4-iodotamoxifen aziridine, a new affinity labeling agent for the rapid detection of estrogen receptor isoforms

We describe the simple and fast preparation of a new radioiodinated probe for the detection of the estrogen receptor (ER) and its isoforms. Iodotamoxifen aziridine was labeled with iodine 125 ([125I]TAZ) in position 4 of the alpha aromatic ring. The yield was high (>75%), the label was stable and the specific activity was near optimal (1900-2170 Ci/mmol). The apparent relative binding affinity of the probe to a recombinant human ER (hER) was high (RBA = 35 vs estradiol = 100). Electrophoretic studies (SDS-PAGE) with this hER indicated the high potency of [125I]TAZ at very low concentration (<1 nM) to reveal ER bands after a short exposure time (1-4 days). Competition between this probe and various compounds as well as chemical treatments of the ER with SH-reactive chemicals, demonstrated the labeling specificity. Analysis of cytosols from a panel of cell lines and various rat reproductive organs displayed characteristic ER bands (67, 50 and 37 kDa) suppressed by unlabeled E2. Detection in nonreproductive organs of 43 kDa E2-nondisplaceable peptide raised the question upon the presence of altered and/or variant ERs in many tissues. Data concerning human breast cancer cytosols were in complete accordance with those established with [3H]TAZ: high ER polymorphism in most ER-positive samples and peculiar forms (mainly 43 kDa) in ER-negative samples. Hence, [125I]TAZ appears especially useful for the detection of altered ER or related peptides in breast cancers.

Evolution towards hormone independence of the MXT mouse mammary tumor is associated with a gradual change in its estrogen receptor molecular polymorphism

Using a method based on [3H]tamoxifenaziridine ([3H]TAZ) labeling, sequential immunoadsorption with anti-ER monoclonal antibodies, sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE) and fluorography, we observed a striking change inthe estrogen receptor (ER) electrophoresis pattern of the transplantable MXT mouse mammary tumor. Early, ER "rich" tumors (approximately 100 fmol/mg prot) displayed classical cytosolic 67 and 50 KDa bands. These bands disappeared in favor of a "cytosolic" 35 KDa band during progression towards undifferentiated ER "poor" tumors (approximately 25 fmol/mg prot). Although we can not rule out that this 35 KDa peptide results from in vivo ER proteolysis, it seems unique in view of the following: 1. It is immunoadsorbed not only by an anti-ER monoclonal antibody (H-222) directed to the hormone-binding domain, but also by an anti-ER monoclonal antibody (H-226) which interacts with an epitope in the A/B region close to the DNA-binding domain and is mainly exposed under activation conditions. 2. It does not bind [3H]estradiol([3H]E2) and a tentative to restore its [3H]E2 binding capacity with calmodulin and ATP was unsuccessful. The observation of similar approximately 35 KDa ERs in the nuclear fraction of early tumor transplants and in control uterus suggests that this peptide is already in an activated form. Structural alterations of ER and/or associated "anchorage" nuclear proteins may beat the origin of its cytosolic localization. Moreover, the fact that the addition of calmodulin and ATP to late MXT transplants cytosols fails to increase their [3H]E2 binding capacity indicates that the low ER content of these tumors does not result from a deficiency in the phosphorylation status of the receptor.

Length increase of the side chain of idoxifene does not improve its antagonistic potency in breast-cancer cell lines

Linkage of specific residues onto steroidal estrogens through a long aliphatic side chain leads to "pure antiestrogens" devoid of residual estrogenic activity. Therefore, we assessed whether an increase in the length of the side chain of the triphenylethylenic antiestrogen idoxifene might increase its antagonistic potency. Culture of MCF-7 and tamoxifen-resistant variant RTX6 cells in the presence of CB 7675, a (CH2)8 derivative of idoxifene [(CH2)2], ruled out this possibility. This compound partly blocked MCF-7 cell growth only at 10(-6) M to almost the same extent as tamoxifen and failed to inhibit the growth of RTX6 cells, whereas the pure antiestrogen RU 58 668 was effective on both cell lines at much lower concentration. This absence of improvement was reflected in the observation of an efficiency for down-regulating progesterone receptor no better than that of tamoxifen. Pure antiestrogens are known to down-regulate the estrogen receptor, whereas triphenylethylenic antiestrogens up-regulate the receptor; CB 7675 behaves as the latter in agreement with its lack of strong antagonistic activity.

