The cellular stress response is a major adaptation strategy to: 1) a changing physical environment, 2) disease states that range from autoimmunity to cancer, and 3) clinical therapy. Heat shock proteins (HSPs) are induced in response to many types of cellular stress, including heat shock, and are a recognized part of the cellular stress response. The focus of our long-term research effort is a novel aspect of the stress response - namely stress-induced protein glycosylation (SIG). We hypothesize that SIG, in addition to classical HSPs, is an integral part of the cellular stress response, and may be essential to cell survival under adverse conditions. Protein glycosylation appears to stabilize proteins and facilitate protein assembly and re-folding by a variety of mechanisms that could be independent or cooperative with HSPs. Thus protein glycosylation and HSPs together may constitute an integrated mechanism that confers stress tolerance (thermotolerance) to surviving cells. Current efforts, supported by this grant, are directed at 1) characterizing major stress glycoproteins identified to date, 2) developing molecular probes, and 3) further investigating the role of SIG in stress biology. Recent progress in our laboratory has led to the identification of specific stress glycoproteins. 1) GP50 was identified as the retinoic acid-inducible J6 gene product. 2) The """"""""prompt"""""""" glycoprotein, P-SG67, was identified as calreticulin. 3) GP62, a third major glycoprotein, was implicated in the heat-resistant phenotype of a cell line expressing high levels of HSP70 and was recently purified, but remains to be characterized at the molecular level. In this competing renewal application, we seek to complete characterization of already identified stress glycoproteins, and to define their functional roles and interaction with HSPs and other proteins.
SPECIFIC AIMS are: 1) To characterize GP62 at the molecular level with the development of antibody and nucleotide probes. Similarly, we will characterize protein glycosylation in other heat-resistant cell lines that overexpress specific stress response elements. 2) We will modulate expression of GP50/J6 and P-SG67/calreticulin in specific cell lines, using both antisense inhibition and overexpression, to examine cause-effect relationships between SIG, HSP expression, and stress resistance. The biophysical consequences of specific glycosylation sites will be examined in subsequent projects (long-term goal), building on the anticipated achievements from this work. The long-term and short-term goals of this project serve to provide an understanding of mechanistic relationships between HSPs and SIG. Potential applications of this stress biology project include adjuvant hyperthermia with drugs or X-irradiation, modification of the tumor cell response to hypoxia and to chemotherapy, and the modification of drug resistance.
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