Fulvestrant-induced expression of erbB3 and erbB4 sensitizes ER-positive breast cancer cells to heregulins

We have previously reported that induction of EGFR and erbB2 in response to antihormones may provide an early mechanism allowing breast cancer cells to evade the growth inhibitory action of such therapies and ultimately drive resistant growth. More recently, another member of the erbB receptor family, erbB3, has been implicated in antihormone resistance in breast cancer. In the present study we have investigated whether induction of erbB3, and related family member erbB4, may provide an alternative resistance mechanism to antihormonal action in a panel of four ER-positive breast cancer cell lines. MCF-7, T47D, BT474 and MDAMB361 cell lines were exposed to fulvestrant (100 nM) for 7 days, and effects on erbB3/4 signalling and growth were assessed. Effects of the erbB3/4 ligand heregulin-β1 were also examined in the absence and presence of fulvestrant. Fulvestrant potently reduced ER expression and transcriptional activity and significantly inhibited growth in all four cell lines. However, alongside this inhibitory activity, fulvestrant also consistently induced protein expression and activity of erbB4 in the four cell lines and also promoted erbB3, erbB2 and EGFR protein expression and activity in MCF-7 and T47D cells. Consequently, fulvestrant treatment sensitised each cell line to the actions of heregulin-β1 with enhanced erbB3/4-driven signalling activity and significant increases in cell proliferation being observed when compared with untreated cells. Indeed, in T47D and MDAMB361, heregulin-β1 was converted from a ligand having negligible or suppressive growth activity into one that potently promoted cell proliferation. Consequently, fulvestrant-induced growth inhibition was completely overridden by heregulin-β1 in all four cell lines. In conclusion, these findings would suggest that although antihormones, such as fulvestrant, may have potent acute growth inhibitory activity in ER-positive breast cancer cells, their ability to induce and sensitize cells to growth factors, such as heregulins, may serve to reduce and ultimately limit their inhibitory activity

Recruitment of insulin receptor substrate-1 by erbB3 impacts on IGF-IR signalling in oestrogen receptor-positive breast cancer cells

Insulin-like growth factor receptor (IGF-IR) signalling classically involves phosphorylation of insulin receptor substrate-1 (IRS-1) to recruit key down-stream signalling pathways effecting breast cancer cell proliferation and survival. Recently, we have shown a further capacity for IRS-1 to associate with the epidermal growth factor receptor (EGFR/erbB1), with activation of EGFR promoting recruitment and phosphorylation of IRS-1 in an oestrogen receptor (ER)-positive tamoxifen-resistant breast cancer cell line. In this study, we examined recruitment of IRS-1 by another member of the erbB receptor family, erbB3, in three ER-positive breast cancer cell lines. Our studies revealed an interaction between erbB3 and IRS-1 in MCF-7, T47D and BT474 cells with HRGβ1 treatment significantly enhancing this recruitment and promoting IRS-1 phosphorylation at tyrosine (Y) 612, a specific phosphoinositide 3-kinase (PI3K) binding site. IRS-1 appears to play a key role in erbB3 signalling in MCF-7 and T47D cells as its knockdown using siRNA greatly impaired HRGβ1 signalling via PI3K/AKT in these cell lines. This novel interaction may have clinical relevance as immunohistochemical analysis of ER-positive breast cancer patient samples revealed IRS-1 Y612 expression positively correlated with total erbB3, p-AKT and Ki67 expression. Importantly, we found that recruitment of IRS-1 by erbB3 impaired IRS-1 recruitment by IGF-IR in both MCF-7 and T47D cells, whilst blockade of IGF-1R enhanced erbB3/IRS-1 interaction and sensitised both cell lines to HRGβ1. Consequently, blockade of erbB3 signalling enhanced the effects of IGF-IR inhibition in these cells. In conclusion, these and previous findings suggest that IRS-1 can be recruited to IGF-1R, EGFR and erbB3 in ER-positive breast cancer cells and this may provide an adaptive resistance mechanism when these receptors are targeted individually. Consequently co-targeting of IGF-IR and erbB receptors may prove to be a more effective strategy for the treatment of ER-positive breast cancer

Endocrine resistance in breast cancer: new roles for ErbB3 and ErbB4

Endocrine resistance is a major limitation to the successful treatment of estrogen receptor-positive (ER+) breast cancer, and the EGFR (epidermal growth factor receptor) and ErbB-2 receptor tyrosine kinases are involved in this process. A recent study now implicates the other two ErbB family members, ErbB-3 and -4. Exposure of ER+ breast cancer cells to the pure antiestrogen, fulvestrant, increased levels of ErbB-3 or ErbB-4 and sensitivity to the growth-stimulatory effects of heregulin ݱ, a potent ligand for these receptors. Thus, the initial growth-inhibitory effects of fulvestrant appear compromised by cellular plasticity that allows rapid compensatory growth stimulation via ErbB-3/4. Further evaluation of pan-ErbB receptor inhibitors in endocrine-resistant disease appears warranted