Human thymocytes become lineage committed at an early postselection CD69+ stage, before the onset of functional maturation

Mature functional CD4 or CD8 single positive (SP) thymocytes differentiate from immature CD4+ 8+ double positive (DP) precursors through a process of positive selection and terminal differentiation. To study CD4/CD8 lineage commitment, human postselection CD69+ thymocytes were separated into distinct subpopulations based on the differential expression of CD27, CD1, and CD45RA/RO. We demonstrate that these CD69+ subpopulations represent transitional stages of a common differentiation pathway during which CD69+ thymocytes that are initially CD27- CD1+ CD45RA- will sequentially up-regulate CD27, down-regulate CD1, and eventually acquire CD45RA upon maturation. Examination of CD4 and CD8 expression on these CD69+ subsets identified an early postselection CD69+ CD27- CD4SP population that gives rise to both CD4SP and CD8SP mature T cells when cultured in mouse thymus organs. In addition, a CD4+ 8+ DP population was identified that is CD69+ and CD27+, which only gives rise to CD8SP progeny upon culture. Although these results suggest that development of CD4SP and CD8SP cells may proceed through distinct intermediates, examination of active biosynthesis of CD4 and CD8 by the various subsets demonstrated that cells that have selectively terminated CD4 synthesis are already present in the CD27- CD4SP and CD27+ DP populations before culture. These data support a model of thymocyte differentiation whereby the decision of thymocytes to differentiate into one or the other lineage occurs concomitantly with, or very soon after, acquisition of CD69 and before the cells acquire CD27, down-regulate CD1, or acquire functional properties.

Human thymocytes become lineage committed at an early postselection CD69+ stage, before the onset of functional maturation

Mature functional CD4 or CD8 single positive (SP) thymocytes differentiate from immature CD4+ 8+ double positive (DP) precursors through a process of positive selection and terminal differentiation. To study CD4/CD8 lineage commitment, human postselection CD69+ thymocytes were separated into distinct subpopulations based on the differential expression of CD27, CD1, and CD45RA/RO. We demonstrate that these CD69+ subpopulations represent transitional stages of a common differentiation pathway during which CD69+ thymocytes that are initially CD27- CD1+ CD45RA- will sequentially up-regulate CD27, down-regulate CD1, and eventually acquire CD45RA upon maturation. Examination of CD4 and CD8 expression on these CD69+ subsets identified an early postselection CD69+ CD27- CD4SP population that gives rise to both CD4SP and CD8SP mature T cells when cultured in mouse thymus organs. In addition, a CD4+ 8+ DP population was identified that is CD69+ and CD27+, which only gives rise to CD8SP progeny upon culture. Although these results suggest that development of CD4SP and CD8SP cells may proceed through distinct intermediates, examination of active biosynthesis of CD4 and CD8 by the various subsets demonstrated that cells that have selectively terminated CD4 synthesis are already present in the CD27- CD4SP and CD27+ DP populations before culture. These data support a model of thymocyte differentiation whereby the decision of thymocytes to differentiate into one or the other lineage occurs concomitantly with, or very soon after, acquisition of CD69 and before the cells acquire CD27, down-regulate CD1, or acquire functional properties.

