Regulation of cyclin D1 by calpain protease

The roles of intracellular proteolysis in cardiac ischemia-reperfusion injury

Ischemic heart disease remains a leading cause of human mortality worldwide. One form of ischemic heart disease is ischemia-reperfusion injury caused by the reintroduction of blood supply to ischemic cardiac muscle. The short and long-term damage that occurs due to ischemia-reperfusion injury is partly due to the proteolysis of diverse protein substrates inside and outside of cardiomyocytes. Ischemia-reperfusion activates several diverse intracellular proteases, including, but not limited to, matrix metalloproteinases, calpains, cathepsins, and caspases. This review will focus on the biological roles, intracellular localization, proteolytic targets, and inhibitors of these proteases in cardiomyocytes following ischemia-reperfusion injury. Recognition of the intracellular function of each of these proteases includes defining their activation, proteolytic targets, and their inhibitors during myocardial ischemia-reperfusion injury. This review is a step toward a better understanding of protease activation and involvement in ischemic heart disease and developing new therapeutic strategies for its treatment.

Calpains, the proteases of two faces controlling the epithelial homeostasis in mammary gland

Calpain-1 and calpain-2 are calcium-dependent Cys-proteases ubiquitously expressed in mammalian tissues with a processive, rather than degradative activity. They are crucial for physiological mammary gland homeostasis as well as for breast cancer progression. A growing number of evidences indicate that their pleiotropic functions depend on the cell type, tissue and biological context where they are expressed or dysregulated. This review considers these standpoints to cover the paradoxical role of calpain-1 and -2 in the mammary tissue either, under the physiological conditions of the postlactational mammary gland regression or the pathological context of breast cancer. The role of both calpains will be examined and discussed in both conditions, followed by a brief snapshot on the present and future challenges for calpains, the two-gateway proteases towards tissue homeostasis or tumor development.

Calpain as a therapeutic target in cancer

INTRODUCTION

Calpain-1 and calpain-2 are prototypical classical isoforms of the calpain family of calcium-activated cysteine proteases. Their substrate proteins participate in a wide range of cellular processes, including transcription, survival, proliferation, apoptosis, migration, and invasion. Dysregulated calpain activity has been implicated in tumorigenesis, suggesting that calpains may be promising therapeutic targets.

AREAS COVERED

This review covers clinical and basic research studies implicating calpain-1 and calpain-2 expression and activity in tumorigenesis and metastasis. We highlight isoform specific functions and provide an overview of substrates and cancer-related signalling pathways affected by calpain-mediated proteolytic cleavage. We also discuss efforts to develop clinically relevant calpain specific inhibitors and spotlight the challenges facing inhibitor development.

EXPERT OPINION

Rationale for targeting calpain-1 and calpain-2 in cancer is supported by pre-clinical and clinical studies demonstrating that calpain inhibition has the potential to attenuate carcinogenesis and block metastasis of aggressive tumors. The wide range of substrates and cleavage products, paired with inconsistencies in model systems, underscores the need for more complete understanding of physiological substrates and how calpain cleavage alters their function in cellular processes. The development of isoform specific calpain inhibitors remains an important goal with therapeutic potential in cancer and other diseases.

CDC25A pathway toward tumorigenesis: Molecular targets of CDC25A in cell-cycle regulation

The cell division cycle 25 (CDC25) phosphatases regulate key transitions between cell-cycle phases during normal cell division, and in the case of DNA damage, they are key targets of the checkpoint machinery that ensure genetic stability. Little is known about the mechanisms underlying dysregulation and downstream targets of CDC25. To understand these mechanisms, we silenced the CDC25A gene in breast cancer cell line MDA-MB-231 and studied downstream targets of CDC25A gene. MDA-MB-231 breast cancer cells were transfected and silenced by CDC25A small interfering RNA. Total messenger RNA (mRNA) was extracted and analyzed by quantitative real-time polymerase chain reaction. CDC25A phosphatase level was visualized by Western blot analysis and was analyzed by 2D electrophoresis and LC-ESI-MS/MS. After CDC25A silencing, cell proliferation reduced, and the expression of 12 proteins changed. These proteins are involved in cell-cycle regulation, programmed cell death, cell differentiation, regulation of gene expression, mRNA editing, protein folding, and cell signaling pathways. Five of these proteins, including ribosomal protein lateral stalk subunit P0, growth factor receptor bound protein 2, pyruvate kinase muscle 2, eukaryotic translation elongation factor 2, and calpain small subunit 1 increase the activity of cyclin D1. Our results suggest that CDC25A controls the cell proliferation and tumorigenesis by a change in expression of proteins involved in cyclin D1 regulation and G1/S transition.

High level of calpain1 promotes cancer cell invasion and migration in oral squamous cell carcinoma

Calpain1, termed conventional calpain and a member of the Ca²⁺-dependent neutral cysteine proteases, is considered to be involved in cancer formation and development. However, the effect of calpain1 on oral squamous cell carcinoma (OSCC) remains poorly understood. The aim of the present study was to evaluate the possibility of calpain1 as a potential molecular target for OSCC diagnosis and therapy. The present study demonstrates that calpain1 was overexpressed in OSCC cell lines and 4/7 of the tumor tissues in paired samples of tumor and noncancerous matched tissues (NCMT). In a cohort of 125 patients with primary OSCC, the high expression of calpain1 was an independent predictor for overall survival in a multivariate analysis (P=0.022). Furthermore, RNA interference-mediated suppression of calpain1 expression reduced the proliferation, migration and invasion potential of the HSC3 and CAL27 OSCC cell lines, but did not increase their apoptosis. These findings indicate that calpain1 may be a useful biomarker for novel prognostic and therapeutic strategies in oral squamous cell carcinoma.

Cell Cycle-independent Role of Cyclin D3 in Host Restriction of Influenza Virus Infection

To identify new host factors that modulate the replication of influenza A virus, we performed a yeast two-hybrid screen using the cytoplasmic tail of matrix protein 2 from the highly pathogenic H5N1 strain. The screen revealed a high-score interaction with cyclin D3, a key regulator of cell cycle early G₁ phase. M2-cyclin D3 interaction was validated through GST pull-down and recapitulated in influenza A/WSN/33-infected cells. Knockdown of Ccnd3 by small interfering RNA significantly enhanced virus progeny titers in cell culture supernatants. Interestingly, the increase in virus production was due to cyclin D3 deficiency per se and not merely a consequence of cell cycle deregulation. A combined knockdown of Ccnd3 and Rb1, which rescued cell cycle progression into S phase, failed to normalize virus production. Infection by influenza A virus triggered redistribution of cyclin D3 from the nucleus to the cytoplasm, followed by its proteasomal degradation. When overexpressed in HEK 293T cells, cyclin D3 impaired binding of M2 with M1, which is essential for proper assembly of progeny virions, lending further support to its role as a putative restriction factor. Our study describes the identification and characterization of cyclin D3 as a novel interactor of influenza A virus M2 protein. We hypothesize that competitive inhibition of M1-M2 interaction by cyclin D3 impairs infectious virion formation and results in attenuated virus production. In addition, we provide mechanistic insights into the dynamic interplay of influenza virus with the host cell cycle machinery during infection.

