Recombinant human decorin suppresses liver HepG2 carcinoma cells by p21 upregulation

Oncosuppressive roles of decorin through regulation of multiple receptors and diverse signaling pathways

Decorin is a stromal-derived prototype member of the small leucine-rich proteoglycan gene family. In addition to its functions as a regulator of collagen fibrillogenesis and TGF-β activity soluble decorin acts as a pan-receptor tyrosine kinase (RTK) inhibitor. Decorin binds to various RTKs including EGFR HER2 HGFR/Met VEGFR2 TLR and IGFR. Although the molecular mechanism for the action of decorin on these receptors is not entirely elucidated overall decorin evokes transient activation of these receptors with suppression of downstream signaling cascades culminating in growth inhibition followed by their physical downregulation via caveosomal internalization and degradation. In the case of Met decorin leads to decreased β-catenin signaling pathway and growth suppression. As most of these RTKs are responsible for providing a growth advantage to cancer cells the result of decorin treatment is oncosuppression. Another decorin-driven mechanism to restrict cancer growth and dissemination is by impeding angiogenesis via vascular endothelial growth factor receptor 2 (VEGFR2) and the concurrent activation of protracted endothelial cell autophagy. In this review we will dissect the multiple roles of decorin in cancer biology and its potential use as a next-generation protein-based adjuvant therapy to combat cancer.

Network of clinically-relevant lncRNAs-mRNAs associated with prognosis of hepatocellular carcinoma patients

Long non-coding RNAs (lncRNAs) are often aberrantly expressed in Hepatocellular Carcinoma (HCC). We hypothesize that lncRNAs modulate HCC prognoses through differential deregulation of key lncRNAs affecting important gene network in key cancer pathways associated with pertinent clinical phenotype. Here, we present a novel approach integrating lncRNA-mRNA expression profiles with clinical characteristics to identify lncRNA signatures in clinically-relevant co-expression lncRNA-mRNA networks residing in pertinent cancer pathways. Notably one network, associated with poorer prognosis, comprises five up-regulated lncRNAs significantly correlated (|Pearson Correlation Coefficient|≥ 0.9) with 91 up-regulated genes in the cell-cycle and Rho-GTPase pathways. All 5 lncRNAs and 85/91 (93.4%) of the correlated genes were significantly associated with higher tumor-grade while 3/5 lncRNAs were also associated with no tumor capsule. Interestingly, 2/5 lncRNAs that are correlated with numerous genes in this oncogenic network were experimentally shown to up-regulate genes involved in cell-cycle and transcriptional regulation. Another network comprising 4 down-regulated lncRNAs and 8 down-regulated metallothionein-family genes are significantly associated with tumor invasion. The identification of these key lncRNAs signatures that deregulate important network of genes in key cancer pathways associated with pertinent clinical phenotype may facilitate the design of novel therapeutic strategies targeting these 'master' regulators for better patient outcome.

Impact of Decorin on the Physical Function and Prognosis of Patients with Hepatocellular Carcinoma

The outcome of patients with hepatocellular carcinoma (HCC) is still poor. Decorin is a small leucine-rich proteoglycan, which exerts antiproliferative and antiangiogenic properties in vitro. We aimed to investigate the associations of decorin with physical function and prognosis in patients with HCC. We enrolled 65 patients with HCC treated with transcatheter arterial chemoembolization (median age, 75 years; female/male, 25/40). Serum decorin levels were measured using enzyme-linked immunosorbent assays; patients were classified into the High or Low decorin groups by median levels. Associations of decorin with physical function and prognosis were evaluated by multivariate correlation and Cox regression analyses, respectively. Age and skeletal muscle indices were not significantly different between the High and Low decorin groups. In the High decorin group, the 6-min walking distance was significantly longer than the Low decorin group and was significantly correlated with serum decorin levels (r = 0.2927, p = 0.0353). In multivariate analysis, the High decorin group was independently associated with overall survival (hazard ratio 2.808, 95% confidence interval 1.016–8.018, p = 0.0498). In the High decorin group, overall survival rate was significantly higher than in the Low decorin group (median 732 days vs. 463 days, p = 0.010). In conclusion, decorin may be associated with physical function and prognosis in patients with HCC.

