Regucalcin and metabolic disorders: osteoporosis and hyperlipidemia are induced in regucalcin transgenic rats

Regucalcin Is a Potential Regulator in Human Cancer: Aiming to Expand into Cancer Therapy

Regucalcin, a calcium-binding protein lacking the EF-hand motif, was initially discovered in 1978. Its name is indicative of its function in calcium signaling regulation. The rgn gene encodes for regucalcin and is situated on the X chromosome in both humans and vertebrates. Regucalcin regulates pivotal enzymes involved in signal transduction and has an inhibitory function, which includes protein kinases, protein phosphatases, cysteinyl protease, nitric oxide dynthetase, aminoacyl-transfer ribonucleic acid (tRNA) synthetase, and protein synthesis. This cytoplasmic protein is transported to the nucleus where it regulates deoxyribonucleic acid and RNA synthesis as well as gene expression. Overexpression of regucalcin inhibits proliferation in both normal and cancer cells in vitro, independent of apoptosis. During liver regeneration in vivo, endogenous regucalcin suppresses cell growth when overexpressed. Regucalcin mRNA and protein expressions are significantly downregulated in tumor tissues of patients with various types of cancers. Patients exhibiting upregulated regucalcin in tumor tissue have shown prolonged survival. The decrease of regucalcin expression is linked to the advancement of cancer. Overexpression of regucalcin carries the potential for preventing and treating carcinogenesis. Additionally, extracellular regucalcin has displayed control over various types of human cancer cells. Regucalcin may hold a prominent role as a regulatory factor in cancer development. Supplying the regucalcin gene could prove to be a valuable asset in cancer treatment. The therapeutic value of regucalcin suggests its potential significance in treating cancer patients. This review delves into the most recent research on the regulatory role of regucalcin in human cancer development, providing a novel approach for treatment.

Functional pleiotropy of calcium binding protein Regucalcin in signaling and diseases

Regucalcin (Mr ∼ 33.38 kDa) is a calcium binding protein, discovered in rat liver. In humans, gene for regucalcin is located on chromosome-11 (p11.3-q11.2) consisting of seven exons and six introns. The protein differs from other calcium binding protein in the way that it lacks EF-hand motif of calcium binding domain. It is also called as Senescence Marker Protein-30 (SMP-30) as previously its weight assumes to be 30 kDa and expression of this protein decreases with aging in androgen independent manner. Among vertebrates, it is a highly conserved protein showing gene homology in Drosophila, Xenopus, fireflies and others too. It is primarily expressed in liver and kidney in addition to brain, lungs, and skeletal muscles. Regucalcin acts as a Ca²⁺ regulatory protein and controls various cellular functions in liver and other organs. It suppresses protein phosphatase, protein kinase, DNA and RNA synthesis. Published evidences suggest regucalcin to be a reliable biomarker in various disorders of liver, kidney, brain and ocular. In over expressed state, it subdues apoptosis in cloned rat hepatoma cells and also induces hyperlipidemia and osteoblastogenesis by regulating various factors. Owing to the multi-functionality of regucalcin this review is presented to elaborate its importance in order to understand its involvement in cellular signaling during various pathologies.

Overexpression of regucalcin blocks the migration, invasion, and bone metastatic activity of human prostate cancer cells: Crosstalk between cancer cells and bone cells

BACKGROUND

Prostate cancer is a bone metastatic cancer and is the second leading cause of cancer-related death in men. Prolonged progression-free survival of prostate cancer patients is associated with high regucalcin expression in the tumor tissues. This study investigates the underlying mechanism by which regucalcin prevents bone metastatic activity of prostate cancer cells.

METHODS

Human prostate cancer PC-3 or DU-145 wild-type cells or regucalcin-overexpressing PC-3 or DU-145 cells (transfectants) were cultured in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum.

