Role of regucalcin in cell nuclear regulation: involvement as a transcription factor

Regucalcin downregulation in human cancer

Regucalcin is a unique calcium-binding protein first discovered in rat liver in 1978. Regucalcin has multiple functions as an inhibitor of various cellular signaling pathways that regulate cell activity. The expression of the regucalcin gene can be altered by various physiological and pathological factors such as diet (nutrients), hormones, diabetes, alcohol and drugs. Several transcription factors have been identified on the regucalcin gene, including AP-1, NF1-A1, RGPR-p117, β-catenin, NF-κB, STAT3 and hypoxia-inducible factor-1α (HIF-1α). Notably, regucalcin plays an important role in the development of several cancers by controlling cell growth. Clinically, many studies have reported that the expression of the regucalcin gene is downregulated in various human cancers. In addition, higher expression of regucalcin in tumor tissue has been associated with longer patient survival, suggesting that regucalcin may act as a potential suppressor of various types of human cancer. Regucalcin may offer a novel therapeutic strategy and diagnostic tool for cancer treatment. However, the underlying mechanism by which regucalcin expression is reduced in human cancer is still unclear. A deeper understanding of regucalcin reduction and function in cancer is needed to discover potential resistance mechanisms and biomarkers, and to improve regucalcin-targeting agents. We review recent findings on regucalcin gene expression in cancer. We discuss the possible mechanisms by which regucalcin expression is downregulated in cancer cells to facilitate understanding of how regucalcin regulates cell growth function. This mini-review may lead to better therapeutic targets with regucalcin.

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.

The overexpressed regucalcin represses the growth via regulating diverse pathways linked to EGF signaling in human ovarian cancer SK-OV-3 cells: Involvement of extracellular regucalcin

AIMS

Regucalcin, which plays a multifunctional role in cell regulation, contributes as a suppressor in carcinogenesis. Survival of cancer patients is prolonged with high expression of regucalcin in tumor tissues. Ovarian cancer is the most lethal in gynecologic malignancies. This study elucidates the repressive role of regucalcin on the growth of human ovarian cancer SK-OV-3 cells that are resistant to cytotoxic cancer drugs.

MATERIALS AND METHODS

SK-OV-3 wild type-cells and regucalcin-overexpressing cells (transfectants) were cultured in Dulbecco's Modification of Eagle's Medium containing 10 % fetal bovine serum.

KEY FINDINGS

Colony formation and proliferation of SK-OV-3 cells were repressed by regucalcin overexpression. The suppressive effects of regucalcin on proliferation were independent of cell death. The proliferation of SK-OV-3 wild-type cells was repressed by various inhibitors, including cell cycle, signaling processes, and transcriptional activity. The effects of all inhibitors were not revealed in transfectants, suggesting the involvement of multiple signaling pathways in regucalcin effects. Of note, the overexpressed regucalcin declined the levels of Ras, Akt, mitogen-activating protein kinase, NF-κB p65, β-catenin, and STAT3, while it raised the levels of tumor suppressors p53 and Rb, and cell cycle inhibitor p21. Interestingly, the stimulatory effects of epidermal growth factor (EGF) on cell proliferation were blocked in regucalcin-overexpressing cells. Extracellular regucalcin repressed the proliferation independent of the death of SK-OV-3 cells and blocked EGF-enhanced cell proliferation.

SIGNIFICANCES

The overexpressed regucalcin may repress cell proliferation by targeting diverse signal pathways, including EGF signaling. This study offers a novel approach to the treatment of ovarian cancer with regucalcin.

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.

Based on Network Pharmacology Tools to Investigate the Mechanism of Tripterygium wilfordii Against IgA Nephropathy

Background: Immunoglobulin A nephropathy (IgAN) is the most common primary glomerular disease and poses a global major public health burden. The preparation of Tripterygium wilfordii Hook F (TwHF) is widely applied for treating patients with Immunoglobulin A nephropathy in China, while the molecular mechanisms remain unclear. This study aimed to verify the therapeutic mechanism of TwHF on IgAN by undertaking a holistic network pharmacology strategy in combination with in vitro and in vivo experiments.

Methods: TwHF active ingredients and their targets were obtained via the Traditional Chinese Medicine Systems Pharmacology Database. The collection of IgAN-related target genes was collected from GeneCards and OMIM. TwHF-IgAN common targets were integrated and visualized by Cytoscape. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to determine the predominant molecular mechanisms and pathways of TwHF on the treatment of IgAN. The protein-protein interaction network was constructed by the STRING online search tool, and hub genes were identified using R software. The expression of hub gene and related signaling were evaluated in TwHF-treated mice through immunohistochemistry and western blot and further validated in human mesangial cells (HMCs). In addition, Cell counting kit 8 (CCK8) and flow cytometry were used to detect the effects of TwHF on cell proliferation and cell cycle of mesangial cells.

