PubMed Health⌕ Search

Biomedical subjects

D Yee

Publications and source records attributed to D Yee.

At least 37 records · Page 2Linked to original sources
PubMed2000

Insulin-like growth factor I-induced degradation of insulin receptor substrate 1 is mediated by the 26S proteasome and blocked by phosphatidylinositol 3'-kinase inhibition.

Insulin receptor substrate 1 (IRS-1) is a critical adapter protein involved in both insulin and insulin-like growth factor (IGF) signaling. Due to the fact that alteration of IRS-1 levels can affect the sensitivity and response to both insulin and IGF-I, we examined the ability of each of these ligands to affect IRS-1 expression. IGF-I (10 nM) stimulation of MCF-7 breast cancer cells caused a transient tyrosine phosphorylation of IRS-1 that was maximal at 15 min and decreased thereafter. The decrease in tyrosine phosphorylation of IRS-1 was paralleled by an apparent decrease in IRS-1 levels. The IGF-mediated decrease in IRS-1 expression was posttranscriptional and due to a decrease in the half-life of the IRS-1 protein. Insulin (10 nM) caused tyrosine phosphorylation of IRS-1 but not degradation, whereas high concentrations of insulin (10 microM) resulted in degradation of IRS-1. IGF-I (10 nM) stimulation resulted in transient IRS-1 phosphorylation and extracellular signal-related kinase (ERK) activation. In contrast, insulin (10 nM) caused sustained IRS-1 phosphorylation and ERK activation. Inhibition of 26S proteasome activity by the use of lactacystin or MG132 completely blocked IGF-mediated degradation of IRS-1. Furthermore, coimmunoprecipitation experiments showed an association between ubiquitin and IRS-1 that was increased by treatment of cells with IGF-I. Finally, IGF-mediated degradation of IRS-1 was blocked by inhibition of phosphatidylinositol 3'-kinase activity but was not affected by inhibition of ERK, suggesting that this may represent a direct negative-feedback mechanism resulting from downstream IRS-1 signaling. We conclude that IGF-I can cause ligand-mediated degradation of IRS-1 via the ubiquitin-mediated 26S proteasome and a phosphatidylinositol 3'-kinase-dependent mechanism and that control of degradation may have profound effects on downstream activation of signaling pathways.

Animals↗
PubMed2000

Elevated levels of p66 Shc are found in breast cancer cell lines and primary tumors with high metastatic potential.

The adapter molecule Shc has been implicated in specific steps of metastasis. In the current study, we show that the expression and activation of the p66 Shc isoform increased in a highly metastatic variant (F-11) of the human breast cancer cell line MDA-MB-231 compared to the parent cell line, whereas the p46 and p52 Shc isoforms were unchanged. Despite reports that p66 Shc can negatively regulate epidermal growth factor signaling to the mitogen-activated protein kinase pathway, we found no change in epidermal growth factor-stimulated activation of mitogen-activated protein kinase in the F-11 cell line. We determined the level of Shc expression by immunoblot in primary breast cancer specimens obtained from patients with or without axillary node involvement. p66 Shc expression increased in tumors obtained from node-positive patients (Spearman correlation coefficient = 0.43377; P = 0.0058) compared to the node-negative specimens. Furthermore, increasing levels of p66 Shc correlated with an increasing number of positive nodes (P = 0.032). This study shows that p66 Shc expression increased in cultured breast cancer cells selected for metastasis and in primary human breast cancer specimens obtained from patients with lymph node involvement, suggesting a possible role for Shc in human breast cancer metastasis.

Adaptor Proteins, Signal Transducing↗
PubMed2000

The role of p21 in interferon gamma-mediated growth inhibition of human breast cancer cells.

