Epidermal growth factor down-regulates the expression of neutrophil gelatinase-associated lipocalin (NGAL) through E-cadherin in pancreatic cancer cells

Lipocalin-2: Structure, function, distribution and role in metabolic disorders

Lipocalin-2 (LCN-2) is a novel, 198 amino acid adipocytokine also referred to as neutrophil gelatinase-associated lipocalin (NGAL). LCN-2 is a circulatory protein responsible for the transportation of small and hydrophobic molecules (steroid, free fatty acids, prostaglandins and hormones) to target organs after binding to megalin/glycoprotein and GP330 SLC22A17 or 24p3R LCN-2 receptors. LCN-2 has been used as a biomarker for acute and chronic renal injury. It is present in a large variety of cells including neutrophil, hepatocytes, lung, bone marrow, adipose tissue, macrophages, thymus, non-neoplastic breast duct, prostate, and renal cells. Different functions have been associated with LCN-2. These functions include antibacterial, anti-inflammatory, and protection against cell and tissue stress. Moreover, LCN-2 can increase the pool of matrix metalloproteinase 9 in human neutrophil granulocytes. Other reported functions of LCN-2 include its ability to destroy the extracellular matrix, which could enable cancer progression and spread of metastasis. Recent reports show that the tissue level of LCN-2 is increased in metabolic disorders such as obesity and type 2 diabetes, suggesting an association between LCN-2 and insulin sensitivity and glucose homeostasis. The precise role of LCN-2 in the modulation of insulin sensitivity, glucose and lipid metabolism is still unclear. This review explores the structure of LCN-2, tissue distribution, and its interaction with important metabolic pathways.

Transplantation of Umbilical Cord-Derived Mesenchymal Stem Cells Overexpressing Lipocalin 2 Ameliorates Ischemia-Induced Injury and Reduces Apoptotic Death in a Rat Acute Myocardial Infarction Model

Myocardial infarction (MI) is a leading cause of death worldwide and requires development of efficient therapeutic strategies . Mesenchymal stem cells (MSCs) -based therapy of MI has been promising but inefficient due to undesirable microenvironment of the infarct tissue. Hence, the current study was conducted to fortify MSCs against the unfavorable microenvironment of infarct tissue via overexpression of Lipocalin 2 (Lcn2) as a cytoprotective factor. The engineered cells (Lcn2-MSCs) were transplanted to infarcted heart of a rat model of MI. According to our findings, Lcn2 overexpression resulted in increased MSCs survival in the MI tissue (p < 0.05) compared to non-engineered cells. Furthermore, the infusion of Lcn2-MSCs mitigated Left ventricle (LV) remodeling, decreased fibrosis (p < 0.0001), and reduced apoptotic death of the LVs' cells (p < 0.0001) compared to the control. Our findings suggest a potential novel therapeutic strategy for MI, however, further investigations such as safety and efficacy assessments in large animals followed by clinical trials are required.

Overexpression of Lipocalin-2 Inhibits Proliferation and Invasiveness of Human Glioblastoma Multiforme Cells by Activating ERK Targeting Cathepsin D Expression

Simple Summary

Lipocalin-2 (LCN2) exhibits pro- and anti-carcinogenic effects in several cancers, but its role in the progression of glioblastoma multiforme (GBM) remains poorly understood. We observed that the overexpression of LCN2 inhibits GBM cell proliferation and invasion via activation of ERK-induced CTSD expression. LCN2 overexpression may be a treatment strategy and prognostic marker for GBM.

Abstract

Lipocalin-2 (LCN2) exhibits pro- and anti-carcinogenic effects in several cancers, but its role in the progression of glioblastoma multiforme (GBM) remains unclear. This study aims to elucidate the effect of LCN2 in human GBM cell, and the mechanism underlying its effects on GBM malignant progression. We observed that LCN2 expression was significantly lower in GBM than in normal tissues and was associated with poorer GBM patient survival. LCN2-overexpressing GBM cells showed significantly reduced proliferation and migration/invasion abilities. Human protease antibody array analysis showed that the expression of cathepsin D (CTSD) protein and mRNA was lower in LCN2-overexpressing GBM cells than in controls. Higher CTSD expression was observed in GBM tumors than in normal tissues, and higher CTSD expression was associated with poorer overall and disease-free survival. LCN2-overexpressing GBM cells exhibited increased ERK phosphorylation. Treatment of these cells with a MEK inhibitor (U0126) restored CTSD expression, cell migration, and cell invasiveness. In conclusion, LCN2 might be serving as a prognostic marker and promising anti-proliferative and anti-metastatic target for treating GBM.