Tumor-specific inhibitory action of decorin on different hepatoma cell lines

BACKGROUND

In spite of therapeutic approaches, liver cancer is still one of the deadliest type of tumor in which tumor microenvironment may play an active role in the outcome of the disease. Decorin, a small leucine-rich proteoglycan is not only responsible for assembly and maintenance of the integrity of the extracellular matrix, but a natural inhibitor of cell surface receptors, thus it exerts antitumorigenic effects. Here we addressed the question whether this effect of decorin is independent of the tumor phenotypes including differentiation, proliferation and invasion.

METHOD

Four hepatoma cell lines HepG2, Hep3B, HuH7 and HLE, possessing different molecular backgrounds, were selected to investigate. After proliferation tests, pRTK arrays, WB analyses, and immunofluorescent examinations were performed on decorin treated and control cells for comparison.

RESULTS

Significant growth inhibitory potential of decorin on three out of four hepatoma cell lines was proven, however the mode of its action was different. Induction of p21^WAF1/CIP1, increased inactivation of c-myc and β-catenin, and decrease of EGFR, GSK3β and ERK1/2 phosphorylation levels were observed in HepG2 cells, pathways already well-described in literature. However, in the p53 deficient Hep3B and HuH7, InsR and IGF-1R were the main receptors transmitting signals. In harmony with its receptor status, Hep3B cells displayed high level of activated AKT. As the cell line is retinoblastoma mutant, ATR/Chk1/Wee1 system might hinder the cell cycle in G2/M phase via phosphorylation of CDK1. In Huh7 cells, all RTKs were inhibited by decorin followed by downregulation of AKT. Furthermore, HuH7 cell line responded with concentration-dependent ERK activation and increased phospho-c-myc level. Decorin had only a non-significant effect on the proliferation rate of HLE cell line. However, it responded with a significant decrease of pAKT, c-myc and β-catenin activity. In this special cell line, the inhibition of TGFβ may be the first step of the protective effect of decorin.

CONCLUSIONS

Based on our results decorin may be a candidate therapeutic agent in the battle against liver cancer, but several questions need to be answered. It is certain that decorin is capable to exert its suppressor effect in hepatoma cells without respect to their phenotype and molecular background.

In vivo and in vitro effects of hyperplasia suppressor gene on the proliferation and apoptosis of lung adenocarcinoma A549 cells

Lung adenocarcinoma is the most common subtype of non-small cell lung cancer (NSCLC). Hyperplasia suppressor gene (HSG) has been reported to inhibit cell proliferation, migration, and remodeling in cardiovascular diseases. However, there lacks systematic researches on the effect of HSG on the apoptosis and proliferation of lung adenocarcinoma A549 cells and data of in vivo experiments. The present study aims to investigate the effects of HSG gene silencing on proliferation and apoptosis of lung adenocarcinoma A549 cells. The human lung adenocarcinoma A549 cell was selected to construct adenovirus vector. Reverse transcription-quantitative PCR (RT-qPCR) and Western blot analysis were conducted to detect expressions of HSG and apoptosis related-proteins. Cell Counting Kit (CCK)-8 assay was performed to assess A549 cell proliferation and flow cytometry to analyze cell cycle and apoptosis rate. The BALB/C nude mice were collected to establish xenograft model. Silenced HSG showed decreased mRNA and protein expressions of HSG, and elevated A549 cell survival rates at the time point of 24, 48, and 72 h. The ratio of cells at G₀/G₁ phase and apoptosis rate decreased and the ratio of cells at S- and G₂/M phases increased following the silencing of HSG. There were decreases of B cell lymphoma-2 (Bcl-2)-associated X protein (Bax), Caspase-3, and Caspase-8 expressions but increases in Bcl-2 induced by silenced HSG. As for the xenograft in nude mice, tumor volume increased, and apoptosis index (AI) decreased after HSG silencing. These results indicate that HSG gene silencing may promote the proliferation of A549 cells and inhibit the apoptosis. HSG may be a promising target for the treatment of lung adenocarcinoma.

