PI3-kinase in concert with Src promotes the S-phase entry of oestradiol-stimulated MCF-7 cells

Abstract

The p85-associated phosphatidylinositol (PI) 3-kinase/Akt pathway mediates the oestradiol-induced S-phase entry and cyclin D1 promoter activity in MCF-7 cells. Experiments with Src, p85alpha and Akt dominant-negative forms indicate that in oestradiol-treated cells these signalling effectors target the cyclin D1 promoter. Oestradiol acutely increases PI3-kinase and Akt activities in MCF-7 cells. In NIH 3T3 cells expressing ERalpha, a dominant-negative p85 suppresses hormone stimulation of Akt. The Src inhibitor, PP1, prevents hormone stimulation of Akt and PI3-kinase activities in MCF-7 cells. In turn, stimulation of Src activity is abolished in ERalpha-expressing NIH 3T3 fibroblasts by co-transfection of the dominant-negative p85alpha and in MCF-7 cells by the PI3-kinase inhibitor, LY294002. These findings indicate a novel reciprocal cross-talk between PI3-kinase and Src. Hormone stimulation of MCF-7 cells rapidly triggers association of ERalpha with Src and p85. In vitro these proteins are assembled in a ternary complex with a stronger association than that of the binary complexes composed by the same partners. The ternary complex probably favours hormone activation of Src- and PI3-kinase-dependent pathways, which converge on cell cycle progression.

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

“…In agreement with our previous findings (Castoria et al, 2001), LNCaP or MCF-7 cells treated with R1881 or estradiol for 8 h show an increase in cyclin D1 expression and the Src-kinase inhibitor, PP2, abolished this hormonal effect (Figure 4a and c). The increased expression of cyclin D1 was clearly prevented by the S1 peptide and slightly decreased by the Ss peptide (Figure 4a and c).…”

“…In recent years, much evidence has shown that in multiple cell types under different experimental conditions, steroid receptors directly interact with several signaling effectors and trigger various biological effects. In addition to Src, these effectors include calmodulin (Castoria et al, 1988), the regulatory subunit of the phosphoinositide 3-kinase, p85a (Simoncini et al, 2000;Castoria et al, 2001), Shc (Song et al, 2002), modulator of non genomic activity of receptor (Wong et al, 2002), protein kinase Cz (Castoria et al, 2004), EGF receptor (Marquez et al, 2001;Migliaccio et al, 2005), and many other signaling or signaling-related proteins. Therefore, approaches similar to those followed in this report, that is, recognition of new receptor/signaling effector interactions and identification of new inhibitors of such interactions, could enable us to specifically inhibit different hormone actions mediated by signal transducing pathways in multiple cell types and in different pathological conditions.…”

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

“…E2 treatment has been reported to lead to rapid and transient activation of the Ras-MAPK pathway that is thought to proceed through a multistep process involving E2-bound ERa, Src and the p85 regulatory subunit of PI3K. 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).…”

“…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].…”