Abnormal processing of autophagosomes in transformed B lymphocytes form SCARB2-deficient subjects
Date
2013
Authors
Gleich, K.
Desmond, M.J.
Lee, D.
Berkovic, S.F.
Dibbens, L.M.
Katerlos, M.
Bayly, M.A.
Fraser, S.A.
Martinello, P.
Vears, D.F.
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Journal article
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BioResearch Open Access, 2013; 2(1):40-46
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Abstract
Mutations of the intrinsic lysosomal membrane protein SCARB2 cause action myoclonus-renal failure syndrome (AMRF syndrome), a rare disease characterized by renal and neurological manifestations. In this study, examination of Cos7 cells transfected with SCARB2 cDNA derived from two patients with AMRF syndrome showed that the resultant protein was truncated and was not incorporated into vesicular structures, as occurred with full-length SCARB2 cDNA. Mutant SCARB2 protein failed to colocalize with lysosomes and was found in the endoplasmic reticulum or the cytosol indicating a loss of function. Cultured skin fibroblast and Epstein-Barrvirus-transformed lymphoblastoid B cell lines (LCLs) were created from these two patients. Despite the loss ofSCARB2 function, studies with lysosomal-associated membrane protein (LAMP) 1 and LAMP2 demonstratednormal lysosomal numbers in fibroblasts and LCLs. Immunofluorescence microscopy using anti-LAMP1 andanti-LAMP2 antibodies also showed normal lysosomal structures in fibroblasts. There was no change in themorphology of fibroblasts examined by electron microscopy compared with cells from unaffected individuals.By contrast, LCLs from individuals bearing SCARB2 mutations had large intracellular vesicles that resembled autophagosomes and contained heterogeneous cellular debris. Some of the autophagosomes were seen to beextruding cellular contents into the media. Furthermore, LCLs had elevated levels of microtubule-associated protein light chain 3-II, consistent with increased autophagy. These data demonstrate that SCARB2 mutations are associated with an inability to process autophagosomes in B lymphocytes, suggesting a novel function for SCARB2 in immune function.
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Copyright 2013 Mary Ann Liebert