Systems analysis of key genes and pathways in the progression of hepatocellular carcinoma

The carcinogenesis of hepatocellular carcinoma (HCC) is a complex process, starting from a chronically altered hepatic microenvironment due to liver cirrhosis and ultimately progressing to HCC. However, the sequential molecular alterations driving the malignant transformation in liver cirrhosis are not clearly defined.In this study, we obtained gene expression profiles of HCC, including 268 tumor tissues, 243 adjacent tumor tissues, and 40 cirrhotic tissues (GSE25097) from Gene Expression Omnibus (GEO), to comprehensively define changes in the transcriptome of HCC during the sequential evolution of liver cirrhosis into HCC.We showed that changes in the molecular profiles of cirrhotic and adjacent tumor samples were small and quite uniform, whereas there was a striking increase in the heterogeneity of tumors in HCC tissues at the mRNA level. A massive deregulation of key oncogenic molecules and pathways was observed from cirrhosis to HCC tumors. In addition, we focused on FOXO1 and DCN, 2 critical tumor suppressor genes that play an important role in liver cirrhosis and HCC development. FOXO1 and DCN expression levels were significantly reduced in tumor tissues compared with adjacent tumor tissues in HCC. Kaplan-Meier analysis revealed that FOXO1 and DCN expression was positively correlated with overall survival, defining FOXO1 and DCN as adverse prognostic biomarkers for HCC.This system-level research provided new insights into the molecular mechanisms of HCC carcinogenesis. FOXO1 and DCN may be applied as potential targets for HCC treatment in the future.

Cadherin-6 type 2, K-cadherin (CDH6) is regulated by mutant p53 in the fallopian tube but is not expressed in the ovarian surface

High-grade serous ovarian cancer (HGSOC) is the most lethal gynecological malignancy and may arise in either the fallopian tube epithelium (FTE) or ovarian surface epithelium (OSE). A mutation in p53 is reported in 96% of HGSOC, most frequently at R273 and R248. The goal of this study was to identify specific gene targets in the FTE that are altered by mutant p53, but not in the OSE. Gene analysis revealed that both R273 and R248 mutant p53 reduces CDH6 expression in the oviduct, but CDH6 was not detected in murine OSE cells. p53^R273H induced SLUG and FOXM1 while p53^R248W did not induce SLUG and only modestly increased FOXM1, which correlated with less migration as compared to p53^R273H. An oviduct specific PAX8^Cre/+/p53^R270H/+ mouse model was created and confirmed that in vivo mutant p53 repressed CDH6 but was not sufficient to stabilize p53 expression alone. Overexpression of mutant p53 in the p53 null OVCAR5 cells decreased CDH6 levels indicating this was a gain-of-function. SLUG knockdown in murine oviductal cells with p53^R273H restored CDH6 repression and a ChIP analysis revealed direct binding of mutant p53 on the CDH6 promoter. NSC59984, a small molecule that degrades mutant p53^R273H, rescued CDH6 expression. In summary, CDH6 is expressed in the oviduct, but not the ovary, and is repressed by mutant p53. CDH6 expression with further validations may aide in establishing markers that inform upon the cell of origin of high grade serous tumors.

