investigating integrin ανβ6 activation status in breast cancer

PhDbackground The extracellular matrix receptor integrin ανβ6 is known to potentiate breast cancer (BrCa) cell invasion, metastasis and tumour-trophic growth factor receptor crosstalk during tumourigenesis. Monoclonal antibody blockade of ανβ6 diminishes invasion in vitro and arrests BrCa tumour growth and metastasis in vivo. Aberrant integrin activation status has been implicated in progression to metastatic disease in BrCa; with differential internalisation and endocytic trafficking kinetics reported for active versus inactive integrin species in malignant disease. Despite its emerging potential for targeted therapy, little is known regarding regulation of integrin ανβ6–mediated activation and signalling during progression to an invasive, metastatic state. It is hypothesised that the aetiopathological significance of integrin ανβ6 during neoplastic transformation and malignant progression in BrCa is dependent specifically upon its activation status and associated conformation, since this active state will permit establishment of known integrin–mediated oncogenic signalling underpinning acquisition of a malignant phenotype, including activation of invasion and metastasis. results Canonical integrin activation studies using divalent cations and cognate ligand stimulation indicated antibodies 6.2E5 and 6.2G2 recognise activation-associated epitopes, which are also ligand-induced binding sites (LIBS) in live-labelled cells by FCM and IMF. However, their utility to discriminate the active fraction distinct from the total or inactive fractions of ανβ6 by IHC in primary BrCa samples could not be robustly established. Evaluation of the 6.2E5 and 6.2G2 epitopes in the MCF10 isogenic model revealed that relative surface abundance of these active epitopes determined by FCM was not significantly altered; but their subcellular redistribution upon neoplastic transformation and malignant progression was observed by IMF, implicating derailed internalisation and trafficking of active ανβ6 during breast tumourigenesis and metastatic disease progression. Proteomic interrogation and network analysis of the 2D-enriched adhesion assays identified 7 novel putative molecular regulators of a ligand-engaged, activated ανβ6–mediated adhesion environment (DMBT-1, MARCKS, MXRA5, SEPT6, SEPT9, MYH9, MYH10) in the BT-20 TNBC cell line. Functional validation of these candidate mediators of the “β6 adhesome” by siRNA strategies was not achieved due to inconsistent stable knockdown. Phosphoproteomic definition of LAP ligand-engaged, active ανβ6–mediated signalling (“β6 kinome”) during receptor-ligand internalisation revealed EGFR-dependency for downstream ERK1/2 signal activation in BT-20 and SUM159, but not MDA-MB-468 TNBC cells. Kinase substrate enrichment analysis (KSEA) identified 5 novel putative mediators of downstream ανβ6 signalling (COT, MAPKAPK2, PDPK1, Nuak1, TBK1) and implicated Akt1 isoform-specific activation downstream of ανβ6–LAP internalisation. Following LAP-induced ανβ6 activation and internalisation, EGFR underwent phosphorylation at multiple known activation sites, including a residue (Thr693) critical for EGFR receptor internalisation; suggesting integrin ανβ6–EGFR reciprocity during respective receptor activation and internalisation. conclusion The active conformer of integrin ανβ6 may be studied using antibodies 6.2E5 and 6.2G2 in live-labelled cells by FCM and IMF. Subcellular redistribution of activation-associated epitopes during BrCa progression implicates derailed internalisation and intracellular trafficking kinetics of active ανβ6 during tumourigenesis, while protein expression studies identified 7 putative molecular regulators of ligand-engaged, active ανβ6–mediated adhesion. Integrin ανβ6-mediated signalling during internalisation revealed an ανβ6–EGFRAkt1 signalling axis during breast tumourigenesis and disease progression, while further understanding of integrin biology and growth factor receptor crosstalk may provide additional rationale for potential combination therapies in breast cancer.Cancer Research UK

Integrin αVβ6-EGFR crosstalk regulates bidirectional force transmission and controls breast cancer invasion

The mechanical properties of the extracellular matrix within tumours control multiple cellular functions that drive cancer invasion and metastasis. However, the mechanisms controlling microenvironmental force sensation and transmission, and how these regulate transcriptional reprogramming and invasion, are unclear. Our aim was to understand how mechanical inputs are transmitted bidirectionally and translated into biochemical and transcriptional outputs to drive breast cancer progression. We reveal that adhesion receptor and growth factor receptor crosstalk regulates a bidirectional feedback mechanism co-ordinating force-dependent transcriptional regulation and invasion. Integrin αVβ6 drives invasion in a range of carcinomas and is a potential therapeutic target. αVβ6 exhibits unique biophysical properties that promote force-generation and increase matrix rigidity. We employed an inter-disciplinary approach incorporating proteomics, biophysical techniques and multi-modal live-cell imaging to dissect the role of αVβ6-EGFR crosstalk on transmission of mechanical signals bidirectionally between the extracellular matrix and nucleus. We show that αVβ6 expression correlates with poor prognosis in triple-negative breast cancer (TNBC) and drives invasion of TNBC cells. Moreover, our data show that a complex regulatory mechanism exists involving crosstalk between αVβ6 integrin and EGFR that impacts matrix stiffness, force transmission to the nucleus, transcriptional reprogramming and microenvironment rigidity. αVβ6 engagement triggers EGFR & MAPK signalling and αVβ6-EGFR crosstalk regulates mutual receptor trafficking mechanisms. Consequently, EGF stimulation suppresses αVβ6-mediated force-application on the matrix and nuclear shuttling of force-dependent transcriptional co-activators YAP/TAZ. Finally, we show that crosstalk between αVβ6 & EGFR regulates TNBC invasion. We propose a model whereby αVβ6-EGFR crosstalk regulates matrix stiffening, but also the transmission of extracellular forces into the cell in order to co-ordinate transcriptional reprogramming and invasion. To exploit adhesion receptors and receptor tyrosine kinases therapeutically, it will be essential to understand the integration of their signalling functions and how crosstalk mechanisms influence invasion and the response of tumours to molecular therapeutics