Lipocalin-2 expression and function in pancreatic diseases

Lipocalin-2 (LCN2) is a secreted molecule, expressed in various cell types, that is involved in the progression of numerous diseases and disorders. The biological functions and expression levels of LCN2 in diseases including pancreatic cancer, pancreatitis (acute and chronic), and diabetes mellitus, suggest the potential role of LCN2 as a biomarker and/or therapeutic target. However, findings on the role of LCN2 in pancreatic diseases have been contradictory. In pancreatic cancer and pancreatitis, LCN2 has been identified as a potential biomarker; increased expression levels in various biological specimens correlate with the presence of the disease and may be able to differentiate cancer and chronic pancreatitis from healthy subjects. LCN2 is also known to be an adipokine; it is upregulated in obesity and is a common co-factor in the development of pancreatic diseases. Emerging research suggests LCN2 is elevated in type 2 diabetes mellitus, but the exact role of LCN2 in this disease is not clear. In this review, we summarize research on LCN2 as it relates to pancreatic diseases, highlighting the discrepancies in the literature. By explaining and clarifying the role of LCN2 in these disorders, we aim to promote research in developing novel diagnostic and treatment strategies to reduce the burden of pancreatic diseases.

Implication and role of neutrophil gelatinase-associated lipocalin in cancer: lipocalin-2 as a potential novel emerging comprehensive therapeutic target for a variety of cancer types

Cancer is a leading cause of mortalities worldwide. Over the past few decades, exploration of molecular mechanisms behind cancer initiation and progression has been of great interest in the viewpoint of both basic and clinical scientists. It is generally believed that identification of key molecules implicated in cancer pathology not only improves our understanding of the disease, but also could result in introduction of novel therapeutic strategies. Neutrophil gelatinase-associated lipocalin (NGAL)/lipocalin-2 (LCN2) is a member of lipocalin superfamily with a variety of functions. Although the main function of LCN2 is still unknown, many studies confirmed its significant role in the initiation, progression, and metastasis of various types of cancer. Furthermore, aberrant expression of LCN2 is also concerned with the chemo- and radio-resistant phenotypes of tumors. Here, we will review the contribution of known functions of LCN2 to the pathophysiology of cancer. We also highlight how the deregulated expression of LCN2 is associated with a variety of fatal types of cancer for which there are no effective therapeutic modalities. The unique and multiple functions of LCN2 and its widespread expression in different types of cancer prompted us to suggest LCN2 could be considered either as a valuable diagnostic and prognostic biomarker or as a potential novel therapeutic target.

An early-screening biomarker of endometrial carcinoma: NGAL is associated with epithelio-mesenchymal transition

neutrophilgelatinase-associated lipocalin is currently one of the most interesting and enigmatic proteins involved in the development of malignancies. In this study, we found that the expression of neutrophilgelatinase-associated lipocalin was up-regulated in endometrial cancer tissues and cell lines, significantly increased in early-grade ones, suggesting it may serve as a biomarker for early-stage screening for endometrial carcinoma. Moreover, neutrophilgelatinase-associated lipocalin was up-regulated in Ishikawa cells under going epithelio-mesenchymal transition induced by epidermal growth factor (5 ng/ml). Up-regulation of neutrophilgelatinase-associated lipocalin may correlate with the down-regulation of E-cadherin expression, up-regulation of Vimentin expression, enhanced cell migration, invasion and proliferation, which are the typical hallmarks of epithelio-mesenchymal transition processes. neutrophilgelatinase-associated lipocalin may play a dual role during tumorigenetic and developmental processes of endometrial carcinoma. These results suggested neutrophilgelatinase-associated lipocalin to be a potential molecular target in the early diagnosis and treatment of endometrial carcinoma. Further studies are warranted to clarify the molecular mechanisms behind the expression and function of neutrophilgelatinase-associated lipocalin and epithelio-mesenchymal transition.

