Energetic communication between mitochondria and nucleus directed by catalyzed phosphotransfer

Abstract

Exchange of information between the nucleus and cytosol depends on the metabolic state of the cell, yet the energy-supply pathways to the nuclear compartment are unknown. Here, the energetics of nucleocytoplasmic communication was determined by imaging import of a constitutive nuclear protein histone H1. Translocation of H1 through nuclear pores in cardiac cells relied on ATP supplied by mitochondrial oxidative phosphorylation, but not by glycolysis. Although mitochondria clustered around the nucleus, reducing the distance for energy transfer, simple nucleotide diffusion was insufficient to meet the energetic demands of nuclear transport. Rather, the integrated phosphotransfer network was required for delivery of high-energy phosphoryls from mitochondria to the nucleus. In neonatal cardiomyocytes with low creatine kinase activity, inhibition of adenylate kinase-catalyzed phosphotransfer abolished nuclear import. With deficient adenylate kinase, nucleoside diphosphate kinase, which secures phosphoryl exchange between ATP and GTP, was unable to sustain nuclear import. Up-regulation of creatine kinase phosphotransfer, to mimic metabolic conditions of adult cardiac cells, rescued H1 import, suggesting a developmental plasticity of the cellular energetic system. Thus, mitochondrial oxidative phosphorylation coupled with phosphotransfer relays provides an efficient energetic unit in support of nuclear transport. E fficient communication between the cytosol and nucleus is essential in cellular homeostasis, regulating proper processing of genetic and metabolic information. Central in nucleocytoplasmic exchange is the transport of macromolecules across the nuclear envelope (1, 2), a multistep process that initially proceeds by signal-mediated recognition of the macromolecule to be transported, following by docking events and, ultimately, translocation through nuclear pores (1-5). In energy-depleted cells, molecules that are actively transported into the nucleus, such as the constitutive chromatin protein histone H1, tend to accumulate on the cytosolic surface of the nuclear membrane (2, 4). While formation and docking of the transported protein, complexed with a transport receptor, may be energy-independent, the actual translocation and accumulation of molecules in the nuclear compartment against a concentration gradient may, however, require an energy source (4).Energy-consuming enzymes, including nucleoside triphosphatases, are associated with the nuclear envelope, and their activity is stimulated in the presence of the transported substrate (6, 7). Underscoring the energetic cost of nuclear transport, receptor cycling and continued signal processing mandate catalytic conversion of the guanine nucleotide-binding protein Ran from Ran-GTP to Ran-GDP, which is accomplished by the RanGTPase and the subsequent regeneration of GTP (1, 2). Yet, transport of macromolecules across the nuclear envelope that can proceed in an apparently energy-independent manner also has been reported (8, 9). This observation was, however, made i...

Nucleotide-gated KATPchannels integrated with creatine and adenylate kinases: Amplification, tuning and sensing of energetic signals in the compartmentalized cellular environment

“…7C, lower trace). This indicates a contribution of the AK system in the maintenance of submembrane ATP levels facilitated by AMP diffusional efflux, consistent with the demonstrated ability of AK to promote energetic communication and facilitate ATP delivery between cellular compartments [35,48].…”

“…7C, lower trace). This indicates a contribution of the AK system in the maintenance of submembrane ATP levels facilitated by AMP diffusional efflux, consistent with the demonstrated ability of AK to promote energetic communication and facilitate ATP delivery between cellular compartments [35,48].That modulation in CK flux amplifies bulk energetic signals in the vicinity of K ATP channels can be shown by the experimentally obtained relationships of ATP-induced channel inhibition measured in permeabilized cardiac cells in the presence (J CK >> 0) and absence (J CK = 0) of CrP (Fig. 7D).…”

“…While the AK-catalyzed reaction facilitates delivery and maintenance of ATP levels at ATPase sites [35,48], under metabolic stress AMP produced by AK can drive the reaction towards ADP generation at the channel site promoting K ATP channel opening [11,32,33]. Under severe stress, reversal of mitochondrial F 0 F 1 -ATP synthase into an ATPase associated with significant lowering of mitochondrial and cytosolic ATP, would drive the AK reaction towards AMP production.…”

“…8B). While the AK-catalyzed reaction facilitates delivery and maintenance of ATP levels at ATPase sites [35,48], under metabolic stress AMP produced by AK can drive the reaction towards ADP (Fig. 8C).…”

New Insights into the Bioenergetics of Mitochondrial Disorders Using Intracellular ATP Reporters

“…For example, it was suggested that in normal smooth muscle cells the contractile functions are supported by mitochondrial ATP derived from the respiratory chain and oxidative phosphorylation (OXPHOS), whereas the plasma membrane proton pumps are supported by ATP from anaerobic glycolysis (Ishida et al, 1994). In addition, recent studies showed that the import of histones into the nuclei of neonatal cardiomyocytes is strictly dependent on a concerted interaction between mitochondrial ATP synthesis and the trafficking of high-energy phosphoryls (Dzeja et al, 2002).In a technical advance, targeted luciferase has been used as an ATP sensor to investigate the kinetics of the variation of ATP concentration beneath the plasma membrane, in the mitochondria, and in the cytosol of pancreatic ␤-cells in response to glucose stimulation (Kennedy et al, 1999). These experiments demonstrated that in response to the administration of glucose and potassium, ATP levels increased in the plasma membrane of ␤-cells in concert with that in mitochondria, whereas cytosolic ATP showed only a transient increase.…”