Molecular cloning and sequencing of the cDNA coding for a novel regucalcin gene promoter region-related protein in rat, mouse and human liver

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.

Regucalcin expression in bovine tissues and its regulation by sex steroid hormones in accessory sex glands

Regucalcin (RGN) is a mammalian Ca2+-binding protein that plays an important role in intracellular Ca2+ homeostasis. Recently, RGN has been identified as a target gene for sex steroid hormones in the prostate glands and testis of rats and humans, but no studies have focused on RGN expression in bovine tissues. Thus, in the present study, we examined RGN mRNA and protein expression in the different tissues and organs of veal calves and beef cattle. Moreover, we investigated whether RGN expression is controlled through sex steroid hormones in bovine target tissues, namely the bulbo-urethral and prostate glands and the testis. Sex steroid hormones are still illegally used in bovine husbandry to increase muscle mass. The screening of the regulation and function of anabolic sex steroids via modified gene expression levels in various tissues represents a new approach for the detection of illicit drug treatments. Herein, we used quantitative PCR, western blot and immunohistochemistry analyses to demonstrate RGN mRNA and protein expression in bovine tissues. In addition, estrogen administration down-regulated RGN gene expression in the accessory sex glands of veal calves and beef cattle, while androgen treatment reduced RGN gene expression only in the testis. The confirmation of the regulation of RGN gene expression through sex steroid hormones might facilitate the potential detection of hormone abuse in bovine husbandry. Particularly, the specific response in the testis suggests that this tissue is ideal for the detection of illicit androgen administration in veal calves and beef cattle.

Regulatory role of regucalcin in heart calcium signaling: Insight into cardiac failure (Review)

Regucalcin was first identified in 1978 as a regulatory protein of Ca²⁺ signaling in liver cells. Regucalcin was shown to play a multifunctional role in cell regulation, such as maintainance of intracellular Ca²⁺ homeostasis and suppression of signal transduction, protein synthesis, nuclear function, cell proliferation and apoptosis in various types of cells and tissues. Cardiac excitation-contraction coupling is based on the regulation of intracellular Ca²⁺ concentration by the Ca²⁺ pump in the sarcoplasmic reticulum of heart muscle cells. Regucalcin, which is expressed in the heart, was found to increase rat heart sarcoplasmic reticulum Ca²⁺-ATPase activity and ATP-dependent Ca²⁺ uptake and mitochondrial Ca²⁺-ATPase activity. Regucalcin was also shown to suppress Ca²⁺-dependent protein tyrosine phosphatase, Ca²⁺/calmodulin-dependent protein phosphatase (calcineurin) and nitric oxide (NO) synthase activity in the heart cytoplasm. Moreover, regucalcin was found to activate superoxide dismutase (SOD), which plays a significant role in the prevention of cell death and apoptosis in the heart. Regucalcin may be a key molecule in heart muscle cell regulation through Ca²⁺ signaling. Regucalcin may also play a pathophysiological role in heart failure. The aim of this study was to review the recent findings regarding the role of regucalcin in Ca²⁺ signaling in the heart.

Suppressive role of regucalcin in liver cell proliferation: involvement in carcinogenesis

Regucalcin (RGN/SMP30) was discovered in 1978 and is a unique calcium-binding protein contains no EF-hand motif calcium-binding domain. Its name, regucalcin, was proposed as it suppresses activation of enzymes related to calcium signalling. The regucalcin gene (rgn) is localized on the X chromosome. Regucalcin plays its role of suppressor protein in intracellular signalling pathways, including of protein kinases and protein phosphatase activities, protein synthesis, and DNA and RNA synthesis in liver cells. Overexpression of endogenous regucalcin has a suppressive effect on cell proliferation in modelled rat hepatoma H4-II-E cells, which are induced by various signalling stimulations in vitro. This suppressive effect is independent of apoptosis. Endogenous regucalcin plays a suppressive role on overproduction of proliferating cells in regenerating rat liver in vivo. Regucalcin mRNA expression is uniquely down-regulated in development of carcinogenesis in liver of rats in vivo. Regucalcin mRNA and protein expressions are also depressed in human hepatoma HepG2 cells, MCF-7 breast cancer cells, and prostate cancer LNCaP cells. Depression of regucalcin expression may be associated with activity progression of carcinogens. Regucalcin may be a key molecule suppressor protein in cell proliferation and carcinogenesis.

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.