Limoniastrum guyonianum aqueous gall extract induces apoptosis in colorectal cancer cells by inhibiting calpain activity

Several studies have reported that plant-derived natural products have cancer chemopreventive and chemotherapeutic properties. The aim of the present study was to determine the antiproliferative and pro-apoptotic potential of Limoniastrum guyonianum aqueous gall extract (G extract) on human colorectal cancer BE cell line and, if so, to characterize the mechanism involved. The G extract-induced growth inhibitory effect was associated with an arrest of cell cycle progression in G2/M phase as shown by the cell phase distribution. In addition, G extract promoted in a concentration-dependent manner these cells towards apoptosis as indicated by the presence of cleaved poly(ADP-ribose) polymerase (PARP). In order to characterize the mechanism involved in the antiproliferative and pro-apoptotic signaling pathway activated by G extract, calpain activity and the expression of the cell cycle inhibitor p16(INK4A) were determined. The present findings indicated that G extract exhibited significant inhibitory activity against calpain and caused a marked and concentration-dependent upregulation of p16(INK4A). These effects could be ascribed to the presence of condensed tannins and polyphenols such as epicatechin and epigallocatechin gallate in G extract.

20(S)-protopanaxadiol triggers mitochondrial-mediated apoptosis in human lung adenocarcinoma A549 cells via inhibiting the PI3K/Akt signaling pathway

20(S)-Protopanaxadiol (PPD), an aglycone saponin ginsenoside isolated from Panax quinquefolium L, has been shown to inhibit the growth and proliferation in several cancer lines. However, the underlying molecular mechanisms remain poorly understood. In this study, we investigated the apoptosis-induced effects and the mechanism of 20(S)-PPD on human lung adenocarcinoma A549 cells. 20(S)-PPD showed a potent antiproliferative activity against A549 cells by triggering apoptosis. 20(S)-PPD-induced apoptosis was characterized by a dose-dependent loss of the mitochondrial membrane, release of cytochrome c, second mitochondria-derived activator of caspase (Smac) and apoptosis-inducing factor (AIF), activation of caspase-9/-3, and cleavage of poly (ADP-ribose) polymerase (PARP). Caspase-dependence was indicated by the ability of the pan-caspase inhibitor z-VAD-fmk to attenuate 20(S)-PPD-induced apoptosis. After treatment with 20(S)-PPD, the proportion of A549 cells at the G0/G1 phase increased, while cells at the S and G2/M phases decreased. Furthermore, 20(S)-PPD also triggered down-regulation of phosphorylated Akt (Ser473/Thr308) and glycogen synthase kinase 3β (GSK 3β). Knockdown of GSK 3β with siRNA promoted the apoptotic effects of 20(S)-PPD. These results revealed an unexpected mechanism of action for this unique ginsenoside: triggering a mitochondrial-mediated, caspase-dependent apoptosis via down-regulation of the PI3K/Akt signaling pathway in A549 cells. Our findings encourage further studies of 20(S)-PPD as a promising chemopreventive agent against lung cancer.

MEK drives cyclin D1 hyperelevation during geroconversion

When the cell cycle becomes arrested, MTOR (mechanistic Target of Rapamycin) converts reversible arrest into senescence (geroconversion). Hyperexpression of cyclin D1 is a universal marker of senescence along with hypertrophy, beta-Gal staining and loss of replicative/regenerative potential (RP), namely, the ability to restart proliferation when the cell cycle is released. Inhibition of MTOR decelerates geroconversion, although only partially decreases cyclin D1. Here we show that in p21- and p16-induced senescence, inhibitors of mitogen-activated/extracellular signal-regulated kinase (MEK) (U0126, PD184352 and siRNA) completely prevented cyclin D1 accumulation, making it undetectable. We also used MEL10 cells in which MEK inhibitors do not inhibit MTOR. In such cells, U0126 by itself induced senescence that was remarkably cyclin D1 negative. In contrast, inhibition of cyclin-dependent kinase (CDK) 4/6 by PD0332991 caused cyclin D1-positive senescence in MEL10 cells. Both types of senescence were suppressed by rapamycin, converting it into reversible arrest. We confirmed that the inhibitor of CDK4/6 caused cyclin D1 positive senescence in normal RPE cells, whereas U0126 prevented cyclin D1 expression. Elimination of cyclin D1 by siRNA did not prevent other markers of senescence that are consistent with the lack of its effect on MTOR. Our data confirmed that a mere inhibition of the cell cycle was sufficient to cause senescence, providing MTOR was active, and inhibition of MEK partially inhibited MTOR in a cell-type-dependent manner. Second, hallmarks of senescence may be dissociated, and hyperelevated cyclin D1, a marker of hyperactivation of senescent cells, did not necessarily determine other markers of senescence. Third, inhibition of MEK was sufficient to eliminate cyclin D1, regardless of MTOR.

Expression of calpain-calpastatin system (CCS) member proteins in human lymphocytes of young and elderly individuals; pilot baseline data for the CALPACENT project

BACKGROUND

Ubiquitous system of regulatory, calcium-dependent, cytoplasmic proteases - calpains - and their endogenous inhibitor - calpastatin - is implicated in the proteolytic regulation of activation, proliferation, and apoptosis of many cell types. However, it has not been thoroughly studied in resting and activated human lymphocytes yet, especially in relation to the subjects' ageing process. The CALPACENT project is an international (Polish-Italian) project aiming at verifying the hypothesis of the role of calpains in the function of peripheral blood immune cells of Polish (Pomeranian) and Italian (Sicilian) centenarians, apparently relatively preserved in comparison to the general elderly population. In this preliminary report we aimed at establishing and comparing the baseline levels of expression of μ- and m-calpain and calpastatin in various, phenotypically defined, populations of human peripheral blood lymphocytes for healthy elderly Sicilians and Poles, as compared to these values observed in young cohort.

RESULTS

We have found significant differences in the expression of both μ- and m-calpain as well as calpastatin between various populations of peripheral blood lymphocytes (CD4+, CD8+ and CD19+), both between the age groups compared and within them. Interestingly, significantly higher amounts of μ- and m-calpains but not of calpastatin could be demonstrated in the CD4+CD28- and CD8+CD28- lymphocytes of old subjects (but not in the cells of young individuals), as compared to their CD28+ counterparts. Finally, decreased expression of both calpains in the elderly T cells is not related to the accumulation of effector/memory (CD45RO+) cells in the latter, as the expression of both calpains does not differ significantly between the naïve and memory T cells, while is significantly lower for elderly lymphocytes if both populations are taken separately.

CONCLUSIONS

Observed differences in the amounts of CCS member proteins between various populations of lymphocytes of young and elderly subjects may participate in the impaired proliferative activity of these cells in the elderly.

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.

Immunological detection of m- and µ-calpains in the skeletal muscle of Marchigiana cattle

Calpains are Ca²⁺-dependent proteases able to cleave a large number of proteins involved in many biological functions. Particularly, in skeletal muscle they are involved in meat tenderizing during post mortem storage. In this report we analyzed the presence and expression of µ- and m-calpains in two skeletal muscles of the Marchigiana cattle soon after slaughter, using immunocytochemical and immunohistochemical techniques, Western blotting analysis and Casein Zymography. Therefore, the presence and the activity of these proteases was investigated until 15^th day post mortem during normal process of meat tenderizing. The results showed m- and µ-calpain immunosignals in the cytoplasm both along the Z disk/I band regions and in the form of intracellular stores. Moreover, the expression level of µ-calpain but not m-calpain decreased after 10 days of storage. Such a decrease in µ-calpain was accompanied by a gradual reduction of activity. On the contrary, m-calpain activity persisted up to 15 days of post mortem storage. Such data indicate that expression and activity of both µ-calpain and m-calpain analyzed in the Marchigiana cattle persist longer than reported in literature for other bovines and may be related to both the type of muscle and breed examined.