IFN-gamma-mediated growth inhibition requires signal transducers and activators of transcription (STAT)-1 activation and may require induction of the cyclin-dependent kinase inhibitor p21. Using an electrophoretic mobility shift assay, we identified STAT1 activation after IFN-gamma treatment in breast cancer cell lines. Accordingly, IFN-gamma inhibited proliferation of monolayer cultured MCF-7 and MDA-MB-231 breast cancer cells. Interestingly, IFN-gamma inhibited anchorage-independent growth of MCF-7 cells but had no effect on MDA-MB-231 colony formation. Because p21 has been shown to play a role in anchorage-independent growth and is a transcriptional target of STAT1, we examined the effect of IFN-gamma on p21 mRNA. We found that IFN-gamma induced p21 mRNA in MCF-7 cells but not in MDA-MB-231 cells. Furthermore, IFN-gamma induced activation of a p21 promoter-luciferase reporter construct that contained the STAT1-inducible element in MCF-7 cells, but not in MDA-MB-231 cells. IFN-gamma treatment resulted in increased p21 protein in MCF-7 cells, whereas MDA-MB-231 cells did not appear to express detectable p21, even after IFN-gamma treatment. However, in MDA-MB-231 cells, p21 protein was detected only after proteosome inhibition, suggesting that degradation may be responsible for the undetectable level of p21 in these cells, despite the abundant mRNA levels. Finally, focus formation of MDA-MB-231 cells was inhibited by overexpression of p21. In conclusion, STAT1 activation does not appear to be sufficient for IFN-gamma-mediated growth inhibition. Furthermore, the role of p21 appears to be complex because monolayer growth inhibition occurs in the absence of p21, but anchorage-independent growth inhibition may require p21. Breast cancer cells may provide a unique model for further study of IFN-gamma signaling.

Blotting, Western↗
PubMed1999

Strain-specific differences in formation of apoptotic DNA ladders in MCF-7 breast cancer cells.

We tested the ability of seven MCF-7 strains to undergo DNA fragmentation, as measured by DNA laddering, following doxorubicin-induced apoptosis. Four strains were found to undergo DNA laddering while three were not. All strains were inhibited by doxorubicin, although sensitivity differed. Finally, we show by detection of sub-G1 DNA that doxorubicin induced the same fold increase in apoptosis in MCF-7-ATCC, which did not ladder, and MCF-7-MG, which did ladder. Therefore, detection of DNA ladders is not an accurate indicator of apoptosis in MCF-7 cells as fragmentation of DNA appears to vary between strains.

Apoptosis↗
PubMed1999

Insulin-like growth factor (IGF)-I rescues breast cancer cells from chemotherapy-induced cell death--proliferative and anti-apoptotic effects.

Insulin-like growth factor (IGF)-I protects many cell types from apoptosis. As a result, it is possible that IGF-I-responsive cancer cells may be resistant to apoptosis-inducing chemotherapies. Therefore, we examined the effects of IGF-I on paclitaxel and doxorubicin-induced apoptosis in the IGF-I-responsive breast cancer cell line MCF-7. Both drugs caused DNA laddering in a dose-dependent fashion, and IGF-I reduced the formation of ladders. We next examined the effects of IGF-I and estradiol on cell survival following drug treatment in monolayer culture. IGF-I, but not estradiol, increased survival of MCF-7 cells in the presence of either drug. Cell cycle progression and counting of trypan-blue stained cells showed that IGF-I was inducing proliferation in paclitaxel-treated but not doxorubicin-treated cells. However, IGF-I decreased the fraction of apoptotic cells in doxorubicin- but not paclitaxel-treated cells. Recent work has shown that mitogen-activated protein kinase (MAPK) and phosphotidylinositol-3 (PI-3) kinase are activated by IGF-I in these cells. PI-3 kinase activation has been linked to anti-apoptotic functions while MAPK activation is associated with proliferation. We found that IGF-I rescue of doxorubicin-induced apoptosis required PI-3 kinase but not MAPK function, suggesting that IGF-I inhibited apoptosis. In contrast, IGF-I rescue of paclitaxel-induced apoptosis required both PI-3 kinase and MAPK, suggesting that IGF-I-mediated protection was due to enhancement of proliferation. Therefore, IGF-I attenuated the response of breast cancer cells to doxorubicin and paclitaxel by at least two mechanisms: induction of proliferation and inhibition of apoptosis. Thus, inhibition of IGF-I action could be a useful adjuvant to cytotoxic chemotherapy in breast cancer.

Antineoplastic Agents, Phytogenic↗
PubMed1999

IRS-1 expression and activation are not sufficient to activate downstream pathways and enable IGF-I growth response in estrogen receptor negative breast cancer cells.

IGF-responsive breast cancer cells activate insulin receptor substrate (IRS)-1 after IGF-I treatment. To determine if IRS-1 expression was sufficient to enable IGF-responsiveness, two IGF-I unresponsive breast cancer cell lines (MDA-MB-435A and MDA-MB-468) were transfected with IRS-1. While IGF-I caused tyrosine phosphorylation of IRS-1 in both transfected cell lines, increased MAP kinase activity was not seen. IGF-I treatment of 435A IRS-1 transfected cells resulted in minimal increased PI3 kinase activity associated with IRS-1, while IRS-2/PI3 kinase was greatly reduced. In MDA-MB-468 IRS-1 transfected cells, IGF-I caused increased IRS-1 associated PI3 kinase activity compared to parental cells, but at levels far below those observed in IGF-responsive MCF-7 cells. The transfected cells were also not responsive to IGF-I in monolayer growth. Thus, IRS-1 expression and activation alone are insufficient to mediate a proliferative response to IGF-I in breast cancer cells, and it is likely that maximal activation of downstream signaling pathways must also occur.

