Ferdinando Auricchio

Tyrosine kinase/p21ras/MAP-kinase pathway activation by estradiol-receptor complex in MCF-7 cells.

The mechanism by which estradiol acts on cell multiplication is still unclear. Under conditions of estradiol‐dependent growth, estradiol treatment of human mammary cancer MCF‐7 cells triggers rapid and transient activation of the mitogen‐activated (MAP) kinases, erk‐1 and erk‐2, increases the active form of p21ras, tyrosine phosphorylation of Shc and p190 protein and induces association of p190 to p21ras‐GAP. Both Shc and p190 are substrates of activated src and once phosphorylated, they interact with other proteins and upregulate p21ras. Estradiol activates the tyrosine kinase/p21ras/MAP‐kinase pathway in MCF‐7 cells with kinetics which are similar to those of peptide mitogens. It is only after introduction of the human wild‐type 67 kDa estradiol receptor cDNA that Cos cells become estradiol‐responsive in terms of erk‐2 activity. This finding, together with the inhibition by the pure anti‐estrogen ICI 182 780 of the stimulatory effect of estradiol on each step of the pathway in MCF‐7 cells proves that the classic estradiol receptor is responsible for the transduction pathway activation. Transfection experiments of Cos cells with the estradiol receptor cDNA and in vitro experiments with c‐src show that the estradiol receptor activates c‐src and this activation requires occupancy of the receptor by hormone. Our experiments suggest that c‐src is an initial and integral part of the signaling events mediated by the estradiol receptor.

Two Domains of the Progesterone Receptor Interact with the Estrogen Receptor and Are Required for Progesterone Activation of the c-Src/Erk Pathway in Mammalian Cells

ABSTRACT In breast cancer cells, estrogens activate the Src/Erk pathway through an interaction of the estrogen receptor alpha (ERα) with the SH2 domain of c-Src. Progestins have been reported to activate also this pathway either via an interaction of the progesterone receptor isoform B (PRB) with ERα, which itself activates c-Src, or by direct interaction of PRB with the SH3 domain of c-Src. Here we identify two domains of PRB, ERID-I and -II, mediating a direct interaction with the ligand-binding domain of ERα. ERID-I and ERID-II flank a proline cluster responsible for binding of PRB to c-Src. In mammalian cells, the interaction of PRB with ERα and the progestin activation of the Src/Erk cascade are abolished by deletion of either ERID-I or ERID-II. These regions are not required for transactivation of a progesterone-responsive reporter gene. Mutations in the proline cluster of PRB that prevent a direct interaction with c-Src do not affect the strong activation of c-Src by progestins in the presence of ERα. Thus, in cells with ERα, ERID-I and ERID-II are necessary and sufficient for progestin activation of the endogenous Src/Erk pathway.

Sex steroid hormones act as growth factors

We observed that sex steroid hormones, like growth factors, stimulate the Src/Ras/erk pathway of cell lines derived from human mammary or prostate cancers. In addition, hormone-dependent pathway activation can be induced in Cos cells, upon transfection of classic steroid receptors. Cross-talks between sex steroid receptors regulate their association with Src and consequent pathway activation. Oestradiol treatment of MCF-7 cells triggers simultaneous association of ER with Src and p85, the regulatory subunit of phosphatidylinositol-3-kinase (PI3-kinase) and activation of Src- and PI3-K-dependent pathways. Activation of the latter pathway triggers cyclin D1 transcription, that is unaffected by Mek-1 activation. This suggests that simultaneous activation of different signalling effectors is required to target different cell cycle components. Thus, a novel reciprocal cross-talk between the two pathways appears to be mediated by the ER. In all tested cells, activation of the signalling pathways has a proliferative role. Transcriptionally inactive ER expressed in NIH 3T3 cells responds to hormone causing Src/Ras/Erk pathway activation and DNA synthesis. This suggests that in these cells genomic activity is required for later events of cell growth.

