|dc.description.abstract||Kindlin-1 is a focal adhesion (FA) protein and the founding member of the Kindlin family of proteins (Kindlins 1-3), which all have an important role in integrin signalling. Loss of functional Kindlin-1 has been associated with a congenital disease called Kindler syndrome that is characterised by a number of skin abnormalities including atrophy and blistering. Increased or decreased expression of the Kindlin family of proteins has been linked to a number of tumour types and Kindlin-1 is specifically associated with pulmonary metastasis in basal-like breast cancer. The mechanisms by which Kindlin-1 mediates metastasis to the lungs in breast cancer remain relatively unknown and this study aimed to investigate the role of Kindlin-1 in breast cancer. In line with previous reports, we have shown that Kindlin-1 regulates primary breast tumour formation. Our data suggest that the interaction of Kindlin-1 with integrins is specifically important for tumour initiation.
The Kindlins have also been shown to have roles independent of integrin and have been found outside of focal adhesions; Kindlin-2 has been shown to have a nuclear localisation signal (NLS) and initial studies have identified a nuclear role for Kindlin-2 in the promotion of breast cancer, however, nuclear roles of the Kindlins remain mostly unexplored. We explored a potential nuclear role for Kindlin-1 and revealed a novel cellular location for Kindlin-1 in cancer cells. We show that Kindlin-1 is present in the nucleus of breast cancer and squamous cell carcinoma cells and that Kindlin-1 has an NLS that can be altered to prevent protein localisation to the nucleus. Furthermore, we show that presence of Kindlin-1 in the nucleus is important for primary tumour growth and mice inoculated with cells that express mutant Kindlin-1 that cannot localise to the nucleus, have significantly lower tumour growth compared to mice inoculated with cells expressing wild-type Kindlin-1. We also provide evidence that the immune system impacts on the Kindlins ability to regulate tumour growth. Specifically, Kindlin-1 was shown to inhibit IL-6 production, which promotes differentiation of naïve CD4+ T cells into Tregs and results in tumour development due to suppression of the anti-tumour response of the immune system. Our findings are particularly interesting as the FA protein FAK has previously been reported to have an immune-modulatory role in the nucleus of squamous cell carcinoma cells through regulation of the transcription of inflammatory cytokines and chemokines. Our data suggest that Kindlin-1 may also have similar important roles in the nucleus that warrants further investigation. As Kindlin-1 does not have catalytic activity, further studies are warranted to investigate the nuclear roles of Kindlin-1 and the interaction of Kindlin-1 with the immune system, as understanding these roles may offer new avenues for therapeutic intervention.
Very few binding partners have been identified for the Kindlin family and known binding partners include phosphoinositides and some focal adhesions proteins such as integrin-linked kinase (ILK) and migfilin. We carried out proteomic analyses and identified a number of novel binding partners of Kindlin-1 in different breast cancer cell models. Our findings suggest that Kindlin-1 is an adaptor protein in the cell that regulates a number of key signalling hubs, which control several cellular processes including metabolism, cell proliferation, cell migration, apoptosis and signal transduction.||en