RESULTS

Overexpressed regucalcin suppressed the migration and invasion of bone metastatic human prostate cancer cells in vitro, and it reduced the levels of key proteins in metastasis including Ras, Akt, MAPK, RSK-2, mTOR, caveolin-1, and integrin β1. Invasion of prostate cancer cells was promoted by coculturing with preosteoblastic MC3T3-E1 or preosteoclastic RAW264.7 cells. Coculturing with cancer cells and bone cells repressed the growth of preosteoblastic cells and enhanced osteoclastogenesis of preosteoclastic cells, and these alterations were caused by a conditioned medium from cancer cell culture. Disordered differentiation of bone cells was prevented by regucalcin overexpression. Production of tumor necrosis factor-α (TNF-α) in cancer cells was blocked by overexpressed regucalcin. Of note, the effects of conditioned medium on bone cells were prevented by NF-κB inhibitor. TNF-α may be important as a mediator in the crosstalk between cancer cells and bone cells.

CONCLUSION

Overexpression of regucalcin suppressed the migration, invasion, and bone metastatic activity of human prostate cancer cells. This study may provide a new strategy for therapy with the regucalcin gene transfer.

Extracellular Regucalcin Suppresses the Growth, Migration, Invasion and Adhesion of Metastatic Human Prostate Cancer Cells

Regucalcin plays a multifunctional role in the regulation of cellular function including metabolism, signaling process and transcriptional activity in maintaining cell homeostasis. Downregulated expression or activity of regucalcin contributes to the development of malignancies in various types of human cancer. Survival of cancer patients, including metastatic prostate cancer, is prolonged with high expression of regucalcin in the tumor tissues. Furthermore, we elucidate whether extracellular regucalcin conquers the growth, migration, invasion and adhesion of metastatic human prostate cancer PC-3 and DU-145 cells. Extracellular regucalcin (0.1, 1, and 10 nM) of physiologic levels inhibited colony formation and growth of PC-3 and DU-145 cells, while it did not have an effect on cell death. Repressive effects of extracellular regucalcin on the proliferation were not exhibited by the presence of inhibitors of cell cycle, intracellular signaling process and transcriptional activity, suggesting that the signals of extracellular regucalcin are transmitted to block cell growth. Furthermore, extracellular regucalcin (0.1, 1, or 10 nM) inhibited migration, invasion and adhesion of PC-3 and DU-145 cells. Mechanistically, extracellular regucalcin (10 nM) decreased the levels of various signaling proteins including Ras, hosphatidylinositol-3 kinase, mitogen-activated protein kinase, mTOR, RSK-2, caveolin-1 and integrin β1 in PC-3 cells. Thus, extracellular regucalcin may play a suppressive role in growth, migration, invasion and adhesion, which are involved in metastatic activity of human prostate cancer cells, via affecting diverse signaling processes. This study may provide a new strategy in preventing metastatic prostate cancer with exogenous regucalcin.

Chemical inducer of regucalcin attenuates lipopolysaccharide-induced inflammatory responses in pancreatic MIN6 β-cells and RAW264.7 macrophages

We previously isolated derrisfolin A, a novel rotenoid derivative, from the stems of Derris trifoliata Lour. (Leguminosae). Here, we report that derrisfolin A induces the expression of endogenous regucalcin (RGN) protein in both pancreatic MIN6 β-cells and RAW264.7 macrophages. Induction of RGN expression by derrisfolin A or retrovirus-mediated gene transfer in MIN6 cells and RAW264.7 macrophages significantly decreased lipopolysaccharide (LPS)-induced mRNA expression of Nos2, Il1b, and Tnf via nuclear factor-κB activation; reduced LPS-induced apoptosis in MIN6 cells, accompanied by decreased production of nitric oxide, interleukin-1β, and tumor necrosis factor-α; and attenuated generation of LPS-induced reactive oxygen species, malondialdehyde, and 3-nitrotyrosine in MIN6 cells. Additionally, in co-cultures of MIN6 cells with RAW264.7 macrophages in the presence of LPS, induction of RGN expression by derrisfolin A or retrovirus-mediated gene transfer in RAW264.7 macrophages attenuated apoptosis and oxidative/nitrosative stress in MIN6 cells. These results suggest that the induction of RGN expression in MIN6 cells was effective in suppressing LPS-induced inflammatory cytotoxicity and that in co-culture conditions, the induction of RGN expression in RAW264.7 macrophages blocked LPS-induced paracrine effects of RAW264.7 macrophages on inflammatory cytotoxicity in MIN6 cells. Our findings suggest that derrisfolin A, a chemical inducer of RGN, might be useful for developing a new drug against macrophage-associated β-cell inflammation in type 2 diabetes.

