Targeting Fibroblast Growth Factor Receptors Blocks PI3K/AKT Signaling, Induces Apoptosis, and Impairs Mammary Tumor Outgrowth and Metastasis

Abstract

Members of the fibroblast growth factor receptor (FGFR) family have essential roles in normal physiology and in cancer where they control diverse processes. FGFRs have been associated with breast cancer development. Thus, models to study the role of FGFR in breast cancer and their targeting potential are important. We present an in vitro and in vivo analysis of FGFRs in the breast cancer model cell lines 67NR and 4T1. We show that both tumor cell lines coexpress FGFRs and ligands and display autocrine FGFR signaling activity. Fibroblast growth factor receptor substrate 2 (FRS2), a downstream mediator of FGFR, is constitutively tyrosine phosphorylated and multiple signaling pathways are active. Treatment of 67NR and 4T1 cultures with TKI258, an FGFR tyrosine kinase inhibitor (TKI), caused a rapid decrease in FRS2 phosphorylation; decreased the activity of extracellular signal-regulated kinase 1/2 (ERK1/2), AKT, and phospholipase Cγ; and blocked proliferation of both tumor lines. Furthermore, TKI258 induced 4T1 apoptotic cell death via blockade of the phosphoinositide 3-kinase/AKT pathway. In vivo, one dose of TKI258 rapidly lowered FRS2 phosphorylation and ERK1/2 and AKT activity in mammary tumors. Long-term TKI258 treatment of 4T1 tumor-and 67NR tumor-bearing mice had a significant effect on primary tumor outgrowth and 4T1 tumor-induced lung metastases. A microarray analysis was carried out to identify targets with roles in TKI258 antitumor activity and potential prognostic markers in human breast tumors. Of interest are the downregulated matrix metalloproteases (MMP), in particular MMP9, which is essential for metastatic spread of 4T1 tumors.

Contribution of the R-Ras2 GTP-binding protein to primary breast tumorigenesis and late-stage metastatic disease

“…10). Although challenging the signalling dogma holding that the GTPase-dependent stimulation of PI3Ka is mostly mediated by direct physical interactions with oncogenic Ras proteins 33 , these results are consistent with previous data indicating that the PI3Ka/Akt axis can be activated in Ras-independent manners in some Ras-transformed cells 16,24,[34][35][36][37] . Interestingly, the influence of R-Ras2 on the PI3K/Akt pathway is highly dependent on the experimental conditions used.…”

“…These cells represent good tools to address functional redundancy issues, because they exhibit constitutive activation of classical Ras proteins due to the presence of either oncogenic mutations (MDA-MB-231-Luc cells) 22,23 or autocrine signalling loops (4T1 cells) 24 . These cell lines also differ in metastatic potential, thus facilitating the use of both gain-and loss-of-function approaches to analyse the role of R-Ras2 in this process 25 .…”

Biological reprogramming in acquired resistance to endocrine therapy of breast cancer

“…Accordingly, the expression of FGFR1 and FGFR2 is partially regulated by E2F1 (Tashiro et al, 2003;Kanai et al, 2009). Furthermore, targeting FGFR-mediated signaling that acts in an autocrine manner in a subset of breast cancers of poor prognosis has been shown to impair tumor outgrowth and metastasis (Dey et al, 2010). These data, together with observations linking FGFR2 and risk of breast cancer (Easton et al, 2007;Hunter et al, 2007;Meyer et al, 2008), further support that FGFR-mediated signaling is central in breast carcinogenesis.…”

The novel miR-9500 regulates the proliferation and migration of human lung cancer cells by targeting Akt1

“…Akt1 expression is associated with cell survival, growth, and migration in cancer, 26,27 and a decrease in p-AKT expression levels due to Akt1 knockdown considerably affects cell proliferation. 29 We found that the proliferation of the A549 cells was inhibited by the overexpression of miR-9500 compared with the overexpression of the NC (Figures 4a and b).…”

“…23,24 The primary regulator of the PI3K pathway is Akt, a protein kinase B that mediates cell survival, cell death, 25 cell growth, cell migration and angiogenesis. [26][27][28] The silencing of the Akt1 gene has been shown to inhibit the proliferation of gastric cancer cells both in vitro and in vivo. 29 Other studies have shown that aberrant AKT activation has a critical role in tumorigenesis.…”