Introduction/Background

High levels of abnormal or damaged proteins is a cellular feature of aging, cancer, adult-onset neurodegenerative diseases, and many rare genetic conditions. In neurodegeneration, failure to degrade aberrant proteins leads to cellular dysfunction; whereas some types of cancer cells are able to survive and proliferate despite chronic protein damage. Treating these conditions requires knowledge of the cellular pathways that normally function to remove unwanted proteins, and how they become mis-regulated in disease. The Lehrbach lab uses C. elegans to discover these pathways, understand how they work, and investigate their roles in health and disease.

Our work focuses on regulation of the proteasome, an elaborate molecular machine that carries out the majority of targeted protein degradation in eukaryotic cells. Proteasome inhibitor drugs are used to treat some kinds of cancer and dysfunction of the ubiquitin-proteasome system is found in many neurodegenerative diseases. By revealing how the proteasome is regulated, our work may lead to new ways to treat these diseases.

Regulation of the proteasome by the SKN-1A/Nrf1 transcription factor

Transcriptional control of proteasome subunit gene expression is a conserved mechanism of proteasome regulation in eukaryotes. This mechanism is particularly important if proteasome function is impaired by drugs or genetic mutations. Under these conditions, transcriptional activation of the proteasome subunit genes allows cells to compensate by making more proteasomes. In animals, this response is carried out by a transcription factor called SKN-1A (NFE2L1 or Nrf1 in humans).

We established a GFP-based reporter system to monitor the activation of proteasome gene expression by SKN-1A in live C. elegans. We have used this reporter in genetic screens to systematically identify the factors that are required for regulation of the proteasome. Using genetic, cell biology and biochemical analyses, we have developed a detailed picture of the mechanisms by which these factors control SKN-1A. We are also using the C. elegans model to investigate the roles of SKN-1A-dependent proteasome regulation in normal and disease physiology. As well as mediating resistance to proteasome inhibitor drugs, we have found that SKN-1A responds to cytosolic protein misfolding and is protective during aging and in neurodegenerative disease models. We are building on this work to more deeply understand the mechanisms and functions of the SKN-1A/Nrf1 pathway.

New regulators of protein degradation

We are developing reporters to monitor regulation and function of the proteasome and other protein homeostasis pathways in live C. elegans. We are using these tools do design massively high-throughput mutagenesis screens that utilize next-generation whole genome sequencing to identify the genes and proteins that control protein degradation. The fast life cycle, simple genetics, and small genome of C. elegans is ideal for this approach. Our screens for modifiers of proteasome expression and function reveal unexpected roles for several genes not previously linked to protein degradation. We are using C. elegans genetics, biochemical and in vitro approaches to understand the mechanism by which these new regulators control protein degradation. We are also using C. elegans to investigate how these factors affect aging, neurodegeneration, and resistance to proteasome inhibitors.

Understanding NGLY1 deficiency

NGLY1 deficiency is a rare genetic disease caused by loss of function mutations in the NGLY1 gene. The symptoms of NGLY1 deficiency include neurological defects that affect cognition and motor skills. We discovered that regulation of the proteasome is disrupted in C. elegans deficient for PNG-1, the C. elegans NGLY1 ortholog. We hypothesize that many of the symptoms of NGLY1 deficiency are caused by mis-regulation of the proteasome. We are using large-scale genetic screens in C. elegans to discover ways to restore proteasome function in the absence of PNG-1/NGLY1. We aim to pinpoint conserved pathways that might be targeted for treatment of NGLY1 deficiency or other diseases that involve impaired proteasome function.