The involvement of a regucalcin in suppressing hemocyte apoptosis in Pacific oyster Crassostrea gigas

Regucalcin (RGN), also known as senescence marker protein-30 (SMP30), plays a vital role in the regulation of Ca²⁺ homeostasis. In the present study, a regucalcin (designated as CgRGN) was identified from Pacific oyster Crassostrea gigas. The complete cDNA sequence of CgRGN was of 1059 bp, containing an open reading frame of 933 bp which encoded a protein of 310 amino acids. The deduced amino acid sequence of CgRGN shared similarity with other RGNs from the genome of C. gigas as well as other species. The mRNA transcripts of CgRGN were universally detected in all tested tissues, with higher level in hepatopancreas, labial palp, and gills. The relative expression level of CgRGN in hemocytes was significantly up-regulated (p < 0.05) at 3, 12, 72, and 96 h after the stimulation of lipopolysaccharide (LPS). After CgRGN expression was interfered by specific CgRGN-dsRNA, the hemocytes apoptosis rate increased dramatically at 12 h post LPS stimulation (1.56 fold, p < 0.01), compared to the control group. The caspase-3 activity in hemocytes and NO concentration in hemolymph increased significantly (p < 0.05) in dsCgRGN injection oysters. These results collectively indicated that CgRGN could suppress LPS-induced apoptosis and be involved in the immune response of oysters.

A journey into the world of insect lipid metabolism

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin-like peptides that activate lipogenic transcription factors, such as sterol regulatory element-binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP-response element-binding protein. Calcium is the primary-secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

Towards frailty biomarkers: Candidates from genes and pathways regulated in aging and age-related diseases

OBJECTIVE

Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel.

METHODS

Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers.

RESULTS

A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified.

CONCLUSION

Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.

Targeting Hepatic Protein Carbonylation and Oxidative Stress Occurring on Diet-Induced Metabolic Diseases through the Supplementation with Fish Oils

The present study addressed the ability of long-chain ω-3 polyunsaturated fatty acids (ω-3 PUFA), i.e., eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), to ameliorate liver protein damage derived from oxidative stress and induced by consumption of high-caloric diets, typical of Westernized countries. The experimental design included an animal model of Sprague-Dawley rats fed high-fat high-sucrose (HFHS) diet supplemented with ω-3 EPA and DHA for a complete hepatic proteome analysis to map carbonylated proteins involved in specific metabolic pathways. Results showed that the intake of marine ω-3 PUFA through diet significantly decreased liver protein carbonylation caused by long-term HFHS consumption and increased antioxidant system. Fish oil modulated the carbonylation level of more than twenty liver proteins involved in critical metabolic pathways, including lipid metabolism (e.g., albumin), carbohydrate metabolism (e.g., pyruvate carboxylase), detoxification process (e.g., aldehyde dehydrogenase 2), urea cycle (e.g., carbamoyl-phosphate synthase), cytoskeleton dynamics (e.g., actin), or response to oxidative stress (e.g., catalase) among others, which might be under the control of diet marine ω-3 PUFA. In parallel, fish oil significantly changed the liver fatty acid profile given by the HFHS diet, resulting in a more anti-inflammatory phenotype. In conclusion, the present study highlights the significance of marine ω-3 PUFA intake for the health of rats fed a Westernized diet by describing several key metabolic pathways which are protected in liver.