Inhibition of the SH3 domain-mediated binding of Src to the androgen receptor and its effect on tumor growth

In human mammary and prostate cancer cells, steroid hormones or epidermal growth factor (EGF) trigger association of the androgen receptor (AR)-estradiol receptor (ER) (α or β) complex with Src. This interaction activates Src and affects the G1 to S cell cycle progression. In this report, we identify the sequence responsible for the AR/Src interaction and describe a 10 amino-acid peptide that inhibits this interaction. Treatment of the human prostate or mammary cancer cells (LNCaP or MCF-7, respectively) with nanomolar concentrations of this peptide inhibits the androgen- or estradiol-induced association between the AR or the ER and Src the Src/Erk pathway activation, cyclin D1 expression and DNA synthesis, without interfering in the receptor-dependent transcriptional activity. Similarly, the peptide prevents the S phase entry of LNCaP and MCF-7 cells treated with EGF as well as mouse embryo fibroblasts stimulated with androgen or EGF. Interestingly, the peptide does not inhibit the S phase entry and cytoskeletal changes induced by EGF or serum treatment of AR-negative prostate cancer cell lines. The peptide is the first example of a specific inhibitor of steroid receptor-dependent signal transducing activity. The importance of these results is highlighted by the finding that the peptide strongly inhibits the growth of LNCaP xenografts established in nude mice.

Inhibition of Estradiol Receptor/Src Association and Cell Growth by an Estradiol Receptor Tyrosine-Phosphorylated Peptide

This report offers direct evidence that association of the estradiol receptor (ER) with Src triggered by steroid agonists or growth factors controls breast and prostate cancer cell growth. This association is abolished in whole cells and in vitro by a six-amino-acid peptide that mimics the sequence around the phosphotyrosine residue in position 537 of the human ERα. The phosphorylated peptide, at nanomolar concentrations, is taken up by MCF-7 and LNCaP cells derived from human mammary and prostate cancers, respectively. In addition, to block the ER/Src interaction, the phosphopeptide inhibits Src/Erk pathway, cyclin D1 expression, and DNA synthesis induced by estradiol or androgen or triggered by epidermal growth factor. In contrast, no inhibition of the Src-mediated epidermal growth factor action on DNA synthesis is detectable in human mammary cancer cells that do not express ER (MDA-MB231), indicating that the peptide specifically targets the ER-associated Src. Remarkably, the peptide, in contrast with classic steroid antagonists, does not interfere in ER- or androgen receptor–dependent transcriptional activity. Nevertheless, it markedly inhibits the growth of MCF-7 cell xenografts induced in immunodepressed and estradiol-treated mice. The present report suggests that inhibition of association of steroid receptors with Src or other signaling effectors may have therapeutic applications for patients with ER-positive tumors. (Mol Cancer Res 2007;5(11):1213–21)

Src is an initial target of sex steroid hormone action.

Abstract: Recent observations that steroids use pathways universally known to be regulated by growth factors and interleukins highlight the following points: (1) Steroid stimulation of the canonical pathway Src/Ras/Erk signaling from membrane to nuclei or its single members has been observed in different cell types including human cancer‐derived cells, neurons, osteoblasts, osteocytes, and endothelial cells. This stimulation has been reconstituted and analyzed in transiently transfected cells. (2) Cellular context and intracellular localization of receptors are crucial in determining the biological effects evoked by this hormonal stimulation: proliferation, protection from apoptosis, and vasorelaxation. (3) Classical steroid receptors localized in the extranuclear compartment directly and, in some cases, simultaneously interact with Src. They are capable of unexpected cross talks responsible for the observed effects. (4) Other signaling pathways including P13K/AKT are also stimulated by steroids. The aim of future work will be to arrive at an integrated general view of the different signaling pathways activated by steroids and to analyze the concert between these pathways and the hormonal transcriptional action. This general view should be simultaneously verified in different cell contexts, under different physiologic and pathologic conditions. We expect that the new technologies, above all gene and protein microarray, will make this goal feasible.

Oestradiol stimulates tyrosine phosphorylation and hormone binding activity of its own receptor in a cell-free system.

