Specific increase in calcium-activated neutral protease with low calcium sensitivity (m-calpain) in proerythroblastic K562 cell line cells induced to differentiation by phorbol 12-myristate 13-acetate

Post-translational control of Myc function during differentiation

Myc proteins are deeply involved in multiple biological processes including cell proliferation, growth, metabolism, apoptosis, differentiation, and tumorigenesis. Paradoxically, Myc proteins have been found to be capable of both inhibiting and facilitating differentiation depending on the biological context. Recently we identified a new mode of Myc regulation in differentiating muscle cells in which c-Myc protein is proteolytically cleaved by calcium-dependent calpains in the cytoplasm. This cleavage serves two purposes. First, it inactivates the transcriptional function of Myc by removing its C-terminus, a region responsible for the interaction of Myc with Max and DNA. Second, it alters cytoskeletal architecture and accelerates muscle differentiation through the activity of the remaining N-terminal cleavage product (termed Myc-nick). Here we discuss the roles and regulation of full-length Myc and Myc-nick in terminal differentiation and propose a model in which calpain-mediated cleavage of Myc operates as a functional switch.

Calpain chronicle--an enzyme family under multidisciplinary characterization

Calpain is an intracellular Ca2+-dependent cysteine protease (EC 3.4.22.17; Clan CA, family C02) discovered in 1964. It was also called CANP (Ca2+-activated neutral protease) as well as CASF, CDP, KAF, etc. until 1990. Calpains are found in almost all eukaryotes and a few bacteria, but not in archaebacteria. Calpains have a limited proteolytic activity, and function to transform or modulate their substrates' structures and activities; they are therefore called, "modulator proteases." In the human genome, 15 genes--CAPN1, CAPN2, etc.--encode a calpain-like protease domain. Their products are calpain homologs with divergent structures and various combinations of functional domains, including Ca2+-binding and microtubule-interaction domains. Genetic studies have linked calpain deficiencies to a variety of defects in many different organisms, including lethality, muscular dystrophies, gastropathy, and diabetes. This review of the study of calpains focuses especially on recent findings about their structure-function relationships. These discoveries have been greatly aided by the development of 3D structural studies and genetic models.

Identifying target genes regulated downstream of Cdx2 by microarray analysis

The caudal-related homeobox transcription factor (Cdx2) plays an important role in intestinal development, differentiation, and homeostasis. However, only a limited number of Cdx2-regulated target genes have been elucidated. To delineate the molecular mechanism regulated downstream of Cdx2, we aimed to define Cdx2-regulated genes. We engineered a rat intestinal epithelial cell line, IEC-6, with minimal endogenous Cdx2 expression to express exogenous Cdx2. The gene expression patterns for Cdx2-inducing cells and control cells were examined using oligonucleotide arrays. In the present study, differential expression of 23 genes was confirmed by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis using gene-specific primers. Increased expression of genes was involved in the Notch signaling pathway, xenobiotic metabolism, enzymes associated with tumor suppression, RNA binding protein, receptors, signal transduction, and transcription factors. The wide-ranging collection of such inducing genes suggests to the functions of Cdx2 in cell fate decision and maintenance of intestinal epithelia.

Suppression of oxidative stress-induced hepatocyte injury by calpain antisense

BACKGROUND

Calpain, a cytosolic Ca(2+)-dependent proteinase, plays a pivotal role in cell injury. In this study, we investigated the effect of calpain-mu antisense oligonucleotide on oxidative stress induced-hepatocyte injury.

MATERIALS AND METHODS

Hemagglutinating virus of Japan liposome complex with one of three types of antisense oligonucleotide (AS-1, AS-2, AS-3) or scramble oligonucleotide was added to the culture medium of HuH7 cells and incubated for 6 days. The expression of calpain-mu protein was examined by Western blotting. After the addition of tert-butyl hydroperoxide, bleb formation was examined by phase contrast microscopy, and cell viability was assessed by the release of lactate dehydrogenase.

