Autocrine transforming growth factor-beta 1 and beta 2 expression is increased by cell crowding and quiescence in colon carcinoma cells

COPB2 gene silencing inhibits colorectal cancer cell proliferation and induces apoptosis via the JNK/c-Jun signaling pathway

Objectives

Colorectal cancer (CRC) is one of the most common malignant human tumors. It is associated with high morbidity and mortality rates. In recent years, tumor gene therapy has emerged as a promising new approach for colorectal cancer therapy. Herein, we identify and analyze the role of COPB2 (coatomer protein complex, subunit beta 2) in proliferation and apoptosis of CRC cells.

Methods

To investigate the role of COPB2 in the proliferation and apoptosis of CRC cells, a shCOPB2 vector and a shCtrl vector were constructed for transfection into RKO and HCT116 cells. Cells proliferation was subsequently measured via cell counting kit-8 (CCK8) assay and Celigo cell counting assay. Apoptosis was measured via flow cytometry. The activity level of Caspase 3/7 was measured. Finally, the level of several JNK/c-Jun apoptosis pathway-related proteins were measured to characterize the mechanism of apoptosis.

Results

Our results showed that the proliferation rate was decreased and the apoptosis rate was increased in shCOPB2-treated RKO and HCT116 cells compared to those in controls. After the silencing of COPB2, JNK/c-Jun signal pathway activation was increased, the expression levels of apoptosis pathway-related proteins, such as Bad, p53 and Caspase 3, were also increased.

Conclusion

COPB2 gene silencing can inhibit RKO and HCT116 cells proliferation and induce apoptosis via the JNK/c-Jun signaling pathway.

Dissimilar cytokine patterns in different human liver and colon cancer cell lines

An accurate and simultaneous estimate of cellular levels of a large cytokine number is very useful to obtain information about an organ dysfunction leading to cancer because through the understanding of the evolution of cytokine patterns we can recognize and predict the disease progression. Cancer cell lines are commonly used to study the cancer microenvironment, to analyze their chemosensitivity and carcinogenesis as well as to test in vitro the effect of molecules, such as drugs or anti-oxidants, on the inflammation status and its progression. We noted that various cell lines commonly used as a model for studies on liver and colon cancer possess different patterns of cytokines. This aspect may generate data not comparable in laboratories using different cell lines; thus, to investigate the origin of these abnormalities we compared the cell lines HepG2 and Huh7, and HT-29 and HCT-116, for liver and colon cancer, respectively. In this context we have evaluated and compared the levels of cytokines, chemokines and growth factors in the supernatants of these cellular lines. Our aim was to identify what cytokines were significantly different correlating similarities and differences to the specific inflammation status of each cellular model of cancer.

Particled Mica, STB-HO has chemopreventive potential via G1 arrest, and inhibition of proliferation and vascular endothelial growth factor receptor 2 in HCT colorectal cancer cells

Background

Though Mica, a thin and sheet like mineral, has been used as a mineral medicine for treatment of bleeding, dysentery and inflammation in traditional medicine including Ayurveda, the biological evidences of Mica were not clearly elucidated so far. Thus, in the present study, the antitumor mechanism of particled Mica (STB-HO) was examined in colorectal cancers.

Methods

Athymic nude mice were inoculated with HCT116 colon cancer cells and orally administered STB-HO daily for 41 days, and HCT116 and human umbilical vein endothelial cells (HUVECs) were treated with STB-HO for 0 ~ 24 hours to perform immunoblotting, cytotoxicity assay, FACs analysis and measurement of matrix metalloproteinase 9 (MMP-9) secretion and other experiments. Significant differences of all date were evaluated using Student’s t-test and a Turkey-Kramer multiple-comparison post test.

Results

STB-HO significantly suppressed the tumor volume and weight in athymic nude mice inoculated with HCT116 cells at a dose of 100 mg/kg. Thus, the in vivo antitumor mechanism of STB-HO was to elucidated in vitro as well. STB-HO exerted cytotoxicity in HCT116, SW620 and HCT15 colorectal cancer cells. Also, STB-HO increased G1 cell population in a time and concentration dependent manner, enhanced the expression of p21, p27, p53 as cyclin dependent kinase (CDK) inhibitors, attenuated the expression of proliferating cell nuclear antigen (PCNA) and cyclin D1 and also reduced the production of vascular endothelial growth factor (VEGF) and matrix metalloproteinase 9 (MMP-9) in HCT116 cells. Consistently, STB-HO suppressed the phosphorylation of VEGFR2 in HCT116, SW620 and HCT15 cells. Also, STB-HO inhibited the VEGF mediated proliferation and also attenuated the phosphorylation of VEGFR2 and Akt in human umbilical vein endothelial cells (HUVECs).