Glucose and glutamine handling in the Sertoli cells of transgenic rats overexpressing regucalcin: plasticity towards lactate production

Sertoli cells (SCs) possess the unparalleled ability to provide the germ line with growth factors and nutrients. Although SCs can oxidize amino acids, e.g., glutamine, they mostly metabolize glucose, producing high amounts of lactate, the germ cells preferential substrate. Regucalcin (RGN) is a calcium-binding protein that has been indicated as a regulator of cell metabolism. In this study, we investigated glucose and glutamine handling in the SCs of transgenic rats overexpressing RGN (Tg-RGN) comparatively with wild-type (Wt) littermates. Primary SCs isolated from adult Tg-RGN animals and maintained in culture for 24 hours, produced and exported more lactate, despite consuming less glucose. These observations were underpinned by increased expression of alanine transaminase, and augmented glutamine consumption, suggesting that alternative routes are contributing to the enhanced lactate production in the SCs of Tg-RGN rats. Moreover, lactate seems to be used by germ cells, with diminished apoptosis being detected in the seminiferous tubules of Tg-RGN animals cultured ex vivo. The obtained results showed a distinct metabolism in the SCs of Wt and Tg-RGN rats widening the roles assigned to RGN in spermatogenesis. These findings also highlighted the plasticity of SCs metabolism, a feature that would be exploited in the context of male infertility.

Involvement of regucalcin gene promoter region-related protein-p117, a transcription factor, in human obesity

Regucalcin gene promoter region-related protein-p117 (RGPR-p117; gene symbol, rgpr-117) was identified in 2001 as a novel transcription factor that specifically binds to a nuclear factor I consensus motif, TTGGC(N)₆CC in the promoter region of the regucalcin (rgn) gene. The human RGPR-p117 gene consists of 26 exons spanning ~4.1 kbp and is localized on chromosome 1q25.2. The nuclear translocation of cytoplasm RGPR-p117 is mediated via the protein kinase C-dependent signaling pathway. Overexpression of RGPR-p117 enhances the transcription activity of rgn, and a protective effect on cell death by inhibition of gene expression levels of caspase-3, caspase-8 and FADD proteins that possess the TTGGC motif in the promoter region of those genes was revealed. RGPR-p117 has a crucial role as a transcription factor. Notably, RGPR-p117 was shown to localize in the plasma membranes, mitochondria and microsomes (endoplasmic reticulum; ER). RGPR-p117, which is located in the ER, was also shown to have a role as an ER export factor implicated in the transports of proteins and lipids. As a result of this finding, it was proposed in 2007 that RGPR-p117 is renamed SEC 16 homolog B, endoplasmic reticulum export factor (SEC16B). Recently, there is increasing evidence that RGPR-p117/SEC16B may be involved in human obesity. Thus, the current review presents data regarding the involvement of RGPR-p117 in human obesity.

Suppressed glycolytic metabolism in the prostate of transgenic rats overexpressing calcium-binding protein regucalcin underpins reduced cell proliferation

Regucalcin (RGN) is a calcium-binding protein underexpressed in human prostate cancer cases, and it has been associated with the suppression of cell proliferation and the regulation of several metabolic pathways. On the other hand, it is known that the metabolic reprogramming with augmented glycolytic metabolism and enhanced proliferative capability is a characteristic of prostate cancer cells. The present study investigated the influence of RGN on the glycolytic metabolism of rat prostate by comparing transgenic adult animals overexpressing RGN (Tg-RGN) with their wild-type counterparts. Glucose consumption was significantly decreased in the prostate of Tg-RGN animals relatively to wild-type, and accompanied by the diminished expression of glucose transporter 3 and glycolytic enzyme phosphofructokinase. Also, prostates of Tg-RGN animals displayed lower lactate levels, which resulted from the diminished expression/activity of lactate dehydrogenase. The expression of the monocarboxylate transporter 4 responsible for the export of lactate to the extracellular space was also diminished with RGN overexpression. These results showed the effect of RGN in inhibiting the glycolytic metabolism in rat prostate, which was underpinned by a reduced cell proliferation index. The present findings also suggest that the loss of RGN may predispose to a hyper glycolytic profile and fostered proliferation of prostate cells.

