Autophagy is a major mechanism for cellular quality control, as it is responsible for the elimination of altered intracellular components in lysosomes. Autophagy also contributes to the maintenance of cellular protein and organelle homeostasis. Among these organelles, the endoplasmic reticulum (ER) plays a central role in protein biosynthesis and undergoes dramatic changes to accommodate the cellular demands of particular proteins. Chaperones resident in the ER are critical to assure proper folding of many newly synthesized proteins. Tight synthetic regulation of these chaperones ensures cell survival under a variety of both stress and non-stress conditions. Thus, increased synthesis of these chaperones is one of the first cellular responses to compromised protein folding in the ER, and the mechanisms leading to their upregulation are now well-characterized. However, comparatively little is known about the normal turnover of these chaperones or their eventual fate following their stress-induced translational upregulation. We have recently found that a selective type of autophagy, known as chaperone-mediated autophagy (CMA), may play a central role in the turnover of ER chaperones and in the recovery of normal ER homeostasis after stress. The purpose of this project is to elucidate the mechanism(s) of degradation of ER chaperones with special emphasis on the role of chaperone mediated autophagy (CMA) in their turnover. We will: 1) Examine the mechanisms for degradation of specific ER chaperones (GRP94, BiP and calreticulin) under normal basal conditions;2) Determine if these mechanisms of degradation change in response to two stress conditions (ER stress and starvation), and 3) examine whether the previously described decline in CMA activity with age affects the degradation of ER chaperones and could contribute to the poor cellular response to ER stress in aging. For this purpose we will use both biochemical and image-based assays developed in our laboratory to track the degradation of ER chaperones in lysosomes by CMA. Furthermore, using genetic manipulations of critical components of CMA, both in cells in culture and in different tissues in rodents we will determine the consequences of failure in proper turnover of ER chaperones. Public Health Relevance: Inadequate cellular adaptation to ER stress has been identified as the pathogenetic basis of a growing list of devastating human disorders such as neurodegenerative disorders, metabolic diseases such as diabetes and severe liver diseases, among others. Consequently, a better understanding of the molecular mechanisms involved in the cellular response to ER stress could lead to novel approaches to modulate this response and to prevent its failure.
|Bandyopadhyay, Urmi; Sridhar, Sunandini; Kaushik, Susmita et al. (2010) Identification of regulators of chaperone-mediated autophagy. Mol Cell 39:535-47|