Pyk2‐Dependent Phosphorylation of Mitochondrial Ca 2+ Uniporter Modulates Mitochondrial Ca 2+ Uptake

The Ca2+ influx into mitochondrial matrix is primarily mediated via the mitochondrial calcium uniporter (MCU). Basal tyrosine phosphorylation (P‐Y) of MCU was shown in mass spectroscopy of human tissues, but the functional relevance of MCU post‐translational modifications including P‐Y is still unknown. Here we show that adrenergic signaling activates mitochondria matrix‐localized proline‐rich tyrosine kinase 2 (Pyk2), and accelerates mitochondrial Ca2+ uptake via Pyk2‐dependent P‐Y of MCUin cardiac cells.MCU contains 15 tyrosine residues and the phosphorylation prediction programs showed only 3 of these tyrosine residues (Y157 at N‐terminus, Y288, and Y316 at C‐terminus in mouse MCU) as potential phosphorylation candidate sites for tyrosine kinases. These tyrosine residues were mutated into phenylalanine and non‐phosphorylation mimetic MCU mutants (MCU‐YFs) were stably expressed in HEK 293T cells. We found that only two tyrosine sites were phosphorylated in response to adrenergic stimulation in situ. In addition, overexpression of these MCU‐YFs failed to increase mitochondrial Ca2+ uptake in response to cytosolic Ca2+ elevation, whereas wild‐type MCU transfection dramatically accelerates mitochondrial Ca2+ uptake compared to non‐transfected cells. We conclude that MCU contains Pyk2‐specific phosphorylation site(s) and Pyk2‐dependent P‐Y of MCU can modulate its channel functions and regulate mitochondrial Ca2+ uptake.