Respiratory chain enzyme deficiency induces mitochondrial location of actin-binding gelsolin to modulate the oligomerization of VDAC complexes and cell survival

Abstract

Despite considerable knowledge on the genetic basis of mitochondrial disorders, their pathophysiological consequences remain poorly understood. We previously used two-dimensional difference gel electrophoresis analyses to define a protein profile characteristic for respiratory chain complex III-deficiency that included a significant overexpression of cytosolic gelsolin (GSN), a cytoskeletal protein that regulates the severing and capping of the actin filaments. Biochemical and immunofluorescence assays confirmed a specific increase of GSN levels in the mitochondria from patients' fibroblasts and from transmitochondrial cybrids with complex III assembly defects. A similar effect was obtained in control cells upon treatment with antimycin A in a dose-dependent manner, showing that the enzymatic inhibition of complex III is sufficient to promote the mitochondrial localization of GSN. Mitochondrial subfractionation showed the localization of GSN to the mitochondrial outer membrane, where it interacts with the voltage-dependent anion channel protein 1 (VDAC1). In control cells, VDAC1 was present in five stable oligomeric complexes, which showed increased levels and a modified distribution pattern in the complex III-deficient cybrids. Downregulation of GSN expression induced cell death in both cell types, in parallel with the specific accumulation of VDAC1 dimers and the release of mitochondrial cytochrome c into the cytosol, indicating a role for GSN in the oligomerization of VDAC complexes and in the prevention of apoptosis. Our results demonstrate that respiratory chain complex III dysfunction induces the physiological upregulation and mitochondrial location of GSN, probably to promote cell survival responses through the modulation of the oligomeric state of the VDAC complexes.

Differential gene expression in chicken primary B cells infected ex vivo with attenuated and very virulent strains of infectious bursal disease virus (IBDV)

“…Only one contradiction was found: the GSN gene was found to be down-regulated in our study, yet up-regulated in one in vivo study [17]. GSN encodes Gelsolin, which regulates actin assembly and has also been associated with inhibiting apoptosis [41]. The reason for this discrepancy is unknown; it could be because our experiment characterized gene expression at 18 h p.i., whereas the in vivo study was conducted at 3 and 4 days p.i.…”

Altered Expression Ratio of Actin-Binding Gelsolin Isoforms Is a Novel Hallmark of Mitochondrial OXPHOS Dysfunction

“…Previous studies in mitochondrial complex III (CIII)-deficient cell lines revealed a specific upregulation of cytosolic GSN and its localization to the mitochondrial outer membrane (mGSN), where it interacts with VDAC1 to promote protective antiapoptotic responses [ 12 , 40 ]. To discriminate whether this phenomenon is specific to CIII deficiency, rather than occurring as a general response to OXPHOS enzyme defects, we analyzed control and mutant cybrids with different types of OXPHOS deficiency ( Figure 1 ).…”

“…To exclude that these effects were specific to cybrid cell lines, we tested pGSN levels in the secretomes from primary cultured fibroblasts from patients harboring pathogenic mutations in the complex III assembly factor BCS1L ( Figure 3 A), which previously showed a marked respiratory chain dysfunction [ 12 ] together with an upregulated expression and mitochondrial location of GSN ( Table 3 ) [ 40 ]. SDS-PAGE gels were stained with Coomassie blue and densitometric measurements per lane were used as loading controls for the normalization of subsequent pGSN immunoreactive signals.…”

“…Studies in cancer cells showed that cytosolic GSN expression may impact the cellular redox milieu and cell survival by modulating intracellular O 2.− /H 2 O 2 levels, possibly by the interaction and suppression of superoxide dismutase 1 (Cu/Zn SOD) enzymatic activity [ 38 , 39 ]. Other studies in human cell lines with MRC complex III deficiency demonstrated the upregulation and location of GSN at the mitochondrial outer membrane (henceforth mitochondrial GSN or mGSN), where it interacts with the voltage-dependent anion channel (VDAC) to prevent the release of mitochondrial cytochrome c into the cytosol and apoptotic cell death [ 40 ]. However, whether these GSN-mediated survival adaptations occur as a general response to oxidative stress or are specific to OXPHOS dysfunction remains largely unknown.…”

Differential gene expression in chicken primary B cells infectedex vivowith attenuated and very virulent strains of infectious bursal disease virus (IBDV)

“…Only one contradiction was found: the GSN gene was found to be down-regulated in our study, yet up-regulated in one in vivo study (17). GSN encodes Gelsolin, which regulates actin assembly and has also been associated with inhibiting apoptosis (40). The reason for this discrepancy is unknown; it could be because our experiment characterised gene expression at 18 hours post-infection, whereas the in vivo study was conducted at 3 and 4 days post infection.…”