Tumor associated mesenchymal stem cells protects ovarian cancer cells from hyperthermia through CXCL12

Hyperthermic intraperitoneal chemotherapy (HIPEC) has shown promise in treatment of ovarian carcinosis. Despite its efficiency for the treatment of peritoneal carcinosis from digestive tract neoplasia, it has failed to demonstrate significant benefit in ovarian cancers. It is therefore essential to understand the mechanism underlying resistance to HIPEC in ovarian cancers. Mesenchymal stem cells (MSC) play an important role in the development of ovarian cancer metastasis and resistance to treatments. A recent study suggests that MSCs may be cytotoxic for cancer cells upon heat shock. In contrast, we describe the protective role of MSC against hyperthermia. Using cytokine arrays we determined that the tumor associated MSC (TAMC) secrete pro‐tumoral cytokines. We studied the effect of hyperthermia in co‐culture setting of TAMC or BM‐MCS associated with ovarian cancer cell lines (SKOV3 and CaOV3) with polyvariate flow cytometry. We demonstrate that hyperthermia does not challenge survival of TAMC or bone marrow derived MSC (BM‐MSC). Both TAMC and BM‐MSC displayed strong protective effect inducing thermotolerance in ovarian cancer cells (OCC). Transwell experiments demonstrated the role of secreted factors. We showed that CXCL12 was inducing thermotolerance and that inhibition of CXCL12/CXCR4 interaction restored cytotoxicity of hyperthermia in co‐culture experiments. Contrary to the previous published study we demonstrated that TAMC and BM‐MSC co‐cultured with OCC induced thermotolerance in a CXCL12 dependant manner. Targeting the interaction between stromal and cancer cells through CXCL12 inhibition might restore hyperthermia sensitivity in ovarian cancers, and thus improve HIPEC efficiency.     

Extracellular vesicles derived from renal cancer stem cells induce a pro-tumorigenic phenotype in mesenchymal stromal cells

Renal carcinomas have been shown to contain a population of cancer stem cells (CSCs) that present self-renewing capacity and support tumor growth and metastasis. CSCs were shown to secrete large amount of extracellular vesicles (EVs) that can transfer several molecules (proteins, lipids and nucleic acids) and induce epigenetic changes in target cells. Mesenchymal Stromal Cells (MSCs) are susceptible to tumor signalling and can be recruited to tumor regions. The precise role of MSCs in tumor development is still under debate since both pro- and anti-tumorigenic effects have been reported. In this study we analysed the participation of renal CSC-derived EVs in the interaction between tumor and MSCs. We found that CSC-derived EVs promoted persistent phenotypical changes in MSCs characterized by an increased expression of genes associated with cell migration (CXCR4, CXCR7), matrix remodeling (COL4A3), angiogenesis and tumor growth (IL-8, Osteopontin and Myeloperoxidase). EV-stimulated MSCs exhibited in vitro an enhancement of migration toward the tumor conditioned medium. Moreover, EV-stimulated MSCs enhanced migration of renal tumor cells and induced vessel-like formation. In vivo, EV-stimulated MSCs supported tumor development and vascularization, when co-injected with renal tumor cells. In conclusion, CSC-derived EVs induced phenotypical changes in MSCs that are associated with tumor growth.     

Direct and indirect contribution of bone marrow‐derived cells to cancer

Stromal‐epithelial interactions may control the growth and initiation of cancers. Here, we not only test the hypothesis that bone marrow‐derived cells may effect development of cancers arising from other tissue cells by forming tumor stroma but also that sarcomas may arise by transformation of stem cells from the bone marrow and epithelial cancers may arise by transdifferentiation of bone marrow stem cells to epithelial cancers. Lethally irradiated female FVB/N mice were restored with bone marrow (BM) transplants from a male transgenic mouse carrying the polyoma middle T‐oncoprotein under the control of the mouse mammary tumor virus promoter (MMTV‐PyMT) and followed for development of lesions. All of 8 lethally irradiated female FVB/N recipient mice, restored with BM transplants from a male MMTV‐PyMT transgenic mouse, developed Y‐chromosome negative (Y−) cancers of various organs surrounded by Y+ stroma. One of the female FVB/N recipient mice also developed fibrosarcoma and 1, a diploid breast adenocarcinoma containing Y chromosomes. In contrast, only 1 of 12 control female mice restored with normal male BM developed a tumor (lymphoma) during the same time period. These results indicate not only that the transgenic BM‐derived stromal cells may indirectly contribute to development of tumors in recipient mice but also that sarcomas may arise by transformation of BM stem cells and that breast cancers arise by transdifferentiation of BM stem cells, presumably by mesenchymal‐epithelial transition.     

