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PubMed1998

Binding characteristics of novel nonsteroidal antiestrogens to the rat uterine estrogen receptors.

Tamoxifen (TAM), the only antiestrogen currently available for the endocrine therapy of breast cancer behaves as a mixed agonist/antagonist of estrogen action, thus limiting its therapeutic potential. We report the binding characteristics of a novel series of nonsteroidal antiestrogens to the rat uterine estrogen receptor. As measured by competition studies, the affinity of EM-652, the active metabolite of the prodrug EM-800, for the estrogen receptor is 7-11 times higher than that of 17beta-estradiol (E2), ICI 182780, and hydroxy-tamoxifen (OH-TAM), the active metabolite of Tamoxifen. EM-652 is 20x more potent than ICI 164384 and Droloxifene while it is 400 times more potent than Toremifene in displacing [3H]E2 from the rat uterine estrogen receptor. On the other hand, the prodrug EM-800 and Tamoxifen have respectively 150-fold and 410-fold less affinity for the estrogen receptor than the pure antiestrogen EM-652. No significant binding of EM-652, EM-800, TAM or OH-TAM was observed to the rat uterine progesterone receptor at concentrations up to 10,000 nM except for TAM that caused a 50% displacement of labeled R5020 at 4000 nM. No significant binding of EM-652 or EM-800 was observed on the rat ventral prostate androgen receptor or the rat uterine progesterone receptor. The present data demonstrate the high affinity and specificity of the new antiestrogen, EM-652, for the rat uterine estrogen receptor. The antiestrogen EM-652 thus becomes the compound having the highest known affinity for the estrogen receptor. Due to its unique potency and its pure antiestrogenic activity already demonstrated in many systems, this antiestrogen could well offer an important advance for the endocrine therapy of breast cancer, uterine cancer, and other estrogen-sensitive diseases in women.

Androgens↗
PubMed1998

Antiestrogen stimulated human endometrial cancer growth: laboratory and clinical considerations.

The new antiestrogen toremifene (TOR) is currently on the market for the treatment of advanced breast cancer in postmenopausal women. TOR is known to exhibit a similar efficacy profile as tamoxifen (TAM) in the treatment of advanced breast cancer and there are studies to suggest that the beneficial side effects of TAM on bone and blood lipids are also achieved with TOR. However, the data concerning the action of TOR on the endometrium is sorely lacking. In light of the estrogenic effect of TAM on the uterus and the 2-3-fold increased incidence in endometrial carcinoma detected in patients receiving TAM therapy, it is imperative to investigate the effect of TOR on endometrial carcinoma. We compared the actions of TAM and TOR on the EnCa101 human endometrial tumor model and find that both antiestrogens have similar growth stimulatory effects. To investigate a potential mechanism of antiestrogen-stimulated endometrial tumor growth, we have examined known activators of the AP-1 signal transduction pathway, the protein kinase C (PKC) family of isozymes, in the EnCa101 human endometrial tumor model. We find that increased PKC isozyme expression correlates with hormone-independent breast cancer as well as antiestrogen-stimulated endometrial cancer.

Antineoplastic Agents, Hormonal↗
PubMedDate not supplied

Selective estrogen receptor modulators (SERMs) in clinical practice.

The objective of this literature review is to familiarize the reader with the clinical data on selective estrogen receptor modulators (SERMs) and antiestrogens currently in use in the US, excluding data on breast effects. Four compounds in the SERM and antiestrogen families are presently in clinical use in the US: clomiphene (CC), tamoxifen (TAM), toremifene (TOR), and raloxifene (RLX). The clinical database on these compounds is among the largest available. Each compound demonstrates a specific profile for its target tissue effects, and this may differ between premenopausal and postmenopausal women. CC is the most widely used agent for ovulation induction. TAM is indicated in the management of breast cancer and for prevention in women at high risk. TAM may have additional effects on the cardiovascular and skeletal systems. TOR also is used for its effects on breast tissue and may have positive cardiovascular effects. RLX is approved in the management of osteoporosis with data supporting favorable effects on the cardiovascular system and breast tissue. TAM and TOR appear to have stimulatory effects on the uterus and endometrium, whereas RLX is neutral. Few adverse events have been attributed to these agents, with hot flashes being the most common one. There appears to be an increased risk of thromboembolic events with continuous use of TAM, TOR, and RLX. SERMs and antiestrogens continue to be studied extensively. Their evolving profiles support key roles for these agents in modern day medicine, particularly in the management of postmenopausal women's health.

