The role of DELE1 in mitochondrial stress signaling

• Applicant: Professor Dr. Lucas Jae, Ph.D.
• Subject Area: Biochemistry ; General Genetics and Functional Genome Biology ; Cell Biology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 470553481

Mitochondria are critical organelles and their malfunction is central to many metabolic and neuromuscular diseases. Perturbations of mitochondrial homeostasis need to be communicated to the cell such that appropriate countermeasures can be launched. In 2020, we and others have identified the long-sought pathway that relays mitochondrial stress to the cytosol in humans: The previously little-studied protein DELE1 is cleaved by the mitochondrial protease OMA1, after which its C-terminal fragment (S-DELE1) relocates from mitochondria to the cytosol, where it binds and activates the stress kinase HRI. While this discovery represents a major step forward, we still have very limited insight into the function of DELE1 in the steady state, how its processing by OMA1 allows mitochondrial release, which types of mitochondrial stress can be sensed by this module and how the cellular response is tuned to the nature of the experienced perturbation.1. It is currently unclear, how DELE1 is sorted and processed in healthy mitochondria. Using our unique haploid genetic screening strategy, we have identified regulators of DELE1 in unperturbed cells. Guided by these leads, we will first clarify the mitochondrial sorting of DELE1. In particular, we will elucidate how sorting of DELE1 is regulated by its unusually long mitochondrial targeting sequence and its modification by mitochondrial proteases along the way. 2. A major question is how DELE1 is released from mitochondria upon cleavage by OMA1. With the exception of mitochondrial permeabilization during apoptosis and a handful of very specialized cases, no dedicated mitochondrial export mechanisms are known to date. Using DELE1 chimeras, we will clarify which mitochondrial subcompartments are compatible with DELE1 release. Furthermore, we will illuminate whether cleavage of DELE1 is sufficient for its mitochondrial release or if OMA1 serves additional functions in this process. A genome-wide approach will be taken to identify any additional release factors and their mechanistic contribution will be characterized. 3. Our preliminary data suggest that DELE1 may serve as a sensor of mitochondrial import defects via its own import into the organelle and that different species of cytosolic DELE1 may allow the cell to differentiate between different types of mitochondrial perturbations. To mechanistically characterize this scenario, we will first clarify with which proteins different cytosolic species of DELE1 interact and how they are affected by them. We will then test DELE1 signaling in response to mitochondrial import perturbation and systematically analyze the cellular response to different cytosolic DELE1 species. Finally, we will examine the role of this feature of DELE1 signaling in the context of pathogenic protein species that interfere with mitochondrial import.

• DFG Programme: Research Grants