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* Division of Life Sciences and Silver Biotechnology Research Center, Hallym University, Chunchon, 200–702, Korea,
** Department of Food Science and Nutrition, Dankook University, Seoul, 140–714, Korea, and
Division of Applied Life Sciences, Graduate School, Gyeongsang National University, Chinju, 660–901, Korea
2To whom correspondence should be addressed. E-mail: jyoon{at}hallym.ac.kr.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • insulin-receptor substrate-1 • Akt • extracellular signal-regulated kinase
Conjugated linoleic acid (CLA) is the common element of a group of C18 fatty acids with two double bonds exhibiting strong anticarcinogenic effects in a variety of animal models (1). CLA is found naturally in food such as milk fat and the meat of ruminant animals. In spite of the abundance of studies reporting the anticarcinogenic properties of CLA, the molecular mechanisms that facilitate these effects are not currently well known.
The insulin-like growth factor (IGF) system consists of the peptide growth factors IGF-I and IGF-II, the type I and II IGF receptors, the IGF-binding proteins (IGFBP), and their corresponding proteases (2). Initially identified as potent physiological mitogens, IGF are now known to be polypeptides with effects on cell proliferation, differentiation, apoptosis and transformation (3). The actions of IGF are mediated by the IGF-I receptor (IGF-IR). Similar to the insulin receptor in structure, the IGF-IR is a heterotetrameric glycoprotein with two extracellular 
-subunits and two transmembrane ß-subunits. Ligand binding to the receptor induces receptor autophosphorylation in the intracellular domain of the ß-subunit and results in activation of the intrinsic tyrosine kinase of the IGF-IR. Signaling pathways known to be activated by IGF-IR include the extracellular signal-regulated kinase (ERK) subfamily of mitogen-activated protein kinases (MAPK) and phosphatidylinositol 3-kinase (PI3K) (4).
Insulin-receptor substrate (IRS)-1, IRS-2, and Shc are immediate substrates of the IGF-IR and are phosphorylated after binding to the activated receptor through its phosphotyrosine-binding domain. IRS-1 is phosphorylated on multiple tyrosine residues that serve as docking sites for a variety of signaling molecules including the p85 regulatory subunit of PI3K (4). Tyrosine-phosphorylated IRS-1 binds p85 and thereby activates the associated catalytic subunit (p110) of the enzyme (5). The serine/threonine kinase Akt, or protein kinase B (PKB) appears to be critical for a variety of cellular signaling pathways and serves as a transducer of multiple functions initiated by growth factor receptors that activate PI3K. Tyrosine phosphorylated Shc activates the Ras-ERK signaling pathway through a Grb2-Son of Sevenless complex (6). PI3K, through its downstream target Akt/PKB, as well as the MAPK pathway, promotes growth factor-mediated mitogenesis and blocks programmed cell death or apoptosis (7,8).
The aberrant activation of the IGF-IR induces growth, neoplastic transformation, and tumorigenesis (9). The critical role played by the IGF-IR in the development of tumors suggests that this receptor might be an attractive target for dietary intervention for cancer prevention. Colon cancer is one of the most frequent malignant diseases in the developed world, and experimental and clinical data implicate the IGF-IR in colon cancer etiology. Compared with normal tissues, the IGF-IR is overexpressed by tumors in colorectal cancer (10,11). In addition, IGF-I protects colon cancer cells from death factor-induced apoptosis (12). Furthermore, IGF-II mRNA is overexpressed in human colon carcinoma compared with normal adjacent tissues (13). Therefore, the discovery of agents that inhibit the IGF-I signaling pathway could lead to the development of highly successful prevention strategies for colon cancer.