Lipocalin-2 Promotes Pancreatic Ductal Adenocarcinoma by Regulating Inflammation in the Tumor Microenvironment

Lipocalin-2 (LCN2) promotes malignant development in many cancer types. LCN2 is upregulated in patients with pancreatic ductal adenocarcinoma (PDAC) and in obese individuals, but whether it contributes to PDAC development is unclear. In this study, we investigated the effects of Lcn2 depletion on diet-induced obesity, inflammation, and PDAC development. Mice with acinar cell-specific expression of KrasG12D were crossed with Lcn2-depleted animals and fed isocaloric diets with varying amounts of fat content. Pancreas were collected and analyzed for inflammation, pancreatic intraepithelial neoplasia (PanIN), and PDAC. We also used a syngeneic orthotopic PDAC mouse model to study tumor growth in the presence or absence of Lcn2 expression. In addition, to understand the mechanistic role of how LCN2 could be mediating PDAC, we studied LCN2 and its specific receptor solute carrier family 22 member 17 (SLC22A17) in human pancreatic cancer stellate cells (PSC), key mediators of the PDAC stroma. Depletion of Lcn2 diminished extracellular matrix deposition, immune cell infiltration, PanIN formation, and tumor growth. Notably, it also increased survival in both obesity-driven and syngeneic orthotopic PDAC mouse models. LCN2 modulated the secretion of proinflammatory cytokines in PSC of the PDAC tumor microenvironment, whereas downregulation of LCN2-specific receptor SLC22A17 blocked these effects. Our results reveal how LCN2 acts in the tumor microenvironment links obesity, inflammation, and PDAC development. Cancer Res; 77(10); 2647-60. ©2017 AACR.

Antimicrobial Activity of Mesenchymal Stem Cells: Current Status and New Perspectives of Antimicrobial Peptide-Based Therapies

While mesenchymal stem cells (MSCs)-based therapy appears to be promising, there are concerns regarding possible side effects related to the unwanted suppression of antimicrobial immunity leading to an increased risk of infection. Conversely, recent data show that MSCs exert strong antimicrobial effects through indirect and direct mechanisms, partially mediated by the secretion of antimicrobial peptides and proteins (AMPs). In fact, MSCs have been reported to increase bacterial clearance in preclinical models of sepsis, acute respiratory distress syndrome, and cystic fibrosis-related infections. This article reviews the current evidence regarding the direct antimicrobial effector function of MSCs, focusing mainly on the role of MSCs-derived AMPs. The strategies that might modulate the expression and secretion of these AMPs, leading to enhanced antimicrobial effect, are highlighted. Furthermore, studies evaluating the presence of AMPs in the cargo of extracellular vesicles (EVs) are underlined as perspective opportunities to develop new drug delivery tools. The antimicrobial potential of MSCs-derived EVs can also be heightened through cell conditioning and/or drug loading. Finally, improving the pharmacokinetics and delivery, in addition to deciphering the multi-target drug status of AMPs, should synergistically lead to key advances against infections caused by drug-resistant strains.

Antimicrobial Activity of Mesenchymal Stem Cells: Current Status and New Perspectives of Antimicrobial Peptide-Based Therapies

While mesenchymal stem cells (MSCs)-based therapy appears to be promising, there are concerns regarding possible side effects related to the unwanted suppression of antimicrobial immunity leading to an increased risk of infection. Conversely, recent data show that MSCs exert strong antimicrobial effects through indirect and direct mechanisms, partially mediated by the secretion of antimicrobial peptides and proteins (AMPs). In fact, MSCs have been reported to increase bacterial clearance in preclinical models of sepsis, acute respiratory distress syndrome, and cystic fibrosis-related infections. This article reviews the current evidence regarding the direct antimicrobial effector function of MSCs, focusing mainly on the role of MSCs-derived AMPs. The strategies that might modulate the expression and secretion of these AMPs, leading to enhanced antimicrobial effect, are highlighted. Furthermore, studies evaluating the presence of AMPs in the cargo of extracellular vesicles (EVs) are underlined as perspective opportunities to develop new drug delivery tools. The antimicrobial potential of MSCs-derived EVs can also be heightened through cell conditioning and/or drug loading. Finally, improving the pharmacokinetics and delivery, in addition to deciphering the multi-target drug status of AMPs, should synergistically lead to key advances against infections caused by drug-resistant strains.

