated cystic fibrosis transmembrane conductance regulator (CFTR) in the 100kD+70kD split forms as well as a degradation of proteins associated to the CFTR complex. Specifically, the scaffolding protein Na(+)/H(+) exchanger 3 regulatory factor-1 (NHERF-1) is converted in two distinct fragments showing masses of 35kD and 20kD, being however the latter form the most represented one, thereby indicating that in CF-PBMC the CFTR complex undergoes a large disorganization. In conclusion, our observations are providing new information on the role of calpain in the regulation of plasma membrane ion conductance and provide additional evidence on the transition of this protease activity from a physiological to a pathological function.

Calpains are involved in Entamoeba histolytica-induced death of HT-29 colonic epithelial cells

Entamoeba histolytica is an enteric tissue-invading protozoan parasite that can cause amebic colitis and liver abscess in humans. E. histolytica has the capability to kill colon epithelial cells in vitro; however, information regarding the role of calpain in colon cell death induced by ameba is limited. In this study, we investigated whether calpains are involved in the E. histolytica-induced cell death of HT-29 colonic epithelial cells. When HT-29 cells were co-incubated with E. histolytica, the propidium iodide stained dead cells markedly increased compared to that in HT-29 cells incubated with medium alone. This pro-death effect induced by ameba was effectively blocked by pretreatment of HT-29 cells with the calpain inhibitor, calpeptin. Moreover, knockdown of m- and µ-calpain by siRNA significantly reduced E. histolytica-induced HT-29 cell death. These results suggest that m- and µ-calpain may be involved in colon epithelial cell death induced by E. histolytica.

Calpain digestion and HSP90-based chaperone protection modulate the level of plasma membrane F508del-CFTR

We are here showing that peripheral mononuclear blood cells (PBMC) from cystic fibrosis (CF) patients contain almost undetectable amounts of mature 170 kDa CF-transmembrane conductance regulator (CFTR) and a highly represented 100 kDa form. This CFTR protein, resembling the form produced by calpain digestion and present, although in lower amounts, also in normal PBMC, is localized in cytoplasmic internal vesicles. These observations are thus revealing that the calpain-mediated proteolysis is largely increased in cells from CF patients. To characterize the process leading to the accumulation of such split CFTR, FRT cells expressing the F508del-CFTR mutated channel protein and human leukaemic T cell line (JA3), expressing wild type CFTR were used. In in vitro experiments, the sensitivity of the mutated channel to the protease is identical to that of the wild type, whereas in Ca(2+)-loaded cells F508del-CFTR is more susceptible to digestion. Inhibition of intracellular calpain activity prevents CFTR degradation and leads to a 10-fold increase in the level of F508del-CFTR at the plasma membrane, further indicating the involvement of calpain activity in the maintenance of very low levels of mature channel form. The higher sensitivity to calpain of the mutated 170 kDa CFTR results from a reduced affinity for HSP90 causing a lower degree of protection from calpain digestion. The recovery of HSP90 binding capacity in F508del-CFTR, following digestion, explains the large accumulation of the 100 kDa CFTR form in circulating PBMC from CF patients.

Role of calpain in the regulation of CFTR (cystic fibrosis transmembrane conductance regulator) turnover

The level of the mature native 170 kDa form of CFTR (cystic fibrosis transmembrane conductance regulator) at the plasma membrane is under the control of a selective proteolysis catalysed by calpain. The product of this limited digestion, consisting of discrete fragments still associated by strong interactions, is removed from the plasma membrane and internalized in vesicles and subject to an additional degradation. This process can be monitored by visualizing the accumulation of a 100 kDa fragment in a proliferating human leukaemic T-cell line and in human circulating lymphocytes. In reconstructed systems, and in intact cells, the conversion of native CFTR into the 100 kDa fragment linearly correlated with calpain activation and was prevented by addition of synthetic calpain inhibitors. A reduction in Ca2+ influx, by blocking the NMDA (N-methyl-D-aspartate) receptor Ca2+ channel, inhibited the conversion of the native 170 kDa fragment into the 100 kDa fragment, whereas an endosome acidification blocker promoted accumulation of the digested 100 kDa CFTR form. An important role in calpain-mediated turnover of CFTR is exerted by HSP90 (heat-shock protein 90), which, via association with the protein channel, modulates the degradative effect of calpain through a selective protection. Taken together these results indicate that CFTR turnover is initiated by calpain activation, which is induced by an increased Ca2+ influx and, following internalization of the cleaved channel protein, and completed by the lysosomal proteases. These findings provide new insights into the molecular mechanisms responsible for the defective functions of ion channels in human pathologies.

