Mammary gland-specific ablation of focal adhesion kinase reduces the incidence of p53-mediated mammary tumour formation.

BACKGROUND: Elevated expression of focal adhesion kinase (FAK) occurs in numerous human cancers including colon-, cervix- and breast cancer. Although several studies have implicated FAK in mammary tumour formation induced by ectopic oncogene expression, evidence supporting a role for FAK in spontaneous mammary tumour development caused by loss of tumour suppressor genes such as p53 is lacking. Alterations in the tumour suppressor gene p53 have been implicated in over 50% of human breast cancers. Given that elevated FAK expression highly correlates with p53 mutation status in human breast cancer, we set out to investigate the importance of FAK in p53-mediated spontaneous mammary tumour development. METHODS: To directly assess the role of FAK, we generated mice with conditional inactivation of FAK and p53. We generated female p53(lox/lox)/FAK(+/+)/WapCre, p53(lox/lox)/FAK(flox/+)/WapCre and p53(lox/lox)/FAK(flox/-)/WapCre mice, and mice with WapCre-mediated conditional expression of p53(R270H), the mouse equivalent of human p53(R273H) hot spot mutation, together with conditional deletion of FAK, P53(R270H/+)/FAK(lox/+)/WapCre and p53(R270H/+)/FAK(flox/-)/WapCre mice. All mice were subjected to one pregnancy to induce WapCre-mediated deletion of p53 or expression of p53 R270H, and Fak genes flanked by two loxP sites, and subsequently followed the development of mammary tumours. RESULTS: Using this approach, we show that FAK is important for p53-induced mammary tumour development. In addition, mice with the mammary gland-specific conditional expression of p53 point mutation R270H, the mouse equivalent to human R273H, in combination with conditional deletion of Fak showed reduced incidence of p53(R270H)-induced mammary tumours. In both models these effects of FAK were related to reduced proliferation in preneoplastic lesions in the mammary gland ductal structures. CONCLUSIONS: Mammary gland-specific ablation of FAK hampers p53-regulated spontaneous mammary tumour formation. Focal adhesion kinase deletion reduced proliferative capacity of p53 null and p53(R270H) mammary epithelial cells but did not lead to increased apoptosis in vivo. Our data identify FAK as an important regulator in mammary epithelial cell proliferation in p53-mediated and p53(R270H)-induced mammary tumour development.

Annexin A2 depletion delays EGFR endocytic trafficking via cofilin activation and enhances EGFR signaling and metastasis formation.

Enhanced epidermal growth factor receptor (EGFR) activity has been strongly linked to breast cancer progression and mediators of EGFR endocytosis may well be involved. We developed a semi-automated high-content fluorescence microscopy-based EGFR endocytosis screen to identify proteins that mediate EGFR endocytosis in human HBL100 breast cancer cells. Knockdown of 172 individual endocytosis and actin-regulatory genes with small interfering RNAs led to the identification of 14 genes of which the contribution to EGFR endocytosis in breast cancer is until now poorly defined, including DNAJC6, GDI2, FGD6, HAX1, NECAP2 and AnxA2. We show that depletion of the actin and endocytosis regulatory protein annexin A2 (AnxA2) in a panel of four triple negative breast cancer (TNBC) cell lines affected EGFR endocytosis. Depletion of AnxA2 in the aggressive and highly metastatic MDA-MB-231 TNBC cell line resulted in the inhibition of EGFR transport beyond the early endosomes. This inhibition coincided with enhanced epidermal growth factor (EGF)-induced cell migration and downstream signaling via c-Jun N-terminal kinase (JNK) and Akt. Moreover, AnxA2 knockdown increased lung metastasis formation in mice. The effect of AnxA2 knockdown on EGFR endocytosis in MDA-MB-231 was related to dephosphorylation/activation of the actin-severing protein cofilin, as re-expression of an inactive S3E-cofilin mutant, but not an active S3A-cofilin mutant, re-established EGFR endocytosis to control levels. Together, our data provide evidence for AnxA2 as a mediator of EGFR endocytosis and signaling in breast cancer via regulation of cofilin activation.

p140Cap suppresses the invasive properties of highly metastatic MTLn3-EGFR cells via impaired cortactin phosphorylation.

We have recently shown that the adaptor protein p140Cap regulates tumor properties in terms of cell motility and growth. Here, by using the highly metastatic rat adenocarcinoma cell line MTLn3-epidermal growth factor receptor (EGFR), we assess the role of p140Cap in metastasis formation. Orthotopic transplantation of MTLn3-EGFR cells over-expressing p140Cap in Rag2(-/-)γ(c)(-/-) mice resulted in normal primary tumor growth compared with the controls. Strikingly, p140Cap over-expression causes an 80% inhibition in the number of lung metastases. p140Cap over-expressing cells display a 50% reduction in directional cell migration, an increased number and size of focal adhesions, and a strong impairment in the ability to invade in a 3D matrix. p140Cap over-expression affects EGFR signaling and tyrosine phosphorylation of cortactin in response to EGF stimulation. Intriguingly, p140Cap associates with cortactin via interaction with its second proline-rich domain to the cortactin SH3 domain. The phosphomimetic cortactin tyrosine 421 mutant rescues migration and invasive properties in p140Cap over-expressing cells. Taken together, these data demonstrate that p140Cap suppresses the invasive properties of highly metastatic breast carcinoma cells by inhibiting cortactin-dependent cell motility.