Heme, Ubiquitin, and Lung Cancer

Discover how the heme-oxidative stress pathway controls protein degradation via the Ubiquitin-Proteasome system

Protein degradation regulated by the ubiquitin-proteasome system (UPS) is an irreversible mechanism used by many biological processes. This system enables the selective elimination of proteins, making the UPS the ultimate on-off switch in a cell. The ubiquitylation process is controlled by an enzymatic cascade involving :

• An E1 enzyme that activates ubiquitin molecules.
• An E2 enzyme that transfers ubiquitin.
• An E3 ubiquitin ligase that recognizes the substrate protein.

In humans, this cascade comprises two E1 enzymes, around 30 E2 enzymes and around 600 E3 enzymes, enabling extreme specificity in ubiquitylation. Over 80% of proteins undergo UPS-mediated degradation, making E3 ubiquitin ligases central regulators in response to specific stimuli.

To explore these mechanisms, our laboratory is pursuing two main avenues:

Defining the heme degradome

We are identifying new substrates for heme-UPS and characterizing their downstream pathways. We are also investigating molecular mechanisms involving E3 ubiquitin ligases and deubiquitylation enzymes, which act as heme sensors by coupling protein degradation to variations in heme signaling.

Determine the mechanisms underlying heme-regulated protein destruction

Our studies demonstrate a novel role for heme in promoting the interaction between a ubiquitin ligase (FBXO22) and its substrates (BACH1). We aim to understand how heme modulates the dynamics of substrate-ubiquitin ligase interactions to regulate protein stability.

Understanding how the hemato-oxidative stress pathway regulates gene expression by modulating the activity of intracellular transcriptional sensors

Recent pioneering studies have revealed how heme signaling regulates a number of pathways, from mitochondrial respiration to metabolism and circadian rhythms, by reversibly binding to heme-sensor proteins and modulating their activity. These proteins are involved in a variety of biological processes, including protein translation and transcription.

Our team is currently focusing on two main areas:

1. Regulation of the heme-sensor transcription factor BACH1

BACH1 is a major molecular link between cellular heme levels, redox status and transcriptional response. It functions as a transcriptional repressor and activator, regulating various biological processes such as metabolism and cell growth. However, little is known about the specific transcriptional coregulators that work in conjunction with BACH1 to control certain transcriptional programs in response to heme fluctuations. To identify these protein complexes, we integrate techniques such asimmuno-purification and proximity labeling (BioID) followed by mass spectrometry analysis.

2. Identification of new hematopoietic transcription factors

We combine proteomic and genetic strategies to discover novel transcriptional regulators. These approaches include proximity tagging to identify regulators interacting with heme, and genome-wide CRISPR screens coupled with transcriptomic profiling techniques to identify factors implementing heme-controlled transcription.

Determine the mechanisms linking alteration of the hemato-oxidative stress pathway to the development and progression of lung tumors

In cancer, heme signaling can be deregulated by altered oxidative stress homeostasis, induced by high levels of reactive oxygen species (ROS). ROS play a complex role in tumorigenesis, being both pro-tumorigenic and cytotoxic at high levels. Cancer cells, thanks to aberrant redox homeostasis, manage to optimize ROS-induced proliferation while avoiding critical thresholds triggering senescence or apoptosis.

To gain an in-depth understanding of these mechanisms, our laboratory is focusing on two main areas:

1. Understanding the impact of KEAP1/NRF2 mutations on heme-UPS-regulated protein degradation

We use combined biochemical, proteomic and murine genetic approaches to identify heme-UPS substrates deregulated in lung cancers and determine their role in tumorigenesis.

2. Study the impact of alteration of the heme-BACH1 pathway in specific lung cancer models.

Using CRISPR/Cas9, we are developing mouse models reproducing specific mutations (KRAS and LKB1) observed in ~30% and ~45% of lung cancer patients with KEAP1 mutations. These models enable us to identify the transcriptional targets of the heme-BACH1 pathway and understand their influence on tumor progression.