Animals↗
PubMed1999

FKHR binds the insulin response element in the insulin-like growth factor binding protein-1 promoter.

The insulin response element (IRE) in the IGFBP-1 promoter, and in other gene promoters, contains a T(A/G)TTT motif essential for insulin inhibition of transcription. Studies presented here test whether FKHR may be the transcription factor that confers insulin inhibition through this IRE motif. Immunoblots using antiserum to the synthetic peptide FKHR413-430, RNase protection, and Northerns blots show that FKHR is expressed in HEP G2 human hepatoma cells. Southwestern blots, electromobility shift assays, and DNase I protection assays show that Escherichia coli-expressed GST-FKHR binds specifically to IREs from the IGFBP-1, PEPCK and TAT genes; however, unlike HNF3beta, another protein proposed to be the insulin regulated factor, GST-FKHR does not bind the insulin unresponsive G/C-A/C mutation of the IGFBP-1 IRE. When HEP G2 cells were cotransfected with FKHR expression vectors and with IGFBP-1 promoter plasmids containing either native or mutant IREs, FKHR expression induced a 5-fold increase in activity of the native IGFBP-1 promoter but no increase in activity of promoter constructs containing insulin unresponsive IRE mutants. These data suggest that FKHR, and/or a related family member, is the important T(G/A)TTT binding protein that confers the inhibitory effect of insulin on gene transcription.

DNA-Binding Proteins↗
PubMed1999

Enhancement of insulin-like growth factor signaling in human breast cancer: estrogen regulation of insulin receptor substrate-1 expression in vitro and in vivo.

Cross-talk between insulin-like growth factor (IGF)- and estrogen receptor (ER)-signaling pathways results in synergistic growth. We show here that estrogen enhances IGF signaling by inducing expression of three key IGF-regulatory molecules, the type 1 IGF receptor (IGFR1) and its downstream signaling molecules, insulin receptor substrate (IRS)-1 and IRS-2. Estrogen induction of IGFR1 and IRS expression resulted in enhanced tyrosine phosphorylation of IRS-1 after IGF-I stimulation, followed by enhanced mitogen-activated protein kinase activation. To examine whether these pathways were similarly activated in vivo, we examined MCF-7 cells grown as xenografts in athymic mice. IRS-1 was expressed at high levels in estrogen-dependent growth of MCF-7 xenografts, but withdrawal of estrogen, which decreased tumor growth, resulted in a dramatic decrease in IRS-1 expression. Finally, we have shown that high IRS-1 expression is an indicator of early disease recurrence in ER-positive human primary breast tumors. Taken together, these data not only reinforce the concept of cross-talk between IGF- and ER-signaling pathways, but indicate that IGF molecules may be critical regulators of estrogen-mediated growth and breast cancer pathogenesis.

Animals↗
PubMed1998

Interleukin 4 inhibits growth and induces apoptosis in human breast cancer cells.

Interleukin-4 (IL-4) is a pleiotropic cytokine produced by mast cells and T lymphocytes that promotes proliferation and immunoglobulin class-switching in B cells. IL-4 receptors (IL-4Rs) are also expressed by nonhematopoietic cells as well as some tumor cells. Unlike its mitogenic effect on B cells, IL-4 inhibits the growth of some cancer cells in vitro. In this study, we show that IL-4R is expressed by breast and ovarian cancer cell lines. Furthermore, anchorage-dependent and -independent growth of breast cancer cell lines MCF-7 and MDA-MB-231 is inhibited by IL-4 treatment, and this effect requires IL-4R. Interestingly, IL-4 only inhibited proliferating breast cancer cells and had no effect on basal, unstimulated growth. We therefore characterized the effect of IL-4 on breast cancer cell growth stimulated by either estradiol or insulin-like growth factor I (IGF-I). In both anchorage-dependent and -independent growth assays, IL-4 inhibited estradiol-stimulated growth. The antiestrogen effect of IL-4 was not due to IL-4 interference with the estrogen receptor, because IL-4 did not interfere with estrogen receptor-mediated reporter gene transactivation. In contrast, IL-4 had no effect on IGF-I-stimulated proliferation. Because IGF-I is known to inhibit programmed cell death, we examined apoptosis as a possible mechanism of IL-4 action. We established that IL-4 induced apoptosis in breast cancer cells by five independent criteria: (a) morphological indicators including pyknotic nuclei and cytoplasmic condensation; (b) DNA fragmentation; (c) the formation of DNA laddering; (d) the cleavage of poly(ADP-ribose) polymerase; and (e) the presence of cells with sub-G1 DNA content. IL-4 increased the percentage of apoptotic cells in MCF-7 and MDA-MB-231 cells 6.0- and 6.7-fold over that of the control, respectively. Finally, the addition of IGF-I reversed IL-4-induced apoptosis, suggesting that the mechanism of IL-4-induced growth inhibition in human breast cancer cells is the induction of programmed cell death.