Connexin-mimetic peptide Gap 27 decreases osteoclastic activity

BACKGROUND: Bone remodelling is dependent on the balance between bone resorbing osteoclasts and bone forming osteoblasts. We have shown previously that osteoclasts contain gap-junctional protein connexin-43 and that a commonly used gap-junctional inhibitor, heptanol, can inhibit osteoclastic bone resorption. Since heptanol may also have some unspecific effect unrelated to gap-junctional inhibition we wanted to test the importance of gap-junctional communication to osteoclasts using a more specific inhibitor. METHODS: A synthetic connexin-mimetic peptide, Gap 27, was used to evaluate the contribution of gap-junctional communication to osteoclastic bone resorption. We utilised the well-characterised pit-formation assay to study the effects of the specific gap-junctional inhibitor to the survival and activity of osteoclasts. RESULTS: Gap 27 caused a remarked decrease in the number of both TRAP-positive mononuclear and multinucleated rat osteoclasts cultured on bovine bone slices. The decrease in the cell survival seemed to be restricted to TRAP-positive cells, whereas the other cells of the culture model seemed unaffected. The activity of the remaining osteoclasts was found to be diminished by measuring the percentage of osteoclasts with actin rings of all TRAP-positive cells. In addition, the resorbed area in the treated cultures was greatly diminished. CONCLUSIONS: On the basis of these results we conclude that gap-junctional communication is essential for the action of bone resorbing osteoclasts and for proper remodelling for bone

Prognostic significance of the expression of GFRα1, GFRα3 and Syndecan-3, Proteins binding ARTEMIN, In mammary carcinoma

10.1186/1471-2407-13-34BMC Cancer13-BCMA

Transphosphorylation of kinase-dead HER3 and breast cancer progression: a new standpoint or an old concept revisited?

Although neither kinase-dead human epidermal growth factor receptor (HER)3 nor orphan HER2 can be activated by HER-related ligands on their own, the formation of HER2/HER3 heterodimers creates the most mitogenic and transforming receptor complex within the HER (erbB) family of transmembrane receptor tyrosine kinases. The incorporation of markers such as HER3 transactivation, HER2/HER3 dimer, or others that may provide information regarding the level of HER pathway engagement has been demonstrated to allow identification of patients who respond to or escape HER-targeted therapies. Pioneering studies showed that high expression of kinase-dead HER3 can predict early escape from the anti-HER2 monoclonal antibody trastuzumab. Also, the growth-inhibitory effects of HER1/2 tyrosine kinase inhibitors (TKIs) were previously found to be attenuated in the presence of heregulin, which is a high-affinity combinatorial ligand for HER3. All of these concepts are being revisited with respect to the efficacy of HER family TKI therapies; in particular, HER3 signalling buffered against incomplete inhibition of HER2 kinase activity has been suggested to be the mechanism that allows HER2 over-expressing breast cancer cells to escape HER TKIs. It remains to be elucidated whether reactivation of HER3 signalling can also account for the poor efficacy of HER TKIs in treating breast carcinomas that contain low overall levels of HER2 receptors. However, it appears that regardless of the mechanism that triggers the formation of oncogenic HER2/HER3 heterodimers (HER2 over-expression or overall low HER2 but high levels of the HER3 ligand heregulin), HER3 transphosphorylation is a common response of breast cancer cells upon treatment with current inhibitors of the HER receptor tyrosine kinase network. Because kinase-inactive HER3 is not presently an amenable target for forthcoming HER TKIs, molecular approaches that can efficiently block heregulin-triggered HER3 transactivation or nucleocytoplasmic trafficking of heregulin might offer novel strategies with which to manage HER-driven breast cancer disease

Daily egg consumption in hyperlipidemic adults - Effects on endothelial function and cardiovascular risk

<p>Abstract</p> <p>Background</p> <p>Limiting consumption of eggs, which are high in cholesterol, is generally recommended to reduce risk of cardiovascular disease. However, recent evidence suggests that dietary cholesterol has limited influence on serum cholesterol or cardiac risk.</p> <p>Objective</p> <p>To assess the effects of egg consumption on endothelial function and serum lipids in hyperlipidemic adults.</p> <p>Methods</p> <p>Randomized, placebo-controlled crossover trial of 40 hyperlipidemic adults (24 women, 16 men; average age = 59.9 ± 9.6 years; weight = 76.3 ± 21.8 kilograms; total cholesterol = 244 ± 24 mg/dL). In the acute phase, participants were randomly assigned to one of the two sequences of a single dose of three medium hardboiled eggs and a sausage/cheese breakfast sandwich. In the sustained phase, participants were then randomly assigned to one of the two sequences of two medium hardboiled eggs and 1/2 cup of egg substitute daily for six weeks. Each treatment assignment was separated by a four-week washout period. Outcome measures of interest were endothelial function measured as flow mediated dilatation (FMD) and lipid panel.</p> <p>Results</p> <p>Single dose egg consumption had no effects on endothelial function as compared to sausage/cheese (0.4 ± 1.9 vs. 0.4 ± 2.4%; <it>p </it>= 0.99). Daily consumption of egg substitute for 6 weeks significantly improved endothelial function as compared to egg (1.0 ± 1.2% vs. -0.1 ± 1.5%; <it>p </it>< 0.01) and lowered serum total cholesterol (-18 ± 18 vs. -5 ± 21 mg/dL; <it>p </it>< 0.01) and LDL (-14 ± 20 vs. -2 ± 19 mg/dL; <it>p </it>= 0.01). Study results (positive or negative) are expressed in terms of change relative to baseline.</p> <p>Conclusions</p> <p>Egg consumption was found to be non-detrimental to endothelial function and serum lipids in hyperlipidemic adults, while egg substitute consumption was beneficial.</p