Stroma‐directed imatinib therapy impairs the tumor‐promoting effect of bone marrow‐derived mesenchymal stem cells in an orthotopic transplantation model of colon cancer

Bone marrow‐derived mesenchymal stem cells (MSCs) are reported to contribute to formation of tumor‐promoting stromal cells. We reported recently that, in an orthotopic nude mice model of colon cancer, MSCs traveled to tumor stroma, where they differentiated into carcinoma‐associated fibroblast (CAF)‐like cells. We also found that CAFs express platelet‐derived growth factor receptor (PDGFR) at a high level and that imatinib therapy targeting PDGFR in CAFs inhibits growth and metastasis of human colon cancer. These findings led us to examine whether the tumor‐promoting effect of MSCs is impaired by blockade of PDGFR signaling achieved with imatinib. Orthotopic transplantation and splenic injection of human MSCs along with KM12SM human colon cancer cells, in comparison with transplantation of KM12SM cells alone, resulted in significantly greater promotion of tumor growth and liver metastasis. The KM12SM + MSC xenograft enhanced cell proliferation and angiogenesis and inhibited tumor cell apoptosis. When tumor‐bearing animals were treated with imatinib, there was no significant increase in primary tumor volume or total volume of liver metastases, despite the KM12SM+MSC xenograft, and survival in the mixed‐cell group was prolonged by imatinib treatment. Moreover, the ability of MSCs to migrate to tumor stroma was impaired, and the number of MSCs surviving in the tumor microenvironment was significantly decreased. In in vitro experiments, treatment with imatinib inhibited migration of MSCs. Our data suggest that blockade of PDGF signaling pathways influences the interaction between bone marrow‐derived MSCs and tumor cells in the tumor microenvironment and, hence, inhibits the progressive growth of colon cancer.     

Mesenchymal stem cell‐derived CXCL16 promotes progression of gastric cancer cells by STAT3‐mediated expression of Ror1

Bone marrow‐derived mesenchymal stem or stromal cells (MSC) have been shown to be recruited to various types of tumor tissues, where they interact with tumor cells to promote their proliferation, survival, invasion and metastasis, depending on the type of the tumor. We have previously shown that Ror2 receptor tyrosine kinase and its ligand, Wnt5a, are expressed in MSC, and Wnt5a‐Ror2 signaling in MSC induces expression of CXCL16, which, in turn, promotes proliferation of co–cultured MKN45 gastric cancer cells via the CXCL16‐CXCR6 axis. However, it remains unclear how CXCL16 regulates proliferation of MKN45 cells. Here, we show that knockdown of CXCL16 in MSC by siRNA suppresses not only proliferation but also migration of co–cultured MKN45 cells. We also show that MSC‐derived CXCL16 or recombinant CXCL16 upregulates expression of Ror1 through activation of STAT3 in MKN45 cells, leading to promotion of proliferation and migration of MKN45 cells in vitro. Furthermore, co–injection of MSC with MKN45 cells in nude mice promoted tumor formation in a manner dependent on expression of Ror1 in MKN45 cells, and anti–CXCL16 neutralizing antibody suppressed tumor formation of MKN45 cells co–injected with MSC. These results suggest that CXCL16 produced through Ror2‐mediated signaling in MSC within the tumor microenvironment acts on MKN45 cells in a paracrine manner to activate the CXCR6‐STAT3 pathway, which, in turn, induces expression of Ror1 in MKN45 cells, thereby promoting tumor progression.     

The G801A Polymorphism in the CXCL12 Gene and Risk of Breast Carcinoma: Evidence from a Meta-Analysis Including 2,931 Subjects