Results: A total of 51 active ingredients were screened from TwHF and 61 overlapping targets related to IgAN were considered potential therapeutic targets, GO functions and KEGG analyses demonstrated that these genes were primarily associated with DNA-binding transcription factor binding, lipid and atherosclerosis pathway. Genes with higher degrees including AKT1, CXCL8, MMP9, PTGS2, CASP3, JUN are hub genes of TwHF against IgAN. Verification of hub gene JUN both in vitro and in vivo showed that TwHF significantly attenuated JUN phosphorylation in the kidneys of IgAN mice and aIgA1-activated HMCs, meanwhile suppressing HMCs proliferation and arresting G1-S cell cycle progression.

Conclusion: Our research strengthened the mechanisms of TwHF in treating IgAN, inhibition of JUN activation may play a pivotal role in TwHF in alleviating IgAN renal injury.

Progression-free survival of prostate cancer patients is prolonged with a higher regucalcin expression in the tumor tissues: Overexpressed regucalcin suppresses the growth and bone activity in human prostate cancer cells

Prostate cancer, which is a bone metastatic cancer, is the second leading cause of cancer-related death in men. There is no effective treatment for metastatic prostate cancer. Regucalcin has been shown to contribute as a suppressor in various types of human cancers. In the present study, furthermore, we investigate an involvement of regucalcin in suppression of prostate cancer. Regucalcin expression was compared in 131 primary tumor tissues and 19 metastatic tumor tissues in prostate cancer patients. Regucalcin expression in the metastatic tumor was found to be reduced as compared with that in primary tumor. The progression-free survival rate was prolonged in patients with a higher regucalcin expression. Translationally, overexpression of regucalcin in bone metastatic human prostate cancer PC-3 and DU-145 cells suppressed colony formation and cell growth in vitro. Mechanistically, overexpressed regucalcin enhanced the levels of p53, Rb, and p21, and decreased the levels of Ras, PI3 kinase, Akt, and mitogen-activated protein kinase, leading to suppression of cell growth. Furthermore, higher regucalcin expression suppressed the levels of nuclear factor-κB p65, β-catenin, and signal transducer and activator of transcription 3, which regulate a transcription activity. Cell growth was promoted by culturing with the calcium agonist Bay K 8644. This effect was blocked by overexpression of regucalcin. Notably, overexpressed regucalcin suppressed bone metastatic activity of PC-3 and DU-145 cells when cocultured with preosteoblastic or preosteoclastic cells. Regucalcin may suppress the development of human prostate cancer, suggesting that gene delivery systems in which its expression is forced may be a novel therapeutic strategy.

Extracellular regucalcin suppresses colony formation and growth independent of tumor suppressor p53 in human mammary epithelial cells

Regucalcin plays a multifunctional role in cell regulation as a suppressor in the processes of intracellular signaling and transcription, leading to inhibition of cell growth. The downregulated expression or activity of regucalcin has been shown to contribute to the development of carcinogenesis in various types of human cancer. The wild-type tumor suppressor TP53 gene encodes for a transcriptional factor p53. This protein may play a role in cell proliferation. Loss of p53 function may induce cell transformation during carcinogenesis and tumor progression of human cancer. We investigate whether or not extracellular regucalcin suppresses the proliferation of non-tumorigenic human mammary epithelial MCF 10A cells with loss of p53 in vitro. Loss of p53 did not impact colony formation and proliferation of the cells. Interestingly, p53 loss caused decrease in the cell cycle suppressor p21, but not retinoblastoma and regucalcin, as compared with those of wild-type MCF 10A cells. Notably, extracellular regucalcin suppressed colony formation and proliferation of wild-type MCF 10A cells and p53 (-/-) cells, while it did not have an effect on cell death. Mechanistically, extracellular regucalcin decreased levels of various signaling factors including Ras, phosphatidylinositol-3 kinase, mitogen-activated protein kinase (MAPK), phospho-MAPK, and signal transducer and activator of transcription 3 in wild-type MCF 10A cells and p53 (-/-) cells. Thus, extracellular regucalcin was found to suppress the growth of MCF 10A cells with loss of p53. Extracellular regucalcin may play a role as a suppressor in the growth of human mammary epithelial cells with p53 loss, providing a novel strategy for cancer.

