Expression of insulin-like growth factor-II and insulin-like growth factor binding proteins during Caco-2 cell proliferation and differentiation

c-Myc-Regulated lncRNA-IGFBP4 Suppresses Autophagy in Cervical Cancer-Originated HeLa Cells

LncRNAs are known to regulate a plethora of key events of cellular processes; however, little is known about the function of lncRNAs in autophagy. Here in the current study, we report lncRNA-IGFBP4 which has previously been known to regulate the proliferation and reprogramming of cancer cells, but its role in autophagy is not yet known. We found that serum starvation provokes autophagy-induced downregulation of lncRNA-IGFBP4 levels. Next, we determined that c-Myc can negatively regulate lncRNA-IGFBP4 in HeLa cells. Phenotypically, we found that upon depletion of lncRNA-IGFBP4, the HeLa cells undergo autophagy through ULK1/Beclin1 signaling. Furthermore, through TCGA data analysis, we found lncRNA-IGFB4 overexpressed in most cancers including cervical cancer. Based on these findings, we conclude that c-Myc maintains cellular homeostasis through negatively regulating lncRNA-IGFBP4 in cervical cancer cells.

Overexpression of lncRNA IGFBP4-1 reprograms energy metabolism to promote lung cancer progression

BACKGROUND

Reprogrammed energy metabolism as an emerging hallmark of cancer has recently drawn special attention since it facilitate cell growth and proliferation. Recently, long noncoding RNAs (lncRNAs) have been served as key regulators implicated in tumor development and progression by promoting proliferation, invasion and metastasis. However, the associations of lncRNAs with cellular energy metabolism in lung cancer (LC) need to be clarified.

METHODS

Here, we conducted bioinformatics analysis and found insulin-like growth factor binding protein 4-1 (IGFBP4-1) as a new candidate lncRNA located in the upstream region of IGFBP4 gene. The expression levels of lnc-IGFBP4-1, mRNA levels of IGFBP4 in 159 paired lung cancer samples and adjacent, histological normal tissues by qRT-PCR. Over-expression and RNA interference (RNAi) approaches were adopted to investigate the biological functions of lnc-IGFBP4-1. The intracellular ATP level was measured using the Cell Titer-Glo Luminescent Cell Viability Assay kit, and changes in metabolic enzymes were examined in cancer cells and normal pulmonary epithelial cells with qRT-PCR.

RESULTS

Our results showed that lnc-IGFBP4-1 was significantly up-regulated in LC tissues compared with corresponding non-tumor tissues (P < 0.01), and its expression level was significantly correlated with TNM stage (P < 0.01) and lymph node metastasis (P < 0.05). Further investigation showed that overexpression of lnc-IGFBP4-1 significantly promoted LC cell proliferation in vitro and in vivo, while downregulation of endogenous lnc-IGFBP4-1 could inhibited cell proliferation and induce apoptosis. Moreover, we found lnc-IGFBP4-1 could influences ATP production levels and expression of enzymes including HK2, PDK1 and LDHA, in addition, decline in both ATP production and these enzymes in response to 2-DG and 2-DG-combined Rho123, respectively, was observed in lnc-IGFBP4-1-overespressing LC cells, indicative of an enhanced aerobic glycolysis rate. Finally, lnc-IGFBP4-1 was observed to negatively correlate with gene IGFBP4, and lower expression level of IGFPB4 was found after lnc-IGFBP4-1-overexpression was transfected into PC9 cells, higher expression level of IGFPB4 was also found after lnc-IGFBP4-1-downregulation was transfected into GLC-82 cells, which indicates that IGFBP4 may exert its targeting function regulated by lnc-IGFBP4-1.

CONCLUSIONS

Taken together, these findings provide the first evidence that lnc-IGFBP4-1 is significantly up-regulated in LC tissues and plays a positive role in cell proliferation and metastasis through possible mechanism of reprogramming tumor cell energy metabolism, which suggests that lnc-IGFBP4-1 may be a promising biomarker in LC development and progression and as a potential therapeutic target for LC intervention.