Conclusions

Collectively, these findings suggest that STB-HO has chemopreventive potential via G1 arrest and inhibition of proliferation and VEGFR2 in HCT116 colorectal cancer cells.

EGCG-meditated cyto- and genotoxicity in HaCat keratinocytes is impaired by cell-mediated clearance of auto-oxidation-derived H2O2: an algorithm for experimental setting correction

Several lines of evidence suggest that besides antioxidant also prooxidant properties are crucially involved in cytotoxic and protective activities of the major green tea catechin epigallocatechin-3-gallate (EGCG) in vitro (Elbling et al., 2011). Furthermore recent data suggest that EGCG induces oxidative stress also in vivo (Li et al., 2010). Here we set out to identify factors modulating cellular effects of EGCG in vitro. Using the HaCat keratinocytes model, we demonstrate that the cytotoxic, genotoxic and signal-activating effects of EGCG are significantly dependent on the ratio of cell number to working volume. Treatment with identical EGCG concentrations at altered experimental settings resulted in IC(50) values differing up to orders of magnitude and could even exert contradictory effects. This effect was based on cell-mediated clearance of autooxidation-derived H(2)O(2) from the supernatant. In order to estimate EGCG/H(2)O(2) concentrations equally effective under different settings, we have rationally derived and experimentally verified a simple algorithm relating concentration, working volume, cell number and - indirectly - exposure time. Algorithm application resulted in similar H(2)O(2) clearance curves from cell supernatants as well as comparable EGCG/H(2)O(2) effects at different settings. Our results demonstrate the importance of standardized experimental settings when investigating cytotoxic and/or beneficial effects of autooxidizing compounds.

Restoration of transforming growth factor-beta receptor II expression in colon cancer cells with microsatellite instability increases metastatic potential in vivo

Microsatellite instability (MSI), which occurs in 15% of colorectal cancer, has been shown to have a lower incidence of metastasis and better patient survival rates compared with microsatellite stable colorectal cancer. However, a mechanistic understanding of the basis for this difference is very limited. Here, we show that restoration of TGFβ signaling by re-expression of TGFβ receptor II in MSI colon cancer cells increased PI3K/AKT activation, conferred resistance to growth factor deprivation stress-induced apoptosis, and promoted cell motility in vitro. Treatment with a potent PI3K inhibitor (LY294002) blocked the prosurvival and promotility effects of TGFβ, indicating that TGFβ-mediated promotion of cell survival and motility is dependent upon activation of the PI3K/AKT pathway. Analysis of apoptotic effectors that are affected by TGFβ signaling indicated that Bim is an effector of TGFβ-mediated survival. In addition, TGFβ-induced down-regulation of E-cadherin contributed to the prosurvival effect of TGFβ, and restoration of TGFβ signaling in MSI colon cancer cells increased liver metastasis in an orthotopic model in vivo. Taken together, our results demonstrate that restoration of TGFβ signaling promotes cell survival, motility, and metastatic progression in MSI colon cancer cells and indicate that TGFβ receptor II mutations contribute to the favorable outcomes in colon cancer patients with MSI.

Fibroblast and prostate tumor cell cross-talk: fibroblast differentiation, TGF-β, and extracellular matrix down-regulation

Growth and survival of tumors at a site of metastasis involve interactions with stromal cells in the surrounding environment. Stromal cells aid tumor cell growth by producing cytokines as well as by modifying the environment surrounding the tumor through modulation of the extracellular matrix (ECM). Small leucine-rich proteoglycans (SLRPs) are biologically active components of the ECM which can be altered in the stroma surrounding tumors. The influence tumor cells have on stromal cells has been well elucidated. However, little is understood about the effect metastatic cancer cells have on the cell biology and behavior of the local stromal cells. Our data reveal a significant down-regulation in the expression of ECM components such as collagens I, II, III, and IV, and the SLRPs, decorin, biglycan, lumican, and fibromodulin in stromal cells when grown in the presence of two metastatic prostate cancer cell lines PC3 and DU145. Interestingly, TGF-β down-regulation was observed in stromal cells, as well as actin depolymerization and increased vimentin and α5β1 integrin expression. MT1-MMP expression was upregulated and localized in stromal cell protrusions which extended into the ECM. Moreover, enhanced stromal cell migration was observed after cross-talk with metastatic prostate tumor cells. Xenografting metastatic prostate cancer cells together with "activated" stromal cells led to increased tumorigenicity of the prostate cancer cells. Our findings suggest that metastatic prostate cancer cells create a metastatic niche by altering the phenotype of local stromal cells, leading to changes in the ECM.