An aryl hydrocarbon receptor agonist suppresses the growth of human umbilical vein endothelial cells in vitro: Potent effect with polyunsaturated fatty acids

Human umbilical vein endothelial cells (HUVECs) are a pivotal component of the hematopoietic microenvironment linked to the modulation of the immune response, inflammation and carcinogenesis. HUVEC expresses the aryl hydrocarbon receptor (AHR), which regulates gene expression by binding to the xenobiotic-responsive element. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent agonist for AHR signalling. Treatment with TCDD (0.1-100 nmol/L) was found to suppress the proliferation and to stimulate the death of HUVEC. TCDD's effects were abolished by culturing with CH223191, an inhibitor of AHR signalling. Mechanistically, TCDD treatment increased the protein levels of cell growth suppressors, including p53, Rb, p21 and regucalcin, and caspase-3 implicated in apoptotic cell death, and decreased the levels of Stat3, mitogen-activated protein kinase (MAPK/Erk1/2) and phospho-MAPK/Erk1/2. Treatment with polyunsaturated fatty acids (PUFAs), including docosahexaenoic acid, eicosapentaenoic acid and arachidonic acid, suppressed the proliferation and stimulated the death of HUVEC in vitro, and decreased the levels of Stat3, MAPK/Erk1/2 and phospho-MAPK/Erk1/2 and increased caspase-3. Notably, the effects of TCDD in suppressing proliferation and stimulating death of HUVEC were modulated by coculturing with PUFAs. These effects were reversed by treatment with CH223191, an inhibitor of AHR. Treatment with both TCDD and PUFAs collaboratively enhanced the levels of AHR, CYP1A1, p53, p21, Rb and regucalcin. Moreover, TCDD suppressed migration with wound healing of HUVEC. Notably, the combination of TCDD and PUFAs revealed potent suppressive effects on angiogenesis of HUVEC, potentially related to disorders of the stromal microenvironment.

The calcium channel agonist Bay K 8644 promotes the growth of human liver cancer HepG2 cells in vitro: suppression with overexpressed regucalcin

Hepatocellular carcinoma is one of the most prevalent malignant diseases and causes a third of cancer-related death. The consequences of altered calcium homeostasis in cancer cells may contribute to tumor progression. Regucalcin plays an inhibitory role in calcium signaling linked to transcription regulation. Regucalcin gene expression is downregulated in the tumor tissues of liver cancer patients, suggesting an involvement as a suppressor in hepatocarcinogenesis. We investigated whether Bay K 8644, an agonist of the L-type Ca2+ channel, promotes the growth of human liver cancer and if the effect of Bay K 8644 is suppressed by overexpressed regucalcin using the HepG2 cell model. The colony formation and growth of HepG2 cells were promoted by culturing with Bay K 8644 (0.1-10 nM). This effect was suppressed by inhibitors of signaling processes linked to cell proliferation, including PD98059 and wortmannin. Death of HepG2 cells was stimulated by Bay K 8644 with higher concentrations (25 and 100 nM). The effects of Bay K 8644 on cell growth and death were abolished by verapamil, an antagonist of calcium channel. Mechanistically, culturing with Bay K 8644 increased levels of mitogen-activated protein kinase (MAPK) and phospho-MAPK. Notably, overexpressed regucalcin suppressed Bay K 8644-promoted growth and death of HepG2 cells. Furthermore, overexpressed regucalcin prevented growth and increased death induced by thapsigargin, which induces the release of intracellular stored calcium. Thus, higher regucalcin expression suppresses calcium signaling linked to the growth of liver cancer cells, providing a novel strategy in treatment of hepatocellular carcinoma with delivery of the regucalcin gene.

Regucalcin enhances adipocyte differentiation and attenuates inflammation in 3T3-L1 cells

Dysregulation of adipocyte differentiation and dysfunction play key roles in the pathogenesis of obesity and associated disorders such as diabetes and metabolic syndrome, and as such, a better understanding of the molecular mechanism of adipogenesis may help to elucidate the pathological condition of obesity and its associated disorders. Regucalcin (RGN) plays multiple regulatory roles in intracellular Ca²⁺ signaling pathways in mammalian cells. Here, we report that overexpression of RGN enhances lipid accumulation in 3T3‐L1 adipocyte cells after adipogenic stimulation, accompanied by upregulation of adipocyte differentiation marker proteins. In contrast, genetic disruption of RGN inhibited adipogenic stimulation‐induced differentiation of 3T3‐L1 cells. Furthermore, RGN overexpression in differentiated 3T3‐L1 adipocytes blocked inflammatory crosstalk between 3T3‐L1 adipocytes and RAW264.7 macrophages in a transwell coculture system. Knockdown of RGN expression in cocultured 3T3‐L1 adipocytes enhanced their susceptibility to RAW264.7 macrophage‐mediated inflammation. These results suggest that RGN is required for 3T3‐L1 adipocyte differentiation and that it exerts anti‐inflammatory activity against 3T3‐L1 adipocyte inflammation after coculture with RAW264.7 macrophages. Thus, RGN may be a novel regulator of adipocyte differentiation and act as a suppressor of inflammation in macrophage‐infiltrated adipocyte tissue.