Breast Neoplasms↗
PubMed1998

Specific bone-protective effects of metabolites/derivatives of tamoxifen and clomiphene in ovariectomized rats.

In the ovariectomized (ovx) rat, the nonsteroidal antiestrogens, clomiphene (CLO) and tamoxifen (TAM), at dose levels that prevent development of osteopenia to a degree approaching that of 17beta-estradiol are, in contrast to 17beta-estradiol, only weakly uterotrophic. Metabolites of CLO and TAM might contribute differentially to these effects. Thus, we have evaluated bone protective and uterine effects in ovx rats of two such metabolites: 4-hydroxy CLO, produced by p-hydroxylation of CLO; and 4HTA, produced from TAM by stepwise replacement of its dimethylaminoethyl side chain with an acetic acid moiety, accompanied by p-hydroxylation. Also reported are effects of D4HTA, the dihydrodesethyl derivative of 4HTA previously characterized as a full estrogen mimetic in vitro. Administration of 4-hydroxy CLO (2.5 mg/kg subcutaneously) 5 days/week for 5 weeks to 3-month-old ovx rats resulted in complete prevention of bone loss and suppression of bone turnover to levels comparable to those of intact controls and to those of ovx animals similarly receiving 17beta-estradiol (10 microg/kg). However, uterine weight in animals receiving 4-hydroxy CLO was 64% less than that in 17beta-estradiol-treated animals. Although 4HTA (3.7 mg/kg s.c.) had a modest uterotrophic effect, it did not prevent bone loss associated with ovariectomy. In contrast, D4HTA (3.6 mg/kg s.c.) partially reduced bone turnover indicators and cancellous bone loss in a manner similar in many ways to that observed in TAM-treated ovx animals, but it had no uterotrophic effect. These results suggest that, although 4HTA does not contribute to the bone-protective effect of TAM, 4-hydroxy CLO might augment that of CLO.

Animals↗
PubMed2000

Coaggregation of paramagnetic d- and f-block metal ions with a podand-framework amine phenol ligand.

This report covers initial studies in the coaggregation of nickel (Ni2+) and lanthanide (Ln3+) metal ions to form complexes with interesting structural and magnetic properties. The tripodal amine phenol ligand H3tam (1,1,1-tris(((2-hydroxybenzyl)amino)methyl)ethane) is shown to be particularly accommodating with respect to the geometric constraints of both transition and lanthanide metal ions, forming isolable complexes with both of these ion types. In the solid-state structure of [Ni(H2tam)(CH3CN)]PF6.2.5CH3CN.0.5CH3OH (1), the Ni(II) center has a distorted octahedral geometry, with an N3O2 donor set from the [H2tam]- ligand and a coordinated solvent (acetonitrile) occupying the sixth site. The reaction of stoichiometric amounts of H3tam with the Ni(II) ion in the presence of lanthanide(III) ions provides [LnNi2(tam)2]+ cationic complexes which contain coaggregated metal ions. These complexes are isolable and have been characterized by a variety of analytical techniques, with mass spectrometry proving to be particularly diagnostic. The solid-state structures of [LaNi2(tam)2(CH3OH)1/2(CH3CH2OH)1/2(H2O)]ClO4.0.5CH3OH.0.5CH3CH2OH.4H2O (2), [DyNi2(tam)2(CH3OH)(H2O)]ClO4.CH3OH. H2O(6), and [YbNi2(tam)2(H2O)]ClO4.2.58H2O(9) have been determined. Each complex contains two octahedral Ni(II) ions, each of which is encapsulated by the ligand tam3- in an N3O3 coordination sphere; each [Ni(tam)]-unit caps the lanthanide(III) ion via bridging phenoxy oxygen donor atoms. In 2, La3+ is eight-coordinated, while in 6, Dy(III) is seven- (to "weakly eight-") coordinated, and Yb(III) in 9 has a six-coordination environment. The complexes are symmetrically different, 2 possessing C2 symmetry and 6 and 9 having C1 symmetry. Magnetic studies of 2, 6, and 9 indicate that antiferromagnetic exchange coupling between the Ni(II) and Ln(III) ions increases with decreasing ionic radius of Ln(III).