Antineoplastic Agents, Phytogenic↗
PubMed1998

Insulin receptor substrate-1 is the predominant signaling molecule activated by insulin-like growth factor-I, insulin, and interleukin-4 in estrogen receptor-positive human breast cancer cells.

Because insulin-like growth factor-I (IGF-I), insulin, and interleukin-4 (IL-4) have known biological effects in breast cancer cells and signal through insulin-receptor substrate (IRS) adaptor proteins, we examined the expression and function of IRS-1 and IRS-2 in breast tumors and cell lines. IRS-1 and IRS-2 were expressed by cell lines and primary breast tumor specimens. IGF-I, insulin, and IL-4 treatment of MCF-7 and ZR-75, and IGF-I treatment of T47-D breast cancer cells, resulted in much greater tyrosine phosphorylation of IRS-1 compared with IRS-2. Furthermore, IGF-I stimulated greater tyrosine phosphorylation of IRS-1 than either insulin or IL-4. IGF-I treatment also enhanced association of the p85 regulatory subunit of phosphatidylinositol 3-kinase with IRS-1 and stimulated increased enzymatic activity compared with IL-4 and insulin in all three cell lines. Similarly, mitogen-activated protein kinase activity was greater in IGF-I-stimulated cells. To determine the functional significance of the activation of these pathways, we inhibited activation of phosphatidylinositol 3-kinase with wortmannin and mitogen-activated protein kinase with PD098059. Both compounds inhibited IGF-stimulated growth, suggesting that both pathways contributed to the mitogenic response to IGF-I. We conclude that IRS-1, and not IRS-2, is the predominant signaling molecule activated by IGF-I, insulin, and IL-4. Furthermore, enhanced tyrosine phosphorylation of IRS-1 by IGF-I, compared with either insulin or IL-4, is associated with greater activation of mitogenic downstream signaling pathways resulting in enhanced cell growth.

Androstadienes↗
PubMed1998

IGF system components as prognostic markers in breast cancer.

The insulin-like growth factor (IGF) family of ligands, receptors, and binding proteins can regulate breast cancer cell proliferation in vitro, and interruption of these pathways inhibits IGF-mediated cell proliferation. If the IGF family members are key regulators of breast cancer growth and progression in vivo, we would expect their expression to be an indicator of the prognosis of the disease. Thus, measurement of IGF expression may provide an indicator of the growth effect within a tumor, and provide new targets for treatment of the disease. In this review we will summarize the data generated thus far indicating that IGF family members are indicators of prognosis of breast cancer, and that measurement of the whole IGF family in concert may provide useful information for treatment strategies of breast cancer.

Breast Neoplasms↗
PubMed1998

The insulin-like growth factors and breast cancer--revisited.

In 1992, a special issue of Breast Cancer Research and Treatment was devoted to the insulin-like growth factors and breast cancer. In that issue, identification of the key components of the IGF system was reviewed and their potential role in breast cancer growth was described. In this issue, we revisit the IGF system with particular attention to data that further supports their role in the growth regulation of breast cancer. Several new facets of the IGF system are described, and several laboratories have more clearly defined how each individual component of the IGF system may influence breast cancer biology.

Breast Neoplasms↗
PubMed1998

Modulation of the insulin-like growth factor-I system by N-(4-hydroxyphenyl)-retinamide in human breast cancer cell lines.