RESULTS

Incubation of HuH7 cells with AS-2 resulted in a decrease in the amount of calpain on day 4 and a further decrease to almost undetectable levels on day 6, whereas scramble oligonucleotide had no effect. Bleb formation was observed 120 min after the addition of tert-butyl hydroperoxide in scramble oligonucleotide-treated cells as in untreated cells. In contrast, it was rarely observed in AS-2-treated cells. Lactate dehydrogenase release was significantly suppressed in AS-2-treated cells, compared with that in scramble oligonucleotide treated-cells.

CONCLUSIONS

Our findings suggest that calpain activation is involved in the pathogenesis of oxidative stress injury and that transfection of calpain antisense may potentially protect against ischemia/reperfusion liver injury.

Heterogeneous increases of cytoplasmic calcium: distinct effects on down-regulation of cell surface sodium channels and sodium channel subunit mRNA levels

1. Long-term (> or = 12 h) treatment of cultured bovine adrenal chromaffin cells with A23187 (a Ca(2+) ionophore) or thapsigargin (TG) [an inhibitor of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)] caused a time- and concentration-dependent reduction of cell surface [(3)H]-saxitoxin (STX) binding capacity, but did not change the K:(D:) value. In A23187- or TG-treated cells, veratridine-induced (22)Na(+) influx was reduced (with no change in veratridine EC(50) value) while it was enhanced by alpha-scorpion venom, beta-scorpion venom, or Ptychodiscus brevis toxin-3, like in nontreated cells. 2. The A23187- or TG-induced decrease of [(3)H]-STX binding was diminished by BAPTA-AM. EGTA also inhibited the decreasing effect of A23187. A23187 caused a rapid, monophasic and persistent increase in intracellular concentration of Ca(2+) ([Ca(2+)](i)) to a greater extent than that observed with TG. 2,5-Di-(t-butyl)-1,4-benzohydroquinone (DBHQ) (an inhibitor of SERCA) produced only a rapid monophasic increase in [Ca(2+)](i), without any effect on [(3)H]-STX binding. 3. Reduction in [(3)H]-STX binding capacity induced by A23187 or TG was attenuated by Gö6976 (an inhibitor of conventional protein kinase C) or calpastatin peptide (an inhibitor of calpain). When the internalization rate of cell surface Na(+) channels was measured in the presence of brefeldin A (an inhibitor of vesicular exit from the trans-Golgi network), A23187 or TG accelerated the reduction of [(3)H]-STX binding capacity. 4. Six hours treatment with A23187 lowered Na(+) channel alpha- and beta(1)-subunit mRNA levels, whereas TG had no effect. 5. These results suggest that elevation of [Ca(2+)](i) caused by A23187, TG or DBHQ exerted differential effects on down-regulation of cell surface functional Na(+) channels and Na(+) channel subunit mRNA levels.

Antisense RNA-mediated deficiency of the calpain protease, nCL-4, in NIH3T3 cells is associated with neoplastic transformation and tumorigenesis

We previously have described the use of an antisense RNA strategy termed random homozygous knock-out (RHKO) to identify negative regulators of cell proliferation. Here we report the discovery that RHKO-mediated deficiency of the nCL-4 calpain protease results in cellular transformation of and tumorigenesis by murine NIH3T3 fibroblasts. We isolated cell clones able to form colonies on 0.5% soft agar and found that these cells generated tumors when injected subcutaneously into nude mice. The gene inactivated by RHKO was identified as nCL-4 by genomic library screening, transcript analysis, and DNA sequencing. Anchorage-independent growth, as indicated by colony formation on soft agar, was reversed by reversal of antisense-mediated homozygous inactivation, but continued haplo-insufficiency of nCL-4 resulting from insertional mutagenesis of one nCL-4 allele was associated with persistent tumorigenesis. nCL-4 cDNA expressed in naive 3T3 cells in the antisense, but not sense, direction under control of the cytomegalovirus early promoter reproduced the anchorage-independent growth effects of RHKO. Our results implicate deficiency of the nCL-4 calpain protease in neoplastic transformation.