A novel NHE1-centered signaling cassette drives epidermal growth factor receptor-dependent pancreatic tumor metastasis and is a target for combination therapy

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers principally because of early invasion and metastasis. The epidermal growth factor receptor (EGFR) is essential for PDAC development even in the presence of Kras, but its inhibition with erlotinib gives only a modest clinical response, making the discovery of novel EGFR targets of critical interest. Here, we revealed by mining a human pancreatic gene expression database that the metastasis promoter Na⁺/H⁺ exchanger (NHE1) associates with the EGFR in PDAC. In human PDAC cell lines, we confirmed that NHE1 drives both basal and EGF-stimulated three-dimensional growth and early invasion via invadopodial extracellular matrix digestion. EGF promoted the complexing of EGFR with NHE1 via the scaffolding protein Na +/H + exchanger regulatory factor 1, engaging EGFR in a negative transregulatory loop that controls the extent and duration of EGFR oncogenic signaling and stimulates NHE1. The specificity of NHE1 for growth or invasion depends on the segregation of the transient EGFR/Na +/H + exchanger regulatory factor 1/NHE1 signaling complex into dimeric subcomplexes in different lipid raftlike membrane domains. This signaling complex was also found in tumors developed in orthotopic mice. Importantly, the specific NHE1 inhibitor cariporide reduced both three-dimensional growth and invasion independently of PDAC subtype and synergistically sensitized these behaviors to low doses of erlotinib.

From cell membrane to the nucleus: an emerging role of E-cadherin in gene transcriptional regulation

E-cadherin is a well-known mediator of cell–cell adherens junctions. However, many other functions of E-cadherin have been reported. Collectively, the available data suggest that E-cadherin may also act as a gene transcriptional regulator. Here, evidence supporting this claim is reviewed, and possible mechanisms of action are discussed. E-cadherin has been shown to modulate the activity of several notable cell signalling pathways, and given that most of these pathways in turn regulate gene expression, we proposed that E-cadherin may regulate gene transcription by affecting these pathways. Additionally, E-cadherin has been shown to accumulate in the nucleus where documentation of an E-cadherin fragment bound to DNA suggests that E-cadherin may directly regulate gene transcription. In summary, from the cell membrane to the nucleus, a role for E-cadherin in gene transcription may be emerging. Studies specifically focused on this potential role would allow for a more thorough understanding of this transmembrane glycoprotein in mediating intra- and intercellular activities.

Neutrophil gelatinase-associated lipocalin in cancer

Neutrophil gelatinase-associated lipocalin (NGAL), also known as lipocalin-2, is a 178-amino acid protein which exists in three molecular forms, including a 25-kDa monomer, a 45-kDa homodimer, and a 135-kDa heterodimer complexed with matrix metalloproteinase 9 (MMP-9). Polymorphonuclear neutrophils and tubular cells of the kidney are the most representative cellular sources. As such, NGAL is now considered the biochemical gold standard for early diagnosis of acute kidney injury. Recent evidence suggests, however, that ectopic or enhanced expression of NGAL may occur in many other pathologic conditions including cancer. Several epidemiologic studies, as reviewed in this chapter, showed that a variety of malignant tumors consistently overexpressed NGAL with increased concentration in blood, urine, and other biologic fluids. In addition, NGAL was frequently associated with tumor size, stage, and invasiveness. These features thus make it a potential biomarker for malignancy. A number of experimental studies also demonstrated that the ability to bind MMP-9, to scavenge iron into cancer cells along with the effect on subcellular localization of transmembrane proteins such as cadherins and catenins, confers this protein the potential to enhance can cer aggressiveness and makes it an appealing target of future anticancer research.

Lipocalin-2 is associated with a good prognosis and reversing epithelial-to-mesenchymal transition in pancreatic cancer

BACKGROUND

Lipocalin-2 is a multifaceted modulator in cancer progression. Its clinical significance is not clear in pancreatic cancer. The purpose of this study was to investigate whether lipocalin-2 is associated with good prognosis by reversing epithelial-to-mesenchymal transition (EMT) in pancreatic cancer.

METHODS

Lipocalin-2, E-cadherin, or vimentin expression was detected in 60 pancreatic adenocarcinoma specimens. Correlations between lipocalin-2 expression and EMT, the clinicopathologic characteristics, and prognosis were investigated. Whether pancreatic cancer cells' migration and invasion (some characteristics of EMT) were affected by lipocalin-2 was also explored.

RESULTS

High lipocalin-2 expression was significantly associated with a good prognosis in pancreatic cancer (p < 0.05). Overexpression of lipocalin-2 correlated with a lower extent of EMT (p < 0.05), increased E-cadherin expression (p < 0.05), decreased vimentin expression (p < 0.05), and reduced cancer cell migration and invasion in pancreatic cancer.