Amines↗
PubMed2000

Treatment with the pure antiestrogen faslodex (ICI 182780) induces tumor necrosis factor receptor 1 (TNFR1) expression in MCF-7 breast cancer cells.

Apoptosis induction by the pure antiestrogen faslodex, also known as ICI 182780 (ICI), is associated with an effective down-regulation of Bcl-2 expression in the human breast cancer cell line MCF-7. Recent observations point out that beside members of the Bcl-2 family also the TNFR1 signaling pathway may be involved in apoptosis induction by antiestrogens. In this report we have analyzed the expression of members of the TNFR1 signaling pathway during the apoptotic process induced by the pure antiestrogen faslodex and by tamoxifen (Tam) in MCF-7 breast cancer cells. Treatment with 10(-7) M ICI or 10(-7) M Tam leads to a time dependent increase of TNFR1 and TRADD steady-state mRNA levels in MCF-7 cells. In contrast, Bcl-2 expression was strongly decreased following administration of ICI but only weakly after administration of Tam. Western blot analysis and studies by the use of fluorescence microscopy and flow cytometry revealed a time dependent induction of TNFR1 protein and cell surface expression in MCF-7 cells in response to treatment with ICI. To investigate if TNFR1 is functionally involved in apoptosis induction by antiestrogens, we tested whether TNFR1 blocking antibodies can counteract the growth inhibitory action of Tam and ICI. Coincubation of MCF-7 cells with antiestrogens (ICI or Tam) and blocking TNFR1 antibodies lead to an increase in cell viability. Our results provide evidence for a cross talk between the TNFR1 signaling pathway and antiestrogens during the process of apoptosis induction in MCF-7 breast cancer cells. The superiority of the pure antiestrogen ICI to induce apoptosis in MCF-7 cells may result from its capability to modulate the induction of apoptosis via Bcl-2 as well as TNF-associated signal transduction pathways.

Antigens, CD↗
PubMed2026

A pro-inflammatory metastasis-associated macrophage subset induces tumor-promoting mesothelial cell conversion in ovarian cancer via IL-1α secretion.

Tumor-associated macrophages (TAMs) are key regulators of the tumor microenvironment, yet the functional specialization of TAM subsets in metastatic progression remains incompletely defined. Here, we characterized distinct TAM populations contributing to tumor-promoting mesothelial cell conversion in high-grade ovarian carcinoma using single-cell RNA sequencing of patient-derived macrophages from ascites (ascTAMs) and omental metastases (omTAMs). TAMs from these anatomical sites were clearly distinguishable by polarization states, with omTAMs exhibiting a mixed M1⁺/M2⁺ phenotype, in contrast to the M1low/M2⁺ profile observed in ascTAMs. Transcriptomic analysis further revealed functional divergence of these subsets. Notably, omTAMs displayed gene signatures associated with mesothelial-to-mesenchymal transition (MMT), a critical process enabling tumor invasion across the peritoneal lining. Functionally, conditioned media from omTAMs, similar to that from classically activated M1 macrophages, induced MMT in primary mesothelial cells via TGFβ and ERK/p38 MAPK signaling pathways. This phenotypic transition enhanced transmesothelial tumor cell invasion. Proteomic analysis identified IL-1α as a key MMT-inducing factor secreted by pro-inflammatory macrophages. Mechanistically, IL-1α cooperates with TGFβ by activating an autocrine TGFβ/TGFBR1 feedback loop in mesothelial cells, thereby amplifying MMT. Consistent with these findings, IL1A expression was enriched in omTAM clusters across independent patient samples and was confirmed by immunohistochemical analysis of clinical samples. From a therapeutic perspective, our study identifies new avenues to counteract the mesothelial reprogramming driven by IL-1α⁺ TAMs, potentially impeding metastatic progression. Created in BioRender. Heidemann, S. (2026) https://BioRender.com/aeu6yd0 .

Female↗
PubMed2004

Concomitant use of tamoxifen with radiotherapy enhances subcutaneous breast fibrosis in hypersensitive patients.

