Regulation of UCP3 by nucleotides is different from regulation of UCP1

Echtay, Karim S.; Liu, Qingyun; Caskey, Tom; Winkler, Edith; Frischmuth, Karina; Bienengräber, Martin; Klingenberg, Martin

doi:10.1016/s0014-5793(99)00460-3

Cited by 66 publications

(49 citation statements)

References 23 publications

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“…We have also demonstrated that ADP is a slightly stronger UCP2 inhibitor than ATP. The same finding has previously been reported for UCP3 (58). GTP and GDP exhibited a slightly lower inhibitory ability.…”

Section: Discussionsupporting

confidence: 90%

“…We must admit that sulfate used in our assay media strongly decreases the PN affinity to UCP1 (25) and presumably also to UCP2/UCP3, which might explain the discrepancies between our K i values and those measured by Klingenberg and co-workers (21,58) and partly also between the K i values (Table II) (Table III). We chose sulfate to ensure that the anion used would be membrane impermeant, would not quench the SPQ probe, and that UCPs would not transport it.…”

Section: Discussionmentioning

confidence: 57%

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Activating ω-6 Polyunsaturated Fatty Acids and Inhibitory Purine Nucleotides Are High Affinity Ligands for Novel Mitochondrial Uncoupling Proteins UCP2 and UCP3

Žáčková

Škobisová

Urbánková

et al. 2003

Journal of Biological Chemistry

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 57%

Activating ω-6 Polyunsaturated Fatty Acids and Inhibitory Purine Nucleotides Are High Affinity Ligands for Novel Mitochondrial Uncoupling Proteins UCP2 and UCP3

Žáčková

Škobisová

Urbánková

et al. 2003

Journal of Biological Chemistry

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“…UCP1 is fully inhibited by millimolar concentrations of nucleotides (38), and it has been reported that homologues of UCP1 share this property (13,24,39,40). The inability of GDP to inhibit proton conductance in UCP2high yeast mitochondria is in agreement with evidence from mammalian mitochondria.…”

Section: Effect Of Supraphysiological Concentrations Of Ucp2 On Protosupporting

confidence: 76%

Physiological Levels of Mammalian Uncoupling Protein 2 Do Not Uncouple Yeast Mitochondria

Stuart

Harper

Brindle

et al. 2001

Journal of Biological Chemistry

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We assessed the ability of human uncoupling protein 2 (UCP2) to uncouple mitochondrial oxidative phosphorylation when expressed in yeast at physiological and supraphysiological levels. We used three different inducible UCP2 expression constructs to achieve mitochondrial UCP2 expression levels in yeast of 33, 283, and 4100 ng of UCP2/mg of mitochondrial protein. Yeast mitochondria expressing UCP2 at 33 or 283 ng/mg showed no increase in proton conductance, even in the presence of various putative effectors, including palmitate and all-trans-retinoic acid. Only when UCP2 expression in yeast mitochondria was increased to 4 g/mg, more than an order of magnitude greater than the highest known physiological concentration, was proton conductance increased. This increased proton conductance was not abolished by GDP. At this high level of UCP2 expression, an inhibition of substrate oxidation was observed, which cannot be readily explained by an uncoupling activity of UCP2. Quantitatively, even the uncoupling seen at 4 g/mg was insufficient to account for the basal proton conductance of mammalian mitochondria. These observations suggest that uncoupling of yeast mitochondria by UCP2 is an overexpression artifact leading to compromised mitochondrial integrity. Uncoupling protein 1 (UCP1)1 uncouples brown adipose tissue mitochondria, causing physiologically important, hormonally regulated, thermogenic proton cycling across the inner membrane. The functions of the UCP1 homologues, UCP2 and UCP3 (1-4), are currently uncertain (5-12). They have been demonstrated to uncouple mitochondrial oxidative phosphorylation in a number of experimental models, including proteoliposomes (13), yeast heterologous expression systems (1, 2, 14 -16), and transgenic mice (17). It is clear that, under some experimental conditions, heterologous or transgenic expression of these proteins can cause an increase in the proton conductance of the inner membrane (16, 18). However, it is less obvious whether these experimental observations of uncoupling are due to a native protein activity of the UCP1 homologues, or represent a more general disruption of mitochondrial function. None of the effects observed in genetically manipulated model systems has been repeated in natural systems where changes in the levels of UCP2 and/or UCP3 occur as a response to some environmental or physiological condition (19 -21).We have demonstrated that expression of UCP1 in yeast mitochondria can cause a nonspecific uncoupling that is not due to protein activity per se (22,23). This uncoupling artifact is present only at higher levels of UCP1 expression. At these levels, UCP1 expression in yeast also interferes with mitochondrial substrate oxidation. Similarly, Heidkaemper et al. (24) have concluded that both UCP1 and UCP3 can be expressed in an incompetent form that interferes with ATP production. They suggest that most of the UCP3 expressed in yeast mitochondria is nonfunctional. There is considerable evidence that, under some expression regimes, a substantial proportion o...