Vitamin D analogs, 20-Epi-22-oxa-24a,26a,27a,-trihomo-1alpha,25(OH)2-vitamin D3, 1,24(OH)2-22-ene-24-cyclopropyl-vitamin D3 and 1alpha,25(OH)2-lumisterol3 prime NB4 leukemia cells for monocytic differentiation via nongenomic signaling pathways, involving calcium and calpain

Side-chain modified vitamin D analogs including 20-Epi-22-oxa-24a,26a,27a-trihomo-1alpha,2 5-dihydroxyvitamin D3 (KH1060), and 1,24-dihydroxy-22-ene-24-cyclopropyl-vitamin D3 (MC903) were originally designed to aid in the treatment of hyperproliferative disorders including psoriasis and cancer. Here we demonstrate that these analogs, as well as the 6-cis-locked conformer, 1alpha,25-dihydroxy-lumisterol3 (JN) prime NB4 cells for monocytic differentiation. Previously, the action of MC903 and KH1060 was presumed to be mediated by the nuclear vitamin D receptor (VDRnuc). Differentiation in response to all analogs was shown to be inhibited by 1beta,25-dihydroxyvitamin D3 (HL), the antagonist to the nongenomic activities of 1,25D3. These data suggest that although MC903 and KH1060 may bind the VDRnuc, that the differentiative activities of these agents requires nongenomic signaling pathways. Here we show that 1alpha,25(OH)2-d5-previtamin D3 (HF), JN, KH1060, and MC903 induce expression of PKC alpha and PKC delta and translocation of both isoforms to the particulate fraction, and PKC alpha to the nuclear fraction. The full differentiation response with combinations of analogs and TPA was inhibited 50% by the membrane permeable Ca2+ chelator, 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) or calpain inhibitor I. These data demonstrate that intracellular free calcium and the calcium-dependent protease, calpain play critical roles in monocytic differentiation. Intracellular calcium appears to be most critical in the 1,25D3-priming stage of differentiation, while calpain is essential in the TPA maturation response.

Role of calpain in adipocyte differentiation

Evidence is presented that the calcium-activated protease, calpain, is required for differentiation of 3T3-L1 preadipocytes into adipocytes induced by methylisobutylxanthine (a cAMP phosphodiesterase inhibitor), dexamethasone, and insulin. Calpain is expressed by preadipocytes and its level falls during differentiation. Exposure of preadipocytes to the calpain inhibitor N-acetyl-Leu-Leu-norleucinal or overexpression of calpastatin, a specific endogenous inhibitor of calpain, blocks expression of adipocyte-specific genes, notably the CCAAT/enhancer-binding protein (C/EBP)alpha gene, and acquisition of the adipocyte phenotype. The inhibitor disrupts the differentiation-inducing effect of methylisobutylxanthine (by means of the cAMP-signaling pathway), but is without effect on differentiation induced by dexamethasone or insulin. N-acetyl-Leu-Leu-norleucinal, or overexpression of calpastatin, inhibits reporter gene expression mediated by the C/EBPalpha gene promoter by preventing C/EBPbeta, a transcriptional activator of the C/EBPalpha gene, from binding to the promoter. These findings implicate calpain in the transcriptional activation of the C/EBPalpha gene, a process required for terminal adipocyte differentiation.

Upregulation of the calcium-dependent protease, calpain, during keratinocyte differentiation

Calpain is a ubiquitous neutral calcium-activated thiol protease that is implicated in various cellular functions including exocytosis, cell fusion, apoptosis and proliferation. The calpain system is composed of the enzymes mu-calpain and m-calpain and their endogenous inhibitor, calpastatin. We employed the spontaneously immortalized human HaCaT keratinocytes, which retain their ability to differentiate in vitro and in vivo, to study the modulation of the calpain system during keratinocyte differentiation. The cellular levels of keratinocyte differentiation markers and of the components of the calpain system were monitored by immunoblotting. Three established differentiation stimuli: increase in cell density as a function of time in culture, elevation of extracellular calcium concentration and exposure to 1,25-dihydroxyvitamin D3 enhanced the expression of the three keratinocyte differentiation markers keratin 10, involucrin and transglutaminase. The differentiation of HaCaT cells was accompanied by elevation of the components of the calpain system, although the pattern of increase varied according to the specific differentiation stimulus. A higher increase in calpains as compared with the increase in calpastatin suggests an increase in net calpain activity during differentiation. Such an increase may play a part in the differentiation process itself and/or in the regulation of key events in differentiating keratinocyte metabolism.

