Redox regulation of the mitochondrial Ca2+ export machinery

• Applicant: Dr. Christine Silvia Gibhardt
• Subject Area: Anatomy and Physiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555969813

Mitochondria as powerhouses and metabolic hubs are indispensable for normal cellular function. Depending on their metabolic needs, mitochondria take up or release calcium (Ca2+) via a tightly regulated Ca2+-handling protein machinery. The import across the inner mitochondrial membrane is almost exclusively controlled by the mitochondrial Ca2+ uniporter (MCU) complex. The export of Ca2+ from the mitochondrial matrix is less well understood and is executed by several proteins, that include the Na+/Ca2+ (/Li+) exchanger NCLX and its recently described regulator TMEM65. Additionally, two Ca2+/H+ antiporters, LETM1 and TMBIM5, have been demonstrated to extrude Ca2+ from the mitochondrial matrix. In the matrix, Ca2+ controls the mitochondrial dehydrogenases and is thus essential for ATP production. Notably, the Ca2+-controlled alterations of electron availability also affect reactive oxygen species (ROS) release via different complexes of the electron transport chain. ROS can be cell toxic and cause oxidative stress in high concentrations. On the other hand, ROS can act as important signal messengers by controlling protein function via oxidation of cysteine residues. Given the functional relevance, mitochondrial bioenergetics and metabolic output need to be tightly regulated and are frequently dysregulated in cancer. Our previous work identified mitochondrial Ca2+ (mitoCa2+) and redox signals as essential regulators of melanoma aggressive behavior and therapeutic sensitivity. Moreover, it was shown that cysteine oxidation affects mitoCa2+ import via the MCU complex, which is a regulatory mechanism highly relevant for melanoma pathobiology. The impact of redox regulation on the mitoCa2+ export machinery, however, has been not investigated so far. The current proposal aims to address these questions by focusing on the following aims: 1) Identification and characterization of thiol switches in LETM1, TMBIM5, NCLX and TMEM65. 2) Functional characterization of the identified thiol modifications within the mitochondrial Ca2+ export machinery. 3) Evaluation of the impact of mitochondrial Ca2+ export redox regulation on melanoma (patho-) physiology.

• DFG Programme: Research Grants