Dietary CLA inhibits colon tumor incidence in rats treated with 1,2-dimethylhydrazine (14). In vitro studies have shown that CLA inhibits cell proliferation and induces apoptosis of HT-29 cells, the human colon adenocarcinoma cell line (15). The present study examined whether the growth inhibitory effect of CLA is related to changes in the IGF system in HT-29 cells. HT-29 cells synthesize and secrete IGF-II, IGFBP-2, -4, and -6 (16), and IGF-II acts as an autocrine growth regulator of these cells (17). Therefore, this study examined the effect of CLA on IGF-II production and the activation of several key proteins in the IGF-I signal transduction pathway.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Reagents were purchased from suppliers as follows: monoclonal anti-ß-actin, essentially fatty acid-free bovine serum albumin (BSA), a mixture of CLA isomers (18), and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) (Sigma Chemical Co., St. Louis, MO); DMEM/Ham’s F-12 nutrient mixture (DMEM/F12), fetal bovine serum (FBS), transferrin, and selenium (Life Technologies, Gaithersburg, MD); horseradish peroxidase (HRP)-conjugated anti-rabbit and anti-mouse Ig (Amersham, Piscataway, NJ); anti-PI3K p85 and anti-IRS-1 antibody (Upstate Biotechnogy, Lake Placid, NY); anti-Akt (29752), anti-phospho-Akt (p-Akt, 473) and [
-32P]ATP (NEN Life Sciences, Boston, MA); anti-phosphotyrosine-RC20 antibody linked to HRP (PY20; BD Transduction Laboratories, Palo Alto, CA); antibodies against phospho-p44/42 MAP kinase (p-ERK-1/2, Thr202/Tyr203), p44/42 MAP kinase (ERK-1/2), phosphoinositide-dependent protein kinase 1 (PDK-1), p-PDK-1, phosphatase and tensin homologue deleted on chromosome ten (PTEN), and p-PTEN (Cell Signaling Technology, Beverly, MA); and antibodies against IGF-IRß (C-20) (Santa Cruz Biotechnology, Santa Cruz, CA). Recombinant human IGF-I and IGF-II were generously provided by Genentech (San Francisco, CA) and Eli Lilly (Greenfield, IN), respectively.
Cell culture.
The HT-29 cell line was purchased from the American Type Culture Collection (Manassas, VA) and maintained in DMEM/F12 containing 100 mL/L of FBS with 100,000 U/L penicillin and 100 mg/L of streptomycin. HT-29 cells between passages 135 and 145 were used in these studies. To examine the effect of CLA and IGF, cells were plated in 24-well plates at 50,000 cells/well with DMEM/F12 containing 100 mL/L of FBS. Prior to CLA treatment, the cell monolayers were rinsed and serum starved for 24 h with DMEM/F12 supplemented with 5 mg/L of transferrin, 0.1 g/L of BSA and 5 µg/L of selenium (serum-free medium). After serum starvation, fresh serum-free medium containing the indicated concentrations of CLA and/or recombinant human IGF-I or IGF-II was replaced. Fatty acids were complexed to essentially fatty acid-free BSA, with the molar ratio of fatty acid to BSA being 4:1 (19). Media were changed every two days. Viable cell numbers were estimated by the MTT assay as described previously (20).
IGF-II immunoblot analysis.
HT-29 cells were cultured as described above. Conditioned media (24-h) were collected between d 2 and 3 of culture, concentrated 10-fold and used for immunoblot analysis of IGF-II as described previously (20). The relative abundance of each band was measured by a densitometric scanning of the exposed films using the Bio-profile Bio-1D application (Vilber-Lourmat, France).
Immunoprecipitation and immunoblotting analyses.