Concomitant use of adjuvant tamoxifen (TAM) and radiation therapy (RT) is not widely accepted. We aim to assess whether this treatment is associated with an increased risk of developing subcutaneous fibrosis after conservative or radical surgery in breast cancer patients. We analysed 147 women with breast cancer treated with adjuvant RT, and who were included in the KFS 00539-9-1997/SKL 00778-2-1999 prospective study aimed at evaluating the predictive value of CD4 and CD8 T-lymphocyte apoptosis for the development of radiation-induced late effects. TAM (20 mg day(-1)) with concomitant RT was prescribed in 90 hormone receptor-positive patients. There was a statistically significant difference in terms of complication-relapse-free survival (CRFS) rates at 3 years, 48% (95% CI 37.2-57.6%) vs 66% (95% CI 49.9-78.6%) and complication-free survival (CFS) rates at 2 years, 51% (95% CI 40-61%) vs 80% (95% CI 67-89%) in the TAM and no-TAM groups, respectively. In each of these groups, the CRFS rates were significantly lower for patients with low levels of CD8 radiation-induced apoptosis, 20% (95% CI 10-31.9%), 66% (95% CI 51.1-77.6%), and 79% (95% CI 55-90.9%) for CD8 </=16, 16-24, and >24%, respectively. Similar results were observed for the CFS rates. The concomitant use of TAM with RT is significantly associated with an increased incidence of grade 2 or greater subcutaneous fibrosis; therefore, caution is needed for radiosensitive patients.

Adult↗
PubMed2004

Antileukemic and long-term effects of two regimens with or without TBI in allogeneic bone marrow transplantation for childhood acute lymphoblastic leukemia.

Between September 1986 and June 1997, 24 children with high-risk ALL in CR1 were allografted after TAM (fractionated TBI, high-dose Ara-C, and melphalan; n = 10) or BAM protocol (busulfan, high-dose Ara-C, and melphalan; n = 14). The EFS for transplants from sibling donors was 33% with TAM and 62% with BAM (P = 0.148). The probability of acute GvHD was 70% with TAM and 15% with BAM (P = 0.003). Four of 17 evaluable patients relapsed: one after TAM and three after BAM. In all, 46 other children transplanted in CR beyond CR1 were studied for sequelae. Long-term side effects were more frequent in TAM vs BAM. In children with ALL, busulfan may be a good alternative to TBI to improve the quality of life.

Adolescent↗
PubMed2004

Inhibition of tumor-associated fatty acid synthase activity antagonizes estradiol- and tamoxifen-induced agonist transactivation of estrogen receptor (ER) in human endometrial adenocarcinoma cells.

Overexpression of the lipogenic enzyme fatty acid synthase (FAS) is a common molecular feature in subsets of sex-steroid-related tumors including endometrium and breast carcinomas that are associated with poor prognosis. Pharmacological inhibition of tumor-associated FAS hyperactivity is under investigation as a chemotherapeutic target. We examined the effects of the mycotoxin cerulenin (a covalent FAS inactivator), and the novel small compound C75 (a slow-binding FAS inhibitor) on estradiol (E2)- and tamoxifen (TAM)-stimulated ER-driven molecular responses in Ishikawa cells, an in vitro model of well-differentiated human endometrial carcinoma. We evaluated the effects of FAS inhibition on E2- and TAM-induced estrogen receptor (ER) transcriptional activity by using transient cotransfection assays with an estrogen-response element reporter construct (ERE-Luciferase). Antiestrogenic effects of cerulenin and C75 were observed by dose-dependent inhibition of E2-stimulated ERE-dependent transcription, whereas FAS inhibitors did not significantly increase the levels of ERE transcriptional activity in the absence of E2. Moreover, pharmacological blockade of FAS activity completely abolished TAM-stimulated ERE activity. To address the reliability of transient transfection assays, the effects of FAS inhibitors on E2-inducible gene products were evaluated. FAS blockade induced a dose-dependent decrease in E2-inducible alkaline phosphatase activity. E2-stimulated accumulation of progesterone receptor (PR) and HER-2/neu oncogene was abolished in the presence of FAS blockers. FAS inhibition also resulted in a marked downregulation of E2-stimulated ERalpha expression, and noticeably impaired E2-induced ERalpha nuclear accumulation. A dose-dependent decrease in cell proliferation and cell viability was observed after FAS blockade. A Cell Death ELISA, detecting DNA fragmentation, demonstrated that FAS inhibitors stimulated apoptosis of Ishikawa cells. The analysis of critical E2- and TAM-related cell cycle proteins revealed an increase of both the expression and the nuclear accumulation of cyclin-dependent kinase inhibitors p21WAF1/CIP1 and p27Kip1 following FAS inhibition. To rule out non-FAS cerulenin- and C75-related effects, we finally monitored ER signaling after silencing of FAS gene expression using the highly sequence-specific mechanism of RNA interference (RNAi). The concentrations of E2 and TAM inducing half-maximal ERE activity (EC50) dramatically increased (>100 times) in FAS RNAi-transfected Ishikawa cells. Moreover, depletion of FAS by RNAi also caused loss of ERalpha expression, downregulation of PR, and accumulation of p21WAF1/CIP1 and p27Kip1 in E2-stimulated Ishikawa cells. If chemically stable FAS inhibitors or cell-selective vector systems able to deliver RNAi targeting FAS gene demonstrate systemic anticancer effects in vivo, our results render FAS as a novel target for the prevention and treatment of endometrial carcinoma.