Active site-directed antibodies identify calpain II as an early-appearing and pervasive component of neurofibrillary pathology in Alzheimer's disease

Calpain proteases influence intracellular signaling pathways and regulate cytoskeleton organization, but the neuronal and pathological roles of individual isoenzymes are unknown. In Alzheimer's disease (AD), the activated form of calpain I is significantly increased while the fate of calpain II has been more difficult to address. Here, calpain II antibodies raised to different sequences within a cryptic region around the active site, which becomes exposed during protease activation, were shown immunohistochemically to bind extensively to neurofibrillary tangles (NFT), neuritic plaques, and neuropil threads in brains from individuals with AD. Additional 'pre-tangle' granular structures in neurons were also intensely immunostained, indicating calpain II mobilization at very early stages of NFT formation. Total levels of calpain II remained constant in the prefrontal cortex of AD patients but were increased 8-fold in purified NFT relative to levels of calpain I. These results implicate activated calpain II in neurofibrillary degeneration, provide further evidence for the involvement of the calpain system in AD pathogenesis, and imply that neuronal calcium homeostasis is altered in AD.

The calpain-calpastatin system and cellular proliferation and differentiation in rodent osteoblastic cells

The calpain-calpastatin system, which consists of calpains I and II (two ubiquitously distributed calcium-activated papain-like cysteine proteases), as well as calpastatin (the endogenous calpain inhibitor), plays an important role in cell proliferation and differentiation in many tissues. However, its contribution to the regulation of osteoprogenitor or pluripotent stem cell proliferation and differentiation into osteoblasts remains poorly defined. In these studies, rat pluripotent mesodermal cells (ROB-C26) and mouse MC3T3-E1 preosteoblasts were induced to differentiate into osteoblasts by long-term culture or in response to bone morphogenetic protein (BMP). The occurrence and distribution of calpain-calpastatin system proteins were determined by immunofluorescent microscopy, measurement of calcium-dependent proteolytic activity, and Western blotting. Treatment of intact MC3T3-E1 cells with an irreversible, membrane-permeable cysteine protease inhibitor attenuated proliferation and alkaline phosphatase upregulation under differentiation-enhancing conditions. Calpain II activity increased during differentiation of MC3T3-E1 cells in postconfluent culture. When ROB-C26 cells were maintained in long-term culture, neutral protease, calpain I, and calpain II activities increased 2- to 3-fold in the absence of BMP. In the presence of partially purified native BMP, neutral protease and calpain I activities also increased similarly, but calpain II activity increased by 10-fold in 3 days. The maximal increase in alkaline phosphatase occurred 4 to 11 days after the calpain II activity had peaked. Induction of differentiation in long-term MC3T3-E1 cultures was associated with higher calpain II and 70- and 110-kDa calpastatin protein levels and lower 17-kDa calpastatin degradation product levels. In conclusion, cysteine protease activity is essential for preosteoblastic proliferation and differentiation. The calpain-calpastatin system is regulated during osteoprogenitor proliferation and differentiation, as it is in other cells, and bone morphogenetic protein is a specific regulator of calpain II.

Proteolytic cleavage of human p53 by calpain: a potential regulator of protein stability

The p53 tumor suppressor protein is activated in cells in response to DNA damage and prevents the replication of cells sustaining genetic damage by inducing a cell cycle arrest or apoptosis. Activation of p53 is accompanied by stabilization of the protein, resulting in accumulation to high levels within the cell. p53 is normally degraded through the proteasome following ubiquitination, although the mechanisms which regulate this proteolysis in normal cells and how the p53 protein becomes stabilized following DNA damage are not well understood. We show here that p53 can also be a substrate for cleavage by the calcium-activated neutral protease, calpain, and that a preferential site for calpain cleavage exists within the N terminus of the p53 protein. Treatment of cells expressing wild-type p53 with an inhibitor of calpain resulted in the stabilization of the p53 protein. By contrast, in vitro or in vivo degradation mediated by human papillomavirus E6 protein was unaffected by the calpain inhibitor, indicating that the stabilization did not result from inhibition of the proteasome. These results suggest that calpain cleavage plays a role in regulating p53 stability.