Calpain3 is expressed in a proteolitically active form in papillomavirus-associated urothelial tumors of the urinary bladder in cattle

Background

Calpain 3 (Capn3), also named p94, is a skeletal muscle tissue-specific protein known to be responsible for limb-girdle muscular dystrophy type 2A (LGMD2A). Recent experimental studies have hypothesized a pro-apoptotic role of Capn3 in some melanoma cell lines. So far the link between calpain3 and tumors comes from in vitro studies. The objective of this study was to describe Capn3 activation in naturally occurring urothelial tumors of the urinary bladder in cattle.

Methods and Findings

Here we describe, for the first time in veterinary and comparative oncology, the activation of Capn3 in twelve urothelial tumor cells of the urinary bladder of cattle. Capn3 protein was initially identified with nanoscale liquid chromatography coupled with tandem mass spectrometry (nano LC-MS/MS) in a co-immunoprecipitation experiment on E2F3, known to be a transcription factor playing a crucial role in bladder carcinogenesis in humans. Capn3 expression was then confirmed by reverse transcription polymerase chain reaction (RT-PCR). Finally, the Ca²⁺-dependent proteolytic activity of Capn3 was assayed following ion exchange chromatography. Morphologically, Capn3 expression was documented by immunohistochemical methods. In fact numerous tumor cells showed an intracytoplasmic immunoreactivity, which was more rarely evident also at nuclear level. In urothelial tumors, bovine papillomavirus type 2 (BPV-2) DNA was amplified by PCR and the expression of E5 protein, the major oncogenic protein of BVP-2, was detected by western blotting, immunohistochemistry, and immunofluorescence. E2F3 overexpression and pRb protein downregulation were shown by western blotting.

Conclusion

The role of capn3 protein in urothelial cancer of the urinary bladder remains to be elucidated: further studies would be required to determine the precise function of this protease in tumor development and progression. However, we suggest that activated Capn3 may be involved in molecular pathways leading to the overexpression of E2F3, which in turn could be responsible for urothelial tumor cell proliferation also in cattle, though other mechanisms are likely to exist. If further studies corroborate the important role of Capn3 in urothelial tumors of the urinary bladder, cattle with urinary tumors may prove useful as animal model for bladder carcinogenesis.

Adaptive modifications in the calpain/calpastatin system in brain cells after persistent alteration in Ca2+ homeostasis

Persistent dysregulation in Ca(2+) homeostasis is a pervasive pathogenic mechanism in most neurodegenerative diseases, and accordingly, calpain activation has been implicated in neuronal cells dysfunction and death. In this study we examined the intracellular functional state of the calpain-calpastatin system in -G93A(+) SOD1 transgenic mice to establish if and how uncontrolled activation of calpain can be prevented in vivo during the course of prolonged [Ca(2+)](i) elevation. The presented data indicate that 1) calpain activation is more extensive in motor cortex, in lumbar, and sacral spinal cord segments compared with the lower or almost undetectable activation of the protease in other brain areas, 2) direct measurements of the variations of Ca(2+) levels established that the degree of the protease activation is correlated to the extent of elevation of [Ca(2+)](i), 3) intracellular activation of calpain is always associated with diffusion of calpastatin from perinuclear aggregated forms into the cytosol and the formation of a calpain-calpastatin complex, and 4) a conservative fragmentation of calpastatin is accompanied by its increased expression and inhibitory capacity in conditions of prolonged increase in [Ca(2+)](i). Thus, calpastatin diffusion and formation of the calpain-calpastatin complex together with an increased synthesis of the inhibitor protein represent a cellular defense response to conditions of prolonged dysregulation in intracellular Ca(2+) homeostasis. Altogether these findings provide a new understanding of the in vivo molecular mechanisms governing calpain activation that can be extended to many neurodegenerative diseases, potentially useful for the development of new therapeutic approaches.

Involvement of exon 6-mediated calpastatin intracellular movements in the modulation of calpain activation

BACKGROUND

To establish the physiological role of calpain, it is necessary to define how the protease can escape from the effect of its natural inhibitor calpastatin, since both proteins co-localize into the cell cytosol.

METHODS

To answer this question, we have overexpressed four fluorescent calpastatin constructs, differing in the composition of their XL- and L-domains, and the intracellular trafficking of this protein inhibitor has been followed by single cell fluorescence imaging.

RESULTS AND CONCLUSIONS

By the use of these calpastatin forms differing in the type of exon-derived sequences contained in the XL- and L-domains, we have demonstrated that the sequence coded by exon 6, containing multiple phosphorylation sites, is directly involved in determining the cell localization of calpastatin. In fact, exposure to cAMP promotes the recruitment into aggregates of those calpastatin forms containing the exon 6 sequence. These protein movements are directly related to the level of cytosolic inhibitory capacity and thereby to the extent of intracellular calpain activation.

GENERAL SIGNIFICANCE

The recruitment of calpastatin into aggregates allows the translocation and activation of the protease to the membranes; on the contrary, the presence of large amounts of calpastatin in the cytosol prevents both processes, protecting the cell from undesired proteolysis.