MSI-H colorectal cancers preferentially retain and expand intraepithelial lymphocytes rather than peripherally derived CD8+ T cells

The healthy colorectal mucosa contains many resident intraepithelial lymphocytes (IELs) consisting of partially activated yet hyporesponsive CD8(+) T cells. A predominant feature of colorectal cancers (CRCs) characterized by high levels of microsatellite instability (MSI-H) is heavy infiltration by an intraepithelial population of tumor infiltrating lymphocytes (iTILs). While it has been assumed that these iTILs originate from tumor infiltration by peripheral CD8(+) effector T cells, their origin remains unknown. In light of the phenotypic and functional differences exhibited by IELs and peripheral T cells, elucidation of the precursor population of iTILs in MSI-H CRCs could clarify the role played by these lymphocytes in tumor progression. The aim of the present study was to investigate whether MSI-H CRCs interact differently with IEL- versus peripherally-derived CD8(+) T cells. Using a Transwell assay system to mimic basolateral infiltration of tumor cells by lymphocytes, T cell migration, retention, proliferation and phenotypic alterations were investigated. Results indicate that MSI-H CRCs preferentially retain and expand IEL-derived cells to a greater degree than their microsatellite stable (MSS) counterparts. While MSI-H CRCs also retained more peripherally derived T cells, this number was considerably less than that from the IEL population. While interaction of IELs with either CRC type led to baseline lymphocyte activation, MSS CRCs induced upregulation of additional activation markers on retained IELs compared to MSI-H CRCs. These results suggest that the abundant iTILs present in MSI-H CRCs result from expansion of the preexisting mucosal IEL population and imply a limited prognostic role for iTILs in MSI-H CRC.

Transforming growth factor beta induces apoptosis through repressing the phosphoinositide 3-kinase/AKT/survivin pathway in colon cancer cells

FET cells, derived from an early-stage colon carcinoma, are nontumorigenic in athymic mice. Stable transfection of a dominant-negative transforming growth factor beta (TGFbeta) type II receptor (DNRII) into FET cells that express autocrine TGFbeta shows loss of TGFbeta signaling and increased tumorigenicity in vivo indicating tumor suppressor activity of TGFbeta signaling in this model. The ability of tumorigenic cells to withstand growth factor and nutrient deprivation stress (GFDS) is widely regarded as a key attribute for tumor formation and progression. We hypothesized that increased tumorigenicity of FET/DNRII cells was due to loss of participation of autocrine TGFbeta in a "fail-safe" mechanism to generate cell death in response to this stress. Here, we document that loss of autocrine TGFbeta in FET/DNRII cells resulted in greater endogenous cell survival in response to GFDS due to activation of the phosphoinositide 3-kinase (PI3K)/Akt/survivin pathway. Treatment of FET DNRII cells with a PI3K inhibitor (LY294002) inhibited Akt phosphorylation and reduced survivin expression resulting in increased apoptosis in FET/DNRII cells. We also show that exogenous TGFbeta increased apoptosis in FET cells through repression of the PI3K/Akt/survivin pathway during GFDS. These results indicate that the PI3K/Akt/survivin pathway is blocked by TGFbeta signaling and that loss of autocrine TGFbeta leads to increased cell survival during GFDS through the novel linkage of TGFbeta-mediated repression of survivin expression. Inhibition of survivin function by dominant-negative approaches showed that this inhibitor of apoptosis family member is critical to cell survival in the FET/DNRII cells, thus indicating the importance of this target for TGFbeta-mediated apoptosis.

Microsatellite unstable colorectal cancer cell lines with truncating TGFβRII mutations remain sensitive to endogenous TGFβ