Overexpression of Regucalcin Suppresses the Growth of Human Osteosarcoma Cells in Vitro: Repressive Effect of Extracellular Regucalcin

Regucalcin plays a pivotal role as a suppressor of human carcinogenesis, and downregulation of regucalcin expression may contribute to the promotion of human osteosarcoma. Overexpression of regucalcin suppressed the proliferation of Saos-2 human osteosarcoma cells in vitro and decreased the protein levels of multiple signaling components, transcription factors, and tumor suppressors. Interestingly, extracellular regucalcin repressed colony formation and proliferation of Saos-2 cells, and reduced the protein levels of multiple signaling components, cell cycle inhibitor, and various transcription factors. Thus, regucalcin suppressed the growth of human osteosarcoma cells, providing a novel strategy with the gene therapy for treatment of osteosarcoma.

Serum regucalcin is a useful indicator of liver injury severity in patients with hepatitis B virus-related liver diseases

Regucalcin is a soluble protein that is principally expressed in hepatocytes. Studies of regucalcin have mainly been conducted in animals due to a lack of commercially available kits. We aimed to develop an enzyme-linked immunosorbent assay (ELISA) to quantify serum regucalcin in patients with hepatitis B virus (HBV)-related disease. High-titer monoclonal antibodies and a polyclonal antibody to regucalcin were produced, a double-antibody sandwich ELISA method was established, and serum regucalcin was determined in 47 chronic hepatitis B (CHB) patients, 91 HBV-related acute-on-chronic liver failure (HBV-ACLF) patients, and 33 healthy controls. The ELISA demonstrated an appropriate linear range, and high levels of reproducibility, sensitivity, specificity, accuracy, and stability. The median serum regucalcin concentrations in HBV-ACLF and CHB patients were 5.46 and 3.76 ng/mL, respectively (P<0.01), which were much higher than in healthy controls (1.72 ng/mL, both P<0.01). For the differentiation of CHB patients and healthy controls, the area under curve (AUC) was 0.86 with a cut-off of 2.42 ng/mL, 85.7% sensitivity, and 78.8% specificity. In contrast, the AUC of alanine aminotransferase (ALT) was lower (AUC=0.80, P=0.01). To differentiate ACLF from CHB, the AUC was 0.72 with a cut-off of 4.26 ng/mL, 77.0% sensitivity, and 61.2% specificity while the AUC of ALT was 0.41 (P=0.07). Thus, we have developed an ELISA that is suitable for measuring serum regucalcin and have shown that serum regucalcin increased with the severity of liver injury due to HBV-related diseases, such that it appears to be more useful than ALT as a marker of liver injury.

2,3,7,8‑tetrachlorodibenzo‑p‑dioxin suppresses the growth of human colorectal cancer cells in vitro: Implication of the aryl hydrocarbon receptor signaling

Human colorectal cancer is the third most common cancer disease with a 5‑year survival rate of 55% in USA in 2016. The investigation to identify novel biomarker factors with molecular classification may provide notable clinical information to prolong the survival of patients with colorectal cancer. The aryl hydrocarbon receptor (AHR) binds the AHR nuclear translocator in the cytoplasm of various types of cells, including liver cells, and then binds to the xenobiotic responsive element on various genes. AHR was initially discovered via its ligand, the polychlorinated hydrocarbon, 2,3,7,8‑tetrachlorodibenzo‑p‑dioxin (TCDD). The present study was undertaken to determine whether TCDD, an agonist of AHR signaling, impacts the growth of RKO human colorectal cancer cells in vitro. Treatment with TCDD (0.1‑100 nM) revealed suppressive effects on colony formation and proliferation of RKO cells, and stimulated death of these cells with subconfluence. These effects of TCDD were abolished by pretreatment with CH223191, an inhibitor of AHR signaling. Western blot analysis demonstrated that TCDD treatment decreased AHR levels and elevated cytochrome P450 family 1 subfamily A member 1 (CYP1A1) levels, indicating a stimulation of AHR signaling. TCDD treatment caused an increase in nuclear factor‑κB p65 and β‑catenin levels, although it did not have an effect on Ras levels. Notably, TCDD treatment increased the levels of p53, retinoblastoma, p21 and regucalcin, which are depressors of carcinogenesis. Additionally, action of TCDD on cell proliferation and death were not revealed in regucalcin‑overexpressing RKO cells, and regucalcin overexpression depressed AHR signaling associated with CYP1A1 expression. Thus, AHR signaling suppresses the growth of colorectal cancer cells, indicating a role as a significant targeting molecule for colorectal cancer.