CONCLUSIONS

Lipocalin-2 may be considered an epithelial inducer, which may reverse EMT and predict a good prognosis in pancreatic cancer.

MUC4-mediated regulation of acute phase protein lipocalin 2 through HER2/AKT/NF-κB signaling in pancreatic cancer

PURPOSE

MUC4 shows aberrant expression in early pancreatic lesions and a high specificity for pancreatic cancer. It thus has a high potential to be a sensitive and specific biomarker. Unfortunately, its low serum level limits its diagnostic/prognostic potential. We here report that a multifaceted acute phase protein lipocalin 2, regulated by MUC4, could be a potential diagnostic/prognostic marker for pancreatic cancer. Experimental Designs and

RESULTS

Overexpression/knockdown, luciferase reporter and molecular inhibition studies revealed that MUC4 regulates lipocalin 2 by stabilizing HER2 and stimulating AKT, which results in the activation of NF-κB. Immunohistochemical analyses of lipocalin 2 and MUC4 showed a significant positive correlation between MUC4 and lipocalin 2 in primary, metastatic tissues (Spearman correlation coefficient 0.71, P = 0.002) from rapid autopsy tissue sample from patients with pancreatic cancer as well as in serum and tissue samples from spontaneous KRASG(12)D mouse pancreatic cancer model (Spearman correlation coefficient 0.98, P < 0.05). Lipocalin 2 levels increased progressively with disease advancement (344.2 ± 22.8 ng/mL for 10 weeks to 3067.2 ± 572.6 for 50 weeks; P < 0.0001). In human pancreatic cancer cases, significantly elevated levels of lipocalin 2 were observed in patients with pancreatic cancer (148 ± 13.18 ng/mL) in comparison with controls (73.27 ± 4.9 ng/mL, P = 0.014). Analyses of pre- and postchemotherapy patients showed higher lipocalin 2 levels in prechemotherapy patients [121.7 ng/mL; 95% confidence interval (CI), 98.1-150.9] in comparison with the postchemotherapy (92.6 ng/mL; 95% CI, 76.7-111.6; P = 0.06) group.

CONCLUSIONS

This study delineates the association and the downstream mechanisms of MUC4-regulated elevation of lipocalin-2 (via HER2/AKT/NF-κB) and its clinical significance for prognosis of pancreatic cancer.

Lipocalin-2-mediated upregulation of various antioxidants and growth factors protects bone marrow-derived mesenchymal stem cells against unfavorable microenvironments

Despite many advantages of mesenchymal stem cells (MSCs) that make them suitable for cell therapy purposes, their therapeutic application has been limited due to their susceptibility to several stresses (e.g., nutrient-poor environment, oxidative stress, and hypoxic and masses of cytotoxic factors) to which they are exposed during their preparation and following transplantation. Hence, reinforcing MSCs against these stresses is a challenge for both basic and clinician scientists. Recently, much attention has been directed toward equipping MSCs with cytoprotective factors to strengthen them against unfavorable microenvironments. Here, we engineered MSCs with lipocalin 2 (Lcn2), a cytoprotective factor that is naturally induced following exposure of cells to stresses imposed by the microenvironment. Lcn2 overexpression not only did not interfere with the multidifferentiation capacity of the MSCs but also granted many protective properties to them. Lcn2 potentiated MSCs to withstand oxidative, hypoxia, and serum deprivation (SD) conditions via antagonizing their induced cytotoxicity and apoptosis. Adhesion rate of MSCs to coated culture plates was also enhanced by Lcn2 overexpression. In addition, Lcn2 induced antioxidants and upregulated some growth factors in MSCs. Our findings suggested a new strategy for prevention of graft cell death in MSC-based cell therapy.

Elevated neutrophil gelatinase-associated lipocalin contributes to erlotinib resistance in non-small cell lung cancer

PURPOSE

The EGFR tyrosine kinase inhibitors (TKIs) demonstrate efficacy in NSCLC patients whose tumors harbor activating EGFR mutations. However, patients who initially respond to EGFR TKI treatment invariably develop resistance to the drugs. Known mechanisms account for approximately 70% of native and acquired EGFR TKI resistance. In the current study we investigated a novel mechanism of NSCLC resistance to erlotinib.