Targeting of short TRPM8 isoforms induces 4TM-TRPM8-dependent apoptosis in prostate cancer cells

Since its cloning a decade ago, TRPM8 channel has emerged as a promising prognostic marker and a putative therapeutic target in prostate cancer (PCa). However, recent studies have brought to light the complexity of TRPM8 isoforms in PCa. Consequently, the respective role of each TRPM8 isoform needs to be deciphered prior to considering TRPM8 as an attractive therapeutic target. Full-length (6 transmembrane (TM)-domain) TRPM8 channel is overexpressed in early PCa and repressed in advanced prostate tumors whereas the localization of the truncated, 4TM-TRPM8 channel (4 transmembrane (TM)-domain), in the membranes of endoplasmic reticulum (ER) is independent of the pathogenic status of epithelial cells. In the same line, expression of non-channel cytoplasmic small TRPM8 isoforms (namely sM8) is conserved in cancer cells. In this study, we identify sM8s as putative regulator of PCa cell death. Indeed, suppression of sM8 isoforms was found to induce concomitantly ER stress, oxidative stress, p21 expression and apoptosis in human epithelial prostate cancer cells. We furthermore demonstrate that induction of such mechanisms required the activity of 4TM-TRPM8 channels at the ER-mitochondria junction. Our study thus suggests that targeting sM8 could be an appropriate strategy to fight prostate cancer.

β-defensin 1 expression in HCV infected liver/liver cancer: an important role in protecting HCV progression and liver cancer development

β-defensin family plays a role in host defense against viral infection, however its role in HCV infection is still unknown. In this study, we demonstrated that β-defensin 1 was significantly reduced in HCV-infected liver specimens. Treatment with interferon and ribavirin upregulated β-defensin-1, but not other β-defensin tested, with the extent and duration of upregulation associated with treatment response. We investigated β-defensin family expression in liver cancer in publicly available datasets and found that among all the β-defensins tested, only β-defensin 1 was significantly downregulated, suggesting β-defensin 1 plays a crucial role in liver cancer development. Further analysis identified E-cadherin as the top positive correlated gene, while hepatocyte growth factor-regulated tyrosine kinase substrate as the top negative correlated gene. Expression of two proteoglycans were also positively correlated with that of β-defensin 1. We have also identified small molecules as potential therapeutic agents to reverse β-defensin 1-associated gene signature. Furthermore, the downregulation of β-defensin 1 and E-cadherin, and upregulation of hepatocyte growth factor-regulated tyrosine kinase substrate, were further confirmed in liver cancer and adjacent normal tissue collected from in-house Chinese liver cancer patients. Together, our results suggest β-defensin 1 plays an important role in protecting HCV progression and liver cancer development.

Adenovirus-mediated decorin expression induces cancer cell death through activation of p53 and mitochondrial apoptosis

Decorin (DCN) is a small leucine-rich proteoglycan that plays an important role in the regulation of apoptosis, proliferation, intercellular contact, and cell migration. Here we have investigated the detailed mechanism of apoptotic cell death induced by DCN expression. A marked increase in cytotoxicity was observed for both DCN-expressing replication-incompetent (dE1/DCN) and -competent (dB/DCN) adenoviruses (Ads) compared to the corresponding control Ads. FACS and TUNEL assays revealed that the expression of DCN induced apoptotic cell death. Specifically, the expression and stability of p53 were increased by DCN. In addition, western blot data showed that DCN expression activated mitochondrial apoptosis by increasing the expression level of p53. Similarly, DCN-expressing oncolytic Ads induced a greater antitumor effect in a murine xenograft model compared with control Ads. Tissue staining and western blot data from in vivo experiments demonstrated significantly higher levels of apoptosis in tumor tissues from mice treated with DCN-expressing Ads compared to those treated with control Ads. Collectively, these data support that cell killing effect is enhanced with Ad-mediated DCN expression via the induction of p53-mediated mitochondrial apoptosis, which could be a valuable benefit for antitumor efficacy.