More and more evidence indicates that the G801A polymorphism in the CXCL12 gene might be associatedwith susceptibility to breast carcinoma in humans being. However, individually published results havebeen inconsistent. The purpose of this meta-analysis was to investigate the association between the G801Apolymorphism in the CXCL12 gene and breast carcinoma risk. A complete search strategy was done by theelectronic databases including PubMed and Chinese Biomedical Literature Database. A meta-analysis includingseven individual studies was carried out in order to explore the association between the G801A polymorphism inthe CXCL12 gene polymorphisms and breast carcinoma. The pooled odds ratios (ORs) and their corresponding95% confidence intervals (95%CIs) between the G801A polymorphism in the CXCL12 gene and breast carcinomarisk were assessed by the random-effects model. A significant relationship between the G801A polymorphism inthe CXCL12 gene and breast carcinoma was discovered in an allelic genetic model (OR: 1.214, 95%CI: 1.085-1.358, p=0.001), a homozygote model (OR: 1.663, 95%CI: 1.240-2.232, p=0.001), a heterozygote model (OR:1.392, 95%CI: 1.190-1.629, p=0.000), a recessive genetic model (OR: 1.407, 95%CI: 1.060-1.868, p=0.018) and adominant genetic model (OR: 1.427, 95%CI: 1.228-1.659, p=0.000). On sub-group analysis based on ethnicity,significance was observed between the European group and the mixed group. A significant relationship wasfound between the G801A polymorphism in the CXCL12 gene and breast carcinoma risk. Individuals with theA allele of the G801A polymorphism in the CXCL12 gene are under a higher risk for breast carcinoma.     

SDF‐1α stiffens myeloma bone marrow mesenchymal stromal cells through the activation of RhoA‐ROCK‐Myosin II

Multiple myeloma (MM) is a B lymphocyte malignancy that remains incurable despite extensive research efforts. This is due, in part, to frequent disease recurrences associated with the persistence of myeloma cancer stem cells (mCSCs). Bone marrow mesenchymal stromal cells (BMSCs) play critical roles in supporting mCSCs through genetic or biochemical alterations. Previously, we identified mechanical distinctions between BMSCs isolated from MM patients (mBMSCs) and those present in the BM of healthy individuals (nBMSCs). These properties of mBMSC contributed to their ability to preferentially support mCSCs. To further illustrate mechanisms underlying the differences between mBMSCs and nBMSCs, here we report that (i) mBMSCs express an abnormal, constitutively high level of phosphorylated Myosin II, which leads to stiffer membrane mechanics, (ii) mBMSCs are more sensitive to SDF‐1α‐induced activation of MYL2 through the G_(i./o)‐PI3K‐RhoA‐ROCK‐Myosin II signaling pathway, affecting Young's modulus in BMSCs and (iii) activated Myosin II confers increased cell contractile potential, leading to enhanced collagen matrix remodeling and promoting the cell–cell interaction between mCSCs and mBMSCs. Together, our findings suggest that interfering with SDF‐1α signaling may serve as a new therapeutic approach for eliminating mCSCs by disrupting their interaction with mBMSCs.     

患乳腺癌大鼠骨髓间充质干细胞定向分化能力实验研究

目的：探讨患乳腺癌大鼠骨髓来源的骨髓间充质干细胞（BMSCs）多向分化潜能是否受到机体荷瘤状态影响。方法：以SHZ-88细胞接种sD大鼠,成瘤后,无菌取骨髓进行体外BMSCs的培养和传代,经不同诱导培养基培养后,分别检测其成脂、成骨和成心肌能力;将BMSCs经尾静脉移植于健康SD大鼠,观察患癌大鼠BMSCs的体内应用安全性。结果：患乳腺癌大鼠骨髓来源的BMSCs表达同正常骨髓来源的BMSCs相同的表面标志分子,可经体外诱导培养,分化为脂肪细胞、骨细胞或心肌细胞;体内应用患乳腺癌大鼠骨髓来源的BMSCs未见乳腺癌细胞污染所致的植入性肿瘤发生。结论：患乳腺癌大鼠骨髓来源的BMSCs具有多向分化能力,未受机体荷瘤状态影响,且体内应用较为安全。     