Estrogen receptor-negative/progesterone receptor-positive Evsa-T mammary tumor cells: a model for assessing the biological property of this peculiar phenotype of breast cancers

In 1986 we reported the appearance of a progestin binding protein in the human breast cancer cell line Evsa-T, originally described as lacking both estrogen and progesterone receptors (ER and PR). In this report we show that PR of this cell line displays a binding affinity for [3H]ORG 2058 and a sucrose gradient sedimentation profile similar to those ascribed to PR from MCF-7 or T47D breast cancer cell lines. PR from Evsa-T cells is down-regulated by the progestin R-5020 as well as by the two antiprogestins, ZK 112.993 and ZK 98.299, but does not confer growth sensitivity to these compounds. ER remains undetectable by ligand binding assay, enzyme immunoassay and northern blotting. Our Evsa-T clone could be a valuable model for assessing the mechanisms leading the ER-/PR+ phenotype occurring occasionally in breast cancers and frequently in meningiomas.

Decrease of hormone binding capacity of estrogen receptor by calcium

We have addressed the question as to whether calcium may modify the [3H]estradiol ([3H]E2) binding properties of the estrogen receptor (ER). A human recombinant full length ER (yER) expressed in yeast was used to limit the potential interference of ER-associated proteins and proteases present in the target tissues. Ca++ (0.1-10 mM) always produced an important loss of [3H]E2 binding capacity without any effect on the hormone binding affinity of residual receptors. This loss was reflected in a decrease of immunoreactivity for monoclonal antibodies raised against the hormone binding domain. An ER recombinant expressing solely this domain confirmed that the ion operated at this level. Binding of [125I]Z-17 alpha-(2-iodovinyl)-11 beta-chloromethyl estradiol-17 beta (an compound with very high selectivity for ER) as well as [125I]tamoxifen aziridine were similarly affected. Size-exclusion chromatography failed to reveal the emergence of any ER isoforms of low molecular weight rejecting the hypothesis of a Ca(++)-induced proteolysis. In agreement with this conclusion, EDTA reversed the loss of [3H]E2 binding capacity. Phosphoamino acids (PY, PT and PS) partly antagonized the effect of Ca++ suggesting its interaction with phosphoamino acid residues. Worthy of note, the effect of Ca++ appeared more marked when assessed by DCC than HAP assay. The phosphocalcic nature of the HAP matrix may explain this phenomenon which was observed with cytosolic ER from various origins.

Optimization of glottic exposure during intubation of a patient lying supine on the ground

Two methods of endotracheal intubation of patients lying on the ground were compared for ease and speed of intubation and minimization of complications in a crossover study of prehospital-oriented emergency physicians. Intubation of a mannequin was attempted by the physicians in either a left lateral decubitus (LLD) position or a kneeling (K) position, followed by the alternate position. The LLD position afforded more rapid intubation, better glottic visualization, and less dental trauma. Eighty-seven percent of physicians completely visualized the glottis in the LLD position, versus 33% of the K position group. Intubation times were 10.5 versus 14.6 seconds in the LLD and K positions, respectively (P < .001). The LLD position is a more effective position (in a mannequin model) than the K position for intubation of patients found lying on the ground, a frequent situation in prehospital care.

Varying sensitivity of human mammary carcinoma cells to the toxic effect of parvovirus H-1

We have previously demonstrated lysis of non-established cultures of human mammary carcinoma cells by parvovirus H-1, which has little effect on the proliferation of corresponding normal cultures. In the present study, we examined this effect in a number of breast-tumour specimens and found them to differ as to the amplitude of their response to parvoviral attack. We first investigated whether the differences in cell sensitivity to parvovirus infection reflected the differentiation level of the initial tumour. Among the biochemical and anatomopathological indicators of original tumour differentiation, the presence of oestrogenic receptors (ER) was found to have a predictive value as to the sensitivity of derived cultures to the cytopathic effect of H-1 virus. The ER+ tumour-derived cultures showed an increased sensitivity to the lytic effect of H-1 virus compared with the ER-tumour-derived cultures, in spite of similar average proliferation rates for the two types of cultures. The proliferation rate was more heterogeneous among ER+ tumour-derived cultures and, in this group, the faster growing cultures were also the most sensitive. This observation was corroborated by the study of established cell lines retaining ER expression under in vitro culture conditions. Oestradiol was found to increase the sensitivity of these cells to the parvovirus in parallel with induction of proliferation. This effect appeared to be mediated by ER activation, since it was not observed in the ER-negative cell line MDA-MB-231. These data point to the importance of hormonal influences and cellular parameters, notably differentiation and proliferation, in determining the extent to which human cancer cells can be targets for the cytopathic effect of parvoviruses.