Disruptions to the TGFbeta signalling pathway have been implicated in most human adenocarcinomas. As cancers progress, many acquire resistance to the growth-suppressing properties of TGFbeta while retaining sensitivity to its tumour-promoting effects. Microsatellite unstable colorectal cancers (MSI-H CRCs) possess truncating mutations in the type II TGFbeta receptor (TGFbetaRII) gene that have been assumed to render these tumours insensitive to TGFbeta. However, numerous reports of TGFbetaRII bypass exist and this study was thus undertaken in order to clarify the true extent of TGFbeta sensitivity in MSI-H CRCs. Using stimulation with exogenous TGFbeta, we demonstrated that, while MSI-H CRCs are capable of binding soluble TGFbeta, two out of three cell lines examined remain refractory to its signalling effects. In contrast, use of a specific inhibitor of the type I TGFbeta receptor (TGFbetaRI) revealed that all remain sensitive to signalling by endogenously produced TGFbeta. Specifically, autocrine signalling via TGFbetaRI mediates constitutive activation of Smad2 as well as repression of Erk signalling. Real-time PCR confirmed that these effects are sufficient to affect the expression level of various TGFbeta-modulated genes. An invasion assay revealed that autocrine TGFbetaRI signalling also promotes the invasion capacity of MSI-H CRCs to an extent similar to that seen in their non-MSI-H counterparts. Independent TGFbetaRI signalling, however, has no effect on the rate of proliferation of MSI-H CRC cells. Together, these results demonstrate that MSI-H CRC cell lines are not completely refractory to TGFbeta, despite lacking functional TGFbetaRII. In addition to clarifying the true consequences of natural TGFbetaRII loss and the independent function of TGFbetaRI, our results highlight the selective nature of TGFbeta resistance developed by cancers.

Cell density mediated pericellular hypoxia leads to induction of HIF-1alpha via nitric oxide and Ras/MAP kinase mediated signaling pathways

Environmental signals in the cellular milieu such as hypoxia, growth factors, extracellular matrix (ECM), or cell-surface molecules on adjacent cells can activate signaling pathways that communicate the state of the environment to the nucleus. Several groups have evaluated gene expression or signaling pathways in response to increasing cell density as an in vitro surrogate for in vivo cell-cell interactions. These studies have also perhaps assumed that cells grown at various densities in standard in vitro incubator conditions do not have different pericellular oxygen levels. However, pericellular hypoxia can be induced by increasing cell density, which can exert profound influences on the target cell lines and may explain a number of findings previously attributed to normoxic cell-cell interactions. Thus, we first sought to test the hypothesis that cell-cell interactions as evaluated by the surrogate approach of increasing in vitro cell density in routine normoxic culture conditions results in pericellular hypoxia in prostate cancer cells. Second, we sought to evaluate whether such interactions affect transcription mediated by the hypoxia response element (HRE). Thirdly, we sought to elucidate the signal transduction pathways mediating the induction of HRE in response to cell density induced pericellular hypoxia in routine normoxic culture conditions. Our results indicate that paracrine cell interactions can induce nuclear localization of HIF-1a protein and this translocation is associated with strong stimulation of the HRE-reporter activity. We also make the novel observation that cell density-induced activity of the HRE is dependent on nitric oxide production, which acts as a diffusible paracrine factor secreted by densely cultured cells. These results suggest that paracrine cell interactions associated with pericellular hypoxia lead to the physiological induction of HRE activity via the cooperative action of Ras, MEK1, HIF-1a via pericellular diffusion of nitric oxide. In addition, these results highlight the importance of examining pericellular hypoxia as a possible stimulus in experiments involving in vitro cell density manipulation even in routine normoxic culture conditions.

Placental bone morphogenetic protein (PLAB) gene expression in normal, pre-malignant and malignant human prostate: relation to tumor development and progression

The second most common target of prostate-cancer metastasis is bone, and the phenomenon of skeletal metastasis represents the incurable stage of disease. Histologically, skeletal metastasis from prostate cancer is distinctive due to its osteoblastic nature. The osteoblastic bone metastasis shows extensive new bone formation, with possible involvement of the soluble growth factors secreted by tumor cells, such as bone morphogenetic proteins (BMPs). In the present study, we analyzed the gene expression of one of the new members of the BMP family, placental bone morphogenetic protein (PLAB). In situ hybridization studies showed high levels of this gene in normal prostate. However, the gene is down-regulated during the progression of cancer at the primary site. The most significant finding was re-expression of the PLAB gene in osseous metastatic lesions. Our results demonstrate that tumor cells, when released from the primary site and after re-growth elsewhere, are capable of re-expressing specific genes that may play a different role at metastatic sites than at the primary site.

The alphaVbeta6 integrin regulates its own expression with cell crowding: implications for tumour progression

Expression of the growth-promoting integrin alphavbeta6 in colon cancer cells induces gelatinase B secretion and activation, the inhibition of which abolishes alphavbeta6-mediated tumour cell growth within a collagen matrix. Herein, we show that high cell density selectively enhances alphavbeta6 expression in a protein kinase C (PKC)-dependent manner in preference to other beta integrin subunits, resulting in a marked increase in gelatinase B secretion as cells reach confluence. Moreover, PKC activity increases with cell confluence, and the rise in PKC activity is much greater for alphavbeta6-expressing cells than for colon cancer cells which lack alphavbeta6. We propose a self-perpetuating system of colon cancer progression in which the integrin alphavbeta6 provides a means of sustaining tumour cell proliferation. In this model, alphavbeta6 regulates its own expression via a PKC-mediated signalling pathway as tumour cells become crowded and quiescent. The alphavbeta6-mediated induction of gelatinase B secretion facilitates peri-cellular matrix degradation, which helps overcome crowding and restores cell proliferation.