Molecular cloning, expression analysis, and function of decorin in goat ovarian granulosa cells

Decorin (DCN), a component of the extracellular matrix (ECM), participates in ECM assembly and influences cell proliferation and apoptosis in many mammalian tissues and cells. However, expression and function of DCN in the ovary remain unclear. This study cloned the full-length cDNA of goat DCN obtained from the ovary of an adult goat. Sequence analysis revealed that the putative DCN protein shared a highly conserved amino acid sequence with known mammalian homologs. The tissue distribution of DCN mRNA expression was evaluated by real-time PCR, and the results showed that DCN was widely expressed in the tissues of adult goat. Immunohistochemistry results suggested that DCN protein existed in the granulosa cells and oocytes from all types of follicles and theca cells of antral follicles. Moreover, hCG-induced DCN mRNA expression was significantly reduced by the inhibitors of protein kinase A, PI3K, or p38 kinase (P < 0.05), which are key mediators involved in hCG-induced DCN expression. Overexpression of DCN significantly increased apoptosis and blocked cell cycle progression in cultured granulosa cells (P < 0.05). Western blot analysis also showed that overexpression of DCN upregulated the expression levels of p21 protein (P < 0.05), whereas no effects were observed on the expression of Bax and Bcl-2 and on Bcl-2/Bax ratio (P > 0.05). These findings suggested that DCN regulates the apoptosis and cell cycle of granulosa cells.

Cetuximab promotes epithelial to mesenchymal transition and cancer associated fibroblasts in patients with head and neck cancer

Purpose

To investigate if cetuximab induces epithelial to mesenchymal transition (EMT) and activation of cancer associated fibroblast (CAF) in the tumors of patients with squamous cell carcinoma of the head and neck (SCCHN).

Methods

Cetuximab was administered for two weeks prior to surgery to 20 treatment-naïve patients. Five untreated patients were included as controls. Tumor biopsies were performed at baseline and before surgery. Gene expression profiles and quantitative real-time PCR (qRT-PCR) analysis of the pre-and post-treatment biopsies were compared. To further investigate EMT and CAF, correlations between previously described EMT and CAF markers and our microarray data set were calculated.

Results

Gene expression profile analyses and qRT-PCR showed that some of the genes modified by cetuximab were related to CAFs and EMT (ZNF521, CXCL12, ASPN, OLFML3, OLFM1, TWIST1, LEF1, ZEB1, FAP). We identified 2 patient clusters with different EMT and CAF characteristics. Whereas one cluster showed clear upregulation of expression of genes implicated in CAF and EMT including markers of embryologic pathways like NOTCH and Wnt, the other did not.

Conclusion

Even if EMT and CAFs are implicated in cetuximab resistance in pre-clinical models, we demonstrate for the first time that these molecular processes may occur clinically early on.

Screening glioma stem cells in U251 cells based on the P1 promoter of the CD133 gene

Cluster of differentiation (CD)133 is an important cell surface marker of glioma stem cells (GSCs). The transcription of the CD133 gene is controlled by five alternative promoters (P1, P2, P3, P4 and P5), which are expressed in a tissue-specific manner. In the present study, gene recombination technology was used to construct two types of gene expression vectors that contained the P1 promoter of the CD133 gene, which regulated either the neomycin-resistance gene or the herpes simplex virus thymidine kinase (HSV-TK) gene. Following the stable transfection of U251 glioblastoma cells with these two gene vectors, the cells expressing the P1 promoter that regulated the neomycin-resistance gene were named CD133 (+) cells, while the cells expressing the P1 promoter regulating the HSV-TK gene were called CD133 (−) cells. The expression of CD133 was detected by flow cytometry and reverse transcription-quantitative polymerase chain reaction. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to assess cell proliferation ability, while the cell cycle was analyzed by flow cytometry, and a clone formation test was performed to evaluate the invasive capability of the cells. The results demonstrated that, due to CD133 expression, the cell proliferation ability and the invasive capability of CD133 (+) cells were significantly higher than those of CD133 (−) cells. In conclusion, the present study successfully established a novel method of screening GSCs in U251 cells based on the P1 promoter of the CD133 gene.

