Many protein-misfolding diseases are caused by proteins carrying prion-like domains. These proteins show sequence similarity to yeast prion proteins, which can interconvert between an intrinsically disordered and an aggregated prion state. The natural presence of prions in yeast has provided important insight into disease mechanisms and cellular proteostasis. However, little is known about prions in other organisms, and it is not yet clear whether the findings in yeast can be generalized. Using bioinformatics tools, we show that Dictyostelium discoideum has the highest content of prion-like proteins of all organisms investigated to date, suggesting that its proteome has a high overall aggregation propensity. To study mechanisms regulating these proteins, we analyze the behavior of several well-characterized prion-like proteins, such as an expanded version of human huntingtin exon 1 (Q103) and the prion domain of the yeast prion protein Sup35 (NM), in D. discoideum. We find that these proteins remain soluble and are innocuous to D. discoideum, in contrast to other organisms, where they form cytotoxic cytosolic aggregates. However, when exposed to conditions that compromise molecular chaperones, these proteins aggregate and become cytotoxic. We show that the disaggregase Hsp101, a molecular chaperone of the Hsp100 family, dissolves heat-induced aggregates and promotes thermotolerance. Furthermore, prion-like proteins accumulate in the nucleus, where they are targeted by the ubiquitin-proteasome system. Our data suggest that D. discoideum has undergone specific adaptations that increase the proteostatic capacity of this organism and allow for an efficient regulation of its prion-like proteome. molecular chaperones | proteostasis | Dictyostelium discoideum | protein aggregation | prion

The bone marrow (BM) microenvironment provides critical physical cues for hematopoietic stem and progenitor cell (HSPC) maintenance and fate decision mediated by cell-matrix interactions. However, the mechanisms underlying matrix communication and signal transduction are less well understood. Contrary, stem cell culture is mainly facilitated in suspension cultures. Here, we used bone marrow-mimetic decellularized extracellular matrix (ECM) scaffolds derived from mesenchymal stromal cells (MSCs) to study HSPC-ECM interaction. Seeding freshly isolated HSPCs adherent (AT) and non-adherent (SN) cells were found. We detected enhanced expansion and active migration of AT-cells mediated by ECM incorporated stromal derived factor one. Probing cell mechanics, AT-cells displayed naïve cell deformation compared to SN-cells indicating physical recognition of ECM material properties by focal adhesion. Integrin αIIb (CD41), αV (CD51) and β3 (CD61) were found to be induced. Signaling focal contacts via ITGβ3 were identified to facilitate cell adhesion, migration and mediate ECM-physical cues to modulate HSPC function.