Rescue of silenced UCHL1 and IGFBP4 expression suppresses clonogenicity of giant cell tumor-derived stromal cells

Giant cell tumor (GCT) of bone is a generally benign tumor with a locally aggressive behavior. Histologically, GCTs consist of multinucleated giant cells, mononuclear histiocytes and the neoplastic fibroblast-like stromal cells (GCTSC). Growing evidence exists that GCTSCs develop from mesenchymal stem cells (MSCs), but little is known about the underlying molecular mechanisms. In previous studies we observed inactivation of the ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) gene in primary GCTSC due to strong DNA hypermethylation, indicating that epigenetic silencing might be involved in neoplastic transformation of MSCs. Here we investigated further candidate genes and identified strong hypermethylation of the insulin-like growth factor binding protein 4 (IGFBP4) promoter, resulting in IGFBP4 downregulation in GCTs compared to MSCs. Overexpression of UCHL1 and IGFBP4 by stable transfection of GCTSC did not influence cell viability, proliferation, migration and chemosensitivity compared to parental cells. However, colony-formation was significantly decreased suggesting that rescue of UCHL1 and IFGBP4 suppresses clonogenicity of GCT stromal cells. The observation of reduced expression of the stem-cell-specific transcription factors OCT4 and SOX2 in these cell lines further supported our findings. Epigenetic silencing of UCHL1 and IGFBP4 in GCTs might thus be a crucial event during the malignant transformation of MSCs in the context of GCT development and represent promising targets for the development of new diagnostic and therapeutic strategies.

Suppressor of cytokine signaling-2 limits intestinal growth and enterotrophic actions of IGF-I in vivo

Suppressors of cytokine signaling (SOCS) typically limit cytokine receptor signaling via the JAK-STAT pathway. Considerable evidence demonstrates that SOCS2 limits growth hormone (GH) action on body and organ growth. Biochemical evidence that SOCS2 binds to the IGF-I receptor (IGF-IR) supports the novel possibility that SOCS2 limits IGF-I action. The current study tested the hypothesis that SOCS2 normally limits basal or IGF-I-induced intestinal growth and limits IGF-IR signaling in intestinal epithelial cells. Intestinal growth was assessed in mice homozygous for SOCS2 gene deletion (SOCS2 null) and wild-type (WT) littermates at different ages and in response to infused IGF-I or vehicle or EGF and vehicle. The effects of SOCS2 on IGF-IR signaling were examined in ex vivo cultures of SOCS2 null and WT intestine and Caco-2 cells. Compared with WT, SOCS2 null mice showed significantly enhanced small intestine and colon growth, mucosal mass, and crypt cell proliferation and decreases in radiation-induced crypt apoptosis in jejunum. SOCS2 null mice showed significantly greater growth responses to IGF-I in small intestine and colon. IGF-I-stimulated activation of IGF-IR and downstream signaling intermediates were enhanced in the intestine of SOCS2 null mice and were decreased by SOCS2 overexpression in Caco-2 cells. SOCS2 bound directly to the endogenous IGF-IR in Caco-2 cells. The intestine of SOCS2 null mice also showed enhanced growth responses to infused EGF. We conclude that SOCS2 normally limits basal and IGF-I- and EGF-induced intestinal growth in vivo and has novel inhibitory effects on the IGF-IR tyrosine kinase pathway in intestinal epithelial cells.

Interleukin-5 potentiates the growth response of Caco-2 cells to IGF-II: a role in colonic carcinogenesis complicating ulcerative colitis?

Longstanding ulcerative and Crohn's colitis increases the risk of colorectal cancer (CRC) compared to the general population. Elevated IGF-II mRNA and protein have been found in tumour tissue in sporadic CRC. The association of IGF-II in colitis-related-CRC is unknown.

OBJECTIVES

To determine whether pro-inflammatory cytokines associated with colitis, namely IL-5, TNF-alpha and IL-1beta, alter the proliferative effect of IGF-II on the colorectal cancer cell line, Caco-2.

DESIGN

Caco-2 cells were cultured with IGF-II and IL-5, TNF-alpha or IL-1beta. At 24 h intervals cell proliferation was assessed. The mechanism of action of any synergistic affect was investigated by RT-PCR to determine change in mRNA expression of IGF-II, IGF-1R or IGF-2R.

RESULTS

After 72 h, IGF-II increased absorption (corresponding to cell density) compared to controls by 25% (p < 0.02). Co-incubation with IGF-II and IL-5 increased absorption by 42% (p < 0.001) compared to controls and 18% (p < 0.03) compared to IGF-II alone. Enhanced growth response was also seen with TNF-alpha and IL-1beta, but less so than IL-5. The IL-5 receptor was not expressed by Caco-2 cells and mRNA expression of the IGF-1R or IGF-2R was unchanged by incubation with cytokines.