The "comparative growth assay": examining the interplay of anti-cancer agents with cells carrying single gene alterations

We have developed a "comparative growth assay" that complements current assays of drug effects based on cytotoxicity. A co-culture of two cell lines, one of which is fluorescently labeled, is exposed to a cytotoxic agent and the proportion of fluorescent cells is compared with that of a baseline unexposed co-culture. For demonstration purposes, two HCT116 cell lines (an hMLH1 homozygous and an hMLH1 heterozygous mutant), altered by insertion of vector alone or the same vector carrying an insert for the expression of enhanced green fluorescent protein (EGFP), were exposed to numerous "anti-cancer" agents. The assay was further validated in a system of two cell lines differing only in the expression of the breast cancer resistance protein (BRCP). The assay allowed the estimation of the duration of action of a particular agent. Assessment of the agent's differential activity over a given time in culture could be expressed as a selection rate, which we chose to describe on an "average selection per day" basis. We conclude that this assay: 1) provides insight into the differential dynamic effects of chemotherapeutic agents or radiation; and 2) allows, through the use of matched cell lines, the investigation of critical physiologic features that govern cell sensitivity.

Efficacy and specificity of antisense laminin chain-specific expression vectors in blocking laminin induction by TGFbeta1: effect of laminin blockade on TGFbeta1-mediated cellular responses

Transforming growth factorbeta1 (TGFbeta1) elicits a multitude of cellular responses from the epithelial-derived human colon cancer Moser cells. TGFbeta1 induces the expression of laminin and fibronectin, and previous studies show that the induction of fibronectin is functionally associated with the regulation of carcinoembryonic antigen (CEA) expression by TGFbeta1 (Huang and Chakrabarty, 1994, J Biol Chem 269:28764-28768). In this study we constructed antisense laminin chain-specific expression vectors and determined their efficacy in blocking the expression and the induction of the large multichain laminin molecule by TGFbeta1. We also determined the functional role of laminin in several TGFbeta1-mediated responses: growth inhibition, downmodulation of anchorage-independent growth, and cellular invasion. Expression of either antisense laminin chain A, B1, or B2 RNA resulted in a downmodulation of endogenous laminin mRNA expression and blocked the induction of laminin protein by TGFbeta1 without affecting the induction of other adhesion molecules such as fibronectin or CEA. It is concluded that antisense RNA directed to only one of the laminin chains was sufficient to disrupt the induction of the complex laminin molecule in quite a specific manner. Expression of antisense laminin RNA downregulated cellular adhesion to extracellular matrix (ECM) laminin and blocked the ability of TGFbeta1 to upmodulate adhesion to ECM laminin. Expression of antisense laminin RNA, however, did not alter the downregulating effect of TGFbeta1 on cellular proliferation, anchorage-independent growth, or cellular invasion, suggesting that the induction of laminin did not play a significant functional role in these TGFbeta1-mediated cellular responses. It is likely that other adhesion pathways may be involved in mediating the action of TGFbeta1 in this cell line.

Human intestinal epithelial cells down-regulate IL-8 expression in human intestinal microvascular endothelial cells; role of transforming growth factor-beta 1 (TGF-beta1)

Cytokines produced from intestinal epithelial cells may function as signals to neighbouring immune cells. In the present study we analysed the effects of colonic epithelial cell lines (HT-29, Caco-2, HCT-116, Colo-320) and freshly isolated intestinal epithelial cells on IL-8 expression in the SV-40T transfected human microvascular endothelial cell line (HMEC-1). Epithelial cell-conditioned media and transwells preventing physical contact between epithelial and endothelial cells were used. TGF-beta1 and IL-8 levels were determined by ELISA and Northern blot analysis. Increasing concentrations of IL-1beta led to increasing production of IL-8. The addition of epithelial cell-conditioned medium or epithelial cells to HMEC-1 cells in a two-compartment co-culture system resulted in a strong decrease in IL-8 at the protein and mRNA level. Decrease of IL-8 was markedly stronger when epithelial cells were co-cultured in contact with HMEC-1 cells, indicating that not only soluble factor(s) play a role in the induction of IL-8 suppression in HMEC-1 cells. MoAbs against TGF-beta1 partially inhibited down-regulation of endothelial IL-8 expression. In further studies, IL-8 expression in freshly isolated human intestinal microvascular endothelial cells (HIMEC) was also down-regulated by intestinal epithelial cells. Our results demonstrate that intestinal epithelial cells down-regulate IL-8 expression in HMEC-1 cells. TGF-beta1 is a candidate factor of epithelial-endothelial communication in the colonic mucosa.