ERK信号转导通路在CXCL12促进子宫内膜癌细胞增殖和侵袭中的作用

目的:探讨趋化因子CXCL12及其受体CXCR4 (CXCL12/CXCR4)生物学轴通过细胞外信号调节激酶(extracellular signal-regulated kinase,ERK)信号转导通路发挥促子宫内膜癌细胞增殖和侵袭的作用.方法:应用外源性CXCL12处理子宫内膜癌Ishikawa细胞株,通过Western blotting检测不同时间位点ERK1/2的磷酸化水平和Survivin蛋白的表达;通过ELISA检测细胞培养上清液中MMP-2的分泌水平.同时分析AMD3100和PD98059对细胞ERK1/2磷酸化水平、Survivin蛋白水平和MMP-2分泌水平的影响.结果:外源性CXCL12刺激后,可迅速上调ERK1/2的磷酸化水平(t=0.887,P＜0.01),促进Survivin蛋白和MMP-2蛋白的表达(t=0.861,P＜0.01;t=0.297,P＜0.01),且三者均呈时间依赖性.PD98059和AMD3100均能明显抑制外源性CXCL12诱导后ERK1/2的磷酸化水平,而且在两者共同作用下,能完全抑制ERK1/2的磷酸化水平,阻断ERK通路的激活,下调Survivin蛋白和MMP-2蛋白的表达.结论:CXCL12/CXCR4生物学轴通过激活ERK通路上调Survivin蛋白和MMP-2蛋白表达,从而引发Ishikawa细胞一系列增殖和侵袭的生物学效应.     

Wnt5a‐Ror2 signaling in mesenchymal stem cells promotes proliferation of gastric cancer cells by activating CXCL16–CXCR6 axis

Wnt5a‐Ror2 signaling has been shown to play important roles in promoting aggressiveness of various cancer cells in a cell‐autonomous manner. However, little is known about its function in cancer‐associated stromal cells, including mesenchymal stem cells (MSCs). Thus, we examined the role of Wnt5a‐Ror2 signaling in bone marrow‐derived MSCs in regulating proliferation of undifferentiated gastric cancer cells. Coculture of a gastric cancer cell line, MKN45, with MSCs either directly or indirectly promotes proliferation of MKN45 cells, and suppressed expression of Ror2 in MSCs prior to coculture inhibits enhanced proliferation of MKN45 cells. In addition, conditioned media from MSCs, treated with control siRNA, but not siRNAs against Ror2, can enhance proliferation of MKN45 cells. Interestingly, it was found that expression of CXCL16 in MSCs is augmented by Wnt5a‐Ror2 signaling, and that recombinant chemokine (C‐X‐C motif) ligand (CXCL)16 protein can enhance proliferation of MKN45 cells in the absence of MSCs. In fact, suppressed expression of CXCL16 in MSCs or an addition of a neutralizing antibody against CXCL16 fails to promote proliferation of MKN45 cells in either direct or indirect coculture with MSCs. Importantly, we show that MKN45 cells express chemokine (C‐X‐C motif) receptor (CXCR)6, a receptor for CXCL16, and that suppressed expression of CXCR6 in MKN45 cells results in a failure of its enhanced proliferation in either direct or indirect coculture with MSCs. These findings indicate that Wnt5a‐Ror2 signaling enhances expression of CXCL16 in MSCs and, as a result, enhanced secretion of CXCL16 from MSCs might act on CXCR6 expressed on MKN45, leading to the promotion of its proliferation.     

Adenosine upregulates CXCR4 and enhances the proliferative and migratory responses of human carcinoma cells to CXCL12/SDF-1alpha

The level of expression of the chemokine receptor CXCR4 has been shown to play a crucial role in determining the ability of cancer cells to metastasize from the primary tumor and become established in tissue sites that are rich in the CXCR4 ligand CXCL12/SDF-1alpha. High CXCR4 expression on cancer cells is associated with an increased risk of recurrence and poorer overall survival. We propose that local tissue mediators within the primary tumor or at secondary sites may modulate the level of CXCR4 expression and, therefore, potentially affect the ability of the cancer cells to metastasize. The purine nucleoside adenine-9-beta-D-ribofuranoside (adenosine) is generated at high concentrations within the extracellular fluid of solid tumors because of their hypoxia. We show here that adenosine acts through A(2A) and A(2B) adenosine receptors on human colorectal carcinoma cells to upregulate CXCR4 mRNA expression up to 10-fold and selectively increases cell-surface CXCR4 protein up to 3-fold. This increase in cell-surface CXCR4 enables the carcinoma cells to migrate toward CXCL12, and enhances their proliferation in response to CXCL12. Adenosine may therefore be one of the factors within the tumor microenvironment that facilitates tumor dissemination, by upregulating CXCR4 on certain cancer cells and enhancing cellular responses to CXCL12.     

