The role of focal adhesion kinase catalytic activity on the proliferation and migration of squamous cell carcinoma cells

Abstract

Focal adhesion kinase (FAK) is upregulated in several epithelial tumours and there has been considerable interest in developing small molecule kinase inhibitors of FAK. However, FAK also has important adaptor functions within the cell, integrating signals from both integrins and growth factors. To investigate the role of FAKs kinase domain, we generated fakdeficient squamous cell carcinoma (SCC) cell lines. Re-expression of a wild type or kinase dead FAK allowed us to delineate its kinase dependent functions. In addition, we used the novel FAK kinase inhibitor PF-562,271. The kinase activity of FAK was important for tumour cell migration and polarity but more striking was its requirement for the anchorage independent 3 dimensional (3D) proliferation of SCC cells and their growth as xenografts in mice. Inhibition of FAK activity and prevention of growth in 3D correlated with Src inhibition. We further identified a mechanism whereby FAK regulates proliferation in 3D via regulation of the kinase activity of Src. This was dependent on the kinase activity of FAK and its resulting phosphorylation on Y397 that provides a high affinity binding site for Src. These data support the further development of FAK kinase inhibitors as agents that have the potential to inhibit both tumour cell migration and proliferation.Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase found at focal adhesions, which are sites of integrin clustering at the cell-extracellular matrix interface, where it provides both signalling and scaffolding functions. It is involved in the dynamic regulation of these adhesion sites, a process that is critical for the control of cell migration. 1,2 FAK is also important for tumour cell invasion and metastasis, 3 where it is believed to integrate growth factor and integrin signals to promote both tumour cell migration and invasion. 2-4 FAK has also been linked to the protection of cells from suspension-induced apoptosis or anoikis 5-8 and introduction of inhibitory FAK constructs into tumour cells can lead to cell detachment and apoptosis. 9 FAK is therefore involved in a number of processes that can impact on the malignant phenotype, the importance of which is not fully understood. In support however, of a direct role for FAK in tumourigenesis we have shown, using targeted deletion of fak in mouse skin, the absolute requirement for FAK in malignant tumour formation. 10 More recently deletion of FAK has also been shown to be required for mammary tumour progression and the androgen-independent formation of neuroendocrine carcinoma in a prostate mouse model. [11][12][13][14][15] FAK is over-expressed in a number of human epithelial tumours [16][17][18] and FAK has therefore emerged as a potential target for cancer therapy 18-20 with a number of FAK kinase inhibitors being developed, one of which PF-562,271 is currently in clinical development. 21 There has been some debate surrounding the development of such agents as in addition to having kinase activity the adaptor function of FAK plays a key role in...

The MacBlue Binary Transgene (csf1r-gal4VP16/UAS-ECFP) Provides a Novel Marker for Visualisation of Subsets of Monocytes, Macrophages and Dendritic Cells and Responsiveness to CSF1 Administration

“…We speculated that the MacBlue transgene would enable live imaging of monocyte infiltration in tumours. To enable the use of the MacBlue transgene in tumour biology, we bred it to the FVB background, where we have an established model of squamous cell carcinoma which attracts very large numbers of TAMs [37], [38]. Figure 8 shows representative FACS profiles of the purified TAMs, and an intravital image of their location within established tumours, revealing their close association with the vasculature.…”

Focal adhesion complex proteins in epidermis and squamous cell carcinoma

“…1B). 56 This inhibition of FAK activity correlated with a decrease in phosphorylation of Src at tyrosine 416. 56 Skin-specific loss of FAK also prevented phorbol ester-induced skin carcinogenesis, potentially due to prevention of β-catenin-induced stem cell mobilization in the bulge of the hair follicle.…”

“…56 This inhibition of FAK activity correlated with a decrease in phosphorylation of Src at tyrosine 416. 56 Skin-specific loss of FAK also prevented phorbol ester-induced skin carcinogenesis, potentially due to prevention of β-catenin-induced stem cell mobilization in the bulge of the hair follicle. 57 Inhibition of Src, a kinase that intricately associates with FAK at FA complexes also showed the same effect on preventing stem cell mobilization.…”

FAK in cancer: mechanistic findings and clinical applications

“…Despite similarities between FAK- and Src-associated signaling pathways 116, 117 , unique FAK substrates have been identified and combined treatment with FAK and Src inhibitors shows enhanced anti-tumor activity in non-small cell lung cancer models 118 . FAK inhibitors have also exhibited enhanced activity in combination with cytotoxic drugs 65, 95 or agents targeting angiogenesis, like the receptor tyrosine kinase inhibitor sunitinib 96 .…”