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

Regucalcin transgenic (TG) rat has been generated to determine the role in metabolic disorders. Regucalcin homozygote male and female rats induce a prominent increase in regucalcin protein in the various tissues. Bone loss has been found to induce in regucalcin TG rats with growing (5 weeks old) and aging (50 weeks old). Osteoclastogenesis has been shown to stimulate in culture with the bone marrow cells obtained from regucalcin TG rats. Exogenous regucalcin stimulates osteoclastogenesis in mouse marrow culture in vitro. Regucalcin has a suppressive effect on the differentiation and mineralization in osteoblastic MC3T3-E1 cells in vitro. The mechanism by which regucalcin TG rat induces bone loss may result from the enhancement of osteoclastic bone resorption and the suppression of osteoblastic bone formation. Moreover, regucalcin TG rat has been found to induce hyperlipidemia with increasing age (14-50 weeks); serum triglyceride, high-density lipoprotein (HDL)-cholesterol, free fatty acid, albumin and calcium concentrations are markedly increased in regucalcin TG male and female rats with increasing age. The decrease in lipid and glycogen contents in liver tissues is induced in regucalcin TG rats. The gene expression of leptin and adiponectin is suppressed in the TG rats. Overexpression of regucalcin has been shown to enhance glucose utilization and lipid production in the cloned rat hepatoma H4-II-E cells in vitro, and insulin resistance is seen in the cells. The expression of glucose transporter 2 mRNA is increased in the transfectants, while it has been shown to suppress insulin receptor and phosphatidylinositol 3-kinase mRNA expressions that are involved in insulin signaling. This review proposes that regucalcin relates in osteoporosis and hyperlipidemia, and that the regucalcin TG rat model may be useful in determining the pathophysiologic state and the development of therapeutic tool for osteoporosis and hyperlipidemia.

Novel protein RGPR-p117: its role as the regucalcin gene transcription factor

RGPR-p117 was originally discovered as a novel protein that binds to a nuclear factor I (NFI) consensus motif TTGGC(N)(6)CC, which is present in the 5'-flanking region of the regucalcin gene (rgn). RGPR-p117 has been identified in human, rat, mouse, bovine, rabbit, and chicken livers. Phylogenetic analysis of six vertebrates shows that RGPR-p117 appears to form a single cluster, indicating a common evolutionary relationship of the RGPR-p117 family. The RGPR-p117 gene consists of at least 26 exons spanning approximately 4.1 kbp and is localized on human chromosome 1q25.2. RGPR-p117 mRNA is expressed in the liver, kidney, heart, spleen, and brain of rats. RGPR-p117 mRNA expression is stimulated through signaling mechanisms. Mammalian RGPR-p117 conserves a leucine zipper motif, which is present in many gene regulatory proteins. RGPR-p117 has been shown to translocate from the cytoplasm to the nucleus in NRK52E cells, a process which is mediated through protein kinase C signaling following hormonal stimulation. The phosphorylated RGPR-p117 binds to the TTGGC motif in the promoter region of the regucalcin gene and enhances regucalcin mRNA expression in the cells, indicating a role as a transcriptional factor. RGPR-p117 is also localized in the plasma membranes, nucleus, mitochondria, microsomes, and cytoplasm. Overexpression of RGPR-p117 has been found to induce a significant decrease in protein and DNA contents in cells, suggesting that RGPR-p117 may regulate the gene expression of other related proteins as well as the transcription factor. Also, overexpression of RGPR-p117 has a suppressive effect on cell death by inhibiting the gene expression of caspase-3, caspase-8, and Fas-associating death domain protein whose TTGGC motif is present in the promoter region of their genes. The novel protein RGPR-p117 has been shown to play an important role as a transcription factor.

Two mammalian Sec16 homologues have nonredundant functions in endoplasmic reticulum (ER) export and transitional ER organization

Budding yeast Sec16 is a large peripheral endoplasmic reticulum (ER) membrane protein that functions in generating COPII transport vesicles and in clustering COPII components at transitional ER (tER) sites. Sec16 interacts with multiple COPII components. Although the COPII assembly pathway is evolutionarily conserved, Sec16 homologues have not been described in higher eukaryotes. Here, we show that mammalian cells contain two distinct Sec16 homologues: a large protein that we term Sec16L and a smaller protein that we term Sec16S. These proteins localize to tER sites, and an N-terminal region of each protein is necessary and sufficient for tER localization. The Sec16L and Sec16S genes are both expressed in every tissue examined, and both proteins are required in HeLa cells for ER export and for normal tER organization. Sec16L resembles yeast Sec16 in having a C-terminal conserved domain that interacts with the COPII coat protein Sec23, but Sec16S lacks such a C-terminal conserved domain. Immunoprecipitation data indicate that Sec16L and Sec16S are each present at multiple copies in a heteromeric complex. We infer that mammalian cells have preserved and extended the function of Sec16.