Overexpression of cellular repressor of E1A-stimulated genes inhibits TNF-α-induced apoptosis via NF-κB in mesenchymal stem cells

CREG Protects Retinal Ganglion Cells loss and Retinal Function Impairment Against ischemia-reperfusion Injury in mice via Akt Signaling Pathway

PURPOSE

The irreversible death of retinal ganglion cells (RGCs) plays an important role in the pathogenesis of glaucoma. Cellular repressor of E1A-stimulated genes (CREG), a secreted glycoprotein involved in cellular proliferation and differentiation, has been shown to protect against myocardial and renal ischemia-reperfusion damage. However, the role of CREG in retinal ischemia-reperfusion injury (RIRI) remains unknown. In this study, we aimed to explore the effect of CREG on RGCs apoptosis after RIRI.

METHODS

We used male C57BL/6J mice to establish the RIRI model. Recombinant CREG was injected at 1 day before RIRI. The expression and distribution of CREG were examined by immunofluorescence staining and western blotting. RGCs survival was assessed by immunofluorescence staining of flat-mounted retinas. Retinal apoptosis was measured by the staining of TdT-mediated dUTP nick-end labeling and cleaved caspase-3. Electroretinogram (ERG) analysis and optomotor response were conducted to evaluate retinal function and visual acuity. The expressions of Akt, phospho-Akt (p-Akt), Bax, and Bcl-2 were analyzed by western blotting to determine the signaling pathways of CREG.

RESULTS

We found that CREG expression was decreased after RIRI, and intravitreal injection of CREG attenuated RGCs loss and retinal apoptosis. Besides, the amplitudes of a-wave, b-wave, and photopic negative response (PhNR) in ERG, as well as visual function, were significantly restored after treatment with CERG. Furthermore, intravitreal injection of CREG upregulated p-Akt and Bcl-2 expression and downregulated Bax expression.

CONCLUSION

Our results demonstrated that CREG protected RGCs from RIRI and alleviated retinal apoptosis by activating Akt signaling. In addition, CREG also improved retinal function and visual acuity.

GATA3 improves the protective effects of bone marrow-derived mesenchymal stem cells against ischemic stroke induced injury by regulating autophagy through CREG

BACKGROUND

Bone marrow-derived mesenchymal stem cells (BMSCs) transplantation has been demonstrated to benefit functional recovery after ischemic stroke, however, the low survival rate of BMSCs in ischemic microenvironment largely limits its use.

METHODS

Rat BMSCs (rBMSCs) were isolated from SD rats and treated with oxygen glucose deprivation/reoxygenation (OGD) to mimic ischemic microenvironment in vitro. Expression of mRNAs and proteins were assessed by qRT-PCR and western blot, respectively. Cell viability was detected using MTT. ROS level was evaluated by DCFH-DA Assay Kit. TUNEL and flow cytometry analysis were adopted to detect cell apoptosis. Immunofluorescence analysis was used to examine LC3 expression. Dual-luciferase reporter and ChIP assays were employed to determine the interaction between CREG and GATA3. Middle cerebral artery occlusion (MCAO) model was established to mimic ischemic stroke in vivo. TTC staining was used to measure the infarcts area in the brain of MCAO rats. Nissl staining was used to examine the quantity of neurons, and mNSS test was applied to compare behavioral functions of animals.

RESULTS

The rBMSCs were successfully isolated from SD rats. OGD exposure decreased the expression of GATA3 in rBMSCs, GATA3 overexpression alleviated OGD-induced cell injury and enhanced autophagy. Treatment with autophagy inhibitor (3-MA) abolished the protective effects of GATA3 against OGD-induced cell injury. GATA3 targeted the promoter of CREG and positively regulated its expression. The protective effect of GATA3 overexpression on autophagy during OGD exposure was reversed by CREG knockdown. Moreover, GATA3 overexpression improved the therapeutic effects of BMSCs transplantation on ischemic stroke in vivo.

CONCLUSION

Our results indicated that GATA3 overexpression improved the therapeutic effects of rBMSCs transplantation against ischemic stroke induced injury by regulating autophagy through CREG.