Adenocarcinoma↗
PubMed2004

Interferon-regulatory factor-1 is critical for tamoxifen-mediated apoptosis in human mammary epithelial cells.

Unlike estrogen receptor-positive (ER(+)) breast cancers, normal human mammary epithelial cells (HMECs) typically express low nuclear levels of ER (ER poor). We previously demonstrated that 1.0 microM tamoxifen (Tam) promotes apoptosis in acutely damaged ER-poor HMECs through a rapid, 'nonclassic' signaling pathway. Interferon-regulatory factor-1 (IRF-1), a target of signal transducer and activator of transcription-1 transcriptional regulation, has been shown to promote apoptosis following DNA damage. Here we show that 1.0 microM Tam promotes apoptosis in acutely damaged ER-poor HMECs through IRF-1 induction and caspase-1/3 activation. Treatment of acutely damaged HMEC-E6 cells with 1.0 microM Tam resulted in recruitment of CBP to the gamma-IFN-activated sequence element of the IRF-1 promoter, induction of IRF-1, and sequential activation of caspase-1 and -3. The effects of Tam were blocked by expression of siRNA directed against IRF-1 and caspase-1 inhibitors. These data indicate that Tam induces apoptosis in HMEC-E6 cells through a novel IRF-1-mediated signaling pathway that results in activated caspase-1 and -3.

Antineoplastic Agents, Hormonal↗
PubMed2006

Combinatorial fluorescence energy transfer molecular beacons for probing nucleic acid sequences.

We report the design, synthesis, and characterization of molecular beacons (MB) consisting of three distinct fluorophores, 6-carboxyfluorescein (Fam), N,N,N',N'-tetramethyl-6-carboxyrhodamine (Tam), and Cyanine-5 (Cy5). The primary light absorber/energy donor (Fam) is located on one terminus of the MB, whereas the primary energy acceptor/secondary donor (Tam) and secondary acceptor (Cy5) are located at the other terminus of the MB. In the absence of target DNA or RNA, the MB exists in the stem-closed form. Excitation of Fam initiates an energy transfer cascade from Fam to Tam and further to Cy5 generating unique fluorescence signatures defined as the ratio of the emission from each of the three fluorophores. This energy transfer cascade was investigated in detail by steady-state and time-resolved fluorescence spectroscopy, as well as fluorescence depolarization studies. In the presence of the complementary target DNA, the MB opened efficiently and hybridized with the target separating Fam and Tam by a large distance, so that energy transfer from Fam to Tam was blocked in the stem-open form. This opening of the MB generates a "bar code" fluorescence signature, which is different from the signature of the stem-closed MB. The fluorescence signature of this combinatorial fluorescence energy transfer MB can be tuned by variation of the spacer length between the individual fluorophores.

Base Sequence↗
PubMedDate not supplied

Antitumoral activity of a new series of 5,6-dihydrobenzo(a)carbazoles.