The potent mitogenic activity of insulin-like growth factor I (IGF-I) on breast epithelium is inhibited by retinoic acid in oestrogen receptor-positive (ER+) breast cancer cell lines. We studied and compared the effects of N-(4-hydroxyphenyl)-retinamide (4-HPR) in terms of growth inhibition and modulation of the IGF-I system in ER+ (MCF-7) and oestrogen receptor-negative (ER-) (MDA-MB231) breast cancer cell lines. Treatment with 1-10 microM 4-HPR for up to 96 h induced a dose- and time-dependent inhibition of proliferation in both breast cancer cell lines. Induction of apoptosis was much more evident in MCF-7 than in MDA-MB231 cells (30-40% compared with 0-5% respectively at 5 microM for 48 h). Exogenous human recombinant IGF-I (hr-IGF-I)-stimulated cell proliferation was abolished by 1 microM 4-HPR in MCF-7 cells. Immunoreactive IGF-I-like protein concentration in conditioned medium was reduced by 38% in MCF-7 and by 90% in MDA-MB231 cell lines following treatment for 48 h with 5 microM 4-HPR. Western ligand blot analysis showed a reduction of IGF-binding protein 4 (BP4) and BP5 by 67% and 87%, respectively, in MCF-7, whereas IGF-BP4 and -BP1 were reduced by approximately 20% in MDA-MB231 cells. Exposure to 5 microM 4-HPR for 48 h inhibited [125I]IGF-I binding and Scatchard analysis revealed a decrease of more than 50% in maximum binding capacity (Bmax) and a reduced receptor number/cell in both cancer cell lines. Steady-state type I IGF-receptor mRNA levels were reduced by approximately 30% in both tumour cell lines. We conclude that 4-HPR induces a significant down-regulation of the IGF-I system in both ER+ (MCF-7) and ER- (MDA-MB231) breast cancer cell lines. These findings suggest that, in our model, interference with the ER signalling pathway is not the only mechanism of breast cancer growth inhibition by 4-HPR.

Antineoplastic Agents↗
PubMed1997

Cloning, chromosome localization, expression, and characterization of an Src homology 2 and pleckstrin homology domain-containing insulin receptor binding protein hGrb10gamma.

hGrb10alpha (previously named Grb-IR) is a Src-homology 2 domain-containing protein that binds with high affinity to the tyrosine-phosphorylated insulin receptor and insulin-like growth factor-1 receptor. At least two isoforms of human Grb10, (hGrb10alpha and hGrb10beta), which differ in the pleckstrin homology (PH) domain and the N-terminal sequence, have previously been identified in insulin target tissues such as human skeletal muscle and fat cells. Here we report the cloning of the third isoform of the hGrb10 family (hGrb10gamma) from human skeletal muscle and its localization to human chromosome 7. We have also determined the human chromosome localization of Grb7 to 17q21-q22 and Grb14 to chromosome 2. hGrb10gamma contains an intact PH domain and an N-terminal sequence that is present in hGrb10alpha but absent in hGrb10beta. RNase protection assays and Western blot analysis showed that hGrb10alpha and hGrb10gamma are differentially expressed in insulin target cells including skeletal muscle, liver, and adipocyte cells. hGrb10gamma is also expressed in HeLa cells and various breast cancer cell lines. The protein bound with high affinity to the insulin receptor in cells, and the interaction was dependent on the tyrosine phosphorylation of the receptor. hGrb10gamma also underwent insulin-stimulated membrane translocation and serine phosphorylation. hGrb10gamma phosphorylation was inhibited by PD98059, a specific inhibitor of mitogen-activated protein kinase kinase, and wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase. Taken together, our data suggest that hGrb10 isoforms are potential downstream signaling components of the insulin receptor tyrosine kinase and that the PH domain may play an important role in the involvement of these isoforms in signal transduction pathways initiated by insulin and other growth factors.

Amino Acid Sequence↗
PubMed1997

Genealogy of the 129 inbred strains: 129/SvJ is a contaminated inbred strain.

The 129 mouse is the most widely used strain in gene targeting experiments. However, numerous substrains exist with demonstrable physiological differences. In this study a set of simple sequence length polymorphisms (SSLPs) was used to determine the relatedness of selected 129 substrains. 129/SvJ was significantly different from the other 129 substrains and is more accurately classified as a recombinant congenic strain (129cX/Sv), being derived from 129/Sv and an unknown strain. This mixed genetic background could complicate gene targeting experiments by reducing homologous recombination efficiency when constructs and ES cells are not derived from the same 129 substrain. Additionally, discrepancies due to different genetic backgrounds may arise when comparing phenotypes of genes targeted in different 129-derived ES cell lines.

