Mechanisms of cytoprotection induced by stress proteins

University Of California, San Diego, La Jolla CA

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Abstract

DESCRIPTION (provided by applicant): Heat shock proteins (hsps) play a major role in polypeptide folding and translocation across membranes and have been coined molecular chaperones. During stress conditions, hsps are induced to participate in the repair of damage occurring after the insult and to protect cells from subsequent stresses, a condition known as stress tolerance. Thus, hsps are envisioned as natural mechanisms of cellular protection. A new role for hsps, in particular the Hsp70 family, has recently been revealed: their ability to interact with membranes. Hsp70 and Hsc70 integrate into membranes, forming ion conductance pathways. In addition, they modulate the traffic of cellular vesicles. In this regard, a significant increase in CD14 endocytosis was observed after incubation of macrophages (MPh) with geldanamycin (GA). This drug is a specific inhibitor of the HspQO family, which also induces the expression of hsps. Moreover, accumulation of newly synthesized CD14 within the endoplasmic reticulum (ER) was observed after treatment with GA, which is related to the inhibition of Grp94, an ER chaperone belonging to the Hsp90 family. Other endocytic processes (clathrin-dependent and caveolae/raft endocytosis), as well as phagocytosis, were enhanced after treatment with GA and required new gene expression, suggesting a direct role for hsps. Thus, it is hypothesized that hsps participate in the endocytic/phagocytic process as part of the stress response. The central objectives of this investigation are: Specific Aim 1. Investigate the role of hsps in endocytosis. This investigation will confirm and extend the observations that hsps are involved in endocytic and phagocytic processes, identify the hsp(s) that is (are) involved, and demonstrate the physical interaction between hsps and endocytic vesicles. The final part of this aim will uncover the mechanism of ligand-independent endocytosis of CD14, which is also increased in the presence of hsps. Specific Aim 2. Determine the mechanisms of CD14 accumulation within the ER after GA treatment. The hypothesis to be tested is that accumulation of CD14 within the ER is the result of newly synthesized protein that is retained in this compartment because of improper folding or deficient post-translational modifications, such as the attachment of GPI tail.