Prolonged survival of renal cancer patients is concomitant with a higher regucalcin gene expression in tumor tissues: Overexpression of regucalcin suppresses the growth of human renal cell carcinoma cells in vitro

Renal cell carcinoma (RCC), which is a type of cancer found in the kidney tubule, is among the 10 most frequently occurring human cancers. Regucalcin plays a potential role as a regulator of transcriptional activity, and its downregulated expression or activity may contribute to the promotion of human cancers. In this study, we investigated the involvement of regucalcin in human RCC. Regucalcin expression was compared in 23 normal and 29 tumor samples of kidney cortex tissues of patients with clear cell RCC obtained through the Gene Expression Omnibus (GEO) database (GSE36895). Regucalcin expression was downregulated in the tumor tissues. The prolonged survival of patients with clear cell RCC was demonstrated to be associated with a higher regucalcin gene expression in the TCGA dataset. The overexpression of regucalcin suppressed the colony formation, proliferation and the death of human clear cell RCC A498 cells in vitro. Mechanistically, the overexpression of regucalcin induced the G1 and G2/M phase cell cycle arrest of A498 cells through the suppression of multiple signaling components, including Ras, PI3 kinase, Akt and mitogen‑activated protein (MAP) kinase. Importantly, the overexpression of regucalcin led to an elevation in the levels of the tumor suppressors, p53, Rb and the cell cycle inhibitor, p21. The levels of the transcription factors, c‑fos, c‑jun, nuclear factor‑κB p65, β‑catenin and signal transducer and activator of transcription 3, were suppressed by regucalcin overexpression. On the whole, the findings of this study suggest that regucalcin plays a suppressive role in the promotion of human RCC. The overexpression of regucalcin by gene delivery systems may thus prove to be a novel therapeutic strategy for RCC.

Senescence marker protein 30 protects intestinal epithelial cells against inflammation-induced cell death by enhancing Nrf2 activity

Senescence marker protein 30 (SMP30) is a calcium-binding protein whose expression decreases during senescence. SMP30 deficiency increases susceptibility to cytokine-induced apoptosis in the liver and to radiation-induced apoptosis in the small intestine. Furthermore, colonic epithelial cell death is associated with the severity of colitis. Therefore, in the present study, we investigated the function of SMP30 during intestinal inflammation. In SMP30 deficient mice, colitis was significantly exacerbated as demonstrated by increased mortality (p = 0.001), body weight loss (p = 0.0105 at day 8), rectal bleeding (p = 0.0047 at day 8) and diarrhea (p = 0.0030 at day 8), histological scores (ulcers, p = 0.0002; edema, p = 0.0125; leukocyte infiltration, p = 0.0016) and productions of pro-inflammatory cytokines (IL-1α, p = 0.0452; IL-6, p = 0.0074; G-CSF, p = 0.0036). In addition, greater proportions of apoptotic cells and lower levels of anti-apoptotic marker proteins (total PARP-1 and Bcl-2) were observed in the inflamed intestines of SMP30 deficient mice than in wild type controls. In vitro experiments on colonic epithelial cells showed that stable SMP30 expression inhibited but that SMP30 siRNA expression increased TNF-α-induced apoptosis. SMP30 inhibition decreased Nrf2 mRNA expression levels (p < 0.0001), but SMP30 overexpression increased Nrf2 mRNA expression levels (p = 0.0495). The underlying mechanism by which SMP30 protected cells appeared to be by inhibiting Nrf2 ubiquitination and Keap1 expression, and thus enhancing Nrf2 activity. Moreover, SMP30 deficiency increased the incidence of colitis-associated colon cancer as determined by increased mortality (p = 0.0572) and average polyp number (p = 0.0277). Collectively, these findings suggest that SMP30 protects intestinal epithelial cells from apoptosis and this can contribute to amelioration of colitis and colitis-associated colon cancer.