CONCLUSIONS

IGF-II promotes Caco-2 growth, an effect enhanced with IL-5, TNF-alpha and IL-1beta. The greatest response was with IL-5. This was IL-5 receptor-independent. Possible mechanisms include IL-5 interaction on an un-identified receptor or interference with IGF-binding proteins, as occurs with IL-1beta and IL-6. The enhanced growth response of Caco-2 cells to pro-inflammatory cytokines and IGF-II may have implications for the pathogenesis of CRC formation in colitis.

Suppressor of cytokine signaling-2: a growth hormone-inducible inhibitor of intestinal epithelial cell proliferation

BACKGROUND & AIMS

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) increase intestinal growth. GH is thought to act indirectly via IGF-I. In several models, including rats given total parenteral nutrition (TPN), IGF-I more potently stimulates mucosal growth than GH, even when GH induces similar circulating IGF-I levels. These studies test the hypothesis that GH induces a suppressor of cytokine signaling (SOCS), which inhibits intestinal epithelial cell (IEC) proliferation.

METHODS

Rats on TPN received vehicle, GH, or IGF-I. Jejunal SOCS (SOCS-1, -2, -3, and cytokine-inducible SH2-domain-containing protein [CIS]) and IGF-I messenger RNA (mRNA) were quantified. Caco-2, IEC-6 cells, and SOCS-2 null and wild-type (WT) mice were used to examine the expression and functional role of SOCS-2.

RESULTS

As reported previously, IGF-I, but not GH, prevented mucosal atrophy during TPN, although GH elevated plasma IGF-I and increased body weight. GH, but not IGF-I, induced jejunal SOCS-2 mRNA. SOCS-2 mRNA levels in GH and IGF-I-treated rats inversely correlated with mucosal weight. SOCS-2 is expressed in Caco-2 cells, and elevated SOCS-2 expression in postconfluent cells is associated with reduced proliferative rates. SOCS-2 overexpression in Caco-2 cells inhibited cell proliferation and promoted differentiation. In IEC-6 cells, GH induced SOCS-2 and reduced basal or IGF-I-induced proliferation. GH also reduced proliferative activity in isolated crypts from WT but not SOCS-2 null mice, and SOCS-2 null crypts showed enhanced proliferative responses to GH and IGF-I. SOCS-2 null mice have increased intestinal weight and length.

CONCLUSIONS

SOCS-2 is a GH-inducible, novel inhibitor of intestinal epithelial cell proliferation and intestinal growth.

trans-10, cis-12 conjugated linoleic acid reduces insulin-like growth factor-II secretion in HT-29 human colon cancer cells

We previously demonstrated that a mixture of conjugated linoleic acid (CLA) isomers decreases colon cancer incidence in rats treated with 1,2-dimethylhydrazine. Our in vitro studies have also shown that CLA inhibits the growth of HT-29 cells, a human colon cancer cell line. When we compared the individual potencies of the two main isomers found in the mixture of CLA isomers (e.g., cis-9, trans-11 [c9t11] and trans-10, cis-12 [t10c12]), t10c12 CLA decreased viable cell numbers in a dose-dependent manner. By contrast, c9t11 CLA had no effect. Therefore, the present study examined whether the decreased cell growth is related to changes in secretion of insulin-like growth factor (IGF)-II and/or IGF-binding proteins (IGFBPs) that have been shown to regulate HT-29 cell proliferation. Cells were incubated in serum-free medium with various concentrations of the individual CLA isomers, and immunoblot analysis of 24-hour, serum-free, conditioned media using a monoclonal anti-IGF-II antibody was performed. HT-29 cells secreted both mature 7,500 apparent molecular weight (M(r)) and higher-M(r) forms of IGF-II. t10c12 CLA decreased the levels of the higher-M(r) and the mature form of IGF-II in a dose-dependent manner, whereas c9t11 CLA had no effect. Ligand blot analysis of conditioned medium using (125)I-IGF-II revealed that the production of IGFBP-2 and IGFBP-4 was also decreased by t10c12 CLA, whereas c9t11 CLA had no effect. Exogenous IGF-II abrogated the growth inhibition induced by t10c12 CLA. These results indicate that inhibition of HT-29 cell growth by t10c12 CLA may be mediated by decreasing IGF-II secretion in these cells.