Chemo/radiotherapy-Induced Bone Marrow Niche Alterations

Bone marrow (BM) niche is a specific microenvironment for hematopoietic stem cells (HSCs) as well as non-hematopoietic cells. Evidence shows that chemo/radiotherapy can lead to the disruption of different properties of HSCs such as proliferation, differentiation, localization, self-renewa, and steady-state of cell populations. Investigations have shown that the deregulation of balance within the marrow cavity due to chemo/radiotherapy could lead to bone loss, abnormal hematopoiesis, and enhanced differentiation potential of mesenchymal stem cells towards the adipogenic lineage. Therefore, understanding the underlying mechanisms of chemo/radiotherapy induced BM niche changes may lead to the application of appropriate therapeutic agents to prevent BM niche defects. Highlights Chemo/radiotherapy disrupts the steady-state of bone marrow niche cells and result in deregulation of normal balance of stromal cell populations. Chemo/radiotherapy agents play a significant role in reducing of bone formation as well as fat accumulation in the bone marrow niche. Targeting molecular pathways may lead to recovery of bone marrow niches after chemo/radiotherapy.

Creg in Hepatocytes Ameliorates Liver Ischemia/Reperfusion Injury in a TAK1-Dependent Manner in Mice

Hepatic ischemia/reperfusion (I/R) is a major challenge for liver surgery and specific severe conditions of chronic liver disease. Current surgical and pharmacological strategies are limited to improve liver function after hepatic I/R injury. Thus, an in-depth understanding of the liver I/R mechanism is pivotal to develop new therapeutic methods. The cellular repressor of E1A-stimulated genes (Creg), a key regulator of cellular proliferation, exerts protective roles in cardiovascular diseases and participates in lipid accumulation and inflammatory response in the liver. However, the role of Creg in hepatic I/R remains largely unknown. A genetic engineering technique was used to explore the function of Creg in hepatic I/R injury. Hepatocyte-specific Creg knockout (Creg^ΔHep ) and transgenic mice were generated and subjected to hepatic I/R injury, as were the controls. Creg in hepatocytes prevented against liver I/R injury by suppressing cell death and inflammation. In vitro studies were performed using primary hepatocytes isolated from Creg^ΔHep that were challenged by hypoxia/reoxygenation insult. These cells exhibited more cell death and inflammatory cytokines production similar to observations in vivo. Moreover, further molecular experiments showed that Creg suppressed mitogen-activated protein kinase (MAPK) signaling by inhibiting TAK1 (TGF-β-activated kinase 1) phosphorylation. Inhibiting TAK1 by 5Z-7-ox or mutating the TAK1-binding domain of Creg abolished the protective role of Creg indicating that Creg binding to TAK1 was required for prevention against hepatic I/R injury. Conclusion: These data demonstrate that Creg prevents hepatocytes from liver I/R injury. The Creg-TAK1 interaction inhibited the phosphorylation of TAK1 and the activation of MAPK signaling, which protected against cell death and inflammation during hepatic I/R injury.

CREG1 heterozygous mice are susceptible to high fat diet-induced obesity and insulin resistance

Cellular repressor of E1A-stimulated genes 1 (CREG1) is a small glycoprotein whose physiological function is unknown. In cell culture studies, CREG1 promotes cellular differentiation and maturation. To elucidate its physiological functions, we deleted the Creg1 gene in mice and found that loss of CREG1 leads to early embryonic death, suggesting that it is essential for early development. In the analysis of Creg1 heterozygous mice, we unexpectedly observed that they developed obesity as they get older. In this study, we further studied this phenotype by feeding wild type (WT) and Creg1 heterozygote (Creg1^+/-) mice a high fat diet (HFD) for 16 weeks. Our data showed that Creg1^+/- mice exhibited a more prominent obesity phenotype with no change in food intake compared with WT controls when challenged with HFD. Creg1 haploinsufficiency also exacerbated HFD-induced liver steatosis, dyslipidemia and insulin resistance. In addition, HFD markedly increased pro-inflammatory cytokines in plasma and epididymal adipose tissue in Creg1^+/- mice as compared with WT controls. The activation level of NF-κB, a major regulator of inflammatory response, in epididymal adipose tissue was also elevated in parallel with the cytokines in Creg1^+/- mice. These pro-inflammatory responses elicited by CREG1 reduction were confirmed in 3T3-L1-derived adipocytes with CREG1 depletion by siRNA transfection. Given that adipose tissue inflammation has been shown to play a key role in obesity-induced insulin resistance and metabolic syndrome, our results suggest that Creg1 haploinsufficiency confers increased susceptibility of adipose tissue to inflammation, leading to aggravated obesity and insulin resistance when challenged with HFD. This study uncovered a novel function of CREG1 in metabolic disorders.