Cell lysates were prepared as previously described (15). For immunoprecipitation, cell lysates (0.75 mg protein) were precleared by incubation on a rotating platform for 1 h at 4°C with 1 µg of normal rabbit IgG and 50 µL of a resuspended volume of protein A-Sepharose beads (Amersham) and centrifuged at 1000 x g for 5 min at 4°C. The supernatants were incubated with 1 µg of anti-IGF-IRß antibody for 2 h at 4°C. Protein A-Sepharose beads were added to the lysate-antibody mix, which was then incubated for 2 h at 4°C. The beads were washed four times with lysis buffer. The immunoprecipitates or total cell lysates were resolved on sodium dodecyl sulfate (SDS), 40–200 g/L of polyacrylamide gel and transferred onto polyvinylidene fluoride membrane (Millipore). The blots were blocked for 1 h in 10 g/L of BSA in TBS-T (20 mmol/L Tris-Cl, pH 7.5, 150 mmol/L NaCl, 1 g/L Tween 20) or 50 g/L of milk TBS-T and incubated for 1 h with either anti-phospho-Tyr (PY20-HRP, 1:5,000), anti-IGF-IRß (1:500), anti-IRS-1 (1:720), anti-PI3K (1:1000), anti-Akt (1:1000), anti-p-Akt (1:1000), anti-ERK-1/2 (1:1000), anti-p-ERK-1/2 (1:1000), anti-PDK-1 (1:1000), anti-p-PDK-1 (1:1000), anti-PTEN (1:1000), anti-p-PTEN (1:1000), or anti-ß-actin (1:2000) antibody. The blots were then incubated with anti-mouse or anti-rabbit HRP-conjugated antibody. Signals were detected by using the enhanced chemiluminescence method using SuperSignal west dura extended duration substrate (Pierce, Rockford, IL). The relative abundance of each protein band was analyzed by densitometric scanning of the exposed films. Immunoblots were probed with an antibody for ß-actin as a control for protein loading.
Reverse transcriptase-polymerase chain reaction (RT-PCR).
Total RNA was isolated using the guanidium isothiocyanate-phenol-chloroform method and RT-PCR was performed as previously described (21). Each PCR cycle consisted of denaturing at 94°C for 1 min, annealing at temperatures listed in Table 1for 1 min and extending at 72°C for 1 min. Sequences for PCR primer sets and numbers of cycles used for PCR amplication are listed in Table 1. The relative abundance of each band was estimated by densitometric scanning of the exposed films. The levels of mRNA were corrected as a ratio to the corresponding ß-actin level.
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An assay for PI3K activity was performed as previously described (22). Cell lysate (0.75 mg protein) was immunoprecipitated with polyclonal antibody against IGF-IRß followed by incubation with protein A-Sepharose beads. After washing, the beads were resuspended in 20 µL of kinase buffer (20 mmol/L Hepes, pH 7.2, 50 mmol/L NaCl, 1 mmol/L EGTA) containing 4 µg of phosphatidylinositol (Sigma), 10 µmol/L of ATP, 5 mmol/L of MnCl2, and 10 µCi of [-32P]ATP and incubated for 20 min at 30°C. The resulting 32P-labeled phosphatidylinositol 3-phosphate (PIP) lipids were separated from other reaction products by TLC and visualized by autoradiography. The radioactive PIP signals were quantitated by densitometry.
Statistical analyses.
For all studies, 3–6 independent experiments were performed with separate batches of cells. For each independent experiment duplicate samples were analyzed. Data were analyzed by one-way, two-way, or two-factor repeated measurements ANOVA and are expressed as the mean ± SEM. Differences between treatment groups were analyzed by Duncan’s multiple range test or t test. Means were considered significantly different at P < 0.05. All statistical analyses were done using the SAS System for Windows V8 (SAS Institute, Cary, NC).
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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To examine the effect of CLA on IGF-II production of HT-29 cells, monolayer cultures were treated with CLA (0–20 µmol/L) in serum-free medium, and the IGF-II level in conditioned media was determined by Western blot analysis. CLA decreased the levels of both pro (Mr 14,300) and mature (Mr 7500) IGF-II in a dose-dependent manner (Fig. 1A). Results of the RT-PCR analysis revealed that CLA decreased IGF-II transcripts in HT-29 cells in a dose-dependent manner (Fig. 1B).