Protein synthesis is not implicated in the ligand-dependent activation of the estrogen receptor in MCF-7 cells

In MCF-7 cells, estrogen receptor (ER) elimination occurs rapidly under stimulation with estradiol (E2) at 1 nM ('ER processing'); cycloheximide (CHX) at 50 microM impedes this phenomenon. ER processing is also observed when E2 is removed after the first hour of incubation, indicating that the role of the hormone would be limited to the initiation of this process. When CHX is removed at the same time, receptor processing and, later, the induction of progesterone receptor (PgR) both proceed. The initial estrogenic signal which activates ER is therefore not influenced by CHX. In support of this conclusion, no effect of the drug on E2 binding affinity of residual ER was detected. A similar result was recorded for a series of estrogens and antiestrogens, indicating that CHX exerts no influence on the potential agonistic/antagonistic potency of any ligand. Size-exclusion chromatography (FPLC) revealed that [3H]E2-induced ER activation leads to the cleavage of the native receptor (67 kDa) into low molecular weight isoforms which subsequently become less detectable over time (proteolysis). In the presence of CHX, such ER isoforms persist, confirming the absence of interference of the drug with the activation step. When the cells were prelabelled with [3H]tamoxifen aziridine ([3H]TAZ) before their exposure to E2, ER cleavage could not be detected due to the lack of activation potency of the antiestrogenic ligand. However, the [3H]TAZ-ER complexes were subjected to E2-induced processing; CHX blocked this phenomenon, which is associated with the maintenance of ER synthesis and activation.

Phenotypic and functional maturation of TCR gammadelta cells in the human thymus

In contrast to thymic differentiation of TCR alphabeta cells, differentiation stages of TCR gammadelta cells are largely unknown. This report shows that CD1, a known marker of immature TCR alphabeta thymocytes, was expressed on some postnatal TCR gammadelta thymocytes. Only CD1+ TCR gammadelta thymocytes expressed recombination-activating gene-1 mRNA, and they were shown to differentiate into CD1- TCR gammadelta thymocytes. Functionally, sorted CD1- TCR gammadelta thymocytes proliferated in the presence of immobilized anti-CD3 Ab plus exogenous rIL-2 or rIL-15. Interestingly, in contrast to CD1- TCR alphabeta cells, CD1- TCR gammadelta thymocytes also proliferated extensively when cultured with exogenous rIL-2 or rIL-15 alone. FACS analysis as well as reverse transcription-PCR analysis showed that only CD1- TCR gammadelta thymocytes expressed IL-2Rbeta protein and mRNA. The differential expression of maturation markers, such as CD27, CD45RO, and CD45RA, as a function of expression of CD1 was similar in TCR gammadelta and TCR alphabeta thymocytes. An important exception is the expression of CD4 and CD8. Whereas TCR alphabeta thymocytes are mainly CD4-CD8 double positive at the immature CD1+ stage and CD4 or CD8 single positive at the mature CD1- stage, CD1(bright) TCR gammadelta thymocytes all expressed CD4, but only some of them expressed CD8. Some CD1- TCR gammadelta thymocytes also expressed CD8, but were negative for CD4. Collectively, our data clearly show that CD1 is a useful marker to distinguish immature human TCR gammadelta thymocytes from functional mature gammadelta cells based on recombination-activating gene-1 expression, in vitro differentiation, and phenotypic and functional characteristics.

