BSTRACTNestin, an intermediate filament protein and marker of undifferentiated cells, is expressed in several cancers. Nestin is important for neuronal survival and is a regulator of myogenesis but its function in malignancy is ambiguous. We show that nestin downregulation leads to a redistribution of phosphorylated focal adhesion kinase (pFAK, also known as PTK2) to focal adhesions and alterations in focal adhesion turnover. Nestin downregulation also leads to an increase in the protein levels of integrin a5b1 at the cell membrane, activation of integrin b1 and an increase in integrin clustering. These effects have striking consequences for cell invasion, as nestin downregulation leads to a significant increase in pFAK-and integrin-dependent matrix degradation and cell invasion. Our results indicate that nestin regulates the localisation and functions of FAK and integrin. Because nestin has been shown to be prevalent in a number of specific cancers, our observations have broad ramifications for the roles of nestin in malignant transformation.
Aberrant activation of the PI3K pathway is one of the commonest oncogenic events in human cancer. AKT is a key mediator of PI3K oncogenic function, and thus has been intensely pursued as a therapeutic target. Multiple AKT inhibitors, broadly classified as either ATP-competitive or allosteric, are currently in various stages of clinical development. Herein, we review the evidence for AKT dependence in human tumours and focus on its therapeutic targeting by the two drug classes. We highlight the future prospects for the development and implementation of more effective context-specific AKT inhibitors aided by our increasing knowledge of both its regulation and some previously unrecognised non-canonical functions.
The HER2 transmembrane receptor is a well-characterised predictive marker for trastuzumab benefit and may be associated with decreased benefit from endocrine therapy use. Despite the clinical effectiveness of anti-HER2 agents in such cases, resistance represents a significant limiting factor. Focal adhesion kinase (FAK) plays an important role in HER2 signalling, mediating downstream Akt activation in addition to HER2 cross talk with other growth factor receptors. In this study, we investigated the therapeutic potential of FAK in oestrogen receptor-positive (ERC)/HER2C breast cancer using the novel FAK-specific inhibitor PF4554878 ('PF878'). The activation of the FAK/HER2 signalling pathway was assessed in ERC/HER2K (MCF7 and T47D) and ERC/HER2C (BT-474 and MDAMB361) breast cancer cells in the presence or absence of PF878 and PF878Gtrastuzumab. The effects of PF878 on cell growth as a monotherapy and in combination with trastuzumab were assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Coulter counting with isobologram analysis to determine synergy/additive effects. FAK activation (at Y861 but not at Y397) was highest in ERC/HER2C cells, which also demonstrated the greatest sensitivity to PF878. As a monotherapy, PF878 prevented heregulin-induced MDA361 cell migration, but had no significant effect on cell growth. The treatment of ERC/HER2C cells with PF878 and trastuzumab in combination resulted in the synergistic inhibition of cell proliferation. Underlying this was an abrogation of Akt activity and increased poly(ADP-ribose) polymerase cleavage, effects that were greatest in trastuzumab-refractory MDA361 cells. Collectively, these data support a role for FAK in ERC/HER2C breast cancer, where its targeting has the potential to improve trastuzumab response. This is particularly important in the context of ERC/HER2C, trastuzumab-refractory disease, where FAK inhibition may present an important strategy to restore trastuzumab sensitivity.
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