Transmembrane BAX Inhibitor-1 Motif Containing Protein 5 (TMBIM5) Sustains Mitochondrial Structure, Shape, and Function by Impacting the Mitochondrial Protein Synthesis Machinery

Bruno Seitaj,Li Zhang,Christina Wolf,Ute Distler,Rita La Rovere,Jan B Parys,Philipp Schippers,Geert Bultynck,Verena Wüllner,Axel Methner,Felicia Maull,Stefan Tenzer

doi:10.3390/cells9102147

Bruno Seitaj, Li Zhang + Show 10 more

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https://doi.org/10.3390/cells9102147

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The Transmembrane Bax Inhibitor-1 motif (TMBIM)-containing protein family is evolutionarily conserved and has been implicated in cell death susceptibility. The only member with a mitochondrial localization is TMBIM5 (also known as GHITM or MICS1), which affects cristae organization and associates with the Parkinson’s disease-associated protein CHCHD2 in the inner mitochondrial membrane. We here used CRISPR-Cas9-mediated knockout HAP1 cells to shed further light on the function of TMBIM5 in physiology and cell death susceptibility. We found that compared to wild type, TMBIM5-knockout cells were smaller and had a slower proliferation rate. In these cells, mitochondria were more fragmented with a vacuolar cristae structure. In addition, the mitochondrial membrane potential was reduced and respiration was attenuated, leading to a reduced mitochondrial ATP generation. TMBIM5 did not associate with Mic10 and Mic60, which are proteins of the mitochondrial contact site and cristae organizing system (MICOS), nor did TMBIM5 knockout affect their expression levels. TMBIM5-knockout cells were more sensitive to apoptosis elicited by staurosporine and BH3 mimetic inhibitors of Bcl-2 and Bcl-XL. An unbiased proteomic comparison identified a dramatic downregulation of proteins involved in the mitochondrial protein synthesis machinery in TMBIM5-knockout cells. We conclude that TMBIM5 is important to maintain the mitochondrial structure and function possibly through the control of mitochondrial biogenesis.

Highlights

The mammalian Transmembrane Bax Inhibitor-1 motif (TMBIM)-containing family consists of six proteins with a heterogeneous intracellular localization [1]
To study the mitochondrial and cellular consequences of TMBIM5 deficiency, we obtained a custom-made human TMBIM5-KO HAP1 cell line generated by CRISPR/Cas9-mediated deletion of 32 base pairs in exon 3 of TMBIM5 (Figure 1A)
This deletion resulted in a frame-shift after the mitochondrial-targeting sequence and a complete loss of TMBIM5 protein expression (Figure 1B)

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The mammalian Transmembrane Bax Inhibitor-1 motif (TMBIM)-containing family consists of six proteins with a heterogeneous intracellular localization [1]. TMBIM1, known as Responsive to centrifugal force and shear stress gene 1 (RECS1) or protein Lifeguard 3 (LFG3), is mainly localized. TMBIM2 localizes at the endoplasmic reticulum (ER), the Golgi apparatus, and possibly in lipid rafts of the plasma membrane with a predominant expression in the nervous system [4,5]. It is known as Fas Apoptotic Inhibitory Molecule 2. It was implicated in ER stress and the unfolded protein response [8,9]

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