p53 Aggregates Penetrate Cells and Induce the Co-Aggregation of Intracellular p53

Abstract

Prion diseases are unique pathologies in which the infectious particles are prions, a protein aggregate. The prion protein has many particular features, such as spontaneous aggregation, conformation transmission to other native PrP proteins and transmission from an individual to another. Protein aggregation is now frequently associated to many human diseases, for example Alzheimer’s disease, Parkinson’s disease or type 2 diabetes. A few proteins associated to these conformational diseases are part of a new category of proteins, called prionoids: proteins that share some, but not all, of the characteristics associated with prions. The p53 protein, a transcription factor that plays a major role in cancer, has recently been suggested to be a possible prionoid. The protein has been shown to accumulate in multiple cancer cell types, and its aggregation has also been reproduced in vitro by many independent groups. These observations suggest a role for p53 aggregates in cancer development. This study aims to test the «prion-like» features of p53. Our results show in vitro aggregation of the full length and N-terminally truncated protein (p53C), and penetration of these aggregates into cells. According to our findings, the aggregates enter cells using macropinocytosis, a non-specific pathway of entry. Lastly, we also show that once internalized by the cell, p53C aggregates can co-aggregate with endogenous p53 protein. Together, these findings suggest prion-like characteristics for p53 protein, based on the fact that p53 can spontaneously aggregate, these aggregates can penetrate cells and co-aggregate with cellular p53.

Aggregation and Prion-Like Properties of Misfolded Tumor Suppressors: Is Cancer a Prion Disease?

“…A prion is a type of amyloid fibril that is capable of converting a normal endogenous cellular protein to an amyloid conformation, spreading these fibrils between cells (Prusiner 1982(Prusiner , 1998Prusiner et al 1998). p53 and other amyloid fibrils have been referred to as prion-like, owing to the ability of these aggregates to propagate to other cells by penetrating cell membranes (Brundin et al 2010;Ano Bom et al 2012;Forget et al 2013;Rangel et al 2014).…”

“…Despite these findings, it may be premature to classify p53 as a prion because the mechanisms underlying its transmission have yet to be definitively shown. However, recent studies have shown independent mechanisms of p53 secretion and uptake by cells (Lee et al 2009aForget et al 2013), suggesting that p53 may act as a transmissible agent. In initial experiments, the oncogenic protein Kristen-Ras (K-Ras) was shown to participate in p53 suppression by inducing Snail.…”

“…Snail suppresses p53 in response to the oncogenic functions of K-Ras, including the secretion of p53 from cells and its subsequent uptake by K-Ras mutant cells via caveolin-1-mediated endocytosis . Furthermore, aggregates of full-length p53 were shown to penetrate HeLa and NIH-3T3 cells via macropinocytosis and to induce the aggregation of intracellular p53 (Forget et al 2013). Although mouse models remain inadequate, these surprising mechanisms of between-cell p53 transmissibility have prompted new discussions about its proposed prion-like mechanism and have indicated the need for ongoing experiments by our group and others to demonstrate the involvement of p53 aggregates in cancer pathogenesis and progression.…”

The aggregation of mutant p53 produces prion-like properties in cancer

“…The most traditional explanation for this observation involves the formation of heterotetramers containing both mutant and wild-type forms of the protein that are inactive. 54 Recent data suggest that this effect could be associated with the misfolding and aggregation of mutant p53 and the resultant prion-like effect on the wild-type form of the protein 8,9,13,55 (see Fig. 1).…”

“…The ability of p53 to form aggregates and the kinetics associated with this process have been widely explored and discussed by different investigators. [5][6][7][8][9][10][11][12] In addition, the prionoid behavior of p53 has been described by our group 8 and by Forget et al 13 These studies have enabled new opportunities for the investigation of the modulation of p53 and suggested new potential chemotherapeutic targets. However, the following questions remain to be answered: to what degree is p53 prionoid behavior important in cancer pathogenesis?…”