FAK activates AKT-mTOR signaling to promote the growth and progression of MMTV-Wnt1-driven basal-like mammary tumors

Abstract

Background: Breast cancer is a heterogeneous disease. Hence, stratification of patients based on the subtype of breast cancer is key to its successful treatment. Among all the breast cancer subtypes, basal-like breast cancer is the most aggressive subtype with limited treatment options. Interestingly, we found focal adhesion kinase (FAK), a cytoplasmic tyrosine kinase, is highly overexpressed and activated in basal-like breast cancer. Methods: To understand the role of FAK in this subtype, we generated mice with conditional deletion of FAK and a knock-in mutation in its kinase domain in MMTV-Wnt1-driven basal-like mammary tumors. Tumor initiation, growth, and metastasis were characterized for these mice cohorts. Immunohistochemical and transcriptomic analysis of Wnt1-driven tumors were also performed to elucidate the mechanisms underlying FAK-dependent phenotypes. Pharmacological inhibition of FAK and mTOR in human basal-like breast cancer cell lines was also tested. Results: We found that in the absence of FAK or its kinase function, growth and metastasis of the tumors were significantly suppressed. Furthermore, immunohistochemical analyses of cleaved caspase 3 revealed that loss of FAK results in increased tumor cell apoptosis. To further investigate the mechanism by which FAK regulates survival of the Wnt1-driven tumor cells, we prepared an isogenic pair of mammary tumor cells with and without FAK and found that FAK ablation increased their sensitivity to ER stress-induced cell death, as well as reduced tumor cell migration and tumor sphere formation. Comparative transcriptomic profiling of the pair of tumor cells and gene set enrichment analysis suggested mTOR pathway to be downregulated upon loss of FAK. Immunoblot analyses further confirmed that absence of FAK results in reduction of AKT and downstream mTOR pathways. We also found that inhibition of FAK and mTOR pathways both induces apoptosis, indicating the importance of these pathways in regulating cell survival. Conclusions: In summary, our studies show that in a basal-like tumor model, FAK is required for survival of the tumor cells and can serve as a potential therapeutic target.

The Role of Csmd1 during Mammary Gland Development

“…The potential impact of these changes is that the duct cells in the KO mice are able to generate an increased number of cell-ECM interactions, via increased focal adhesion action [ 57 , 58 , 59 ]. Since the changes in Fak and Akt expression are similar, this suggests that increased Fak mediated signalling of Akt pathways is occurring in the Csmd1 KO mice [ 60 , 61 , 62 ]. In which this signalling cascade then promotes increased cell migration and invasion in the KO mice, via the increased action of focal adhesions [ 60 , 61 , 62 ].…”

Focal Adhesion Kinase Fine Tunes Multifaced Signals toward Breast Cancer Progression

“…In this regard, the rapid loss of FAK phosphorylation followed by poly (ADP-ribose) polymerase (PARP) cleavage was linked to a decrease of both caspase 3 activation and Akt and BCL2 associated agonist of cell death (Bad) phosphorylation toward anoikis of breast tumor cells [ 59 ]. Likewise, the ablation of FAK expression or the disruption of its kinase activity in a mouse model of a mouse mammary virus tumor (MMTV)-Wnt1-driven breast cancer, enhanced tumor cell apoptosis with an increase of cleaved caspase 3-positive cells [ 60 ]. Besides, a transcriptomic analysis performed in the isogenic FAK-knock out (KO)-Wnt1 cells revealed the reduction of a gene signature associated with survival transduction pathways, including the Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling cascade [ 60 ].…”

“…Likewise, the ablation of FAK expression or the disruption of its kinase activity in a mouse model of a mouse mammary virus tumor (MMTV)-Wnt1-driven breast cancer, enhanced tumor cell apoptosis with an increase of cleaved caspase 3-positive cells [ 60 ]. Besides, a transcriptomic analysis performed in the isogenic FAK-knock out (KO)-Wnt1 cells revealed the reduction of a gene signature associated with survival transduction pathways, including the Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling cascade [ 60 ]. Next, the dual inhibition of FAK and epidermal growth factor receptor (EGFR) cooperatively led to apoptosis of breast cancer cells via caspase-3 and caspase-8 activation, cleavage of PARP and caspase-3-mediated AKT degradation [ 61 ].…”

“…However, this response was evident in only expressing FRNK one day before the injection of tumor cells, but it was absent expressing FRNK many days after injection, hence suggesting the requirement of FAK in the early phases of the breast metastatic process [ 123 ]. FAK deletion and knock-in mutation of its kinase domain also suppressed the metastasis of basal-like mammary tumor driven by MMTV-Wnt1 [ 60 ]. In addition, the intravenously injection of FAK-deficient breast cancer cells in NOD/SCID mice nicely corroborated the pivotal role elicited by FAK in lung metastasis, as mice injected with FAK-null cells did not develop detectable lung metastasis over a 53-day period [ 58 ].…”

“…Comprehensive bioinformatics analyses based on the molecular taxonomy of breast cancer international consortium (METABRIC) and TCGA databases have assessed the significance of PTK2 expression in breast cancer patients. The acquired information has indicated that patients harboring amplified PTK2 levels exhibit a poorer overall survival (OS) with respect to patients without PTK2 amplification [ 60 , 62 ]. Other investigations have revealed that high PTK2 levels are associated with a short relapse-free survival (RFS) and tumor relapse in breast cancer [ 207 ].…”