Prolonged survival of patients with colorectal cancer is associated with a higher regucalcin gene expression: Overexpression of regucalcin suppresses the growth of human colorectal carcinoma cells in vitro

Regucalcin plays a crucial role as a regulator of transcriptional signaling activity, and its decreased expression or activity may contribute to the promotion of human carcinogenesis. A higher regucalcin expression in the tumor tissues has been demonstrated to prolong the survival of patients with various types of cancer, including pancreatic cancer, breast cancer, liver cancer and lung adenocarcinoma. The involvement of regucalcin in human colorectal cancer was investigated in the current study. Regucalcin gene expression and the survival data of 62 patients with colorectal cancer were obtained though the Gene Expression Omnibus (GEO) database (GSE12945) for outcome analysis. The data of gene expression revealed that the prolonged survival of patients with colorectal cancer was associated with a higher regucalcin gene expression in tumor tissues. The overexpression of regucalcin suppressed colony formation and proliferation, and induced the death of human colorectal carcinoma RKO cells cultured in a medium containing fetal bovine serum in vitro. Mechanistically, the overexpression of regucalcin induced the G1 and G2/M phase cell cycle arrest of the RKO cells through the suppression of multiple signaling pathways, including Ras, Akt, mitogen-activated protein (MAP) kinase and SAPK/JNK. Of note, the overexpression of regucalcin induced an increase in the levels of the tumor suppressors, p53 and Rb, and the cell cycle inhibitor, p21. Moreover, the levels of the transcription factors, c‑fos, c‑jun, nuclear factor (NF)‑κB p65, β-catenin and signal transducer and activator of transcription 3 (Stat3), were suppressed by the overexpression of regucalcin. On the whole, the findings of this study suggest that regucalcin plays a crucial role as a suppressor in human colorectal cancer, and that the suppressed expression of the regucalcin gene may predispose patients to the promotion of colorectal cancer. The overexpression of regucalcin by gene delivery may thus prove to be a novel therapeutic strategy for colorectal cancer.

Regucalcin confers resistance to amyloid-β toxicity in neuronally differentiated PC12 cells

Amyloid‐β (Aβ), a primary component of amyloid plaques, has been widely associated with the pathogenesis of Alzheimer's disease. The Ca²⁺‐binding protein regucalcin (RGN) plays multiple roles in maintaining cell functions by regulating intracellular calcium homeostasis, various signaling pathways, and gene expression systems. Here, we investigated the functional role of RGN against Aβ‐induced cytotoxicity in neuronally differentiated PC12 cells. Overexpression of RGN reduced Aβ‐induced apoptosis by reducing mitochondrial dysfunction and caspase activation. It also attenuated Aβ‐induced reactive oxygen species production and oxidative damage and decreased Aβ‐induced nitric oxide (NO) overproduction, upregulation of inducible NO synthase by nuclear factor‐κB, and nitrosative damage. Interestingly, the genetic disruption of RGN increased the susceptibility of neuronally differentiated PC12 cells to Aβ toxicity. Thus, RGN possesses antioxidant activity against Aβ‐induced oxidative and nitrosative stress and may play protective roles against Aβ‐induced neurotoxicity in Alzheimer's disease.

Mitochondrial T3 receptor and targets

The demonstration that TRα1 mRNA encodes a nuclear thyroid hormone receptor and two proteins imported into mitochondria with molecular masses of 43 and 28 kDa has brought new clues to better understand the pleiotropic influence of iodinated hormones. If p28 activity remains unknown, p43 binds to T3 responsive elements occurring in the organelle genome, and, in the T3 presence, stimulates mitochondrial transcription and the subsequent synthesis of mitochondrial encoded proteins. This influence increases mitochondrial activity and through changes in the mitochondrial/nuclear cross talk affects important nuclear target genes regulating cell proliferation and differentiation, oncogenesis, or apoptosis. In addition, this pathway influences muscle metabolic and contractile phenotype, as well as glycaemia regulation. Interestingly, according to the process considered, p43 exerts opposite or cooperative effects with the well-known T3 pathway, thus allowing a fine tuning of the physiological influence of this hormone.

Survival of lung cancer patients is prolonged with higher regucalcin gene expression: suppressed proliferation of lung adenocarcinoma A549 cells in vitro