The overlapping of three-dimensional structures of 5,6-dihydrobenzo(a)carbazole (DHBC) derivatives over the structure of 4-hydroxytamoxifen (4-OH-TAM), by means of the MDL CHEMLAB 11.0 computational program, shows a reasonable structural and spatial resemblance. This finding raised the hypothesis of their possible antitumoral activity, similar to that of tamoxifen (TAM). A number of DHBCs with an alkyl chain and a second basic nitrogen as substituent were synthesized in our laboratory and their possible antitumoral activity was tested by means of: 1) competitive radioligand assays to determine relative drug affinity for the estrogen receptor (ER); 2) in vivo studies, giving the synthetic drugs subcutaneously (1 mg kg-1 day-1) to Sprague-Dawley rats with N-nitroso-N-methylurea (NMU)-induced mammary tumors; and 3) in vitro cell proliferation experiments employing the soft agar clonogenic technique. Besides, studies on toxicity and histopathological analyses of organs and tumors from treated animals were performed. Results obtained showed that: 1) relative binding affinities (RBA) for the ER were similar to that of TAM; 2) some structures showed significant antitumoral activity and induced tumoral regression similar to TAM; and 3) these compounds had in vitro inhibitory effect on cell proliferation. Even though all the compounds of the series of synthesized DHBCs showed affinity for the ER similar to TAM, the results of in vivo experiments confirmed the crucial role of hydroxyl groups in the molecule and of the interatomic distance between them, similar to that of estradiol, as well as the necessary presence of the aminoalkyl chain on the annular N atom. However, the effect of alkyl chain enlargement in the nitrogen substituent on the biological activity of those drugs is as yet unclear.

Animals↗
PubMed2003

Usefulness of tamsulosin hydrochloride and naftopidil in patients with urinary disturbances caused by benign prostatic hyperplasia: a comparative, randomized, two-drug crossover study.

BACKGROUND: The aim of the study presented here was to stratify drug therapy for patients with benign prostatic hyperplasia (BPH) displaying various voiding symptoms. METHODS: Two different alpha1-adrenoceptor antagonists; tamsulosin hydrochloride (Tam) and naftopidil (Naf ), were administered to 96 patients with BPH for 8 weeks in a crossover study. RESULTS: With the administration of both drugs, the International Prostate Symptom Score (I-PSS) significantly decreased and the maximum urinary flow significantly increased. Whereas Naf monotherapy decreased the I-PSS for storage symptoms, Tam monotherapy decreased the I-PSS for voiding symptoms. In both the Naf-to-Tam and Tam-to-Naf groups, crossover was effective when the initial drug was judged subjectively and objectively to have been ineffective. Compliance was acceptable with both drugs. CONCLUSION: Our results show that either Naf or Tam can be used to treat patients on the basis of objective and subjective assessment of voiding symptoms. Our findings should be helpful for patient guidance and treatment of BPH.

Adrenergic alpha-Antagonists↗
PubMed1996

Transforming growth factor beta 1-induced cell death in preneoplastic foci of rat liver and sensitization by the antiestrogen tamoxifen.

Previous studies have shown 5- to 10-fold higher rates of apoptosis in prestages of liver cancer (putative preneoplastic cell foci [PPF]) than in unaltered liver; fasting or withdrawal of tumor promoters enhanced apoptosis even further. We studied whether transforming growth factor beta 1 (TGF-beta 1), an inducer of apoptosis in normal liver, might be involved in induction of apoptosis in PPF. PPF were produced in 7-week-old female Sprague-Dawley rats with a single oral dose of the genotoxic carcinogen 7,12-dimethylbenz(a)anthracene (DMBA). At 24 weeks of age, TGF-beta 1 was injected into animals (40 micro g/kg intravenously) either once and they were killed 4 hours later (single-dose experiment) or eight times at 24-hour intervals and they were killed 24 hours after the last administration (multiple-dose experiment). Further subgroups received daily subcutaneous injections of tamoxifen (TAM) (8 mg/kg) for 4 consecutive weeks before TGF-beta 1 treatment. In normal liver, the apoptosis incidence was low in solvent- and TAM-only-treated animals, in the single- as well as the multiple-dose experiment. TGF-beta 1, increased the apoptosis incidence severalfold, and the combined administration of TGF-beta 1 with TAM caused a further strong increase. The already-elevated basal apoptotic incidence in PPF was further increased by TGF-beta 1, and particularly by TGF-beta 1 plus TAM treatments, which resulted in a reduction of foci number and size. In summary, these results show that TGF-beta 1 can induce apoptosis in PPF. This apoptosis-inducing activity is strongly enhanced by the additional treatment with the antiestrogen TAM, which by itself does not have any cell death-inducing effect in the liver or PPF. The elevated apoptotic activity of PPF in response to TGF-beta 1 can lead to a selective reduction of the liver load with preneoplastic cells.