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To investigate whether CLA influences IGF-IR expression in HT-29 cells, total cell lysates were immunoblotted with an antibody specific for IGF-IRß. Two bands with Mr 95,000 (mature IGF-IR ß-subunit) and 200,000 (IGF-IR precursor) were detected. Treatment of HT-29 cells with increasing concentrations of CLA led to decreased mature IGF-IR levels but increased IGF-IR precursors (Fig. 3A). To determine whether CLA regulates the expression of IGF-IR at a transcriptional level, mRNA levels were determined by RT-PCR analysis. CLA decreased IGF-IR transcripts (Fig. 3B).
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25% in cells treated with 20 µmol/L of CLA (P < 0.05). IGF-I similarly induced IGF-IR activation but to a lesser degree in cells treated with CLA (P < 0.05) indicating the ability to respond to the stimulation of IGF-I. Thus CLA appeared to negatively regulate IGF-IR phosphorylation by causing a decrease in the expression levels of this signaling protein.
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IGF-I–induced activation of PI3K and Akt is inhibited by CLA.
Expression of the p85 regulatory subunit of PI3K in HT-29 cells treated with increasing amounts of CLA was examined by the use of immunoblotting. Whereas decreased levels of mature IGF-IR were detected (Fig. 3A), expression of PI3K was not altered by addition of CLA (data not shown). CLA influences on the IGF-I–induced association of IGF-IR and PI3K were determined by the use of immunoprecipitation with an anti-IGF-IR antibody followed by immunoblotting with the p85 antibody. IGF-I stimulated the association of the p85 regulatory subunit of PI3K with IGF-IR, and the association was reduced in CLA-treated cells (Table 2). The levels of PI3K associated with IGF-IR were normalized to that of IGF-IR expression to determine whether the reduced association after CLA treatment was a result of decreased IGF-IR levels or of an inhibition of p85 recruitment. After normalization and addition of CLA, the reduced association was not evident (Table 2) indicating that the decrease in PI3K association to IGF-IR was a result of decreased IGF-IR levels but not of an inhibition of p85 recruitment.
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To examine the effect of CLA on the ERK subfamily of MAPK, Western blotting was performed with the total lysates prepared from cells treated with or without 20 µmol/L of CLA and/or 10 nmol/L of IGF-I as described above using antibodies specific for ERK-1/2 and p-ERK-1/2. IGF-I activation of IGF-IR signaling resulted in a time-dependent increase in ERK phosphorylation in HT-29 cells. Phosphorylated ERK levels were increased at 5 min after IGF-I stimulation but the magnitude of the increase was much smaller compared with that of p-Akt. Both basal and IGF-I-induced p-ERK levels were markedly decreased by 20 µmol/L of CLA. Total ERK levels also decreased after CLA treatment (Fig. 7).
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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This study provided the first evidence that CLA reduces IGF-IR protein expression and IGF-IR-mediated signaling, which is consistent with the finding that CLA blunts the effect of exogenous IGF-I on HT-29 cell growth. When HT-29 cells were incubated with IGF-I or IGF-II in serum-free medium, the cells responded by increasing in number. However, treatment of HT-29 cells with 20 µmol/L of CLA for 96 h completely inhibited the IGF-I–induced increase in cell number, suggesting that CLA attenuated the IGF-IR signaling pathway. Indeed, decreased levels of the IGF-IR were noted at 72 h after treatment with CLA. The autocrine production of IGF-IR–binding ligands, IGF by tumor cells or the tumor-induced production of ligands by surrounding stromal cells has also been implicated in IGF-IR-mediated tumor growth (10). The expression of IGF-II in HT-29 cells was also decreased by CLA, and IGF-II is an autocrine growth regulator of HT-29 cells (26). Therefore, it is likely that CLA inhibits HT-29 cell growth by limiting the production of this growth factor and the ability to respond to IGF-II. The effect of CLA was specific for the IGF system because no effect of CLA on other important proteins (e.g., IRS-1, p85, PTEN, p-PTEN, PDK-1, and p-PDK-1) in these cells was observed.
