A novel protein quality control system and its role in tumorigenesis

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PROJECT DESCRIPTION The overall goal of this application is to characterize a novel protein quality control (PQC) system in mammalian cells and to elucidate its role in tumorigenesis. Oncogenic transformation is a progressive process during which normal cells acquire a set of traits to overcome various constraints that govern their proliferation. Here we will test the notion that a heightened ability to remove misfolded proteins may be a new characteristic of tumor cells. Protein folding is a challenging process in normal unstressed cells, and even more so in incipient and established neoplastic cells, which frequently encounter high oxidative stresses that damage proteins. However, PQC systems that remove misfolded proteins in mammalian cells and the role of these systems in tumorigenesis are not well understood. Our lab recently found that many mammalian tripartite motif (TRIM) proteins can specifically recognize misfolded proteins and mark them for proteasomal degradation, and that certain TRIM can also directly activate the proteasome. Moreover, we observed that the capacity to remove misfolded proteins is markedly increased in cancer cells due to the up-regulation of TRIMs. This higher degradation power mitigates oxidative stress associated with oncogenic growth and permits oncogenic growth. These findings indicate TRIMs as versatile regulators of protein quality, connect the clearance of misfolded proteins to antioxidant defense, and suggest a previously unrecognized characteristic of tumor cells. Our central hypothesis is that TRIM proteins constitute a major PQC system in mammalian cells that are critical for antioxidant defense and oncogenic transformation. We propose three specific aims. First, TRIM proteins exist in a large number including over 70 in humans. To gain a comprehensive view of the TRIM system, we will systematically investigate the role of all human TRIMs in proteasomal degradation of misfolded proteins and define the molecular basis for their different potency. Second, we will investigate how the accumulation of misfolded proteins causes high oxidative stress, and how TRIMs ameliorate this stress through the clearance of misfolded proteins. Third, we will determine the role of the TRIM system in cancer progression using cell and animal models. Moreover, our results suggest that the removal of misfolded protein is highly sensitive to proteasome inhibition, which may provide an explanation for proteasome-inhibitor-based therapies for cancer. We will test the notion that increasing production of misfolded proteins, combined with proteasome blockage, may be highly effective in killing cancer cells. Collectively, these aims will address critical issues pertaining to protein homeostasis and oncogenic transformation, and will likely provide valuable information for the development of effective therapies.