Cassia tora L. (Jue-ming-zi) has anticancer activity in TCA8113 cells in vitro and exerts anti-metastatic effects in vivo

Cassia tora L. (Jue-ming-zi) is a traditional Chinese medicine widely used in East Asia. The in vitro anticancer effects of Jue-ming-zi were evaluated in TCA8113 human tongue carcinoma cells using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. At a concentration of 1.0 mg/ml, Cassia tora L. inhibited the growth of TCA8113 cells by 72%; this inhibiton was greater than that by 0.5 and 0.25 mg/ml Cassia tora L. (43 and 16%, respectively). To elucidate the inhibitory mechanisms underlying the anticancer effect of Cassia tora L. in cancer cells, the expression of genes associated with apoptosis, inflammation and metastasis were measured using RT-PCR and western blot analysis. Cassia tora L. significantly induced apoptosis in cancer cells (P<0.05) by upregulating Bax, caspase-3 and caspase-9, and by downregulating Bcl-2. The expression of genes associated with inflammation, including NF-κB, iNOS and COX-2, was significantly downregulated (P<0.05) by Cassia tora L., demonstrating its anti-inflammatory properties. Cassia tora L. also exerted a significant anti-metastatic effect on cancer cells as demonstrated by decreased mRNA expression of matrix metalloprotease (MMP) genes and increased expression of tissue inhibitors of metalloproteinases (TIMPs), and as confirmed by the inhibition of induced tumor metastasis induced in 26-M3.1 colon cells in BALB/c mice. Our results demonstrated that Cassia tora L. exhibited the most potent in vitro anticancer effects, induced apoptosis, had anti-inflammatory activities and exerted in vivo anti-metastatic effects. Additionally, the anticancer, anti-inflammatory and anti-metastatic effects of the higher Cassia tora L. concentrations were stronger compared with those of the lower Cassia tora L. concentrations tested.

Involvement of the p38 MAPK signaling pathway in S-phase cell-cycle arrest induced by Furazolidone in human hepatoma G2 cells

Given the previously described essential role for the p38 mitogen-activation protein kinase (p38 MAPK) signaling pathway in human hepatoma G2 cells (HepG2), we undertook the present study to investigate the role of the p38 MAPK signaling pathway in cell-cycle arrest induced by Furazolidone (FZD). The aim of this study was to determine the effects of FZD on HepG2 cells by activating and inhibiting the p38 MAPK signaling pathway. The cell cycle and proliferation of HepG2 cells treated with FZD were detected by flow cytometry and MTT assay in the presence or absence of p38 MAPK inhibitors (SB203580), respectively. Cyclin D1, cyclin D3 and CDK6 were detected by quantitative real-time PCR and western blot analysis. Our data showed that p38 MAPK became phosphorylated after stimulation with FZD. Activation of p38 MAPK could arise S-phase cell-cycle arrest and suppress cell proliferation. Simultaneously, inhibition of the p38 MAPK signaling pathway significantly prevented S-phase cell-cycle arrest, increased the percentage of cell viability and decreased the expression of cyclin D1, cyclin D3 and CDK6. These results demonstrated that FZD arose S-phase cell-cycle arrest via activating the p38 MAPK signaling pathway in HepG2 cells. Cyclin D1, cyclin D3 and CDK6 are target genes functioning at the downstream of p38 MAPK in HepG2 cells induced by FZD.

Calpain modulates cyclin-dependent kinase inhibitor 1B (p27(Kip1)) in cells of the osteoblast lineage

The ubiquitously expressed calpains-1 and -2 belong to a family of calcium-dependent intracellular cysteine proteases. Both calpains are heterodimers consisting of a large catalytic subunit and a small regulatory subunit encoded by the gene Capn4. Ablation of the calpain small subunit eliminates calpain activity and leads to embryonic lethality. We previously created osteoblast-specific Capn4 knockout mice to investigate a physiological role for the calpain small subunit in cells of the osteoblast lineage. Deletion of Capn4 reduced trabecular and cortical bone, mainly due to impaired proliferation and differentiation of cells of the osteoblast lineage. To further investigate an underlining mechanism by which osteoblast-specific Capn4 knockout mice develop an osteoporotic bone phenotype, we established osteoblastic cell lines stably expressing either control or Capn4 RNA interference for this study. Capn4 knockdown cells showed reduced cell proliferation, accumulation of total and phosphorylated cyclin-dependent kinase inhibitor 1B (p27(Kip1)) on serine 10, and reduced phosphorylation of retinoblastoma protein on threonine 821. Moreover, ablation of Capn4 increased 27 ( Kip1 ) mRNA levels, likely due to stabilized binding of Akt to protein phosphatase 2A, which presumably results in reduced phosphorylation of Akt on S473 and forkhead Box O (FoxO) 3A on T32. Collectively, calpain regulates cell proliferative function by modulating both transcription and degradation of p27(Kip1) in osteoblasts. In conclusion, calpain is a critical modulator for regulation of p27(Kip1) in cells of the osteoblast lineage.

Calpain-catalyzed proteolysis of human dUTPase specifically removes the nuclear localization signal peptide

Background

Calpain proteases drive intracellular signal transduction via specific proteolysis of multiple substrates upon Ca²⁺-induced activation. Recently, dUTPase, an enzyme essential to maintain genomic integrity, was identified as a physiological calpain substrate in Drosophila cells. Here we investigate the potential structural/functional significance of calpain-activated proteolysis of human dUTPase.

Methodology/Principal Findings

Limited proteolysis of human dUTPase by mammalian m-calpain was investigated in the presence and absence of cognate ligands of either calpain or dUTPase. Significant proteolysis was observed only in the presence of Ca(II) ions, inducing calpain action. The presence or absence of the dUTP-analogue α,β-imido-dUTP did not show any effect on Ca²⁺-calpain-induced cleavage of human dUTPase. The catalytic rate constant of dUTPase was unaffected by calpain cleavage. Gel electrophoretic analysis showed that Ca²⁺-calpain-induced cleavage of human dUTPase resulted in several distinctly observable dUTPase fragments. Mass spectrometric identification of the calpain-cleaved fragments identified three calpain cleavage sites (between residues ⁴SE⁵; ⁷TP⁸; and ³¹LS³²). The cleavage between the ³¹LS³² peptide bond specifically removes the flexible N-terminal nuclear localization signal, indispensable for cognate localization.

Conclusions/Significance

Results argue for a mechanism where Ca²⁺-calpain may regulate nuclear availability and degradation of dUTPase.

Calpains as potential anti-cancer targets

INTRODUCTION

The intracellular signaling cysteine proteases, calpains (specifically the ubiquitous calpains 1 and 2), are involved in numerous physiological and pathological phenomena. Several works have highlighted the implication of calpains in processes crucial for cancer development and progression. For these reasons, calpains are considered by several authors as potential anti-cancer targets.

AREAS COVERED

How calpains are implicated in cancer formation and development, how these enzymes are deregulated in cancer cells and how these proteases could be targeted by anti-cancer drugs. Studies published in the last 10 years are focused on.

EXPERT OPINION

Targeting calpain activity with specific inhibitors could be a novel approach to limiting development of primary tumors and formation of metastases, by inhibiting tumor cell migration and invasion, which allows dissemination as well as tumor neovascularization, which in turn allows expansion. However, such drugs could interfere with anti-cancer treatments, as ubiquitous calpains play crucial roles in chemotherapy-induced apoptosis. For these reasons, drugs targeting calpains would have to be used selectively to avoid interference with other treatments and physiological processes. Further studies will be required concerning the other members of the calpain family and their potential implication in cancer development before considering treatments targeting their activity.