Controlled Inhibition of the Mesenchymal Stromal Cell Pro-inflammatory Secretome via Microparticle Engineering

Mesenchymal stromal cells (MSCs) are promising therapeutic candidates given their potent immunomodulatory and anti-inflammatory secretome. However, controlling the MSC secretome post-transplantation is considered a major challenge that hinders their clinical efficacy. To address this, we used a microparticle-based engineering approach to non-genetically modulate pro-inflammatory pathways in human MSCs (hMSCs) under simulated inflammatory conditions. Here we show that microparticles loaded with TPCA-1, a small-molecule NF-κB inhibitor, when delivered to hMSCs can attenuate secretion of pro-inflammatory factors for at least 6 days in vitro. Conditioned medium (CM) derived from TPCA-1-loaded hMSCs also showed reduced ability to attract human monocytes and prevented differentiation of human cardiac fibroblasts to myofibroblasts, compared with CM from untreated or TPCA-1-preconditioned hMSCs. Thus, we provide a broadly applicable bioengineering solution to facilitate intracellular sustained release of agents that modulate signaling. We propose that this approach could be harnessed to improve control over MSC secretome post-transplantation, especially to prevent adverse remodeling post-myocardial infarction.

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Soluble TPCA-1 attenuates pro-inflammatory secretome in TNF-α-stimulated hMSCs

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TPCA preconditioning fails to inhibit pro-inflammatory secretome in TNF-hMSCs

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TPCA-μP-hMSCs demonstrate sustained inhibition of pro-inflammatory secretome

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Engineered hMSCs inhibit α-SMA expression and collagen deposition in cardiac fibroblasts

Up-Regulation of CREG Expression by the Transcription Factor GATA1 Inhibits High Glucose- and High Palmitate-Induced Apoptosis in Human Umbilical Vein Endothelial Cells

Background

Endothelial cell (EC) apoptosis plays a vital role in the pathogenesis of atherosclerosis in patients with diabetes mellitus (DM), but the underlying mechanism remains unclear. Cellular repressor of E1A-stimulated genes (CREG) is a novel gene reported to be involved in maintaining the homeostasis of ECs. Therefore, in the present study, we investigated the role of CREG in high glucose/high palmitate-induced EC apoptosis and to decipher the upstream regulatory mechanism underlying the transcriptional regulation of CREG.

Methods

The expression of CREG and the rate of apoptosis were assessed in lower-limb atherosclerotic lesions from patients with type 2 DM (T2DM). Primary human umbilical vein endothelial cells (HUVECs) were isolated and cultured in a high glucose/high palmitate medium (25 mmol/L D-glucose, 0.4 mmol/L palmitate), and the over-expression and knock-down of CREG were performed in HUVECs to determine the role of CREG in EC apoptosis. The upstream regulatory mechanism of CREG was identified using a promoter-binding transcription-factor profiling array, chromatin immunoprecipitation (ChIP) assay and a mutation analysis.

Results

Compared with normal arteries from non-diabetic patients, reduced CREG expression and increased apoptosis were found in the endothelium of atherosclerotic lesions from patients with T2DM. In vitro treatment of HUVECs with a high glucose/high palmitate medium also resulted in decreased CREG expression and increased apoptosis. Moreover, high glucose/high palmitate induced-HUVEC apoptosis was increased by the knock-down of CREG and rescued by the over-expression of CREG. We also demonstrated that GATA1 was able to bind to the promoter of the human CREG gene. A deletion mutation at -297/-292 in the CREG promoter disrupted GATA1 binding and reduced the activation of CREG transcription by approximately 83.3%. Finally, the overexpression of GATA1 abrogated the high glucose/high palmitate-induced apoptosis in HUVECs.

Conclusions

The over-expression of CREG inhibits high glucose/high palmitate-induced apoptosis in HUVECs. CREG is transcriptionally upregulated by GATA1. Thus, CREG might be a potential therapeutic target for intervention of vascular complications related to diabetes.

Genetic Engineering of Mesenchymal Stem Cells to Induce Their Migration and Survival

Mesenchymal stem cells (MSCs) are very attractive for regenerative medicine due to their relatively easy derivation and broad range of differentiation capabilities, either naturally or induced through cell engineering. However, efficient methods of delivery to diseased tissues and the long-term survival of grafted cells still need improvement. Here, we review genetic engineering approaches designed to enhance the migratory capacities of MSCs, as well as extend their survival after transplantation by the modulation of prosurvival approaches, including prevention of senescence and apoptosis. We highlight some of the latest examples that explore these pivotal points, which have great relevance in cell-based therapies.