Recent experiments have shown that calf uterus oestrogen receptor exists in a tyrosine‐phosphorylated hormone binding form and in non‐phosphorylated, non‐hormone binding form. We report here that physiological concentrations of oestradiol in complex with the receptor stimulate the calf uterus receptor kinase that converts the non‐hormone binding receptor into hormone binding receptor through phosphorylation of the receptor on tyrosine. The activity of this enzyme has been followed by reactivation of hormone binding sites and phosphorylation on tyrosine of calf uterus phosphatase‐inactivated receptor. Phosphorylation of the receptor has been demonstrated by interaction of kinase 32P‐phosphorylated proteins with anti‐receptor antibody followed either by sucrose gradient centrifugation or SDS‐PAGE of the immunoprecipitated proteins. Hormone stimulation of the kinase is inhibited by receptor occupancy of the anti‐oestrogen tamoxifen. Oestradiol‐receptor complex increases the affinity of the kinase for the dephosphorylated receptor. Findings of this report are consistent with the observation that several protein tyrosine kinases that are associated with peptide hormone receptors are stimulated by the binding of the hormone to the receptor. This is the first report on the activation of a tyrosine kinase by a steroid hormone. The finding that hormones can regulate their own receptor binding activity through a tyrosine kinase is also new.

Tyrosine phosphorylation of estradiol receptor by Src regulates its hormone-dependent nuclear export and cell cycle progression in breast cancer cells

We report that in breast cancer cells, tyrosine phosphorylation of the estradiol receptor alpha (ERalpha) by Src regulates cytoplasmic localization of the receptor and DNA synthesis. Inhibition of Src or use of a peptide mimicking the ERalpha p-Tyr537 sequence abolishes ERalpha tyrosine phosphorylation and traps the receptor in nuclei of estradiol-treated MCF-7 cells. An ERalpha mutant carrying a mutation of Tyr537 to phenylalanine (ER537F) persistently localizes in nuclei of various cell types. In contrast with ERalpha wt, ER537F does not associate with Ran and its interaction with Crm1 is insensitive to estradiol. Thus, independently of estradiol, ER537F is retained in nuclei, where it entangles FKHR-driving cell cycle arrest. Chromatin immunoprecipitation analysis reveals that overexpression of ER537F in breast cancer cells enhances FKHR interaction with cyclin D1 promoter. This mutant also counteracts cell transformation by the activated forms of Src or PI3-K. In conclusion, in addition to regulating receptor localization, ERalpha phosphorylation by Src is required for hormone responsiveness of DNA synthesis in breast cancer cells.

In vitro phosphorylation and hormone binding activation of the synthetic wild type human estradiol receptor

A tyrosine kinase purified from calf uterus activates the hormone binding of endogenous estradiol receptor (ER) predephosphorylated and preinactivated by a nuclear phosphotyrosine phosphatase. The kinase also activates and phosphorylates the human estradiol receptor HEO synthesized in vitro, which differs from the wild type receptor HEGO because a glycine is replaced by a valine at position 400. Moreover, the kinase activates and phosphorylates a deletion mutant of HEO which consists almost exclusively of the hormone binding domain. Using HEGO and HEO in parallel and measuring both binding activation and phosphorylation of ER we now observe that the wild type receptor is a good kinase substrate, slightly better than HEO. Furthermore, HEGO like the calf uterus receptor in the presence of estradiol, stimulates the kinase. From present findings it appears that ER and uterus tyrosine kinase are functionally associated and that this association is abolished by glycine to valine substitution at position 400 of ER.

Role of non-genomic androgen signalling in suppressing proliferation of fibroblasts and fibrosarcoma cells.

The functions of androgen receptor (AR) in stromal cells are still debated in spite of the demonstrated importance of these cells in organ development and diseases. Here, we show that physiological androgen concentration (10 nM R1881 or DHT) fails to induce DNA synthesis, while it consistently stimulates cell migration in mesenchymal and transformed mesenchymal cells. Ten nanomolar R1881 triggers p27 Ser10 phosphorylation and its stabilization in NIH3T3 fibroblasts. Activation of Rac and its downstream effector DYRK 1B is responsible for p27 Ser10 phosphorylation and cell quiescence. Ten nanomolar androgen also inhibits transformation induced by oncogenic Ras in NIH3T3 fibroblasts. Overexpression of an AR mutant unable to interact with filamin A, use of a small peptide displacing AR/filamin A interaction, and filamin A knockdown indicate that the androgen-triggered AR/filamin A complex regulates the pathway leading to p27 Ser10 phosphorylation and cell cycle arrest. As the AR/filamin A complex is also responsible for migration stimulated by 10 nM androgen, our report shows that the androgen-triggered AR/filamin A complex controls, through Rac 1, the decision of cells to halt cell cycle and migration. This study reveals a new and unexpected role of androgen/AR signalling in coordinating stromal cell functions.