Regucalcin plays a crucial role as a suppressor of transcription signaling, and its diminished expression or activity may play a key role in human carcinogenesis. Higher regucalcin expression has been demonstrated to prolong survival of the patients of pancreatic cancer, breast cancer, and hepatocellular carcinoma. Moreover, we investigated an involvement of regucalcin in human lung cancer. Human non-small cell lung cancer (NSCLC) accounts for over 80% in human lung cancer and is one of the leading causes of malignancy-related mortality with fewer than 16% patients surviving beyond 5 years. In this study, gene expression and survival data of 204 lung adenocarcinoma patients were obtained through the gene expression omnibus database (GSE31210) for outcome analysis. Gene expression data demonstrated that prolonged survival in lung cancer patients is associated with higher regucalcin gene expression. Overexpression of regucalcin suppressed the proliferation, cell death, and migration of human lung adenocarcinoma NSCLC A549 cells in vitro. Mechanistically, regucalcin induced G1 and G2/M phase cell cycle arrest of A549 cells through suppression of multiple signaling pathways including Ras, Akt, MAP kinase, and SAPK/JNK. Moreover, overexpression of regucalcin caused decreases in the oncogenes c-fos and c-myc and elevation of the tumor suppressers p53 and Rb. These findings suggest that regucalcin may play a potential role as a suppressor of human lung cancer, and that downregulation of regucalcin expression may predispose patients to development of lung cancer. Overexpression of regucalcin using gene delivery may constitute a novel therapeutic approach to treating lung cancer.

Prolonged survival in hepatocarcinoma patients with increased regucalcin gene expression: HepG2 cell proliferation is suppressed by overexpression of regucalcin in vitro

Hepatocellular carcinoma (HCC) is one of the most common malignant cancers worldwide and ranks third in overall global cancer-related mortality rates. Importantly, in this study gene expression data demonstrate that prolonged survival in HCC patients is associated with increased regucalcin gene expression. Regucalcin has been shown to play a pivotal role as a transcription repressor and diminished expression or activity of regucalcin may play a key role in the development of human carcinogenesis. Indeed, overexpression of regucalcin suppressed the proliferation, cell death, and migration of human HCC HepG2 cells in vitro. Mechanistically, regucalcin induced G1 and G2/M phase cell cycle arrest of HepG2 cells through suppression of multiple signaling pathways including Ras, Akt, MAP kinase and SAPK/JNK and by increasing the tumor suppressors p53 and Rb. Furthermore, the oncogenes c-fos and c-myc were suppressed by overexpression of regucalcin, and overexpression of regucalcin caused an increase in p21 and a decrease in NF-κB p65 and β-catenin. These findings suggest that regucalcin may play a potential role as a suppressor of human HCC, and that diminished expression of regucalcin may predispose patients to development of HCC. Overexpression of regucalcin may constitute a novel therapeutic approach to treating HCC.

Increased regucalcin gene expression extends survival in breast cancer patients: Overexpression of regucalcin suppresses the proliferation and metastatic bone activity in MDA-MB-231 human breast cancer cells in vitro

Human breast cancer is highly metastatic to bone and drives bone turnover. Breast cancer metastases cause osteolytic lesions and skeletal damage that leads to bone fractures. Regucalcin, which plays a pivotal role as an inhibitor of signal transduction and transcription activity, has been suggested to act as a suppressor of human cancer. In the present study, we compared the clinical outcome between 44 breast cancer patients with higher regucalcin expression and 43 patients with lower regucalcin expression. Prolonged relapse-free survival was identified in the patients with increased regucalcin gene expression. We further demonstrated that overexpression of full length, but not alternatively spliced variants of regucalcin, induces G1 and G2/M phase cell cycle arrest, suppressing the proliferation of MDA-MB-231 cells, a commonly used in vitro model of human breast cancer that metastasize to bone causing osteolytic lesions. Overexpression of regucalcin was found to suppress multiple signaling pathways including Akt, MAP kinase and SAPK/JNK, and NF-κB p65 and β-catenin along with increased p53, a tumor suppressor, and decreased K-ras, c-fos and c-jun. Moreover, we found that co-culture of regucalcin-overexpressing MDA-MB-231 cells with mouse bone marrow cells prevented enhanced osteoclastogenesis and suppressed mineralization in mouse bone marrow cells in vitro. Taken together, the present study suggests that regucalcin may have important anticancer properties in human breast cancer patients. Mechanistically, these effects are likely mediated through suppression of multiple signaling pathways, upregulation of p53 and downregulation of oncogenes leading to anti-proliferative effects and reduced metastases to bone, a phenotype associated with poor clinical outcome.