Naringin rescued the TNF-α-induced inhibition of osteogenesis of bone marrow-derived mesenchymal stem cells by depressing the activation of NF-кB signaling pathway

Naringin exhibits antiinflammatory activity and is shown to induce bone formation. Yet the impact of naringin on inflammation-affected bone marrow-derived mesenchymal stem cell (BM-MSC), a promising tool for the regenerative treatment of bone injury, remained to be investigated. We first cultured and characterized the BM-MSCs in vitro and observe the effects of treatments of TNF-α, naringin, or the combination of both on osteogenic differentiation. TNF-α administered at the concentration of 20 ng/ml results in significant reductions in MSC's cell survival, alkaline phosphatase activity and expressions of two osteogenic genes, Runx2 and Osx. Simultaneous treatment of both TNF-α and naringin is able to rescue such reductions. Further mechanistic studies indicate that TNF-α treatment activates the NF-кB signaling pathway, evidenced by elevated p-IкBα level as well as the increased nuclear fraction of NF-кB subunit, p65. Finally, treatment with both TNF-α and naringin decreases expressions of p-IкBα and nuclear p65, and thus represses NF-кB pathway activated by sole TNF-α treatment. Our findings provide a molecular basis by which naringin restores the TNF-α-induced damage in MSCs and provide novel insights into the application of naringin in the MSC-based treatments for inflammation-induced bone injury.

Glycoproteomic Approach Identifies KRAS as a Positive Regulator of CREG1 in Non-small Cell Lung Cancer Cells

Protein glycosylation plays a fundamental role in a multitude of biological processes, and the associated aberrant expression of glycoproteins in cancer has made them attractive biomarkers and therapeutic targets. In this study, we examined differentially expressed glycoproteins in cell lines derived from three different states of lung tumorigenesis: an immortalized bronchial epithelial cell (HBE) line, a non-small cell lung cancer (NSCLC) cell line harboring a Kirsten rat sarcoma viral oncogene homolog (KRAS) activation mutation and a NSCLC cell line harboring an epidermal growth factor receptor (EGFR) activation deletion. Using a Triple SILAC proteomic quantification strategy paired with hydrazide chemistry N-linked glycopeptide enrichment, we quantified 118 glycopeptides in the three cell lines derived from 82 glycoproteins. Proteomic profiling revealed 27 glycopeptides overexpressed in both NSCLC cell lines, 6 glycopeptides overexpressed only in the EGFR mutant cells and 19 glycopeptides overexpressed only in the KRAS mutant cells. Further investigation of a panel of NSCLC cell lines found that Cellular repressor of E1A-stimulated genes (CREG1) overexpression was closely correlated with KRAS mutation status in NSCLC cells and could be down-regulated by inhibition of KRAS expression. Our results indicate that CREG1 is a down-stream effector of KRAS in a sub-type of NSCLC cells and a novel candidate biomarker or therapeutic target for KRAS mutant NSCLC.

Nilotinib reduces muscle fibrosis in chronic muscle injury by promoting TNF-mediated apoptosis of fibro/adipogenic progenitors

Depending on the inflammatory milieu, injury can result either in a tissue's complete regeneration or in its degeneration and fibrosis, the latter of which could potentially lead to permanent organ failure. Yet how inflammatory cells regulate matrix-producing cells involved in the reparative process is unknown. Here we show that in acutely damaged skeletal muscle, sequential interactions between multipotent mesenchymal progenitors and infiltrating inflammatory cells determine the outcome of the reparative process. We found that infiltrating inflammatory macrophages, through their expression of tumor necrosis factor (TNF), directly induce apoptosis of fibro/adipogenic progenitors (FAPs). In states of chronic damage, however, such as those in mdx mice, macrophages express high levels of transforming growth factor β1 (TGF-β1), which prevents the apoptosis of FAPs and induces their differentiation into matrix-producing cells. Treatment with nilotinib, a kinase inhibitor with proposed anti-fibrotic activity, can block the effect of TGF-β1 and reduce muscle fibrosis in mdx mice. Our findings reveal an unexpected anti-fibrotic role of TNF and suggest that disruption of the precisely timed progression from a TNF-rich to a TGF-β-rich environment favors fibrotic degeneration of the muscle during chronic injury.

