Levels of human Fis1 at the mitochondrial outer membrane regulate mitochondrial morphology

Abstract

Mitochondria undergo balanced fission and fusion events that enable their appropriate networking within the cell. In yeast, three factors have been identified that co-ordinate fission events at the mitochondrial outer membrane. Fis1p acts as the outer membrane receptor for recruitment of the dynamin member, Dnm1p and the WD40-repeat-containing protein Mdv1p. In mammals, the Dnm1p counterpart Drp1 has been characterized, but other components have not. Here, we report the characterization of human Fis1 (hFis1). hFis1 is inserted into the mitochondrial outer membrane via a C-terminal transmembrane domain that, along with a short basic segment, is essential for its targeting. Although expression of hFis1 does not complement the phenotype of yeast cells lacking Fis1p, overexpression of hFis1 in tissue culture cells nevertheless causes mitochondrial fragmentation and aggregation. This aggregation could be suppressed by expressing a dominant-negative Drp1 mutant (Drp1K38A). Knockdown of hFis1 in COS-7 cells using RNA interference results in mitochondrial morphology defects with notable extensions in the length of mitochondrial tubules. These results indicate that the levels of hFis1 at the mitochondrial surface influences mitochondrial fission events and hence overall mitochondrial morphology within the cell.

Mitochondrial fission proteins regulate programmed cell death in yeast

“…results are also consistent with a previous report showing that overexpression of yeast Fis1 in yeast cells displayed no enhanced mitochondrial fragmentation (Mozdy et al 2000). However, overexpression of human Fis1 in mammalian cells was reported to induce mitochondrial fragmentation and cytochrome c release (James et al 2003), though others have described alternative human Fis1-induced morphologies in mammalian cells (Yoon et al 2003;Stojanovski et al 2004). …”

“…Fis1 of Saccharomyces cerevisiae is an 18-kDa protein that is anchored to the outer mitochondrial membrane by a C-terminal hydrophobic-basic domain characteristic of Bcl-2, Tom 5, and other proteins targeted to the outer mitochondrial membrane (Mozdy et al 2000;Kaufmann et al 2003). Consistent with its role in yeast, depletion of endogenous human Fis1 decreases mitochondrial fission (James et al 2003;Yoon et al 2003;Stojanovski et al 2004).…”

Evidence implicating the candidate schizophrenia/bipolar disorder susceptibility gene G72 in mitochondrial function

“…2 Previous experiments have demonstrated that mitochondrial fragmentation cannot be caused by overexpression of any mitochondrial protein. 17,18 Nevertheless, production of high nonphysiological levels of G72 may be a confounding factor in the interpretation of the results outlined above. Because we could not detect and, therefore, monitor the levels of endogenous G72 protein in six tested human cell lines, we have been unable to complement our overexpression analysis with siRNA-based loss-offunction approaches.…”

Mitochondrial network in the heart

“…Mitochondrial fusion mixes mitochondria contents, thus enabling protein complementation (Detmer and Chan, 2007). The disruption of fusion leads to the fragmentation of the mitochondrial tubular network (Griparic et al, 2004), while abnormal fission causes elongated and interconnected tubules (Stojanovski et al, 2004).…”