alpha B-crystallin (alpha BC) is a small heat shock protein. Mutations in the alpha BC gene are linked to alpha-crystallin-opathy, a hereditary myopathy histologically characterized by intracellular accumulation of protein aggregates. The disease-causing R120G alpha BC mutant, harboring an arginine-to-glycine replacement at position 120, is an aggregate-prone protein. We previously showed that the R120G mutant's aggregation in HeLa cells was prevented by enforced expression of alpha BC on the endoplasmic reticulum (ER). To elucidate the molecular nature of the preventive effect on the R120G mutant, we isolated proteins binding to ER-anchored alpha BC (TM alpha BC). The ER transmembrane CLN6 protein was identified as a TM alpha BC's binder. CLN6 knockdown in HeLa cells attenuated TM alpha BC's anti-aggregate activity against the R120G mutant. Conversely, CLN6 overexpression enhanced the activity, indicating that CLN6 operates as a downstream effector of TMaBC. CLN6 physically interacted with the R120G mutant, and repressed its aggregation in HeLa cells even when TM alpha BC was not co-expressed. Furthermore, CLN6's antagonizing effect on the R120G mutant was compromised upon treatment with a lysosomal inhibitor, suggesting CLN6 requires the intact autophagy-lysosome system to prevent the R120G mutant from aggregating. We hence conclude that CLN6 is not only a molecular entity of the anti-aggregate activity conferred by the ER manipulation using TM alpha BC, but also serves as a potential target of therapeutic interventions. (C) 2017 Elsevier Inc. All rights reserved.