Paclitaxel‐releasing mesenchymal stromal cells inhibit the growth of multiple myeloma cells in a dynamic 3D culture system

Multiple myeloma is an aggressive tumour able to suppress osteoblastogenesis probably mediated by bone marrow mesenchymal stromal cells (BM‐MSCs) that can also support plasma cell growth/survival. The use of MSCs for multiple myeloma therapy is a controversial topic because of the contradictory results on the capacity of MSCs to inhibit or to promote cancer growth. Our previous studies demonstrated that MSCs could be loaded with Paclitaxel (PTX) and used to deliver the drug in situ in amount affecting tumour growth (in vitro and in vivo). Therefore, independently on the discussed action of MSCs in myeloma, MSCs could represent a ‘trojan horse’ to vehicle and deliver anti‐tumour agents into bone marrow. This study confirms, by an in vitro 3D dynamic culture system, that PTX loaded BM‐MSCs (PTXr‐MSCs) are active on the proliferation of RPMI 8226, a human myeloma cell line. Our results demonstrated a dramatic suppression of myeloma cell growth by PTXr‐MSCs, suggesting that drug loaded MSCs could be a tool to deliver drug into the bone marrow. Drug releasing MSCs provide a therapeutic approach to potentiate the existing treatments against a very aggressive malignancy as multiple myeloma. Copyright © 2016 John Wiley & Sons, Ltd.     

Lipopolysaccharides increase the amount of CXCR4, and modulate the morphology and invasive activity of oral cancer cells in a CXCL12-dependent manner

Recently, it has been reported that bacterial infections play an important role in the development of cancers of the upper aero digestive tract. To examine the influence of bacterial infections on oral cancer, human oral carcinoma T3M-1 cells were treated with lipopolysaccharide (LPS) for 24 h as a model of infection. The LPS treatment increased the mRNA expression of CXCR4 and invasiveness in T3M-1 cells stimulated with CXCL12.The Rho family of small guanosine triphosphatases regulates the dynamics of the actin cytoskeleton that underlie cellular functions such as cell shape changes, migration and polarity. In T3M-1 cells treated with LPS and stimulated with CXCL12, Rac and Cdc42 were activated and caused an increase in the development of filopodia. The present findings suggest that bacterial infections enhance the invasiveness of T3M-1 cells via CXCL12/CXCR4 interaction and Cdc42-activation. Furthermore, filopodia are critical to this process.     

单纯疱疹病毒-胸苷激酶基因转染骨髓基质干细胞治疗大鼠脑胶质瘤

目的研究转染单纯疱疹病毒-胸苷激酶(HSV-tk)基因的骨髓基质干细胞(BMSCs)对大鼠脑胶质瘤的治疗作用。方法原代培养BMSCs,AdCMV-tk转染BMSCs。逆转录-多聚酶链反应(RT-PCR)检测BMSCs/tk对tk基因的转录。以BrdU标记BMSCs/tk,观察其趋瘤性。四甲基偶氮唑盐(MTT)法检测其对C6细胞的旁观者效应。将BMSCs/tk注入脑胶质瘤大鼠肿瘤对侧脑组织,原位末端标记(TUNEL)法检测脑内肿瘤细胞凋亡,动态MRI监测肿瘤体积的变化,观察荷瘤鼠生存期。结果全骨髓细胞培养法可获得纯化的BMSCs。感染AdCMV-tk 21 d后,BMSCs仍有明显的tk基因表达。转染tk基因后的BMSCs仍具有明显的趋瘤性。BMSCs/tk不仅在体外可产生明显的旁观者效应,在荷瘤鼠脑内也显示了明显的诱导肿瘤细胞凋亡的旁观者效应,凋亡阳性率为20.38%±2.57%,与BMSCs组(2.56%±0.52%)和对照组(2.74%±0.38%)相比,差异均有统计学意义(P值分别为0.023和0.025)。BMSCs/tk移植3周时,BMSCs/tk组、BMSCs组和对照组肿瘤体积分别为(8.28±2.64)、(134.51±16.37)和(147.22±31.05)mm3,BMSCs/tk组远小于BMSCs组(P=0.001)和对照组(P<0.01),并且部分大鼠脑内肿瘤消失。BMSCs/tk组大鼠生存期为(52.60±13.11)d,与对照组相比明显延长(P=0.01)。结论HSV-tk转染的BMSCs可能成为脑胶质瘤治疗的有效手段。     

Hyperthermia‐treated mesenchymal stem cells exert antitumor effects on human carcinoma cell line

BACKGROUND:

Mesenchymal stem cells (MSCs) possess the potential for differentiation into multilineages. MSCs have been reported to play a role as precursors for tumor stroma in providing a favorable environment for tumor progression. Hyperthermia destroys cancer cells by raising the temperature of tumor‐loaded tissue to 40°C to 43°C and causes indirect sensitizing effects when combined with chemo‐ and/or radiotherapy. However, how hyperthermia affects the tumor‐supportive stroma is unknown. Here, the authors investigated the effects of hyperthermia‐treated MSCs, from different sources, on the human ovarian cancer cell line SK‐OV‐3.