Identification of a novel SP3 binding site in the promoter of human IGFBP4 gene: role of SP3 and AP-1 in regulating promoter activity in CaCo2 cells

Insulin-like growth factor binding protein 4 (IGFBP4/BP4) gene expression plays an important role in the transition from proliferation to differentiation of a human colon cancer cell line, CaCo2. We recently cloned and identified multiple cis elements (including putative binding sites for activator protein 1 (AP-1) and specificity proteins (Sps) ) in the promoter of human BP4 gene, and measured a significant upregulation of the promoter activity in response to c-Jun. We therefore examined the role of the single AP-1 site (-869/-863) and other cis elements, in regulating the expression of hBP4 gene, in the current studies. Deletion of a 25 bp sequence from -872 to -848, which contains the AP-1 site, significantly reduced BP4 promoter activity by approximately 50%. Surprisingly, mutation of the AP-1 site did not produce significant alteration in the activity of the BP4 promoter. However, mutation of 7 bp (5'-TGCTGCA) at the 3' end of the AP-1 site resulted in significantly decreasing the promoter activity by >50%. Proteins bound to the 25 bp probe (-872/-848) could be supershifted by antibodies specific for JunD and Sp3 in an EMSA. JunD binding was abolished on mutation of the AP-1 site and Sp3 binding was abolished on mutation of the 7 bp at -861/-855; binding of the purified Sp3 protein to the 25 bp probe was similarly abolished on mutation of the newly discovered Sp3 binding site (TGCTGCA). BP4 promoter activity was upregulated in insect cells in response to Sp3 expression, confirming a functional importance of the novel Sp3 binding site. These studies suggest that the Sp3 binding site, rather than the AP-1 site, may be playing a significant role in regulating the expression of IGFBP4 gene in CaCo2 cells.

Transcriptome analysis of a human colorectal cancer cell line shows molecular targets of insulin-like growth factor-binding protein-4 overexpression

Insulin-like growth factor II (IGF-II) is expressed commonly in colorectal tumors. IGF-binding protein-4 (IGFBP-4) counteracts the tumor promoting activities of IGF-II by binding this growth factor. We have shown previously that in LS1034 cells, which highly express IGF-II, overexpression of IGFBP-4 led to a strong reduction in proliferation, colony formation and invasive capacity. To investigate the effects of IGFBP-4 at the molecular level we analyzed growth parameters of LS1034 human colon cancer cells vs. cells expressing the murine IGFBP-4 (mIGFBP-4) and used a subtractive cDNA library approach in combination with cDNA array hybridization to detect changes in the mRNA expression profiles. The mRNA levels for several proteins that are known to affect important biological properties of neoplastic cells, such as proteolysis, proliferation and differentiation were altered by overexpression of IGFBP-4. Transcript levels for tumor markers, like the carcinoembryonic antigen-related cell adhesion molecule (CEACAM), were reduced by elevated mIGFBP-4. Changes at the mRNA level were confirmed by Western blotting for CST1 (proteolysis or protease inhibitor), COX-2 (cell motility) and CEACAM5 (tumor marker). Furthermore, the effect of mIGFBP-4 on apoptosis was investigated and no increase of apoptosis could be detected in the IGFBP-4 overexpressing LS1034 cells. Our data indicate that IGFBP-4 is involved in the regulation of gene products that are known or supposed to be important for the pathogenesis of colon cancer cells.

Proteome analysis reveals novel proteins associated with proliferation and differentiation of the colorectal cancer cell line Caco-2

Here, we describe a proteomics approach to study protein expression changes in differentiating Caco-2 cells. Caco-2 is a colorectal carcinoma cell line, which upon differentiation loses its tumorigenic phenotype and displays characteristics of mature enterocytes, including brush borders with microvilli. Cells were grown in culture flasks and harvested at different stages of differentiation (days post-confluence: -3, 0, 3, 7, 10, 14, and 18). Two-dimensional gel electrophoresis was used to analyse proteome changes. Approximately 1400 protein spots were detected within the Caco-2 proteome, within the pH 4-7 range. Two-dimensional gel electrophoresis allowed for the detection of 18 proteins from which the levels of expression were found to be associated with differentiation. Of these proteins, 11 were identified by means of MALDI-TOF or NANO-ESI-MS/MS mass spectrometry and include liver fatty acid binding protein (FABL), three forms of alpha-enolase (ENOA), nucleoside diphosphate kinase A (NDKA), cofilin-1 (COF1), translationally controlled tumour protein (TCTP), mitochondrial 60-kDa heat shock protein (CH60), probable protein disulfide isomerase (ER60), creatine kinase B (KCRB), and glutathione S-transferase alpha (GTA1). Thus, proteomics revealed that the differentiation-related change in phenotype of Caco-2 involves changes in a variety of distinct biochemical pathways. Some of these proteins have not been shown before to be associated with Caco-2 differentiation (ER60; COF1; CH60; NDKA; TCTP and ENOA). Therefore, processes related to protein folding and disulfide bridge formation, cytoskeleton formation and maintenance, nucleotide metabolism, glycolysis as well as tumorigenesis-associated proteins may be involved in Caco-2 differentiation. Changes in the expression of CH60, TCTP, GTA1, NDKA, and FABL have also been reported to be associated with in vivo colon carcinogenesis. These findings illustrate that a combination of proteomics and cell culture is a useful approach to find markers for Caco-2 differentiation, which could contribute to the comprehension of the process of colon carcinogenesis.

