Intercellular transmission of a bacterial cytotoxic prion-like protein in mammalian cells

RepA is a bacterial protein that builds intracellular amyloid oligomers acting as inhibitory complexes of plasmid DNA replication. When carrying a mutation enhancing its amyloidogenesis (A31V), the N-terminal domain (WH1) generates cytosolic amyloid particles that are inheritable within a bacterial lineage. Such amyloids trigger in bacteria a lethal cascade reminiscent to mitochondria impairment in human cells affected by neurodegeneration. To fulfil all the features of a prion-like protein, horizontal (intercellular) transmissibility remains to be demonstrated for RepA-WH1. Since this is experimentally intractable in bacteria, here we transiently expressed in a murine neuroblastoma cell line the soluble, barely cytotoxic RepA-WH1(WT) and assayed its response to co-incubation with in vitro assembled RepA-WH1(A31V) amyloid fibres. In parallel, cells releasing RepA-WH1(A31V) aggregates were co-cultured with human neuroblastoma cells expressing RepA-WH1(WT). Both the assembled fibres and the extracellular RepA-WH1(A31V) aggregates induce, in the cytosol of recipient cells, the formation of cytotoxic amyloid particles. Mass spectrometry analyses of the proteomes of both types of injured cells point to alterations in mitochondria, protein quality triage, signalling and intracellular traffic.\n\nSummary blurbThe horizontal, cell-to-cell spread of a bacterial prion-like protein is shown for the first time in mammalian cells. Amyloid cross-aggregation of distinct variants, and their associated toxicities, follow the same trend found in bacteria, underlining the universality of prion biology.