Animals↗
PubMed1995

A comparison of the interaction of Shc and the tyrosine kinase ZAP-70 with the T cell antigen receptor zeta chain tyrosine-based activation motif.

Tyrosine-based activation motifs (TAMs) define a conserved signaling sequence, EX2YX2L/IX7YX2L/I, that couples the T cell antigen receptor to protein tyrosine kinases and adapter molecules. The present study shows that phosphorylation of both tyrosines within the motif is required for high affinity binding of the tyrosine kinase ZAP-70 whereas phosphorylation of the single COOH-terminal tyrosine within the motif is optimal for the binding of the adapter Shc. There were also quantitative differences in the ZAP-70 and Shc association with the zeta 1-TAM since nM concentrations of the doubly phosphorylated zeta 1-TAM are sufficient for ZAP-70 recruitment whereas micromolar levels of singly phosphorylated TAMs are necessary for Shc binding. Shc is tyrosine phosphorylated in antigen receptor-activated T cells and can potentially form a complex with the adapter molecule Grb2 and could thus recruit the Ras guanine nucleotide exchange protein Sos into the antigen receptor complex. The present data show that Grb2 can bind to the phosphorylated TAM, but this binding is independent of Shc and there is no formation of zeta 1-TAM.Shc.Grb2.Sos complexes in antigen receptor-activated cells. Accordingly, Shc function should not be considered in the context of Grb2/Sos recruitment to the T cell antigen receptor complex.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Tandem SH2 domains confer high specificity in tyrosine kinase signaling.

SH2 domain proteins transmit intracellular signals initiated by activated tyrosine kinase-linked receptors. Recent three-dimensional structures suggest mechanisms by which tandem SH2 domains might confer higher specificity than individual SH2 domains. To test this, binding studies were conducted with tandem domains from the five signaling enzymes: phosphatidylinositol 3-kinase p85, ZAP-70, Syk, SHP-2, and phospholipase C-gamma1. Bisphosphorylated TAMs (tyrosine-based activation motifs) were derived from biologically relevant sites in platelet-derived growth factor, T cell, B cell, and high affinity IgE receptors and the receptor substrates IRS-1 (insulin receptor substrate-1) and SHPS-1/SIRP. Each tandem SH2 domain binds a distinct TAM corresponding to its appropriate biological partner with highest affinity (0.5-3.0 nM). Alternative TAMs bind the tandem SH2 domains with 1,000- to >10,000-fold lower affinity than biologically relevant TAMs. This level of specificity is significantly greater than the approximately 20-50-fold typically seen for individual SH2 domains. We conclude that high biological specificity is conferred by the simultaneous interaction of two SH2 domains in a signaling enzyme with bisphosphorylated TAMs in activated receptors and substrates.

Amino Acid Sequence↗
PubMed2003

Identification of genes expressed in tumor-associated macrophages.

Most malignant tumors contain so-called tumor-associated macrophages (TAM) as a major component of their leukocytic infiltrate. To investigate the impact of the tumor microenvironment on activation and differentiation of macrophages, we established a 3-dimensional model system by culturing human monocytes within multicellular tumor spheroids. After 7 days, monocyte-derived TAM were isolated and analyzed for phenotypic alterations as compared to macrophages cultured without tumor cell contact. We found the known macrophage differentiation marker Carboxypeptidase M to be suppressed while CD14, HLA-DR, and CD16 were up-regulated. Using Differential Display, we identified several genes that were differentially expressed between TAM and control macrophages. Prolidase, a peptidase known to influence the chemoattraction of neutrophils and macrophage activity, was down-regulated in TAM. In contrast, the Toll-like receptor family-related molecules MD-1 and RP105 were up-regulated by tumor cell contact, both at the RNA and protein level. From our data we conclude that TAM represent a distict macrophage population characterized by low expression of differentiation-associated macrophage antigens but also by a constitutive state of activation.

Antigens, CD↗