Targeted deletion of Capn4 in cells of the chondrocyte lineage impairs chondrocyte proliferation and differentiation

Calpains are calcium-dependent intracellular cysteine proteases, which include ubiquitously expressed mu- and m-calpains. Both calpains are heterodimers consisting of a large catalytic subunit and a small regulatory subunit. The calpain small subunit encoded by the gene Capn4 directly binds to the intracellular C-terminal tail of the receptor for the parathyroid hormone (PTH) and PTH-related peptide and modulates cellular functions in cells of the osteoblast lineage in vitro and in vivo. To investigate a physiological role of the calpain small subunit in cells of the chondrocyte lineage, we generated chondrocyte-specific Capn4 knockout mice. Mutant embryos had reduced chondrocyte proliferation and differentiation in embryonic growth plates compared with control littermates. In vitro analysis further revealed that deletion of Capn4 in cells of the chondrocyte lineage correlated with impaired cell cycle progression at the G(1)/S transition, reduced cyclin D gene transcription, and accumulated cell cycle proteins known as calpain substrates. Moreover, silencing of p27(Kip1) rescued an impaired cell growth phenotype in Capn4 knockdown cells, and reintroducing the calpain small subunit partially normalized cell growth and accumulated cyclin D protein levels in a dose-dependent manner. Collectively, our findings suggest that the calpain small subunit is essential for proper chondrocyte functions in embryonic growth plates.

Effects of the Chinese prescription Kangen-karyu and its crude drug Tanjin on ageing process in rats

The effects of the Chinese prescription Kangen-karyu and its crude drug Tanjin on the ageing process were investigated in rats. Diets supplemented with Kangen-karyu and Tanjin extracts decreased glycosylated protein levels in serum, a risk marker of ageing and ageing-related diseases. In addition, they inhibited the levels of thiobarbituric acid reactive substance in the serum and liver; Kangen-karyu in particular led to a strong decrease in hepatic mitochondrial thiobarbituric acid reactive substance. The decline in the reduced glutathione/oxidized glutathione ratio in the liver observed with ageing was ameliorated by Kangen-karyu and Tanjin, while these groups attenuated the increase in glutathione peroxidase activity of hepatic tissue against ageing. This suggests that Kangen-karyu and Tanjin regulate the glutathione redox cycle that maintains the cellular redox condition against age-related oxidative stress. Moreover, the overexpression of cytoplasmic cytochrome c observed with ageing was attenuated by Kangen-karyu and Tanjin. This provides new evidence that Kangen-karyu and Tanjin inhibit leakage of superoxide in mitochondria and attenuate cellular oxidative damage. Furthermore, Kangen-karyu and Tanjin would maintain mitochondrial function with ageing through the regulation of related protein expression such as bax and bcl-2 proteins. In addition, Kangen-karyu reduced the expression of nuclear factor kappa B; Kangen-karyu and Tanjin did not affect the expression of inhibitor kappa B. The present study demonstrated that Kangenkaryu prevented oxidative damage and mitochondrial dysfunction with ageing. Furthermore, Kangen-karyu showed a stronger protective effect against ageing by oxidative stress than Tanjin, probably through synergistic and/or additive effects.

Calpain 2 is required for sister chromatid cohesion

Calpains form a family of Ca(2+)-dependent cysteine proteases involved in diverse cellular processes. However, the specific functions of each calpain isoform remain unknown. Recent reports have shown that calpain 2 (Capn2) is essential for cell viability. We have recently shown that Capn2 is a nuclear protease associated with chromosomes during mitosis in mammalian embryonic cells. We now report that Capn2 depletion impairs mitosis and induces apoptosis in murine cells. Low Capn2 levels induce chromosome alignment defects, the loss of histone H3 threonine 3 phosphorylation at centromeres, and premature sister chromatid separation. Thus, Capn2 may play a role in fundamental mitotic functions, such as the maintenance of sister chromatid cohesion.

Inhibition of tumor cell motility by the interferon-inducible GTPase MxA

To identify pathways controlling prostate cancer metastasis we performed differential display analysis of the human prostate carcinoma cell line PC-3 and its highly metastatic derivative PC-3M. This revealed that a 78-kDa interferon-inducible GTPase, MxA, was expressed in PC-3 but not in PC-3M cells. The gene encoding MxA, MX1, is located in the region of chromosome 21 deleted as a consequence of fusion of TMPRSS2 and ERG, which has been associated with aggressive, invasive prostate cancer. Stable exogenous MxA expression inhibited in vitro motility and invasiveness of PC-3M cells. In vivo exogenous MxA expression decreased the number of hepatic metastases following intrasplenic injection. Exogenous MxA also reduced motility and invasiveness of highly metastatic LOX melanoma cells. A mutation in MxA that inactivated its GTPase reversed inhibition of motility and invasion in both tumor cell lines. Co-immunoprecipitation studies demonstrated that MxA associated with tubulin, but the GTPase-inactivating mutation blocked this association. Because MxA is a highly inducible gene, an MxA-targeted drug discovery screen was initiated by placing the MxA promoter upstream of a luciferase reporter. Examination of the NCI diversity set of small molecules revealed three hits that activated the promoter. In PC-3M cells, these drugs induced MxA protein and inhibited motility. These data demonstrate that MxA inhibits tumor cell motility and invasion, and that MxA expression can be induced by small molecules, potentially offering a new approach to the prevention and treatment of metastasis.

Expanded cells in monoclonal TCR-alphabeta+/CD4+/NKa+/CD8-/+dim T-LGL lymphocytosis recognize hCMV antigens

Recent studies suggest the potential involvement of common antigenic stimuli on the ontogeny of monoclonal T-cell receptor (TCR)-alphabeta(+)/CD4(+)/NKa(+)/CD8(-/+dim) T-large granular lymphocyte (LGL) lymphocytosis. Because healthy persons show (oligo)clonal expansions of human cytomegalovirus (hCMV)-specific TCRVbeta(+)/CD4(+)/cytotoxic/memory T cells, we investigate the potential involvement of hCMV in the origin and/or expansion of monoclonal CD4(+) T-LGL. Peripheral blood samples from patients with monoclonal TCR-alphabeta(+)/CD4(+) T-LGL lymphocytosis and other T-chronic lymphoproliferative disorders were evaluated for the specific functional response against hCMV and hEBV whole lysates as well as the "MQLIPDDYSNTHSTRYVTVK" hCMV peptide, which is specifically loaded in HLA-DRB1*0701 molecules. A detailed characterization of those genes that underwent changes in T-LGL cells responding to hCMV was performed by microarray gene expression profile analysis. Patients with TCR-alphabeta(+)/CD4(+) T-LGL displayed a strong and characteristic hCMV-specific functional response, reproduced by the hCMV peptide in a subset of HLA-DRB1*0701(+) patients bearing TCRVbeta13.1(+) clonal T cells. Gene expression profile showed that the hCMV-induced response affects genes involved in inflammatory and immune responses, cell cycle progression, resistance to apoptosis, and genetic instability. This is the first study providing evidence for the involvement of hCMV in the ontogeny of CD4(+) T-LGL, emerging as a model disorder to determine the potential implications of quite a focused CD4(+)/cytotoxic immune response.

Synthesis and calpain inhibitory activity of peptidomimetic compounds with constrained amino acids at the P2 position

The effect of incorporating alpha,alpha'-diethylglycine and alpha-aminocyclopentane carboxylic acid at the P(2) position of inhibitors on mu-calpain inhibition was studied. Compound 3 with alpha,alpha'-diethylglycine was over 20-fold more potent than 2 with alpha-aminocyclopentane carboxylic acid. Additionally, 3 was over 35-fold selective for mu-calpain compared to cathepsin B, while 2 was 3-fold selective for cathepsin B compared to mu-calpain. Thus, the conformation induced by the P(2) residue influenced the activities of the compounds versus the closely related cysteine proteases, and suggests an approach to the discovery of selective mu-calpain inhibitors.