Proteoglycans in liver cancer

Proteoglycans are a group of molecules that contain at least one glycosaminoglycan chain, such as a heparan, dermatan, chondroitin, or keratan sulfate, covalently attached to the protein core. These molecules are categorized based on their structure, localization, and function, and can be found in the extracellular matrix, on the cell surface, and in the cytoplasm. Cell-surface heparan sulfate proteoglycans, such as syndecans, are the primary type present in healthy liver tissue. However, deterioration of the liver results in overproduction of other proteoglycan types. The purpose of this article is to provide a current summary of the most relevant data implicating proteoglycans in the development and progression of human and experimental liver cancer. A review of our work and other studies in the literature indicate that deterioration of liver function is accompanied by an increase in the amount of chondroitin sulfate proteoglycans. The alteration of proteoglycan composition interferes with the physiologic function of the liver on several levels. This article details and discusses the roles of syndecan-1, glypicans, agrin, perlecan, collagen XVIII/endostatin, endocan, serglycin, decorin, biglycan, asporin, fibromodulin, lumican, and versican in liver function. Specifically, glypicans, agrin, and versican play significant roles in the development of liver cancer. Conversely, the presence of decorin could potentially provide protective effects.

Circulating microRNAs as diagnostic and prognostic tools for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an aggressive malignancy and the second leading cause of cancer-related deaths worldwide. Conventional biomarkers exhibit poor performance in the surveillance, diagnosis, and prognosis of HCC. MicroRNAs (miRNAs) are a class of evolutionarily conserved small non-coding RNAs that are involved in the regulation of gene expression and protein translation, and they play critical roles in cell growth, differentiation, and the development of various types of cancers, including HCC. Recent evidence revealed the role of miRNAs as potential novel and ideal biomarkers for HCC. miRNAs are released to extracellular spaces, and they are extremely stable in bodily fluids, including serum or plasma, where they are packaged into various microparticles or associated with RNA-binding proteins. Numerous studies have demonstrated that circulating miRNAs have potential applications as minimally invasive biomarkers for HCC diagnosis and prognosis. The present review highlights current understanding of miRNA biogenesis and the origins and types of circulating miRNAs. We summarize recent progress in the use of circulating miRNAs as diagnostic and prognostic biomarkers for HCC. We also discuss the challenges and perspectives of the clinical utility of circulating miRNAs in HCC.

Decorin deficiency promotes hepatic carcinogenesis

Hepatocellular carcinoma represents one of the most-rapidly spreading cancers in the world. In the majority of cases, an inflammation-driven fibrosis or cirrhosis precedes the development of the tumor. During malignant transformation, the tumor microenvironment undergoes qualitative and quantitative changes that modulate the behavior of the malignant cells. A key constituent for the hepatic microenvironment is the small leucine-rich proteoglycan decorin, known to interfere with cellular events of tumorigenesis mainly by blocking various receptor tyrosine kinases (RTK) such as EGFR, Met, IGF-IR, PDGFR and VEGFR2. In this study, we characterized cell signaling events evoked by decorin deficiency in two experimental models of hepatocarcinogenesis using thioacetamide or diethyl nitrosamine as carcinogens. Genetic ablation of decorin led to enhanced tumor occurrence as compared to wild-type animals. These findings correlated with decreased levels of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) and a concurrent elevation in retinoblastoma protein phosphorylation via cyclin dependent kinase 4. Decreased steady state p21(Waf1/Cip1) levels correlated with enhanced expression of transcription factor AP4, a known transcriptional repressor of p21(Waf1/Cip1), and enhanced c-Myc protein levels. In addition, translocation of β-catenin was a typical event in diethyl nitrosamine-evoked tumors. In parallel, decreased phosphorylation of both c-Myc and β-catenin was observed in Dcn(-/-) livers likely due to the hindered GSK3β-mediated targeting of these proteins to proteasomal degradation. We discovered that in a genetic background lacking decorin, four RTKs were constitutively activated (phosphorylated), including three known targets of decorin such as PDGFRα, EGFR, IGF-IR, and a novel RTK MSPR/RON. Our findings provide powerful genetic evidence for a crucial in vivo role of decorin during hepatocarcinogenesis as lack of decorin in the liver and hepatic stroma facilitates experimental carcinogenesis by providing an environment devoid of this potent pan-RTK inhibitor. Thus, our results support future utilization of decorin as an antitumor agent in liver cancer.