Phenotypic and functional maturation of TCR gammadelta cells in the human thymus

In contrast to thymic differentiation of TCR alphabeta cells, differentiation stages of TCR gammadelta cells are largely unknown. This report shows that CD1, a known marker of immature TCR alphabeta thymocytes, was expressed on some postnatal TCR gammadelta thymocytes. Only CD1+ TCR gammadelta thymocytes expressed recombination-activating gene-1 mRNA, and they were shown to differentiate into CD1- TCR gammadelta thymocytes. Functionally, sorted CD1- TCR gammadelta thymocytes proliferated in the presence of immobilized anti-CD3 Ab plus exogenous rIL-2 or rIL-15. Interestingly, in contrast to CD1- TCR alphabeta cells, CD1- TCR gammadelta thymocytes also proliferated extensively when cultured with exogenous rIL-2 or rIL-15 alone. FACS analysis as well as reverse transcription-PCR analysis showed that only CD1- TCR gammadelta thymocytes expressed IL-2Rbeta protein and mRNA. The differential expression of maturation markers, such as CD27, CD45RO, and CD45RA, as a function of expression of CD1 was similar in TCR gammadelta and TCR alphabeta thymocytes. An important exception is the expression of CD4 and CD8. Whereas TCR alphabeta thymocytes are mainly CD4-CD8 double positive at the immature CD1+ stage and CD4 or CD8 single positive at the mature CD1- stage, CD1(bright) TCR gammadelta thymocytes all expressed CD4, but only some of them expressed CD8. Some CD1- TCR gammadelta thymocytes also expressed CD8, but were negative for CD4. Collectively, our data clearly show that CD1 is a useful marker to distinguish immature human TCR gammadelta thymocytes from functional mature gammadelta cells based on recombination-activating gene-1 expression, in vitro differentiation, and phenotypic and functional characteristics.

MHC class II molecules are required for initiation of positive selection but not during terminal differentiation of human CD4 single positive thymocytes

Positive selection of T cell precursors is an MHC dependent, multistep process by which functionally mature CD4+8- helper and CD4-8+ cytotoxic single positive (SP) T cells are generated from immature CD4+8+ double positive (DP) thymocytes. We investigated the requirement for TCR/MHC class II interactions during different stages of positive selection of human CD4 SP thymocytes. We show that sorted CD69- CD4+8+ DP preselection thymocytes cultured in fetal thymus lobes of normal mice were subject to positive selection and differentiated to CD3(high) CD69+, mature CD8 SP, and CD4 SP cells. When cultured in thymus lobes from MHC class II-deficient mice, these precursors failed to develop into mature CD4 SP T cells, indicating that in the hybrid cultures, murine MHC class II molecules are required for the development of mature human CD4 SP T cells. We have previously identified CD4 SP intermediate thymocytes that have received at least some of the signals involved in positive selection, since these cells are CD69+, CD3/TCR(high), and CD8beta- but that are still phenotypically and functionally immature. Here we demonstrate that in contrast to preselection thymocytes, these CD4 SP intermediate thymocytes can give rise to phenotypically mature and functionally CD4 SP progeny both in normal and in MHC class II-deficient thymus lobes. These results suggest that TCR/MHC interactions are required for the initial stages of positive selection, but are not essential during terminal differentiation to functionally mature CD4 SP T cells.

MHC class II molecules are required for initiation of positive selection but not during terminal differentiation of human CD4 single positive thymocytes

Positive selection of T cell precursors is an MHC dependent, multistep process by which functionally mature CD4+8- helper and CD4-8+ cytotoxic single positive (SP) T cells are generated from immature CD4+8+ double positive (DP) thymocytes. We investigated the requirement for TCR/MHC class II interactions during different stages of positive selection of human CD4 SP thymocytes. We show that sorted CD69- CD4+8+ DP preselection thymocytes cultured in fetal thymus lobes of normal mice were subject to positive selection and differentiated to CD3(high) CD69+, mature CD8 SP, and CD4 SP cells. When cultured in thymus lobes from MHC class II-deficient mice, these precursors failed to develop into mature CD4 SP T cells, indicating that in the hybrid cultures, murine MHC class II molecules are required for the development of mature human CD4 SP T cells. We have previously identified CD4 SP intermediate thymocytes that have received at least some of the signals involved in positive selection, since these cells are CD69+, CD3/TCR(high), and CD8beta- but that are still phenotypically and functionally immature. Here we demonstrate that in contrast to preselection thymocytes, these CD4 SP intermediate thymocytes can give rise to phenotypically mature and functionally CD4 SP progeny both in normal and in MHC class II-deficient thymus lobes. These results suggest that TCR/MHC interactions are required for the initial stages of positive selection, but are not essential during terminal differentiation to functionally mature CD4 SP T cells.