Discovery of prognostic biomarkers for predicting lung cancer metastasis using microarray and survival data

BACKGROUND

Few studies have investigated prognostic biomarkers of distant metastases of lung cancer. One of the central difficulties in identifying biomarkers from microarray data is the availability of only a small number of samples, which results overtraining. Recently obtained evidence reveals that epithelial-mesenchymal transition (EMT) of tumor cells causes metastasis, which is detrimental to patients' survival.

RESULTS

This work proposes a novel optimization approach to discovering EMT-related prognostic biomarkers to predict the distant metastasis of lung cancer using both microarray and survival data. This weighted objective function maximizes both the accuracy of prediction of distant metastasis and the area between the disease-free survival curves of the non-distant and distant metastases. Seventy-eight patients with lung cancer and a follow-up time of 120 months are used to identify a set of gene markers and an independent cohort of 26 patients is used to evaluate the identified biomarkers. The medical records of the 78 patients show a significant difference between the disease-free survival times of the 37 non-distant- and the 41 distant-metastasis patients. The experimental results thus obtained are as follows. 1) The use of disease-free survival curves can compensate for the shortcoming of insufficient samples and greatly increase the test accuracy by 11.10%; and 2) the support vector machine with a set of 17 transcripts, such as CCL16 and CDKN2AIP, can yield a leave-one-out cross-validation accuracy of 93.59%, a test accuracy of 76.92%, a large disease-free survival area of 74.81%, and a mean survival prediction error of 3.99 months. The identified putative biomarkers are examined using related studies and signaling pathways to reveal the potential effectiveness of the biomarkers in prospective confirmatory studies.

CONCLUSIONS

The proposed new optimization approach to identifying prognostic biomarkers by combining multiple sources of data (microarray and survival) can facilitate the accurate selection of biomarkers that are most relevant to the disease while solving the problem of insufficient samples.

Statins impair survival of primary human mesenchymal progenitor cells via mevalonate depletion, NF-κB signaling, and Bnip3

Circulating progenitor cells of bone marrow origin have been implicated in transplant cardiac allograft vasculopathy (CAV) and cardiac fibrosis. HMG-CoA reductase inhibitors, called "statins," have been shown to impair the progression of CAV and improve patient survival. We examined the in vitro effects of three HMG-CoA reductase inhibitors atorvastatin, simvastatin, and pravastatin on the viability of MSCs and expression of nuclear factor kappa B (NF-κB). Mesenchymal stem cells (MSCs) isolated from human patients were treated with atorvastatin, simvastatin, and pravastatin at 0.1, 1.0, or 10 μM ± mevalonate. Human MSC treatment with 1 and 10 μM simvastatin or atorvastatin resulted in progressively reduced cell viability, which was associated with a decline in NF-κB p65. Viability was rescued by co-incubation with mevalonate or by pretreatment with Inhibitor of nuclear factor kappa-B kinase subunit beta (Iκκ-β). Pravastatin did not affect MSC viability or NF-κB expression. Mevalonate depletion through HMG-CoA reductase inhibition impairs the viability of primary human MSC through down-regulating NF-κB.

microRNA-378 promotes mesenchymal stem cell survival and vascularization under hypoxic-ischemic conditions in vitro

Introduction

Mesenchymal stem cells (MSCs) transplantation has been demonstrated to be an effective strategy for the treatment of cardiovascular disease. However, the low survival rate of MSCs at local diseased tissue reduces the therapeutic efficacy. We therefore investigated the influence of MicroRNA-378 (miR-378) transfection on MSCs survival and vascularization under hypoxic-ischemic condition in vitro.

Methods

MSCs were isolated from bone marrow of Sprague–Dawley rats and cultured in vitro. The third passage of MSCs were divided into the miR-378 group and control group. For the miR-378 group, cells were transfected with miR-378 mimic. Both groups experienced exposure to hypoxia (1% O₂) and serum deprivation for 24 hours, using normoxia (20% O₂) as a negative control during the process. After 24 hours of reoxygenation (20% O₂), cell proliferation and apoptosis were evaluated. Expressions of apoptosis and angiogenesis related genes were detected. Both groups were further co-cultured with human umbilical vein endothelial cells to promote vascular differentiation for another 6 hours. Vascular density was assessed thereafter.