Recombinant human decorin upregulates p57KIP² expression in HepG2 hepatoma cell lines

Increasing the expression of cyclin-cyclin-dependent kinase inhibitors (cyclin-CDK) using small molecule inhibitors is a therapeutic strategy used to suppress cancer cell growth. Decorin (DCN), a functional component of the extracellular matrix, has been implicated in the suppression of cell proliferation by upregulating p21, a cyclin-CDK inhibitor. The purpose of this study was to examine the effect of recombinant decorin on the reactivation of p57KIP2, whose expression is silenced in hepatocellular carcinoma (HCC). Cell viability assay, cell cycle analysis, apoptosis assay and quantitative real time-PCR experiments were performed in three groups of HepG2 human cells: Uninfected HepG2 cells (control group), pcDNA3.1 vector-infected HepG2 cells (pcDNA3.1 group) and pcDNA3.1-DCN-infected HepG2 cells (pcDNA3.1‑DCN group). Our results revealed that recombinant human decorin inhibited cell proliferation, induced G0/G1 phase arrest and induced apoptosis by increasing the expression of caspase-3 in the pcDNA3.1-DCN group. The expression of p57KIP2 mRNA in the pcDNA3.1-DCN group was higher than in the pcDNA3.1 and control groups (P<0.05); however, there was no statistically significant difference between the control and pcDNA3.1 groups (P>0.05). In conclusion, recombinant human decorin reactivated p57KIP2 expression in HepG2 cells. As the expression level of p57KIP2 is downregulated in HCC, our finding may serve as a basis for the therapy and prognosis of HCC, although further studies are required.

Decorin interferes with platelet-derived growth factor receptor signaling in experimental hepatocarcinogenesis

Decorin, a secreted small leucine-rich proteoglycan, acts as a tumor repressor in a variety of cancers, mainly by blocking the action of several receptor tyrosine kinases such as the receptors for hepatocyte, epidermal and insulin-like growth factors. In the present study we investigated the effects of decorin in an experimental model of thioacetamide-induced hepatocarcinogenesis and its potential role in modulating the signaling of platelet-derived growth factor receptor-α (PDGFRα). Genetic ablation of decorin in mice led to enhanced tumor prevalence and a higher tumor count compared with wild-type mice. These findings correlated with decreased levels of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1) and concurrent activation (phosphorylation) of PDGFRα in the hepatocellular carcinomas generated in the decorin-null vis-à-vis wild-type mice. Notably, in normal liver PDGFRα localized primarily to the membrane of nonparenchymal cells, whereas in the malignant counterpart PDGFRα was expressed by the malignant cells at their cell surfaces. This process was facilitated by a genetic background lacking endogenous decorin. Double immunostaining of the proteoglycan and the receptor revealed only minor colocalization, leading to the hypothesis that decorin would bind to the natural ligand PDGF rather than to the receptor itself. Indeed, we found, using purified proteins and immune-blot assays, that decorin binds to PDGF. Collectively, our findings support the idea that decorin acts as a secreted tumor repressor during hepatocarcinogenesis by hindering the action of another receptor tyrosine kinase, such as the PDGFRα, and could be a novel therapeutic agent in the battle against liver cancer.