FBXW8 is shifted into insolubility in <i>Atxn2</i>-CAG42-KIN mice due to interaction with expanded ATXN2.

<p>(A) Pulling either with anti-ATXN2 or anti-FBXW8 antibody, ATNX2 and FBXW8 show an interaction in the cerebellum of 18-month-old <i>Atxn2</i>-CAG42-KIN mice independent of the polyQ length (experiment repeated three times for anti-ATXN2 and once with anti-FBXW8, representative images). (B) In cerebellar tissue of 18-month-old <i>Atxn2</i>-CAG42-KIN mice FBXW8 protein level is downregulated in the RIPA-soluble fraction while it is upregulated in the SDS-soluble fraction (two independent experiments each with 4 <i>Atxn2</i>^CAG1/CAG1 vs. 4 <i>Atxn2</i>^CAG42/CAG42 mice).</p

PARK2 interacts with FBXW8 and is recruited into insolubility in <i>Atxn2</i>-CAG42-KIN mice.

<p>(A) In HeLa cells overexpressing Cherry-GFP-PARK2 and FBXW8-HA, pulling with anti-FBXW8 antibody resulted in the detection of FBXW8 as well as of PARK2 in Co-IP lysates, demonstrating their interaction (experiment repeated twice, representative image). (B) PARK2 interacts with FBXW8 in Co-IP samples of <i>Atxn2</i>-CAG42-KIN mice independent of the polyQ length. Lower bands represent PARK2 protein (experiment repeated once). (C) PARK2 protein level is decreased in the RIPA-soluble fraction while it is increased in the SDS-soluble fraction (8 <i>Atxn2</i>^CAG1/CAG1 mice vs. ≥ 6 <i>Atxn2</i>^CAG42/CAG42 mice).</p

FBXW8 protein levels are dysregulated in SCA2 patient material.

<p>FBXW8 expression is upregulated at the transcript level in SCA2 patient skin fibroblasts (A; 4 CTL individuals vs. 4 SCA2 patients) as well as in SCA2 patient blood samples (B; 5 CTL individuals vs. 3 SCA2 patients). (C) At the protein level FBXW8 is decreased in the RIPA-soluble fraction while it is increased in the SDS-soluble fraction in SCA2 patient fibroblasts (4 CTL individuals vs. 4 SCA2 patients).</p

Increased apoptosis in cells with PINK1 knockdown.

<p>5A) nt and PINK1 knockdown (kd) SH-SY5Y cells were either kept in RPMI medium with 5% FCS or starved with HBSS for 12 h. DEVD cleavage as parameter for caspase-3 activity was analyzed and normalized to the protein content. Cells with PINK1 knockdown demonstrated a significantly increased caspase-3 activity under both conditions; n = 4; RPMI+5% FCS: p<0.05; HBSS: p<0.01. 5B) nt and PINK1 knockdown (kd) SH-SY5Y cells were either kept in RPMI medium with 5% FCS for 48 h or starved with HBSS for the indicated time points. In the representative western blot the appearance of the PARP 89 kDa cleaved product is depicted as well as GAPDH for normalizing. 5C) nt and PINK1 knockdown (kd) SH-SY5Y cells were either kept in RPMI medium with 5% FCS for 48 h or starved with HBSS for the indicated time points. For quantification the cleaved PARP 89 kDa product was normalized to the full length 113 kDa PARP and the resulting value normalized to GAPDH. Cells with PINK1 knockdown demonstrated increased PARP cleavage that was significant after 24 h starvation; n = 4; 24 h: p<0.005. 5D) HeLa cells were transfected with scrambled siRNA or PINK1 siRNA and GFP or GFP-Parkin or PINK1-GFP or PINK1G309D-GFP. After transfection cells were starved for additional 24 h with HBSS and afterwards the amount of adherent cells was determined. The number of adherent cells transfected with scrambled siRNA and the indicated plasmid was set as 1. Starvation-mediated increased cell loss after PINK1 knockdown could be rescued by PINK1 or PINK1G309D-GFP but not by GFP or Parkin; GFP: n = 5, p<0.005; Parkin: n = 3, p<0.05; PINK1: n = 5, ns; PINK1G309D-GFP: n = 3, ns. 5E) HeLa cells and HeLa cells stably overexpressing LC3 were transfected with scrambled siRNA or PINK1 siRNA. After 48 h cells were starved in HBSS for additional 24 h and afterwards DEVD cleavage as parameter for caspase-3 activity was analyzed and normalized to 1,000,000 cells. PINK1 knockdown increased caspase-3 activity significantly, which was prevented by LC3 overexpression; n = 3; p<0.05. 5F) HeLa cells and HeLa cells stably expressing LC3 were transfected with scrambled or PINK1 siRNA. 48 h post transfection cells were either left untreated (+ medium) or starved (+HBSS) for additional 24 h and afterwards the amount of adherent cells was determined. The amount of non-starved cells was set as 1. PINK1 knockdown resulted in elevated cell loss, which was prevented by LC3 overexpression; HeLa: n = 6, p<0.05; HeLa LC3: n = 5.</p

Reduced autophagy after PINK1 knockdown.