Results

Compared with the control group, MSCs transfected with miR-378 showed more rapid growth. Their proliferation rates were much higher at 72 h and 96 h under hypoxic condition (257.33% versus 246.67%, P <0.01; 406.84% versus 365.39%, P <0.05). Cell apoptosis percentage in the miR-378 group was significantly declined under normoxic and hypoxic condition (0.30 ± 0.10% versus 0.50 ± 0.10%, P <0.05; 0.60 ± 0.40% versus 1.70 ± 0.20%, P <0.01). The miR-378 group formed a larger number of vascular branches on matrigel. BCL2 level was decreased accompanied with an upregulated expression of BAX in the two experimental groups under the hypoxic environment. BAX expression was reduced in the miR-378 group under the hypoxic environment. In the miR-378 group, there was a decreased expression of tumor necrosis factor-α on protein level and a reduction of TUSC-2 under normoxic environment. Their expressions were both downregulated under hypoxic environment. For the angiogenesis related genes, enhanced expressions of vascular endothelial growth factorα, platelet derived growth factor-β and transforming growth factor-β1 could be detected both in normoxic and hypoxic-ischemic conditions.

Conclusion

MiR-378 transfection could effectively promote MSCs survival and vascularization under hypoxic-ischemic condition in vitro.

Drosophila melanogaster cellular repressor of E1A-stimulated genes is a lysosomal protein essential for fly development

Mammalian cellular repressor of E1A-stimulated genes is a lysosomal glycoprotein implicated in cellular growth and differentiation. The genome of the fruit fly Drosophila melanogaster encodes a putative orthologue (dCREG), suggesting evolutionarily conserved physiological functions of this protein. In D. melanogaster S2 cells, dCREG was found to localize in lysosomes. Further studies revealed that intracellular dCREG is subject of proteolytic maturation. Processing and turnover could be substantially reduced by RNAi-mediated silencing of cathepsin L. In contrast to mammalian cells, lysosomal delivery of dCREG does not depend on its carbohydrate moiety. Furthermore, depletion of the putative D. melanogaster lysosomal sorting receptor lysosomal enzyme receptor protein did not compromise cellular retention of dCREG. We also investigated the developmental consequences of dCREG ablation in whole D. melanogaster flies. Ubiquitous depletion of dCREG proved lethal at the late pupal stage once a knock-down efficiency of > 95% was achieved. These results demonstrate that dCREG is essential for proper completion of fly development.

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The lysosomal localization of CREG is evolutionarily conserved.

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Lysosomal delivery of CREG is mediated by different mechanisms in mammals and flies.

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Cathepsin L is the main protease responsible for CREG processing and turnover.

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CREG deficiency causes developmental lethality in D. melanogaster.

CREG promotes the proliferation of human umbilical vein endothelial cells through the ERK/cyclin E signaling pathway

Cellular repressor of E1A-stimulated genes (CREG) is a recently discovered secreted glycoprotein involved in homeostatic modulation. We previously reported that CREG is abundantly expressed in the adult vascular endothelium and dramatically downregulated in atherosclerotic lesions. In addition, CREG participates in the regulation of apoptosis, inflammation and wound healing of vascular endothelial cells. In the present study, we attempted to investigate the effect of CREG on the proliferation of vascular endothelial cells and to decipher the underlying molecular mechanisms. Overexpression of CREG in human umbilical vein endothelial cells (HUVEC) was obtained by infection with adenovirus carrying CREG. HUVEC proliferation was investigated by flow cytometry and 5-bromo-2′-deoxy-uridine (BrdU) incorporation assays. The expressions of cyclins, cyclin-dependent kinases and signaling molecules were also examined. In CREG-overexpressing cells, we observed a marked increase in the proportion of the S and G2 population and a decrease in the G0/G1 phase population. The number of BrdU positively-stained cells also increased, obviously. Furthermore, silencing of CREG expression by specific short hairpin RNA effectively inhibited the proliferation of human umbilical vein endothelial cells (HUVEC). CREG overexpression induced the expression of cyclin E in both protein and mRNA levels to regulate cell cycle progression. Further investigation using inhibitor blocking analysis identified that ERK activation mediated the CREG modulation of the proliferation and cyclin E expression in HUVEC. In addition, blocking vascular endothelial growth factor (VEGF) in CREG-overexpressed HUVEC and supplementation of VEGF in CREG knocked-down HUVEC identified that the pro-proliferative effect of CREG was partially mediated by VEGF-induced ERK/cyclin E activation. These results suggest a novel role of CREG to promote HUVEC proliferation through the ERK/cyclin E signaling pathway.