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“…7 for a more detailed review). Studies on protontranslocating activities of UCP2 (and UCP3) have, so far, been limited to mitochondrial and proteoliposome systems (9,(18)(19)(20). Thus, the potential of UCP2 to uncouple respiration in intact mammalian cells has not been addressed.…”

Section: Discussionmentioning

confidence: 99%

A significant portion of mitochondrial proton leak in intact thymocytes depends on expression of UCP2

Krauß

Zhang

Lowell

2001

Proc. Natl. Acad. Sci. U.S.A.

161

106

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The uncoupling protein homologue UCP2 is expressed in a variety of mammalian cells. It is thought to be an uncoupler of oxidative phosphorylation. Uncoupling proteins previously have been shown to be capable of translocating protons across phospholipid bilayers in proteoliposome systems. Furthermore, studies in mitochondria from yeast overexpressing the proteins have led to suggestions that they may act as uncouplers in cells. However, this issue is controversial, and to date, definitive experimental evidence is lacking as to whether UCP2 mediates part or all of the basal mitochondrial proton leak in mammalian cells in situ. In the present study, by using thymocytes isolated from UCP2-deficient and wild-type (WT) mice, we addressed the question whether UCP2 is directly involved in catalyzing proton leak in intact cells. Over a range of mitochondrial membrane potentials (⌬⌿ m), proton leak activity was lower in thymocytes from UCP2-deficient mice compared with WT mice. At physiological levels of ⌬⌿ m, a significant portion (50%) of basal proton leak in resting cells depended on UCP2. Of note, proton leak in whole cells from WT mice, but not UCP2-deficient mice, responded to stimulation by 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-napthalenyl)-1-propenyl]benzoic acid (TTNPB), a known activator of UCP2 activity. Consistent with the observed changes in proton leak, ⌬⌿ m and ATP levels were increased in untreated thymocytes from UCP2-deficient mice. Interestingly, resting respiration was unaltered, suggesting that UCP2 function in resting cells may be concerned with the control of ATP production rather than substrate oxidation. This study establishes that UCP2, expressed at endogenous levels, mediates proton leak in intact cells.

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Regulation of UCP3 by nucleotides is different from regulation of UCP1

Cited by 66 publications

References 23 publications

Activating ω-6 Polyunsaturated Fatty Acids and Inhibitory Purine Nucleotides Are High Affinity Ligands for Novel Mitochondrial Uncoupling Proteins UCP2 and UCP3

Activating ω-6 Polyunsaturated Fatty Acids and Inhibitory Purine Nucleotides Are High Affinity Ligands for Novel Mitochondrial Uncoupling Proteins UCP2 and UCP3

Physiological Levels of Mammalian Uncoupling Protein 2 Do Not Uncouple Yeast Mitochondria

A significant portion of mitochondrial proton leak in intact thymocytes depends on expression of UCP2

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