Trans-10,cis-12-conjugated linoleic acid inhibits Caco-2 colon cancer cell growth

A commercially available mixture of conjugated linoleic acid (CLA) isomers decreases colon cancer cell growth. We compared the individual potencies of the two main isomers in this mixture [cis-9,trans-11 (c9t11) and trans-10,cis-12 (t10c12)] and assessed whether decreased cell growth is related to changes in secretion of insulin-like growth factor II (IGF-II) and/or IGF-binding proteins (IGFBPs), which regulate Caco-2 cell proliferation. Cells were incubated in serum-free medium with different concentrations of the individual CLA isomers. t10c12 CLA dose dependently decreased viable cell number (55 +/- 3% reduction 96 h after adding 5 microM t10c12 CLA). t10c12 CLA induced apoptosis and decreased DNA synthesis, whereas c9t11 CLA had no effect. Immunoblot analysis of 24-h serum-free conditioned medium using a monoclonal anti-IGF-II antibody revealed that Caco-2 cells secreted both a mature 7,500 molecular weight (M(r)) IGF-II and higher M(r) forms of IGF-II. The levels of the higher M(r) and the mature form of IGF-II were decreased 50 +/- 3% and 22 +/- 2%, respectively, by 5 microM t10c12 CLA. c9t11 CLA had no effect. Ligand blot analysis of conditioned medium using 125I-labeled IGF-II revealed that t10c12 CLA slightly decreased IGFBP-2 production; c9t11 CLA had no effect. Exogenous IGF-II reversed t10c12 CLA-induced growth inhibition and apoptosis. These results indicate that CLA-inhibited Caco-2 cell growth is caused by t10c12 CLA and may be mediated by decreasing IGF-II secretion in Caco-2 cells.

Insulin-like growth factor binding protein-4 expression is dependent on the carbohydrate in the media in HT-29 cells

HT-29 are colonic carcinoma cells that follow a unique pattern of differentiation dependent on the medium's carbohydrate source. This study compared levels of insulin-like growth factor (IGF)-II and IGF binding protein (IGFBP)-4 when HT-29 cells were grown with standard glucose-containing medium versus galactose-containing (glucose-free) medium. Serum-free media conditioned for 24h were collected at low density, pre-confluence, confluence, and 48-h post-confluence. Ligand blotting of the conditioned galactose medium demonstrated low IGFBP-4 levels until the cells approached confluence, when the levels increased significantly. In standard medium, IGFBP-4 levels increased with increasing cell numbers except for a transient decrease at confluence. Radioimmunoassay showed little change in IGF-II concentrations, although HT-29 cells grown with galactose had lower IGF-II concentrations. HT-29 cells treated with retinoic acid had dose-dependent increases in IGFBP-4 and reduced IGF-II expression. These studies suggest that HT-29 cell differentiation correlates with an increase in IGFBP-4 levels.

Decreased production of insulin-like growth factor-binding protein (IGFBP)-6 by transfection of colon cancer cells with an antisense IGFBP-6 cDNA construct leads to stimulation of cell proliferation

BACKGROUND

: Previously, we have observed that highly unsaturated dietary (n-3) fatty acids inhibit cell proliferation in conjunction with stimulation of insulin-like growth factor-binding protein (IGFBP)-6 secretion in Caco-2 cells, a human colon carcinoma cell line.

METHODS

: To test the converse hypothesis that inhibition of endogenous IGFBP-6 secretion stimulates Caco-2 cell proliferation, cells were transfected with the antisense IGFBP-6 expression construct or pcDNA3 vector only, and single colonies resistant to G418 sulfate were isolated.