Cathepsin L inhibitor I blocks mitotic chromosomes decondensation during cleavage cell cycles of sea urchin embryos

We have previously reported that sperm histones (SpH) degradation after fertilization is catalyzed by a cystein-protease (SpH-protease). Its inhibition blocks the degradation of SpH in vivo and also aborts sea urchin development at the initial embryonic cell cycles. It remains unknown if this effect is a consequence of the persistence of SpH on zygotic chromatin, or if this protease is involved per-se in the progression of the embryonic cell cycles. To discriminate among these two options we have inhibited this protease at a time when male chromatin remodeling was completed and the embryos were engaged in the second cell cycle of the cleavage divisions. The role of this enzyme in cell cycle was initially analyzed by immuno-inhibiting its SpH degrading activity in one of the two blastomeres after the initial cleavage division, while the other blastomere was used as a control. We found that in the blastomere injected with the anti-SpH-protease antibodies the cytokinesis was arrested, the chromatin failed to decondense after mitosis and BrdU incorporation into DNA was blocked. Since the N-terminal sequence and the SpH protease was homologous to the cathepsin L (Cat L) family of proteases, we subsequently investigated if the deleterious effect of the inhibition of this protease is related to its Cat L activity. In this context we analyzed the effect of Cat L inhibitor I (Z-Phe-Phe-CH(2)F) on embryonic development. We found that the addition of 100 uM of this inhibitor to the embryos harvested at the time of the initial cleavage division (80 min p.i.) mimics perfectly the effects of the immuno-inhibition of this enzyme obtained by microinjecting the anti-SpH-protease antibodies. Taken together these results indicate that the activity of this protease is required for embryonic cell cycle progression. Interestingly, we observed that when this protease was inhibited the chromatin decondensation after mitosis was abolished indicating that the inhibition of this enzyme affects chromosomes decondensation after mitosis.

In vivo targeted deletion of calpain small subunit, Capn4, in cells of the osteoblast lineage impairs cell proliferation, differentiation, and bone formation

Calpains are intracellular cysteine proteases, which include widely expressed mu- and m-calpains (1). Both mu-calpains and m-calpains are heterodimers consisting of a large catalytic subunit and a small regulatory subunit. The calpain small subunit encoded by the gene Capn4 directly binds to the intracellular C-terminal tail (C-tail) of the receptor for parathyroid hormone and parathyroid hormone-related peptide and modulates its cellular functions in osteoblasts in vitro (2). To investigate a potential role of the calpain small subunit in osteoblasts in vivo, we generated osteoblast-specific Capn4 knock-out mice using the Cre-LoxP system (3). Mutant mice had smaller bodies with shorter limbs, reduced trabecular bone with thinner cortices, and decreased osteoblast number. In vitro analysis confirmed that deletion of Capn4 in osteoblasts severely affected multiple osteoblast functions including proliferation, differentiation, and matrix mineralization. Collectively, our findings provide the first in vivo demonstration that the calpain small subunit is essential for proper osteoblast activity and bone remodeling.

Characterization and comparative expression of zebrafish calpain system genes during early development

The classic calpain system has been implicated in regulating a variety of cellular processes including cell adhesion, migration, and intracellular signaling; however, little is known regarding the function of this system in vivo. Two heterodimeric Ca(2+)-dependent cysteine proteases, mu-calpain (CAPN1) and m-calpain (CAPN2), and the endogenous inhibitor calpastatin (CAST) comprise the classic/ubiquitous calpain system in mammals. Recently, knockout of two murine classic calpain genes, Capn2 and Capn4/Capns1, revealed that components of the classic system are indispensable for preimplantation development. We identified four classic calpain catalytic subunit genes (capn1a, 1b, 2a, 2b), two regulatory subunit genes (capns1a, 1b), and calpastatin (cast) from the zebrafish. Our data suggest that the components of the classic mammalian system are both conserved and expanded in the teleost lineage. In contrast to the classic/ubiquitous mammalian system, zebrafish calpain system genes acquire unique, tissue-specific patterns of expression within the first 2 days of development.

Calcium-dependent proteolytic system and muscle dysfunctions: a possible role of calpains in sarcopenia

The calcium-dependent proteolytic system is composed of cysteine proteases named calpains. They are ubiquitous or tissue-specific enzymes. The two best characterised isoforms are the ubiquitously expressed mu- and m-calpains. Besides its regulation by calcium, calpain activity is tightly controlled by calpastatin, the specific endogenous inhibitor, binding to phospholipids, autoproteolysis and phosphorylation. Calpains are responsible for limited proteolytic events. Among the multitude of substrates identified so far are cytoskeletal and membrane proteins, enzymes and transcription factors. Calpain activity is involved in a large number of physiological and pathological processes. In this review, we will particularly focus on the implication of the calcium-dependent proteolytic system in relation to muscle physiology. Because of their ability to remodel cytoskeletal anchorage complexes, calpains play a major role in the regulation of cell adhesion, migration and fusion, three key steps of myogenesis. Calcium-dependent proteolysis is also involved in the control of cell cycle. In muscle tissue, in particular, calpains intervene in the regeneration process. Another important class of calpain substrates belongs to apoptosis regulating factors. The proteases may thus play a role in muscle cell death, and as a consequence in muscle atrophy. The relationships between calcium-dependent proteolysis and muscle dysfunctions are being further developed in this review with a particular emphasis on sarcopenia.

Amla (Emblica officinalisGaertn.) prevents dyslipidaemia and oxidative stress in the ageing process

Amla (Emblica officinalisGaertn.) is widely used in Indian medicine for the treatment of various diseases. We have investigated the effects of amla on the lipid metabolism and protein expression involved in oxidative stress during the ageing process. SunAmla or ethyl acetate extract of amla, a polyphenol-rich fraction, was administered at a dose of 40 or 10 mg/kg body weight per d for 100 d to young rats aged 2 months and aged rats aged 10 months. The lipid levels, such as cholesterol and TAG, in serum and liver were markedly elevated in aged control rats, while they were significantly decreased by the administration of amla. The PPARα is known to regulate the transcription of genes involved in lipid and cholesterol metabolism. The PPARα protein level in liver was reduced in aged control rats. However, the oral administration of amla significantly increased the hepatic PPARα protein level. In addition, oral administration of amla significantly inhibited the serum and hepatic mitochondrial thiobarbituric acid-reactive substance levels in aged rats. Moreover, the elevated expression level of bax was significantly decreased after the oral administration of amla, while the level of bcl-2 led to a significant increase. Furthermore, the expressions of hepatic NF-κB, inducible NO synthase (iNOS), and cyclo-oxygenase-2 (COX-2) protein levels were also increased with ageing. However, amla extract reduced the iNOS and COX-2 expression levels by inhibiting NF-κB activation in aged rats. These results indicate that amla may prevent age-related hyperlipidaemia through attenuating oxidative stress in the ageing process.

The regulation of cyclin D1 degradation: roles in cancer development and the potential for therapeutic invention

Cyclin D1 is an important regulator of cell cycle progression and can function as a transcriptionl co-regulator. The overexpression of cyclin D1 has been linked to the development and progression of cancer. Deregulated cyclin D1 degradation appears to be responsible for the increased levels of cyclin D1 in several cancers. Recent findings have identified novel mechanisms involved in the regulation of cyclin D1 stability. A number of therapeutic agents have been shown to induce cyclin D1 degradation. The therapeutic ablation of cyclin D1 may be useful for the prevention and treatment of cancer. In this review, current knowledge on the regulation of cyclin D1 degradation is discussed. Novel insights into cyclin D1 degradation are also discussed in the context of ablative therapy. A number of unresolved questions regarding the regulation of cellular cyclin D1 levels are also addressed.

