Coenzyme Q distribution in HL-60 human cells depends on the endomembrane system

Coenzyme Q (Q) is an essential factor in the mitochondrial electron chain but also exerts important antioxidant functions in the rest of cell membranes of aerobic organisms. However, the mechanisms of distribution of Q among cell membranes are largely unclear. The aim of the present work is to study the mechanisms of distribution of endogenous Q10 and exogenous Q9 among cell membranes in human HL-60 cells. Endogenous Q10 synthesized using the radiolabelled precursor [14C]-pHB was first detected in mitochondria, and it was later incorporated into mitochondria-associated membranes and endoplasmic reticulum (ER). Plasma membrane was the last location to incorporate [14C]-Q10. Brefeldin A prevented Q10 incorporation in plasma membrane. Exogenous Q9 was preferably accumulated into the endo-lysosomal fraction but a significant amount was distributed among other cell membranes also depending on the brefeldin-A-sensitive endomembrane system. Our results indicate that mitochondria are the first location for new synthesized Q. Exogenous Q is mainly incorporated into an endo-lysosomal fraction, which is then rapidly incorporated to cell membranes mainly to MAM and mitochondria. We also demonstrate that both endogenous and dietary Q is distributed among endomembranes and plasma membrane by the brefeldin A-sensitive endo-exocytic pathway.