RESULTS

: Our initial studies indicated that three antisense clones grew faster and produced less IGFBP-6 than two pcDNA3 clones, so antisense IGFBP-6 #5 and pcDNA3 #8 were selected for further detailed analysis. Both the control and antisense clones grew in serum-free medium reaching a plateau density at day eight. However, the antisense clone grew at a rate faster than that of the control and reached a final density that was 31 +/- 3% higher than the control. Northern blot, ligand blot and immunoblot analyses revealed that accumulation of IGFBP-6 mRNA and concentrations of IGFBP-6 peptide produced by the antisense clone were decreased by 80-90% compared to the control. The doubling times of the antisense and control clones were 21.9 +/- 0.4 and 24.8 +/- 0.3 h (P < 0.05), respectively. Exogenous IGF-I and IGF-II (0.2-200 nmol/L) stimulated proliferation of both the control and antisense clones in a dose-dependent manner, but the relative potency and efficacy of IGF-II was higher in the antisense clone compared to the control. These results indicate that suppression of IGFBP-6 secretion correlates with an increase in the basal rate of Caco-2 cell growth.

CONCLUSIONS

: Our findings are consistent with the hypothesis that IGFBP-6 inhibits cell growth by binding to endogenously produced IGF-II, thereby preventing IGF-II from interacting with the IGF-I receptor to stimulate cellular proliferation by an autocrine mechanism.

Inhibition of Caco-2 cell proliferation by all-trans retinoic acid: role of insulin-like growth factor binding protein-6

The present study examined the effects of all-trans retinoic acid (tRA) on proliferation and expression of the IGF system in Caco-2 human colon adenocarcinoma cells. tRA inhibited Caco-2 cell proliferation in a dose-dependent manner, with a 40 +/- 2% decrease in cell number observed 48 h after the addition of 1 microM tRA. Ligand blot analysis of IGFBPs in conditioned media revealed that Caco-2 cells produced three IGFBPs of M(r): 34,000 (IGFBP-2), 24,000 (IGFBP-4), and 32,000 (IGFBP-6). The concentrations of IGFBP-2 and IGFBP-4 decreased by 48 +/- 6 and 70 +/- 13%, respectively, whereas that of IGFBP-6 increased by 698 +/- 20% with 1 microM tRA. tRA decreased mRNA levels of IGFBP-2 and IGFBP-4 by 20 +/- 3 and 50 +/- 8%, respectively, whereas tRA increased IGFBP-6 mRNA by 660 +/- 20%. tRA did not alter levels of IGF-II mRNA or peptide. To examine if endogenous IGFBP-6 inhibits cell proliferation, Caco-2 cells were transfected with an IGFBP-6 cDNA expression construct or pcDNA3 vector only and stable clones were selected. Clones overexpressing IGFBP-6 grew more slowly than vector controls and achieved final densities 30-55% lower than those of vector controls. Accumulation of IGFBP-6 mRNA and concentrations of IGFBP-6 peptide in conditioned media were increased by 200-250 and 220-250%, respectively, in the IGFBP-6 clones compared with controls. Increased expression of IGFBP-6, which has a high binding affinity for IGF-II, following tRA treatment suggests that the decreased proliferation caused by tRA may result, at least in part, from IGFBP-6-mediated disruption of the IGF-II autocrine loop in these colon cancer cells.

Synthetic low-calcaemic vitamin D(3) analogues inhibit secretion of insulin-like growth factor II and stimulate production of insulin-like growth factor-binding protein-6 in conjunction with growth suppression of HT-29 colon cancer cells

The aims of the present study were to compare the ability of various synthetic analogues of 1 alpha,25-dihydroxyvitamin D(3) [1 alpha,25-(OH)(2)D(3)] to inhibit proliferation of HT-29 cells, a human colon adenocarcinoma cell line. HT-29 cells were incubated for 144 h with various concentrations (0-100 nM) of 1 alpha,25-(OH)(2)D(3), or the analogues EB1089, CB1093 or 1 beta,25-(OH)(2)D(3). All these analogues except 1 beta,25-(OH)(2)D(3) inhibited cell proliferation, but relative potencies and efficacies of EB1089 and CB1093 were much greater than that of the native vitamin. Cells grew in serum-free medium, reaching a plateau density at day 10 of culture, and addition of 10 nM 1 alpha,25-(OH)(2)D(3) or 1 beta,25-(OH)(2)D(3) did not alter the long-term growth characteristics of HT-29 cells. However, cells treated with 10 nM EB1089 or CB1093 grew at a rate slower than control and reached final densities that were 53+/-1 and 36+/-2% lower than control, respectively. Immunoblot analysis of serum-free conditioned medium using a monoclonal anti-insulin-like growth factor-(IGF)-II antibody showed that both 10 nM EB1089 and CB1093 markedly inhibited secretion of both mature 7500 M(r) and higher M(r) forms of IGF-II. Ligand blot and immunoblot analyses of conditioned media revealed the presence of IGFBPs of M(r) 24,000 (IGFBP-4), 30,000 (glycosylated IGFBP-4), 35,000 (IGFBP-2) and 32,000-34,000 (IGFBP-6). The level of IGFBP-2 was decreased by 42+/-8 and 49+/-7% by 10 nM EB 1089 and CB1093, respectively, compared to controls. IGFBP-6 was increased approximately twofold by EB1089 and CB1093, and exogenously added IGFBP-6 inhibited HT-29 cell proliferation. These results suggest that inhibition of HT-29 cell proliferation by EB1089 and CB1093 may be attributed, at least in part, to the decreased secretion of IGF-II. The increase in IGFBP-6 concentration coupled with its high affinity for IGF-II may also contribute to decreased cellular proliferation by an indirect mechanism involving sequestration of endogenously produced IGF-II.