Extracellular matrix-associated transforming growth factor-beta: role in cancer cell growth and invasion

Growth factors of the transforming growth factor-beta (TGF-beta) family inhibit the proliferation of epithelial, endothelial, and hematopoietic cells, and stimulate the synthesis of extracellular matrix components. TGF-beta s are secreted from cells in high-molecular-mass protein complexes that are composed of three proteins, the mature TGF-beta-dimer, the TGF-beta propeptide dimer, or latency-associated protein (LAP), and the latent TGF-beta binding protein (LTBP). Mature TGF-beta is cleaved from its propeptide during secretion, but the proteins remain associated by noncovalent interactions. LTBP is required for efficient secretion and processing of latent TGF-beta and it binds to LAP via disulfide bond(s). LTBP is a component of extracellular matrix microfibrils, and it targets the latent TGF-beta complex to the extracellular matrix. TGF-beta signaling is initiated by proteolytic cleavage of LTBP that results in the release of the latent TGF-beta complex from the extracellular matrix. TGF-beta is activated by dissociation of LAP from the mature TGF-beta. Subsequent signaling involves binding of active TGF-beta to its type II cell surface receptors, which phosphorylate and activate type I TGF-beta receptors. Type I receptors, in turn, phosphorylate cytoplasmic transcriptional activator proteins Smad2 and Smad3, inducing their translocation to the nucleus. Recent evidence suggests that acquisition of resistance to TGF-beta growth inhibition plays a major role in the progression of epithelial and hematopoietic cell malignancies. The role of secretion of TGF-beta in tumorigenesis is more complex. The secretion of TGF-beta s by tumor cells may contribute to autocrine growth inhibition, but on the other hand, it may also promote invasion, metastasis, angiogenesis, and even immunosuppression. Tumor cells may also fail to deposit LTBP:TGF-beta complexes to the extracellular matrix. The elucidation of the mechanisms of the release of TGF-beta from the matrix and its subsequent activation aids the understanding of the pathophysiologic roles of TGF-beta in malignant growth, and allows the development of therapeutic agents that regulate the activity of TGF-beta.

Colon carcinoma cell lines stimulate monocytes and lamina propria mononuclear cells to produce IL-10

Cytokines released from tumour cells may have function as signals to neighbouring immune and inflammatory cells. Several studies have shown that the immunoregulatory cytokines IL-10 and transforming growth factor-beta1 (TGF-beta1) as well as prostaglandin-E2 (PGE2) play an important role in tumour-induced immunosuppression. The aim of the study was to investigate the effect of colon carcinoma cell lines on IL-10 production in peripheral monocytes (PBMC) and lamina propria mononuclear cells (LPMC). We examined four colon carcinoma cell lines (HT-29, Caco-2, Colo-320 and HCT-116) and determined their production of TGF-beta1, IL-10 and PGE2. Peripheral monocytes were isolated by density gradient centrifugation and LPMC were isolated from surgical specimens using a collagenase digestion method. Monocytes and LPMC were cultured with colon carcinoma cell conditioned medium or in co-culture with colon carcinoma cells. Supernatants were then determined for the production of IL-10 by ELISA assays. All colon carcinoma cell lines stimulated peripheral monocytes as well as LPMC to produce markedly increased levels of IL-10. Colon cancer cells secreted negligible levels of IL-10, but high amounts of TGF-beta1 and PGE2. Neutralization of TGF-beta1 by administration of anti-TGF-beta as well as neutralization of PGE2 with anti-PGE2 antisera reduced the IL-10 production of monocytes markedly, indicating that tumour cell-derived TGF-beta1 and PGE2 are major factors for IL-10 stimulation. In vitro stimulation of monocytes with TGF-beta1 and PGE2 could confirm that TGF-beta1 as well as PGE2 at picogram concentrations were able to prime monocytes for enhanced IL-10 production. Our results demonstrate that colon carcinoma cell lines enhance the ability of monocytes and intestinal macrophages to produce IL-10. The stimulation of monocyte IL-10 by colon cancer cell-derived TGF-beta1 and PGE2 may act as a tumour-protecting mechanism by impairing the activation of anti-tumour cytokines.

