Conference Agenda

In the last years, mitochondrial ultrastructural and morphological changes have been implied in the control of several physiological and pathological changes, including the progression of apoptosis, inflammation, differentiation, tumorigenesis. However, the role of mitochondrial dynamics in the control of complex cellular cues and in response to reversible and irreversible cellular damage is not yet clarified. We will overview the key experiments that shed light on the role of mitochondrial shape and ultrastructure in cell physiology, pathology and in disease and offer a personal perspective on the missing pieces of the puzzle that await to be studied.

Proteins from the Bcl-2 family play an essential role in the regulation of intrinsic/mitochondrial apoptotic signaling, but they also display cell death-unrelated, less comprehended roles in cellular/mitochondrial metabolism. Thus in this communication, we aimed to contribute to a better understanding of apoptosis-unrelated activities of the Bax and Bak, pro-apoptotic members of the Bcl-2 family. Using CRISPR-Cas9 gene editing, we prepared Bax/Bak-deficient human cancer cells of epithelial, neural and hematopoietic origin and discovered that while respiration and cell proliferation of the glioblastoma-derived U87 Bax/Bak-deficient cells was greatly enhanced, respiration as well as in vitro proliferation of Bax/Bak-deficient B lymphoma HBL-2 cells was attenuated. Interestingly, Bax/Bak-deficient U87 cells also more rapidly formed tumours in mice, and showed modulation of metabolism with a considerably increased NAD+/NADH ratio. Follow-up analyses uncovered increased/decreased expression of mitochondria-encoded subunits of respiratory complexes and stabilization/destabilization of the mitochondrial transcription elongation factor TEFM in Bax/Bak-deficient U87 and HBL-2 cells, respectively. ShRNA-mediated downregulation of TEFM expression attenuated mitochondrial respiration in Bax/Bak-deficient U87 as well as in parental HBL-2 cells. Our findings suggest that (post)translational regulation of TEFM levels in Bax/Bak-deficient cells modulates the expression of subunits of mitochondrial respiratory complexes that, in turn, contribute to respiration and the accompanying changes in metabolism and proliferation in these cells.

Bcl-xL is an anti-apoptotic Bcl2 family protein that localizes primarily to the outer mitochondrial membrane (OMM) and exerts inhibition of the Bak/Bax-mediated apoptotic membrane permeabilization. Bcl-xL also interacts with the IP3 receptor Ca2+ release channel (IP3R) of the endoplasmic reticulum (ER). It is unknown if the IP3Rs interact with ER or OMM localized Bcl-xL. We have studied if OMM-targeted Bcl-xl engages the IP3R forming a tether between ER and mitochondria and regulating the ER-mitochondrial calcium coupling.

MCL-1 is a cardinal regulator of programmed cell death, responsible for maintaining cellular life in the face of unexpected cellular stress. Cancer cells hijack this critical functionality of MCL-1, namely mitochondrial apoptotic blockade, to ensure cellular immortality. Why MCL-1 is cancer’s top choice among BCL-2 family anti-apoptotic proteins for overexpression has been a mechanistic mystery. In investigating additional roles for MCL-1 during homeostasis and disease, we uncovered that MCL-1 dependent cancer cells specifically rely on fatty acid oxidation as a fuel source – a metabolic wiring enforced by MCL-1 itself. Metabolomic, proteomic, and genomic profiling confirmed that the regulation of fatty acid oxidation by MCL-1 is independent of its anti-apoptotic functionality. These data inform novel opportunities to overcome treatment-resistant cancer by targeting the multifaceted roles of MCL-1.