Insulin-like growth factor (IGF)-binding protein-6 inhibits IGF-II-induced but not basal proliferation and adhesion of LIM 1215 colon cancer cells

IGF-II is an autocrine growth factor for many colon cancer cells. This study aimed to determine the role of IGF-II in proliferation and adhesion of LIM 1215 colon cancer cells. RT-PCR demonstrated expression of IGF-I and IGF-II mRNA. Addition of IGF-I or -II increased monolayer proliferation in a dose-dependent manner. Although addition of IGFBP-6 had no effect on basal proliferation, coincubation of IGFBP-6 decreased IGF-II but not IGF-I-induced proliferation. Colony formation in agar was increased by IGF-II, an effect inhibited by coincubation with IGFBP-6. IGFBP-6 alone significantly decreased colony formation. Preincubation of cells with IGF-II increased adhesion to type IV collagen, fibronectin and laminin. IGFBP-6 had no effect on basal cell adhesion but completely inhibited the effects of IGF-II. LIM 1215 colon cancer cells are therefore IGF-responsive but IGF-II is not a major autocrine factor for these cells in monolayer, suggesting heterogeneity between colon carcinoma cell lines with respect to the role of the IGF system.

Peptide growth factors regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts

Insulin-like growth factor (IGF) binding proteins (IGFBPs) are expressed in fetal lung and may provide important post-translational regulation of IGF-induced mitogenesis during lung organogenesis. Because of the observation that growth factors can control cell growth through regulation of IGFBPs, we examined IGFBP production by fetal lung fibroblasts following stimulation by peptide growth factors important for fetal lung growth and development. Fetal lung fibroblasts were cultured in serum-free medium supplemented with various growth factors for up to 48 h, and IGFBPs in conditioned medium (CM) were analyzed by ligand blot and immunoblot techniques. Accumulation of CM IGFBP-3 was increased and IGFBP-2 decreased by incubation with either keratinocyte growth factor (KGF) or epidermal growth factor (EGF). The effect of these factors on IGFBP-3 accumulation increased with time but the effects of KGF on CM IGFBP-2 decreased over 48 h of incubation. CM IGFBP-4 was increased by 24 and 48 h incubation with basic fibroblast growth factor (bFGF; 2.1- and 2.7-fold increases at 24 and 48 h, respectively) and platelet-derived growth factor-BB (PDGF-BB; 4.2- and 14.9-fold increases at 24 and 48 h, respectively), and 48 h incubation with EGF (6.3-fold increase). In 48-h coincubation experiments, EGF in combination with PDGF-BB or with bFGF, and bFGF in combination with PDGF-BB, resulted in IGFBP-4 accumulations twice that expected from a summation of the effects of either growth factor alone (IGFBP-4 increased 9.8-, 4.0-, and 1.8-fold by PDGF-BB, EGF, and bFGF, respectively; and 27.1-, 37.3-, and 13.0-fold by PDGF-BB plus EGF, PDGF-BB plus bFGF, and EGF plus bFGF, respectively). These results suggest synergistic effects of these growth factors on IGFBP-4 accumulation in fetal lung fibroblast CM. Because IGFBPs are known to regulate DNA synthesis, we speculate that peptide growth factors may alter cell proliferation in fetal lung, in part through their effect on IGFBPs.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth inhibition and differentiation of the human colon carcinoma cell line, Caco-2, by constitutive expression of insulin-like growth factor binding protein-3