Expression of transforming growth factor beta type III receptor suppresses tumorigenicity of human breast cancer MDA-MB-231 cells

Transforming growth factor beta (TGF-beta) promotes tumor progression in some model systems including human breast cancer cells. In this study, we report that human breast cancer cell lines express reduced amounts of TGF-beta type III receptor (RIII) when compared with untransformed human mammary epithelial cells. Consequently, we examined whether expression of RIII in human breast cancer MDA-MB-231 cells could reduce TGF-beta's tumor promoting activity by sequestering active TGF-beta isoforms produced by the cells. A tetracycline-repressible human RIII expression vector was stably transfected into the cell line. RIII expression in a pool of transfected clones and a single clone was found to be reversibly repressed by tetracycline treatment. Expression of RIII reduced the amount of active TGF-beta1 and TGF-beta2 in the conditioned medium. The medium conditioned by control cells showed a significantly higher growth inhibitory effect than that conditioned by RIII-transfected cells on the growth of the mink lung epithelial CCL64 cells. A conditioned medium collected from RIII-transfected cells treated with tetracycline significantly increased its growth inhibitory activity to that of control cells. Expression of RIII also reduced tumor incidence and growth rate in two separate experiments when the cells were inoculated in athymic nude mice. Treatment of the mice with tetracycline repressed RIII expression in the tumors generated by RIII-transfected cells and increased tumor incidence and growth rate. These results suggest that TGF-beta RIII can reduce tumorigenicity of MDA-MB-231 cells apparently by sequestering TGF-beta isoforms produced by these cells.

Expression of transforming growth factor beta (TGFbeta) type III receptor restores autocrine TGFbeta1 activity in human breast cancer MCF-7 cells

While transforming growth factor beta (TGFbeta) type III receptor (RIII) is known to increase TGFbeta1 binding to its type II receptor (RII), the significance of this phenomenon is not known. We used human breast cancer MCF-7 cells to study the role of RIII in regulating autocrine TGFbeta1 activity because they express very little RIII and no detectable autocrine TGFbeta activity. A tetracycline-repressible RIII expression vector was stably transfected into this cell line. Expression of RIII increased TGFbeta1 binding to TGFbeta type I receptor (RI) as well as RII. Treatment with tetracycline suppressed RIII expression and abolished TGFbeta1 binding to RI and RII. Growth of RIII-transfected cells was reduced by 40% when plated at low density on plastic. This reduction was reversed by tetracycline treatment and was partially reversed by treatment with a TGFbeta1 neutralizing antibody. The activity of a TGFbeta-responsive promoter construct when transiently transfected was more than 3-fold higher in the RIII-transfected cells than in the control cells. Treating the cells with tetracycline or the TGFbeta1 neutralizing antibody also significantly attenuated the increased promoter activity. These results suggest that expression of RIII restored autocrine TGFbeta1 activity in MCF-7 cells. The RIII-transfected cells were also much less clonogenic in soft agarose than the control cells indicating a reversion of progression. Thus, RIII may be essential for an optimal level of the autocrine TGFbeta activity in some cells, especially in the transformed cells with reduced RII expression.

Differential control of expression of type I and type II receptors of transforming growth factor-beta in colon carcinoma cells

We investigated TGF-beta response and the expression of TGF-beta receptors in clones of MOSER colon carcinoma cells (designated MOSER II and MOSER III-10) as a function of their growth state. TGF-beta 1 response as assessed by induction of fibronectin expression was higher (3.0-fold) in exponentially growing cells than in quiescent cells. The expression of type I receptor (RI) mRNA was greater (2.5 to 3.0-fold) in exponentially growing cells than in quiescent cells. In contrast, the expression of type II receptor (RII) mRNA was marginally increased in quiescent cells relative to exponential cells. Nuclear run-off assays, and actinomycin-D treatment indicated that the increased expression of RI mRNA in exponentially growing cells was primarily due to an increase in transcription, while a marginal increase in mRNA level for RII in quiescent cells was primarily due to an increase in mRNA stability. Affinity cross-linking with 125I-labeled TGF-beta 1, showed that the exponentially growing cells displayed greater amounts of 125I TGF-beta 1 binding to RI and RII than quiescent cells, indicating that increased cell surface expression of receptors was correlated with increased response in the exponential growth state. Immunoblot analysis also indicated greater amounts of RI protein in exponential compared to quiescent cells; however, no difference in RII protein was observed in the two growth states. These data indicate that expression of the receptors responsible for TGF-beta signal transduction are differentially controlled.

