PKA Phosphorylates the ATPase Inhibitory Factor 1 and Inactivates Its Capacity to Bind and Inhibit the Mitochondrial H+-ATP Synthase

Abstract

The mitochondrial H(+)-ATP synthase synthesizes most of cellular ATP requirements by oxidative phosphorylation (OXPHOS). The ATPase Inhibitory Factor 1 (IF1) is known to inhibit the hydrolase activity of the H(+)-ATP synthase in situations that compromise OXPHOS. Herein, we demonstrate that phosphorylation of S39 in IF1 by mitochondrial protein kinase A abolishes its capacity to bind the H(+)-ATP synthase. Only dephosphorylated IF1 binds and inhibits both the hydrolase and synthase activities of the enzyme. The phosphorylation status of IF1 regulates the flux of aerobic glycolysis and ATP production through OXPHOS in hypoxia and during the cell cycle. Dephosphorylated IF1 is present in human carcinomas. Remarkably, mouse heart contains a large fraction of dephosphorylated IF1 that becomes phosphorylated and inactivated upon in vivo β-adrenergic stimulation. Overall, we demonstrate the essential function of the phosphorylation of IF1 in regulating energy metabolism and speculate that dephosho-IF1 might play a role in signaling mitohormesis.

Overexpression of the ATPase Inhibitory Factor 1 Favors a Non-metastatic Phenotype in Breast Cancer

“…The activity of IF1 as an inhibitor of the ATP synthase is regulated by matrix pH under conditions of mitochondrial de-energization (13, 23–25) and by the phosphorylation of S39 under several physiological situations such as progression through the cell cycle, hypoxia, rapid changes in metabolic demand, and cancer (26). In the specific case of breast carcinomas, we have recently described that IF1 is found essentially in its dephosphorylated form and hence able to bind and inhibit the ATP synthase activity of the enzyme (13, 26).…”

“…In the specific case of breast carcinomas, we have recently described that IF1 is found essentially in its dephosphorylated form and hence able to bind and inhibit the ATP synthase activity of the enzyme (13, 26). Remarkably, the overexpression of IF1 in different cancer cells promotes the acquisition of a pro-oncogenic phenotype by inducing metabolic reprogramming to an enhanced glycolysis (21, 22, 27).…”

Mitochondrial cAMP signaling

“…Given that CO 2 is the end product of the TCA cycle, the cAMP-PKA pathway provides a feed-forward regulation on two modules of energy metabolism: TCA cycle and ETC complexes. Recently, Complex V activity has also been found under the regulation of matrix cAMP-PKA pathway [123–125]. Complex V (mitochondrial ATP synthase) catalyzes the synthesis of ATP through the proton gradient generated by the ETC complexes and executes the reverse hydrolysis when the membrane potential falls below a threshold (pH of ~6.7 or below) [126].…”

“…An ATPase inhibitory factor 1 (IF1) is thought to act as a “reverse rotation brake” for the ATP synthase motor, preventing the “wasteful” ATP hydrolysis under the anaerobic condition [126, 127]. A recent study demonstrated that IF1 binds to Complex V and inhibits not only its hydrolase but also its ATP synthase activity [123]. IF1 can be phosphorylated by PKA, which prevents it from binding to Complex V, and thereby relieves its inhibitory effects on both the hydrolytic and synthetic activities of Complex V [123].…”

“…A recent study demonstrated that IF1 binds to Complex V and inhibits not only its hydrolase but also its ATP synthase activity [123]. IF1 can be phosphorylated by PKA, which prevents it from binding to Complex V, and thereby relieves its inhibitory effects on both the hydrolytic and synthetic activities of Complex V [123]. Thus the phosphorylation status of IF1 appears to be key in regulating the flux of glycolysis and OXPHOS corresponding to certain physiological context [124].…”