Agouti Signaling Protein↗
PubMed1997

Polyethylene glycol conjugated insulin-like growth factor binding protein-1 (IGFBP-1) inhibits growth of breast cancer in athymic mice.

Insulin-like growth factor (IGF) binding protein-1 (BP-1) inhibits IGF-mediated proliferation of some breast cancer cell lines in vitro. Here we examined whether recombinant human wild-type IGFBP-1 (WT-BP-1) and IGFBP-1 conjugated with polyethylene glycol (PEG-BP-1) could inhibit breast cancer growth. Three breast cancer cell lines were used: MCF-7, MDA-MB-231 and MDA-MB-435A (ascites model). The cells were grown in agar with or without the BP-1 conjugates to investigate their effect on colony formation. Both WT-BP-1 and PEG-BP-1 inhibited anchorage-independent growth (AIG) of MCF-7 and MDA-MB-435A cells. AIG of MDA-MB-231 cells was not inhibited by PEG-BP-1, whereas WT-BP-1 significantly stimulated colony number. We also tested both forms of BP-1 in xenograft tumour models. Two solid breast tumour models were studied using MCF-7 and MDA-MB-231 cell lines, and one ascites model using the MDA-MB-435A cell line. PEG-BP-1 inhibited malignant ascites formation in the MDA-MB-435A model. Conversely, PEG-BP-1 did not significantly inhibit MCF-7 xenograft growth. However, the MDA-MB-231 tumour growth curves were significantly different by a constant amount, suggesting that PEG-BP-1 treatment inhibited early tumour growth of this cell line. In contrast, WT-BP-1 was ineffective in the MDA-MB-231 tumours. These data show that anti-IGF strategies can be used to inhibit breast cancer cell growth. Since PEG-BP-1 inhibited the in vivo, but not in vitro, growth of MDA-MB-231, we speculate that PEG-BP-1 may block host IGF functions required for optimal tumorigenesis. Because PEG-BP-1 has a prolonged serum half-life compared to WT-BP-1, we conclude that improvements in BP-1 pharmacological properties enhanced its antitumour effects in vivo.

Analysis of Variance↗
PubMed1997

Activation of estrogen receptor-mediated gene transcription by IGF-I in human breast cancer cells.

Estrogen and IGF-I are potent mitogens for most breast cancer cell lines, and although their signaling pathways contrast, there is considerable interaction between them. Recent evidence indicating that IGF-I can alter estrogen receptor (ER) action led us to investigate whether an inhibitor of IGF-I action. IGF-binding protein-1 (IGFBP-1), could affect transcriptional activation of ER. First, we confirmed that tamoxifen (TAM) could inhibit IGF-I-mediated proliferation of MCF-7 cells. Although TAM can increase IGFBP-3 expression in MCF-7 cells, and this binding protein has been shown to be able to inhibit IGF action, TAM had no effect on IGF-I-stimulated tyrosine phosphorylation of IGF-I receptor or the downstream signaling molecule, insulin receptor substrate-1. Therefore, to confirm that IGF-I was affecting transcriptional activation of ER, we utilized a gene reporter assay using a single consensus estrogen response element (ERE-tk-luc) upstream of luciferase. As expected, estradiol (E2; 1nM) increased transcriptional activation three- to fivefold from the ERE in three ER-positive breast cancer cell lines (MCF-7, ZR-75 and T47D). A 2.5-to 4-fold increase was also seen with IGF-I (5 nM). TAM (1 microM) effectively blocked activation by E2 and IGF-I, indicating disruption of ER-mediated transcription. As expected, human recombinant IGFBP-1 (80 nM) completely inhibited IGF-I-mediated activation of ER, however, IGFBP-1 also caused a significant decrease in E2-mediated activation. We also noticed that IGF-I increased the activity of all plasmids that we cotransfected including TATA-luc, SV40-luc and pGL Basic. This effect was post-transcriptional, as it was not affected by actinomycin D (2 micrograms/ml), while we were able to completely inhibit E2-mediated transcriptional activation of ERE-tk-luc. Unlike the complete inhibition of ER-mediated transcriptional activation by actinomycin D, IGF-I-mediated transactivation was reduced by only 50%, indicating that the activation by IGF-I represented both transcriptional and post-transcriptional effects. This study confirmed that IGF-I can cause transcriptional activation of endogenous ER in human breast cancel cells, and inhibition of ER action by IGFBP-1 suggests that IGF-1 signaling may be necessary for maximal ER activation.

Breast Neoplasms↗