Novel regulatory roles of omega-3 fatty acids in metabolic pathways: a proteomics approach

Background

Omega-3 polyunsaturated fatty acids (n-3 PUFA) have been shown to alleviate the symptoms of metabolic disorders, such as heart disease, diabetes, obesity and insulin resistance. Several putative mechanisms by which n-3 PUFA elicit beneficial health effects have been proposed; however, there is still a shortage of knowledge on the proteins and pathways that are regulated by n-3 PUFA.

Methods

Using two dimensional polyacrylamide gel electrophoresis (2D-PAGE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, we investigated the effects of diets high or low in n-3 PUFA on hepatic proteomic profile of C57BL/6 mice.

Results

The findings show for the first time that high dietary n-3 PUFA reduced the expression of regucalcin, adenosine kinase and aldehyde dehydrogenase. On the other hand, diets high in n-3 PUFA increased the expression of apolipoprotein A-I, S-adenosylmethionine synthase, fructose-1, 6-bisphosphatase, ketohexokinase, malate dehydrogenase, GTP-specific succinyl CoA synthase, ornithine aminotransferase and protein disulfide isomerase-A3.

Conclusions

Our findings revealed for the first time that n-3 PUFA causes alterations in several novel functional proteins involved in regulating lipid, carbohydrate, one-carbon, citric acid cycle and protein metabolism, suggesting integrated regulation of metabolic pathways. These novel proteins are potential targets to develop therapeutic strategies against metabolic disorders.

The diverse roles of calcium-binding protein regucalcin in cell biology: from tissue expression and signalling to disease

Regucalcin (RGN) is a calcium (Ca(2+))-binding protein widely expressed in vertebrate and invertebrate species, which is also known as senescence marker protein 30, due to its molecular weight (33 kDa) and a characteristically diminished expression with the aging process. RGN regulates intracellular Ca(2+) homeostasis and the activity of several proteins involved in intracellular signalling pathways, namely, kinases, phosphatases, phosphodiesterase, nitric oxide synthase and proteases, which highlights its importance in cell biology. In addition, RGN has cytoprotective effects reducing intracellular levels of oxidative stress, also playing a role in the control of cell survival and apoptosis. Multiple factors have been identified regulating the cell levels of RGN transcripts and protein, and an altered expression pattern of this interesting protein has been found in cases of reproductive disorders, neurodegenerative diseases and cancer. Moreover, RGN is a serum-secreted protein, and its levels have been correlated with the stage of disease, which strongly suggests the usefulness of this protein as a potential biomarker for monitoring disease onset and progression. The present review aims to discuss the available information concerning RGN expression and function in distinct cell types and tissues, integrating cellular and molecular mechanisms in the context of normal and pathological conditions. Insight into the cellular actions of RGN will be a key step towards deepening the knowledge of the biology of several human diseases.

Involvement of regucalcin in lipid metabolism and diabetes

Regucalcin (RGN/SMP30) was originally discovered in 1978 as a unique calcium-binding protein that does not contain the EF-hand motif of calcium-binding domain. The regucalcin gene (rgn) is localized on the X chromosome and is identified in over 15 species consisting the regucalcin family. Regucalcin has been shown to play a multifunctional role in cell regulation; maintaining of intracellular calcium homeostasis and suppressing of signal transduction, translational protein synthesis, nuclear deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) synthesis, proliferation, and apoptosis in many cell types. Moreover, regucalcin may play a pathophysiological role in metabolic disorder. The expression of regucalcin is stimulated through the action of insulin in liver cells in vitro and in vivo and it is decreased in the liver of rats with type I diabetes induced by streptozotocin administration in vivo. Overexpression of endogenous regucalcin stimulates glucose utilization and lipid production in liver cells with glucose supplementation in vitro. Regucalcin reveals insulin resistance in liver cells. Deficiency of regucalcin induces an impairment of glucose tolerance and lipid accumulation in the liver of mice in vivo. Overexpression of endogenous regucalcin has been shown to decrease triglyceride, total cholesterol and glycogen contents in the liver of rats, inducing hyperlipidemia. Leptin and adiponectin mRNA expressions in the liver tissues are decreased in regucalcin transgenic rats. Decrease in hepatic regucalcin is associated with the development and progression of nonalcoholic fatty liver disease and fibrosis in human patients. Regucalcin may be a key molecule in lipid metabolic disorder and diabetes.