EXPERIMENTAL DESIGN

The mechanisms of acquired erlotinib resistance were evaluated by microarray analysis in thirteen NSCLC cell lines and in vivo in mice. Correlations between plasma neutrophil gelatinase associated lipocalin (NGAL) levels, erlotinib response and the EGFR mutational status were assessed in advanced stage NSCLC patients treated with erlotinib.

RESULTS

In 5 of 13 NSCLC cell lines NGAL was significantly upregulated. NGAL knockdown in erlotinib-resistant cells increased erlotinib sensitivity in vitro and in vivo. NGAL overexpression in erlotinib-sensitive cells augmented apoptosis resistance. This was mediated by NGAL-dependent modulation of the pro-apoptotic protein Bim levels. Evaluation of the plasma NGAL levels in NSCLC patients that received erlotinib revealed that patients with lower baseline NGAL demonstrated a better erlotinib response. Compared to patients with wild type EGFR, patients with activating EGFR mutations had lower plasma NGAL at baseline and weeks 4 and 8.

CONCLUSIONS

Our studies uncover a novel mechanism of NGAL-mediated modulation of Bim levels in NSCLC that might contribute to TKI resistance in lung cancer patients. These findings provide the rationale for the further investigations of the utility of NGAL as a potential therapeutic target or diagnostic biomarker.

The multifaceted roles of neutrophil gelatinase associated lipocalin (NGAL) in inflammation and cancer

Neutrophil gelatinase associated lipocalin (NGAL), also known as oncogene 24p3, uterocalin, siderocalin or lipocalin 2, is a 24kDa secreted glycoprotein originally purified from a culture of mouse kidney cells infected with simian virus 40 (SV-40). Subsequent investigations have revealed that it is a member of the lipocalin family of proteins that transport small, hydrophobic ligands. Since then, NGAL expression has been reported in several normal tissues where it serves to provide protection against bacterial infection and modulate oxidative stress. Its expression is also dysregulated in several benign and malignant diseases. Its small size, secreted nature and relative stability have led to it being investigated as a diagnostic and prognostic biomarker in numerous diseases including inflammation and cancer. Functional studies, conducted primarily on lipocalin 2 (Lcn2), the mouse homologue of human NGAL have revealed that Lcn2 has a strong affinity for iron complexed to both bacterial siderophores (iron-binding proteins) and certain human proteins like norepinephrine. By sequestering iron-laden siderophores, Lcn2 deprives bacteria of a vital nutrient and thus inhibits their growth (bacteriostatic effect). In malignant cells, its proposed functions range from inhibiting apoptosis (in thyroid cancer cells), invasion and angiogenesis (in pancreatic cancer) to increasing proliferation and metastasis (in breast and colon cancer). Ectopic expression of Lcn2 also promotes BCR-ABL induced chronic myelogenous leukemia in murine models. By transporting iron into and out of the cell, NGAL also regulates iron responsive genes. Further, it stabilizes the proteolytic enzyme matrix metalloprotease-9 (MMP-9) by forming a complex with it, and thereby prevents its autodegradation. The factors regulating NGAL expression are numerous and range from pro-inflammatory cytokines like interleukins, tumor necrosis factor-α and interferons to vitamins like retinoic acid. The purpose of this review article is to examine the expression, structure, regulation and biological role of NGAL and critically assess its potential as a novel diagnostic and prognostic marker in both benign and malignant human diseases.

YueF overexpression inhibits cell proliferation partly through p21 upregulation in renal cell carcinoma

YueF is a novel putative tumor suppressor gene that can inhibit proliferation and induce apoptosis in hepatoma cells, but its role in renal cell carcinoma (RCC) remains unclear. Here, we examined the expression of the YueF gene in RCC tissues and the effect of YueF on cell proliferation in RCC 786-0 cells. The results showed that YueF was expressed at high levels in normal kidney tissues and cell lines but was reduced or absent in RCC tissues and 786-0 cells. Lentivirus-mediated YueF overexpression in RCC 786-0 cells caused cell-cycle arrest in the G1 phase and dramatically reduced proliferation in culture. YueF overexpression resulted in increased protein levels of p53 and p21^WAF1/Cip1, whereas the protein levels of cyclin D1 and pRb were decreased. The proliferation defects caused by YueF overexpression could be partially rescued by the expression of p21 siRNA. These findings suggest a critical role for p21 in the YueF-induced growth inhibition of 786-0 cells and provide novel insights into the mechanism underlying the tumor-suppressive action of YueF.