Ever since Stephen Paget’s 1889 hypothesis, metastatic organotropism has remained one of cancer’s greatest mysteries. Here we demonstrate that exosomes from mouse and human lung-, liver- and brain-tropic tumour cells fuse preferentially with resident cells at their predicted destination, namely lung fibroblasts and epithelial cells, liver Kupffer cells and brain endothelial cells. We show that tumour-derived exosomes uptaken by organ-specific cells prepare the pre-metastatic niche. Treatment with exosomes from lung-tropic models redirected the metastasis of bone-tropic tumour cells. Exosome proteomics revealed distinct integrin expression patterns, in which the exosomal integrins α6β4 and α6β1 were associated with lung metastasis, while exosomal integrin αvβ5 was linked to liver metastasis. Targeting the integrins α6β4 and αvβ5 decreased exosome uptake, as well as lung and liver metastasis, respectively. We demonstrate that exosome integrin uptake by resident cells activates Src phosphorylation and pro-inflammatory S100 gene expression. Finally, our clinical data indicate that exosomal integrins could be used to predict organ-specific metastasis.

Highlights d Proteomic profiles of extracellular vesicles and particles (EVPs) from 426 human samples d Identification of pan-EVP markers d Characterization of tumor-derived EVP markers in human tissues and plasma d EVP proteins can be useful for cancer detection and determining cancer type

ERK signaling regulates the expression of target genes, but it is unclear how ERK activity dynamics are interpreted. Here, we investigate this question using simultaneous, live, single-cell imaging of two ERK activity reporters and expression of Fra-1, a target gene controlling epithelial cell identity. We find that Fra-1 is expressed in proportion to the amplitude and duration of ERK activity. In contrast to previous "persistence detector" and "selective filter" models in which Fra-1 expression only occurs when ERK activity persists beyond a threshold duration, our observations demonstrate that the network regulating Fra-1 expression integrates total ERK activity and responds to it linearly. However, exploration of a generalized mathematical model of the Fra-1 coherent feedforward loop demonstrates that it can perform either linear integration or persistence detection, depending on the basal mRNA production rate and protein production delays. Our data indicate that significant basal expression and short delays cause Fra-1 to respond linearly to integrated ERK activity.

The formation of functional kinetochores requires the accurate assembly of a large number of protein complexes. The Hsp90–Sgt1 chaperone complex is important for this process; however, its targets are not conserved and its exact contribution to kinetochore assembly is unclear. Here, we show that human Hsp90–Sgt1 interacts with the Mis12 complex, a so-called keystone complex required to assemble a large fraction of the kinetochore. Inhibition of Hsp90 or Sgt1 destabilizes the Mis12 complex and delays proper chromosome alignment due to inefficient formation of microtubule-binding sites. Interestingly, coinhibition of Sgt1 and the SCF subunit, Skp1, increases Mis12 complexes at kinetochores and restores timely chromosome alignment but forms less-robust microtubule-binding sites. We propose that a balance of Mis12 complex assembly and turnover is required for the efficient and accurate assembly of kinetochore–microtubule binding sites. These findings support a novel role for Hsp90–Sgt1 chaperones in ensuring the fidelity of multiprotein complex assembly.