Exogenous regucalcin suppresses osteoblastogenesis and stimulates adipogenesis in mouse bone marrow culture

Regucalcin plays a pivotal role in regulating intracellular calcium homeostasis and consequently has a profound effect on multiple intracellular signal transduction pathways. The regucalcin transgenic rat displays pronounced bone loss and hyperlipidemia. Consistent with these effects exogenous regucalcin has been shown to promote osteoclastogenesis in mouse bone marrow cultures and to suppress the differentiation and mineralization of MC3T3 osteoblast precursors. Regucalcin may induce hyperlipidemia in vivo by suppressing osteoblast differentiation and stimulating adipogenesis in bone marrow mesenchymal stem cells. The present study demonstrates that exogenous regucalcin suppresses differentiation to osteoblasts and stimulates adipogenesis in mouse bone marrow cell culture ex vivo. Moreover, exogenous regucalcin was found to enhance adipogenesis stimulated by insulin which is involved in the extracellular signal-related kinase pathway in 3T3-L1 adipocytes in vitro.

Vitamin C deficiency accelerates bone loss inducing an increase in PPAR-γ expression in SMP30 knockout mice

Senescence marker protein (SMP) 30 knockout (KO) mice display symptoms of scurvy, including spontaneous bone fractures, and this was considered to be induced by a failure of collagen synthesis owing to vitamin C deficiency. However, low bone mineral density is also known to be associated with spontaneous bone fracture. Therefore, we investigated the effects of vitamin C deficiency on the balance between osteoblasts and osteoclasts in SMP30 KO mice as evidenced by histopathology. All mice were fed a vitamin C-free diet, and only one group (KV) mice were given water containing 1.5 g/l of vitamin C, whereas wild-type (WT) and KO mice were given normal drinking tap water without vitamin C for 16 weeks. After 16 weeks, all femur samples were removed for histopathological examination. The femurs of KO mice showed significantly reduced bone area and decreased number of osteoblasts compared with those of WT mice and KV mice. KO mice also exhibited the lowest level of alkaline phosphatase (ALP) expression in their femurs. However, KO mice showed the most elevated expression of the receptor activator of nuclear factor kappa-B ligand (RANKL). Moreover, KO mice had the strongest peroxisome proliferator-activated receptor (PPAR)-γ expression level in their osteoblasts and the highest number of TUNEL-positive bone marrow cells. Therefore, we concluded that vitamin C deficiency plays an important role in spontaneous bone fracture by inhibiting osteoblast differentiation and promoting transition of osteoblasts to adipocytes, and this could in turn be related to the increased PPAR-γ expression.

Comparative hepatic proteome analysis between lean and obese rats fed a high-fat diet reveals the existence of gender differences

Gender differences in obesity stem from metabolic and hormonal differences between sexes and contribute to differences between women and men in health risks attributable to obesity. We hypothesized that liver may be an ideal target for the evaluation of gender differences in obesity development in response to a high-fat diet (HFD). Therefore, to test this hypothesis, we performed a global proteome analysis in the liver of lean and obese rats of both genders who were fed an HFD through 2-DE combined with MALDI-TOF-MS. When rats were exposed to HFD, male rats gained more body weight with increased values of plasma biochemical parameters than female rats. Image analysis and further statistical analysis of a 2-DE protein map allowed for the detection and identification of 34 proteins that were significantly modulated in a gender-dependent manner. We found 19 proteins showing identical gender-different regulation in both normal diet (ND) and HFD. Five proteins also showed clear gender differences in both ND and HFD; however, their regulation modes in HFD were opposite to those in ND. Of particular interest, 10 proteins showed gender differences only in either ND or HFD rats. Present proteomic insight into gender-dimorphic protein modulation in liver would aid in the improvement of gender awareness in the health-care system and in implementation of evidence-based gender-specific clinical recommendations.

