Examining the Effects of Manipulating Chaperone-Mediated Autophagy on Stress-Induced Nuclear Granules (SINGs) within the Nuclei of Oocytes of Caenorhabditis elegans

Abstract

Proteostasis is the cyclical protein quality control system of biological organisms. The cycle begins with protein synthesis, followed by specific regulated function within the cell and tissues, and then degradation unto the cycle repeating. Degradation allows for obsolete proteins (e.g. no longer used, damaged, or misfolded proteins) to be broken down into reusable amino acid and polypeptide subunits. This degradation process occurs through two main systems: 1. The ubiquitin-proteasome system; and 2. Lysosomes that utilize autophagy. One of the types of autophagy that the cell uses is called chaperone-mediated autophagy. The purpose of this study was to examine the effects of manipulating chaperone-mediated autophagy on stress-induced nuclear granules (SINGs) within the nuclei of the oocytes of Caenorhabditis elegans. Stress-Induced Nuclear Granules (SINGs) form within the nuclei of oocytes of C. elegans as a result of the accumulation of misfolded proteins in a suspected area of protein quality control. Ribonucleic acid interference (RNAi) was used to separately knock down the activity of two genes, lmp-1 and lmp-2 of lysosomes, which code for the receptor proteins LMP-1 and LMP-2 respectively in C. elegans (LAMP-1 and LAMP-2 in mammals and Homo sapiens ). These proteins are responsible for binding to the chaperone-substrate misfolded protein complex and translocating it across the lysosomal membrane for subsequent degradation. With the translational activity reduced of either the lmp-1 gene or the lmp-2 gene, the process of lysosomal chaperone-mediated autophagy was potentially halted, thus causing a buildup of misfolded proteins in the cytosol. An increase of SING formation was then observed during salt stress conditions in the RNAi knockdown stressed models compared to the control models. Two possibilities for this increase include: 1. Cytosolic misfolded proteins are potentially included in SING formation; or 2. An increase in cytosolic misfolded proteins potentially triggers a chaperone sink in the cytosol, which partially hinders normal chaperone function in the nucleus.