Proximal Events in Signaling by Plasma Membrane Estrogen Receptors

Abstract

Estradiol (E2) rapidly stimulates signal transduction from plasma membrane estrogen receptors (ER) that are G protein-coupled. This is reported to occur through the transactivation of the epidermal growth factor receptor (EGFR) or insulin-like growth factor-1 receptor, similar to other G protein-coupled receptors. Here, we define the signaling events that result in EGFR and ERK activation. E2-stimulated ERK required ER in breast cancer and endothelial cells and was substantially prevented by expression of a dominant negative EGFR or by tyrphostin AG1478, a specific inhibitor for EGFR tyrosine kinase activity. Transactivation/phosphorylation of EGFR by E2 was dependent on the rapid liberation of heparin-binding EGF (HB-EGF) from cultured MCF-7 cells and was blocked by antibodies to this ligand for EGFR. Expression of dominant negative mini-genes for G␣ q and G␣ i blocked E2-induced, EGFR-dependent ERK activation, and G␤␥ also contributed. G protein activation led to activation of matrix metalloproteinases (MMP)-2 and -9. This resulted from Src-induced MMP activation, implicated using PP2 (Src family kinase inhibitor) or the expression of a dominant negative Src protein. Antisense oligonucleotides to MMP-2 and MMP-9 or ICI 182780 (ER antagonist) each prevented E2-induced HB-EGF liberation and ERK activation. E2 also induced AKT up-regulation in MCF-7 cells and p38␤ MAP kinase activity in endothelial cells, blocked by an MMP inhibitor, GM6001, and tyrphostin AG1478. Targeting of only the E domain of ER␣ to the plasma membrane resulted in MMP activation and EGFR transactivation. Thus, specific G proteins mediate the ability of E2 to activate MMP-2 and MMP-9 via Src. This leads to HB-EGF transactivation of EGFR and signaling to multiple kinase cascades in several target cells for E2. The E domain is sufficient to enact these events, defining additional details of the important cross-talk between membrane ER and EGFR in breast cancer.

RASSF1A inhibits estrogen receptor alpha expression and estrogen-independent signalling: implications for breast cancer development

“…11,13,47,48 In turn, Src mediates activation of matrix metalloproteinases that liberate HB-EGF bound to the surface of the MCF7 cells, leading to epidermal growth factor receptor transactivation and activation of Ras-MAPK pathway. 11 Our results are consistent with the notion that RASSF1A suppresses E2-mediated liberation of membrane-bound HB-EGF, in turn inhibiting the rapid and transient activation of the Ras-MAPK pathway (Figure 8). On the other hand, Akt activity inhibits Raf signalling in MCF7 cells.…”

“…7,8 In addition to direct transcriptional effects, ERs localized to the plasma membrane can influence the activity of signalling pathways through coupling directly or indirectly to G-proteins by non-genomic mechanisms. 7 This leads to activation of downstream effectors such as protein kinase C-d, 9 mitogen activated protein kinase ERK (MAPK) 9,10,11 and phosphatidylinositol-3-OH kinase (PI3K). 12,13 Thus, ERa is a key player in E2-mediated proliferation, survival and differentiation through regulating the transcription of E2-target genes as well as through activation of signal transduction pathways.…”

Dual targeting of Src and ER prevents acquired antihormone resistance in breast cancer cells

“…Further studies [36,37] also provide compelling evidence that targeting Src may be of value in combination with existing chemotherapy to provide an augmented antitumour response. In breast cancer cells, Src is implicated as a key element in non-genomic, oestrogen-induced MAPK and MMP activation [16,38,39] and oestrogen-mediated cellular proliferation and cell-cycle progression [40,41]. Interestingly, tamoxifen treatment itself has been reported to promote activation of intercellular signalling elements, including Src, resulting in cellular migration [42] and tamoxifen-mediated adhesion-dependent cell survival occurs through a Src-dependent process [43].…”

“…Steroidinduced cellular responses involve activation of Src and, although the molecular pathways involved in these responses have yet to be fully defined, can involve growth factor receptor signalling. For example, targeting of the Cterminal region of the ER to the membrane of ER-negative breast cancer cells results in oestrogen-stimulated, c-Srcdependent responses including activation of the epidermal growth factor receptor (EGFR) [16]. Furthermore, oestrogen stimulation results in the recruitment and activation of Src leading to activation of Shc, MEK/MAPK, and PI3K/ PKB [17].…”

Expression of estrogen receptor α (ERα) in the rat temporomandibular joint

“…In contrast, an alternative pathway for estrogen action-nongenomic action of this molecule-has been predicted under physiological conditions; however, this is still the subject of ongoing discussions. Cytoplasmic and plasma membrane complexes of estrogen/ER␣ appear to participate in signal transduction, resulting in the regulation of cell growth, survival, and migration (for review, see Levin, 2002;Razandi et al, 2003). The activity of p38, a member of the mitogen-activated protein (MAP) kinase family, is stimulated by estrogen.…”