Senescence Marker Protein 30: Functional and Structural Insights to its Unknown Physiological Function

Senescence marker protein 30 (SMP30) is a multifunctional protein involved in cellular Ca(2+) homeostasis and the biosynthesis of ascorbate in non-primate mammals. The primary structure of the protein is highly conserved among vertebrates, suggesting the existence of a significant physiological function common to all mammals, including primates. Enzymatic activities of SMP30 include aldonolactone and organophosphate hydrolysis. Protective effects against apoptosis and oxidative stress have been reported. X-ray crystallography revealed that SMP30 is a six-bladed β-propeller with structural similarity to paraoxonase 1, another protein with lactonase and organophosphate hydrolase activities. SMP30 has recently been tied to several physiological conditions including osteoporosis, liver fibrosis, diabetes, and cancer. This review aims to describe the recent advances made toward understanding the connection between molecular structure, enzymatic activity and physiological function of this highly conserved, multifaceted protein.

Exogenous regucalcin stimulates osteoclastogenesis and suppresses osteoblastogenesis through NF-κB activation

Regucalcin plays a pivotal role in regulating intracellular calcium homeostasis and consequently has a profound effect on multiple intracellular signal transduction pathways. The regucalcin transgenic rat displays pronounced bone loss, and bone marrow from these animals exhibits significantly elevated osteoclast formation. Consistent with these effects exogenous regucalcin promotes osteoclastogenesis in mouse bone marrow cultures, but interestingly regucalcin suppresses the differentiation and mineralization of MC3T3 osteoblast precursors. However, the molecular mechanisms involved are presently unclear. As the nuclear factor-kappa B (NF-κB) signal transduction pathway is critical to osteoclastogenesis but inhibitory of osteoblastogenesis, we hypothesized that regucalcin may promote osteoclastogenesis and suppress osteoblastogenesis upregulating NF-κB signal transduction. In this study, we examined the effect of regucalcin on receptor activator of NF-κB (RANK) ligand (RANKL) -induced osteoclast formation using the RAW264.7 monocytic cell line and osteoblast formation using the pre-osteoblastic cell line MC3T3. As expected, culture with exogenous regucalcin was found to enhance RANKL-induced osteoclastogenesis. Consistent with this effect regucalcin increased basal and RANKL-induced NF-κB activation as assessed by NF-κB luciferase assay. The capacity of regucalcin to augment RANKL-induced NF-κB activity was inhibited by menaquinone-7, a potent NF-κB antagonist, while the Erk inhibitor PD98059 and staurosporine had no effect, demonstrating a specific effect on NF-κB signaling. By contrast, regucalcin inhibited mineralization of MC3T3 cells and enhanced tumor necrosis factor-α (TNFα)-induced NF-κB activation. As with NF-κB induction in osteoclasts, NF-κB activation was abolished by addition of the NF-κB antagonist menaquinone-7, but not by PD98059 and staurosporine. Transforming growth factor-β (TGFβ) and bone morphogenic protein-2 (BMP2) are potent early commitment and late osteoblast differentiation factors, respectively, and both mediate their actions through the Smad-signal transduction pathway, a system that is extremely sensitive to and inhibited by TNFα-induced NF-κB. We consequently examined the effect of regucalcin on TGFβ and BMP2-induced Smad activation in the presence and absence of TNFα. While regucalcin had no effect on basal Smad activation by TGFβ and BMP2, it enhanced the suppressive effect of TNFα on both TGFβ- and BMP2-induced Smad activations. Taken together, present data suggest that regucalcin may induce bone loss in vivo by promoting osteoclasts and simultaneously suppressing osteoblasts through amplification of basal and/or cytokine-induced NF-κB activation. Regucalcin may have a role as a modulator in NF-κB activation.

