Angi-12. Identification of a Novel Tyrosine Kinase/integrin Complex That Drives Brain Metastases
Year: 2017
Type: conference-abstract
Abstract: Brain metastases, the most common brain tumors, confer a poor prognosis. Studies have suggested roles for β1-integrin and c-Met, but the mechanisms remain unelucidated. We hypothesized that a c-Met/b1integrin complex drives breast cancer cells to metastasize to the brain and elsewhere. We utilized immunoprecipitation, proximity ligation assays (PLAs), and inducible heterodimerization assays. MDA-MB-231 breast cancer cells were injected in mammary fat pads of athymic mice, of which 20% developed metastases. Primary metastasized tumors had 10-fold more c-Met/b1 complexes than non-metastasized tumors (P=0.004). Gastrointestinal and brain metastases demonstrated 12-fold (P=0.0006) and 18-fold (P=0.01) more c-Met/b1 complexes than primary tumors. Inducing c-Met/b1 complex formation through an engineered inducible heterodimerization system reduced cellular circularity shape factor (P=6X10-7), increased scratch assay motility (P=0.001–0.02), increased matrigel invasion (P=0.007), and promoted two of four metastatic cascade steps in vivo: primary site tumor cell migration and extravasation out of circulation. MDA-MB-231-BR brain-seeking cells selected for brain metastatic capacity in vivo exhibited upregulated c-Met/b1 complex levels compared to MDA-MB-231 cells. Biotinylation revealed that complex formation began intracellularly before membrane trafficking. Complex formation promoted ligand-independent allosteric receptor activation, with integrin-linked kinase phosphorylating c-Met and crystallography revealing c-Met/b1 complex to maintain the high-affinity b1 integrin conformation. Far western blotting and sequential immunoprecipitation revealed that c-Met displaced a5 integrin from extracellular binding of b1 integrin, creating a complex with much greater affinity for fibronectin than a5b1. PLA revealed increased c-Met/b1 integrin complexes in patient breast cancer brain metastases compared to paired primary breast tumors from the same patients (P=0.0006–0.004). Metastatic tumor cells co-opt receptors promoting both modes of cell migration: chemotaxis, movement towards chemoattractants, and haptotaxis, movement controlled by peripheral adhesions. Tumor cells redirect these receptors away from their conventional binding partners, forming a powerful c-Met/b1 complex whose ligand-independent cross-activation and robust affinity for fibronectin drives metastases.
Source: Neuro-Oncology
Institution: University of California, San Francisco
Language: English
Subfield: Immunology and Allergy
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2768075944