Endoplasmic Reticulum-associated Degradation (ERAD) and Autophagy Cooperate to Degrade Polymerogenic Mutant Serpins

Abstract

The serpinopathies are a family of diseases characterized by the accumulation of ordered polymers of mutant protein within the endoplasmic reticulum. They are a diverse group including ␣ 1 -antitrypsin deficiency and the inherited dementia familial encephalopathy with neuroserpin inclusion bodies or FENIB. We have used transient transfection of COS7 cells and mouse embryonic fibroblasts, PC12 cell lines that conditionally express wild type and mutant neuroserpin and fly models of FENIB to assess the cellular handling of wild type and mutant serpins. By using a polymer-specific monoclonal antibody, we show that mutant neuroserpin forms polymers after a delay of at least 30 min and that polymers can be cleared in PC12 cell lines and from the brain in a fly model of FENIB. At steady state, the fractions of intracellular polymerogenic G392E mutant neuroserpin in the monomeric and polymeric states are comparable. Inhibition of the proteasome with MG132 reveals that both mutant neuroserpin and ␣ 1 -antitrypsin are degraded predominantly by endoplasmic reticulum-associated degradation (ERAD). Pharmacological and genetic inhibitions demonstrate that autophagy is responsible for bulk turnover of wild type and mutant serpins, but can be stimulated by rapamycin to compensate for proteasome inhibition. The significance of these findings to the treatment of serpinopathies is discussed.

Proteasome inhibition rescues clinically significant unstable variants of the mismatch repair protein Msh2

“…The pathology of ubiquitin-mediated turnover of missense variants of Msh2 is in keeping with mounting evidence that other human diseases, such as cystic fibrosis and Huntington, Alzheimer's, and Parkinson diseases are linked to proteinfolding abnormalities resulting in instability and ubiquitin-positive aggregates (18,19). Interestingly, diseases including neurofibromatosis (20), multiple endocrine neoplasia Type 1 (21), α-1 antitrypsin deficiency (22), classic late-infantile neuronal ceroid lipofuscinosis (23), and phenylketonuria (24) all have incidences in which missense variants are targeted by the ubiquitin-proteasome pathway. Thus, small-molecule stabilization of missense variants or the targeted inhibition of the ubiquitin pathway represent exciting avenues for therapeutic exploration for many diseases, not just Lynch syndrome.…”

Protein Folding and Quality Control in the ER

“…Cells possess additional degradation pathways to cope with a variety of situations based on the characteristics of the misfolded proteins (Fu and Sztul 2009;Kroeger et al 2009;Wong and Cuervo 2010). We have reported previously that the aggregated or insoluble form of type I collagen in the ER is degraded by autophagy-mediated lysosomal degradation, whereas nonaggregated forms are subject to ERAD (Fig.…”

A Novel Interaction Between Aging and ER Overload in a Protein Conformational Dementia

“…This finding unifies current concepts of disturbed proteostasis in FENIB (Lawless et al 2004;Hidvegi et al 2005;Davies et al 2009). Since IRE1 signaling has been linked to autophagy, the relatively low induction of IRE1 signaling in our murine FENIB model may help to explain the fact that autophagy is only mildly increased in FENIB (Hetz et al 2009;Kroeger et al 2009). Other than the serpinopathies, ER stress has been shown to be prominently involved in the pathophysiology of other dementias with intracellular protein accumulation (Hoozemans et al 2009;Salminen et al 2009).…”