Prolonged survival in pancreatic cancer patients with increased regucalcin gene expression: Overexpression of regucalcin suppresses the proliferation in human pancreatic cancer MIA PaCa-2 cells in vitro

Approximately 90% of all pancreatic cancers are pancreatic ductal adenocarcinomas (PDAC). PDAC is a highly aggressive malignancy and is one of the deadliest. This poor clinical outcome is due to the prominent resistance of pancreatic cancer to drug and radiation therapies. Regucalcin plays a pivotal role as a suppressor protein in signal transduction in various types of cells including tumor tissues. We demonstrated that the prolonged survival is induced in PDAC patients with increased regucalcin gene expression using a dataset of PDAC obtained from GEO database (GSE17891) together with the clinical annotation data file. Moreover, overexpression of regucalcin with full length was demonstrated to suppress the proliferation, cell death and migration in human pancreatic cancer MIA PaCa-2 (K-ras mutated) cells that possess resistance to drug and radiation therapies. Suppressive effects of regucalcin on cell proliferation and death were not seen in the cells overexpressed with regucalcin cDNA alternatively spliced variants (deleted exon 4 or deleted exon 4 and 5). Regucalcin was suggested to induce G1 and G2/M phase cell cycle arrest in MIA PaCa-2 cells. Suppressive effects of regucalcin on cell proliferation were independent of cell death. Overexpression of regucalcin was found to suppress signaling pathways including Akt, MAP kinase and SAPK/JNK, to increase the protein levels of p53, a tumor suppresser, and to decrease K-ras, c-fos and c-jun, a oncogene, by suppressing signaling pathways that are related to signaling of K-ras. Regucalcin may play a potential role as a suppressor protein in human pancreatic cancer.

Stem Cell Replacement Improves Expression of SMP30 in db/db Mice

We have previously reported that replacing bone marrow stem cells may improve hyperglycemia and oxidative stress in db/db mice, a type 2 diabetic mouse model. Senescence marker protein 30 (SMP30) is an antioxidant protein that decreases with aging. However, it has not been clear whether SMP30 decreases in the livers of obese mice, and whether stem cell replacement would improve SMP30 expression in the liver. Bone marrow stem cells of db/db mice were replaced with the bone marrow stem cells of C57BL/6 mice. Plasma cytokine and insulin levels were measured, and glycogen content, expression of SMP30, and fibrosis in the liver were assessed. Our results showed that stem cell replacement increased the expression of SMP30 in the liver, resulting from decreased plasma inflammation cytokines and hyperinsulinemia in db/db mice. This is the first report that stem cell replacement increased the expression of SMP30 in the liver, and may help prevent fibrosis in the liver of db/db mice.

Involvement of regucalcin as a suppressor protein in human carcinogenesis: insight into the gene therapy

Regucalcin, which its gene is located on the X chromosome, plays a multifunctional role as a suppressor protein in cell signal transduction in various types of cells and tissues. The suppression of regucalcin gene expression has been shown to involve in carcinogenesis. Regucalcin gene expression was uniquely downregulated in carcinogenesis of rat liver in vivo, although the expression of other many genes was upregulated, indicating that endogenous regucalcin plays a suppressive role in the development of hepatocarcinogenesis. Overexpression of endogenous regucalcin was found to suppress proliferation of rat cloned hepatoma cells in vitro. Moreover, the regucalcin gene and its protein levels were demonstrated specifically to downregulate in human hepatocellular carcinoma by analysis with multiple gene expression profiles and proteomics. Regucalcin gene expression was also found to suppress in human tumor tissues including kidney, lung, brain, breast and prostate, suggesting that repressed regucalcin gene expression leads to the development of carcinogenesis in various tissues. Regucalcin may play a role as a suppressor protein in carcinogenesis. Overexpression of endogenous regucalcin is suggested to reveal preventive and therapeutic effects on carcinogenesis. Delivery of the regucalcin gene may be a novel useful tool in the gene therapy of carcinogenesis. This review will discuss regarding to an involvement of regucalcin as a suppressor protein in human carcinogenesis in insight into the gene therapy.

Alternatively spliced variants of the regucalcin gene in various human normal and tumor tissues

Regucalcin plays a pivotal role as a suppressor protein in signal transduction in various cell types. The regucalcin gene, which is localized on the X chromosome, consists of 7 exons and 6 introns. Decreased liver regucalcin gene expression has been suggested to play a suppressive role in the development of hepatocellular carcinogenesis in animal models. This study was undertaken to determine the changes in regucalcin gene expression in various human normal and tumor tissues, including liver, kidney, brain and lung tissues. The full-length and alternatively spliced variants of regucalcin mRNA were found to be expressed in various human tissues. This expression was suppressed in tumor tissues of hepatocellular carcinoma, kidney transitional cell carcinoma, brain malignant meningioma and lung non-small cell carcinoma. The full-length regucalcin protein was found to be highly expressed in normal human liver and kidney tissues; its expression was suppressed, however, in the liver and kidney tumor tissues. The spliced variant proteins were found to be expressed in the normal liver and kidney tissues, and decreased in the tumor tissues. Such alternative variants were not observed in the liver and kidneys of rats and mice. The alternatively spliced variants of the regucalcin gene were found to be expressed in various human normal and tumor tissues.

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.