In addition to autocrine/paracrine effects, IGF has been reported to exert an effect on colon cancer by an endocrine mechanism. Long-term prospective studies have clearly shown that high circulating levels of IGF-I and low levels of IGFBP-3 are associated with a higher risk of developing colorectal cancer (27,28). A recent case-control study in Northern Sweden has also shown a positive relationship between the levels of plasma IGF-I and colon cancer risk (29). Studies utilizing liver-specific IGF-I–deficient mice have shown that circulating IGF-I levels regulate colon cancer growth and metastasis (30). CLA could decrease IGF-I production in the liver and other tissues and thereby reduce serum levels of IGF, which could be one of the mechanisms by which CLA reduces colon tumor incidence in animals. Future studies are needed to determine whether dietary CLA reduces serum IGF levels in animals.
CLA decreased IGF-II and IGF-IR mRNA levels suggesting that CLA regulated the expression of these proteins at the transcriptional level. The present study did not determine the mechanisms responsible for the CLA regulation of these transcript levels. CLA has been reported to be an activator of the peroxisome proliferator-activated receptor (PPAR) (31). CLA or its metabolites may influence transcription of genes that regulate growth by acting as a ligand for the PPAR. Ligands for PPAR induce apoptosis and exert antiproliferative effects on several carcinoma cell lines (32,33). The two promoters of the IGF-II gene, P3 and P4, each contains several putative peroxisome proliferator response elements. It remains to be determined whether CLA inhibits expression of IGF-II and IGF-IR transcripts by activating PPAR. In addition to reduced IGF-IR transcripts by CLA, we observed that CLA increased pro IGF-IR levels indicating that CLA also regulates the expression of this protein at the post translational level.
Activation of the IGF-IR requires tyrosine phosphorylation of the ß-subunits of the receptor. CLA decreased the protein levels of the mature IGF-I receptor in HT-29 cells in a dose-dependent manner. IGF-I induced tyrosine phosphorylation of the IGF-IR in cells treated with CLA but the degree of the phosphorylation was lower in CLA-treated cells. CLA decreased IGF-IR levels and phosphorylation to a similar degree, suggesting that CLA inhibited activation of these receptors by decreasing receptor protein levels. In addition we observed that IGF-I stimulated the recruitment of PI3K to the IGF-I receptor, and CLA decreased IGF-IR–associated PI3K protein levels and PI3K activities. These decreases do not appear to be attributed to changes in either the PI3K protein expression or p85 recruitment but rather a result of the decrease in IGF-IR protein levels.
Akt is a downstream target of PI3K and the PI3K/Akt pathway has recently been recognized as one of the most important signals ensuring protection against apoptosis (34). The present data showed that CLA inhibited IGF-I–induced activation of Akt, which could have been due to decreased IGF-IR levels and the subsequent decrease in IGF-IR activation. The moderate decrease in Akt protein levels may also have contributed to the decreased p-Akt levels. In addition to p-Akt, p-ERK-1/2 levels were decreased in CLA-treated cells, a result of both decreased total ERK-1/2 levels and protein phosphorylation. These results implied that CLA inhibited DNA synthesis and induced apoptosis of HT-29 cells by inhibiting the Akt and MAPK signaling pathways. Increased expression of the IGF-IR and downstream signaling proteins such as Akt and ERK are frequent events in cancer. Future studies are needed to study the effect of Akt and ERK on HT-29 cell growth.