METHODS:

MSCs from adipose tissue and amniotic fluid were untreated or heat‐treated (HS‐MSCs). The culture supernatant of each treatment group was collected and transferred to the SK‐OV‐3 cells.

RESULTS:

The morphological analysis and cell proliferation assay showed a reduced viability of the tumor cells in the conditioned medium with the HS‐MSCs. Further investigations revealed that the conditioned medium of the HS‐MSCs induced a higher nuclear condensation and a greater number of sub‐G1 cells among the tumor cells. Analysis of the mRNA expression demonstrated that the conditioned medium of the HS‐MSCs induced up‐regulation or down‐regulation of several tumor‐associated molecules. Finally, the cytokine array of each conditioned medium showed that angiogenin, insulin‐like growth factor binding protein 4, neurotrophin 3, and chemokine (C‐C motif) ligand 18 are involved as main factors.

CONCLUSIONS:

This study showed that the conditioned medium of the HS‐MSCs exerted a suppressive effect on tumor progression and malignancy, suggesting that hyperthermia enables tumor stromal cells to provide a sensitizing environment for tumor cells to undergo cell death. Cancer 2009. © 2009 American Cancer Society.     

Mesenchymal stem cell‐derived CCN2 promotes the proliferation,migration and invasion of human tongue squamous cell carcinoma cells

Recent studies have demonstrated that mesenchymal stem cells (MSC) exhibit a tropism to tumors and form the tumor stroma. In addition, we found that MSC can secrete different types of factors. However, the involvement of MSC‐derived factors in human tongue squamous cell carcinoma (TSCC) growth has not been clearly addressed. The CCN family includes multifunctional signaling molecules that affect the initiation and development events of various tumors. In our study, we report that CCN2/connective tissue growth factor (CTGF) was the most highly induced among the CCN family members in MSC that were co‐cultured with TSCC cells. To evaluate the relationship between CCN2 and TSCC growth, we downregulated MSC‐derived CCN2 expression with shRNA targeting CCN2 and found that MSC‐secreted CCN2 promotes TSCC cell proliferation, migration and invasion. We also confirmed that MSC‐derived CCN2 partially accelerated tumor growth in vitro. Taken together, these results suggest that MSC‐derived CCN2 contributes to the promotion of proliferation, migration and invasion of TSCC cells and may be a possible therapy target in the future.     

Paracrine activation of hepatic stellate cells in platelet‐derived growth factor C transgenic mice: Evidence for stromal induction of hepatocellular carcinoma

Cirrhosis is the primary risk factor for the development of hepatocellular carcinoma (HCC), yet the mechanisms by which cirrhosis predisposes to carcinogenesis are poorly understood. Using a mouse model that recapitulates many aspects of the pathophysiology of human liver disease, we explored the mechanisms by which changes in the liver microenvironment induce dysplasia and HCC. Hepatic expression of platelet‐derived growth factor C (PDGF‐C) induces progressive fibrosis, chronic inflammation, neoangiogenesis and sinusoidal congestion, as well as global changes in gene expression. Using reporter mice, immunofluorescence, immunohistochemistry and liver cell isolation, we demonstrate that receptors for PDGF‐CC are localized on hepatic stellate cells (HSCs), which proliferate, and transform into myofibroblast‐like cells that deposit extracellular matrix and lead to production of growth factors and cytokines. We demonstrate induction of cytokine genes at 2 months, and stromal cell‐derived hepatocyte growth factors that coincide with the onset of dysplasia at 4 months. Our results support a paracrine signaling model wherein hepatocyte‐derived PDGF‐C stimulates widespread HSC activation throughout the liver leading to chronic inflammation, liver injury and architectural changes. These complex changes to the liver microenvironment precede the development of HCC. Further, increased PDGF‐CC levels were observed in livers of patients with nonalcoholic fatty steatohepatitis and correlate with the stage of disease, suggesting a role for this growth factor in chronic liver disease in humans. PDGF‐C transgenic mice provide a unique model for the in vivo study of tumor–stromal interactions in the liver.