Regional differences in gene expression for calcium activated neutral proteases (calpains) and their endogenous inhibitor calpastatin in mouse brain and spinal cord

The family of calpains (CANP or calcium activated neutral proteases) and their endogenous inhibitor calpastatin have been implicated in many neural functions; however, functional distinctions between the major calpain isoforms, calpain I and II, have not been clearly established. In the present study we analyzed the gene expression patterns for calpain I and II and calpastatin in mouse brain and spinal cord by measuring both their mRNA and protein levels. Our results show that the overall mRNA level measured by competitive reverse transcription polymerase chain reaction for calpain II is 15-fold higher and for calpastatin is three-fold higher than that for calpain I. Overall, both mRNA and protein expression levels for the calpains and calpastatin showed no significant difference between the spinal cord and the brain. The cellular distributions of mRNA for calpain I or calpastatin, measured by in situ hybridization, are relatively uniform throughout the brain. In contrast, calpain II gene expression is selectively higher in certain neuron populations including pyramidal neurons of the hippocampus and the deep neocortical layers, Purkinje cells of cerebellum, and motor neurons of the spinal cord. The motor neurons were the most enriched in calpain message. Motor neurons possessed 10-fold more calpain II mRNA than any other spinal cord cell type. The differential distribution of the two proteases in the brain and the spinal cord at the mRNA level indicates that the two calpain genes are differentially regulated, suggesting that they play different physiological roles in neuronal activities and that they may participate in the pathogenesis of certain regional neurological degenerative diseases.

Proteolytic processing of nuclear factor kappa B by calpain in vitro

Nuclear factor kappaB (NF-kappaB) is a transcription factor that is critical for the inducible expression of multiple cellular and viral genes. Using the electrophoretic mobility shift assay, we demonstrated that DNA binding activity of NF-kappaB was abolished by proteolysis with mu- and m-calpains in vitro. The proteolysis of NF-kappaB by calpains and hence the abolition of its DNA binding was prevented by calpastatin, calpain inhibitor I and proteasome inhibitor. We also provided evidence that calpains degrade the C-terminal domain of NF-kappaB by Western blot using anti-NF-kappaB (p65) C-terminal antibody. These observations indicate that calpains regulate gene expression through processing of NF-kappaB.

The role of the calpain-calpastatin system in thyrotropin-releasing hormone-induced selective down-regulation of a protein kinase C isozyme, nPKC epsilon, in rat pituitary GH4C1 cells

We have examined the mechanism for the selective down-regulation of protein kinase C epsilon (nPKC epsilon) in rat pituitary GH4C1 cells responding to thyrotropin-releasing hormone (TRH) stimulation. Among various low molecular weight protease inhibitors examined, only a cysteine protease inhibitor (calpain inhibitor I, N-acetyl-Leu-Leu-norleucinal) blocked the down-regulation of nPKC epsilon. Furthermore, the introduction of a synthetic calpastatin peptide, an exclusively specific inhibitor of calpain, into the cells also reduced the down-regulation, suggesting the involvement of calpain among all the intracellular cysteine proteases in this process. In accordance, we observed TRH-induced translocation of m-calpain from the cytosol to the membrane and the concomitant up-regulation of calpastatin isoforms; presumably, the former represents activation of the protease initiating the kinase degradation, while the latter constitutes a negative feedback system protecting the cells from activated calpain. These results suggest that in GH4C1 cells, TRH mobilizes both protease (m-calpain) and inhibitor (calpastatin) as a strictly regulating system for the nPKC epsilon pathway mediating TRH signals.