In conclusion, we demonstrated that CLA negatively regulated levels of IGF-II and mature IGF-IR and subsequent activation of Akt and MAPK pathways in HT-29 cells. Inhibition of IGF-I receptor signaling may be one of the mechanisms by which CLA inhibits cancer cell growth. The activation of the IGF-I/IGF-IR system has recently been shown to be a critical event in the development of several murine and human tumors. The results reported herein indicate that inhibition of Akt phosphorylation may be a major mechanism by which CLA inhibits IGF-IR signaling and cell proliferation and induces apoptosis.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: BSA, bovine serum albumin; CLA, conjugated linoleic acid; ERK, extracellular signal-regulated kinase; FBS, fetal bovine serum; HRP, horseradish peroxidase; IGF, insulin-like growth factor; IGFBP, IGF-binding proteins; IGF-IR, insulin-like growth factor-I receptor; IRS, insulin-receptor substrate; MAPK, mitogen-activated protein kinase; MTT, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide; PDK, phosphoinositide-dependent protein kinase; PIP, phosphatidylinositol 3-phosphate; PI3K, phosphatidylinositol 3-kinase; PKB, protein kinase B; PPAR, peroxisome proliferator-activated receptor; SDS, sodium dodecyl sulfate; PTEN, phosphatase and tensin homologue deleted on chromosome ten.
Manuscript received 14 March 2003. Initial review completed 1 April 2003. Revision accepted 29 April 2003.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Belury, M. A. (2002) Inhibition of carcinogenesis by conjugated linoleic acid: potential mechanisms of action. J. Nutr. 132:2995-2998.
2. Jones, J. I. & Clemmons, D. R. (1995) Insulin-like growth factors and their binding proteins: biological actions. Endocrine Rev. 16:3-34.[Medline]
3. Baserga, R., Hongo, A., Rubini, M., Prisco, M. & Valentinis, B. (1997) The IGF-I receptor in cell growth, transformation and apoptosis. Biochim. Biophys. Acta. 1332:F105-F126.[Medline]
4. Dupont, J. & LeRoith, D. (2001) Insulin and insulin-like growth factor I receptors: similarities and differences in signal transduction. Horm. Res. 55(Suppl 2):22-26.
5. Le Roith, D., Bondy, C., Yakar, S., Liu, J. L. & Butler, A. (2001) The somatomedin hypothesis: 2001. Endocr. Rev. 22:53-74.
6. Boguski, M. S. & McCormick, F. (1993) Proteins regulating Ras and its relatives. Nature 366:643-654.[Medline]
7. Kandel, E. S. & Hay, N. (1999) The regulation and activities of the multifunctional serine/threonine kinase Akt/PKB. Exp. Cell Res. 253:210-229.[Medline]
8. Parrizas, M., Saltiel, A. R. & LeRoith, D. (1997) Insulin-like growth factor 1 inhibits apoptosis using the phosphatidylinositol 3'-kinase and mitogen-activated protein kinase pathways. J. Biol. Chem. 272:154-161.
9. Baserga, R. (1999) The IGF-I receptor in cancer research. Exp. Cell Res. 253:1-6.[Medline]
10. Weber, M. M., Fottner, C., Liu, S. B., Jung, M. C., Engelhardt, D. & Baretton, G. B. (2002) Overexpression of the insulin-like growth factor I receptor in human colon carcinomas. Cancer 95:2086-2095.[Medline]
11. Guo, Y., Narayan, S., Yallampalli, C. & Singh, P. (1992) Characterization of insulinlike growth factor I receptors in human colon cancer. Gastroenterology 102:1101-1108.[Medline]
12. Remacle-Bonnet, M. M., Garrouste, F. L., Heller, S., Andre, F., Marvaldi, J. L. & Pommier, G. J. (2000) Insulin-like growth factor-I protects colon cancer cells from death factor-induced apoptosis by potentiating tumor necrosis factor alpha-induced mitogen-activated protein kinase and nuclear factor kappaB signaling pathways. Cancer Res 60:2007-2017.
13. Zhang, L., Zhou, W., Velculescu, V. E., Kern, S. E., Hruban, R. H., Hamilton, S. R., Vogelstein, B. & Kinzler, K. W. (1997) Gene expression profiles in normal and cancer cells. Science 276:1268-1272.
