SCA8 RAN polySer protein preferentially accumulates in white matter regions and is regulated by eIF3F

Spinocerebellar ataxia type 8 (SCA8) is caused by a bidirectionally transcribed CTG·CAG expansion that results in the in vivo accumulation of CUG RNA foci, an ATG‐initiated polyGln and a polyAla protein expressed by repeat‐associated non‐ATG (RAN) translation. Although RAN proteins have been reported in a growing number of diseases, the mechanisms and role of RAN translation in disease are poorly understood. We report a novel toxic SCA8 polySer protein which accumulates in white matter (WM) regions as aggregates that increase with age and disease severity. WM regions with polySer aggregates show demyelination and axonal degeneration in SCA8 human and mouse brains. Additionally, knockdown of the eukaryotic translation initiation factor eIF3F in cells reduces steady‐state levels of SCA8 polySer and other RAN proteins. Taken together, these data show polySer and WM abnormalities contribute to SCA8 and identify eIF3F as a novel modulator of RAN protein accumulation.     

Derivation of Airway Basal Stem Cells from Human Pluripotent Stem Cells

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A Highlights from MBoC Selection: DNAJB12 and Hsp70 triage arrested intermediates of N1303K-CFTR for endoplasmic reticulum-associated autophagy

The transmembrane Hsp40 DNAJB12 and cytosolic Hsp70 cooperate on the endoplasmic reticulum’s (ER) cytoplasmic face to facilitate the triage of nascent polytopic membrane proteins for folding versus degradation. N1303K is a common mutation that causes misfolding of the ion channel CFTR, but unlike F508del-CFTR, biogenic and functional defects in N1303K-CFTR are resistant to correction by folding modulators. N1303K is reported to arrest CFTR folding at a late stage after partial assembly of its N-terminal domains. N1303K-CFTR intermediates are clients of JB12-Hsp70 complexes, maintained in a detergent-soluble state, and have a relatively long 3-h half-life. ER-associated degradation (ERAD)-resistant pools of N1303K-CFTR are concentrated in ER tubules that associate with autophagy initiation sites containing WIPI1, FlP200, and LC3. Destabilization of N1303K-CFTR or depletion of JB12 prevents entry of N1303K-CFTR into the membranes of ER-connected phagophores and traffic to autolysosomes. In contrast, the stabilization of intermediates with the modulator VX-809 promotes the association of N1303K-CFTR with autophagy initiation machinery. N1303K-CFTR is excluded from the ER-exit sites, and its passage from the ER to autolysosomes does not require ER-phagy receptors. DNAJB12 operates in biosynthetically active ER microdomains to triage membrane protein intermediates in a conformation-specific manner for secretion versus degradation via ERAD or selective-ER-associated autophagy.     

Interaction between rat serum phosphorylcholine binding protein and platelet activating factor

The binding of rat serum phosphorylcholine binding protein (PCBP) to platelet activating factor (PAF) has been demonstrated using a HPLC-gel filtration technique. The bulk of the bound [3H]-PAF eluted with a higher molecular weight species of PCBP, possibly an aggregated form of PCBP. A smaller amount of [3H]-PAF co-eluted with the major monomeric species of PCBP. Formation of the PCBP-PAF complex was calcium dependent and could be inhibited by phosphorylcholine, suggesting the involvement of the phosphorylcholine binding site on PCBP. Binding of albumin and alpha 1-acid glycoprotein to PAF was not affected by phosphorylcholine or calcium. The specificity of this binding may explain the inhibitory effect of PCBP and related phosphorylcholine binding proteins on PAF induced aggregation of platelets.