<p>2A) SH-SY5Y cells were starved for 2 h in HBSS with Bafilomycin (+Baf) or left untreated in RPMI+5% FCS (- Baf). The LC3-II and actin content were determined by western blotting. A representative blot is shown on the right, showing only LC3-II bands in the Bafilomycin-treated samples. The LC3-II bands of Bafilomycin treated samples were normalized to actin and the relative LC3-II content of nt cells was set as 1. Cells with stable PINK1 knockdown exhibited a reduced LC3-II/actin ratio compared to the control (nt) cells; n = 4, p<0.005. 2B) Cortical neurons from 3 different isolations (10-20 DIV) of WT and PINK1 KO mice were either non-starved or starved for 2 h in HBSS and the LC3-II and actin content was determined by western blotting. A representative blot is shown on the right. The relative LC3-II content of WT and PINK1 KO mice, respectively, was set as 1. Primary neurons showed a strong upregulation of autophagy in reaction to starvation but cells derived from PINK1 KO mice exhibited a reduced LC3-II/actin ratio compared to the WT cells; n = 5, p<0.001. 2C) HeLa cells were transiently transfected with scrambled siRNA or PINK1 siRNA. After 48 h the LC3-II and actin content was determined by western blotting. A representative blot is shown on the right. The relative LC3-II content of cells transfected with scrambled siRNA was set as 1. Transient PINK1 knockdown resulted in a reduced LC3-II/actin ratio compared to the cells transfected with scrambled siRNA; n = 6; p<0.005. 2D) HeLa cells were transiently transfected with PINK1-GFP, PINK1G309D-GFP or GFP. After 24 h cells were starved for 2 h in HBSS. Afterwards the LC3-II and actin content were determined by western blotting. A representative blot is shown on the right. The relative LC3-II content of cells transfected with GFP was set as 1. Transient PINK1 or PINK1G309D overexpression resulted in an increased LC3-II/actin ratio compared to cells transfected with GFP; n = 3, PINK1: p<0.01; PINK1G309D: p<0.05.</p

Stable PINK1 knockdown in SH-SY5Y cells.

<p>A) SH-SY5Y neuroblastoma cells were either cultivated in RPMI+10% FCS or starved in HBSS with or without addition of LY294002 or rapamycin. After 16 h PINK1 mRNA expression was determined by RT-qPCR and the PINK1 mRNA content of cells kept in RPMI+10% FCS was set as 1. Induction of autophagy by starvation or rapamycin resulted in an induction of PINK1 expression, comparable to the positive control LY294002; n = 4; * expression changes compared to the PINK1 expression in RPMI+10% FCS: LY294002: p<0.01; rapamycin: p<1×10⁻⁴; HBSS: p<0.005; HBSS+LY294002: p<5×10⁻⁶; HBSS+ rapamycin: p<0.0005; # expression changes compared to the PINK1 expression in RPMI+10% FCS+LY294002: p<0.05; <b>+</b> expression changes compared to the PINK1 expression in RPMI+10% FCS+rapamycin: p<0.0005. B) SH-SY5Y cells were either stably transduced with a control (nt) shRNA or a shRNA directed against PINK1 and cultivated in RPMI medium containing 5% or 10% FCS. Their PINK1 mRNA content was determined by RT-qPCR and PINK1 mRNA content of nt cells kept in medium with 10% FCS was set as 1. Serum reduction increased PINK1 mRNA in nt cells in accordance with the data shown in Fig. 1A, while stable PINK1 knockdown (kd) reduced PINK1 content under both conditions; n = 3; * expression changes compared to the PINK1 expression in RPMI+10% FCS: PINK1 kd 10% FCS p<0.0005; PINK1 induction by 5% FCS: p<0.05; # expression changes compared to the PINK1 expression in RPMI+5% FCS: PINK1 kd 5% FCS: p<0.005. C) SH-SY5Y cells without (nt) or with stable PINK1 knockdown (kd) were kept in medium with 5% FCS and either untreated or treated for 2 h with CCCP to stabilize PINK1. Afterwards the PINK1 63 kDa protein (arrowhead) and actin protein levels were determined by western blotting (see representative gel on the right). The quantification revealed a reduction of PINK1 protein under both conditions in PINK1 kd cells.</p