14. Park, H. S., Ryu, J. H., Ha, Y. L. & Park, J.H.Y. (2001) Dietary conjugated linoleic acid (CLA) induces apoptosis of colonic mucosa in 1, 2-dimethylhydrazine-treated rats: a possible mechanism of the anticarcinogenic effect by CLA. Br. J. Nutr. 86:549-555.[Medline]
15. Cho, H. J., Kim, W. K., Kin, E. J., Jung, K. C., Park, S., Lee, H. S., Tyner, A. L. & Park, J.H.Y. (2003) Conjugated linoleic acid inhibits cell proliferation and ErbB3 signaling in the HT-29 human colon cancer cell line. Am. J. Physiol Gastrointest. Liver Physiol. 284:G996-G1005.
16. Oh, Y. S., Kim, E. J., Schaffer, B. S., Kang, Y. H., Binderup, L., MacDonald, R. G. & Park, J. H. (2001) 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. Mol. Cell. Endocrinol. 183:141-149.[Medline]
17. Pommier, G. J., Garrouste, F. L., el Atiq, F., Roccabianca, M., Marvaldi, J. L. & Remacle-Bonnet, M. M. (1992) Potential autocrine role of insulin-like growth factor II during suramin-induced differentiation of HT29–D4 human colonic adenocarcinoma cell line. Cancer Res 52:3182-3188.
18. Pariza, M. W., Ha, Y. L., Benjamin, H., Sword, J. T., Gruter, A., Chin, S. F., Storkson, J., Faith, N. & Albright, K. (1991) Formation and action of anticarcinogenic fatty acids. Adv. Exp. Med. Biol. 289:269-272.[Medline]
19. Kim, E. J., Kim, W. Y., Kang, Y. H., Ha, Y. L., Bach, L. & Park, J.H.Y. (2000) Inhibition of Caco-2 cell proliferation by (n-3) fatty acids: possible mediation by increased secretion of insulin-like growth factor binding protein-6. Nutr. Res. 20:1409-1421.
20. Kim, E. J., Holthuizen, P. E., Park, H. S., Ha, Y. L., Jung, K. C. & Park, J. H. Y. (2002) Trans-10, cis-12 conjugated linoleic acid inhibits Caco-2 colon cancer cell growth. Am. J. Physiol. Gastrointest. Liver Physiol. 283:G357-G367.
21. Kwon, Y. H., Jovanovic, A., Serfas, M. S., Kiyokawa, H. & Tyner, A. L. (2002) P21 functions to maintain quiescence of p27-deficient hepatocytes. J. Biol. Chem. 277:41417-41422.
22. Gu, C. & Park, S. (2001) The EphA8 receptor regulates integrin activity through p110gamma phosphatidylinositol-3 kinase in a tyrosine kinase activity-independent manner. Mol. Cell. Biol. 21:4579-4597.
23. O’Shea, M., Stanton, C. & Devery, R. (1999) Antioxidant enzyme defence responses of human MCF-7 and SW480 cancer cells to conjugated linoleic acid. Anticancer Res 19:1953-1959.[Medline]
24. Palombo, J. D., Ganguly, A., Bistrian, B. R. & Menard, M. P. (2002) The antiproliferative effects of biologically active isomers of conjugated linoleic acid on human colorectal and prostatic cancer cells. Cancer Lett 177:163-172.[Medline]
25. Shultz, T. D., Chew, B. P., Seaman, W. R. & Luedecke, L. O. (1992) Inhibitory effect of conjugated dienoic derivatives of linoleic acid and beta-carotene on the in vitro growth of human cancer cells. Cancer Lett 63:125-133.[Medline]
26. Lahm, H., Amstad, P., Wyniger, J., Yilmaz, A., Fischer, J. R., Schreyer, M. & Givel, J. C. (1994) Blockade of the insulin-like growth factor-I receptor inhibits growth of human colorectal cancer cells: evidence of a functional IGF-II-mediated autocrine loop. Int J. Cancer 58:452-459.[Medline]
27. Ma, J., Pollak, M. N., Giovannucci, E., Chan, J. M., Tao, Y., Hennekens, C. H. & Stampfer, M. J. (1999) Prospective study of colorectal cancer risk in men and plasma levels of insulin-like growth factor (IGF)-I and IGF-binding protein-3 [see comments]. J. Natl. Cancer. Inst. 91:620-625.