Nutritional regulation of proteases involved in fetal rat insulin secretion and islet cell proliferation

Epidemiological studies have indicated that malnutrition during early life may programme chronic degenerative disease in adulthood. In an animal model of fetal malnutrition, rats received an isoenergetic, low-protein (LP) diet during gestation. This reduced fetal β-cell proliferation and insulin secretion. Supplementation during gestation with taurine prevented these alterations. Since proteases are involved in secretion and proliferation, we investigated which proteases were associated with these alterations and their restoration in fetal LP islets. Insulin secretion and proliferation of fetal control and LP islets exposed to different protease modulators were measured. Lactacystin and calpain inhibitor I, but not isovaleryl-l-carnitine, raised insulin secretion in control islets, indicating that proteasome and cysteinyl cathepsin(s), but not μ-calpain, are involved in fetal insulin secretion. Insulin secretion from LP islets responded normally to lactacystin but was insensitive to calpain inhibitor I, indicating a loss of cysteinyl cathepsin activity. Taurine supplementation prevented this by restoring the response to calpain inhibitor I. Control islet cell proliferation was reduced by calpain inhibitor I and raised by isovaleryl-l-carnitine, indicating an involvement of calpain. Calpain activity appeared to be lost in LP islets and not restored by taurine. Most modifications in the mRNA expression of cysteinyl cathepsins, calpains and calpastatin due to maternal protein restriction were consistent with reduced protease activity and were restored by taurine. Thus, maternal protein restriction affected cysteinyl cathepsins and the calpain–calpastatin system. Taurine normalised fetal LP insulin secretion by protecting cysteinyl cathepsin(s), but the restoration of LP islet cell proliferation by taurine did not implicate calpains.

Beta-lapachone, a quinone isolated from Tabebuia avellanedae, induces apoptosis in HepG2 hepatoma cell line through induction of Bax and activation of caspase

The DNA topoisomerase inhibitor beta-lapachone is a quinone obtained from the bark of the lapacho tree (Tabebuia avellanedae) in South America. It has been reported to possess a wide range of pharmacological properties, and is a promising cancer chemopreventive agent. In this study, the effects of beta-lapachone on the growth of the human hepatoma cell line HepG2 were investigated. The results showed that beta-lapachone inhibits the viability of HepG2 by inducing apoptosis, as evidenced by the formation of apoptotic bodies and DNA fragmentation. Reverse transcription-polymerase chain reaction and immunoblotting results indicated that treatments of cells with beta-lapachone resulted in down-regulation of anti-apoptotic Bcl-2 and Bcl-X(L) and up-regulation of pro-apoptotic Bax expression. beta-Lapachone-induced apoptosis was associated with a proteolytic activation of caspase-3 and -9 and degradation of poly(ADP-ribose) polymerase protein. However, beta-lapachone treatment did not affect the inhibitor of apoptosis proteins family and the Fas/FasL system. Taken together, our study indicated that beta-lapachone may have potential as a chemopreventive agent for liver cancer.

15-deoxy-Delta(12,14)-prostaglandin J2 inhibits G2-M phase progression in human breast cancer cells via the down-regulation of cyclin B1 and survivin expression

The cyclopentenone prostaglandin 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) exerts a growth inhibitory effect on cancer cells, and this effect is linked to the induction of apoptosis or cell cycle arrest. Induction of apoptosis by 15d-PGJ(2) is associated with the down-regulation of anti-apoptotic proteins. G(0)-G(1)-->S phase progression is inhibited by 15d-PGJ(2) via the degradation of cyclin D1. In this study, we further investigated the mechanism by which 15d-PGJ(2) inhibits cancer cell growth by using the breast cancer cell lines MCF-7 and T-47D. Treatment with 20 microM 15d-PGJ(2) for 72 h completely blocked the growth in both cell lines. However, the proportions of apoptotic MCF-7 and T-47D cells were 21.1% and 40.9%, respectively, indicating that the induction of apoptosis did not appear to fully account for growth inhibition by 15d-PGJ(2). Cell cycle analysis using cells synchronized at the G(0)-G(1) or S phase revealed that 15d-PGJ(2) blocked not only G(0)-G(1)-->S phase progression but also G(2)-M phase progression. The expression of both cyclins D1 and B1 was decreased by 15d-PGJ(2). Furthermore, 15d-PGJ(2) inhibited aurora-B kinase activity, which coincided with the down-regulation of survivin. Thus, 15d-PGJ(2) induced cell cycle arrest at the G(2)-M phase via inhibition of cyclin B1 expression and aurora-B kinase activity. We conclude that survivin may be an important target for 15d-PGJ(2), and its down-regulation may lead to a decrease in aurora-B kinase activity.

Calpain activation is required for glutamate-induced p27 down-regulation in cultured cortical neurons

Recent evidence suggests that cell cycle-related molecules play pivotal roles in multiple forms of cell death in post-mitotic neurons. Nevertheless, it remains unclear what molecular mechanisms are involved in the regulation of expression levels and activities of these molecules. We showed previously that treatment with extracellular glutamate decreases cyclin-dependent kinase inhibitor p27 before neuronal cell death. In this study, we demonstrate that reductions of both p27 and neuronal viability were dependent on activity of calpain, a Ca(2+)-dependent protease, but not on activity of caspase 3. Interestingly, the glutamate-induced reduction of p27 was not dependent on the ubiquitin-proteasome system. In fact, p27 was present only in the neuronal nucleus, whereas calpain 1, a ubiquitous calpain, was observed both in the neuronal nucleus and cytoplasm in control cultures. Glutamate treatment did not change the localization patterns of p27 and calpain 1. It reduced p27 expression level in the nucleus in a calpain-dependent manner. In vitro experiments using neuronal cell lysate and p27 recombinant protein revealed that p27 was degraded as a substrate of activated calpain 1. These results suggest that calpain(s), activated by glutamate treatment, degrade(s) p27 in the nucleus of neurons, which might promote aberrant cell cycle progression.

Role of complex cyclin d1/cdk4 in somatostatin subtype 2 receptor-mediated inhibition of cell proliferation of a medullary thyroid carcinoma cell line in vitro

Somatostatin (SRIH) inhibits cell proliferation by interacting with five distinct SRIH receptor subtypes (SSTRs) activating several pathways in many tissues. We previously demonstrated that SRIH, by activating Src homology-2-containing protein, inhibits cell proliferation of the human medullary thyroid carcinoma cell line, TT, which expresses all SSTRs. However, the effects of SRIH on cell cycle proteins have not been investigated so far. We therefore evaluated the effects of SRIH and a selective SSTR2 agonist on cell cycle protein expression, mainly focusing on cyclin D1 and its associated kinases. Our data show that SRIH and the selective SSTR2 agonist, BIM-23120, reduce cell proliferation and DNA synthesis as well as induce a delay of the cell cycle in G(2)/M phase. Moreover, treatment with both SRIH and BIM-23120 decreases cyclin D1 levels, with a parallel increase in phosphocyclin D1 levels, suggesting protein degradation. Moreover, our data show an increase in glycogen synthase kinase-3beta activity, which triggers phosphorylation-dependent cyclin D1 degradation. Indeed, we observed a reduction in cyclin D1 protein half-life under treatment with SRIH or the SSTR2 selective agonist. A reduction in cdk4 protein levels is also observed with a parallel reduction in Rb phosphorylation levels at Ser-780. Our data indicate that the subtype 2 receptor-mediated antiproliferative effect of SRIH on TT cell proliferation may be exerted through a decrease in cyclin D1 levels.

