The TDH–GCN5L1–Fbxo15–KBP axis limits mitochondrial biogenesis in mouse embryonic stem cells

Abstract

Self-renewing naïve mouse embryonic stem cells (mESCs) contain few mitochondria, which increase in number and volume at the onset of differentiation. KBP (encoded by Kif1bp) is an interactor of the mitochondrial-associated kinesin Kif1Bα. We found that TDH, responsible for mitochondrial production of acetylCoA in mESCs, and the acetyl-transferase GCN5L1 cooperate to acetylate Lys501 in KBP, allowing its recognition by and degradation via Fbxo15, an F-box protein transcriptionally controlled by the pluripotency core factors and repressed upon differentiation. Defects in KBP degradation in mESCs result in unscheduled increase in mitochondrial biogenesis, enhanced respiration and ROS production, and inhibition of cell proliferation. Silencing of Kif1Bα reverts the aberrant increase in mitochondria induced by KBP stabilization. Notably, upon differentiation, Kif1bp−/− mESCs display impaired expansion of the mitochondrial mass and form smaller embryoid bodies. Thus, KBP proteolysis limits the accumulation of mitochondria in mESCs to preserve their optimal fitness, whereas KBP accumulation promotes mitochondrial biogenesis in differentiating cells.

Ubiquitin Dynamics in Stem Cell Biology: Current Challenges and Perspectives

“…E3 Ub ligase FBXO15, one of the substrate recognition subunits of the SCF (Skp1‐Cul1‐F‐Box‐protein) is strictly expressed in mESC. Its inactivation does not affect the expression of pluripotency or developmental genes in pluripotent state but it limits the expansion of mitochondria . In absence of Fbxo15 ESC accumulates mitochondria, primarily by a de novo production mechanism, increases respiratory capacity and ATP production.…”

Ubiquitin-Dependent Regulation of Stem Cell Biology

“…In a similar manner, the E3 ligase CUL4-DDB1 supports the self-renewal of hematopoietic precursors [72], while the E3 mLin41/TRIM71 performs this task in neural precursors [13]. Extending these concepts to energy metabolism, SCF FBXO15 , a stem cell-specific E3 that was initially used as a marker for induced pluripotent stem cells [70], ubiquitylates a regulator of mitochondrial biogenesis, which likely reduces the exposure of ESCs to reactive oxygen species [73]. By limiting the abundance of crucial receptors, transcription factors, and metabolic regulators, ubiquitylation allows stem cells of multiple tissues to translate signals emerging from their niche into efficient self-renewal.…”

“…Given the role of ubiquitylation in development, it is important to understand how stem cells are able to translate such organismal signals into proper activation or inhibition of critical ubiquitylation enzymes. In many cases, it is the abundance of E3 ligases or deubiquitylases that is tightly controlled, with several enzymes being preferentially expressed in the pluripotent state [10, 11, 24, 73, 113]. The activity of these enzymes can be further fine-tuned by binding partners, such as the R-spondin proteins that titrate the ZNRF3 and RNF43 E3 ligases away from their membrane localized substrates [46, 47].…”

Mitochondrial General Control of Amino Acid Synthesis 5 Like 1 Regulates Glutaminolysis, Mammalian Target of Rapamycin Complex 1 Activity, and Murine Liver Regeneration

“…As background, GCN5L1 has been found to reside in mitochondria and in the cytosol, and it was initially identified as a putative component of a mitochondrial acetyltransferase, although this protein itself does not contain an acetyltransferase catalytic domain . Moreover, no mitochondrial acetyltransferase has been identified to interact with GCN5L1, although it is interesting that mitochondrial‐linked GCN5L1 is dependent on an acetyl‐CoA–generating enzyme, to acetylate a lysine residue on a molecular motor protein, kinesin‐binding protein . In contrast, the cytosolic GCN5L1 has been found to bind to a canonical acetyltransferase and modulate microtubular acetylation .…”

“…In contrast, the cytosolic GCN5L1 has been found to bind to a canonical acetyltransferase and modulate microtubular acetylation . The mitochondrial phenotype following the disruption of GCN5L1 suggests that this protein plays an integral role in fatty acid and glucose metabolism, mitochondrial turnover, and retrograde signaling from the mitochondria to nucleus for regulation of gluconeogenesis …”