28. Giovannucci, E., Pollak, M. N., Platz, E. A., Willett, W. C., Stampfer, M. J., Majeed, N., Colditz, G. A., Speizer, F. E. & Hankinson, S. E. (2000) A prospective study of plasma insulin-like growth factor-1 and binding protein-3 and risk of colorectal neoplasia in women. Cancer Epidemiol. Biomarkers Prev. 9:345-349.
29. Palmqvist, R., Hallmans, G., Rinaldi, S., Biessy, C., Stenling, R., Riboli, E. & Kaaks, R. (2002) Plasma insulin-like growth factor 1, insulin-like growth factor binding protein 3, and risk of colorectal cancer: a prospective study in northern Sweden. Gut 50:642-646.
30. Wu, Y., Yakar, S., Zhao, L., Hennighausen, L. & LeRoith, D. (2002) Circulating insulin-like growth factor-I levels regulate colon cancer growth and metastasis. Cancer Res 62:1030-1035.
31. Yu, Y., Correll, P. H. & Vanden Heuvel, J. P. (2002) Conjugated linoleic acid decreases production of pro-inflammatory products in macrophages: evidence for a PPAR gamma-dependent mechanism. Biochim Biophys. Acta 1581:89-99.[Medline]
32. Elstner, E., Muller, C., Koshizuka, K., Williamson, E. A., Park, D., Asou, H., Shintaku, P., Said, J. W., Heber, D. & Koeffler, H. P. (1998) Ligands for peroxisome proliferator-activated receptorgamma and retinoic acid receptor inhibit growth and induce apoptosis of human breast cancer cells in vitro and in BNX mice. Proc. Natl. Acad. Sci. USA 95:8806-8811.
33. Kubota, T., Koshizuka, K., Williamson, E. A., Asou, H., Said, J. W., Holden, S., Miyoshi, I. & Koeffler, H. P. (1998) Ligand for peroxisome proliferator-activated receptor gamma (troglitazone) has potent antitumor effect against human prostate cancer both in vitro and in vivo. Cancer Res 58:3344-3352.
34. Franke, T. F., Kaplan, D. R. & Cantley, L. C. (1997) PI3K: downstream AKTion blocks apoptosis. Cell 88:435-437.[Medline]
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 H. J. Cho, E. J. Kim, S. S. Lim, M. K. Kim, M.-K. Sung, J.-S. Kim, and J. H. Y. Park Trans-10,cis-12, Not cis-9,trans-11, Conjugated Linoleic Acid Inhibits G1-S Progression in HT-29 Human Colon Cancer Cells J. Nutr., April 1, 2006; 136(4): 893 - 898. [Abstract] [Full Text] [PDF]
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S. C. Degner, M. Q. Kemp, G. T. Bowden, and D. F. Romagnolo Conjugated Linoleic Acid Attenuates Cyclooxygenase-2 Transcriptional Activity via an Anti-AP-1 Mechanism in MCF-7 Breast Cancer Cells J. Nutr., February 1, 2006; 136(2): 421 - 427. [Abstract] [Full Text] [PDF]
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X. Lu, J. i. Jung, H. J. Cho, D. Y. Lim, H. S. Lee, H. S. Chun, D. Y. Kwon, and J. H. Park Fisetin Inhibits the Activities of Cyclin-Dependent Kinases Leading to Cell Cycle Arrest in HT-29 Human Colon Cancer Cells J. Nutr., December 1, 2005; 135(12): 2884 - 2890. [Abstract] [Full Text] [PDF]
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