Regucalcin (RGN/SMP30) alters agonist- and thapsigargin-induced cytosolic [Ca2+] transients in cells by increasing SERCA Ca(2+)ATPase levels

Regucalcin (RGN), also reported as senescence marker protein-30 (SMP30), plays a role in Ca(2+) homeostasis by modulating a number of Ca(2+)-dependent proteins. RGN also plays a cyto-protective role and its decrease is linked to age-related diseases and cell death. This study shows that RGN reduces agonist (histamine)-induced Ca(2+) transients in RGN(+) transfected COS-7 cells (RGN(+)) and also increases their Ca(2+) storage capacity. These observations are explained by RGN(+) cells having increased mRNA and protein expression levels of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA). Therefore down-regulation of RGN expression may contribute to characteristics of age-dependent Ca(2+) homeostasis dis-regulation, by decreasing SERCA levels.

SP1 suppresses phorbol 12-myristate 13-acetate induced up-regulation of human regucalcin expression in liver cancer cells

There is a growing evidence that regucalcin (RGN) plays a multifunctional role in liver cancer cells. Previous reports showed that the presence of phorbol 12-myristate 13-acetate (PMA) caused a significant increase in RGN mRNA expression and promoter activity in rat hepatoma cells. In this study, we confirmed that human RGN is also up-regulated by PMA treatment independent of translation, and we identified the mechanism by which PMA up-regulates the expression of human RGN via driving SP1 away from a SP1 motif located within -188/-180 of the promoter in HepG2 cells. Overexpression of SP1 dramatically reduces PMA-induced up-regulation of both internal expression of mRNA and promoter activity, whereas knockdown of SP1 has the opposite effect. Therefore, the present study delineates the fundamental elements in the promoter which will be helpful in the future studies on the regulation of RGN expression in liver cancer.

The transcriptional regulation of regucalcin gene expression

Regucalcin, which is discovered as a calcium-binding protein in 1978, has been shown to play a multifunctional role in many tissues and cell types; regucalcin has been proposed to play a pivotal role in keeping cell homeostasis and function for cell response. Regucalcin and its gene are identified in over 15 species consisting of regucalcin family. Comparison of the nucleotide sequences of regucalcin from vertebrate species is highly conserved in their coding region with throughout evolution. The regucalcin gene is localized on the chromosome X in rat and human. The organization of rat regucalcin gene consists of seven exons and six introns and several consensus regulatory elements exist upstream of the 5'-flanking region. AP-1, NF1-A1, RGPR-p117, β-catenin, and other factors have been found to be a transcription factor in the enhancement of regucalcin gene promoter activity. The transcription activity of regucalcin gene is enhanced through intracellular signaling factors that are mediated through the phosphorylation and dephosphorylation of nuclear protein in vitro. Regucalcin mRNA and its protein are markedly expressed in the liver and kidney cortex of rats. The expression of regucalcin mRNA in the liver and kidney cortex has been shown to stimulate by hormonal factors (including calcium, calcitonin, parathyroid hormone, insulin, estrogen, and dexamethasone) in vivo. Regucalcin mRNA expression is enhanced in the regenerating liver after partial hepatectomy of rats in vivo. The expression of regucalcin mRNA in the liver and kidney with pathophysiological state has been shown to suppress, suggesting an involvement of regucalcin in disease. Liver regucalcin expression is down-regulated in tumor cells, suggesting a suppressive role in the development of carcinogenesis. Liver regucalcin is markedly released into the serum of rats with chemically induced liver injury in vivo. Serum regucalcin has a potential sensitivity as a specific biochemical marker of chronic liver injury with hepatitis. Regucalcin has been proposed to be a key molecule in cellular regulation and metabolic disease.