Antagonism of estrogen receptor and calmodulin association by antiestrogens is not dependent on an interaction with calmodulin

Previously, two antiestrogens estradiol derivatives (3 and 4) bearing the basic side chain of tamoxifen were shown to impede the binding of the estrogen receptor (ER) to calmodulin (CaM)-Sepharose. In this study, the interaction of these and related compounds with calmodulin was examined using the cyclic AMP phosphodiesterase (cAMP-PDE) assay. Neither of the steroids gave any significant inhibition of the calmodulin dependent cAMP-PDE activity up to a final concentration of 20 microM. For comparison, tamoxifen and nafoxidine produced IC50 values of 6.7 microM +/- 1.0 and 7.4 microM +/- 1.1, respectively. In addition, a comparison was made of the activity of some triphenylethylene derivatives against CaM dependent cAMP-PDE and the ER-CaM Sepharose assays, but no relationship was observed. Overall, these results demonstrate that inhibition of the ER-CaM association by various steroidal and triphenylethylene antiestrogens does not relate to antagonism of calmodulin function or their binding affinity for the estrogen receptor.

Tamoxifen-induced estrogen receptor up-regulation in mammary tumor cells is not related to growth inhibition

Treatment of estrogen receptor (ER)-positive mammary tumors with tamoxifen produces a dramatic accumulation of ER in the cell nucleus. We investigated whether this phenomenon might be related to the antitumor activity of the drug. Five tamoxifen derivatives for which an influence on MCF-7 cell growth had previously been established were tested for that purpose; two of them inhibited growth, one was growth-stimulatory, and the remaining two were without significant effect. At 1 microM all compounds up-regulated ER in the cell nucleus after 3 days of culture, suggesting that the ER accumulation does not predict the response to tamoxifen treatment. An analysis of a tamoxifen-resistant clone (RT x 6 cells) under similar experimental conditions led to the same conclusion: the ER level significantly increased in the presence of tamoxifen and its 4-hydroxy metabolite.

Interleukin-7 is a critical growth factor in early human T-cell development

Highly purified human CD34+ fetal liver stem cells differentiate to mature T cells when seeded in vitro into isolated fetal thymic lobes of severe combined immunodeficient (SCID) mice followed by fetal thymus organ culture (FTOC). Here, this chimeric human-mouse FTOC was used to address the role of interleukin-7 (IL-7) and of the alpha chain of the IL-7 receptor (IL-7R alpha) in early human T-cell development. We report that addition of either the monoclonal antibody (MoAb) M25, which neutralizes both human and mouse IL-7, or the MoAb M21, which recognizes and blocks exclusively the human high-affinity alpha-chain of the IL-7R, results in a profound reduction in human thymic cellularity. Analysis of lymphoid subpopulations indicates that a highly reduced number of cells undergo maturation from CD34+ precursor cells toward CD4+CD3-CD1+ progenitor cells and subsequently toward CD4+CD8+ thymocytes. Our results reveal a critical role for IL-7 during early human thymocyte development, and may explain the absence or highly reduced levels of T cells in patients with X-linked SCID. The molecular defect in these patients has been shown to be a mutation in the gamma chain of the IL-2R. Although this gamma chain is not only present in the IL-2R, but also forms an essential part of other cytokine receptors, including IL-4, IL-7, IL-9, IL-13, and IL-15, the T-cell defect in these patients can be explained by the fact that IL-7 is not able to transduce its signal by the molecular defect of the common gamma (gamma c) chain and that IL-7 is indispensable for T-cell development.

