FAIM opposes stress-induced loss of viability and blocks the formation of protein aggregates

Abstract

A number of proteinopathies are associated with accumulation of misfolded proteins, which form pathological insoluble deposits. It is hypothesized that molecules capable of blocking formation of such protein aggregates might avert disease onset or delay disease progression. Here we report that Fas Apoptosis Inhibitory Molecule (FAIM) counteracts stress-induced loss of viability. We found that levels of ubiquitinated protein aggregates produced by cellular stress are much greater in FAIM-deficient cells and tissues. Moreover, in an in vitro cell-free system, FAIM specifically and directly prevents pathological protein aggregates without participation by other cellular elements, in particular the proteasomal and autophagic systems. Although this activity is similar to the function of heat shock proteins (HSPs), FAIM, which is highly conserved throughout evolution, bears no homology to any other protein, including HSPs. These results identify a new actor that protects cells against stress-induced loss of viability by preventing protein aggregates.

FAIM Opposes Aggregation of Mutant SOD1 That Typifies Some Forms of Familial Amyotrophic Lateral Sclerosis

“…The expression and evolution pattern of faim and the related faim-Gm6432 gene suggested that FAIM might be involved more generally in cellular stress response pathways, rather than narrowly protecting against death receptor demise (Turner and Lysiak, 2008;Qiu et al, 2013;Durairajanayagam et al, 2015). This turned out to be correct and in the course of this work we found that loss of FAIM was associated with increased levels of stress-induced protein aggregation in FAIM-deficient cell lines and animals (Kaku and Rothstein, 2019). This raised the possibility that FAIM can act directly on dysfunctional proteins that aggregate.…”

“…In this assay, large aggregated proteins are not able to pass through a 0.2 µm pore-sized filter, remain on the filter, and are blotted with anti-GFP antibody (Myeku et al, 2011). We found that much more aggregated mutant SOD1 was filter trapped in FAIM-deficient HeLa cells than in WT HeLa cells ( Figure 1D; Kaku and Rothstein, 2019). These results demonstrate the essential role of FAIM in blocking formation of mutant SOD1 aggregates.…”

“…In retrospect, its role was likely obscured by the lack of stress in vivarium mouse life. Recently, we showed that FAIM uniquely and non-redundantly opposes stress-induced cell death and stress-induced accumulation of protein aggregates in multiple cell types in vitro and in mice in vivo (Kaku and Rothstein, 2019). Here we show that FAIM plays a key role in cellular proteostasis, and specifically acts to prevent mutant SOD1 aggregation (in cell lines and in vitro) and to reverse established mutant SOD1 aggregates (in vitro).…”

“…In this assay, cells containing aggregated proteins have a narrower and higher pulse shape of eGFP fluorescence than those that do not express protein aggregates (Ramdzan et al, 2012). We found that regardless of transfection efficiency, the fraction of HeLa cells expressing aggregated mutant SOD1 was significantly higher in FAIMdeficient HeLa cells than in WT HeLa cells, especially at late stages after transfection (Figures 1A-C; Kaku and Rothstein, 2019). 2We used filter trap assay (FTA) to evaluate the level of aggregated protein.…”

“…To examine the activity of FAIM with respect to the diseaseassociated, aggregation-prone mutant protein, SOD1, we first deleted FAIM from HeLa cells by CRISPR/Cas9 excision (Kaku and Rothstein, 2019). We then transiently transfected FAIMdeficient HeLa cells and WT HeLa cells with eGFP-tagged mutant SOD1-G93A, which spontaneously forms aggregates.…”