Identification of calpain cleavage sites in the G1 cyclin-dependent kinase inhibitor p19(INK4d)

Calpains are a large family of Ca2+-dependent cysteine proteases that are ubiquitously distributed across most cell types and vertebrate species. Calpains play a role in cell differentiation, apoptosis, cytoskeletal remodeling, signal transduction and the cell cycle. The cell cycle proteins cyclin D1 and p21(KIP1), for example, have been shown to be affected by calpains. However, the rules that govern calpain cleavage specificity are poorly understood. We report here studies on the pattern of mu-calpain proteolysis of the p19(INK4d) protein, a cyclin-dependent kinase 4/6 inhibitor that negatively regulates the mammalian cell cycle. Our data show new characteristics of calpain action: mu-calpain cleaves p19(INK4d) immediately after the first and second ankyrin repeats that are structurally less stable compared to the other repeats. This is in contrast to features observed so far in the specificity of calpains for their substrates. These results imply that calpain may be involved in the cell cycle by regulating the cell cycle regulatory protein turnover through CDK inhibitors and cyclins.

Histone deacetylase inhibitor, trichostatin A induces ubiquitin-dependent cyclin D1 degradation in MCF-7 breast cancer cells

BACKGROUND

Cyclin D1 is an important regulator of G1-S phase cell cycle transition and has been shown to be important for breast cancer development. GSK3beta phosphorylates cyclin D1 on Thr-286, resulting in enhanced ubiquitylation, nuclear export and degradation of the cyclin in the cytoplasm. Recent findings suggest that the development of small-molecule cyclin D1 ablative agents is of clinical relevance. We have previously shown that the histone deacetylase inhibitor trichostatin A (TSA) induces the rapid ubiquitin-dependent degradation of cyclin D1 in MCF-7 breast cancer cells prior to repression of cyclin D1 gene (CCND1) transcription. TSA treatment also resulted in accumulation of polyubiquitylated GFP-cyclin D1 species and reduced levels of the recombinant protein within the nucleus.

RESULTS

Here we provide further evidence for TSA-induced ubiquitin-dependent degradation of cyclin D1 and demonstrate that GSK3beta-mediated nuclear export facilitates this activity. Our observations suggest that TSA treatment results in enhanced cyclin D1 degradation via the GSK3beta/CRM1-dependent nuclear export/26S proteasomal degradation pathway in MCF-7 cells.

CONCLUSION

We have demonstrated that rapid TSA-induced cyclin D1 degradation in MCF-7 cells requires GSK3beta-mediated Thr-286 phosphorylation and the ubiquitin-dependent 26S proteasome pathway. Drug induced cyclin D1 repression contributes to the inhibition of breast cancer cell proliferation and can sensitize cells to CDK and Akt inhibitors. In addition, anti-cyclin D1 therapy may be highly specific for treating human breast cancer. The development of potent and effective cyclin D1 ablative agents is therefore of clinical relevance. Our findings suggest that HDAC inhibitors may have therapeutic potential as small-molecule cyclin D1 ablative agents.

The cyclin D1 proto-oncogene is sequestered in the cytoplasm of mammalian cancer cell lines

BACKGROUND

The cyclin D1 proto-oncogene is an important regulator of G1 to S-phase transition and an important cofactor for several transcription factors in numerous cell types. Studies on neonatal cardiomyocytes and postmitotic neurons indicate that the activity of cyclin D1 may be regulated through its cytoplasmic sequestration. We have demonstrated previously, that TSA induces the ubiquitin-dependent degradation of cyclin D1 in MCF-7 breast cancer cells. Additional studies were initiated in order to further investigate the effect of TSA on cyclin D1 regulation using sub-cellular fractionation techniques.

RESULTS

Our studies revealed cyclin D1 to be localized predominantly within the cytoplasmic fraction of all cell lines tested. These observations were confirmed by confocal microscopy. GSK3beta was found to be localized within both the nucleus and cytoplasm throughout the cell cycle. Inhibition of GSK3beta or CRM1-dependent nuclear export resulted in only modest nuclear accumulation, suggesting that the cytoplasmic localization of cyclin D1 results from the inhibition of its nuclear import.

CONCLUSION

We have shown by several different experimental approaches, that cyclin D1 is in fact a predominantly cytoplasmic protein in mammalian cancer cell lines. Recent studies have shown that the cytoplasmic sequestration of cyclin D1 prevents apoptosis in neuronal cells. Our results suggest that cytoplasmic sequestration may additionally serve to regulate cyclin D1 activity in mammalian cancer cells.

Difference of cell cycle arrests induced by lidamycin in human breast cancer cells

Lidamycin (LDM) is a member of the enediyne antibiotic family. It is undergoing phase I clinical trials in China as a potential chemotherapeutic agent. In the present study, we investigated the mechanism by which LDM induced cell cycle arrest in human breast cancer cells. The results showed that LDM induced G1 arrest in p53 wild-type MCF-7 cells at low concentrations, and caused both G1 and G2/M arrests at higher concentrations. In contrast, LDM induced only G2/M arrest in p53-mutant MCF-7/DOX cells. Western blotting analysis indicated that LDM-induced G1 and G2/M arrests in MCF-7 cells were associated with an increase of p53 and p21, and a decrease of phosphorylated retinoblastoma tumor suppressor protein, cyclin-dependent kinase (Cdk), Cdc2 and cyclin B1 protein levels. However, LDM-induced G2/M arrest in MCF-7/DOX cells was correlated with the reduction of cyclin B1 expression. Further study indicated that the downregulation of cyclin B1 by LDM in MCF-7 cells was associated with decreasing cyclin B1 mRNA levels and promoting protein degradation, whereas it was only due to inducing cyclin B1 protein degradation in MCF-7/DOX cells. In addition, activation of checkpoint kinases Chk1 or Chk2 maybe contributed to LDM-induced cell cycle arrest. Taken together, we provide the first evidence that LDM induces different cell cycle arrests in human breast cancer cells, which are dependent on drug concentration and p53 status. These findings are helpful in understanding the molecular anti-cancer mechanisms of LDM and support its clinical trials.

Disruption of protein kinase a regulation causes immortalization and dysregulation of D-type cyclins

Phosphorylation is a key event in cell cycle control, and dysregulation of this process is observed in many tumors, including those associated with specific inherited neoplasia syndromes. We have shown previously that patients with the autosomal dominant tumor predisposition Carney complex carry inactivating mutations in the PRKAR1A gene, which encodes the type 1A regulatory subunit of protein kinase A (PKA), the cyclic AMP-dependent protein kinase. This defect was associated with dysregulation of PKA signaling, and genetic analysis has suggested that complete loss of the gene may be required for tumorigenesis. To determine the mechanism by which dysregulation of PKA causes tumor formation, we generated in vitro primary mouse cells lacking the Prkar1a protein. We report that this genetic disruption of PKA regulation causes constitutive PKA activation and immortalization of primary mouse embryonic fibroblasts (MEFs). At the molecular level, knockout of Prkar1a leads to up-regulation of D-type cyclins, and this increase occurs independently of other pathways known to increase cyclin D levels. Despite the immortalized phenotype, known mediators of cellular senescence (e.g., p53 and p19ARF) seem to remain intact in Prkar1a-/- MEFs. Mechanistically, cyclin D1 mRNA levels are not altered in the knockout cells, but protein half-life is markedly increased. Using this model, we provide the first direct genetic evidence that dysregulation of PKA promotes important steps in tumorigenesis, and that cyclin D1 is an essential target of PKA.