Hepatocyte growth factor releases epithelial and endothelial cells from growth arrest induced by transforming growth factor-beta1

Human lung fibroblasts and Mv1Lu mink lung epithelial cells were used as a model to study the role of extracellular matrix in epithelial-mesenchymal interactions. Extracellular matrices of fibroblasts were found to contain growth promoting activity that reduced the sensitivity of Mv1Lu cells to the growth inhibitory effects of transforming growth factor-beta (TGF-beta). The majority of the activity was identified as hepatocyte growth factor/scatter factor (HGF) by inhibition with specific antibodies and by reconstitution of the effect by recombinant HGF. HGF induced cell proliferation when contact-inhibited Mv1Lu cells were trypsinized and plated in the presence of TGF-beta1. The effect was valid also in assays where Madin-Darby canine kidney epithelial cells or bovine capillary endothelial cells were used. The multiplication of chronically TGF-beta1 inhibited Mv1Lu cells was also induced by HGF. In addition, HGF induced anchorage independent growth of Mv1Lu cells that was refractory to TGF-beta1 growth inhibition. Immunoprecipitation analysis indicated that HGF prevented the suppression of Cdk4 and Cdk2, but not the induction of p21, by TGF-beta1. Since both TGF-beta1 and HGF require proteolysis for activation, the results imply that proteolytic activity of epithelial and endothelial cells directs their responses to signals from mesenchymal-type extracellular matrices, and that during development, matrix-bound growth and invasion promoting and suppressing factors are activated in a coordinated manner.

Clonal heterogeneity of the sensitivity of human colon carcinoma cell lines to TGE beta isoforms

Spontaneously arising, TGF beta 1-resistant colonies were isolated directly from the soft agarose plates of MOSER human colon carcinoma cells grown in the presence of TGF beta 1 but in the absence of serum. The colonies were cloned by limiting dilution and screened in a monolayer proliferation assay for sensitivity to TGF beta 1 and TGF beta 2 isoforms. Cell clones selectively sensitive or resistant to these isoforms in the growth inhibition assay displayed similar differential sensitivities to TGF beta isoforms for production of the extracellular matrix proteins laminin and fibronectin, as well as for the expression of the colon cell differentiation marker carcinoembryonic antigen. Differential receptor binding profiles for TGF beta 1 and TGF beta 2 were observed among the clones. The isolation of cell clones selectively resistant or sensitive to TGF beta isoforms as well as the identification of differential receptor binding profiles among the clones indicate the heterogeneity of TGF beta responsiveness that exists naturally in human colon tumor cells and stress the importance of defining mechanisms underlying differential responsiveness to TGF beta isoforms.

Autocrine transforming growth factor beta 1 modulates the expression of integrin alpha 5 beta 1 in human colon carcinoma FET cells

Transforming growth factor beta (TGF-beta) has been extensively studied as an exogenous agent that stimulates the expression of extracellular matrix proteins and their cell-surface integrin receptors in a variety of cell types. However, the recent demonstration of autocrine TGF-beta growth effects in a number of cell types suggests that the steady-state expression of extracellular matrix and integrin proteins and their biological activity may also be under autocrine TGF-beta control. Previously, we reported that repression of autocrine TGF-beta 1 activity by constitutive expression of a full-length TGF-beta 1 antisense cDNA led to abrogation of autocrine negative TGF-beta and, as a result, increased tumorigenicity and anchorage-independent growth of a poorly tumorigenic, well-differentiated colon carcinoma cell line designated FET (Wu, S., Theodorescu, D., Kerbel, R. S., Willson, J. K. V., Mulder, K. M., Humphrey, L. E., and Brattain, M. G. (1992) J. Cell Biol. 116, 187-196). Consequently, we have used this model system to study the effects of repression of autocrine TGF-beta 1 activity on the expression of integrin alpha 5 beta 1 and integrin alpha 5 beta 1-mediated cell adhesion to fibronectin. The expression of the integrin alpha 5 subunit was reduced in TGF-beta 1 antisense transfected FET cells at both mRNA and protein levels as determined by RNase protection assays and immunoprecipitation, respectively. Autocrine TGF-beta 1 had no effect on the transcription of integrin alpha 5 and beta 1 subunits, indicating that autocrine TGF-beta 1 may regulate integrin alpha 5 beta 1 expression at the post-transcriptional level. The diminished expression of integrin alpha 5 beta 1 on the cell surface led to the reduced adhesion of TGF-beta 1 antisense transfected cells to fibronectin. This phenomenon could be reversed by treatment with exogenous TGF-beta 1.