The human colon carcinoma cell line, Caco-2, produces insulin-like growth factor binding protein-3 (IGFBP-3), the secretion of which correlates with markers of enterocyte differentiation. To investigate whether IGFBP-3 inhibits proliferation or induces differentiation, Caco-2 cells were stably transfected with an IGFBP-3 cDNA expression construct or pcDNA3 vector as a control. Accumulation of IGFBP-3 mRNA and secretion of the protein into conditioned medium 9 days after plating were readily detected in the transfected cells, whereas these parameters were undetectable in pcDNA3-transfected cells. Insulin-like growth factor binding protein-3-expressing cells grew at a rate similar to the controls for 6 days after plating, but achieved a much lower final density between days 10 and 12. By day 9 of culture, accumulation of sucrase-isomaltase mRNA, a marker of enterocytic differentiation of Caco-2 cells, was evident in the IGFBP-3-expressing cells, but was undetectable in the controls. These results indicate that IGFBP-3 may inhibit proliferation and induce early differentiation of Caco-2 cells.

Role of insulin-like growth factor-I (IGF-I) receptor, IGF-I, and IGF binding protein-2 in human colorectal cancers

The identification of novel autocrine/paracrine signaling pathways and possible markers represents an important component in the understanding of tumor growth control. In this study, we assessed the potential role of insulin-like growth factor-I (IGF-I), the IGF-I receptor (IGF-IR) and IGF binding protein-2 (IGFBP-2) in human colorectal cancer. Initial studies demonstrating increased IGF-I binding and IGF-IR density in human colon cancer tissue revealed that a component of iodinated (3-[125-I]iodotyrosyl) IGF-I (125I-ICGF-I) binding was not attributable to IGF-IR. Binding studies and Western blot analysis suggested that this second component of 125I-IGF-I binding could be due to IGFBP-2. Further analysis by a specific solution hybridization/RNase protection assay for IGF-IR mRNA levels, IGFBP-2 mRNA levels and in situ hybridization for IGFBP-2 localization, was carried out in nine patients with colon cancer. IGF-IR mRNA levels by RNAse protection assays were unchanged, whereas IGFBP-2 mRNA levels were increased 4-8-fold in patients with colon cancer compared to controls. Three patients with Dukes stage C disease had the highest levels of IGFBP-2 mRNA. In situ hybridization studies localized IGFBP-2 mRNA to malignant cells and not to the surrounding stromal cells, suggesting an autocrine role for IGFBP-2. The discrepancy between increased IGF-I binding, IGF-IR density, IGFBP-2 mRNA and the minimal modulation of the IGF-IR mRNA implies post-transcriptional regulation of IGF-IRs. Our results suggest that IGFBP-2 may be implicated in colon cancer metastases and prognosis. Its usefulness as a potential tumor marker should be further investigated.

Surface-bound plasmin induces selective proteolysis of insulin-like-growth-factor (IGF)-binding protein-4 (IGFBP-4) and promotes autocrine IGF-II bio-availability in human colon-carcinoma cells

Limited proteolysis of insulin-like-growth-factor (IGF)-binding proteins (IGFBPs) represents a key process to modulate IGF bio-availability at the cellular level. In human colon carcinomas, urokinase-type plasminogen activator (u-PA) produced by stroma cells can bind to cancer-cell-associated u-PA receptor (u-PAR), and then catalyze the conversion of plasminogen (Pg) into plasmin (Pm). We therefore investigated the interplay between the IGF and Pm systems in the HT29-D4 human colon-carcinoma-cell model. HT29-D4 cells secreted IGF-II totally complexed to IGFBP-2, IGFBP-4 and IGFBP-6. Approximately 15% of IGFBP-4 was associated with the extracellular matrix. HT29-D4 cells produced neither u-PA- nor IGFBP-specific proteases. However, activation of Pm at the HT29-D4 cell surface obtained by the sequential addition of exogenous u-PA and Pg to mimic the stromal complementation induced selective proteolysis targeted to IGFBP-4 only (>95%). IGFBP-2 and IGFBP-6, though sensitive to proteolysis by soluble Pm, were not altered by cell-bound Pm. IGFBP-4 proteolysis yielded 18- and 14-kDa immunoreactive fragments which were not detectable by Western ligand blotting, indicating that they bound IGF-II with poor affinity. Release of IGF-II from IGF-II-IGFBP complexes after IGFBP-4 proteolysis by cell-bound Pm was indicated by the observation that approximately 20% of the 125I-IGF-II initially associated with endogenous IGFBP in reconstituted complexes was transferred to HT29-D4 cell-surface IGF-I receptors. These results suggest that IGFBP-4 proteolysis by cell-bound Pm can promote autocrine/paracrine IGF-II bio-availability in colon-cancer cells. This may have important consequences on the behavior of cancer cells at the interface between stroma and malignant cells in carcinomas of the colon in vivo.