Thymic and extrathymic T cell development

The majority of T cells located in peripheral blood, spleen and lymph nodes are dependent on the thymus for proper differentiation and function. Only a minority of T lymphocytes located in these lymphoid organs is thymic-independent. In contrast, a large number of thymus-independent T cells is present in the gut epithelium. This review deals with phenotypic and functional characteristics of T cell development, summarizes the knowledge on the cytokine requirement in this process and describes positive and negative selection. The differences between thymic-dependent and thymic-independent T cells are emphasized, including selection processes, CD4-CD8 expression and the composition of the CD3 complex.

Thymic development of V gamma 3 cells

Several characteristics of V gamma 3 cells are clearly different from those of other T cells. V gamma 3 thymocytes mainly originate from fetal precursor cells and only differentiate efficiently in a fetal thymic environment. Evidence is discussed that the early appearance of V gamma 3 cells is probably due to differential gene accessibility which regulates gene rearrangement. Another characteristic of V gamma 3 cells is the canonical sequence of their T-cell receptor (TCR), which seems to be mainly shaped intracellularly by the combination of targeted gene rearrangement, homology-directed recombination and the absence of terminal deoxynucleotidyl transferase, rather than by cellular selection. Contrary to alpha beta cells, V gamma 3 cells express the Fc epsilon RI gamma chain in their TCR complex and other protein tyrosine kinases are important for their thymic differentiation. Also, expression of several cell surface markers is regulated differently on V gamma 3 cells as compared to alpha beta cells. Collectively, these findings show that V gamma 3 cells are a separate lineage of T cells with unique requirements for proper thymic differentiation and survival.

Calmodulin decreases the estrogen binding capacity of the estrogen receptor

We previously demonstrated the ability of calmodulin (CaM) to decrease the binding affinity of estradiol (E2) to the rat uterine estrogen receptor (ER). We show now that CaM induces a loss of E2 binding capacity especially when ER molecules exhibit a lower binding affinity for the hormone. By Western blotting and [125I]tamoxifen aziridine covalent labeling we found that this CaM-induced loss is not associated with a disappearance of the ER protein. In addition, we were able to demonstrate a CaM-mediated decrease in E2 binding of a human recombinant ER expressing solely its hormone binding domain (HBD, aa 282-595). Hence, CaM can modulate the structure of the HBD of the ER without any involvement of a degradative process, this conformational change is not mediated by other domains of the receptor and/or components of the native ER heterocomplex.

Tamoxifen aziridine labeling of the estrogen receptor-potential utility in detecting biologically aggressive breast tumors

Expression of estrogen receptor (ER) is a helpful predictor of response to endocrine therapy and disease free survival in breast cancer patients. The presence of variant estrogen receptors has been demonstrated at the RNA/DNA level and might represent an escape of tumors from hormonal control mechanisms. However, the demonstration that the corresponding peptides do exist is a real challenge. Denaturing polyacrylamide gel electrophoresis (SDS-PAGE) of covalently bound [3H]tamoxifen aziridine ([3H]TAZ) to ER demonstrates a specific, multiband peptide pattern recognized by anti-ER monoclonal antibodies (anti-ER Mo Abs). The native 66 kDa ER form identified through its hormone binding domain by the H-222 Mo Ab was the most prominent one followed by 50, 35, and 28 kDa forms on fluorography. Such patterns from early human breast tumors were compared to the ones of more advanced disease, namely large primary breast cancers, metastatic lymph nodes, and soft tissue relapses: in these cases, molecular forms of 43 and 35 kDa were identified with a remarkable consistency. The 43 kDa peptide was more frequently identified by the H-226 Mo Ab (which maps a region near the DNA binding domain)-albeit with low labeling intensity as compared to H-222 Mo Ab. In addition, the 43 kDa peptide was inversely correlated to ER levels. This altered ER or related peptide could potentially be a marker of biologically aggressive breast tumors.