Down-regulation of cyclooxygenase-2 and telomerase activity by beta-lapachone in human prostate carcinoma cells

Beta-lapachone, the product of a tree Tabebuia avellanedae from South America, is known to exhibit various pharmacologic properties, the mechanisms of which are poorly understood. In the present study, we investigated further possible mechanisms by which beta-lapachone exerts its anti-proliferative action in cultured human prostate carcinoma DU145 cells. Exposure of DU145 cells to beta-lapachone resulted in growth inhibition and induction of apoptosis in a dose-dependent manner as measured by MTT assay, fluorescent microscopy, and flow-cytometry analysis. The increase in apoptosis was associated with a dose-dependent up-regulation in pro-apoptotic Bax expression, down-regulation of anti-apoptotic Bcl-2, and proteolytic activation of caspase-3 protease. We found beta-lapachone decreased the levels of cyclooxygenase (COX)-2 mRNA and protein expression without significant changes in the levels of COX-1, which was correlated with a decrease in prostaglandin E2 (PGE2) synthesis. Furthermore, beta-lapachone treatment markedly inhibited the activity of telomerase in a dose-dependent fashion. Additionally, the expression of human telomerase reverse transcriptase (hTERT), a main determinant of the telomerase enzymatic activity, was progressively down-regulated by beta-lapachone treatment. Taken together, these findings provide important new insights into the possible molecular mechanisms of the anti-cancer activity of beta-lapachone.

Microinjection of an antibody against the cysteine-protease involved in male chromatin remodeling blocks the development of sea urchin embryos at the initial cell cycle

We reported recently that the inhibition of cysteine-proteases with E-64-d disturbs DNA replication and prevents mitosis of the early sea urchin embryo. Since E-64-d is a rather general inhibitor of thiol-proteases, to specifically target the cysteine-protease previously identified in our laboratory as the enzyme involved in male chromatin remodeling after fertilization, we injected antibodies against the N-terminal sequence of this protease that were able to inhibit the activity of this enzyme in vitro. We found that injection of these antibodies disrupts the initial zygotic cell cycle. As shown in this report in injected zygotes a severe inhibition of DNA replication was observed, the mitotic spindle was not correctly bipolarized the embryonic development was aborted at the initial cleavage division. Consequently, the injection of these antibodies mimics perfectly the effects previously described for E-64-d, indicating that the effects of this inhibitor rely mainly on the inhibition of the cysteine-protease involved in male chromatin remodeling after fertilization. These results further support the crucial role of this protease in early embryonic development.

Ircinin-1 induces cell cycle arrest and apoptosis in SK-MEL-2 human melanoma cells

We investigated the effects of ircinin-1, a lipid compound (a C25 sesterterpene tetronic acid) isolated from marine sponges (Sarcotragus sp.), on the modulation of cell cycle and induction of apoptosis in SK-MEL-2 human skin cancer cells (mutant p53). Ircinin-1 treatment on SK-MEL-2 cells resulted in a dose-dependent inhibition of cell growth and induced apoptotic cell death. Flow cytometric analysis revealed that ircinin-1 resulted in G1 arrest in cell cycle progression which was associated with a marked decrease in the protein expression of D-type cyclins and their activating partners Cdk 4 and 6 with concomitant inductions of p21WAF1/CIP1 and p27KIP1. The induction of p21WAF1/CIP1 appears to be transcriptionally upregulated and is p53-independent. In addition, ircinin-1 suppressed the phosphorylation of pRb protein and increased the co-association of pRb or proliferating cell nuclear antigen (PCNA) with p21WAF1/CIP1 in these cells. Ircinin-1 treatment also resulted in induction of apoptosis as determined by morphological changes, DNA fragmentation, alternated ratio of Bax/Bcl-2, cleavages of poly(ADP-ribose) polymerase and PLC-gamma1, and flow cytometric analysis. Ircinin-1 also induced cytochrome c release, cleavage activations of caspase-3 and -9, and upregulation of Fas and Fas-L. Even though the inhibitor of apoptosis protein (IAP) was expressed in ircinin-1-untreated or -treated SK-MEL-2 cells, only the level of cIAP-1, but not XIAP or cIAP-2, was decreased during ircinin-1-induced apoptosis at Western blot and RT-PCR studies. Taken together, these findings suggest that ircinin-1 has strong potential for development as an agent for prevention against skin cancer.

Tumor suppressor SMAR1 mediates cyclin D1 repression by recruitment of the SIN3/histone deacetylase 1 complex

Matrix attachment region binding proteins have been shown to play an important role in gene regulation by altering chromatin in a stage- and tissue-specific manner. Our previous studies report that SMAR1, a matrix-associated protein, regresses B16-F1-induced tumors in mice. Here we show SMAR1 targets the cyclin D1 promoter, a gene product whose dysregulation is attributed to breast malignancies. Our studies reveal that SMAR1 represses cyclin D1 gene expression, which can be reversed by small interfering RNA specific to SMAR1. We demonstrate that SMAR1 interacts with histone deacetylation complex 1, SIN3, and pocket retinoblastomas to form a multiprotein repressor complex. This interaction is mediated by the SMAR1(160-350) domain. Our data suggest SMAR1 recruits a repressor complex to the cyclin D1 promoter that results in deacetylation of chromatin at that locus, which spreads to a distance of at least the 5 kb studied upstream of the cyclin D1 promoter. Interestingly, we find that the high induction of cyclin D1 in breast cancer cell lines can be correlated to the decreased levels of SMAR1 in these lines. Our results establish the molecular mechanism exhibited by SMAR1 to regulate cyclin D1 by modification of chromatin.

Calpains in muscle wasting

Calpains are intracellular nonlysosomal Ca(2+)-regulated cysteine proteases. They mediate regulatory cleavages of specific substrates in a large number of processes during the differentiation, life and death of the cell. The purpose of this review is to synthesize our current understanding of the participation of calpains in muscle atrophy. Muscle tissue expresses mainly three different calpains: the ubiquitous calpains and calpain 3. The participation of the ubiquitous calpains in the initial degradation of myofibrillar proteins occurring in muscle atrophy as well as in the necrosis process accompanying muscular dystrophies has been well characterized. Inactivating mutations in the calpain 3 gene are responsible for limb-girdle muscular dystrophy type 2A and calpain 3 has been found to be downregulated in different atrophic situations, suggesting that it has to be absent for the atrophy to occur. The fact that similar regulations of calpain activities occur during exercise as well as in atrophy led us to propose that the calpains control cytoskeletal modifications needed for muscle plasticity.

Induction of apoptosis and inhibition of telomerase activity by aqueous extract from Platycodon grandiflorum in human lung carcinoma cells

The objective of the present study was to investigate the effect of aqueous extract from the root of Platycodon grandiflorum (AEPG) on the cell growth and apoptosis in human lung carcinoma cell line A549. Exposure of A549 cells to AEPG resulted in growth inhibition and induction of apoptosis in a dose-dependent manner as measured by hemocytometer counts, fluorescence microscopy and flow cytometry analysis. This increase in apoptosis was associated with a decrease in Bcl-2 expression, an increase of Bax and an activation of caspase-3. AEPG treatment markedly inhibited the activity of telomerase in a dose-dependent fashion. Additionally, the expression of human telomerase reverse transcriptase (hTERT), a main determinant of the telomerase enzymatic activity, was progressively down-regulated by AEPG treatment. These findings suggest that the apoptotic events by AEPG were associated with the diminished telomerase activity and down-regulation of Bcl-2 expression.