Identification and characterization of membrane-bound calpains in clathrin-coated vesicles from bovine brain

Calpains are intracellular cysteine proteases activated in a Ca(2+)-dependent manner. Previously, we found that the differentiation of K562 cells induced by 4 beta-phorbol 12-myristate 13-acetate treatment is accompanied by an increase in m-calpain levels and, at the same time, m-calpain becomes localized on the inside of plasma membranes, coated pits, and coated vesicles [Nakamura, M., Mori, M., Morishita, Y., Mori, S. & Kawashima, S. (1992) Exp. Cell Res. 200, 513-522]. We also reported that mu-calpain plays an essential role in morphological changes and membrane fusion of erythrocytes through the degradation of spectrin, a lining protein [Hayashi, M., Saito, Y. & Kawashima, S. (1992) Biochim. Biophys. Res. Commun. 182, 939-946]. Thus, calpains are implicated in endocytosis and/or exocytosis, processes stimulated by Ca2+ and involving intracellular membrane fusion. In this study, we report the biochemical characterization of calpains as components of purified coated vesicles from bovine brain. It was found by Western-blot analysis and chemical cross-linking of proteins that calpains are bound to the membranes of coated vesicles, and not to the coats. The binding of m-calpain to vesicles is Ca(2+)-dependent, while that of mu-calpain is less dependent on the presence of Ca2+. We also identified substrate proteins for calpains in coated vesicles. Upon activation of endogenous calpains, component proteins of coated vesicles such as the clathrin light chain, tubulins, and adaptins, but not the clathrin heavy chain, are highly sensitive to calpain digestion. In the case of exogenously added calpains, low concentrations degraded the same protein components. The degradation pattern differs slightly between added mu-calpain and m-calpain. These results strongly suggest that calpains are involved in the formation of coated vesicles and/or vesicle fusion to endosomes.

Calcium-activated neutral proteinase (calpain) system in aging and Alzheimer's disease

Calpains (CANPs) are a family of calcium-dependent cysteine proteases under complex cellular regulation. By making selective limited proteolytic cleavages, they activate or alter the regulation of certain enzymes, including key protein kinases and phosphatases, and induce specific cytoskeletal rearrangements, accounting for their suspected involvement in intracellular signaling, vesicular trafficking, and structural stabilization. Calpain activity has been implicated in various aging phenomena, including cataract formation and erythrocyte senescence. Abnormal activation of the large stores of latent calpain in neurons induces cell injury and is believed to underlie neurodegeneration in excitotoxicity, Wallerian degeneration, and certain other neuropathologic states involving abnormal calcium influx. In Alzheimer's disease, we found the ratio of activated calpain I to its latent precursor isoform in neocortex to be threefold higher than that in normal individuals and those with Huntington's or Parkinson's disease. Immunoreactivity toward calpastatin, the endogenous inhibitor of calpain, was also markedly reduced in layers II-V of the neocortex in Alzheimer's disease. The excessive calpain system activation suggested by these findings represents a potential molecular basis for synaptic loss and neuronal cell death in the brain in Alzheimer's disease given the known destructive actions of calpain I and its preferential neuronal and synaptic localization. In surviving cells, persistent calpain activation may also contribute to neurofibrillary pathology and abnormal amyloid precursor protein trafficking/processing through its known actions on protein kinases and the membrane skeleton. The degree of abnormal calpain activation in the brain in Alzheimer's disease strongly correlated with the extent of decline in levels of secreted amyloid precursor protein in brain. Cytoskeletal proteins that are normally good calpain substrates become relatively calpain resistant when they are hyperphosphorylated, which may contribute to their accumulation in neurofibrillary tangles. As a major effector of calcium signals, calpain activity may mirror disturbances in calcium homeostasis and mediate important pathologic consequences of such disturbances.

Specific cleavage of transcription factors by the thiol protease, m-calpain

The intracellular nonlysosomal calcium-dependent cysteine protease, m-calpain, is shown to specifically cleave the bHLHzip transcription factor USF leaving the binding and dimerisation domains intact. The resultant protein is capable of efficient DNA binding but is no longer able to activate transcription. A surprisingly high proportion of other transcription factors tested, AP1 (c-Fos/c-Jun), Pit-1, Oct-1, CP1a and b, c-Myc, ATF/CREB, AP2 and AP3 but not Sp1, were similarly cleaved by m-calpain to produce specific partial digestion products. These properties make m-calpain a particularly useful protease for proteolytic studies of transcription factors and also raise the possibility that m-calpain may be involved in vivo in regulation of turnover or transcriptional activity of a number of transcription factors.